An in vitro study of the effects of isoflurane on oxygen transfer

A common anesthetic technique utilized during cardiopulmonary bypass (CPB) includes the use of various inhalation agents, such as isoflurane. The purp ose of this study was to evaluate the effects of this agent on oxygen trans fer during CPB. An in vitro model was designed using bovine blood. Blood flow was held cons tant at 2 l/min, while gas flow was manipulated at 1 and 3 l/min. The perce ntage of inspired oxygen (FiO(2)) was set at 50 and 100%, and isoflurane wa s manipulated to 1.0, 3.0 and 5.0%. Blood gas analysis, oxygen transfer. an d inlet and outlet isoflurane concentrations were measured at each of the g iven conditions. A total of 12 trials with four oxygenators were conducted. In the four oxygenators used in our study, no significant differences in ox ygenator performance were found. At conditions of 1 l/min gas flow 50% FiO( 2) and 1% isoflurane, there were no significant changes in O-2 transfer bet ween baseline and measurements taken during isoflurane administration (100. 18 +/- 12.49 vs 102.35 +/- 10.99 mi O-2/min, p=0.8031). At 3 l/min gas flow , 100% FiO(2) and 5% isoflurane, no significant differences were found (142 .35 +/- 10.76 vs 154.04 +/- 8.95 mi O-2/min, p=0.1459). The only significan t differences found for oxygen transfer were between 50 and 100% FiO(2), al l other conditions being set equal (102.35 +/- 10.99 vs 137.68 +/- 8.62 mi O-2/min,p=0.0023). In conclusion, increasing concentrations of isoflurane up to 5% does not af fect the efficiency of oxygen transfer in an in vitro circuit. Further stud ies are necessary to evaluate the effects in an in vivo setting.