Insufflation system and insufflation method for low-volume body cavities

Abstract

The invention relates to an insufflation system with pressure monitoring for the insufflation of low-volume body cavities, wherein the insufflation volume flow is periodically reduced by approximately 10% for the purpose of pressure measurement.

Description

[0001] Insufflation system and method for insufflation of small volume body cavities

[0002] Subject of the invention

[0003] The invention relates to an insufflation system with pressure monitoring for the insufflation of small-volume body cavities.

[0004] State of the art

[0005] It is well known that endoscopic surgery involves expanding body cavities by introducing fluids (gases or liquids) to allow medical instruments to be inserted into the body cavities and improve visualization of internal organs. During such procedures, it is important to monitor the pressure within the body cavity to prevent tissue damage. A simple approach to this is to insert a pressure sensor into the body cavity. The disadvantage of this approach is that the pressure sensor limits the field of view and the surgical site. Furthermore, for infection control reasons, efforts are made to minimize the number of instruments introduced into the body cavity.

[0006] An alternative to this is to place a pressure sensor in the tube that introduces the fluid into the body. This gives rise to the problem that the pressure in the body cavity is not the same as the pressure in the tube, as pressure losses occur along the length of the tube and the medical instrument (e.g. trocar). Furthermore, the pressure measurement is influenced by the gas flow. To solve this problem, various methods have been developed to calculate pressure losses. To avoid the interference caused by the gas flow mentioned above, the gas flow is often interrupted. In these cases, the gas volume flow is reduced to zero, the system waits until the pressure has equalized between the body cavity and the gas tube (with a gas pressure sensor), the current pressure is measured, and then the gas introduction is continued.The phase during which the gas flow is interrupted is commonly referred to as the "measurement pause," although it is more accurately referred to as an "insufflation pause for pressure measurement." This method produces acceptable results in large body cavities, such as abdominal examinations, without any problems.

[0007] However, there is room for improvement in small body cavities, such as those used for rectal procedures. Small body cavities (such as the aforementioned rectum) are often very sensitive, making it particularly important to precisely adjust the pressure and avoid any overpressure. At the same time, due to their small volume, there is a need for maximum dilation for examination or medical intervention.

[0008] Another problem is that during the aforementioned measurement pauses, the insufflation gases can escape to a greater or lesser extent due to leaks. In the case of large body cavities (e.g., in the abdomen), leaks are generally unproblematic because sufficient gas volume is available. During the insufflation pause, the pressure loss is minimal. The situation is different for small body cavities: Even minor leaks can lead to significant pressure losses and the associated reduction of the body cavity volume, which makes necessary medical interventions very difficult, for example, due to wall movement.

[0009] There is therefore a need for an insufflator that can use an insufflation method suitable for insufflating small body cavities without the insufflation pauses required for pressure measurement leading to significant pressure losses in the small-volume body cavity.

[0010] Inventive solution

[0011] The solution to the above-mentioned problem is achieved by an insufflator according to claim 1, namely a medical device for introducing fluids into body cavities, containing a controllable fluid pump, a supply line, a pressure sensor in the supply line, a control unit with a memory with the possibility of inputting a desired pressure and a volume flow for expanding a small-volume body cavity, a computing unit for calculating the pressure in the body cavity, characterized in that the device is designed to ensure a volume flow of the fluid into the body cavity, to reduce the volume flow every 0.2 - 0.8 seconds for 20-100 milliseconds in order to ensure both in the phase of the reduced volume flow,as well as in the same length phase after the volume flow reduction, to measure the pressure in the supply line by means of the pressure sensor and to output the mean value of the measured pressure during the volume flow reduction and the same length phase after the volume flow reduction as the pressure of the body cavity,

[0012] Surprisingly, it was found that pressure measurement during insufflation can be performed with sufficient precision if the gas volume flow applied for insufflation is not reduced by 100% to zero for the purpose of pressure measurement, but is only reduced by about 10%.

[0013] An insufflator according to the invention therefore contains at least the following components: a fluid pump which enables the regulation of volume flow and pressure, a supply line with a trocar, a pressure sensor in the supply line for supplying the fluid into the body cavity, an electronic control unit with a memory and with the option of inputting a target pressure and a volume flow, a computing unit for calculating the pressure in the body cavity in accordance with the following description.

[0014] For the purpose of insufflation, the insufflator is connected to a trocar via a tube. The trocar is inserted into the body cavity in the usual way. Within the meaning of the invention, small-volume body cavities are considered to be those with a volume of less than 250 ml, in particular less than 150 ml. The advantage of the insufflator according to the invention is particularly evident in body cavities with a volume of less than 100 ml. These include, in particular, body cavities such as the rectum, uterus, or bladder, but also body cavities of small children, infants, and premature babies. At the beginning of insufflation (expansion phase), an initial volume flow is typically required, which is usually in the range of 1–3 l / min. In a preferred embodiment, the insufflator can automatically calculate the size of the cavity from the volume flow and pressure change data, as described in WO 2021 / 24469090 A1.In this case, the volume flow is automatically adjusted based on the determined cavity size and its compliance.

[0015] The flow rate is automatically reduced once the target pressure is reached. The flow rate required to maintain the pressure corresponds to the size of the leak and is typically in the range of 1 to 3 l / min. This pressure maintenance flow rate is preferably calculated and adjusted automatically based on the pressure measurement data.

[0016] During maintenance insufflation, i.e., after the inflation phase until the end of the procedure, the flow rate is reduced regularly by 7.5-15%, e.g., every 0.2-0.8 seconds for 20-100 milliseconds. During this reduced insufflation phase, the pressure is measured using the pressure sensor in the tube. Insufflation is then resumed at the original gas flow rate.

[0017] To determine the pressure in the cavity, the measured values ​​during the reduced flow phase and the equally long phase after the flow reduction are averaged. When the flow rate is reduced for 50 milliseconds, measured values ​​are collected both within the 50 milliseconds and in the 50 milliseconds after the reduction. The measurements are typically taken at a sampling rate of 100-1000 per second (preferably 500 per second). This provides a determination of the so-called driver pressure at the location of the pressure sensor.

[0018] As part of the pressure determination, the measured driver pressures are preferably corrected.

[0019] As described in relevant documents (see e.g. WO 2018 / 064996 A1 ), there is a flow-related pressure difference Ap between the body cavity (cavity pressure) and the location of the sensor (driver pressure), whereby the pressure difference depends mainly on the volume flow and the resistance coefficients of the trocar and is calculated according to the following equation:

[0020] Equation 1 where Ap is the pressure difference between the cavity and the location of the pressure sensor

[0021] V is the volume flow 1 , ^2 are the resistance coefficients of the trocar.

[0022] A further improvement by increasing the measurement accuracy for the pressure values ​​of the driver pressure is achieved if the measured values ​​described above are averaged over 5-10 seconds.

[0023] The quality of the measurements can be determined by calculating the variance of the measured values ​​of the quotient of pressure and the square of the volume flow:

[0024] Equation 2 where p is measured pressure

[0025] V represents the volume flow.

[0026] Typically, 20–40 corrected measurements are used to calculate the statistical variance. For this purpose, the measured pressure p is corrected using Equation 1. The corrected pressure (driver pressure p minus Ap = corrected pressure in the body cavity) then corresponds to the pressure in the body cavity.

[0027] A variance is thus calculated from 20-40% of the pressure values ​​corrected as described above from the already averaged driver pressure values. A variance of the measured values ​​of less than 2% indicates a reliable pressure calculation. If this threshold of 2% is reached or exceeded, the corrected cavity pressure (pressure corrected according to Equation 1) is used as the actual value for controlling the cavity pressure.

[0028] Within the scope of the invention, it was discovered that pressure measurement becomes more precise when the volume flow is reduced more significantly, e.g., by 20% or 25%. However, with a greater reduction in the volume flow, the phase of reduced insufflation becomes longer, so that pressure and volume fluctuations in the body cavity are more pronounced. The aforementioned volume flow reduction of approximately 10% represents a compromise between simultaneously optimizing measurement accuracy and pressure fluctuations in the body cavity. A reduction of only 5% did not lead to the desired precision of the pressure measurements.

[0029] It goes without saying that the pressure measurement becomes more precise the closer the pressure sensor is positioned to the body cavity. However, for cost reasons, it is preferable to install the pressure sensor in the insufflator, so that at least the trocar and tube are located between the pressure sensor and the body cavity. It has been found that the device's design according to the invention enables excellent measurement accuracy.

[0030] The above-mentioned method can also be used during the expansion phase described at the beginning.

[0031] Figure 1 schematically shows the pressure development in the cavity during insufflation according to the invention: a) shows the pressure development in the cavity. The control parameter is the insufflation flow (qinsuffiation). The insufflation flow pulsates according to the invention (regular flow reduction by approximately 10%) for the purpose of the pressure measurement according to the invention. qinsuffiation is the volume flow.

[0032] Preference is the desired target pressure

[0033] Pestimated is the pressure determined by the system

[0034] Pcavity is the actual pressure in the body cavity (determined during a control measurement)

[0035] It can be seen how the pressure determined according to the invention initially deviates from the actual pressure, but then increasingly corresponds to the actual pressure. After 20-40 reductions in the insufflation flow and measurements taken during this time, the difference between the pressure determined according to the invention and the actual pressure is close enough that using the pressure determined according to the invention does not pose any problems. b) shows the development of confidence in the estimated dynamics. The duration of the individual phases depends on the connected instruments and disturbances in the system. After approximately 20-40 flow reductions and the pressure measurements taken according to the invention (corrected according to equation 1), the variance of the measured values ​​falls to a value of less than 2% and thus indicates a reliable pressure determination.The actual pressure in the body cavity pcavity is close enough to the pressure pestimated determined according to the invention for the purpose of the device.

Claims

Patent claims: 1) A medical device for introducing fluids into body cavities, comprising a controllable fluid pump, a supply line with a trocar, a pressure sensor in the supply line, a control unit with a memory with the option of inputting a desired pressure and a volume flow for expanding a small-volume body cavity, a computing unit for calculating the pressure in the body cavity, characterized in that the device is designed to ensure a volume flow of the fluid into the body cavity, to reduce the volume flow by 7.5-15% every 0.2 - 0.8 seconds for 20-100 milliseconds in order to ensure both in the period of the reduced volume flow,as well as in an equally long period after the volume flow reduction, to measure the pressure in the supply line by means of the pressure sensor and to output the mean value of the measured pressure during the volume flow reduction and the equally long period after the volume flow reduction as the pressure of the body cavity. 2) Medical device for introducing fluids into body cavities according to claim 1, wherein the reduction of the first and / or the second volume flow occurs by approximately 10%. 3) Medical device for introducing fluids into body cavities according to claim 1 or 2, wherein the reduction of the volume flow occurs regularly after 0.5 seconds. 4) Medical device for introducing fluids into body cavities according to one of claims 1-3, wherein the phase of the reduced volume flow is 50 milliseconds. 5) Medical device for introducing fluids into body cavities according to one of claims 1-4, wherein the pressure difference Ap between the body cavity and the location of the sensor is calculated according to the following equation 1: Equation 1 Ap = ^ ■ V 2 + (2■ V where Ap is the pressure difference between the cavity and the location of the pressure sensor V is the volume flow 1, the resistance coefficients of the trocar. 6) Medical device for introducing fluids into body cavities according to one of claims 1-5, wherein the body cavity has a volume of less than 250 ml. 7) Medical device for introducing fluids into body cavities according to one of claims 1-5, wherein the body cavity has a volume of less than 100 ml.

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