Effects of sevoflurane and propofol on pulmonary shunt fraction during one-lung ventilation for thoracic surgery

Forty patients requiring one-lung ventilation (OLV) for thoracic surgery we re randomly assigned to receive propofol (4-6 mg kg(-1) h(-1)) or sevoflura ne (1 MAC) for maintenance of anaesthesia. Three sets of measurements were taken: (i) after 30 min of two-lung ventilation (TLV), (ii) after 30 min of one-lung ventilation (OLV-1) in the supine position and (iii) during OLV i n the lateral position (OLV-2) with the chest open and before surgical mani pulation of the lung. There were no differences between groups in patient c haracteristics or preoperative condition. Increases in shunt fraction durin g OLV-1 were 17.4% and 17.2% (P=0.94), those during OLV-2 were 18.3% and 16 .5% (P=0.59) for the propofol and sevoflurane group, respectively. Cardiac index and other haemodynamic and respiratory variables were similar for the two groups. We conclude that inhibition of hypoxic pulmonary vasoconstrict ion by sevoflurane may only account for small increases in shunt fraction a nd that much of the overall shunt fraction during OLV has other causes.