Ambient isoflurane pollution and isoflurane consumption during intensive care unit sedation with the Anesthetic Conserving Device

Objective: To examine ambient isoflurane pollution, scavenging efficacy, and isoflurane consumption using the Anesthetic Conserving Device (ACD) for prolonged isoflurane sedation in the intensive care unit. Design: Prospective observational study. Setting. Multidisciplinary university intensive care unit. Patients: Fifteen adult ventilator-dependent intensive care unit patients sedated with isoflurane for 12-96 hrs. Interventions. Isoflurane was infused to the ACD for sedation of study subjects. Changing of the ACD, isoflurane syringe, and opening of the respiratory circuit were performed in a standardized fashion according to investigator instructions. Active scavenging of waste gas from the ventilator was performed in ten patients; in five patients no active scavenging was performed. Measurements and Main Results: Continuous spectrophotometric measurement of ambient isoflurane pollution in parts per million (ppm) at 0.5 m from the patient's head and passive lapel dosimeter sampling for ten staff nurses over 8-hr shifts. Isoflurane requirement and agent consumption were registered in all patients. Spectrophotometric readings (0.1 +/- 0.2 ppm) were well below internationally recommended long-term exposure limits in all cases. Isoflurane peaks during nursing procedures were brief, infrequent, and of low amplitude. There was no observed difference between isoflurane trace levels with or without an active scavenging system in use. Passive dosimeter values were also low, ranging from undetectable to 0.16 ppm. Mean isoflurane consumption was 2.1 +/- 1.0 mL/hr. This is approximately one fourth of predicted and previously reported consumption of isoflurane with vaporizer-administered Sedation in the intensive care unit setting. Conclusions: In the present setting, isoflurane via the ACD is an environmentally safe method of sedation provided users follow instructions for standardizing procedures with potential spillage of isoflurane. This method of sedation requires considerably less isoflurane than with traditional vaporizer technique.