ABSTRACT
BACKGROUND: A circle system can be closed or semiclosed depending on the amount of fresh gas flow. A closed system is one in which the inflow gas exactly matches that being taken up or consumed by the patient. A semiclosed system is associated with partial rebreathing of gases and is the most commonly used system today. The purpose of this study is to examine the actual consumed amount of volatile anesthetic by closed and semiclosed anesthesia systems. METHODS: Forty-seven patients undergoing general inhalation anesthesia with enflurane and thirty-six patients with isoflurane were examined. Each group was divided into two subgroups by the circle system; enflurane-closed (33 patients), enflurane-semiclosed (14 patients), isoflurane-closed (23 patients), and isoflurane-semiclosed groups (13 patients). Closed system was performed by using PhysioFlex anesthesia machine. The difference of initial (just before anesthesia) and remained (just after anesthesia) enflurane or isoflurane volumes measured by 30 ml-syringe was obtained as consumed amount of anesthetics. This amount was calculated on the base of 1% enflurane or isoflurane for 1 hour anesthesia with a given fresh gas flow (4 to 5 L/min). RESULTS: Consumed amount of liquid enflurane and isoflurane when using closed system was 6.99 +/- 0.26 ml/hr and 4.84 +/- 0.27 ml/hr respectively while 15.99 +/- 1.48 ml/hr and 14.01 +/- 0.92 ml/hr respectively when using semiclosed system. Consumption of liquid anesthetics was significantly lower in closed anesthesia and significantly higher in both systems than those of predicted values. CONCLUSIONS: In closed system by using PhsioFlex anesthesia machine consumed amount of liquid anesthetic for 1 hour anesthesia with 1% of endtidal anesthetic concentration at 25 degrees C, 1 atm and 4 to 5 L/min of fresh gas flow was within 35 to 44% of that in semiclosed system.