Surgery – Respiratory method or device – Means for supplying respiratory gas under positive pressure
Reexamination Certificate
2002-01-14
2004-07-20
Dawson, Glenn K. (Department: 3761)
Surgery
Respiratory method or device
Means for supplying respiratory gas under positive pressure
C128S204180, C128S205230, C251S012000, C137S557000
Reexamination Certificate
active
06763829
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to breathing circuits affording a re-breathing capability and, more specifically, to reliability and safety enhancements to apparatus employed to divert an exhaled breath volume for re-breathing by a patient and to subsequently remove such volume from the breathing circuit after re-breathing.
2. State of the Art
A so-called “airway” valve having a re-breathing mode and installed in a ventilator or other breathing circuit (the term “ventilator” being used generically herein to encompass various types of breathing circuits) selectively controls the diversion of an exhaled breath volume from the primary passage of the circuit into a “deadspace” volume defined by a chamber or other vessel such as a loop of hose for subsequent re-breathing by the patient. The re-breathing of the CO
2
-laden exhaled breath volume initiates a change in respiratory CO
2
concentration which may be employed to estimate cardiac output in a non-invasive manner. A discussion of a partial re-breathing technique wherein an additional, fixed deadspace is intermittently and briefly introduced into the ventilator circuit is discussed in detail in Capek, J. and Roy, R., “Noninvasive Measurement of Cardiac Output Using Partial CO
2
Rebreathing,”
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING
, VOL. 35, NO. 9, SEPTEMBER 1988, pp. 653-661, the disclosure of which is hereby incorporated in its entirety by this reference.
An airway valve employed to divert an exhaled air volume into the deadspace volume, to subsequently add the diverted volume into the ventilator circuit for re-breathing and then to remove it from the breathing circuit requires a high degree of reliability. Specifically, failure to remove the added volume after an appropriately brief period of time results in an increased volume of inspired CO
2
, with an attendant higher level of ventilation and arterial CO
2
.
An exemplary breathing circuit including a deadspace volume for partial re-breathing defined by a loop of hose is schematically illustrated in
FIG. 1
of the drawings. Exemplary breathing circuit
500
includes a tubular airway
502
that communicates air flow to and from the lungs of a patient. Tubular airway
502
may be placed in communication with the trachea of the patient by known intubation processes, by connection to a breathing mask positioned over the nose and/or mouth of the patient, by a mouthpiece for the patient or via an endotracheal tube. A flow meter
504
, which is typically referred to as a pneumotachometer, and a carbon dioxide sensor
506
, which is typically referred to as a capnometer, are disposed between tubular airway
502
and a length of hose
508
, and are exposed to any air that flows through breathing circuit
500
. Suitable pneumotachometers are disclosed in U.S. Pat. Nos. 5,379,650 and 5,535,633, and a suitable capnometer is disclosed in U.S. Pat. No. 5,793,044. If desired, a combined air flow and carbon dioxide sensor such as that disclosed in U.S. Pat. No. 5,789,660 may be employed in lieu of discrete flow and gas sensors. Both ends of another length or loop of tubing
510
, which may be referenced as defining a deadspace or re-breathing volume
512
, communicate with hose
508
. Deadspace volume
512
may optionally include an expandable section
514
, which may be provided by the use of corrugated tubing for tubing loop
510
. A Y-piece
516
, disposed on hose
508
opposite flow meter
504
and carbon dioxide sensor
506
, facilitates the connection of an inspiratory hose
518
and an expiratory hose
520
to breathing circuit
500
and the flow communication of the inspiratory hose
518
and expiratory hose
520
with hose
508
.
The two ends of tubing loop
510
defining deadspace volume
512
are connected to a two-mode airway valve
550
, the two modes being a normal operating mode and a re-breathing mode. During normal breathing, airway valve
550
is maintained in the normal operating mode to prevent inhaled and exhaled air from flowing through deadspace volume
512
. Airway valve
550
may be selectively actuated to shift from the normal operating mode to the re-breathing mode to divert a volume of a patient's exhaled breath into deadspace volume
512
, the breath volume being subsequently removed from deadspace volume
512
for re-breathing by the patient. Subsequent to re-breathing, airway valve
550
is shifted back to the normal operating mode so that the re-breathed air volume is expired through hose
508
and expiratory hose
520
. During inhalation, gas flows into inspiratory hose
518
from the atmosphere or a ventilator (not shown). Processing unit
522
(preferably included within a patient monitor and hereinafter referred to as a “monitor processing unit”) processes air flow and carbon dioxide input signals from flow meter
504
and
506
(or preliminary processing units associated therewith as known in the art), and preferably directly or indirectly controls operation of airway valve
550
to shift same between the normal operating mode and the re-breathing mode.
Airway valves such as valve
550
illustrated in
FIG. 1
may be controlled pneumatically via a control line (tubing) which actuates the valve employing an actuation energy source comprising either a positive air pressure (i.e., a pressure greater than the internal breathing circuit pressure) or a negative air pressure (i.e., a partial vacuum lower than internal breathing circuit pressure). Thus, there is always a risk of a leak, tubing disconnect, pump failure, power loss or, however unlikely, a valve component jam or failure. Accordingly, it would be desirable to provide enhanced assurance that the expired breath volume added to the circuit from the deadspace volume is removed from the circuit by appropriate switching of the airway valve, by reversion of the airway valve to a normal operating mode upon partial or total failure of the actuation energy source or delivery system, and by alerting the clinician to any problems with the actuation or control of the airway valve.
It would also be desirable to afford enhanced reliability to a variety of apparatus which may be employed to provide a deadspace volume or otherwise cause re-breathing of a patient's CO
2
-laden exhalations.
BRIEF SUMMARY OF THE INVENTION
The present invention includes methods and apparatus for enhancing reliability of, and monitoring, the operation of various apparatus for providing a breathing circuit with a re-breathing capability. As used herein, the term “breathing circuit” includes and encompasses any apparatus through which a patient or other subject may breath, such as, without limitation, ventilator breathing circuits, masks, mouthpieces, and endotracheal tubes.
In one aspect of the invention, fluid control line pressure (positive or negative) for actuation of a pneumatic airway valve for diverting an exhalation into a tubing loop or other receptacle or element defining or providing a deadspace volume may be specified as a selected pressure or within a selected range and monitored.
In a positive pressure pneumatic system, pressure reduced below a selected threshold may be compensated by actuation of a pump or a vessel containing compressed air, while pressure elevated above a selected threshold may be compensated by a bleed valve open to the ambient environment.
In a negative pressure pneumatic system, pressure elevated above a selected threshold may be compensated by actuation of a vacuum pump or opening of a valve connected to a vacuum line, while pressure reduced below a selected threshold may be compensated by opening an inlet valve to the ambient environment.
Monitoring of control line pressure may be effected on an intermittent (periodic sampling) or continuous basis and a controller, or processor such as a patient monitor processor linked to the controller, programmed so as to warn the user of any deviation from a selected pressure, a selected pressure range, or pressure deviations of selected magnitudes or frequencies or a combination thereof.
It
Gunneson Paul B.
Jaffe Michael B.
Rich David R.
Triunfo, Jr. John A.
Wigforss Eric P.
Dawson Glenn K.
Haas Michael W.
NTC Technology Inc.
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