Isoflurane elimination via a bubble oxygenator during extracorporeal circulation

Area of Science:

• Anesthesiology
• Cardiovascular Surgery
• Pharmacokinetics

Background:

• Current recommendations advise discontinuing inhalational anesthetics 15 minutes before extracorporeal circulation (ECC) termination to prevent myocardial depression.
• Limited data exist on the elimination kinetics of anesthetic agents from hypothermic, hemodiluted patients undergoing ECC, particularly using bubble oxygenators.

Purpose of the Study:

• To investigate the washout kinetics of isoflurane (ISF) during the termination phase of ECC in cardiac surgical patients.
• To determine if ISF can be safely discontinued closer to ECC cessation than currently recommended.

Main Methods:

• Mass spectrometry was employed to measure isoflurane concentrations in the oxygenator exhaust of ten cardiac surgery patients.
• Washout curves were analyzed to characterize ISF elimination and determine time constants.

Main Results:

• The mean baseline isoflurane concentration in the oxygenator exhaust was 0.85% before ECC termination.
• Oxygenator exhaust concentrations of ISF decreased below 0.05% within a mean of 8.8 ± 2.5 minutes.
• ISF washout followed a one-compartment model in 80% of patients, with a mean time constant of 1.94 minutes, predicting 95% washout in 5.8 minutes.

Conclusions:

• Isoflurane demonstrates rapid elimination via bubble oxygenators in hypothermic, hemodiluted cardiac surgical patients.
• The findings suggest that isoflurane can be administered closer to the termination of ECC than previously advised, potentially without increasing the risk of myocardial depression.