Oxygen therapy after thoracotomy.

Arterial blood samples were taken from patients before thoracotomy, and on the 1st day after operation, with the patient breathing first air, and then 24%, 28% and 35% oxygen from a venturi-type mask. PaO2 was reduced markedly by operation, the reduction being related to the value before operation. Oxygen therapy restored PaO2 to a value greater than the value before operation in nine of 11 patients and was not associated with significant increases in PaCO2. The effect of administration of oxygen on PaO2 could be predicted from the PaO2 when breathing air. The pattern of response to oxygen suggested that the hypoxaemia was caused by ventilation/perfusion mismatch in most of the patients.