Purpose: To compare the effects of isoflurane and sevoflurane on arter
ial oxygenation and middle cerebral artery blood flow velocity during
one lung ventilation. Methods: This was a randomized, crossover study
in 20 patients undergoing thoracotomy for oesophageal cancer and sched
uled for long term one lung ventilation (OLV): They were randomized to
one of two groups: group A, firstly isoflurane was administered follo
wed by sevoflurane, and then isoflurane was resumed; group B, the orde
r of the administration was reversed, Arterial blood gas samples were
drawn at the start of OLV, 30 and 60 min after the initiation of OLV a
nd the end of OLV (the change of volatile anesthetic was done 30 and 6
0 min after the start of OLV). Middle cerebral artery (MCA) was monito
red continuously with the probe positioned over the temporal bone wind
ow. This probe transmitted 2 MHZ wave Doppler signals. Time-averaged M
CA blood flow velocity was calculated from the signals. Results: The P
aO2 values decreased 30 min after the start of OLV (364.4 +/- 33.4 mmH
g vs 179.0 +/- 19.5, and 338.7 +/- 24.8 mmHg vs 139.7 +/- 19.9 in grou
ps A and B respectively), but there was no difference between the grou
ps. Blood flow velocity of MCA did not change after the start of OLV (
53.1 +/- 3.2, 55.9 +/- 3.0, 56.4 +/- 2.4, and 54.1 +/- 1.9 vs 50.8 +/-
2.1, 50.7 +/- 2.4, 53.7 +/- 1.5, 50.8 +/- 2.2 cm.sec(-1) in groups A
and B respectively): there was no difference between the groups, (P <
0.05). Conclusion: In clinical practice, the selection of either isofl
urane and sevoflurane for OLV was of no difference in terms of the art
erial blood oxygenation, With bath agents MCA blood flow velocity was
maintained during OLV.