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ROUTINE PRACTICE OF LOW-FLOW ISOFLURANE ANESTHESIA

Johansen, JW MD, PhD; Nardi, RA MMSc; deCamp, M MMSc

doi: 10.1097/00000539-199802001-00036
Abstracts of Posters Presented at the International Anesthesia Research Society; 72nd Clinical and Scientific Congress; Orlando, FL; March 7-11, 1998: Anesthesia/OR Economics
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Department of Anesthesiology, Emory University School of Medicine, Atlanta, GA 30335.

Abstract S36

Low-flow anesthesia has been predicted to substantially decrease costs, but never demonstrated on a departmental level. [1,2] Previous studies involved limited comparisons of select groups, generally ambulatory patients. [3] Low-flow and closed-circuit techniques have been promoted for many years within our institution. The effect of fresh-gas flow rates above or below 2 L/min on cost and outcome of isoflurane anesthesia was examined.

After Human Investigation Committee approval, prospective collection of operating room (OR) and postanesthesia recovery room (PACU) data on all surgical cases performed at Grady Memorial Hospital during a four-month period of normal practice was initiated. This study examined adult patients undergoing general anesthesia using isoflurane, who were extubated by PACU discharge. Both ambulatory (20%), in-patient (65%) and SICU patients were included. 20% of cases were performed under closed-circuit conditions. Criteria for recovery from PACU included maintaining a modified Aldrete score [4] of >or=to 17/20 for 30 min. In the PACU, intravenous (IV) treatment for analgesia, blood pressure control (BP) and nausea was recorded. (Table 1)

Table 1

Table 1

No difference existed between groups with regard to demographic variables, emergency (20-29%), use of nitrous oxide (75%) or frequency of extubation in the PACU. Average duration, end-tidal concentration and total anesthetic delivery (MAC-h) was similar. A significantly higher fresh-gas flow (217%) resulted in increased isoflurane cost (183%). OR times, PACU times and PACU interventions were not significantly different.

Because average duration and end-tidal concentrations were similar, the increased cost of isoflurane can be directly ascribed to flow rates greater than 2 L/min. Calculation of isoflurane costs from measured end-tidal concentrations during maintenance is a conservative basis for cost estimation ignoring the cost of induction and emergence. Fresh-gas flow did not significantly affect any specific outcome, and no cost shifting was detected. During normal practice, 60% of cases were performed at flow rates below 2 L/min. Staff compliance with low flow recommendations has been one of the most difficult areas of implementing cost-efficient anesthesia. [5] Based on these cost estimates, over $1860 of isoflurane was saved in adult patients during this four-month data collection. (Table 2 and Table 3)

Table 2

Table 2

Table 3

Table 3

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REFERENCES

1. Anaesthesia 1995;50:37-44
2. Anesthesiology 1993;79:1413-18
3. Anesth Analg 1995;81:S67-72
4. Can Anaesth Soc J 1975;22:111
5. Anesthesiology 1997;86:1145-1160
© 1998 International Anesthesia Research Society