High Fresh Gas Flow Research Articles

Anesthetics drug wastage and preventive strategies: Systematic review.

Surgical Patients and hospitals are now facing financial strain due to direct anesthetic demand as a result of the development of new anesthetic drugs, equipment, and techniques. Up to 15% of a hospital's pharmacy budget is currently allocated to anesthetic drug expenses. Drug wastage during anesthesia practice is a widespread hidden source of healthcare waste that leads to anesthetic drug shortages as well as poor operating room efficiency. On the other hand, despite the fact that it is preventable in the vast majority of cases, it is well described that drug wastage is routinely observed, including in developing countries where the consequences significantly affect both hospitals and patients. This review aims to review the prevalence of anesthetic drug waste across the world and systematically formulate and describe preventive strategies. Relevant publications were identified using systematic searches on databases including Google Scholar, Medline (PubMed), the Cochrane Library, and Embase. In addition, papers were detected and then selected through the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) criteria guidelines and the inclusion and exclusion criteria. Using the predetermined terms and dates from the searching databases, a total of 504 articles were identified. Based on the screening criteria, 16 papers were considered eligible and included in the final review. In addition, the Joanna Briggs Institute (JBI) Manual for Evidence Synthesis was used for evaluating the quality of selected articles. This study is registered on PROSPERO, number CRD42024497044. Of the sixteen publications from eleven different nations that were considered suitable for inclusion, only two of them addressed the waste of inhalational anesthetics. In more than half of eligible articles, propofol was the frequently wasted drug that contributed to increased financial loss through drug waste. The first most significant factor contributing to the waste of intravenous and inhalational anesthetics was the disposal of multidrug vials following their use for a single patient and high fresh gas flow, respectively. Anesthetic medication waste is a common occurrence worldwide, despite the fact that it is expensive and has a significant negative impact on operating room efficiency. Because the majority of drug waste is avoidable, preventive measures may lower drug waste and improve patient and hospital efficiency.

Preventing Prolonged Times to Awakening While Mitigating the Risk of Patient Awareness: Gas Man Computer Simulations of Sevoflurane Consumption From Brief, High Fresh Gas Flow Before the End of Surgery.

Prolonged times to tracheal extubation are associated with adverse patient and economic outcomes. We simulated awakening patients from sevoflurane after long-duration surgery at 2% end-tidal concentration, 1.0 minimum alveolar concentration (MAC) in a 40-year-old. Our end-of-surgery target was 0.5 MAC, the Michigan Awareness Control Study's threshold for intraoperative alerts. Consider an anesthetist who uses a 1 liter/minute gas flow until surgery ends. During surgical closure, the inspired sevoflurane concentration isreduced from 2.05% to0.62% (i.e., MAC-awake). The estimated time to reach 0.5 MAC is 28 minutes. From a previous study, 28 minutes exceeded ≥95% of surgical closure times for all 244 distinct surgical procedures (N=23,343 cases). Alternatively, the anesthetist uses 8 liters/minute gas flow with the vaporizer atMAC-awake for 1.8 minutes, which reduces the end-tidal concentration to 0.5MAC. The anesthetist then increases the vaporizer to keep end-tidal 0.5 MAC until the surgery ends. An additional simulation shows that, compared with simulated end-tidal agent feedback control, this approach consumed 0.45 mL extra agent. Simulation results are the same for an 80-year-old patient. The extra 0.45 mL has a global warming potential comparable to driving 26 seconds at 40 kilometers (25 miles) per hour, comparable to route modification to avoid potential roadway hazards.

EFEKTIVITAS TEKNIK ANESTESI LOW FLOW DIBANDINGKAN TEKNIK ANESTESI INHALASI STANDAR PADA ANAK USIA 1-6 TAHUN YANG MENJALANI OPERASI DI PROF. DR. I.G.N.G. NGOERAH DENPASAR

Since the discovery of sevoflurane, it has been commonly used due to its many advantages, including its safety profile for pediatric anesthesia practice. However, currently no ideal recommendation for how much gas flow should be used during induction in children. High fresh gas flow (FGF) causes waste of anesthetic and oxygen gases, making it both uneconomical and environmentally polluting. To date, there have been very few studies on low FGF in children, so there is no best and efficient method for reducing the need for large amounts of induction gas. The aim of this study is to determine the effectiveness of the low low anesthesia (LFA) technique in reducing sevoflurane volume, induction time, and hemodynamics during surgery in children undergoing surgery. This is a case-control study conducted at Prof. Dr. I.G.N.G Ngoerah Hospital in Denpasar. Forty-six children aged 1 - 6 years underwent elective surgery and were anesthetized with sevoflurane and randomly divided into two groups: the case group using the low-flow anesthesia technique and the control group using the standard anesthesia technique. The case and control groups were statistically similar in terms of demographic data. However, the volume of sevoflurane used from the time of premedication to intubation was significantly different (p > 0.05) between the two groups (35.5 ml vs 44.5 ml). The induction times were not significantly different (209s vs 201s, p<0.05). Additionally, no significant difference was observed regarding hemodynamic stability during anesthesia.
 Keywords : anesthesia induction, hemodynamic stability, low flow anesthesia, sevoflurane

Reducing the environmental impact of mask inductions in children: A quality improvement report.

Inhalational anesthetic agents are potent greenhouse gases with global warming potential that far exceed that of carbon dioxide. Traditionally, pediatric inhalation inductions are achieved with a volatile anesthetic delivered to the patient in oxygen and nitrous oxide at high fresh gas flows. While contemporary volatile anesthetics and anesthesia machines allow for a more environmentally conscious induction, practice has not changed. We aimed to reduce the environmental impact of our inhalation inductions by decreasing the use of nitrous oxide and fresh gas flows. Through a series of four plan-do-study-act cycles, the improvement team used content experts to demonstrate the environmental impact of the current inductions and to provide practical ways to reduce this, by focusing on nitrous oxide use and fresh gas flows, with visual reminders introduced at point of delivery. The primary measures were the percentage of inhalation inductions that used nitrous oxide and the maximum fresh gas flows/kg during the induction period. Statistical process control charts were used to measure improvement over time. 33 285 inhalation inductions were included over a 20-month period. nitrous oxide use decreased from 80% to <20% and maximum fresh gas flows/kg decreased from a rate of 0.53 L/min/kg to 0.38 L/min/kg, an overall reduction of 28%. Reduction in fresh gas flows was greatest in the lightest weight groups. Induction times and behaviors remained unchanged over the duration of this project. Our quality improvement group decreased the environmental impact of inhalation inductions and created cultural change within our department to sustain change and foster the pursuit of future environmental efforts.

Low Flow Anesthesia – Mission Impossible?

Because low flow anesthesia reduces waste of environmentally unfriendly inhaled anesthetics, it is coming in the spotlights – again. Despite a detailed theoretical description, considerable teaching efforts of this simple technique have not succeeded in consistently lowering fresh gas flows (FGF) during manual control1. Worse, even though technology has solved the hurdles of manual delivery and the technology is widely available, we fail to maximally implement it. The delivery of inhaled anesthetics with high FGF prior to securing the airway remains common practice. We fail to consistently adjust MAC to age and poorly titrate opioids to reduce the fraction of the MAC we administer. We fail to incorporate hysteresis which is reflected in the use of excessively high FGF and vaporizer settings during wash-in and in the failure to maintain low FGF prior to emergence (“coasting”). By failing to fully appreciate the quantitative effects of the delivery if inhaled anesthetics we miss the opportunity to reduce waste to the absolute minimum. Belief and myth are strong when the environmental impact of inhaled anesthetics is considered. We need better, detailed life cycle analyses with low flow data before making claims pro/con inhaled/TIVA. We tend to lose sight of perspective, and have to continue to weigh the impact of drug selection on patient care.

THE EFFECTS OF MINIMAL, LOW AND HIGH FLOW ANESTHESIA ON BODY TEMPERATURE AND TISSUE OXYGENATION IN NASAL SURGERIES

OBJECTIVE: Intraoperative high fresh gas flow may cause Inadvertent perioperative hypothermia (IPH). For this reason, low and minimal flow anesthesia methods that improve the anesthesia climate are applied. We aimed to investigate the effects of minimal, low and high flow anesthesia on body temperature and tissue oxygenation in patients undergoing elective nasal surgery.MATERIAL AND METHODS: Prospective randomized controlled study included 92 patients aged 18-60 years, ASA1-2 operation time 1-4 hours, scheduled for elective nasal surgery under hypotensive anesthesia. The patients were divided into Group 1 (0.5Lmin-1), Group 2 (1Lmin-1) and Group 3 (2 Lmin-1). Demographic and operative data of the patients, preoperative waiting room temperature, intraoperative operating room temperature, intraoperative body temperature, anesthesia breathing circuit humidity and temperature, tissue oxygen saturation, 0th, 15th, 30th, 60th, 90th, 120th, 150thmin and postoperative shivering, Aldrete score, room temperature and body temperatures in the recovery unit were recorded.RESULTS: Perioperative hypothermia developed in all patients (p=0.001). Tympanic temperatures were similar in all three groups (p&amp;gt;0.05). In the subgroup comparison, it was found that the tissue oxygen saturation (StO2) 60 th min value of Group1 was higher than Group 2 (p=0.046). It was found statistically significant that the StO2 90 th min value of Group1 was higher than that of Group 2 and 3 (p=0.013, p=0.013). It was statistically significant that the StO2 120th min value of Group1 was higher than Group 3 (p=0.008).In Group1, postoperativeAldrete score was found to be significantly higher than the other two groups(p=0.002, p=0.002). A correlation was found between operating room temperature, postoperative recovery room temperature, and body temperature(r=.446, p&amp;lt;0.05;r=.531, p&amp;lt;0.01).CONCLUSIONS: Inadvertent perioperative hypothermia developed in all patients who underwent elective nasal surgery with hypotensive anesthesia in minimal, low and high flow anesthesia applications. It was observed that body temperatures, humidity and the temperature of the anesthesia period were similar in all groups. Tissue oxygen saturation was higher in the minimal flow anesthesia group and Aldrete score was higher in the postoperative recovery unit. Minimal flow anesthesia applications can be a good alternative to prevent IPH. However, we think that more studies are needed for the effects of low-flow anesthesia techniques at the tissue level.

Comparison of mainstream (Capnostat 5) and a low-flow sidestream capnometer (Capnostream) in mechanically-ventilated rabbits anesthetized with a Bain coaxial breathing system.

Introduction: Measurement of end-tidal carbon dioxide (PE'CO2) provides continuous non-invasive estimation of arterial carbon dioxide partial pressure (PaCO2). Agreement can be affected by the high respiratory rates and shallow tidal volumes of rabbits, especially when anesthetizing with a non-rebreathing system and high fresh gas flows. Capnometer function may be improved by increasing tidal volume and decreasing respiratory rate with mechanical lung ventilation.

Predicting the effect of fresh gas flow on tidal volume in volume-controlled mechanically ventilated dogs

ObjectivesTo determine if the tidal volume (VT) delivered (VTDEL) to canine patients being mechanically ventilated by a volume-controlled ventilator differed from the volume set on the ventilator (VTSET) at three fresh gas flow (FGF) rates. To determine if VTDEL could be accurately predicted by an FGF-based mathematical model. Study designProspective proof-of-concept study. AnimalsA total of 23 adult client-owned dogs undergoing elective orthopedic surgery. MethodsDogs were anesthetized and ventilated with a volume-controlled mechanical ventilator with constant respiratory rate (fR) of 10 breaths minute–1, inspiratory-to-expiratory ratio of 1:2 [fraction of inspiratory time (TI) in one respiratory cycle (Ttot) 1:3], and VTSET as body weight (kg) × 15 (mL kg–1). VTDEL was measured in 20 dogs at three FGF (500, 1000 and 4000 mL minute–1). A mathematical model was used to calculate predicted volume (VTPRED) for each animal at each FGF: VTSET + {FGF × [(TI/Ttot)/fR]}. Linear repeated measures models were fit comparing VTDEL to VTSET and to VTPRED by FGF. ResultsVTDEL was significantly higher than VTSET at every FGF (p < 0.05), and differences were larger at higher FGF (p < 0.001). There were no statistically significant differences between VTDEL and VTPRED at FGF rates of 500 and 4000 mL minute–1 and, although the mean VTDEL was statistically significantly higher than VTPRED at FGF 1000 mL minute–1 (p = 0.017), the mean difference of 9 mL was not clinically significant. Conclusions and clinical relevanceDogs on volume-controlled ventilators may be ventilated at a higher VTDEL than intended depending on the FGF settings. Ventilation of small animals at high FGF could inadvertently induce pulmonary damage. A mathematical equation can be used to achieve a desired VTDEL by adjusting VTSET values based on FGF, fR and TI/Ttot.

Reducing Volatile Anesthetic Waste Using a Commercial Electronic Health Record Clinical Decision Support Tool to Lower Fresh Gas Flows.

Volatile anesthetic consumption can be reduced by minimizing excessive fresh gas flows (FGFs). Currently, it is unknown whether decision support tools embedded within commercial electronic health record systems can be successfully adopted to achieve long-term reductions in FGF rates. The authors describe the implementation of an electronic health record-based clinical decision support tool aimed at reducing FGF and evaluate the effectiveness of this intervention in achieving sustained reductions in FGF rates and volatile anesthetic consumption. On August 29, 2018, we implemented a decision support tool within the Epic Anesthesia Information Management System (AIMS) to alert providers of high FGF (>0.7 L/min for desflurane and >1 L/min for sevoflurane) during maintenance of anesthesia. July 22, 2015, to July 10, 2018, served as our baseline period before the intervention. The intervention period spanned from August 29, 2018, to December 31, 2019. Our primary outcomes were mean FGF (L/min) and volatile agent consumption (mL/MAC-h). Because a simple comparison of 2 time periods may result in false conclusions due to underlying trends independent of the intervention, we performed segmented regression of the interrupted time series to assess the change in level at the start of the intervention and the differences in slopes before and after the intervention. The analysis was also adjusted for potential confounding variables. Data included 44,899 cases using sevoflurane preintervention with 26,911 cases postintervention, and 17,472 cases using desflurane with 1185 cases postintervention. Segmented regression of the interrupted times series demonstrated a decrease in mean FGF by 0.6 L/min (95% CI, 0.6-0.6 L/min; P < .0001) for sevoflurane and 0.2 L/min (95% CI, 0.2-0.3 L/min; P < .0001) for desflurane immediately after implementation of the intervention. For sevoflurane, mL/MAC-h decreased by 3.8 mL/MAC-h (95% CI, 3.6-4.1 mL/MAC-h; P < .0001) after implementation of the intervention and decreased by 4.1 mL/MAC-h (95% CI, 2.6-5.6 mL/MAC-h; P < .0001) for desflurane. Slopes for both FGF and mL/MAC-h in the postintervention period were statistically less negative than the preintervention slopes (P < .0001 for sevoflurane and P < .01 for desflurane). A commercial AIMS-based decision support tool can be adopted to change provider FGF management patterns and reduce volatile anesthetic consumption in a sustainable fashion.

The effect of different flow levels and concentrations of sevoflurane during the wash-in phase on volatile agent consumption: a randomized controlled trial.

The standard procedure for low-flow anesthesia usually incorporates a high fresh gas flow (FGF) of 4-6L/minute during the wash-in phase. However, the administration of a high FGF (4-6L/min) increases the inhaled anesthetic agent consumption. This study was designed to compare the sevoflurane consumption at 2 rates of flow and vaporizer concentration during the wash-in period. Patients were randomly enrolled into high FGF (HFGF) (n = 30) and low FGF (LFGF) (n = 30) groups. During the wash-in, the HFGF group received 4L/minute FGF with a sevoflurane vaporizer setting of 2.5%, and the LFGF group received 1L/minute FGF with a vaporizer setting of 8%. Once the wash-in was complete, anesthesia maintenance was performed with 0.5L/min FGF with a vaporizer setting of 2.5-4.5% in both groups. The patient demographic data, bispectral index values, hemodynamic variables, wash-in time, sevoflurane consumption during the wash-in phase, and total sevoflurane consumption were analyzed. The median sevoflurane consumption in the wash-in phase was 8.2 mL (7.1-9.3) in the HFGF group and 2.7 mL (2.2-3.1) in the LFGF group (p = 0.001). The mean total sevoflurane consumption was 17.41 ± 3.58 mL in the patients who received HFGF and 14.93 ± 3.57 mL in the LFGF group (p = 0.001). The mean wash-in completion time was 12.49 ± 2.79min in the HFGF group and 3.35 ± 0.67min in the LFGF group (p = 0.001). The anesthetic agent consumption during the wash-in phase was approximately 3 times lower with the administration of sevoflurane at 1L/minute FGF than the use of 4L/minute FGF.

Effect of high fresh gas flow and pattern of breathing on rapid preoxygenation

Background and Aims:Preoxygenation is supplementation of 100% oxygen prior to induction of general anaesthesia to increase the body’s oxygen stores. Efficacy of preoxygenation can be increased by optimising fresh gas flow (FGF) rate and pattern of breathing.Methods:Based on pattern of breathing—Tidal Volume Breathing (TVB) or Deep Breathing (DB) and FGF-10 L/min or 15 L/min—100 subjects of the American Society of Anesthesiologists physical status I/II posted for elective surgery were recruited and randomised into four groups: T10 - TVB with 10 L/min; D10 - DB with 10 L/min; T15 - TVB with 15 L/min; and D15 - DB with 15 L/min. A tight-fitting anaesthesia mask along with continuous positive airway pressure of 5 cm of H2O with 20° head-up was used for preoxygenation. The total time taken and the total number of breaths required to achieve end tidal oxygen concentration (EtO2) of 90% were noted. Exhaled tidal volume (Vte), end tidal carbon dioxide, fraction of inspired oxygen, and EtO2 were recorded at each breath. Analysis of variance (ANOVA) was used for inferential statistics and Tukey’s honestly significant difference (HSD) test was used to calculate mean difference in total time and number of breaths amongst the groups.Results:Total time taken was significantly low (P < 0.001) in DB compared to TVB (D10: 70.2 ± 19.91, D15: 68.4 ± 20.27 vs T10: 112.28 ± 47.96, T15: 113.6 ± 48.57 seconds). Number of breaths was significantly high (P < 0.001) in TVB with 22.84 ± 8.73, 23.76 ± 11.64, 10.56 ± 3.69, and 8.32 ± 1.8 in T10, T15, D10 and D15, respectively. Vte was significantly low in TVB (P < 0.001).Conclusion:Rapid preoxygenation can be achieved by DB at high FGF of a minimum of 10 L/min.

Minimal fresh gas flow sevoflurane anesthesia and postoperative acute kidney injury in on-pump cardiac surgery: a randomized comparative trial

BackgroundCompound A is generated by sevoflurane when it reacts with carbon dioxide absorbers with strong bases at minimal fresh gas flow (FGF) and is nephrotoxic in animals. No conclusive data has shown increased risk in humans. The aim of this study was to investigate if minimal FGF promotes an increase in the incidence of acute kidney injury (AKI) when compared to high FGF in patients undergoing on-pump cardiac surgery under sevoflurane anesthesia. MethodsTwo hundred and four adult patients scheduled for on-pump cardiac surgery under sevoflurane anesthesia were randomly allocated to two groups differentiated by FGF: minimal FGF (0.5 L.min−1) or high FGF (2.0 L.min−1). Baseline creatinine measured before surgery was compared daily to values assayed on the first five postoperative days, and 24-hour urinary output was monitored, according to the KDIGO (Kidney Disease Improving Global Outcomes) guideline to define postoperative cardiac surgery-associated acute kidney injury (CSA-AKI). Creatinine measurements were also obtained 20 and 120 days after hospital discharge. ResultsPostoperative AKI occurred in 55 patients, 26 patients (29.5%) in the minimal FGF group and 29 patients (31.5%) in the high FGF group (p = 0.774). Twenty days after discharge, 11 patients (6.1%) still had CSA-AKI and 120 days after discharge only 2 patients (1.6%) still had CSA-AKI. ConclusionsWhen compared to high FGF, minimal FGF sevoflurane anesthesia during on-pump cardiac surgery is not associated with increased risk of postoperative AKI in this population at high risk for renal injury.

Going around in circles. Is there a continuing need to use the T-piece circuit in the practice of pediatric anesthesia?

Anesthetic equipment, including breathing circuits, has evolved over time. The T-piece circuit, in its various forms, was designed to meet the needs of its time. As equipment and techniques have moved on, it is timely to consider the place of the T-piece in modern pediatric anesthetic practice. Today the circle system is a ubiquitous part of anesthesia. When integrated with a modern anesthetic machine it offers precise control of ventilation together with continuous monitoring of airway pressure and flow: but at the cost of complexity. In comparison the T-piece offers a simple cheap lightweight design, so ergonomic in use that it almost becomes part of the anesthetist: but lacks the control and the barriers to unsafe use of more sophisticated systems. In addition, it requires high fresh gas flow adding to cost and environmental pollution. This pro-con debate discusses whether there remains a case for continuing to use the T-piece circuit in preference over other options. Possible indications for the T-Piece are discussed together with alternative strategies. The limitations of the circle system, the T-piece, and other alternative (such as self-inflating resuscitator bag) are discussed with respect to pediatric anesthetic practice.

A recurring case of ‘no trace, right place’ during emergency tracheal intubations in the critical care setting

We wish to highlight a safety issue concerning the use of the Mapleson C circuit along with high fresh gas flows and the potential impact this could have on capnography. The authors have encountered a situation where despite successful tracheal intubation, there can be continued failure to detect carbon dioxide. This issue became apparent during the undertaking of a large number of emergency tracheal intubations in the current COVID-19 pandemic. The cases involved patients with uneventful airway management and clear placement of a tracheal tube between the vocal cords using videolaryngoscopy. This was followed in all cases by the clinical confirmation of successful tracheal intubation but the absence of a capnographic trace. A commonly identified feature in all events was very high fresh gas flow to the Mapleson C circuit. This high flow was unintentional and frequently had been commenced by a clinician assisting with the tracheal intubation, before the arrival of the intubator. Furthermore, the high flow was initially unrecognised due to the urgent nature of the situation and the impact of personal protective equipment. The standard oxygen flowmeter present in most wards or resuscitation bays displays flow graduations of up to 15 l.min-1. The authors found that while often the last graduation marked is 15 l.min-1, these devices are not flow-limited and when the valve is opened fully can generate flows much higher than this. Further investigation of the technical data supplied by the manufactures of several flowmeters reveals that the high flows produced when the valve is opened fully are referred to as ‘flush’ or ‘flood’ flows and can be as high as 90 l.min-1 [1]. The authors confirmed this by testing the flows generated from oxygen flowmeters encountered throughout their hospital including the auxiliary oxygen outlet present on the anaesthetic machine which produced 84 l.min-1 oxygen while a standard ward oxygen flowmeter achieved 75 l.min-1. When the situation was encountered again and the high flows identified, a capnographic trace could be produced by turning down the oxygen flow to the Mapleson C circuit. The exact cause of this phenomenon is yet to be determined but correspondence with the manufacturer of the Mapleson C circuit suggests that carbon dioxide washout is the likely cause. However, a number of confounders may also contribute and they include the flowmeters flush rate, the composition of the circuit, the type of heat and moisture exchange filter, the behaviour of the adjustable pressure limiting (APL) valve, the adequacy of the tracheal tube cuff and the patient's pulmonary compliance. A review of the technical data provided by the manufacturers of the Mapleson C circuit, revealed that with the APL valve set in the semi-closed position, a fresh gas flow of 50 l.min-1 will generate a resistance of 32 cmH2O (Technical document, Armstrong Medical, Coleraine). The authors will explore these concepts further in a laboratory setting. The current pandemic has seen oxygen capacity in hospitals come under strain due to the large number of COVID-19 patients [2, 3]. It is, therefore, imperative that we reduce the wastage of oxygen wherever possible.

Are high fresh gas flow rates necessary during the wash-in period in low-flow anesthesia?

In low-flow anesthesia (LFA), there is a wash-in period in which usually high fresh gas flow (FGF) rates are used to achieve the required initial concentration of anesthetic agent in the alveoli. The aim of this study was to compare the efficiency, safety and the consumption of desflurane in LFA using constant FGF (1 L/min) and conventional LFA using high FGF (4 L/min) during the wash-in period. Eighty patients, who were scheduled for elective surgery under general anesthesia with endotracheal intubation, were enrolled in the study. Wash-in was accomplished with 1 L/min FGF (50% O2, 50% air) and 18% desflurane in group 1; and by 4 L/min FGF (50% O2, 50% air) and 6% desflurane in group 2. Throughout the surgery, the vaporizer was adjusted to maintain 0.6 to 0.8 minimum alveolar concentration (MAC). The time required to reach 0.7 MAC was shorter in group 1 (160 seconds [135-181] vs 288 seconds [240-500], P < .001). In 6 patients in group 1 and 13 in group 2, vaporizer settings were adjusted to maintain 0.6 to 0.8 MAC (P = .048). Desflurane consumption in the first hour and total desflurane consumption were higher in group 2 (P < .001 and P = .012, respectively). The efficiency of anesthesia in both the first hour and in total was higher in group 1 (P < .001). It is safe, more efficient, and economical to use 1 L/min FGF during the wash-in period in LFA.

Feasibility, safety, and economic consequences of using low flow anesthesia according to body weight.

Low flow anesthesia (LFA) provides a saving up to 75% and improves the dynamics of inhaled anesthesia gas, increases mucociliary clearance, maintains body temperature, and reduces water loss. LFA has been recommended for anesthesiologists in recent years to avoid high fresh gas flow (FGF). However, LFA use is limited due to associated risks. The main purpose of this study was to investigate whether LFA according to body weight, which is the main determinant of oxygen requirement, is feasible and safe in the normoxia range. The second aim was to show that this method can provide economic benefit. Eighty donor hepatectomy cases were included to study in two groups as prospective, observational. A surgery room and a team were allocated only for this study. Considering the oxygen requirement (approximately 3-3.5mL/kg/min), for the first 40 cases, 10mL/kg (group 10) FGF was applied; for the second 40 cases, 20mL/kg (group 20) was applied. Desflurane (Suprane©) was used as an inhalation agent, and analgesia was achieved with remifentanil infusion. Patients' demographic, respiratory, hemodynamic, and tissue perfusion parameters (SpO2 and NIRS), and comsumption data (anesthetic agent and CO2 absorbent) were collected and compared. No significant differences were detected between the groups in terms of demographic data, duration of surgery, and hemodynamic, respiratory, and tissue perfusion parameters. These parameters were within normal limits in all patients at all times. The maximum O2 concentration in the FGF that maintained FiO2:0.4 and provided adequate oxygenation during the LFA was 61% (min 56%; max 67%) in group 10, and 47% (min 43%; max 51%) in group 20. The hourly anesthetic agent consumption was significantly different in group 10 than in group 20 (12.4 ± 4mL vs. 21.5 ± 8mL/h, respectively (p < 0.001). We performed 10mL/kg FGF speed without deviating from the safety limits to be FiO2:0.4 in donor hepatectomies, reducing the total costs 38% compared with 20mL/kg FGF.

Comparison of mainstream (Capnostat 5) and two low-flow sidestream capnometers (VM-2500-S and Capnostream) in spontaneously breathing rabbits anesthetized with a Bain coaxial breathing system

ObjectiveTo evaluate agreement with PaCO2 of two low sampling rate sidestream capnometers and a mainstream capnometer in rabbits and the effect of using high fresh gas flow from a Bain coaxial breathing system. Study designProspective, crossover study. AnimalsA total of 10 New Zealand White rabbits weighing 3.4 ± 0.3 kg [mean ± standard deviation (SD)]. MethodsTwo sidestream analyzers (Viamed VM-2500-S and Capnostream 35) with a sampling rate of 50 mL minute–1 and a mainstream capnometer (Capnostat 5) were tested. All capnometers used infrared spectroscopy and advanced microprocessor technology. Rabbits were anesthetized and intubated with noncuffed endotracheal tubes of 3 mm internal diameter and adequate seal. A sidestream sampling adapter or the mainstream capnometer was attached to the endotracheal tube and connected to a Bain coaxial breathing system. Oxygen (1.5 L minute–1) delivered sevoflurane to maintain anesthesia. An auricular artery catheter allowed blood sampling for PaCO2 analysis corrected to rectal temperature. Inspired and end-tidal carbon dioxide (Pe′CO2) measurements were recorded during blood sample withdrawal. From each rabbit, 10 paired PaCO2/Pe′CO2 measurements were obtained. Each rabbit was recovered from anesthesia and was anesthetized again with an alternate capnometer after 1 week. Data were analyzed using Bland–Altman and two-way anova for repeated measures. ResultsAnalysis included 100 paired samples. Negative bias reflects underestimation of PaCO2. Bland–Altman mean (±1.95 SD) was –16.7 (–35.2 to 1.8) mmHg for Capnostat 5, –27.9 (–48.6 to –7.2) mmHg for Viamed, and –18.1 (–34.3 to –1.9) mmHg for Capnostream. Viamed PaCO2–Pe′CO2 gradient was greater than other two capnometers. ConclusionsAll three capnometers underestimated PaCO2. Capnostat 5 and Capnostream performed similarly. Clinical relevanceThese capnometers underestimated PaCO2 in spontaneously breathing rabbits anesthetized using a Bain coaxial breathing system with high fresh gas flows.

Predicting cost of inhalational anesthesia at low fresh gas flows: impact of a new generation carbon dioxide absorbent.

It is well known that low fresh gas flows result in lower cost of inhalational agents. A new generation of carbon dioxide absorbents allows low flow anesthesia with all anesthetics but these new compounds are more expensive. This study examines the cost of inhalational anesthesia at different fresh gas flows combined with the cost of absorbent. The cost of sevoflurane and desflurane is lower at low fresh gas flows. Paradoxically the cost of isoflurane is cheaper at 2 L/min than at lower fresh gas flows due to increased cost of carbon dioxide absorbent. Therefore low fresh gas flows should be used when feasible with sevoflurane and desflurane, but higher fresh gas flows up to 2 L/min may be more economical with isoflurane during maintenance phase of anesthesia.

The effect of fresh gas flow during induction of anaesthesia on sevoflurane usage: a quality improvement study.

Reducing fresh gas flow during inhalational anaesthesia results in cost savings and decreases environmental impact. We are interested in the influence of fresh gas flow on the early (induction) phase of overall fresh gas flow and vapour consumption. This stage is often excluded in studies of fresh gas flow. Data were collected from 3199 sevoflurane anaesthetics over an 11-month period in four operating theatres. We determined fresh gas flow at different stages of anaesthesia, and developed an explanatory model for the influence of the 'induction' period. Following a three-month collection of baseline data we emphasised the importance of the early phase to our department repeatedly over a two-week period. We explored the relationship between fresh gas flow and total vapour usage, and used a simple mathematical model to explore the effect of changes in the fresh gas flow and duration of the 'induction' phase. Mean fresh gas flow was 1.15l.min-1 in the baseline period and 0.91l.min-1 in the twomonths following our educational effort (p=0.0005). In the following sixmonths, mean fresh gas flow was 1.17l.min-1 (p=0.7726 compared with baseline). These results were driven by changes in both fresh gas flow and duration of the initial high-flow period. We found some correlation (R2 =0.85) between overall fresh gas flow and vapour consumption; a 1l.min-1 increase in fresh gas flow consumes an additional 18ml.hr-1 of liquid sevoflurane. This preliminary study demonstrates that an episode of high fresh gas flow at the start of anaesthesia has a large and modifiable effect on overall fresh gas flow and vapour consumption. We also confirmed the linear relationship between fresh gas flow and vapour usage.

Minimal flow anesthesia can be initiated early with the use of higher fresh gas flow to facilitate desflurane "Wash-in".

Background and Aims:More than 80% of delivered anesthetic gases get wasted at high fresh gas flows as they are vented out unused. Use of minimal flow anesthesia is associated with less waste anesthetic gas emission and environmental pollution. There is no approved or validated technique to initiate minimal flow anesthesia and simultaneously achieve denitrogenation of the breathing circuit. We studied the wash-in characteristics of desflurane, when delivered with 50% nitrous oxide, to reach a target end-tidal concentration at two different gas flow rates.Material and Methods:Patients were allocated randomly to two groups of 25 adults each. In Group A, with the vaporizer dial fixed at 4 vol %, after an initial fresh gas flow of 4 L/min was administered to wash-in of desflurane using the closed-circuit, with 50% N2O in O2, and in group B, 6 L/min was used. Minimal flow anesthesia, with 0.5 L/min, was initiated in both groups on attaining a target end-tidal desflurane concentration of 3.5 vol %. After initiation of desflurane delivery, the inspired/expired gas concentrations were noted every minute for 15 min.Results:In Group A, the target desflurane end-tidal concentration was reached in 499.2 ± 68.6 s±, and in the Group B (P < 0.001), it was reached significantly faster in 314.4 ± 69.89 s. Denitrogenation of the circuit was adequate in both groups.Conclusion:Minimal flow anesthesia can be initiated, without any gas-volume deficit, in about 5 min with an initial fresh gas flow rate of 6 L/min and the vaporizer set at 4 vol%.