Surgery – Means for introducing or removing material from body for... – Gas application
Reexamination Certificate
2001-04-02
2002-10-01
Nguyen, Anhtuan T. (Department: 3763)
Surgery
Means for introducing or removing material from body for...
Gas application
Reexamination Certificate
active
06458093
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device for insufflating gas, such as CO
2
, into a corporeal cavity of a human or animal body and including a source of gas and a control unit regulating the gas pressure and gas flow through a needle during an endoscopic surgery.
BACKGROUND OF THE INVENTION
A good number of embodiments of generic type devices for insufflating gas are known. With regard to this, reference is made to DE-A-30 00 218, EP-B-O 169 972, DE-C-36 11 018, U.S. Pat. No. 4,874,362 and DE-A-42 19 859. Moreover, reference is explicitly made to these printed publications for the explanation of all details not made more apparent herein.
A typical device for insufflating gas
10
into a corporeal cavity
30
, as shown in
FIG. 3
, possesses a connection for a gas source
32
, such as a pressure cylinder, and the capability of setting the gas pressure and the gas flow. For this purpose, the known devices are provided with, for example, a pressure and the gas flow sensors. Also, the known devices are provided with, a pressure/gas flow regulator
34
which reduces the pressure of the gas source to a insufflation pressure (desired gas pressure), which can be set, of typically between 0 and 50 mm Hg, and a flow regulator which sets the gas flow to a value (desired gas flow).
In the generic devices described in the aforementioned printed publications, the gas pressure or the gas flow can not only be controlled, but they are also regulated. For this purpose, these devices are provided with a measuring device having sensors for the actual gas pressure
36
and the actual gas flow
38
, and with a control unit
40
to which the output signals from these sensors are applied and which controls the pressure regulator and the flow regulator
34
, as shown in FIG.
3
.
However, a problem with the known devices for insufflating gas into a corporeal cavity is measuring the gas pressure, because it is usually impossible or only with great effort to measure the gas pressure directly inside the corporeal cavity. Due to the streaming gas and the drop in pressure (i.e. generated thereby), measuring the pressure outside the corporeal cavity leads to a measuring error, which cannot be readily tolerated in medical applications.
Therefore, it is proposed in that order to measure the “static” gas pressure P, to reduce the gas flow Q to the value 0 and to measure the gas pressure when the gas flow actually reaches the value 0 “statically”. With regard to this, reference is made to
FIG. 6
of U.S. Pat. No. 4,874,362 and the respective specification. Although this method has the advantage that it permits relatively accurate measurement of the gas pressure, it has the disadvantage that it does not permit an even relatively constant gas supply.
Furthermore, it has been proposed to calculate the pressure actually prevailing in the corporeal cavity from the output signal of the sensor while taking into account the flow resistance of the tube instrument and the insufflation instrument, such as a Verres needle, between the pressure sensor and the corporeal cavity whose pressure is to be determined.
However, in practice determining the flow resistance and the drop in pressure between the pressure sensor and the corporeal cavity has proven difficult.
SUMMARY OF THE INVENTION
The invented device is distinguished by the fact that, the control unit calculates the drop in pressure P
drop
between the location of the pressure sensor and the corporeal cavity and therefore the actual gas pressure P
abd
inside the corporeal cavity (intraabdominal pressure), as a function of the gas pressure P
fill
measured outside the corporeal cavity and the measured gas flow Q. The calculated drop in pressure P
drop
as the function of Q is less or at the most equals the actual drop in pressure. The control unit calculates the gas pressure P
abd
in an event and/or time controlled manner during normal insufflation and regulates the insufflation on the basis of the calculated gas pressure P
abd
.
An object of the present invention is to further develop a device for insufflating gas into a corporeal cavity of a human or animal body in such a manner that the drop in pressure between the pressure sensor and the corporeal cavity and therefore the pressure inside the corporeal cavity can be determined as accurately as possible while ensuring highest possible patient safety.
The present invention is based on a generic device for insufflating gas into a corporeal cavity of a human or animal body and further improves this device according to the present invention as follows:
For calculating the drop in pressure P
drop
between the site of the pressure sensor and the corporeal cavity, whose pressure as the actual gas pressure P
abd
(intraabdominal pressure) is the relevant pressure, the control unit uses one of a plurality of simple functions of the gas pressure P
fill
measured outside the corporeal cavity and of the measured gas flow Q. On the basis of these functions, the calculated pressure drop P
drop
as the function of Q is less than or at most equals the actual pressure drop. Furthermore, the control unit continuously calculates the event and/or time controlled gas pressure P
abd
during the normal insufflation and regulates insufflation on the basis of the calculated gas pressure P
abd
Thus, unlike prior art systems, no single complicated mathematical function is used to express the variation in pressure drop from the gas flow rate throughout the entire range of values of gas flow rate. Instead, the function to be employed is selected from a plurality of functions based upon the flow rate. Thus, in the example more fully discussed below, a function having a simple square dependency on the pressure drop of the gas flow rate is used only at low gas flow rates, while a function having a simple linear dependency is used only at high gas flow rates. Thus, to cover the entire range of gas flow rates, either one function or the other is used, as expedient.
Based on the invention method, the intraabdominal pressure prevailing inside the corporeal cavity is not underestimated at any time. As the intraabdominal pressure prevailing inside the corporeal cavity is continuously determined, contrary to the known devices in which the intraabdominal pressure is determined at relatively large time intervals, a too high a pressure can never occur inside the corporeal cavity.
Tests have shown that at usual gas flows of up to 20 liter/min, as are used in medical insufflation procedures, it is sufficient to employ two functions for determining the drop in pressure, which are drawn upon for certain flow rates.
Thus, according to one aspect of the Invention, it is preferred that when the flow rates are less than a specific flow rate Q
ums
, a square dependency of the pressure drop on the flow rate is utilized. At flow rates that are greater than this specific flow rate, it is preferred if a linear dependency of the drop in pressure on the flow rate is utilized. Using these two functions ensures that the calculated drop in pressure is always less than or at most equals the actually occurring drop in pressure between the measurement site and inside the body, so that a too high a pressure can never occur inside the body cavity.
The invented principle for determining the pressure drop in the tubes and in the other instruments in dependency on the flow rate can be applied in a great variety of devices.
For instance, it can be applied in devices in which the control unit determines the constants K
1
and K
2
while taking into account the flow resistance of the insufflation instruments. In particular, it is conceivable that these constants are calculated on the basis of expectancy values and the respective length of the tube instrument as well as of the employed instrument.
However, it is particularly advantageous that according to another aspect of the invention, in order to determine the constants K
1
, and K
2
, the control unit determines the values P
fill
and Q (to be utilized in the equation in the resolution of these equations
Gord John C.
Jones Eric M.
Kraft-Kivikoski Juergen
St. Onge Steward Johnston & Reens LLC
Storz Endoskop GmbH
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