Transcutaneous oxygen and carbon dioxide tensions compared to arterial blood gases in normals

Most hyperbaric medicine centers do not monitor arterial oxygen (P(aO(2))) and carbon dioxide (P(aCO(2))) tensions during hyperbaric oxygen, but many can transcutaneously monitor oxygen (P(tcO(2))) and carbon dioxide (P(tcCO(2))).

We compared P(tcO(2)) and P(tcCO(2)) measurements to simultaneous P(aO(2)) and P(aCO(2)) measurements in 10 healthy volunteers to determine if P(tcO(2)) and P(tcCO(2)) measurements are surrogates for P(aO(2)) and P(aCO(2)) in the hyperbaric environment. We took blood samples via arterial catheter and took P(tcO(2)) and P(tcCO(2)) chest measurements while the subjects were compressed in a monoplace hyperbaric chamber at pressures between 0.85 atmospheres absolute (atm abs) (our local atmospheric pressure, at altitude 1,300 m) and 3.0 atm abs, while the subjects breathed air, then oxygen.

The P(tcO(2)) correlated with P(aO(2)) (r(2) = 0.99). Under all the conditions, the P(tcO(2)) values were lower than P(aO(2)) values by approximately 10%. The P(tcCO(2)) was 2-6 mm Hg higher than the P(aCO(2)), but the correlation was low (r(2) = 0.21).

The P(tcO(2)) in normal humans may be used to estimate the P(aO(2)). The P(tcCO(2)) may not be an adequate reflection of the P(aCO(2)). It is unknown if P(tcO(2)) and P(tcCO(2)) measurements in critically ill patients can replace P(aO(2)) and P(aCO(2)) measurements.