Transcutaneous oxygen measurement during one-lung anaesthesia.

The value of continuous transcutaneous oxygen tension (Ptco2) monitoring was assessed during the rapidly changing conditions of oxygenation associated with the commencement of one-lung ventilation (OLV) during thoracic surgery. In ten patients anaesthetized with enflurane-N2O (Fio2 0.5), Pao2, Ptco2, cardiac output and arterial pressure were measured first during two-lung ventilation (TLV) and thereafter at frequent intervals during OLV. These variables remained stable during TLV. The mean Pao2 dropped from 24.9 kPa to 11.4 kPa during the first 10 min of OLV. The accompanying decrease in Ptco2 was slower, the mean Ptco2 being 1.3-2.1 kPa higher than Pao2. Ptco2 correlated well with Pao2 during OLV (r = 0.907). The elevated Ptco2 index (Ptco2/Pao2) may be partly due to the delayed response of the Ptco2-detection system in vivo. It is concluded that transcutaneous oxygen monitoring may be used to assess oxygenation in those cases where arterial cannulation is not feasible or if the laboratory conditions cause an undue delay between blood sampling and obtaining the blood-gas data.