Measurement of alveolar gas mixing in mechanically ventilated patients.
OBJECTIVE
To evaluate a computer-based, real-time, multibreath nitrogen washout technique in mechanically ventilated patients, incorporating an in-line flow measurement device to measure functional residual capacity and two indices of gas mixing, ventilatory efficiency, and alveolar mixing efficiency.


METHODS
ICU, Charing Cross Hospital, London.


METHODS
Within-patient reproducibility of a multibreath nitrogen washout technique.


METHODS
Seven intubated patients requiring mechanical ventilation. One patient completed two sets of readings.


METHODS
Patients were connected to a pneumatically driven ventilator fitted with a switching device to be operated either by an appropriate oxygen-nitrogen mixture or equivalently blended oxygen-argon mixture. An inspiratory-expiratory, two-way valve was attached to the delivery port of the ventilator, with a pneumotachograph for flow measurement and a gas sampling probe for gas concentration measurement in line with the patient's endotracheal tube. The analog signals were digitized and handled by a microcomputer.


RESULTS
No significant differences were found for any index, with coefficients of variation of 1.5%, 2.9%, and 2.1% for functional residual capacity, ventilatory efficiency, and alveolar mixing efficiency, respectively.


CONCLUSIONS
This method gives excellent reproducibility for biological measurements in a clinical setting and shows that these measurements can readily be made on mechanically ventilated patients.
Kox
W J
WJ
Department of Anaesthesia, Charing Cross and Westminster Medical School, London, UK.
Mills
C J
CJ
D000328:Adult; D000368:Aged; D005652:Functional Residual Capacity; D006801:Humans; D008838:Microcomputers; D008875:Middle Aged; D009584:Nitrogen; D011650:Pulmonary Alveoli / Q000503:physiopathology*; D011653:Pulmonary Diffusing Capacity; D011659:Pulmonary Gas Exchange; D012121:Respiration, Artificial; D012815:Signal Processing, Computer-Assisted
D009584:Nitrogen