[Low flow anesthesia using a fresh gas flow of 600 ml.min-1 for 5 hours]

Low flow anesthesia (LFA) using a fresh gas flow (FGF) of 600 ml.min-1 with oxygen and nitrous oxide flow each set at 300 ml.min-1, and dial setting of sevoflurane 3% was administered to 30 patients for a duration of 5 hours. There were no problems such as unsuitable concentrations of nitrous oxide and sevoflurane in inspired and expired gases or low FIO2 below 0.3 during anesthesia in 15 patients of group A. Their body weight was 53 +/- 5 kg. FIO2 decreased below 0.29 at about 4 hours in 7 patients of group B weighing 62 +/- 6 kg, and at about 1 h in 8 patients of group C weighing 71 +/- 7 kg. In group A and B, the sum of concentrations of oxygen, nitrous oxide and sevoflurane in inspired gas decreased for a moment and recovered as anesthesia progressed, but in group C, it kept decreasing without recovery. The body weight was significantly different among the 3 groups (P < 0.05). It was suggested that in group A the FGF per body weight was suitable; in group B though oxygen flow was larger than oxygen consumption, hypoxia occurred due to saturation of nitrous oxide in the body; and in group C the FGF was insufficient. The compound A was detected in the breathing circuit, and the concentration was around 20 ppm and it did not depend on the duration of LFA. It was concluded in this study that LFA using the FGF of 600 ml.min-1 with setting of 3% sevoflurane, 50% oxygen and nitrous oxide, could be performed safely without risks such as hypoxia and severe delay of induction for patients weighing 53 +/- 5 kg for a duration of 5 hours.