The effects of lowering fresh gas flow during sevoflurane anaesthesia: a clinical study in patients having elective knee arthroscopy.

The potential for minimising anaesthetic gas consumption with a circle absorber system is related to fresh gas flow. This study measured the actual sevoflurane consumption during elective arthroscopy of the knee in 75 ASA I-II patients randomised to three fresh gas flow rates (6, 3, and 1.5 l/min) using sevoflurane and O(2):N(2)O (1:2) after intravenous induction with fentanyl and propofol. A circle absorber system was used with a laryngeal mask airway. Anaesthetic duration, discharge time and postoperative pain did not differ between groups. Sevoflurane consumption was more than doubled with each doubling of fresh gas flow (0.07+/-0.03; 0.16+/-0.05; 0.41+/-0.12 ml sevoflurane/min; for gas flow 1.5, 3, 6 l/min; P<0.01). The hourly sevoflurane related cost decreased from 15.5 to 2.8 US$ when reducing the fresh gas flow from 6 to 1.5 l/min. Decreasing the fresh gas flow from 6 to 1.5 l/min provides good anaesthetic depth with effective reduction in anaesthetic consumption, cost and environmental burden.