Progressive changes in arterial oxygenation during one-lung anaesthesia are related to the response to compression of the non-dependent lung

Background. Arterial oxygenation can change during one-lungventilation for reasons that are not fully understood. Methods. We studied patients during anaesthesia and one-lungventilation, with an inspiratory oxygen fraction of 0.8. Arterialblood gas values were recorded every 10 s with a continuousintra-arterial sensor. The non-dependent lung was compressedseveral times during the surgical procedure, using a retractor.The change in Pa_O2 during and after compression of the non-dependentlung was measured. Results. Pa_O2 increased significantly when the non-dependentlung was compressed, and decreased when the compression wasreleased. The first compression of the non-dependent lung transientlyincreased Pa_O2, but the effect of the second compression onoxygenation was more marked and persistent. Pa_O2 increased bymore than 13 kPa at 10 min after the second compression in fourpatients (responder group). Arterial oxygenation improved markedlyin patients in this group during the surgical procedure. Conclusion. Oxygenation can improve during one-lung ventilationin some patients. This improvement is partly related to a markedincrease in Pa_O2 during compression of the non-dependent lung. Br J Anaesth 2003; 90: 21–6