In Vitro Anesthetic Washin and Washout via Bubble Oxygenators: Influence of Anesthetic Solubility and Rates of Carrier Gas Inflow and Pump Blood Flow

The uptake and elimination of volatile anesthetic agents administered to patients under conditions of hemodilution and hypothermia during cardiopulmonary bypass have not been determined. To define the limitations imposed by oxygenators, we defined washin and washout curves for volatile anesthetic agents administered to bubble oxygenators primed with diluted blood (without connection to a patient). There was rapid equilibration of anesthetic partial pressure between delivered gas and blood (85–90% within 16 minutes). Increasing the gas inflow to the oxygenator from 3 to 12 L/min hastened washin and washout slightly, while increasing the pump blood flow from 3 to 5 L/min had no effect. Rates of washin and washout of anesthetics differed as a function of their blood/gas solubilities: enflurane>isoflurance>halothane during washin; isoflurane>enflurane>halothane during washout. However, these differences were small. Oxygenator exhaust partial pressures of anesthetic correlated with simultaneously obtained blood partial pressures, suggesting that monitoring exhaust gas may be useful clinically.