Transcutaneous arterial carbon dioxide pressure monitoring in critically ill adult patients
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To evaluate the accuracy of transcutaneous PCO2 (PtcCO2) as a surrogate for arterial PCO2 (PaCO2) in a cohort of adult critically ill patients in a medical intensive care unit (ICU).
Prospective observational study comparing paired measures of transcutaneous and arterial PCO2.
A 26-bed medical ICU.
Fifty ICU patients monitored with a SenTec Digital Monitor placed at the ear lobe over prolonged periods.
A total of 189 paired PCO2 measures were obtained. Twenty-one were excluded from analysis, because profound skin vasoconstriction was present (PCO2 bias = −10.8 ± 21.8 mmHg). Finally, 168 were analysed, including 137 obtained during mechanical ventilation and 82 under catecholamine treatment. Body temperature was below 36°C for 27 measurements. Mean duration of monitoring was 17 ± 17 h. The mean difference between PaCO2 and PtcCO2 was −0.2 ± 4.6 mmHg with a tight correlation (R2 = 0.92, p > 0.01). PCO2 bias did not significantly change among three successive measurements. Changes in PaCO2 and in PtcCO2 between two blood samples were well correlated (R2 = 0.78, p > 0.01). Variations of more than 8 mmHg in PtcCO2 had 86% sensitivity and 80% specificity to correctly predict similar changes in PaCO2 in the same direction. Catecholamine dose or respiratory support did not affect PtcCO2 accuracy. Hypothermia has only a small effect on accuracy. No complication related to a prolonged use of the sensor was observed
Transcutaneous PCO2 provides a safe and reliable trend-monitoring tool, provided there is no major vasoconstriction.