Arterial CO.sub.2 Monitor and closed loop controller

Details Arterial CO.sub.2 Monitor and closed loop controller Arterial CO.sub.2 Monitor and closed loop controller

1993-04-21

1995-04-04

Cohen, Lee S.

Surgery

Truss

Pad

12820024, 128204, 128 22, 128716, 73 233, A61B 508

Patent

active

054027969

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION



Field of the Invention

This invention related to a method and apparatus for continuously and non-invasively monitoring arterial blood CO.sub.2 partial pressure (PaCO.sub.2) of artificially ventilated patients.


DESCRIPTION OF RELATED ART

Mechanical ventilation is required by patients in an intensive care unit who are unable to control their own respiration. The rate of ventilation must be adjusted so that arterial CO.sub.2 is within a desirable range. Conventionally clinicians adjust the ventilator settings based on periodically drawn blood samples. In order to monitor rapidly changing PaCO.sub.2 (for monitoring or closed loop control purposes), a continuous and non-invasive monitor is desirable. Known transcutaneous transducers are non-invasive but require heating of the patient's skin to 44.degree. C. and a long stabilization time of 30 minutes which renders them unsatisfactory for continuous monitoring. The known method of assuming a constant arterial to end-tidal CO.sub.2 difference is not reliable during ventilation/perfusion changes, and attempts to implement closed loop ventilation control have failed largely due to the inability to continuously and non-invasively observe the variable to be controlled, that is, the PaCO.sub.2.
Thus, the direct methods of monitoring PaCO.sub.2 are invasive, and indirect methods are not reliable, particularly because end-tidal CO.sub.2 is influenced by deadspace, which is an unmeasurable quality.
It would thus be desirable to provide a method and apparatus for providing a continuous and substantially non-invasive PaCO.sub.2 estimation.


SUMMARY OF THE INVENTION

Briefly, and in general terms the invention provides a method and apparatus for continuously and non-invasively monitoring arterial blood CO.sub.2 partial pressure (PaCO.sub.2) of artificially ventilated patients, by monitoring a patient's breath and determining PaCO.sub.2 based upon a determination of a deadspace ratio, which is the ratio of the alveolar deadspace to alveolar tidal volume. The method generally comprises the steps of continuously monitoring, measurable parameters of a patient's breath; obtaining an input value of PaCO.sub.2 from a blood sample of the patient and using the patients breath parameters and the input value to calculate the deadspace ratio; and continuously determining PaCO.sub.2 based on the assumption that the deadspace ratio subsequently remains constant.
Decision rules obtained from other measurable data are preferably also used to identify the onset of changes in the deadspace ratio, and a new deadspace ratio is then determined from the patient's breath parameters and a further input value of PaCO.sub.2 from the patient's blood sample.
The determination of PaCO.sub.2 is preferably based upon the equation ##EQU1##
where V.sub.D.sup.alv is the alveolar deadspace,
V.sub.T.sup.alv is the alveolar tidal volume,
PE.CO.sub.2 is the mixed-expired CO.sub.2 from the alveolar tidal volume, and
PiCO.sub.2 is inspired CO.sub.2.
The mixed-expired CO.sub.2, inspired CO.sub.2, alveolar tidal volume and the alveolar deadspace are the measurable parameters of the patient's breath.
The other measurable data used to determine decision rules for identifying changes in the deadspace ratio are preferably related to lung mechanics and trends in CO.sub.2 production.
The method preferably further involves adjusting patient ventilation based on the determined value of PaCO.sub.2.
In another aspect of the invention, an apparatus is provided for continuously and non-invasively monitoring arterial blood CO.sub.2 partial pressure (PaCO.sub.2) of artificially ventilated patients. The apparatus preferably includes a capnograph for monitoring continuously measurable parameters relevant to a patient's breath and providing data relating thereto, and means for determining a deadspace ratio connected to the capnograph to receive the breath parameter data and adapted to receive information relating to the PaCO.sub.2 of a blood sample of the patient based upon the PaCO.sub.2 informa

REFERENCES:
patent: 3927670 (1975-12-01), Turney et al.
patent: 4368740 (1983-01-01), Binder
patent: 4393869 (1983-07-01), Boyarsky et al.
patent: 4986268 (1991-01-01), Tehrani
patent: 5107831 (1992-04-01), Halpern et al.
patent: 5129401 (1992-07-01), Corenman et al.
patent: 5320093 (1994-05-01), Raemer

Affiliated with

Also associated with

Rating

Arterial CO.sub.2 Monitor and closed loop controller does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Arterial CO.sub.2 Monitor and closed loop controller, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Arterial CO.sub.2 Monitor and closed loop controller will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2375078