Transcutaneous O2 (Ptco2) tensions were compared with Pao2 measurements in 57 infants and children (age range 2 wk to 15.5 yr) using electrode temperatures of 43° and 44°C. At both temperatures, the relationships between Ptco2 and Pao2 were linear over the whole range of data (Pao2 39.75 to 120 torr) although mean Ptco2/Pao2 fell from 44° to 43°C. Skin stripping by repeated applications of adhesive tape immediately before electrode placement did not improve these relationships. In an additional 20 children with, a mean age of 2.4 yr (range 0.08 to 15.85) who were being investigated for sleep-disordered breathing, the mean Pao2/Ptco2 ratio of 1.22 at 44°C was used as a correction factor during air calibration for Ptco2. This resulted in a mean Ptco2/Pao2 of 0.99 (range 0.83 to 1.15) provided blood flow is not impaired. Extending the monitoring period from 4 to 8 h between site changes did not result in any burns or persisting erythema. In hemodynamically stable infants and children, and at electrode temperatures of 44° and 43°C, Ptco2 is linearly related to Pao2 over a wide range of Pao2 values. At an electrode temperature of 44°C, Ptco2 can be arterialized effectively by allowing for transepidermal O2 loss during air calibration; at this electrode temperature, intervals between site changes can be extended safely up to 8 h.
Hospital for Sick Children, Institute of Child Health, London, United Kingdom.