The Science Journal of the American Association for Respiratory Care

2000 OPEN FORUM Abstracts


Mark Siobal RRT, Edna Warnecke RRT, Rich Kallet RRT, Respiratory Care Services, San Francisco General Hospital, UCSF Dept. of Anesthesia

Background: Use of PtcCO2 monitoring is standard practice in neonatal intensive care units and during sleep diagnostic studies. Due to the high diffusabilitiy of CO2, PtcCO2 as a surrogate for PaCO2 is less dependant on hemodynamic status and skin perfusion than transcutaneous PO2(1). Despite strong to moderate correlation with PaCO2(2) and end-tidal CO2 (PetCO2)(3), PtcCO2 monitoring remains under utilized in adults. We report results that confirm the clinical utility of PtcCO2 monitoring in adults.

Methods: A convenience sample of two comparisons of PtcCO2, PetCO2, and PaCO2 tension were made in 6 critically-ill adults requiring mechanical ventilation using a Novametrix Capnogard, Radiometer TINA, and an AVL Omni blood gas analyzer. The PtcCO2 sensor was place on the forearm or chest 30 minutes prior to data collection with the sensor temperature at 44°C and correction factor = 4. Patients were hemodynamically stable during all measurements.

Results: Mean (± standard deviation) values of PetCO2 (43.2±4.8), PtcCO2 (41±4.9) and PaCO2 (45.4±7.1) were not different. Simple regression showed a strong correlation between PetCO2 and PaCO2 (r =.91, p<.0001) and a moderately strong correlation between PtcCO2 and PaCO2 (r =.78, p =.003). Bland-Altman test revealed that the mean difference between PetCO2 and PaCO2 (-2.25±3.42) was less than the difference between PtcCO2 and PaCO2 (-4.42±4.52).
Conclusion: Our data suggests that PetCO2 may be a more accurate surrogate of PaCO2. However, PtcCO2, as a correlate of PaCO2, appears to be a useful alternative for monitoring hemodynamically stable adult patients when PetCO2 is unavailable or impractical (e.g. during non-invasive face mask ventilation(4)) and should not be overlooked.
1. Martin RJ. Transcutaneous monitoring: instrumentation and clinical application. Respir Care 1990;35:577-583.
2. Goldman MD, et al. Transcutaneous PCO2 in adults. Anaesthesia 1982;37:944-946.
3. Blanchette T, et al. Transcutaneous PCO2 and end-tidal PCO2 in ventilated adults. Respir Care 1992;37:240-248.
4. Janssens JP, et al. Transcutaneous PCO2 to monitor noninvasive mechanical ventilation in adults: assessment of a new transcutaneous PCO2 device. Chest 1998;113:768-773. (See Original for Figure)

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