Device for the intramuscular administration of fluids

Abstract

An apparatus for the intramuscular administration of fluids, containing a syringe with the injectable fluid and comprising a housing (1), needle protection means (2) for the syringe, a spring (6), and skin displacement means in a direction substantially perpendicular to the needle penetration path (2). The apparatus improves the efficiency of the procedure regardless of the user's skill, prevents leakage of the inoculated fluid from the injection site, and reduces or eliminates pain and the risk caused by accidental needle sticks. Applicable in sectors where health-related devices are designed, manufactured, produced, or used. In particular, it is especially suitable for use in hospitals, clinics, prisons, nursing homes, vaccination campaigns, emergency situations, etc., and generally wherever intramuscular injection therapies are required.

Description

APPARATUS FOR INTRAMUSCULAR FLUID ADMINISTRATION TECHNICAL SECTOR The present invention relates to an apparatus for the intramuscular administration or injection of fluids, preferably for injecting medications, and which is reusable. The apparatus contains a syringe with the injectable fluid and comprises a housing (1), means for protecting the syringe needle (2), a spring (6), and means for displacing the skin in a direction substantially perpendicular to the penetration path of the needle (2). The invention is applicable in those health sectors where it is necessary to administer one or more active substances, or active ingredients, or prepared drugs, together with other excipient products or any other liquid or solution, by the intramuscular route, such as, for example, in situations ranging from health promotion with the administration of vaccines to the treatment of chronic and / or acute diseases, including pharmacological restraint in cases of agitation, as well as in sectors where elements or devices related to health are manufactured. BACKGROUND OF THE INVENTION Intramuscular injection is one of the most widely used techniques for administering fluids and medications via indirect parenteral administration. Using a needle and syringe, a specific substance is injected into muscle tissue. It is considered an indirect parenteral route because it is administered through the skin and requires absorption, needing a certain amount of time to reach systemic circulation. This allows for the administration of both aqueous and oily preparations (Polania Gutiérrez, JJ, & Munakomi, S. (2023). Intramuscular Injection. In StatPearls. StatPearls Publishing). Specifically, intramuscular injection is one of the most frequently used techniques for pharmacological restraint in situations of acute agitation due to metabolic, toxicological, neurological, infectious, traumatic, and psychiatric causes, among others. However, the intramuscular administration of fluids, and especially medications, presents many problems from the perspective of patient and healthcare professional safety, as well as regarding the effectiveness of the administration procedure. Some examples of these problems include: improper administration, leakage of the injected fluid from the injection site, possible incomplete administration of the medication, pain or the association of pain with the procedure, and the biological risk to healthcare workers from accidental needlestick injuries with an unprotected needle during administration.This type of administration, if not performed properly, can also lead to side effects such as injury at the injection site, pain, intravascular injection, muscle fibrosis, contracture, tissue necrosis, injury to blood vessels, bone and peripheral nerves, paralysis due to nerve injury, injection into subcutaneous tissue, hematoma, granuloma, cellulitis, abscesses or muscle atrophy, among others (Hunter, J. (2008). "Intramuscular injection techniques". Nursing Standard, 22 (24), 35-40.), (Perry, A., Potter, P., & Ostendorf, W. (2014). "Clinical skills and nursing techniques" (8th ed.). St. Louis, MO: Elsevier-Mosby), (Nicoll, LH, & Hesby, A. (2002). "Intramuscular injection: an integrative research review and guideline for evidence-based practice". Applied nursing research: ANR, 15 (3), 149-162.).All these problems and their consequences are further magnified in situations of psychomotor agitation, a clinical condition that can affect people of all ages, from early to advanced stages, and in any medical specialty. Some of the risks associated with these problems can be reduced through the training and expertise of the healthcare personnel administering the injections. However, not all healthcare personnel have the same level of experience, nor are all users of intramuscular injections necessarily trained healthcare professionals (for example, patients who self-administer adrenaline or their family members). Even the most experienced healthcare personnel may experience a decrease in their vigilance during a single shift or several shifts of intense work, such as during vaccination campaigns. In the manual application of intramuscular injections, there remains a high risk of needlestick injuries with the syringe needle, with the corresponding biological risk of contracting infections such as hepatitis B virus (HBV), hepatitis C virus (HCV) and the AIDS virus (HIV) among others, during the management of agitation (Gabriel J. (2009). Reducing needlestick and sharps injuries among healthcare workers. Nursing Standard, 23: 41-4.). Furthermore, despite all the biosafety measures adopted, healthcare professionals are the most exposed to this type of risk, considered worldwide to be one of the most serious occupational problems with more than two million annual exposures in clinical practice and a global incidence of needlestick injuries of 43% (Hosseinipalangi, Z., Golmohammadi, Z., Ghashghaee, A., Ahmadi, N., Hosseinifard, H., Mejareh, ZN, Dehnad, A., Aghalou, S., Jafarjalal, E., Ar and ankhesal, A., Rafiei, S., Khajehvand, A., Ahmadi Nasab, M., & Kan, F.P. (2022) . Global, regional and national incidence and causes of needlestick injuries: a systematic review and meta-analysis. Eastern Mediterranean health journal = La revue de sante de la Mediterranee orientale = al-Majallah al-sihhiyah li-sharq al-mutawassit, 28 (3), 233-241.). One way to minimize the risk of needlestick injuries and ensure proper dose administration, regardless of the user's skill level, is through technology, and more specifically through the use of portable injection systems (Strauss, K., & WISE Consensus Group (2012). "WISE recommendations to ensure the safety of injections in diabetes." Diabetes & metabolism, 38 Suppl 1, S2-S8). These are typically medication delivery devices that attach to the body and automatically administer a pre-set dose to the patient using pre-filled syringes. In most of these devices, the needle is protected or retracted within the system until the moment of injection, allowing medication to be administered through the needle with varying levels of automation. They are typically self-injector devices for treating conditions such as arthritis, multiple sclerosis, diabetes, osteoporosis, etc., or designed for use in situations requiring a degree of urgency, such as anaphylactic reactions. Examples of such devices include the Syrette, introduced by the U.S. Army in 1950 (Szinicz L. (2005). History of chemical and biological warfare agents. Toxicology, 214 (3), 167-181), and those described in patent documents WO 2010 / 026414 A1, ES 2055648 B1, and ES 2548175 T3. In general, these are pre-filled, ready-to-use devices that only accept a single dose after which they are discarded. This creates several problems, the most obvious being the management of biological waste and the environmental impact of single-use devices. There are also alternative autoinjectors that can incorporate a syringe pre-filled with the medication and be mounted inside, such as the one described in patent document CA 2637147 A1. One device that attempts to address several of the aforementioned drawbacks is described in patent document ES 2956958 A1. It is a reusable device that protects users from accidental needlestick injuries and allows for verification of the correct administration of the intramuscular dose. This device comprises a housing containing a syringe and needle protection means that cover or uncover the needle by moving within the housing when the device is pressed against the skin. The housing also has an inspection window that allows for checking for blood return when aspiration is performed prior to dose inoculation. However, no known portable injection system in the state of the art addresses and resolves the problems related to pain reduction or elimination, painful association with the procedure, or leakage of the inoculated fluid from the injection site. Pain associated with injection procedures is a well-known phenomenon that can trigger fear in patients, a basic emotion that activates fight-or-flight responses. This fear can undermine confidence in medical procedures and even interfere with the ability to administer the injection, causing discomfort for both the patient and the healthcare professional performing the procedure. To mitigate this, certain strategies have been developed based on modulating or blocking pain receptors.Some examples include pre-injection cheek slapping, gentle and constant needle insertion and withdrawal, applying digital pressure for 10 seconds before and immediately before the injection, applying cold before administration, performing a sequence of skin traction with the fingers, pressure, needle insertion and rapid release, applying vibration, and even inserting needles of a different gauge (such as acupuncture needles) prior to the main injection (Cmc, S., Lord, H., Vargese, SS, Kurian, N., Cherian, SA, Mathew, E., & Fernandez, R. (2021). Effectiveness of physical stimulation on injection pain in adults receiving intramuscular injections: a systematic review protocol. JBI evidence synthesis, 19 (2), 419-425). In all cases, these procedures can be explained through what is known as "gate control theory" (Melzack R, Wall PD (1965). "Pain mechanisms: a new theory". Science 150 (3699): 971-9). The basic proposition of this theory is that signals from the periphery that are perceived in the brain as pain can be modulated and suppressed by central influences, such as attention and emotions, and by peripheral input via large, fast-conducting nerve fibers called A-beta fibers. Among the stimuli that activate these pain-suppressing nerve fibers, the authors mentioned vibration, scratching, and the application of light pressure to the skin. Several studies confirm that the application of any of the procedures mentioned effectively mitigates or eliminates the sensation of pain, such as: Öztürk, D., Baykara, ZG, Karadag, A., & Eyikara, E. (2017)."The effect of the application of manual pressure before the administration of intramuscular injections on students' perceptions of postinjection pain: a semi-experimental study". Journal of clinical nursing, 26 (11-12) , 1632-1638. Several products are known in the prior art that attempt to mitigate pain based on previous discoveries and strategies. These are typically individual, disposable devices applied to the skin before needle insertion, either with an adhesive or strap, or by holding them in place with one hand while the other holds the syringe and administers the injection. These devices are used in conjunction with traditional manual injection techniques. One example of such a product is described in US patent 6902554 B2, which proposes a flat, disc-shaped device with a series of small bumps that is pressed against the skin to distract the patient from pain signals. Another example, disclosed in US patent 8740960 B2, consists of a device applied to the skin that combines three methods for pain relief: cold, vibration, and distraction.Similar to the previous one, it is placed 5-10 cm from the puncture point between 30 and 60 seconds before performing the intervention and the effect is maintained 30-60 seconds after completion. Although the aforementioned devices address one of the problems associated with injections (pain and its perception), they fail to resolve other serious problems and risks associated with syringe handling, such as preventing incomplete or inadequate medication administration, facilitating administration for inexperienced users, or preventing leakage of the injected fluid. They also do not eliminate the biological risk to healthcare workers from accidental needlesticks; in fact, they may even increase this risk when the device must be handled and held with one hand while the other hand administers the injection. Intramuscular injection is a technique with specific characteristics compared to other administration methods. Drug absorption in muscle differs from that in subcutaneous tissue or via intravenous administration, making it crucial that medications designed for muscle absorption remain within the muscle. When a needle is inserted into a patient's body, it creates a channel around the needle. When the needle is withdrawn, this channel remains open, connecting the injection site to other tissues or the outside environment, thus providing a pathway for potential leakage of blood or medication. This leakage can result in leakage to the outside, reabsorption by surrounding tissues, or entry into the bloodstream. To mitigate this risk, a manual technique known as the Z-track technique has been developed, illustrated in Figure 1 or in Pullen RL, Jr (2005)."Administering medication by the Z-track method". Nursing, 35 (7) , 24. During the Z-track procedure, the skin and tissue around the needle insertion site are stretched and held taut while the needle is inserted into the muscle. After the medication is injected, the skin and tissue are released. Pulling the skin and tissue taut before the injection causes the needle track to take the shape of the letter "Z" when released, hence the name of the procedure. This zigzag line prevents the medication from leaking out of the muscle into the surrounding tissue or out of the body. In addition to containing the medication at the injection site, the Z-track technique also has effects on pain attenuation (Zeyrek, A., Takmak, J., Kurban, N.K., & Arslan, S. (2019). "Systematic review and meta-analysis: Physical-procedural interventions used to reduce pain during intramuscular injections in adults").Journal of advanced nursing, 75 (12), 3346-3361), especially because to perform it, pressure is also exerted on the skin, which acts as a distracting element from the pain. The Z-track method, while effective in preventing drug leakage into subcutaneous tissue or externally and ensuring adequate muscle absorption, is not without its challenges. In fact, it is a complex injection technique (Doyle, GR, & McCutcheon, JA (2015). "Clinical procedures for safer patient care". BCcampus. https: / / opentextbc.ca / clinicalskills / ). Some problems associated with the Z-track method include: - Greater complexity and time. The Z-track method requires a precise and careful technique, which can result in greater complexity and time required to administer the injection compared to other simpler methods. - Need for specialized training. Healthcare professionals using the Z-track technique must receive adequate training to ensure its correct application, which may require additional resources and training time. - Few effects on pain reduction. In some cases, the ability of the Z-track method to reduce pain on its own without being accompanied by other more effective strategies is questioned (Yilmaz, D., Khorshid, L., & Dedeolu, Y. (2016). "The Effect of the Z-Track Technique on Pain and Drug Leakage in Intramuscular Injections". Clinical nurse specialist CNS, 30 (6), E7-E12). Based on the analysis of the prior art, no technological solution is known that resolves, by itself and simultaneously, the problems and risks detected and associated with the intramuscular administration of fluids, among which the following stand out: the effectiveness of the administration procedure regardless of the user's skill, leakage of the inoculated fluid from the injection site, pain or painful association with the procedure, or the biological risk caused by accidental punctures with an unprotected needle during administration. EXPLANATION OF THE INVENTION The object of this invention is an apparatus for the intramuscular administration or injection of fluids, preferably for intramuscularly injecting medications. The apparatus improves the effectiveness and safety of fluid administration, while also preventing the risk of contamination for the user. It also reduces or eliminates the sensation of pain perceived by the patient and prevents leakage of the fluid once injected into the administration site. Preferably, the apparatus is reusable and can accommodate an interchangeable syringe. Therefore, an object of the present invention is an apparatus for the intramuscular administration of fluids comprising: - A housing containing a syringe. Said syringe comprises a needle that penetrates the skin of a subject through which the injectable fluid circulates, a cylinder that contains the injectable fluid, and a plunger that pushes the fluid through the needle. - Needle protection means that cover or uncover the needle. The needle protection means are movable relative to the housing and comprise a body surrounding the needle with one free end and the other end attached to the housing. The body is movable within the housing between a first configuration in which it covers the needle and a second configuration in which it retracts into the housing and uncovers the needle. For example, one possible embodiment of the body could be a cylinder surrounding the needle with its geometric axis collinear to the direction of the needle; and which can be moved within the housing to uncover the needle when the free end of the cylinder is pressed against a subject's body. - A spring with one end attached to the housing and the other end attached to the body surrounding the needle. When the spring is compressed, it pushes the body to cover the needle between the second and first configurations. - Some means of skin displacement associated with the free end of the body. In the first injection phase, the displacement means press and displace the skin surface in a direction substantially perpendicular to the needle's penetration path. For the purposes of this invention and its description, "substantially perpendicular" means a displacement in a direction that may be between 45 and 135 degrees relative to the penetration path, and preferably in the vicinity of 90 degrees with a margin of 10 degrees. It also means a radial direction relative to the penetration path. This displacement occurs prior to needle penetration when the body is between the first and second configurations. Due to this displacement, the skin transitions from a relaxed to a stretched state. In a second injection phase, the displacement means keep the skin surface in a stretched state while the injectable fluid circulates through the needle. In a third injection phase, the displacing agents reduce the pressure on the skin surface, allowing the skin to shift in a direction substantially perpendicular to the needle's penetration path. This shift occurs after the needle is withdrawn, when the body is between the second and first configurations. The skin then transitions from a stretched to a relaxed state. One way to use the device in a reusable configuration involves the following steps: i) Place the syringe with the fluid to be injected inside the device housing. ii) Perform a puncture in the selected area of ​​the subject's body. When the device is pressed against the subject, the skin displacement mechanisms stretch the skin as the needle's protective mechanisms move within the housing. When pressure on the device continues, the needle penetrates the injection site through the stretched skin. iii) Activate, where appropriate, injection means that induce the displacement of the syringe plunger to inject the fluid or press the syringe plunger with the same hand that holds the device. (iv) Remove the device from the subject's body after administration. This movement causes the needle to be withdrawn first, while simultaneously reducing the pressure of the device against the subject. In this way, the skin gradually transitions from a stretched to a relaxed state. Also, as the device is withdrawn, the spring pushes the needle's protective elements, which move from inside the housing outwards, covering the needle at all times and preventing it from being exposed. v) Safely remove the syringe from the device, thus preparing it for reuse. With this configuration, the user can grasp the device with one hand and operate it entirely with that hand, leaving their other hand free throughout the injection procedure. For example, they can grasp the device with one hand and use the thumb of that same hand to press or manipulate the syringe plunger while injecting or withdrawing the device from the subject's body. With their other hand free, the user can be prepared to address any emerging patient needs, manage any agitation, or hold or manipulate another instrument. In a preferred embodiment, the skin displacement means comprise a head with a proximal portion associated with the free end of the body, an intermediate portion, and a distal portion. The distal portion comprises at least two skin contact areas opposite the needle penetration point. Each contact area is radially displaceable in a direction substantially perpendicular to the needle penetration path when the pressure of the body on the head and on the skin is increased or decreased. In the first injection phase, the contact areas move away from the needle penetration point, and in the third injection phase, the contact areas move toward the needle penetration point, stretching or relaxing the skin. In a more preferred embodiment, the contact areas move differentially toward and away from the needle penetration point. For the purposes of this invention and its description, the term "differential" refers to the fact that the displacement is asymmetric with respect to the needle penetration point. In an even more preferred embodiment, one contact area moves toward and away from the needle penetration point, while the other contact area remains stationary. One advantage of pulling back the skin and tissue before injection is that the needle's penetration path takes on a "Z" shape when the skin is released. This zigzag line prevents fluid from leaking from the muscle into the surrounding tissue or outwards. In another more preferred embodiment, the head is flexible and comprises at least two arms, each with a contact area at its free end. In the first configuration, i.e., when the device is not pressed against the skin and the protective means shield the needle, the arms project toward the subject's skin, each forming an angle between 20° and 90° with respect to the needle's penetration path. In a further preferred embodiment, one arm projects toward the subject's skin at an angle between 20° and 60° with respect to the needle's penetration path, and the other arm projects toward the subject's skin at an angle between 45° and 90° with respect to the needle's penetration path. In yet another preferred embodiment, the head comprises a plurality of arms, each with a contact area at its free end. In another preferred embodiment, the head is flexible and consists of a three-dimensional structure. In an even more preferred embodiment, the three-dimensional structure is a three-dimensional Voronoi-type lattice. In another, more preferred embodiment, the head is flexible and continuous. A continuous head means that the contact areas are not necessarily physically separated, so that, within the continuous surface, there may be areas that can move apart or closer together when the device is pressed against or moved away from the skin. Examples of a continuous head include a toroidal head, a truncated hyperboloid head, or a truncated cone-shaped head. In another more preferred embodiment, the needle-protecting body comprises at least two pairs of slots, each with one open end and one closed end, forming an angle between 20° and 90° with respect to the needle's penetration path. In an even more preferred embodiment, the head is a cut-out piece obtained from a flexible, flat surface and includes an intermediate hole through which the needle passes. The head is attached to the needle-protecting body by inserting one portion of the head into one pair of slots and another portion into a different pair of slots. With this assembly, the head bends and projects toward the subject at an angle to the needle's penetration path, determined by the arrangement of the slots. In another preferred embodiment, the head comprises at least two lever mechanisms. One end of the lever is located in the proximal portion of the head, the fulcrum is located in the intermediate portion, and the other end, free and encompassing each contact area, is located in the distal portion. In this way, the lever pivots about the fulcrum when the pressure of the needle-protecting body against the head and skin is increased or decreased. This displacement causes the contact areas to shift radially in a direction substantially perpendicular to the needle's penetration path. In an even more preferred embodiment of the flexible head comprising at least two arms, the continuous flexible head, and the head that is a cut piece obtained from a flexible flat surface, the head further comprises at least one protrusion that projects towards the subject's skin and comes into contact with it without penetrating it during the first and second injection phases. In another specific embodiment, the body further comprises at least one protrusion that projects towards the subject's skin and comes into contact with it without penetrating it during the first and second injection phases. One advantageous effect of the protrusions is that they allow for the saturation of sensory signals around the injection site. In this way, the device can modulate or suppress pain signals thanks to the pressure stimulation exerted by the protrusions on the skin, which activates pain-suppressing nerve fibers. In another specific embodiment, the skin displacement means are attached to the free end of the body by means of a coupling with a pair of mounting clips. An advantageous aspect of this embodiment is that it facilitates the detachable attachment of the skin displacement means to the rest of the device. This type of attachment enhances the device's capabilities in environments where hygiene and disinfection protocols are more stringent. For example, without detaching the device, a user can attach the skin displacement means by pressing the device against the component. The attachment occurs automatically by pressure. After using the device, the user can dispose of the skin displacement means, if desired, without touching them, simply by pressing the mounting clips. In this way, the skin displacement means can fall by their own weight into a waste disposal container. For the purposes of this invention and its description, the term snap fit refers to a fastening mechanism for securing one flexible part to another by pushing the parts together and interlocking them. The mating elements deform elastically to create interference, allowing the parts to fit together. Snap fit joints are very quick to assemble, requiring only a small elastic deformation of the interference elements. No special tools or machinery are needed. A snap fit joint could be, for example, one or more flexible snap fits arranged on the body that protects the needle and correspond to a pair of holes in the printhead, or vice versa. In another specific embodiment, the casing is transparent or comprises a transparent portion that allows the contents of the syringe to be observed. For the purposes of this invention and its description, the term "transparent" shall be understood as meaning that it can be seen through, and to achieve this function, various strategies may be used, such as, for example, using materials permeable to visible light, or creating gaps or holes in a component through which visible light passes. In another specific embodiment, the body is transparent or comprises a transparent portion that allows the contents of the syringe to be observed. By observing the contents of the syringe, the operator of the device can visually check the characteristics of the fluid (appearance, color), the correct dosage of the fluid (complete or partial dosage) and the presence or absence of blood in the syringe cylinder to decide whether or not to continue with the process. In another preferred embodiment, the apparatus further comprises vibration means. These vibration means are configured to generate vibrations at a predetermined frequency and amplitude to induce controlled vibration in the skin displacement means. Vibration devices can be implemented, for example, with an electronically controlled electric motor and an eccentric counterweight relative to its axis of rotation, which induces the vibration. Alternatively, they can be implemented with a solenoid or a piezoelectric actuator. These elements can be connected to the skin displacement devices with a flexible coupling that transmits the vibration. Electronic control of the vibration can be achieved using a programmable electronic circuit and / or a user-operated switch. This implementation can be supplemented with an electrical power source, such as a rechargeable battery. In a more preferred embodiment, the vibration means are an electric motor associated with a counterweight eccentric with respect to its axis of rotation and coupling means for connecting the electric motor to the skin displacement means. Coupling means can be, for example, a helical spring. A helical spring can be used as a flexible coupling because of its ability to efficiently transmit vibrations while allowing some flexibility and damping. Another example is an elastic gasket. An elastic gasket (such as a rubber ring or a silicone piece) can absorb vibrations and allow their transmission in a controlled manner, reducing the transmission of unwanted shock forces. In another preferred embodiment, the apparatus further comprises means for generating a pressure field, wherein said means for generating a pressure field are configured to generate on the skin an oscillating pressure field of depressions and / or overpressures. In a more preferred embodiment, the means for generating a pressure field comprise: - A flexible, continuous head with an open distal portion and a proximal portion associated with a flexible membrane. In a further preferred embodiment, the membrane is located in the proximal portion of the head. - A chamber comprising at least the head and the membrane, wherein said chamber is formed when the head is in contact with the skin. In a further preferred embodiment, the chamber is formed by the head when the membrane is located on its proximal portion. For example, one embodiment of this embodiment is with a head in the shape of a torus, wherein the chamber is formed inside the torus, the membrane is the upper proximal portion of the torus, and the contact areas are located on the lower distal portion of the torus. In another further preferred embodiment, the chamber is formed by the head and the body. For example, one embodiment of this embodiment is with a head in the shape of a truncated cone open at both ends that fits hermetically to the body, and with the membrane located at the end of the body associated with the housing, forming a flexible wall.In an even more preferred embodiment, the chamber consists of the head and the body, and the apparatus further comprises a second chamber consisting of the housing, the body, and a second membrane. For example, one embodiment of this is with a head in the shape of a truncated hyperboloid, open at both ends, which is hermetically sealed to the body, and with the membrane located at the end of the body associated with the housing. The second chamber, consisting of the housing and the body, shares the membrane with the body and has a second membrane. - Driving means that move the membrane alternately in two opposite directions are configured to generate a volume change in the chamber between a minimum and a maximum volume, thus creating an oscillating pressure field on the skin. These driving means can be implemented in various ways, such as an electric motor with an eccentric wheel, a solenoid, a piezoelectric actuator, a peristaltic pump, or a pneumatic actuator, among others. They can also be electronically controlled by a programmable electronic circuit that generates signals to control the start and stop of the driving means, as well as the amplitude and / or frequency of oscillation or the rotational speed, thereby allowing adjustment of the frequency and amount of pressure on the skin. A user-operated switch can also be included to modulate, start, or stop the effect. In another preferred embodiment, the skin displacement means of the apparatus further comprise cooling means that cool them to a temperature lower than the temperature of the subject's skin surface at the needle penetration site. For the purposes of this invention and its description, "cool" refers to the cooling means reducing the temperature and / or maintaining a reduced temperature, for example, cooling the skin displacement means with an attached cooling device, or cooling the skin by keeping the skin surface cool through conduction between the skin and the cooled skin displacement means. One way to implement this is with a toroidal nozzle containing a non-toxic, liquid-based refrigerant or gel, such as a mixture of water and a thickening or gelling agent like propylene glycol or ethylene glycol, which keeps the nozzle flexible even when frozen. This allows a user to place the nozzle in a freezer to chill it before injection and then attach it to the device to begin the process. Alternatively, the entire device, including the nozzle, can be placed in a refrigerator before injection and removed only when ready to inject. Another way to implement this is with a printhead to which a Peltier device is attached. The Peltier device is a thermoelectric component that can heat or cool the printhead surface by applying an electric current. Furthermore, the Peltier device can be controlled by an electronic circuit. printhead temperature as required. In another, more preferred embodiment, the needle head depicts characters or contains patterns. Although needle phobia, and the consequent fear of pain, is very common in patients of all ages, it is crucial to address this situation with particular sensitivity when dealing with children. An additional way to mitigate fear and pain is through distraction using haptic stimulation, along with accompanying shapes, colors, or stories that focus attention on them. Ideally, haptic stimulation through pressure, vibration, skin stretching, cold, etc., should not be a surprising or novel stimulus to avoid frightening a child. It is preferable to prepare children adequately before a procedure, especially when it involves unfamiliar or potentially painful sensations. Therefore, exposure to these stimulations before the injection is suggested to mask the moment of the intramuscular injection.The child could play with the device before the procedure and experience all these physical stimulations on the body part they voluntarily select. This approach offers several advantages. First, by using appealing aesthetics and animated elements, a playful environment is created that can help reduce the child's anxiety. Furthermore, by allowing the child to select the body part where they wish to experience the tactile sensations, they are given a sense of control over the situation, which can make them feel more comfortable and relaxed. While no one is excluded, this feature is particularly applicable to children, and especially to individuals with Autism Spectrum Disorder (ASD), helping them to better prepare for procedures such as intramuscular injections. The invention described herein provides an apparatus for the intramuscular injection of fluids designed to deliver the intramuscular dose in an efficient and contained manner, painlessly and safely for both the patient and the administrator, even in special situations of patient agitation. Unlike other known technologies, this device features skin displacement mechanisms that allow the Z-track technique to be performed automatically, without requiring the user to be trained in its application or a healthcare professional. This feature prevents the injected dose from migrating from the muscle into the surrounding tissue or outwards, making the intramuscular injection much more effective and safe. The combination of this feature with the needle protection mechanisms, which cover or uncover the needle as the device approaches or moves away from the subject, makes the device highly safe with regard to the risk of accidental needlestick injuries. When the syringe is inserted into the device, the needle is never within reach of the subject or the administrator during the injection process. In general, the operation of the device described here does not depend on the user's dexterity. Some versions of the device include technical specifications that allow it to be designed so that all manipulation can be performed using only one hand, regardless of whether the user is right- or left-handed. Furthermore, the one-handed grip keeps the user's fingers away from the area near the needle tip, which, together with the needle protection features, provides a doubly safe system. The device also mitigates or eliminates pain or the painful association with the injection procedure. In certain embodiments, the device also includes at least one protrusion that comes into contact with the skin, exerting pressure prior to the injection. This pressure, whether exerted by the skin displacement means themselves when they do not include a protrusion, or by the protrusion itself, affects pain-suppressing fibers, substantially improving the subject's experience. In other embodiments, the device includes vibration means that induce a controlled vibration in the skin displacement means and the subject's skin. In still other embodiments, the device includes pressure field generating means that create an oscillating pressure field of depressions and / or overpressures on the skin.In other embodiments, the device includes cooling means that cool the skin's moving parts. All these stimuli allow the subject's perception of pain to be suppressed or attenuated. Unlike traditional methods, this device requires no pre-injection manipulation (massage, manual pressure, applying dressings or other aids, etc.). The device itself incorporates all the necessary technology to prevent pain during use. It is also unnecessary to use one hand to administer the injection and the other to apply pain management techniques. The entire dose can be administered using just one hand. On the other hand, in certain embodiments, the transparency of the components allows verification and assurance of the intramuscular inoculation of the fluid, which is especially relevant for the efficient and safe administration of certain types of medications. Unlike other known devices, the apparatus of the invention allows, by itself, simultaneously and without the need for the user to be specially trained, the resolution of the problems and risks detected and associated with the intramuscular administration of fluids: it improves the efficiency of the administration procedure regardless of the user's skill, prevents leakage of the inoculated fluid from the injection site, reduces or eliminates pain or painful association with the procedure, and eliminates the biological risk caused by accidental needle sticks. The invention is applicable in sectors where health-related devices are designed, manufactured, produced, or used. In particular, the device is especially suitable for use in hospitals, clinics, prisons, nursing homes, vaccination campaigns, emergency situations, etc., and generally wherever intramuscular injection therapies are required. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a sequence demonstrating a manual technique for administering intramuscular injections, which is considered a prior art. 1A A user brings their hand close and touches the patient's skin with their middle finger and thumb. The subject's skin is represented by a horizontal line. In Fig. 1B, the user stretches the skin by moving their middle finger away from their thumb. In Fig. 1C, the user brings a syringe containing a dose of medication, held in their other hand (not shown in this figure), to the area where they will administer the intramuscular injection, while keeping the skin stretched. The injection site is located between the middle finger and thumb, which are holding the skin taut. In Fig. 1D, the user inserts the needle into the patient's body while continuing to hold the skin taut. In Fig. 1E, the user injects the dose into the patient's body while continuing to hold the skin taut with one hand, manipulating the syringe with their other hand (not shown in this figure).1F The user has already removed the syringe, after which they relax the fingers of the hand in contact with the skin so that it returns to the initial situation. Figure 2 shows a partial perspective view of one embodiment of the apparatus. A semi-transparent housing (1) containing a syringe is shown in this figure. Both the housing and the syringe are shown incomplete. A cylinder (3) containing the injectable fluid and the needle (2) are visible within the syringe. A transparent, cylindrical body (5) surrounding the needle (2) is also visible. This body can be moved within the housing (1), either covering or uncovering the needle (2). The body (5) is held in place, covering and protecting the needle (2), by a spring (6) with one end attached to the housing (1) and the other end attached to the body (5) surrounding the needle (2). A flexible head (7) attached to the free end of the body (5) is also visible, with at least two contact areas (8) opposite the point of penetration of the needle (2). Figure 3 shows a sectioned side view of a portion of the device, where a body (5) and a head (7) attached to the free end of the body can be seen, with at least two skin contact areas (8). The skin surface is also shown, represented by an irregular horizontal line. The head (7) is a three-dimensional structure. The figure depicts a first injection phase where the head (7) presses against and displaces the skin surface in a direction substantially perpendicular to the penetration path of the needle (2) (not shown). The head comprises two skin contact areas (8), opposite the needle penetration point (2). Each contact area (8) moves away from the needle penetration point (2) differentially or asymmetrically, dragging the skin along by friction.More specifically, in this figure, one contact area (8) moves away from the needle penetration point (2), while the other contact area (8) remains stationary. The arrows represent the directions of pressure exerted by the contact areas (8) on the skin. Figure 4 shows a schematic side view of an embodiment of the device without associated skin displacement means. The figure shows a housing (1) containing a syringe. The syringe consists of a cylinder (3) containing the injectable fluid, a plunger (4), and a needle (2). The needle (2) is protected by a body (5) that surrounds it and can be moved within the housing (1), covering or uncovering the needle (2). The body (5) is held in place, covering and protecting the needle (2), by the action of a spring (6) with one end attached to the housing (1) and the other end attached to the body (5) surrounding the needle (2). In this embodiment, the body (5) comprises two pairs of grooves (9), each with one open end and one closed end, forming an angle between 20° and 90° with respect to the penetration path of the needle (2).The body (5) also comprises a set of protuberances (10) that project in the direction of the subject's skin. Figure 5 shows a top view of a head (7) with two contact areas (8) that also include wave-shaped protrusions (10). This head (7) can be attached to the apparatus of Figure 4, which comprises two pairs of slots (9). The head (7) is a flexible, cut piece obtained from a flexible flat surface and includes an intermediate hole through which the needle (2) can pass. In this figure, the head (7) is shown prior to its placement in the apparatus. To place it, simply insert one portion of the head (7) into one pair of slots (9) and another portion of the head (7) into the other pair of slots (9), resulting in a configuration similar to that shown in Figure 7. Figure 6 shows a top view of an assembly of heads (7) like that in Figure 5, prior to being cut from a flexible flat surface. The contact areas (8) and protrusions (10) are not shown in this figure. Figure 7 depicts a sequence of use of the device shown in Figure 4, which is associated with the head (7) shown in Figure 5. For clarity, the complete device is not shown in the figure. The housing (1) and spring (6) are not shown in Figures 7A and 7B. A portion of the housing (1) and spring (6) is shown in Figure 7C. The subject's skin is represented by a line when relaxed and by a wavy line when stretched. Figure 7A shows a first injection phase, where the head (7) presses and displaces the skin surface in a direction substantially perpendicular to the penetration path of the needle (2) prior to needle (2) penetration. The body (5) is located between the first and second configurations.The protrusions (10) on the body (5), projecting towards the subject's skin, have made contact with the skin without penetrating it, reducing the sensation of pain when the needle (2) penetrates in the next phase. Figure 7B shows a second injection phase where the needle (2) has penetrated the subject and the plunger (4) has moved to deliver the injectable dose. During this phase, the head (7) maintains the skin surface in a stretched state while the injectable fluid flows through the needle (2). Figure 7C shows the device after it has been withdrawn from the subject's body, following a third injection phase. In this third phase, the head (7) reduces the pressure on the skin surface and allows the skin to move in a direction substantially perpendicular to the penetration path of the needle (2) after the needle (2) is withdrawn.Thus, the skin goes from a stretched state to a relaxed state. Figure 8 shows a partial perspective view of the apparatus where the head (7) is formed by a three-dimensional structure that also includes a set of protrusions (10). The contact areas (8) are opposite the needle penetration point (2), but there is no formal separation between them. The apparatus is represented similarly to Figure 2, although the syringe and spring (6) are not shown in this figure because the housing (1) and body (5) are made of opaque material. Figure 9 shows a partial perspective view of the device where the head (7) is formed by a three-dimensional Voronoi-type structure. In this representation, the contact areas (8) are opposite the needle penetration point (2), but there is no formal separation between them. The rest of the device is represented similarly to Figure 2. Figure 10 shows several partial perspective views of the apparatus with different embodiments of the head (7). In all embodiments shown in this figure, the head (7) is flexible and continuous. The contact areas (8) are opposite the point of penetration of the needle (2), but there is no formal separation between them. The rest of the apparatus is represented similarly to Figure 2. Figure 10A shows an embodiment of a flexible and continuous head (7) in the shape of a truncated hyperboloid. Figure 10B shows an embodiment of a flexible and continuous head (7) in the shape of a truncated cone, offset from the direction of the needle (2). Figure 10C shows an embodiment of a flexible and continuous head (7) in the shape of a torus, offset from the direction of the needle (2). Figure 11 shows a partial perspective view of a device similar to that in Figure 2, with a head (7) similar to that in Figure 9. However, in this embodiment, the head (7) is attached to the free end of the body (5) by means of a couple of mounting clips, facilitating the assembly and disassembly of the head (7). Figure 11A shows the device in the uncoupled state. A pair of snap-fit ​​mounting clips on the body (5) can be seen, corresponding to a pair of holes in the head (7). When the head (7) and body (5) come into contact, the clips flex inwards, allowing sliding and ultimately coupling between the elements. Figure 11B shows the device in the coupled state. To uncouple the elements, the user presses the clips with their fingers to induce flexing and release the coupling. The head can then be slid off and removed from the device. Figure 12 shows a front and side view of a complete device. One view shows a syringe inside, and the other shows the device without a loaded syringe inside. In this device, the head (7), body (5), and part of the housing (1) are transparent or semi-transparent. Figure 13 depicts a sequence of use of the device in Figure 12 with a syringe inside. The subject's skin is represented by a line when relaxed and by a wavy line when stretched. Figure 13A shows a user holding the device prior to injection. Figure 13B shows a user holding the device in the first phase of injection. At this moment, the head (7) presses and displaces the skin surface in a direction substantially perpendicular to the penetration path of the needle (2) prior to needle (2) penetration. The body (5) is located between the first and second configurations. The protrusions (10) on the body (5) projecting towards the subject's skin have made contact with the skin without penetrating it, reducing the sensation of pain when the needle (2) penetrates in the next phase.Figure 13C shows a user holding the device during the second injection phase. At this moment, the needle (2) has penetrated the subject and the plunger (4) has moved to deliver the injectable dose. During this phase, the head (7) holds the skin surface taut while the injectable fluid flows through the needle (2). The body (5) surrounding the needle (2) moves inside the housing (1) as the device is pressed against the subject's skin, between a first configuration where it covers the needle (2) and a second configuration where it retracts into the housing (1), exposing the needle (2). At this moment, the spring (6) is not visible because it is hidden by the opaque part of the housing (1). Once the dosage is delivered, the user will withdraw the device from the patient's body, resulting in a state similar to that shown in Figure 13A.Once the device is withdrawn from the subject's body, after a third injection phase, the head (7) reduces the pressure on the skin surface and allows the skin to move in a direction substantially perpendicular to the needle's penetration path (2), following the needle's withdrawal. Thus, the skin transitions from a stretched state to a relaxed state. Figure 14 depicts a user holding the device during a second injection phase similar to that described in Figure 13C, but in this figure the device includes vibration means and / or pressure field generating means. The wavy lines surrounding the device represent its vibration. The combination of stimuli provided by the device through the vibration means and / or pressure field generating means, along with the protrusions (10), alleviates the subject's pain sensation. Figure 15 depicts an embodiment of the injection head (7) in the shape of a character, which can be accompanied by a narrative during the injection process. This narrative can include all the operating principles: skin stretching, vibration, cooling, pressure, etc. The injection head (7) is shown in a side view. PREFERRED EMBODIMENT OF THE INVENTION For a better understanding of the present invention, the following examples of preferred embodiments are set out, described in detail, which should be understood without limiting the scope of the invention. EXAMPLE 1 A device like the one shown in Fig. 12 was manufactured. For this purpose, plastic injection molding manufacturing techniques were used for most of the components, except for the spring and the syringe, in which case commercial products were used. The device needed to be lightweight for easy one-handed handling, but also strong enough to withstand the stresses generated during injection molding. Therefore, a combination of polypropylene (PP) and polycarbonate (PC) was chosen as the manufacturing materials, the latter for the transparent components. The casing (1) was cylindrical, consisting of two separate parts that could be joined by a thread. One part was opaque and the other part was transparent, allowing the syringe inside to be seen. The syringe also comprised a completely transparent cylinder (3). The body (5) of the needle protection device was formed by another cylinder that could slide inside the housing (1), concentric to it. The body (5) was also transparent, so that even when retracted inside the housing (1), the contents of the syringe could be seen through it. In this way, the intramuscular dose was ensured by verifying the dosage through the transparent components. Between the casing (1) and the body (5), a spring (6) was arranged which exerted a compressive load on the body (5), so that in order for the body (5) to move inside the casing (1), this load had to be overcome by pressing the device on the patient's skin. The device also included inside the casing (1) an electric plunger for the syringe that could be activated at the user's will to start the inoculation process. In this example, the body (5) comprised two pairs of slots (9) with one open end and one closed end, one pair of slots (9) and the other pair of slots (9) forming an angle of 30° and 60° respectively with respect to the penetration path of the needle (2). The body (5) further comprised a set of protrusions (10) projecting towards the subject's skin, the purpose of which was to eliminate the sensation of pain. The body (5) was fitted with a head (7) similar to that shown in Fig. 6, which was made of a flexible, transparent silicone component. This head (7) was previously obtained by cutting a flexible flat plate of the same material. The head (7) also included an intermediate hole through which the needle (2) could pass and two contact areas (8) located at opposite ends of this hole. To attach the head (7) to the device, one portion of the head (7) was simply inserted into one pair of slots (9) and another portion of the head (7) into the other pair of slots (9), resulting in a configuration similar to that shown in Fig. 12. EXAMPLE 2 A device similar to the one described in the previous example was manufactured, although with a different type of head (7), similar to that described and represented in Fig.11, and body (5), similar to that described and represented in Fig.9. For this embodiment, the body (5) was similar to that described in Example 1, although it did not include the set of protrusions (10), as these were located on the head (7). This body (5) also lacked pairs of slots (9) because the coupling with the head (7) was also different. The head (7) was also flexible and deformable and consisted of a three-dimensional Voronoi-type structure. The contact areas (8) were opposite the needle penetration point (2), but there was no formal separation between them. This head (7) was designed so that the contact areas (8) could be differentially moved closer to and further from the needle penetration point (2): one contact area (8) moved substantially closer to and further away from the needle penetration point (2), while the other contact area (8) barely moved. The head (7) was manufactured using Fused Deposition Modeling (FDM), with TPU (Thermoplastic Polyurethane) as the fusible material. This manufacturing method requires little to no post-processing, saving time in the production of complex parts. The head also had protrusions (10) arranged on its distal portion that came into contact with the skin and projected towards the subject's skin. As in the previous example, their purpose was to eliminate the sensation of pain. The head (7) was attached to the free end of the body (5) by means of a couple of mounting clips, facilitating the assembly and disassembly of the head (7). For this purpose, the body (5) had a pair of flexible snap-fit ​​mounting clips that corresponded to a pair of holes located on the proximal portion of the head (7). When the head (7) and body (5) came into contact, the clips flexed inwards, allowing the elements to slide and ultimately connect. To disconnect the elements, the user could simply press the clips with their fingers to induce flexing and release the connection; the head could then be slid off and removed from the device. EXAMPLE 3 This example describes a device similar to the previous example, although with a different type of head (7) and body (5), similar to how it is described and represented in Fig.10B. In this case, the device was constructed with a body (5) that was formed by another cylinder that could slide inside the housing (1), concentric to it. The body (5) was also transparent, so that even when retracted inside the housing (1), the contents of the syringe could be seen through it. In this way, the intramuscular dose was ensured by verifying the dosage through the transparent components. The head (7) was flexible and continuous and was made of silicone. The contact areas (8) were opposite the needle penetration point (2), but there was no formal separation between them. The head (7) was shaped like a truncated cone and was offset from the direction of the needle (2). Due to its offset position relative to the body and the direction of the needle (2), and its ability to deform flexibly, the contact areas (8) could be differentially moved closer to and further from the needle penetration point (2). In this example, the head (7) was associated with the free end of the body (5) by means of a threaded coupling, with the male and female of said thread at the free end of the body (5) and at the proximal portion of the head (7), respectively. EXAMPLE 4 A device similar to that described in Example 1 was manufactured, although it also comprised vibration means that served to generate vibrations at a frequency and amplitude predetermined by the user to induce a controlled vibration in the head (7). For this implementation, the vibration components were housed within the casing (1) and consisted of an electronically controlled electric motor, which also had an eccentric counterweight relative to its axis of rotation that induced the vibration. The motor was electronically controlled by a programmable electronic circuit that generated signals controlling the motor's start and stop times and its rotational speed, thus allowing adjustment of the vibration frequency and amplitude. The electronic circuit was linked to a switch that served as the interface between the user and the device. This switch could be operated with the thumb of the same hand the user used to hold the device. The switch was adjustable and had an on position, an off position, and intermediate positions that allowed for vibration adjustment. The electric motor was connected to the head (7) by means of a coupling between the two components. This coupling was achieved using a helical spring that acted as a flexible coupling due to its ability to transmit vibrations efficiently while allowing for some flexibility and damping. The vibration means were completed with a power source to power the motor and electronic circuit, and this was a rechargeable battery housed at the end of the casing (1). EXAMPLE 5 This example describes the administration of an intramuscular dose of a drug to a patient using the device described in Example 1. The following steps were followed: a) To attach a new head (7) to the device, one portion of the head (7) was simply inserted into one pair of slots (9) and another portion of the head (7) into the other pair of slots (9) of the body (5), thus completing the assembly for use. Subsequently, the syringe filled with the medication was placed inside the device. b) Next, in the first injection phase, the device was pressed against the subject's body. The head (7) pressed against and displaced the skin surface in a direction substantially perpendicular to the needle's (2) penetration path prior to needle (2) penetration. The protrusions (10) on the body (5), projecting towards the subject's skin, made contact with the skin without penetrating it, to reduce the sensation of pain. The pressure of the device against the body also overcame the elastic force of the spring (6), causing the needle guard (5) to move inside the housing (1). c) Then, in a second injection phase, the needle (2) advanced toward the subject's body along with the housing (1) as the body (5) moved inside the housing (1) until it penetrated the skin and entered the subject. The user could then inject the medication by activating the plunger (4) to deliver the injectable dose into the patient. During this phase, the head (7) held the skin surface taut while the injectable fluid circulated through the needle (2). During this process, the user could visually check, using the transparent portions, whether the puncture was performed correctly or if there were any signs of bleeding. If bleeding occurred, this would have indicated that a blood vessel had been punctured, and the device should be withdrawn and a second puncture performed on the patient, again verifying that a blood vessel had not been punctured.If no blood flows back into the area during aspiration, then the medication can be administered. d) After inoculation, in a third injection phase, the device was withdrawn from the subject's body so that the body (5) of the needle protection means was pushed by the spring (6) covering the needle (2) as it was withdrawn from the body. Simultaneously, as the device was withdrawn from the subject, the head (7) reduced the pressure on the skin surface, allowing the skin to move in a direction substantially perpendicular to the needle penetration path (2) after the needle (2) was withdrawn. Thus, the skin transitioned from a stretched state to a relaxed state. e) Finally, the syringe was safely removed from the device for disposal in a biohazardous waste container. The user could also remove the head (7) from the device by simply pulling one portion of the head (7) out of one pair of slots (9) and then pulling another portion of the head (7) out completely of the other pair of slots (9), leaving the head (7) detached for disposal in a biohazardous waste container. As you can see, all injection phases using the device can be performed with only one hand while the user holds the device. This leaves the non-dominant hand free if needed for patient immobilization or other tasks during administration.

Claims

1. An apparatus for the intramuscular administration of fluids comprising: - a housing (1) containing a syringe, wherein said syringe comprises a needle (2) that penetrates the skin of a subject and through which the injectable fluid circulates, a cylinder (3) containing the injectable fluid, and a plunger (4) that pushes the fluid through the needle (2); - needle protection means that cover or uncover the needle (2), wherein the needle protection means are displaceable relative to the housing (1) and comprise a body (5) surrounding the needle (2) with a free end and another end associated with the housing (1) and which is displaceable inside the housing (1) between a first configuration in which it covers the needle (2) and a second configuration in which it is inserted inside the housing (1) and uncovers the needle (2); and - a spring (6) with one end associated with the housing (1) and the other end associated with the body (5) surrounding the needle (2), whichWhen compressed, it pushes the body (5) to cover the needle (2) between the second and first configurations; characterized in that it further comprises skin displacement means associated with the free end of the body (5) which, in a first injection phase, press and displace the skin surface in a direction substantially perpendicular to the penetration path of the needle (2) prior to needle (2) penetration when the body (5) is between the first and second configurations, from a relaxed skin state to a stretched skin state; and which, in a second injection phase, maintain the skin surface in a stretched state while the injectable fluid circulates through the needle (2); and which, in a third injection phase, decrease the pressure on the skin surface and allow it to displace in a direction substantially perpendicular to the penetration pathof the needle (2) after the needle (2) is withdrawn when the body (5) is between the second and first configurations, from a stretched skin state to a relaxed skin state.

2. Apparatus according to claim 1, characterized in that the skin displacement means comprise a head (7) with a proximal portion associated with the free end of the body (5), an intermediate portion, and a distal portion with at least two skin contact areas (8) opposite the needle penetration point (2), wherein each contact area (8) is radially displaceable in a direction substantially perpendicular to the needle penetration path (2) when the pressure of the body (5) on the head (7) and on the skin is increased or decreased, wherein in the first injection phase the contact areas (8) move away from the needle penetration point (2), and in the third injection phase the contact areas (8) areapproach the needle penetration point (2).

3. Apparatus according to claim 2 characterized in that the contact areas (8) approach and move away from the needle penetration point (2) differentially.

4. Apparatus according to the preceding claim characterized in that one contact area (8) approaches and moves away from the needle penetration point (2) and the other contact area (8) does not move.

5. Apparatus according to claim 2 characterized in that the head (7) is flexible and comprises at least two arms at the free ends of which are each contact area (8), wherein in the first configuration the arms project towards the subject's skin, each forming an angle between 20° and 90° with respect to the needle penetration path (2).

6. Apparatus according to the preceding claim characterized in that one arm projects towards the subject's skin, forming an angle between 20° and 60° with respect to the needle penetration path (2) and theAnother arm projects towards the subject's skin, forming an angle between 45° and 90° with respect to the needle penetration path (2).

7. Apparatus according to claim 5, characterized in that it comprises a plurality of arms at whose free ends there is a contact area (8).

8. Apparatus according to claim 2, characterized in that the head (7) is flexible and is formed by a three-dimensional structure.

9. Apparatus according to the preceding claim, characterized in that the structure is a three-dimensional Voronoi-type network.

10. Apparatus according to claim 2, characterized in that the head (7) is flexible and continuous.

11. Apparatus according to claim 2, characterized in that the body (5) comprises at least two pairs of slots (9), each with an open end and a closed end, each pair of slots (9) forming an angle between 20° and 90° with respect to the needle penetration path.

12. Apparatus according to claim 11, characterized in thatthat the head (7) is a cut-out piece obtained from a flexible flat surface comprising an intermediate hole through which the needle (2) passes and which is attached to the body (5) by inserting one portion of the head (7) into a pair of grooves (9) and another portion of the head (7) into another pair of grooves (9).

13. Apparatus according to claim 2 characterized in that the head (7) comprises at least two lever mechanisms with one end of the lever located in the proximal portion, the fulcrum located in the intermediate portion, and the other end, free and comprising each contact area (8), located in the distal portion, such that the lever moves when the pressure of the body (5) on the head (7) and the skin is increased or decreased.

14. Apparatus according to claims 5, 10, or 12 characterized in that the head (7) further comprises at least one protrusion (10) projecting towards the subject's skin and making contact with the subject's skin without15. Apparatus according to claim 1, characterized in that the body (5) further comprises at least one protrusion (10) projecting towards the subject's skin and making contact with the subject's skin without penetrating it during the first and second injection phases.

16. Apparatus according to claim 1, characterized in that the skin displacement means are associated with the free end of the body (5) by coupling with a pair of mounting clips.

17. Apparatus according to claim 1, characterized in that the housing (1) is transparent or comprises a transparent portion allowing observation of the syringe contents.

18. Apparatus according to claim 1, characterized in that the body (5) is transparent or comprises a transparent portion allowing observation of the syringe contents.

19. Apparatus according to claim 1, characterized in that it further comprises means forvibration wherein said vibration means are configured to generate vibrations at a predetermined frequency and amplitude to induce a controlled vibration in the skin displacement means.

20. Apparatus according to the preceding claim, characterized in that the vibration means are an electric motor associated with a counterweight eccentric with respect to its axis of rotation and coupling means for connecting the electric motor to the skin displacement means.

21. Apparatus according to claim 1, characterized in that it further comprises pressure field generating means, wherein said pressure field generating means are configured to generate on the skin an oscillating pressure field of depressions and / or overpressures.

22. Apparatus according to claims 10 and 21, characterized in that the pressure field generating means comprise: - a continuous flexible head (7) with an open distal portion and a23. Apparatus according to claim 1 characterized in that the skin displacement means further comprise cooling means that cool them to a temperature lower than the temperature of the subject's skin surface in the needle penetration zone (2).

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