Transcutaneous and End-Tidal CO2 Measurements in Hypoxia and Hyperoxia

Abstract

BACKGROUND: Transcutaneous measurement of carbon dioxide (CO2) has been proposed for physiological monitoring of tactical jet aircrew because in some clinical settings it mirrors arterial CO2 partial pressure (Paco2). End-tidal monitoring in laboratory settings is known to give high-fidelity estimates of Paco2.METHODS: The correspondence between end-tidal (PETco2) and transcutaneous Pco2 (tcPco2) was examined in healthy volunteers under laboratory conditions of hyperoxia and hypoxia. Rest and exercise, skin heating and cooling, hyperventilation, and induced CO2 retention were employed.RESULTS: Neither measure followed all known changes in Paco2 and tcPco2 changed when the skin temperature near the probe changed. Bland-Altman analysis showed significant nonzero slopes under most conditions. Regression analysis indicated that oxygen partial pressure (Po2) in tissue measured as transcutaneous Po2 (tcPo2) is an important explanatory variable for tcPco2 in addition to PETco2, and that local skin temperature also has an effect. Additionally, absorption atelectasis from breathing 100% O2 may cause PETco2 to deviate from Paco2.DISCUSSION: Even as a trend indicator for Paco2, tcPco2 is not useful under conditions that resemble those in the highly dynamic tactical jet aircraft environment. PETco2 is also not a good indicator of CO2 status in pilots who breathe nearly 100% O2.Shykoff BE, Lee LR, Gallo M, Griswold CA. Transcutaneous and end-tidal CO2 measurements in hypoxia and hyperoxia. Aerosp Med Hum Perform. 2021; 92(11):864–872.