Surgery – Respiratory method or device
Reexamination Certificate
2003-03-17
2004-11-23
Lewis, Aaron J. (Department: 3743)
Surgery
Respiratory method or device
C128S204210, C128S204230
Reexamination Certificate
active
06820613
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to a process for controlling at least one parameter of the breathing gas supply of a respirator with a patient connected to it as well as to a corresponding control device.
BACKGROUND OF THE INVENTION
The parameters of breathing gas supply by the respirator, e.g., the respiration pressure, the breathing gas flow or the respiration rate, are usually set in advance and are then checked for their validity at greater time intervals. If the patient's respiration need changes, this is then taken into account during the treatment when the parameters of the breathing gas supply are correspondingly adapted after a recent check of the respiration need. A breathing gas supply is therefore obtained that may not be oriented uninterruptedly on the patient's current needs.
DE 198 08 543 C2 discloses a process by which the mechanical properties compliance, resistance and, finally, the muscle pressure of the respiratory system of a patient can be determined during both spontaneous breathing and mechanical respiration, and the patient's breathing is disturbed only minimally. The compliance is the quotient of the displaced breathing gas volume and the change in the airway pressure, and the resistance is the quotient of the change of the airway pressure and the change in the breathing gas flow. The muscle pressure is defined as the percentage of the airway pressure caused by the patient's own effort. This process makes it possible to perform the continuous determination of the muscle pressure of the patient and thus to monitor the intensity of his spontaneous breathing. An occlusion, during which the respiration or spontaneous breathing of the patient is interrupted by closing corresponding valves on a respiration tube leading to the patient, is brought about for this purpose for a short time at different points in time during the individual breathing strokes. The mechanical properties of the lungs can be determined from the measured values for the airway pressure and the breathing gas flow. The muscle pressure is in turn determined from these variables.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a process as well as a device for controlling at least one parameter of the breathing gas supply for a patient, which takes into account the current state of his respiratory system.
According to the present invention, the measured values for the airway pressure, P
AW
, and the breathing gas flow, d/dt V, are used continuously for the determination of the mechanical properties of the patient's respiratory system, i.e., the resistance R
L
and the compliance C of his lungs, and, finally for the determination of the muscle pressure P
MUS.
According to the invention, a process is provided for controlling at least one parameter of the breathing gas supply of a respirator with a patient connected to it. With a brief disturbance of the breathing gas supply taking place during a first phase of expiration, the airway pressure P
AW
and the breathing gas flow d/dt V are measured before and during the disturbance, and the resistance R
L
of the patient's lungs is determined as the quotient of the airway pressure P
AW
and the change in the breathing gas flow d/dt V. The airway pressure P
AW
and the breathing gas flow d/dt V are measured during a second, undisturbed phase of expiration, and the compliance C of the patient's lungs is determined from this as well as from the resistance R
L
. The breathing gas flow d/dt V is measured each time during the subsequent breaths, and an airway pressure P
AW
C
is calculated from this together with the resistance R
L
and the compliance C. A muscle pressure P
MUS
is determined as the difference between the calculated airway pressure P
AW
C
and the actually measured airway pressure P
AW
. The at least one parameter of the breathing gas supply is changed such that the breathing gas supply is increased during the further phases of inspiration when the muscle pressure P
MUS
is above a set point P
0
, and the at least one parameter of the breathing gas supply is changed such that the breathing gas supply is reduced during the subsequent phases of inspiration when the muscle pressure P
MUS
is below the set point P
0
until the muscle pressure P
MUS
reaches the set point P
0
.
According to another aspect of the invention a device is provided for controlling at least one parameter of the breathing gas supply of a respirator with a patient connected to it. The device includes means designed to bring about a brief disturbance in the breathing gas supply during a phase of expiration. A first sensor is provided for measuring the airway pressure P
AW
and a second sensor is provided for measuring the breathing gas flow d/dt V. An evaluating and control unit is provided for determining the resistance R
L
and the compliance C of the patient's lungs from the airway pressure P
AW
measured by the first sensor and the breathing gas flow d/dt V measured by the second sensor, for calculating an airway pressure P
AW
C
from the resistance R
L
, the compliance C and the measured breathing gas flow d/dt V, and for determining a muscle pressure P
MUS
as the difference between the calculated airway pressure P
AW
C
and the actually measured airway pressure P
AW
. The at least one parameter of the breathing gas supply is changed by the evaluating and control unit such that the breathing gas supply is increased during the subsequent phases of inspiration when the muscle pressure P
MUS
is above a set point P
0
, and the at least one parameter of the breathing gas supply is changed by the evaluating and control unit such that the breathing gas supply is reduced during the subsequent phases of inspiration when the muscle pressure P
MUS
is below the set point P
0
until the muscle pressure P
MUS
reaches the set point P
0
.
According to another aspect of the invention a process is provided for controlling at least one parameter of the breathing gas supply of a respirator with a patient connected to it. The airway pressure P
AW
and the breathing gas flow d/dt V are measured in a plurality of phases of expiration, and the resistance R
L
and the compliance C of the patient's lungs are determined from this. The breathing gas flow d/dt V is measured during subsequent breaths and an airway pressure P
AW
C
is calculated from this together with the resistance R
L
and the compliance C. A muscle pressure P
MUS
is determined as the difference between the calculated airway pressure P
AW
C
and the actually measured airway pressure P
AW
. The at least one parameter of the breathing gas supply is changed such that the breathing gas supply is increased during the subsequent phases of inspiration when the muscle pressure is above a set point P
0
, and the at least one parameter of the breathing gas supply is changed such that the breathing gas supply is reduced during the subsequent phases of inspiration when the muscle pressure P
MUS
is below the set point P
0
until the muscle pressure P
MUS
reaches the set point.
In the process for controlling at least one parameter of the breathing gas supply of a respirator with a patient connected to it, the breathing gas supply is briefly disturbed during a first phase of expiration. The airway pressure P
AW
and the breathing gas flow d/dt V are measured before and during the disturbance. The resistance R
L
of the patient's lungs is determined from this. The airway pressure P
AW
and the breathing gas flow d/dt V are likewise measured during a second, undisturbed phase of expiration. The compliance C of the patient's lungs is determined from these values as well as the resistance R
L
determined in the preceding step.
The breathing gas flow d/dt V is measuring during the subsequent breaths. Together with the values determined before for the resistance R
L
and the compliance C, an airway pressure P
AW
C
is calculated from this.
The muscle pressure P
MUS
, i.e., the percentage of the airway pressure caused by the patient&a
Weismann Dieter
Wenkebach Ullrich
Dräger Medical AG & Co. KGaA
Lewis Aaron J.
McGlew and Tuttle , P.C.
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