LOW FLOW ANESTHESIA FOR AMBULATORY SURGERY

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S10 For low flow anesthesia (LFA) techniques an initial high flow phase of 15-20 min is required, thus limiting the effectiveness in saving anesthetic vapors in short duration anesthesia. Anesthetic gas monitoring offers the opportunity to reduce the duration of the inital wash-in phase down to 1-2 min. This renders LFA practicable for brief surgical procedures. The aim of the study was to evaluate LFA for brief surgical procedures. METHODS: After IRB approval and written informed consent the anesthetic procedure shown in Figure 1 was employed in an ambulatory surgery unit. After premedication with nordiazepam, anesthesia was induced with propofol (1-2mg/kg body weight) and alfentanil (1mg) and maintained with nitrous oxide in oxygen and isoflurane or enflurane. The patient's age, surgical procedure, duration of anesthesia and post-anesthetic care unit time spent were recorded. The consumption of anesthetic vapors per patient was calculated from the overall consumption.Figure 1: Course of modified low flow anesthesia: T0: preoxygenation, intravenous induction, endotracheal intubation, controlled ventilation: T1: wash in phase - fresh gas flow at 9 L/min for 1-2 min, vaporizer setting 5Vol% isoflurane (Iso) or enflurane (Enf) until the desired endtidal anesthetic gas concentration is reached: T2: low-flow phase - fresh gas flow reduction to 1 L/min, adaptation of the vaporizer setting: T3: discontinuation of Isoflurane/N2 O, patient breathing spontaneously, O2 flow at 9 Lmin: T4: extubationRESULTS: 3185 consecutive patients were included in the study. The age of the patients ranged from 5 months to 94 years with a median of 31 years, duration of anesthesia from 15 min to 4 h with a median of 46 min. 29% of the patients were discharged from the post-anesthetic care unit within 2 h, 56% after 2-4 h and 15% after more than 4 h. On the average 24 l N2 O, 7.1 ml enflurane or 3.7 ml isoflurane (liquid) per patient were needed. CONCLUSION: LFA proved to be a useful, practicable and cost-effective anesthetic technique for brief surgical procedures in ambulatory patients. The extremely short wash-in phase as compared to previously described LFA techniques can be achieved by using anesthetic gas monitoring.