Continuous in-vivo blood-gas determination in man: reliability and safety of a new device.

The Sentorr is a gas chromatograph that monitors Pa2 and PaCO2 every 4 min from a probe placed through an intraarterial cannula. The accuracy of this device and complications resulting from its use were studied in 46 patients undergoing cardiac surgical procedures with oxygen to nitrous oxide-halothane anesthesia. Sentorr blood-gas values were compared with simultaneous samples analyzed with standard electrodes. During relatively steady states of respiration and circulation, and in the lower (50-125 torr) range of oxygen tensions, the measurements correlated closely (r = 0.92). The device also functioned well during low-flow states, but during hypothermic cardiopulmonary bypass, the correlation was only fair (r = 0.62). When nitrous oxide was present in the inspired gas, Sentorr PaO2 readings were a third lower than actual PO2 measurements, an effect corroborated by an in-vitro experiment. Directional changes of oxygen and carbon dioxide tensions were always correct in all situations. Placement of the probe in a radial artery was unsatisfactory because it significantly interfered with blood pressure measurement and resulted in inaccurate results for this patient population. The brachial artery was a satisfactory site for insertion, although attenuation of the arterial pressure tracing by the presence of a Sentorr probe resulted in systolic pressure readings that averaged 12 torr lower with mean arterial pressure readings 5 torr lower. No increase in morbidity due to use of a Sentorr probe for brachial arterial pressure monitoring could be identified. The most potentially serious complication encountered was transient loss of a palpable pulse without interruption of blood flow in one or more distal arteries after decannulation. This was observed in seven patients (four of whom had diminished distal pulses whith normal flow before cannulation).