OBSERVATIONS DURING ENDOBRONCHIAL ANAESTHESIA: II: OXYGENATION

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Abstract
The efficiency of arterial oxygenation was assessed at different stages during noncardiac thoracic surgery in 17 patients who had been intubated with Robertshaw double-lumen endobronchial tubes. Arterial oxygen tension (Pao2), “ideal” alveolar to arterial oxygen tension differences (PAo2 —Pao2), arteriovenous oxygen content differences (Cao2 —Cvo2) and physiological shunt (QS/QT) were measured during ventilation with halothane/oxygen mixtures. Highly significant decreases in Pao2 and increases in QS/QT occurred during periods of one-lung ventilation (OLV), although the changes were significantly greater in a group of patients who were undergoing exploratory thoracotomy and non-pulmonary surgery (non-resection group) than in those undergoing lobectomy or pneumonectomy (resection group). Four out of seven patients in the non-resection group had a Pao2 of less than 80 mm Hg during OLV and the mean shunt in this group was over 40%. In both groups the shunt measured within 10 min of the commencement of OLV was significantly smaller than values obtained after 10–30 min of OLV, probably because of uptake of residual oxygen in the unventilated lung. An increase in shunt between the beginning and the end of the operation was found to correlate with a fall in the ventilation volume of the dependent lung during OLV.

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