Low-flow anaesthesia at a fixed flow rate

Comparison of emergence times with different fresh gas flow rates following desflurane anaesthesia

Objective

To investigate emergence times with different fresh gas flow rates, following desflurane anaesthesia.

Methods

Patients undergoing surgery with desflurane anaesthesia were randomly assigned to receive fresh gas flow rates of 100% oxygen during emergence of 2 l/min (group D2), 4 l/min (group D4) or 6 l/min (group D6). Time to eye opening, spontaneous movement and extubation (emergence time) were assessed after desflurane discontinuation. The end-tidal concentration of desflurane and bispectral index were recorded at each of these timepoints.

Results

A total of 105 patients were included in the study, with 35 in each of the three groups. Mean times to extubation were 17.6 min, 9.9 min and 9.1 min in groups D2, D4 and D6, respectively. Times to eye opening, spontaneous movement and extubation in group D2 were significantly longer than in groups D4 and D6.

Conclusions

These results suggest that there is the potential to predict emergence time based on fresh gas flow rate following desflurane anaesthesia. It should therefore be possible to use a low-flow technique during the emergence period, in addition to the maintenance period, without delaying recovery if the inhaled anaesthetic is stopped at the predicted time before the end of surgery.

Reducing wastage of inhalation anesthetics using real-time decision support to notify of excessive fresh gas flow

BACKGROUND

Reduced consumption of inhalation anesthetics can be safely achieved by reducing excess fresh gas flow (FGF). In this study the authors describe the use of a real-time decision support tool to reduce excess FGF to lower, less wasteful levels.

METHOD

The authors applied a decision support tool called the Smart Anesthesia Manager™ (University of Washington, Seattle, WA) that analyzes real-time data from an Anesthesia Information Management System to notify the anesthesia team if FGF exceeds 1 l/min. If sevoflurane consumption reached 2 minimum alveolar concentration-hour under low flow anesthesia (FGF < 2 l/min), a second message was generated to increase FGF to 2 l/min, to comply with Food and Drug Administration guidelines. To evaluate the tool, mean FGF between surgical incision and the end of procedure was compared in four phases: (1) a baseline period before instituting decision rules, (2) Intervention-1 when decision support to reduce FGF was applied, (3) Intervention-2 when the decision rule to reduce flow was deliberately inactivated, and (4) Intervention-3 when decision rules were reactivated.

RESULTS

The mean ± SD FGF reduced from 2.10 ± 1.12 l/min (n = 1,714) during baseline to 1.60 ± 1.01 l/min (n = 2,232) when decision rules were instituted (P < 0.001). When the decision rule to reduce flow was inactivated, mean FGF increased to 1.87 ± 1.15 l/min (n = 1,732) (P < 0.001), with an increasing trend in FGF of 0.1 l/min/month (P = 0.02). On reactivating the decision rules, the mean FGF came down to 1.59 ± 1.02 l/min (n = 1,845). Through the Smart Anesthesia Messenger™ system, the authors saved 9.5 l of sevoflurane, 6.0 l of desflurane, and 0.8 l isoflurane per month, translating to an annual savings of $104,916.

CONCLUSIONS

Real-time notification is an effective way to reduce inhalation agent usage through decreased excess FGFs.