Mass spectrometer system for long-term continuous measurements of v.O2 and v.CO2 during artificial ventilation.

Abstract

A system for online measurement of respiratory gas exchange in patients undergoing artificial ventilation is described. Expired flow is measured either by a continuous tracer gas injection or by a pneumotachometer. Both systems have a similar degree of accuracy when compared with a reference method (the Douglas bag method). Validation of the whole system by the burning of methanol with a known respiratory quotient is performed. The accuracy of the measurements is within 1·6 per cent. The major problem is that physiological signals recorded from a ventilated patient contain artefacts which may lead to erroneous computations. An algorithm is developed to identify and disregard artefacted signals or an unsteady state of the patient. The technique used for data processing allows reliable continuous measurement of respiratory gas exchange for periods up to 24 h without interfering with the nursing or the ventilatory management.