Epidural device for detection and placement of a needle within the epidural space

Abstract

An epidural device is provided that is configured to inhibit or substantially or completely prevent further advancement of the epidural needle after it enters the epidural space. Once the needle is inserted into the ligaments of the patient's back, the device can be pressurized with fluid, using the resistance of the dense ligaments to maintain pressure. This pressurization may lock the pushing mechanism in place relative to the needle so that the pushing mechanism can be used to advance the needle. Once the epidural space is reached, fluid (e.g., saline or air) enters the epidural space, and release of pressure disengages the trigger mechanism from the sliding pusher, allowing the pusher to slide along the body of the structure. Thus, the device may provide the ability to detect the epidural space using pressure loss while preventing the needle from advancing into the dura once the epidural space is reached. In a preferred embodiment, the device may prevent premature triggering when there is a slow flow of fluid from the epidural needle into the surrounding tissue.

Description

Technical Field

[0001] The following relates to devices used in epidural procedures, which are referred to herein as epidural devices. More specifically, the following relates to epidural devices for facilitating the detection and placement of an epidural needle within the epidural space.

Background Art

[0002] Epidural anesthesia is widely used during childbirth / labor, lower limb and pelvic surgery, and steroid injections for pain relief. Both single-injection and catheter techniques can be used to inject drugs into the epidural space. The ability to maintain continuous anesthesia after placement of an epidural catheter makes the epidural suitable for long-term surgeries and useful during the postoperative period for painlessness.

[0003] Typically, the method of placing the needle in the correct position relies on the loss of resistance to detect the epidural space (i.e., to determine when the epidural needle has entered the cavity). Once the needle tip enters the thick ligament in the back, the anesthesiologist applies a constant or intermittent pressure to the plunger of a syringe filled with air or saline. The anesthesiologist generally uses a glass syringe or a low-resistance plastic syringe. Due to the dense and fibrous nature of the ligaments leading to the epidural space (supraspinous ligament, interspinous ligament, and yellow ligament), saline or air is not easily injected into the tissue, and the syringe maintains its pressurized state. Although the exact technique may vary, generally, the epidural needle is advanced with one hand while the pressure on the syringe plunger is maintained with the other hand. When the tip of the epidural needle enters the epidural space, the anesthesiologist senses the loss of pressure by depressing the plunger of the syringe. To confirm the location of the epidural space, additional saline can be easily injected into the epidural space. At this point, the syringe can be removed, and the drug can be injected, or a catheter can be fed through the needle. In an alternative "incremental" method, the needle is advanced 1 - 2 mm, and then the plunger is pushed to confirm that the needle tip is still within the ligament. This is repeated until the plunger can be easily depressed, and saline or air is released into the epidural space.

[0004] When using the incremental method, it is possible to significantly advance the needle through the epidural space and puncture the dura during the confirmation. The above procedures rely on the anesthesiologist to observe or sense the pressure loss, process that information, and stop the forward progression of the needle without an accidental forward movement of the needle. Inappropriate techniques, such as careless angling of the plunger against the syringe wall, cause unwanted friction and make it difficult to recognize the small changes in pressure required to detect the epidural space. Furthermore, glass syringes typically have very low friction but sometimes stick and generate false negative signals for the physician, causing the needle to be advanced too far.

[0005] The risk of an epidural procedure is an accidental puncture of the dura mater. If the dura mater is punctured, the patient may suffer from post-dural puncture headache, spinal abscess, spinal hematoma, or in severe cases, permanent neurological damage. Furthermore, the occurrence of these complications incurs additional costs.

[0006] Current medical practice requires an anesthesiologist to observe the detection of the epidural space and simultaneously stop the progression of the needle to prevent advancement that could cause a dural puncture. Devices have been developed that provide visual or auditory cues to warn the user of a loss of pressure, thereby assisting the practitioner in the detection of the epidural space. However, those devices are not configured to automatically inhibit or prevent further advancement of the needle once it reaches the epidural space.

Summary of the Invention

Problems to be Solved by the Invention

[0007] In view of the above, it is desirable to provide an improved epidural device.

Means for Solving the Problems

[0008] The following describes an epidural device configured to detect entry of the tip of an epidural needle into the epidural space and to inhibit or prevent further advancement after entry. The device may be filled with a fluid (e.g., saline or air) and may be connected to the epidural needle when the needle is inserted into the patient's back and the tip is positioned within the yellow ligament. The device can be pressurized using the resistance of the dense ligament to prevent fluid flow from the needle. The pressurization may be used by a mechanism that locks a sliding pusher in place (relative to the body of the structure and the needle connected thereto) such that the anesthesiologist can subsequently use a pusher to advance the needle. Once the epidural space is reached, the fluid enters the epidural space and the release of pressure triggers a mechanism within the device to disengage the pusher from the body of the structure. At this point, if the sliding pusher is pushed, the sliding pusher may slide over the device without any significant or further advancement of the needle. The device may provide both the ability to detect the epidural space using a pressure loss and to automatically substantially or completely prevent further advancement of the needle after the device has entered the epidural space.

[0009] In one aspect, an epidural device is provided having an elongated body with a longitudinal axis, an inlet, and an outlet. The epidural device includes a sleeve slidably disposed around an outer surface of the body, a first chamber defined in the body and configured to receive fluid, a second chamber defined in the body and configured to carry fluid to the outlet, wherein the outlet is removably attachable to an epidural needle, a flow restrictor between the first chamber and the second chamber to provide fluid communication therebetween and having a diameter smaller than a diameter of the outlet, the first chamber having a first bias mechanism positioned within the first chamber to pressurize the first chamber, the second chamber having a piston provided within the second chamber, the piston being movable between a primed position where the piston is moved away from the flow restrictor and fluid can proceed between the first chamber and the second chamber, and a triggered (or primed) position where the piston covers the flow restrictor and fluid can exit the second chamber through the outlet, and wherein in the primed position the sleeve is engageable by an extension of the piston to inhibit the sleeve from axially moving towards the outlet, and in the triggered position the sleeve is not engageable by the extension of the piston and the sleeve is axially movable towards the outlet.

[0010] In some implementations, the first chamber is configured to receive fluid from the inlet and has an opening therein opposite the flow restrictor, and the epidural device further includes a plunger extending into the chamber through the opening, the plunger having a flow port defined therein to provide fluid communication between the inlet and the first chamber, a distal end positioned within the first chamber, and a proximal end positioned outside the chamber and configured to engage the inlet.

[0011] In another implementation, the first chamber has an opening therein opposite the flow restrictor, and the epidural device further includes a plunger that extends into the chamber through the opening, the plunger having a distal end positioned within the first chamber and a proximal end positioned outside the chamber.

[0012] In yet another implementation, the first biasing mechanism is a spring provided within the chamber around the plunger intermediate the distal end of the plunger and the opening of the chamber.

[0013] In yet another implementation, a fill port for filling the first chamber extends between the first chamber and the second chamber, the fill port including a one-way valve that permits flow from the second chamber to the first chamber.

[0014] In yet another implementation, when the epidural device is in a primed position, at least a portion of the fluid can exit the second chamber through the outlet without triggering the epidural device.

[0015] In yet another implementation, a second biasing mechanism is disposed within the second chamber, the second biasing mechanism being weaker than the first biasing mechanism.

[0016] In yet another implementation, the second biasing mechanism is a spring.

[0017] In yet another implementation, the piston includes a disk extending radially from the piston, the disk dividing the first chamber into a trigger chamber and a reservoir chamber, the trigger chamber and the reservoir chamber having first and second annular surfaces respectively, the reservoir chamber being in fluid communication with the first chamber via a flow channel extending between the reservoir chamber and the first chamber, the disk being positioned intermediate the flow channel and a flow restrictor when the epidural device is in a primed position, the trigger chamber being in fluid communication with the first chamber and an outlet, the disk covering the flow restrictor when the epidural device is in a triggered position. The trigger chamber is not in fluid communication with the first chamber.

[0018] In yet another implementation, the first annular surface has a larger surface area than the surface area of the second annular surface so that a differential in force is created between the trigger chamber and the reservoir chamber.

[0019] In yet another implementation, the piston includes a button at its end opposite the extension, the button being pressable by a user in a direction toward the extension to prime the epidural device.

[0020] In yet another implementation, the sleeve includes a protrusion extending from the sleeve toward the body of the epidural device, the protrusion being configured to prime the epidural device by pressing a button on the piston when the sleeve slides over the piston, the button being attached to the end of the piston opposite the extension.

[0021] In another aspect, an epidural device is provided having an elongate body with a longitudinal axis, an inlet, and an outlet. The epidural device includes a sleeve slidably disposed about an outer surface of the body, a fluid passage defined in the body and configured to receive fluid from the inlet, a pressure chamber defined in the body and configured to carry fluid to the outlet, wherein the outlet is removably attachable to an epidural needle, a flow restrictor between the fluid passage and the pressure chamber for providing fluid communication therebetween and having a diameter smaller than a diameter of the outlet, the pressure chamber having a piston disposed therein, the piston being movable between a primed position in which the piston is moved away from the flow restrictor and fluid can proceed between the fluid passage and the pressure chamber, and a triggered position in which the piston covers the flow restrictor and fluid can exit the pressure chamber through the outlet, and in the primed position, the sleeve is engagable by an extension of the piston to inhibit the sleeve from moving axially toward the outlet, and in the triggered position, the sleeve is not engagable by the extension of the piston and the sleeve is movable axially toward the outlet.

[0022] In yet another aspect, an epidural device is provided having an elongate body with a longitudinal axis, an inlet, and an outlet. The epidural device includes a sleeve slidably disposed on an outer surface of the body, the body having a chamber defined therein for communicating fluid between the inlet and the outlet, wherein the outlet is removably attachable to an epidural needle, a biasing mechanism for pressurizing the chamber, and a trigger mechanism for engaging the sleeve, the trigger mechanism being at least partially received within the chamber and movable between a first position and a second position in response to a decrease in pressure within the chamber, and in the first position, the sleeve is engagable by the trigger mechanism to inhibit the sleeve from moving axially toward the outlet, and in the second position, the sleeve is not engagable by the trigger mechanism and the sleeve is movable axially toward the outlet.

[0023] In one implementation, the trigger mechanism includes at least one piston having a first end and a second end, the first end being positioned within a chamber such that the first end can be actuated by a biasing mechanism, the second end extending radially outwardly through the body, and in a first position, the second end protruding radially from the body to an extent that the sleeve can be engaged by the second end, and in a second position, the second end being positioned closer to the body than when the epidural device is in the first position such that the sleeve cannot be engaged by the second end.

[0024] In another implementation, the trigger mechanism includes an inflatable membrane that can be inflated by a biasing mechanism, and in a first position, the inflatable membrane is inflated to an extent that the sleeve can be engaged by the membrane, and in a second position, the inflatable membrane is deflated to an extent that the sleeve cannot be engaged by the membrane.

[0025] In yet another implementation, the trigger mechanism includes a compliant component that can be expanded by a biasing mechanism, and in a first position, the compliant component is expanded to an extent that the sleeve can be engaged by the component, and in a second position, the compliant component is deflated to an extent that the sleeve cannot be engaged by the compliant component.

[0026] In yet another implementation, provided herein is a device for an epidural procedure that is filled with a fluid and can be pressurized by an internal spring. The device further includes a sliding pusher on the outer frame of the device and a mechanism configured to have two positions. In one position, the sliding pusher can move freely along the length of the device. In the other position, the fluid pressure holds the mechanism in a predetermined position, and when the sliding pusher interferes with the mechanism, its movement is restricted, enabling the user to advance the needle by pushing forward with the sliding pusher. For example, when the needle tip enters the epidural space, when pressure is reduced, the mechanism returns to the other position and disengages from the sliding pusher, allowing the pusher to move along the body of the device so that the user cannot advance the needle further.

[0027] In one implementation, the mechanism is constituted by a piston that can move vertically within the device. While in its first position, it allows the sliding pusher to move freely, while in its second position, it may suppress the pusher component by one end of the piston that engages with the pusher. The piston may be biased to its first position by a spring and held in the second position by the fluid pressure within the device.

[0028] In one implementation, the sliding pusher component has a flange or wing extending from its front end to provide a pressing surface when advancing the needle.

[0029] In another implementation, the flange or wing is connected to the pusher by an extension to allow the pressing surface to be closer to the patient and improve the stability of the hand placement for the device and the user.

[0030] In yet another implementation, the piston mechanism is movable to its second position by sliding the pusher forward (towards the patient). When the pusher is advanced, a ramp within the pusher may push down on the piston mechanism. When depressurized, the piston can move into the space within the pusher, allowing the pusher to slide freely.

[0031] In yet another implementation, the piston mechanism is movable to its second position by sliding the pusher backward (away from the patient). When the pusher is retracted, a ramp within the pusher can push down on the piston mechanism. When depressurized, the piston moves into the space within the pusher, allowing the pusher to slide freely.

[0032] In yet another implementation, the device may be filled with fluid by using a connector within the plunger of the device. A one-way valve within the plunger prevents the fluid from exiting the chamber by the same path.

[0033] In yet another implementation, the device may be filled with fluid from the front of the device through a fluid path that includes a one-way valve between the trigger mechanism and the fluid reservoir.

[0034] In yet another implementation, the device may be filled with fluid from the front of the device by pushing the trigger mechanism into a predetermined position, through which the fluid passes, and holding the trigger mechanism in this position during a filling procedure.

[0035] In yet another implementation, the trigger mechanism does not include a spring. In this embodiment, the trigger piston may use a differential force from the pressure applied to two surfaces to drive the piston downward or upward or hold the piston in a predetermined position (down or up). The two surfaces may be of different sizes to enhance the differential force. When decompressed, such as when entering the epidural space, the two surfaces of the piston mechanism may receive different forces, which can drive the piston upward and allow the pusher to slide freely.

[0036] In yet another implementation, the trigger mechanism uses at least one pin, preferably two pins or two pistons, that may interfere with the sliding pusher. In yet another implementation, the two pistons may provide an equally balanced force to the sliding pusher.

[0037] In another implementation, the device further includes a flexible or expandable membrane for engaging the sliding pusher when the membrane is pressurized. When decompressed, such as when entering the epidural space, the membrane may contract, allowing the sliding pusher to slide freely.

[0038] In yet another implementation, the device further includes a compliant or flexible mechanism for engaging the sliding pusher when the mechanism is pressurized. When decompressed, such as when entering the epidural space, the compliant mechanism may retract and disengage from the sliding pusher, allowing the pusher to slide freely.

[0039] Next, embodiments will be described with reference to the accompanying drawings.

Brief Description of the Drawings

[0040]

Figure 1A

[0041]

Figure 1B

[0042]

Figure 1C

[0043]

Figure 1D

[0044]

Figure 1E

[0045]

Figure 1F

[0046]

Figure 1G

[0047]

Figure 2

[0048]

Figure 3A

Figure 3B

Figure 3C

[0049]

Figure 4A

Figure 4B

Figure 4C

[0050]

Figure 5

[0051]

Figure 6A

Figure 6B

Figure 6C

[0052]

Figure 7A

Figure 7B

Figure 7C

[0053]

Figure 8A

Figure 8B

[0054]

Figure 9A

Figure 9B

Figure 9C

Figure 9D

DETAILED DESCRIPTION OF THE INVENTION

[0055] One or more of the terms "vertical", "vertically", "horizontal", "horizontally", "top", "bottom", "upward", "downward", "upper", "lower", "right", "left", "forward", and "backward" are used throughout this specification. It will be understood that these terms are not intended to be limiting. These terms are used for convenience and are used, for example, as an aid in describing the configurations in this specification as illustrated in the accompanying drawings.

[0056] As used herein with respect to the operation of an epidural device, the term "fluid" refers to a liquid or gas, such as saline or air, for filling and pressurizing the device.

[0057] The following objective is to provide an epidural device that can detect the entry of a needle into the epidural space and simultaneously suppress or substantially prevent further forward movement of the needle. Such functionality may reduce the likelihood of dural puncture that can occur during the implementation of conventional loss of resistance techniques. In a preferred embodiment, the device is configured to prevent early triggering when there is a slow flow of fluid from the epidural needle into the surrounding tissue.

[0058] (Pressure Loss Design) The epidural devices described with reference to FIGS. 1 - 5 include a trigger mechanism that depends on differential forces between a spring force and a force from the chamber pressure within the trigger barrel. These devices are configurable between a "primed" position or state and a "triggered" (i.e., unprimed) position or state. The device can be manually primed (i.e., shifted from an unprimed state to a primed state) by a user, such as a physician, when attached to a needle positioned on the patient's back and subsequently automatically triggered after the entry of the epidural needle into the epidural space. The unprimed (triggered) state is the default state of the epidural device. The step - by - step operation of these devices is described following the description of their construction.

[0059] Figure 1A shows an epidural device 100 including a syringe body 101 having a first end or open end 106 and a second end or needle connector end 130. The syringe body 101 can have a substantially uniform shape with a rectangular cross-section as shown in Figure 1A. The syringe body 101 can have different shapes. For example, the syringe body 101 can be an elongated body having a different (i.e., non-rectangular) polygonal cross-section, such as a hexagonal cross-section. In Figure 1A, the epidural device 100 is shown in a non-primed position with the reservoir partially filled with fluid (not shown). The syringe body 101 can include a reservoir chamber 144, which is shaped to slidably receive and hold a plunger 138 for filling and pressurizing the reservoir chamber 144. The reservoir plunger 138 can be movable parallel to the longitudinal axis of a fill port 140 extending through the plunger 138. The syringe body 101 can include a fluid flow restrictor 146 between the reservoir chamber 144 and the trigger barrel 131. The restrictor 146 can induce a pressure drop between them when fluid flow occurs between the reservoir chamber 144 and the trigger barrel 131. The diameter of the restrictor 146 can be smaller than the diameter of the outlet port 132. In the non-primed position shown in Figure 1A, the fluid flow between the reservoir chamber 144 and the trigger barrel 131 can be blocked by a pair of disk seals 126 and 128. The device further includes a sleeve or pusher 111 that allows a user to advance an epidural needle 147 (see Figure 1B) connected to the needle connector end 130. The pusher 111 can be slidably disposed on the syringe body 101. The pusher 111 can optionally have an external flange or wing 112 and / or a texture or shape for ergonomic purposes. As further discussed below, the pusher 111 can be configured to interact with the trigger mechanism of the device 100.

[0060] The filling port 140 may provide fluid communication between the filling connector 102 and the reservoir chamber 144. A one-way valve 104 is provided within the filling port 140 to prevent or substantially prevent backflow and enable the reservoir chamber 144 to be filled from the rear end, thereby eliminating the need to manually hold the device in the priming position during filling and fill the reservoir chamber 144 from the needle connector end 130 through the outlet port 132 which may otherwise require this. The expanded portion 141 of the plunger 138 may include a seal 142 and an annular shoulder 103.

[0061] The device 100 further includes a trigger mechanism 149 designed to respond to the pressure of the fluid within the trigger barrel 131, and the trigger mechanism 149 is then affected by the pressure of the fluid within the reservoir chamber 144. A bias mechanism (biasing mechanism), particularly a reservoir spring 136, is disposed around the plunger 138 within a space 137 formed between the reservoir cap 109, which may cover the open end 106, and the annular shoulder 103. Instead of a spring, other bias mechanisms such as a flexible rubber (e.g., an elastic band) or compressed air can be implemented. The reservoir spring 136, which is fixed relative to the reservoir cap 106, can bias the reservoir plunger 138 in the direction towards the restrictor 146, thereby being able to pressurize the fluid within the reservoir chamber 144.

[0062] The trigger mechanism 149 may include a trigger piston 133 having a trigger piston core 127 therein. The trigger piston 133 may be provided within a trigger barrel 131, and a first or lower disk seal 126 and a second or upper disk seal 128 may be provided on the outer periphery of the trigger piston 133. The trigger piston core 127 can be directly connected to the trigger piston 133 such that these components can move in harmony together. A third circumferential priming seal 134 may be disposed around the trigger piston 133. The space defined between the priming seal 134, the disk seal 128, and the wall 145 of the trigger barrel and the trigger piston 133 may be referred to as the trigger chamber 150. The trigger piston core 127 may have a priming or trigger button 114 and trigger pins 122 extending from the upper and lower surfaces of the trigger barrel 131, respectively. The trigger piston 133 is slidable within the trigger barrel 131. The priming seal 134 and the disk seal 128 may substantially prevent fluid leakage from the top and bottom ends of the trigger chamber 150. The two disk seals 126 and 128 of the trigger piston 133 may create a sliding seal between the trigger barrel wall 145 and the trigger piston 133. The priming seal 134 may create a sliding seal between the trigger piston 133 and a narrower section of the trigger barrel wall 145. The trigger cap 123 can be connected to and close the open end of the trigger barrel 131.

[0063] The outlet port 132 may be provided at the "front" end of the trigger barrel 131 (i.e., near the needle connector end 130 of the device 100). The outlet port 132 leads to a needle connector end 130 that can be removably attached to a needle connector 148 (FIG. 1B) for connection to an epidural needle 147 (FIG. 1B). The outlet port 132 allows fluid to exit the trigger barrel 131 and ultimately exit the device 100 through the needle 147.

[0064] The trigger spring 124 can be positioned concentrically with the trigger pin 122 and around the trigger pin 122, and may bias the trigger piston 133 away from the trigger cap 123. The trigger cap 123 may include a trigger pin hole 121 and a vent hole 120. The vent hole 120 can be optional. This is because the trigger pin hole 121 may be doubled as a vent hole. The vent hole 120 in the trigger cap 123 may substantially prevent the air trapped between the trigger cap 123, the trigger barrel 131, and the trigger piston 133 from interfering with the sliding movement of the trigger mechanism 149. Thus, the trigger piston core 127 and the trigger pin 122 can fit inside the trigger piston 133 and the trigger barrel 131 so that the trigger pin 122 can slide vertically through the trigger pin hole 121.

[0065] Figures 1B - 1G show the epidural device 100 in various states or alternative views. For clarity, fewer elements are labeled in Figures 1B - 1G compared to Figure 1A. Figure 1B shows the device 100 in an unprimed filled state where the reservoir plunger 138 is held away from the restrictor 146 by the fluid in the reservoir chamber 144. As shown, in the filled state, the reservoir spring 136 is at least partially compressed and thus may pressurize the fluid in the reservoir chamber 144. In this state, the fluid communication between the trigger chamber 150 and the reservoir chamber 144 can be suppressed by the upper disk seal 128 and preferably can be substantially prevented. The lower disk seal 126 may prevent fluid from leaking out from the bottom of the trigger barrel 131 through the trigger cap 123.

[0066] Figure 1C shows device 100 in a loaded and primed position where button 114 is manually depressed to move trigger piston 133 relative to trigger cap 123, thereby shifting trigger pin 122 such that trigger pin 122 extends from trigger pin hole 121. When the device is in the primed position, the axial movement of sliding pusher 111 can be restricted by trigger pin 122. More specifically, when advanced axially toward needle connector end 130, pusher 111 abuts trigger pin 122 at a specific point, thereby substantially preventing further sliding of pusher 111 relative to body 101. When pusher 111 abuts trigger pin 122, most or substantially all of the force can be transmitted from pusher 111 through device 100 to epidural needle 147 (see the following discussion regarding operation).

[0067] Figure 1D shows device 100 in a partially loaded and triggered position as would be expected after the epidural needle 147 is "unblocked" by entering the epidural space, resulting in a pressure drop across restrictor 146 and subsequent upward movement of trigger piston 133 back to the unprimed state. In this triggered state, trigger pin 122 does not prevent sliding of pusher 111 and preferably does not impede sliding of the pusher at all. Thus, force transmission (in the axial direction) may be substantially reduced, except for the frictional force between pusher 111 and body 101, and preferably is prevented between pusher 111 and needle 147, thereby preventing further advancement of needle 147 into the epidural space.

[0068] Figures 1E and 1F show exploded views of the components of device 100, with Figure 1E showing a cross-sectional exploded view.

[0069] Figure 1G shows an isometric view of the assembled device 100.

[0070] The devices shown in FIGS. 2-5 are functionally similar to the device 100 shown in FIG. 1. Accordingly, like elements retain the same reference numerals.

[0071] FIG. 2 is an isometric view of a similar epidural device 200 in an assembled state, where the pusher 211 has extended wings 212. In this configuration, the wings may be closely aligned with a needle connector (148, not shown in this image) to provide improved handling for the user.

[0072] Figure 3 shows an epidural device 300 similar to device 100, but device 300 can be primed differently in that a pusher can be used to push down the trigger piston to prime the device. Figure 3A shows device 300 in an unprimed position. Device 300 includes a trigger piston 352, which is a single component in this exemplary embodiment, and a pusher 311 having a priming lamp 351 and a reset lamp 353. The trigger piston 352 may function similarly to the trigger mechanism 149 described above. Device 300 can be primed by sliding the pusher 311 forward, whereby the priming lamp 351 engages the priming button 315 of the trigger piston 352, thereby pushing the priming button to a primed state as shown in Figure 3B. As described above, the trigger pin 122 may extend from the trigger hole 121 and prevent forward sliding of the pusher 311, thus transmitting force from the pusher 311 through device 300 to an epidural needle 147 (not shown). Figure 3C shows the device in a triggered state, where the trigger piston 352 is allowed to move upward, thus the trigger pin 122 is not engaged with the pusher 311, allowing the pusher 311 to slide forward without significantly advancing the needle 147 or preferably without advancing it at all. The device can be reset by using the reset lamp 353 to operate the trigger piston 352 as needed and sliding the pusher across the trigger mechanism.

[0073] Figures 4A - 4C show another epidural device 400 similar to devices 100 and 300. The device 400 includes a pusher 411 that, in this case, can be used to prime the trigger piston 452 by pulling the sliding pusher 411 away from the needle connector end 130. Figure 4A shows the primed position of the device at the moment when the sliding pusher 411 is pulled back and the priming lamp 451 engages the priming button 415 of the trigger piston 452 to push the priming button 415 into the primed state, whereby the trigger pin 122 can extend outwardly from the trigger pin hole 121 to abut against a shoulder 413 defined in the pusher 411. Figure 4B is also in the primed state, but the sliding pusher 411 is pushed forward to such an extent that the trigger pin 122 engages the pusher 411 at the shoulder 413 so that further movement of the pusher 411 towards the needle connector end 130 is inhibited or prevented. In this state, most of the pushing force can be transmitted from the pusher 411 through the device 400 to an epidural needle 147 (not shown), thereby enabling the needle 147 to advance towards the epidural cavity. Figure 4C shows the device in a triggered state where a pressure drop due to the entry of the needle 147 into the epidural cavity causes the pin 452 to move upwardly such that the trigger pin 122 may no longer engage the shoulder 413. As a result, the pusher 411 may slide further towards the needle connector end 130, thus inhibiting or preventing the advancement of the needle 147. In Figure 4C, the pusher 411 has been moved towards the needle connector 132 to its full extent.

[0074] Each of the above devices includes a reservoir chamber that can be filled with a fluid that can be pressurized by a bias mechanism within the reservoir chamber. The reservoir chamber may not be required to pressurize the fluid before the restrictor. Instead, for example, the fill port 140 can extend from the valve 104 to the restrictor 146 and can be physically integrated with the body 101 (i.e., the port 140 can extend to the restrictor 146 through the length of the body 101). The fill port 140 can be pressurized, for example, by being connected to a pressurized fluid line (i.e., leading to the one-way valve 104). This can eliminate the need for the reservoir chamber 144.

[0075] Figure 5 shows another epidural device 500 similar to device 100. In this version, the reservoir chamber is filled through a port 132 at the front of the device instead of through the fill port 140 as described with respect to Figure 1A. Thus, device 500 can include a plunger 538 that does not have such a fill port 140 defined in the plunger. Accordingly, the one-way valve 104 and the fill connector 102 are not required in device 500. Fluid may enter the reservoir 144 through the trigger chamber 150 and through the one-way valve 555 by means of a means for pulling back on the reservoir plunger 538. Functionally, this device is similar to device 100 in other respects.

[0076] (Differential pressure design) Figures 6A - 6C show another epidural device 600 that can utilize the differential pressure trigger mechanism 649 but is otherwise similar to device 100. In this exemplary embodiment, the trigger spring is replaced by a trigger reservoir 665 that is connected to the syringe reservoir chamber 144 by a relatively wide reservoir connector 666. The trigger piston 652 is vertically movable and may be constrained at the bottom by a trigger cap 623. Similar to device 100, the trigger chamber 650 may be constrained by a priming seal 634 and an upper disk seal 628. The trigger reservoir 665 may be constrained by a lower disk seal 626, a trigger reservoir seal 668, and a trigger cap 623 and its associated trigger cap seal 667.

[0077] The operation of the differential pressure device 600 depends on the differential force on the trigger piston 652 from the trigger chamber 650 and the trigger reservoir 665. The size of the horizontal plane on the trigger piston 652 can be relatively large with respect to the trigger chamber surface 660 and relatively smaller with respect to the trigger reservoir surface 661, which can create a differential force when chambers 650 and 144 are at the same or approximately the same pressure. The details of the operation of this device are described below.

[0078] (Additional Design) Figures 7A - 7C show another epidural device 700 that is functionally similar to the device 100 shown in FIG. 1 but uses two piston pins 772 that, when pressurized, can move outwardly from both the top and bottom of the device 700 and can inhibit or substantially prevent forward movement of the pusher 711 once the pusher 711 contacts the pins 772. The contact angle between the pins and the pusher may be an angle such that the piston pins can move up and down in response to pressure changes within the chamber. When reaching the epidural space, the device can be depressurized, allowing the piston pins 772 to slide inwardly and the pusher 711 to slide forward.

[0079] Figure 7A shows device 700 in a primed, retracted state with piston pin 772 retracted. Figure 7B shows device 700 in a primed state with piston pin 772 extended, stopping forward movement of pusher 711. Figure 7C shows device 700 in a triggered state with the pusher fully slid forward. When the primed device is not blocked (e.g., due to entry of an epidural needle 147 (not shown) into the epidural space), the pressure in the internal chamber may decrease and piston pin 772 may move inward, allowing pusher 711 to move forward.

[0080] Figures 8A and 8B show another epidural device 800 that is functionally similar to device 100. Epidural device 800 includes a syringe body 801 that has a slit 881 defined therein. Body 801 has a tube 882 coaxially disposed therein. Slit 881 may permit longitudinal movement of a pusher 811 that is at least partially received within body 801. Pusher 811 includes a ring 883 disposed on the outer periphery of tube 882. Ring 883 is axially slidable along tube 882 and may have two wings 812 connected to ring 883, the two wings extending out of body 801 through slit 881. Pusher 811 is slidable coaxially within body 801 by applying a force to wings 812. Tube 882 may have at least one hole 884 defined in the tube to permit fluid communication therebetween that can exit tube 882 and enter a membrane 885 surrounding a hole, the membrane being shown in its expanded (pressurized) state in Figure 8A and being able to expand and contract in response to pressure.

[0081] When an epidural needle 147 (not shown) enters the epidural space, the loss of pressure causes the membrane 885 to contract, thereby enabling the movement of the ring 883 and thus the pusher 811. When the pusher 811 slides over the contracted membrane as shown in FIG. 8B, most of the force applied to the pusher 811 is not transmitted to the needle 147, and thus further advancement of the needle 147 can be inhibited.

[0082] Figures 9A - 9D illustrate yet another exemplary embodiment of an epidural device 900. Similar to device 800, device 900 includes a syringe body 901 having a slit 981 defined therein. Body 901 has a tube 982 coaxially disposed therein. Slit 981 may permit longitudinal movement of a pusher 911 at least partially housed within body 901. Pusher 911 includes a sleeve 992 slidably disposed about the outer periphery of tube 982. Sleeve 992 is axially slidable along tube 982 and has two wings 912 connected to sleeve 992, the two wings 912 extending from body 901 through slit 981. Pusher 911 is slidable coaxially within body 901 by applying a force to wings 912. Tube 982 may have at least one hole 984 through which fluid may exit tube 982 and travel towards a flexible or compliant section 991 of tube 982 surrounding the hole. Flexible section 991 may be made of plastic or another flexible material and may bend and flare outward when exposed to an increase in fluid pressure. As discussed with respect to previous exemplary embodiments, when device 900 is filled with fluid and there is no fluid or substantial resistance flowing out of needle 147 (not shown), the pressure within tube 982 may increase. When pressurized, flexible section 991 expands to press against pusher sleeve 992 surrounding flexible section 991, thereby forming a frictional bond between pusher sleeve 992 and flexible section 991 which can enable advancement of the needle in response to the application of force to wings 912 extending radially from pusher 911. This state is shown in Figure 9A and can be seen in detail in Figure 9C.

[0083] Upon reaching the epidural space, the pressure within device 900 drops, collapsing the flexible section 991, thereby disengaging the sleeve 992. The device 900 in this triggered state is shown in FIG. 9B and can be seen in detail in FIG. 9D. The sleeve 992, and thus the pusher 911, are now disengaged and can move freely from the needle 147, thus halting further advancement of the needle.

[0084] Rather than being removably attachable, the needle 147 can be physically integrated with any of the devices of the present disclosure.

[0085] (Operation of Pressure Loss Design (FIGS. 1-5)) The operation of the epidural device 100 is described below. As noted above, devices 100, 300, 400, and 500 have a number of similar configurations and thus their operations are similar. Discussion of devices 300, 400, and 500 is limited to configurations not included in device 100.

[0086] When the trigger piston 133 is at the upper end of the trigger barrel 131, the trigger pin 122 may be retracted within the outer surface of the trigger cap 123, thus not interfering with the sliding of the pusher 111. This is the unprimed or triggered position and is the default state for the device. In this position, the restrictor 146 is substantially aligned with the space between the two disk seals 126 and 128 of the trigger piston 133, and fluid flow between the reservoir chamber 144 and the trigger chamber 150 may be substantially or completely prevented.

[0087] When the trigger piston 133 is at the bottom of the trigger barrel 131, the trigger pin 122 may extend beyond the outer surface of the trigger cap 123 and interfere with the forward sliding movement of the pusher 111. This is herein referred to as the primed position. To move the trigger piston 133 to this position within devices 100 and 500, the trigger spring 124 may be compressed by pressing the priming button 114. The piston can be moved to such a position within devices 300 and 400 by moving the pusher forward and sliding the pusher backward. In this position, the restrictor 146 is aligned with the trigger chamber 150, allowing fluid communication between the reservoir 144 and the trigger chamber 150, respectively.

[0088] When the device is almost or completely filled with fluid and the epidural needle 147 attached to the outlet port 132 at the needle connector end 130 is blocked or has sufficient resistance to fluid outflow (e.g., when the needle 147 is within a dense ligament), there may be little or no fluid through the restrictor 146, and thus no pressure drop from the reservoir chamber 144 to the trigger chamber 150. In this state, the force due to the chamber pressure within the trigger chamber 150 may maintain the trigger mechanism 149 in the primed position. When the epidural needle 147 is "unblocked" (i.e., when the resistance to fluid outflow is sufficiently reduced), flow through the restrictor occurs, causing a corresponding pressure drop across the restrictor 146 and reducing the pressure within the trigger chamber 150 relative to the reservoir chamber 144. When the pressure within the trigger chamber 150 drops below the pressure required to keep the trigger spring 124 compressed and the trigger piston 133 in the primed position, the trigger spring 124 can push the trigger piston 133 to the triggered position. In such a position, the trigger pin 122 may disengage from the sliding pusher 111. This may, in turn, automatically inhibit or prevent further advancement of the epidural needle 147 into the epidural space.

[0089] Preferably, the restrictor 146 is sized such that a slow outflow of fluid from the needle 147 can occur without triggering the device. This may prevent the device 100 from being triggered before the needle 147 enters the epidural space.

[0090] (Operation of the differential pressure epidural device (FIG. 6)) Once the device 600 is filled with fluid and primed, and the epidural needle 147 is at least partially blocked as described above, for example, by the needle tip within the ligament, there is little or no flow across the restrictor 146, and thus no (or negligible) pressure drop, so the pressures in the trigger reservoir 665 and the trigger chamber 650 are approximately equal. When the pressures in the chambers (665 and 650) are equal, due to the larger area of the trigger chamber surface 660, there may be a greater force on the trigger piston 652 on the trigger chamber 650 side, and thus the device 600 may remain in the primed position. In this position, the trigger pin 622 may prevent axial movement of the pusher. While the device is filled or almost filled with fluid, when the epidural needle is "not blocked" (i.e., when the resistance to fluid outflow is sufficiently reduced), there may be fluid flow and pressure drop across the restrictor 146, so the pressure in the trigger reservoir 665 may be greater than the pressure in the trigger chamber 650. If the pressure difference is large enough, the force on the smaller surface 661 (trigger reservoir) of the trigger piston will overcome the force on the larger surface 660 (trigger chamber), and the trigger piston 652 can move to the triggered position, where the trigger pin 622 may not prevent the pusher from sliding axially towards the needle connector end 130.

[0091] However, if there is a sufficiently slow flow of fluid from the epidural needle 147 (e.g., into muscle tissue), the pressure drop across the restrictor may be negligible, and the force resulting on the trigger piston 652 may not cause an early trigger. If the epidural needle 147 is "blocked" again and there is still pressurized fluid in the reservoir 144, the trigger piston 652 may be returned to the primed position by pressing the priming button 614. If the device runs out of fluid, the force on each of the faces of the trigger piston can both decrease to zero, and the trigger piston 652 may remain in its last or most recent position. This is because there is no fluid pressure to drive the trigger piston 652 in either direction. In this case, even if the needle 147 reaches the epidural space, the device 600 may not be triggered. This can be overcome by incorporating into the reservoir plunger 138 an inclined pin (not shown) that can interact with the piston 652 to push the piston 652 upward when the reservoir 144 runs out of fluid, thereby disengaging the trigger pin 622 from the pusher 111.

[0092] Each of the devices 700, 800, and 900 operates in a manner similar to that described above using variations to the trigger mechanism and pusher configuration. Although not shown, the trigger mechanisms in the devices 700, 800, and 900 can be combined with a configuration similar to that described with reference to FIGS. 1A - 1D and FIGS. 3A - 5 to achieve a similar trigger response, for example, by restricting the outflow of fluid from the outlet port into the patient to reduce the likelihood of an early trigger.

[0093] The automatic disengagement mechanism of the epidural device described herein may have other uses not discussed above. Without being bound by any theory, it is contemplated that a needle and syringe device including a disengagement mechanism in accordance with the present disclosure can be configured for other medical uses. More generally, the automatic disengagement mechanism described herein may be applied when it is desirable to advance a needle through a material having a relatively high resistance to flow from the needle into a material having a relatively low resistance to flow from the needle and ultimately to inhibit or prevent unwanted advancement of the needle beyond the low resistance material. This description is not limited to any particular trigger mechanism for disengaging the pushing means from the epidural needle.

[0094] For simplicity and clarity of illustration, where appropriate, reference numerals may be repeated between figures to indicate corresponding or similar elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the examples described herein. However, it will be understood by those of ordinary skill in the art that the examples described herein may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the examples described herein. Also, this description should not be considered as limiting the scope of the examples described herein.

[0095] It will be understood that the examples and corresponding figures used herein are for illustrative purposes only. Different configurations and terminology may be used without departing from the principles expressed herein. For example, components and modules can be added, removed, modified, or arranged with different connections without departing from these principles.

[0096] While the principles have been described with reference to specific specific examples, various modifications thereof will be apparent to those of ordinary skill in the art as outlined in the appended claims.

Claims

1. An elongated body having a longitudinal axis, An inlet, An outlet removably attachable to a needle having a through passage, A sleeve slidably disposed around the outer surface of the body, A first chamber defined in the body and configured to receive a fluid, A second chamber defined in the body and configured to carry the fluid to the outlet, A flow restrictor between the first chamber and the second chamber for providing fluid communication between the first chamber and the second chamber, the flow restrictor having a diameter smaller than the diameter of the outlet, The first chamber has a first bias mechanism positioned within the first chamber to pressurize the first chamber, The second chamber has a piston including a core provided within the second chamber, the second chamber has a second bias mechanism positioned within the second chamber to bias the piston, the piston being slidable within the second chamber, A primed position in which the piston is moved away from the flow restrictor and the fluid can travel between the first chamber and the second chamber, A triggered position in which the piston covers the flow restrictor and the fluid can exit the second chamber through the outlet And is movable therebetween, In the primed position, the sleeve is engageable by an extension of the core extending outside the body through a hole defined in a trigger cap that forms the body or a part of the body to prevent the sleeve from moving axially towards the outlet, In the triggered position, the sleeve is not engageable by the extension of the piston and the sleeve is axially movable towards the outlet, An epidural device.

2. The first chamber is configured to receive the fluid from the inlet and has an opening in the first chamber opposite the flow restrictor, and the epidural device further includes a plunger extending into the chamber through the opening, the plunger having, A flow port defined within the plunger to provide fluid communication between the inlet and the first chamber, A distal end positioned within the first chamber, A proximal end, positioned outside the chamber and configured to engage the inlet. The epidural device according to claim 1.

3. The first chamber has an opening in the first chamber opposite the flow restrictor, and the epidural device further includes a plunger extending into the chamber through the opening, the plunger having A distal end positioned within the first chamber, and A proximal end positioned outside the chamber. The epidural device according to claim 1.

4. The first biasing mechanism is a spring provided within the chamber around the plunger intermediate the distal end of the plunger and the opening of the chamber. The epidural device according to claim 2 or 3.

5. A filling port for filling the first chamber extends between the first chamber and the second chamber, the filling port including a one-way valve that permits flow from the second chamber to the first chamber. The epidural device according to claim 3 or 4.

6. When the epidural device is in the primed position, at least a portion of the fluid can exit the second chamber through the outlet without triggering the epidural device. The epidural device according to any one of claims 1 to 5.

7. The second biasing mechanism is weaker than the first biasing mechanism. The epidural device according to any one of claims 1 to 6.

8. The second biasing mechanism is a spring. The epidural device according to claim 7.

9. The piston includes a disk extending radially from the piston, the disk dividing the second chamber into a trigger chamber and a trigger reservoir, the trigger chamber and the trigger reservoir having a trigger chamber surface and a trigger reservoir surface respectively, the trigger reservoir being in fluid communication with the first chamber via a reservoir connector extending between the trigger reservoir and the first chamber. When the epidural device is in the primed position, the disk is positioned intermediate the reservoir connector and the flow restrictor, and the trigger chamber is in fluid communication with the first chamber and the outlet. When the epidural device is in the triggered position, the disk covers the flow restrictor. The trigger chamber cannot be in fluid communication with the first chamber. The epidural device according to any one of claims 1 to 6.

10. The surface area of the trigger chamber surface relative to the horizontal plane of the disk is larger than the surface area of the trigger reservoir surface relative to the horizontal plane of the disk so as to create a differential force on the piston from the trigger chamber and the trigger reservoir. The epidural device according to claim 9.

11. The piston includes a button at its end opposite the extension portion that can be pressed by a user in a direction toward the extension portion to prime the epidural device. The epidural device according to any one of claims 1 to 10.

12. The sleeve includes a protrusion extending from the sleeve toward the body of the epidural device, and the protrusion is configured to prime the epidural device by pressing the button of the piston when the sleeve slides over the piston. The button is attached to the end of the piston opposite the extension portion. The epidural device according to any one of claims 1 to 10.

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