Ventilator-assisted priming of an anaesthesia circuit (VAP technique): An exploratory study

Background and Aims

The speed of inhalational induction depends on a variety of factors, of which priming the breathing circuit with volatile anaesthetics plays a vital role. This study compared ventilator-assisted priming (VAP) and a passive priming technique using different fresh gas flows (FGFs) in neonatal, paediatric, and adult anaesthetic circuits.

Methods

In both techniques, FGF with 100% oxygen and 8% sevoflurane vaporiser concentration were set at 2 Lmin^-1, 4 Lmin^-1, and 8 Lmin^-1, representing three groups FGF-2, FGF-4, and FGF-8, respectively. The time taken to achieve 6% sevoflurane concentration at the patient end of the circuit was measured. In addition to this, we explored various combinations of tidal volumes and respiratory rates in the VAP technique and recorded the priming time with each combination. The amount of sevoflurane consumed for priming in both techniques was also calculated.

Results

VAP was three times faster than passive priming in all the FGF groups in the three circuits. In the VAP technique, the shortest priming times were similar for FGF-4 and FGF-8 (P > 0.05) but were significantly higher for FGF-2 (P = 0.001) in the three circuits. Sevoflurane consumption did not differ in FGF-2 and FGF-4 groups, whereas it doubled in the FGF-8 group using the VAP technique in all three circuits.

Conclusion

The VAP technique provides a quick and effective method for priming to achieve a high anaesthetic concentration within the breathing circuit for inhalational induction.

Greenhouse gas reduction in anaesthesia practice: a departmental environmental strategy

Sustainability interventions were implemented at the Royal Brisbane and Women’s Hospital (RBWH) following identification of inhaled anaesthetic gases as a target for reducing medical carbon emissions. This quality improvement study assessed and evaluated the impact of sustainability interventions on the environmental and financial cost of inhaled anaesthetic gas use in order to guide future initiatives and research in reducing carbon emissions from healthcare practice.

Ethical exemption was granted from the RBWH Research Ethics Committee (EX/2021/QRBW/76078). Usage (bottles) and expenditure for desflurane and sevoflurane from January 2016 to December 2021 were obtained. Global warming potential and carbon dioxide equivalent (CO₂e) were used to report environmental impact of volatile agents. Methods to estimate this were performed in Excel based on Campbell and Pierce methodology. An Environmental Protection Agency greenhouse gas equivalency calculator was used to convert CO₂e to equivalent petrol carbon emissions and kilometres travelled by a typical passenger vehicle.

The total number of bottles of sevoflurane and desflurane purchased between January 2016 and December 2021 decreased by 34.76% from 1991 to 1299. The number of desflurane bottles purchased decreased by 95.63% from 800 to 35 bottles. The number of sevoflurane bottles purchased increased by 6.13% from 1191 bottles to 1264 bottles. This was achieved by implementing quality improvement interventions such as staff education of desflurane-sparing practices, distribution of posters and progressive removal of desflurane from operating theatres. Total carbon emission from volatile anaesthetics equalled 2326 tonnes CO₂e. Combined desflurane and sevoflurane emissions decreased by 87.88%. In 2016, desflurane made up 92.39% of the annual CO₂e, which steadily decreased to 33.36% in 2021. Combined sevoflurane and desflurane usage costs decreased by 58.33%.

Substantial reductions in carbon emissions from volatile anaesthetics demonstrate the significant degree to which environmentally sustainable practices have been implemented. Applying desflurane-sparing practice can heavily limit anaesthetic drug expenditure and contribution to environmental waste. This is important given the global health sector’s challenge to optimise patient outcomes in the face of global climate change crisis.

A survey of the choice of general anaesthetic agents in Australia and New Zealand

Strategies to reduce the adverse environmental costs of anaesthesia include choice of agent and fresh gas flows. The current preferences of Australian and New Zealand anaesthetists are unknown. We conducted a survey of Australian and New Zealand anaesthetists to determine the use of volatiles, nitrous oxide and intravenous anaesthesia, lowest fresh gas flow rates, automated end-tidal volatile control, and the rationales for these choices. The survey was answered by 359/1000 (36%), although not all questions and multiple responses within single questions were answered by all respondents. Sevoflurane was preferred by 246/342 (72%, 95% confidence interval (CI) 67%–77%), followed by propofol, 54/340 (16%, 95% CI 12%–20%), desflurane 39/339 (12%, 95% CI 8%–16%) and isoflurane 3/338(1%, 95% CI 0–3%). When asked about all anaesthetics, low-risk clinical profile was the most common reason given for using sevoflurane (129/301 (43%, 95% CI 37%–49%)), reduced postoperative nausea for propofol (297/318 (93%, 95% CI 90%–96%)) and faster induction/awakening times for desflurane (46/313 (79%, 95% CI 74%–83%)). Two-thirds (226/340 (66%, 95% CI 61%–71%)) of respondents used nitrous oxide in 0–20% of general anaesthetics. Low fresh gas flow rates for sevoflurane were used by 310/333 (93%, 95% CI 90%–95%) and for 262/268 (98%, 95% CI 95%–99%) for desflurane. Automated end-tidal control was used by 196/333 (59%, 95% CI 53%–64%). The majority of respondents (>70%) preferred sevoflurane at low flows. These data allow anaesthetists to consider further whether changes are required to the choices of anaesthetic agents for environmental, financial, or any other reasons.

Waste anesthetic gas exposure and strategies for solution

As inhaled anesthetics are widely used, medical staff have inevitably suffered from exposure to anesthetic waste gases (WAGs). Whether chronic exposure to WAGs has an impact on the health of medical staff has long been a common concern, but conclusions are not consistent. Many measures and equipment have been proposed to reduce the concentration of WAGs as far as possible. This review aims to dissect the current exposure to WAGs and its influence on medical staff in the workplace and the environment, and summarize strategies to reduce WAGs.

Economic Evaluation of Pharmacologic Pre- and Postconditioning With Sevoflurane Compared With Total Intravenous Anesthesia in Liver Surgery: A Cost Analysis

BACKGROUND

Pharmacologic pre- and postconditioning with sevoflurane compared with total IV anesthesia in patients undergoing liver surgery reduced complication rates as shown in 2 recent randomized controlled trials. However, the potential health economic consequences of these different anesthesia regimens have not yet been assessed.

METHODS

An expostcost analysis of these 2 trials in 129 patients treated between 2006 and 2010 was performed. We analyzed direct medical costs for in-hospital stay and compared pharmacologic pre- and postconditioning with sevoflurane (intervention) with total IV anesthesia (control) from the perspective of a Swiss university hospital. Year 2015 costs, converted to US dollars, were derived from hospital cost accounting data and compared with a multivariable regression analysis adjusting for relevant covariables. Costs with negative prefix indicate savings and costs with positive prefix represent higher spending in our analysis.

RESULTS

Treatment-related costs per patient showed a nonsignificant change by -12,697 US dollars (95% confidence interval [CI], 10,956 to -36,352; P = .29) with preconditioning and by -6139 US dollars (95% CI, 6723 to -19,000; P = .35) with postconditioning compared with the control group. Results were robust in our sensitivity analysis. For both procedures (control and intervention) together, major complications led to a significant increase in costs by 86,018 US dollars (95% CI, 13,839-158,198; P = .02) per patient compared with patients with no major complications.

CONCLUSIONS

In this cost analysis, reduced in-hospital costs by pharmacologic conditioning with sevoflurane in patients undergoing liver surgery are suggested. This possible difference in costs compared with total IV anesthesia is the result of reduced complication rates with pharmacologic conditioning, because major complications have significant cost implications.

Randomized Comparison of Isoflurane versus Sevoflurane and Desflurane for Maintenance of Ambulatory Anesthesia

Background:

Ambulatory surgeries demand safe anesthesia with faster recovery which makes it expensive due to the cost of inhalational anesthetic agents such as sevoflurane and desflurane. Isoflurane is inexpensive agent but can cause delayed recovery. The aim of this study was to evaluate cost-benefit ratio of all three agent with respect to recovery and safety profile

Materials and Methods:

Patients posted for elective ambulatory surgeries were divided into three groups. Suitable size laryngeal mask airway was inserted following induction with propofol and vecuronium. Anesthesia was maintained on low-flow anesthesia with inhalational agent as isoflurane for Group I, sevoflurane for Group II and Group III received desflurane. Patients were monitored for recovery as per modified Aldrete score and as per postanesthesia discharge scoring system for discharge from hospital. Cost analysis was done by Dion's formula. Statistical analysis was done with analysis of variance for recovery profile, Chi-square test for safety profile and Kruskal Wallis test for cost comparison between groups.

Results:

Patient characteristics and duration of anesthesia were similar in all three groups. Time to eye-opening was significantly less with desflurane than sevoflurane and isoflurane (P = 0.001). Time to home readiness was similar in all three groups (P = 0.451). The incidence of airway irritation, pain, and nausea/vomiting was similar in all three groups. Cost of Group I was statistically lower than other two groups (P = 0.00).

Conclusion:

Home readiness and safety profile were comparable between agents; the cost involved was the least with isoflurane.

Awakening arterial blood and end-tidal concentrations of isoflurane in female surgical patients

Delayed extubation occurs after isoflurane anesthesia, especially following prolonged surgical duration. We aimed to determine the arterial blood concentrations of isoflurane and the correlation with end-tidal concentrations for predicting emergence from general anesthesia.Thirty-four American Society of Anesthesiologists physical status class I-II gynecologic patients were included. General anesthesia was maintained with a fixed 2% inspiratory isoflurane in 6 L/minute oxygen, which was discontinued after surgery. One milliliter of arterial blood was obtained for the determination of isoflurane concentration by gas chromatography at 20 and 10 minutes before and 0, 5, 10, 15, and 20 minutes after discontinuation, in addition to the time of eye opening to verbal command, defined as awakening. Inspiratory and end-tidal concentrations were simultaneously detected by an infrared analyzer.The mean awakening arterial blood concentration of isoflurane was 0.20%, which was lower than the simultaneous end-tidal concentration 0.23%. The differences between arterial and end-tidal concentrations during emergence fell into an acceptable range (±1.96 standard deviation). After receiving a mean time of 108-minute general anesthesia, the time to eye opening after discontinuing isoflurane was 18.5 minutes (range 11-30, median 18 minutes), without statistical significance with anesthesia duration (P = 0.078) and body mass index (P = 0.170).We demonstrated the awakening arterial blood concentration of isoflurane in female patients as 0.20%. With well-assisted ventilation, the end-tidal concentration could be an indicator for the arterial blood concentration to predict emergence from shorter duration of isoflurane anesthesia.

Accuracy of calculated volatile agent consumption from fresh gas content

BACKGROUND

Case-by-case assessment of volatile anesthetic (VA) consumption is necessary to perform agent sparing dosing measures and for billing purposes. The gold standard technique for this purpose is to measure the weight difference of the vaporizer that occurs during VA delivery. Because suitable equipment is rarely available and weighing the vaporizer is only possible in prospectively planned fashion, a calculation method from recorded fresh gas flow (FGF) and VA courses is a viable alternative. The objective was to evaluate the accuracy of VA calculation from fresh gas composition vs. the gold standard of weighing the vaporizer before and after anesthesia.

METHODS

In this prospective laboratory investigation, we compared the formula-based calculations of VA consumption to the measured vaporizer weight differences before and after 10 sevoflurane and 10 desflurane anesthesia. We assessed the average difference and spread of values between the calculated and the measured values.

RESULTS

The calculated sevoflurane consumption overestimated the measured values by 3.0 ± 2.9 ml (6.2%). The calculated desflurane consumption overestimated the measured values by 3.5 ± 6.7 ml (5.0%). All pairs of values from both agents were within ± 1.96 standard deviations.

CONCLUSION

The calculated VA consumption for sevoflurane and desflurane are sufficiently accurate to estimate the economic impact of VA delivery during inhalational anesthesia. This method enables the assessment of VA consumption both ways: (1) retrospectively from sufficiently detailed and accurate anesthesia recordings, as well as (2) by using this method in a prospective setting.

Hemodynamic parameters of low-flow isoflurane and low-flow sevoflurane anesthesia during controlled ventilation with laryngeal mask airway

Background:

Nowadays laryngeal mask airway (LMA) is popular as one of the best choices for airway management. Low-flow anesthesia has some advantages like lower pollution, hemodynamic stability and cost effectiveness. Volatile anesthetics are widely used for anesthesia maintenance during operations. Sevoflurane has more hemodynamic stability compared to isoflurane, but there are few studies comparing the hemodynamic stabilities of these two anesthetics during controlled low flow anesthesia with LMA.

Objectives:

The aim of this study was to compare the effects of low-flow sevoflurane and low-flow isoflurane on hemodynamic parameters of patients through LMA.

Patients and Methods:

Eighty patients, scheduled for elective ophthalmic surgery, were randomly divided into two groups. After induction, an LMA with an appropriate size was inserted in all the patients and they were randomly allocated to two groups of low-flow sevoflurane (n = 40) and low-flow isoflurane (n = 40). Hemodynamic parameters (heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP) and Mean Arterial Pressure (MAP) were recorded at 5, 10, 15, 20, 25 and 30 minutes after the anesthesia induction.

Results:

The mean heart rate values were significantly less in the sevoflurane group (P value < 0.05) at 25 minutes after the surgery. The mean Blood Pressure in the isoflurane group was significantly higher compared with the sevoflurane group in 10, 20 and 30 minutes after the surgery (P values = 0.0131, 0.0373 and 0.0028, respectively). These differences were clinically unimportant because heart rate and mean blood pressure were on normal ranges.

Conclusions:

Seemingly, low-flow sevoflurane with LMA did not have any significant hemodynamic effect on clinical practice. Therefore, low-flow sevoflurane anesthesia with LMA might be considered in patients with short operations who need rapid recovery from anesthesia.

Reliability of the volatile agent consumption display in the Draeger Primus™ anesthesia machine

Knowledge of the consumed amount of volatile anesthetic (VA) expressed in liquid agent is necessary to enable agent sparing dosing measures and for billing purposes. The widespread Draeger Primus™ anesthesia machine displays in its logbook the amount of consumed VA at the end of each anesthesia, but the reliability of this parameter is yet unknown. The objective was to evaluate the precision and reliability of the inbuilt VA consumption display in Draeger Primus™ anesthesia machines as compared with the gold standard of weighing the vaporizer before and after anesthesia. In this prospective laboratory investigation we compared the VA consumption displayed by the Draeger Primus™ anesthesia machine with measured vaporizer weight differences before and after 10 sevoflurane and 10 desflurane anesthesias. We assessed the average difference and spread of values between the predicted (displayed) and measured (control) values for VA consumption. The displayed sevoflurane consumption overestimated the measured values by 4.3 ± 5.4 ml (7.6%). The displayed desflurane consumption underestimated the measured values by -3.5 ± 6.3 ml (6.2%). Nine from 10 sevoflurane pairs of values and all desflurane pairs of values were within ±1.96 SD. The displayed VA consumption calculations for sevoflurane and desflurane in the Draeger Primus™ are sufficiently reliable to estimate the pharmacoeconomic impact of VA delivery during inhalational anesthesia.

Cost analysis of three techniques of administering sevoflurane

Background. This study aimed to evaluate and compare total cost of sevoflurane and propofol for 1.0 MAC-hour of anaesthesia, employing three anaesthetic techniques. Methods. Adult patients scheduled for surgical procedures under general anaesthesia anticipated to last approximately an hour were randomized into three groups (n = 15 each), to receive anaesthesia using one of the following techniques: low flow technique involving induction with propofol, followed by sevoflurane delivered using initial fresh gas flows of 6 L/min till MAC reached 1.0 and then reduced to 0.5 L/min; alternate method of low flow entailing only a difference in fresh gas flow rates being maintained at 1 L/min throughout; the third technique involving use of sevoflurane for both induction and maintenance of anaesthesia. Results. Cost of sevoflurane to maintain 1 MAC-hour of anaesthesia was clinically least with low flow anaesthesia, though statistically similar amongst the three techniques. Once the cost of propofol used for induction in two of the three groups was added to that of sevoflurane, cost incurred was least with the technique using sevoflurane both for induction and maintenance of anaesthesia, as compared to low flow and alternative low flow techniques, a 26% and 32% cost saving, respectively (P < 0.05).

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.

Changing patterns in volatile anaesthetic agent consumption over seven years in Victorian public hospitals

Evidence-based choices of volatile agents can increase health cost efficiencies. In this pharmaco-economic study, we evaluated the trends and costs of volatile agent use in Australian public hospitals. The total number of volatile agent (isoflurane, sevoflurane and desflurane) bottles ordered and inflation-adjusted costs were collected from 65 Victorian public hospitals from 2005 to 2011. Environmental costs were measured through the 100-year global warming potential index as carbon dioxide equivalents. During this time period, the aggregate inflation-adjusted expenditure was $39,209,878. Time series analysis showed that bottles of isoflurane ordered decreased by 419/year (99% confidence interval (CI): -603 to -235); costs decreased by $56,017/year (99% CI: -$93,243 to -$18,791). Bottles of sevoflurane increased by 1,330/year (99% CI: 1141 to 1,519); costs decreased by $423,3573/year (99% CI: -$720,030 to -112,783). Bottles of desflurane increased by 726/year (99% CI: 288 to 1,164); costs increased by $171,578/year (99% CI: $136,951 to $206,205). The amount of calculated greenhouse gas emissions released into the atmosphere over this period was 37,000 tonnes of carbon dioxide equivalents, with isoflurane contributing 6%, sevoflurane 17%, and desflurane 77% of this total. In conclusion, isoflurane is no longer being used in the majority of Victorian public hospitals, with sevoflurane and desflurane remaining as the primary volatile agents, utilised respectively at a ratio of 2.2 to 1, and costs at 0.8 to 1.

Calculation of volatile anaesthetics consumption from agent concentration and fresh gas flow

BACKGROUND

The assessment of volatile agents' consumption can be performed by weighing vapourisers before and after use. This method is technically demanding and unavailable for retrospective analysis of anaesthesia records. Therefore, a method based on calculations from fresh gas flow and agent concentration is presented here.

METHODS

The presented calculation method herein enables a precise estimation of volatile agent consumption when average fresh gas flows and volatile agent concentrations are known. A pre-condition for these calculations is the knowledge of the vapour amount deriving from 1 ml fluid volatile agent. The necessary formulas for these calculations and an example for a sevoflurane anaesthesia are presented.

RESULTS

The amount of volatile agent vapour deriving from 1 ml of fluid agent are for halothane 229 ml, isoflurane 195 ml, sevoflurane 184 m, and desflurane 210 ml. The constant for sevoflurane is used in a fictitious clinical case to exemplify the calculation of its consumption in daily routine resulting in a total expenditure of 23.6 ml liquid agent.

CONCLUSIONS

By application of the presented specific volatile agent constants and equations, it becomes easy to calculate volatile agent consumption if the fresh gas flows and the resulting inhaled concentration of the volatile agent are known. By this method, it is possible to extract data about volatile agent consumption both ways: (1) retrospectively from sufficiently detailed and accurate anaesthesia recordings, as well as (2) by application of this method in a prospective setting. Therefore, this method is a valuable contribution to perform pharmacoeconomical surveys.

Measurement of consumption of sevoflurane for short pediatric anesthetic procedures: Comparison between Dion's method and Dragger algorithm

Background:

The most common drugs used in an operating room are the Inhalation agents for maintenance of anesthesia yet their measurement methods during the procedure are not well-validated. Conventional methods of measuring the vaporizer weight after each use suffers from practical limitations of high error and time constraints.

Aims:

We compared two alternative methods available (Dion's method and Drager Inc. patent protocol) for their degree of concordance and correlation in real-time consumption of sevoflurane for pediatric procedures.

Results:

Both methods showed a very strong correlation (0.895 [P > 0.001]). Dion's method underestimated consumption by 2.59 ml with limits of agreement between 5.188 ml and −0.008 ml. Both test results showed a strong correlation, but poor concordance.

Conclusions:

Dion's method strongly correlates with Drager protocol although concordance between the two methods for measuring anesthetic gas consumption is poor. Dion's method underestimates the consumption and with slight modification addressing this underestimation, it can be electronically incorporated in other workstations to overcome limitations of real-time measurement of inhalation agent consumption.

Effects of Volatile Anesthetic Choice on Hospital Length-of-stay

Background:

Volatile anesthetic prices differ substantially. But differences in drug-acquisition cost would be inconsequential if hospitalization were prolonged by more soluble anesthetics. The authors tested the hypothesis that the duration of hospitalization is prolonged with isoflurane anesthesia.

Methods:

Initially, the authors queried their electronic records and used propensity matching to generate homogeneous sets of adults having inpatient noncardiac surgery who were given desflurane, sevoflurane, and isoflurane. The authors then conducted a prospective alternating intervention trial in which adults (mostly having colorectal surgery) were assigned to isoflurane or sevoflurane, based on protocol.

Results:

In the retrospective analysis, 2,898 matched triplets were identified among 43,352 adults, each containing one patient receiving isoflurane, desflurane, and sevoflurane, respectively. The adjusted geometric mean (95% CI) hospital length-of-stay for the isoflurane cases was 2.85 days (2.78–2.93); this was longer than that observed for both desflurane (2.64 [2.57–2.72]; P &lt; 0.001) and sevoflurane (2.55 [2.48–2.62]; P &lt; 0.001). In the prospective trial (N = 1,584 operations), no difference was found; the adjusted ratio of means (95% CI) of hospital length-of-stay in patients receiving isoflurane versus sevoflurane was 0.98 (0.88–1.10), P = 0.77, with adjusted geometric means (95% CI) estimated at 4.1 (3.8–4.4) and 4.2 days (3.8–4.5), respectively.

Conclusions:

Results of the propensity-matched retrospective analysis suggested that avoiding isoflurane significantly reduced the duration of hospitalization. In contrast, length-of-stay was comparable in our prospective trial. Volatile anesthetic choice should not be based on concerns about the duration of hospitalization. These studies illustrate the importance of following even the best retrospective analysis with a prospective trial.

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.

Desflurane: a clinical update of a third-generation inhaled anaesthetic

Available volatile anaesthetics are safe and efficacious; however, their varying pharmacology provides small but potentially clinically important differences. Desflurane is one of the third-generation inhaled anaesthetics. It is the halogenated inhaled anaesthetic with the lowest blood and tissue solubilities, which promotes its rapid equilibration and its rapid elimination following cessation of administration at the end of anaesthesia. The low fat solubility of desflurane provides pharmacological benefits, especially in overweight patients and in longer procedures by reducing slow compartment accumulation. A decade of clinical use has provided evidence for desflurane's safe and efficacious use as a general anaesthetic. Its benefits include rapid and predictable emergence, and early recovery. In addition, the use of desflurane promotes early and predictable extubation, and the ability to rapidly transfer patients from the operating theatre to the recovery area, which has a positive impact on patient turnover. Desflurane also increases the likelihood of patients, including obese patients, recovering their protective airway reflexes and awakening to a degree sufficient to minimise the stay in the high dependency recovery area. The potential impact of the rapid early recovery from desflurane anaesthesia on intermediate and late recovery and resumption of activities of daily living requires further study.

Managing fresh gas flow to reduce environmental contamination

Anesthetic drugs have the potential to contribute to global warming. There is some debate about the overall impact of anesthetic drugs relative to carbon dioxide, but there is no question that practice patterns can limit the degree of environmental contamination. In particular, careful attention to managing fresh gas flow can use anesthetic drugs more efficiently--reducing waste while achieving the same effect on the patient. The environmental impact of a single case may be minimal, but when compounded over an entire career, the manner in which fresh gas flow is managed by each individual practitioner can make a significant difference in the volume of anesthetic gases released into the atmosphere. The maintenance phase of anesthesia is the best opportunity to reduce fresh gas flow because circuit gas concentrations are relatively stable and it is often the longest phase of the procedure. There are, however, methods for managing fresh gas flow during induction and emergence that can reduce the amount of wasted anesthetic vapor. This article provides background information and discusses strategies for managing fresh gas flow during each phase of anesthesia with the goal of reducing waste when using a circle anesthesia system. Monitoring oxygen and anesthetic gas concentrations is essential to implementing these strategies safely and effectively. Future technological advances in anesthetic delivery systems are needed to make it less challenging to manage fresh gas flow.

Observational Study of Anaesthetists’ Fresh Gas Flow Rates during Anaesthesia with Desflurane, Isoflurane and Sevoflurane

Reducing excessive fresh gas flow rates (FGF) is an established and simple strategy to reduce the administration of volatile anaesthetic agents. We studied clinicians’ FGF use to understand better why two previous clinical trials achieved significant reductions in FGF by using feedback to anaesthetists.

Anaesthesia information management system data from a US academic medical centre were analysed retrospectively. One year of data starting from July 2008 had 11,170 cases. Fresh gas flow rates were measured each minute during cases.

Anaesthetists were more likely to choose FGF of multiples of 1 l/minute and 0.5 l/minute than random. However, the pattern was too inconsistent to be of economic or psychological importance and thus is not needed when describing a target FGF.

Cumulative distributions of FGF were shifted to the left for desflurane and isoflurane compared to sevoflurane (i.e. cost comparisons among agents may need to use different target FGF).

Variation in mean FGF among anaesthetists was small. Even if all anaesthetists had identical mean FGF, the standard deviation of FGF among cases would be reduced by less than 0.1 l/minute for all agents. Most of the achievable reductions in FGF were small reductions in FGF for the many cases with <3 l/minute.

These results show that departments choosing to use inexpensive automatic email feedback on FGF should target all anaesthetists and focus on variation in FGF among anaesthetists’ cases.