An in Vitro Assessment of a Monitor for Continuous Inline Measurement of PO2, PCO2 and pH during Cardiopulmonary Bypass

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Abstract
The Gas STAT is a monitor which continuously measures PO2. PCO2 and pH inline during cardiopulmonary bypass. Using an in vitro model, the monitor's accuracy was compared to standard blood gas analysis over a range of PO2 (2·0–66·7 kPa), PCO2 (2·7–12·0 kPa) and pH (7–8). Its stability as affected by time, temperature, flow and haematocrit and the presence of halothane, enflurane, isoflurane and sodium nitroprusside was examined. Good correlations were found between the monitor and standard blood gas analysis for PO2 (r = 0·999, P < 0·001) and PCO2 (r = 0·996, P < 0·001). However, large and unpredictable systematic errors occurred. It was stable under all conditions examined, except that in one sensor there was a statistically significant decline in PCO2 measurement with time (P < 0·005) and the PCO2 readings were affected by temperature (P < 0·021). The monitor provides useful information for blood gas management during cardiopulmonary bypass, but should not be used without recourse to standard blood gas analysis.