In vivo response time of transcutaneous oxygen measurement to changes in inspired oxygen in normal adults.

We examined the in vivo response time of transcutaneous oxygen measurement (PtcO2) to a step increase (100 per cent oxygen) or decrease (air) of inspired oxygen in five normal adults (age 27 +/- SD 4.5 years). The PtcO2 electrode was placed on the upper chest (sensor temperature 44 degrees C). The mean +/- SEM 63 and 95 per cent response times of PtcO2 to a step increase in inspired oxygen were 2.9 +/- 0.2 and 6.8 +/- 0.2 and to a step decrease were 2.4 +/- 0.2 and 5.1 +/- 0.3 minutes. The 63 and 95 per cent response times for the pulmonary washin of oxygen were 1.0 and 2.6 minutes and washout were 0.8 and 2.3 minutes. We conclude that the in vivo response time of the PtcO2 is reproducible but substantially longer than that of the pulmonary washin and washout times and inadequate to monitor rapid changes in arterial oxygenation during anaesthesia, perioperative period or sleep in adults.