Fresh Gas Flow Research Articles

Comparison of trapezius squeeze test and jaw thrust as clinical indicators for laryngeal mask airway insertion in spontaneously breathing children.

Background and Aims:It is not known whether trapezius squeeze test (TPZ) is a better clinical test than jaw thrust (JT) to assess laryngeal mask airway (LMA) insertion conditions in children under sevoflurane anesthesia.Material and Methods:After the Institutional Ethics Committee approval and written informed parental consent, 124 American Society of Anesthesiologists I and II children of 2–8 years of age undergoing minor surgical procedures were randomized into TPZ and JT groups. The children were induced with 8% sevoflurane in oxygen at a fresh gas flow of 4 L/min. TPZ or JT was performed after 1 min of start of sevoflurane and then every 20 s till the test was negative, when end-tidal (ET) sevoflurane concentration was noted. Classic LMA of requisite size was inserted by a blinded anesthetist and conditions at the insertion of LMA, insertion time, and the number of attempts of LMA insertion were recorded.Results:The mean LMA insertion time was significantly longer (P < 0.001) for TPZ (145 ± 28.7 sec) compared to JT group (111.8 ± 31.0 sec). ET sevoflurane concentration at the time of LMA insertion was comparable in the two groups. LMA insertion conditions were similar in the two groups. There was no difference between the two groups regarding total number of attempts of LMA insertion. Heart rate (HR) decreased in both groups after LMA insertion (P < 0.001) but TPZ group had significantly lower HR compared with the JT group up to 5 min after LMA insertion (P = 0.03).Conclusion:Both JT and TPZ are equivalent clinical indicators in predicting the optimal conditions of LMA insertion in spontaneously breathing children; however, it takes a longer time to achieve a negative TPZ squeeze test.

Ultrasound assessment of subglottic region for estimation of appropriate endotracheal tube size in pediatric anesthesia.

Background and Aims:Endotracheal tube (ETT) selection in pediatric patients is mainly done with the age, height, or weight-based formula. We compared ultrasound assessment of the subglottic area to predict the outer diameter of the ETT, with that of modified Cole's formula. The aim of the study is to compare the appropriateness of uncuffed ETT selection based on modified Cole's formula with that of ultrasound assessment method of subglottic diameter in children undergoing surgical procedures under general anesthesia.Material and Methods:This is a prospective, randomized, parallel group study. One hundred and fifty American Society of Anesthesiologists I and II patients of age 2–6 years were randomly allotted into two groups: Group A - ETT selection based on ultrasound assessment of subglottic diameter. Group B - ETT selection based on modified Cole's formula. The study parameters are the internal diameter and external diameter (OD) of the predicted ETT by the two methods and that of the appropriate size ETT used.Results:The incidence of appropriate tube selection was 74.7% in the ultrasound based group while it was 45.3% in the modified Cole's formula group. There was a strong correlation between OD of the optimal ETT used and the ultrasound assessed subglottic diameter. Bland–Altman analysis of OD of appropriately sized ETT and subglottic diameter by ultrasound assessment has a bias of 0.02 mm with limits of agreement of +1.78 to −1.74.Conclusion:Ultrasonographic assessment of the subglottic diameter at the cricoid region is a better tool in predicting the appropriate size uncuffed ETT than modified Cole's formula.

Referee report. For: The impact of fresh gas flow on wash-in, wash-out time and gas consumption for sevoflurane and desflurane, comparing two anaesthesia machines, a test-lung study. [version 1; referees: 3 approved with reservations

Referee report. For: The impact of fresh gas flow on wash-in, wash-out time and gas consumption for sevoflurane and desflurane, comparing two anaesthesia machines, a test-lung study. [version 1; referees: 3 approved with reservations

Effects of Two Intranasal Dexmedetomidine Doses as Premedication on Sevoflurane EC50 for Successful Laryngeal Mask Airway Placement in Children.

Objective To observe the effects of two different intranasal dexmedetomidine doses as premedication on the EC50 of sevoflurane for successful laryngeal mask airway placement in children. Methods Children aged 3-6 years, of American Society of Anesthesiologists physical status 1, and scheduled for plastic surgery were enrolled in this study. Children were assigned to receive either spray administration of intranasal dexmedetomidine 1 μg/kg (group D1, n=21) or 2 μg/kg (group D2, n=20) approximately 30 minutes before anesthesia. Anesthesia was induced with sevoflurane up to 8% in 100% O2, with fresh gas flow set to 6 L/min. After the pupil fixed to the middle position, sevoflurane dial setting was reduced to 5% and fresh gas flow reduced to 3 L/min. The endtidal sevofluran (ETsevo) concentration for laryngeal mask airway insertion sustained for 10 minutes after vein intubation, which was determined according to the Dixon's up and down method. The initial endtidal sevoflurane concentration in each group was set at 2%. ETsevo was increased/decreased (1:1.2) in the next patient according to the response to laryngeal mask airway insertion. Bispectral index, mask acceptance, all response to laryngeal mask airway insertion, and ETsevo of laryngeal mask airway insertion of children were recorded. Results The bispectral index value was 77.4±3.6 in group D2, which was significantly lower than that (87.4±1.9) in group D1 when children entered operation room (P<0.05). Mask acceptance was 76.2% in group D1 and 90.0% in group D2. The EC50 of sevoflurane for laryngeal mask airway insertion was 1.09% (95% CI=0.89%-1.28%) in group D2, which was lower than 1.59% (95% CI=1.41%-1.78%) in group D1 (P<0.05). Conclusion Compared with the dose of 1 μg/kg, spray administration of intranasal dexmedetomidine 2 μg/kg as premedication can reduce the sevoflurane EC50 for successful laryngeal mask airway placement in children.

A Comparison of Soda Lime (Intersurgical) with Amsorb® plus: The Cost Implications

This was a prospective study comparing the cost implications between two carbon dioxide (CO2) absorbers, soda lime (Intersurgical) and AMSORB® PLUS. The study was conducted over two 4-week periods in two dedicated operating theatres using Datex Ohmeda Aestiva/5 anaesthetic machines. AMSORB® PLUS was used during the first four weeks and soda lime (Intersurgical) the following four weeks. General anaesthesia was administered as routinely done but fresh gas flow (FGF) during the maintenance phase was limited to a maximum flow of 2 L/min. The CO2 absorber was only changed when there was evidence of exhaustion. Total duration of anaesthesia, sevoflurane (bottles) and CO2 absorber (kg) consumption, and amount of waste product (kg) was calculated at the end of each study period. The total cost of delivering general anaesthesia was lower in the AMSORB® PLUS group, RM82.40 (USD19.89)/hour versus the soda lime group, RM91.50 (USD 22.09)/hour (p=0.17), which translates to a 10% reduction in cost per hour. Reduction in sevoflurane consumption in the AMSORB® PLUS compared to the soda lime group was also not statistically significant (p=0.22). The only significant finding was the reduction in CO2 absorber consumption in the AMSORB® PLUS group as compared to soda lime group (p=0.001). In conclusion, AMSORB® PLUS consumption was significantly reduced compared to that of soda lime. However, the use of AMSORB® PLUS did not significantly reduce sevoflurane consumption nor the total cost of delivering general anaesthesia. Given the superior safety profile, AMSORB® PLUS may be a suitable, cost-effective alternative to soda lime in the daily practice of anaesthesia.

Comparative study of minimal fresh gas flow used in Lack-Plus and Lack's circuit in spontaneously breathing anesthetized adults.

BackgroundThe Lack’s circuit is a co-axial Mapleson A breathing system commonly used in spontaneously breathing anesthetized adults but still requires high fresh gas flow (FGF). The Lack-Plus circuit was invented with the advantage of lower FGF requirement. The authors compared the Lack-Plus and Lack’s circuit for the minimal FGF requirement with no rebreathing in spontaneously breathing anesthetized adults.MethodsThis was a randomized crossover study. We enrolled 24 adult patients undergoing supine elective surgery, with a body mass index ≤30 kg/m2 and an American Society of Anesthesiologists physical status I–II. They were randomly allocated to group 1 (LP-L) starting with Lack-Plus then switching to Lack’s circuit or group 2 (L-LP) (with the reverse pattern). After induction and intubation, anesthesia was maintained with 50% N2O/O2 and desflurane (4%–6%) plus fentanyl titration to maintain an optimal respiratory rate between 10 and 16/min. Starting with the first circuit, all the patients were spontaneously breathing with a FGF of 4 L/min for 10 min, gradually decreased by 0.5 L/min every 5 min until FGF was 2.5 L/min. End-tidal CO2, inspired minimum CO2 (ImCO2), mean arterial pressure, and oxygen saturation were recorded until rebreathing (ImCO2 >0 mmHg) occurred. The alternate anesthesia breathing circuit was used and the measurements were repeated.ResultsThe respective minimal FGF at the point of rebreathing for the Lack-Plus and Lack’s circuit was 2.7±0.8 and 3.3±0.5 L/min, respectively, p<0.001. At an FGF of 2.5 L/min, the respective ImCO2 was 1.5±2.0 and 4.2±2.6 mmHg, respectively, p<0.001.ConclusionThe Lack-Plus circuit can be used safely and effectively, and it requires less FGF than Lack’s circuit in spontaneously breathing anesthetized adults.

Inhalation anesthesia with sevoflurane during thyroid surgery: the low-flow or minimal-flow anesthesia?

Aim – to study the consumption of an inhalation anesthetic and to compare of clinical and economic components during using of the low-flow anesthesia or the minimal flow anesthesia by sevoflurane in hyperthyroidism patients undergoing thyroidectomy in a specialized centre of endocrine surgery.Materials and methods. All patients were divided into 2 groups: in a group of «sevoflurane balanced analgesia» (BA-S) were included 35 patients, in a group «sevoflurane control group» (C-S) were included 46 patients. All patients with thyrotoxicosis were undergoing thyroidectomy under general anesthesia with mechanic ventilation and using of the low- flow anesthesia (LFA) or the minimal flow anesthesia (MFA) by sevoflurane. In the groups BA-S was used LFA with the fresh gas flow FGF=500 ml/min for 25 patients (subgroup C-SLFA), with FGF=700 ml/min for 21 patients (subgroup C-SLFA-0,7). We evaluated the consumption of sevoflurane by Dion’s equation and Biro’s equation by assessing the vaporizer dial concentration in percent, FGF in liters/minute and time for which the concentration was set in minutes. We calculated the cost of anesthesia as a cost of average doses of sevoflurane and expendable materials that were used during anesthesia.Results and discussion. The sevoflurane consumptions by Dion’s equation were 6,25±0,23 ml for the BA-S group, 6,77±0,26 ml for the subgroup of C-SFLA and 8,04±0,32ml for the subgroup of C-SLFA-0,7 and were not significant (p&lt;0,05) more than in Biro’s equation, where The sevoflurane consumptions were 5,81±0,24 ml for the BA-S group, 6,37±0,27 ml for the C-SFLA subgroup and 7,52±0,34 ml for the C-SLFA-0,7 subgroup, respectively. Between the values of sevoflurane consumption by Biro’s and Dion’s equations there is a strong direct correlation on Spearman’s correlation coefficient (rs). For the group of CA-C rs=0,87, for C-SLFA rs=0,86, for C-SLFA-0,7 rs=0,84. The sevoflurane consumption was significantly (p&lt;0,05) lower on the criterion of Wilkinson in the BA-S group under MFA with FGF=400 ml/min, as compared to the control subgroups C-SLFA and C-SLFA-0,7, which were used FGF=500 ml/min and 700 ml/min during LFA respectively. In the BA-S group MFA has been demonstrated pharmacy-economic benefits, which were amounted to 100,3±4,1 UAH and 107,8±4,0 UAH for both equations, Biro’s and Dion’s, respectively. These rates were significantly (p&lt;0,05) lower on the criterion of Wilcoxon in the BA-S group than in the control subgroups C-SLFA and C-SLFA-0,7, where applied LFA with FGF=500 ml/ min and 700 ml/min, respectively.Conclusions. Both, Biro’s method and Dion’s equation allow us to estimate the sevoflurane anesthesia consumption. Between the equations there is a strong positive correlation, there is no significant difference between the results of the calculations. In our point of view, Dion’s equation for assessment of volatile anesthetic consumption reflects sevoflurane consumption largely, that Biro’s equation, because Dion’s equation takes into account the sum of products of each segment anesthesia and minimal changes in components, such as the vaporizer dial concentration in percent, FGF and duration which the concentration was set up.The sevoflurane consumption was significantly (p&lt;0,05) lower under MFA with FGF=400 ml/min, compared with LFA with FGF=500 ml/min and 700 ml/ min.When applying the MFA greater influence on sevoflurane consumption has the fresh gas flow than the vaporizer dial concentration, whereas with an increase of FGF to 500–700 ml/min greater influence on consumption has anesthetic vaporizer dial concentration than FGF. The MFA with FGF=400 ml/ min has significantly less the cost of anesthesia, than the LFA with 500–700 ml/min.

Abstract PR463

Background & Objectives: Background: In a climate of cost containment, it is critical to analyze and optimize all perioperative variable costs. Fresh gas flow is one important variable that determines utilization of inhalational agents and can be tightly controlled by the anesthesia provider. Manufacturers of inhalational agents have recommendations for minimum gas flow for their respective agents. Any gas flow above these recommendations is considered misuse and leads to unnecessary expense. The purpose of this study was to characterize and quantify the excess use of inhalational agents by analyzing fresh gas flow rates for long duration cases. Materials & Methods: Methods: Over a span of three months, operating room records were analyzed for all procedures lasting greater than 4 hours. End tidal inhalation agent percentage for Sevoflurane and Isoflurane and fresh gas flows were analyzed. 303 unique patients with at least 4 hours of anesthesia time were included. Analysis excluded the first and last 30 minutes of all anesthetics to account for need for higher gas flows during induction/emergence of anesthesia. 152 patients received sevoflurane alone. 33 patients received isoflurane alone. 107 patients received both isoflurane and sevoflurane and were included in sevoflurane group given the higher gas flow needs of sevoflurane. 11 patients received neither agent and were excluded from analysis. We proceed with n=292 unique patients. (259 in Sevo, 33 in iso) We used the two-sided one sample t-test setting 2ml/min as the null for sevo and 1ml/min as the null for iso; we ran analysis using a nonparametric test that didn’t require the fresh gas flow to be normally distributed-- the two-sided one-sample Wilcoxon rank-sum test: p=value<0.0001 Results: Results: The results of our study revealed a sevoflurane (n=259) mean fresh gas flow (l/min) 2.55 (95%CI, 2.45-2.66)--significantly different from null of 2ml/min:p<0.0001. Isoflurane (n=33) mean fresh gas flows (l/min) 2.33 (95%CI, 2.00-2.66)--significantly different from null of 1l/min:p<0.0001. Conclusion: Conclusion: Manufacturer recommendation for sevoflurane is to maintain gas flows 1-2 l/min and Isoflurane at above 1l/min. Given these recommendations, the anesthesia providers delivered fresh gas flows at least 28% higher than necessary for sevoflurane and at least 130% greater than necessary for isoflurane anesthetics that lasted greater than 4 hours. This is an area where cost reduction can be readily achieved. Future plans to realize a reduction in inhalational agent utilization include education of the benefits of fresh gas flow and instituting a low fresh gas flow policy. Disclosure of Interest: None declared

Abstract PR569

Background & Objectives: Lack’s circuit is a modified co-axial Mapleson A breathing system. Lack-Plus circuit is a modified Lack circuit with additional intraluminal one-way valve. The objective was to compare the Lack-Plus and Lack’s circuit on the minimal fresh gas flow (FGF) requirement with no rebreathing in spontaneously breathing anesthetized adults. Materials & Methods: Twenty-four adult patients with BMI ≤ 30 km/m2, under elective peripheral surgery in supine position with ASA physical status I-II were enrolled. They were allocated into group 1 (LP-L) starting with Lack-Plus then switching to Lack’s circuit or group 2 (L-LP) in reversed pattern. Anesthesia was maintained with 50% N2O/O2 and Desflurane 4 to 6% and fentanyl titration. Starting with the first circuit, all patients were spontaneously breathing with FGF 4 L/min for 10 minutes, and then gradually decreased by 0.5 L/min every five minutes. End-tidal CO2 (ETCO2), inspired minimum CO2 (ImCO2), mean arterial pressure (MAP) and oxygen saturation (SpO2) were recorded until rebreathing (ImCO2 > 0 mmHg) occurred. The anesthesia breathing circuit was then switched to the other and the procedure repeated. Results: The minimal FGF at the point of rebreathing of Lack-Plus and Lack’s circuit were 2.7 ± 0.8 and 3.3 ± 0.5 L/min respectively; P<0.001.Table 1:: FGF, ETCO2, RR, MAP, SpO2 at the point of rebreathing (ImCO2 > 0 mmHg)Conclusion: Lack-Plus circuit can be used safely, effectively, and requires less FGF than Lack’s circuit in spontaneously breathing anaesthetized adults.

Abstract PR419

Background & Objectives: BACKGROUND: Desflurane, a recently introduced volatile anaesthetic drug, has a low blood/gas solubility coefficient that allows rapid changes in anaesthesia depth. It is often used in anaesthesia to facilitate rapid emergence. A faster recovery following desflurane, in fact, may be desirable especially after long surgical procedures, enabling the patient’s full cooperation and facilitating early diagnosis of any potential neurological deficit. The effects of this drug on cancer patients have been poorly treated in literature. 1-1-12 wash-in techniques for desflurane-nitrous oxide (N2O) low flow anesthesia are simple, rapid, and predictable. There remain some situations where N2O should be avoided, which limits the simplicity of this wash-in technique’s. The objective of our study was to determine the performance of this technique in contexts where N2O is not used. Materials & Methods: METHODS: 440 cancer patients underwent for elective oncology surgery under general anesthesia. After induction and intubation, wash-in was started with a fresh gas flow of Air:O2 1:1 L/min and a vaporizer concentration of desflurane of 12%. Controlled ventilation was then adjusted to maintain PACO2 at 30-35 mmHg. Results: RESULTS: The alveolar concentration of desflurane (FAD) rose rapidly from 0% to 6% in 4 minutes in the same pattern as observed in our previous study in which N2O was used. An FAD of 7% was achieved in 5 min. An FAD of 1% to 7% occurred at 0.5, 1, 1.5, 2, 3, 4, and 5 min. The rise in HR during wash-in was statistically significant, although not clinically so. There was a slight but statistically significant decrease in ABP, but this had no clinical significance. Conclusion: CONCLUSION: Performance of the 1-1-12 wash-in technique is independent of the use of N2O. Respective FADs of 1%, 2%, 3%, 4%, 5%, 6%, and 7% can be expected at 0.5, 1, 1.5, 2, 3, 4, and 5 minutes. Disclosure of Interest: None declared

Precautionary practices for administering anesthetic gases: A survey of physician anesthesiologists, nurse anesthetists and anesthesiologist assistants

ABSTRACTScavenging systems and administrative and work practice controls for minimizing occupational exposure to waste anesthetic gases have been recommended for many years. Anesthetic gases and vapors that are released or leak out during medical procedures are considered waste anesthetic gases. To better understand the extent recommended practices are used, the NIOSH Health and Safety Practices Survey of Healthcare Workers was conducted in 2011 among members of professional practice organizations representing anesthesia care providers including physician anesthesiologists, nurse anesthetists, and anesthesiologist assistants. This national survey is the first to examine self-reported use of controls to minimize exposure to waste anesthetic gases among anesthesia care providers. The survey was completed by 1,783 nurse anesthetists, 1,104 physician anesthesiologists, and 100 anesthesiologist assistants who administered inhaled anesthetics in the seven days prior to the survey. Working in hospitals and outpatient surgical centers, respondents most often administered sevoflurane and, to a lesser extent desflurane and isoflurane, in combination with nitrous oxide. Use of scavenging systems was nearly universal, reported by 97% of respondents. However, adherence to other recommended practices was lacking to varying degrees and differed among those administering anesthetics to pediatric (P) or adult (A) patients. Examples of practices which increase exposure risk, expressed as percent of respondents, included: using high (fresh gas) flow anesthesia only (17% P, 6% A), starting anesthetic gas flow before delivery mask or airway mask was applied to patient (35% P; 14% A); not routinely checking anesthesia equipment for leaks (4% P, 5% A), and using a funnel-fill system to fill vaporizers (16%). Respondents also reported that facilities lacked safe handling procedures (19%) and hazard awareness training (18%). Adherence to precautionary work practices was generally highest among nurse anesthetists compared to the other anesthesia care providers. Successful management of waste anesthetic gases should include scavenging systems, hazard awareness training, availability of standard procedures to minimize exposure, regular inspection of anesthesia delivery equipment for leaks, prompt attention to spills and leaks, and medical surveillance.

Isocapnic hyperventilation shortens washout time for sevoflurane - an experimental in vivo study.

Isocapnic hyperventilation (IHV) is a method that fastens weaning from inhalation anaesthesia by increasing airway concentration of carbon dioxide (CO2 ) during hyperventilation (HV). In an animal model, we evaluated a technique of adding CO2 directly to the breathing circuit of a standard anaesthesia apparatus. Eight anaesthetised pigs weighing 28 ± 2 kg were intubated and mechanically ventilated. From a baseline ventilation of 5 l/min, HV was achieved by doubling minute volume and fresh gas flow. Respiratory rate was increased from 15 to 22/min. The CO2 absorber was disconnected and CO2 was delivered (DCO2 ) to the inspiratory limb of a standard breathing circuit via a mixing box. Time required to decrease end-tidal sevoflurane concentration from 2.7% to 0.2% was defined as washout time. Respiration and haemodynamics were monitored by blood gas analysis, spirometry, electric impedance tomography and pulse contour analysis. A DCO2 of 261 ± 19 ml/min was necessary to achieve isocapnia during HV. The corresponding FICO2 -level remained stable at 3.1 ± 0.3%. During IHV, washout of sevoflurane was three times faster, 433 ± 135 s vs. 1387 ± 204 s (P < 0.001). Arterial CO2 tension and end-tidal CO2 , was 5.2 ± 0.4 kPa and 5.6 ± 0.4%, respectively, before IHV and 5.1 ± 0.3 kPa and 5.7 ± 0.3%, respectively, during IHV. In this experimental in vivo model of isocapnic hyperventilation, the washout time of sevoflurane anaesthesia was one-third compared to normal ventilation. The method for isocapnic hyperventilation described can potentially be transferred to a clinical setting with the intention to decrease emergence time from inhalation anaesthesia.

Pre-oxygenation using a mouthpiece

Several authors have previously published studies on pre-oxygenation using a mouthpiece 1, 2. We would like to remind readers of the utility of this technique for pre-oxygenating patients who find close-fitting facemasks alarmingly claustrophobic. Using a standard mouthpiece (Intersurgical Ltd, Wokingham, UK) routinely used in obstetric patients for inhaling oxygen/nitrous oxide mixtures, which is detached from the filter it is usually supplied with and attached to the catheter mount of an anaesthetic breathing circuit (Fig. 3), allows for suitable pre-oxygenation when the patient forms a seal around the mouthpiece with their lips and inspires normal tidal ventilations with a fresh gas flow of 10 l.min−1 and an FiO2 of 1.0. The mouthpiece is changed to a standard anaesthetic mask following induction of general anaesthesia, once pre-oxygenation is complete.

FLOW-i ventilator performance in the presence of a circle system leak.

Recently, the FLOW-i anaesthesia ventilator was developed based on the SERVO-i intensive care ventilator. The aim of this study was to test the FLOW-i's tidal volume delivery in the presence of a leak in the breathing circuit. We ventilated a test lung model in volume-, pressure-, and pressure-regulated volume-controlled modes (VC, PC, and PRVC, respectively) with a FLOW-i. First, the circuit remained airtight and the ventilator was tested with fresh gas flows of 6, 1, and 0.3L/min in VC, PC, and PRVC modes and facing 4 combinations of different resistive and elastic loads. Second, a fixed leak in the breathing circuit was introduced and the measurements repeated. In the airtight system, FLOW-i maintained tidal volume (VT) and circuit pressure at approximately the set values, independently of respiratory mode, load, or fresh gas flow. In the leaking circuit, set VT=500mL, FLOW-i delivered higher VTs in PC (about 460mL) than in VC and PRVC, where VTs were substantially less than 500mL. Interestingly, VT did not differ appreciably from 6 to 0.3L/min of fresh air flow among the 3 ventilatory modes. In the absence of leakage, peak inspiratory pressures were similar, while they were 35-45% smaller in PRVC and VC than in PC mode in the presence of leaks. In conclusion, FLOW-i maintained VT (down to fresh gas flows of 0.3L/min) to 90% of its preset value in PC mode, which was 4-5 times greater than in VC or PRVC modes.

Economic and Environmental Considerations During Low Fresh Gas Flow Volatile Agent Administration After Change to a Nonreactive Carbon Dioxide Absorbent.

Reducing fresh gas flow (FGF) during general anesthesia reduces costs by decreasing the consumption of volatile anesthetics and attenuates their contribution to greenhouse gas pollution of the environment. The sevoflurane FGF recommendations in the Food and Drug Administration package insert relate to concern over potential toxicity from accumulation in the breathing circuit of compound A, a by-product of the reaction of the volatile agent with legacy carbon dioxide absorbents containing strong alkali such as sodium or potassium hydroxide. Newer, nonreactive absorbents do not produce compound A, making such restrictions moot. We evaluated 4 hypotheses for sevoflurane comparing intervals before and after converting from a legacy absorbent (soda lime) to a nonreactive absorbent (Litholyme): (1) intraoperative FGF would be reduced; (2) sevoflurane consumption per minute of volatile agent administration would be reduced; (3) cost savings due to reduced sevoflurane consumption would (modestly) exceed the incremental cost of the premium absorbent; and (4) residual wastage in discarded sevoflurane bottles would be <1%. Inspired carbon dioxide (PICO2), expired carbon dioxide, oxygen, air, and nitrous oxide FGF, inspired volatile agent concentrations (FiAgent), and liquid volatile agent consumption were extracted from our anesthesia information management system for 8 4 week intervals before and after the absorbent conversion. Anesthesia providers were notified by e-mail and announcements at Grand Rounds about the impending change and were encouraged to reduce their average intraoperative sevoflurane FGF to 1.25 L/min. Personalized e-mail reports were sent every 4 weeks throughout the study period regarding the average intraoperative FGF (i.e., from surgery begin to surgery end) for each agent. Batch means methods were used to compare FGF, volatile agent consumption, net cost savings, and residual sevoflurane left in bottles to be discarded in the trash after filling vaporizers. The time from reaching a PICO2 = 3 mm Hg for 3 minutes until agent exhaustion (PICO2 = 5 mm Hg for 5 minutes) was evaluated. A total of N = 20,235 cases were analyzed (80.2% sevoflurane, 15.1% desflurane, and 4.7% isoflurane). Intraoperative FGF was reduced for cases in which sevoflurane was administered by 435 mL/min (95% confidence interval [CI], 391 to 479 mL/min; P < 10). Hypothesis 1 was accepted. Sevoflurane consumption per minute of administration decreased by 0.039 mL/min (95% CI, 0.029 to 0.049 mL/min; P < 10) after the change to the nonreactive absorbent. Hypothesis 2 was accepted. The difference in mean cost for the sum of the sevoflurane and absorbent purchases for each of the 10 4-week intervals before and after the absorbent switch was -$293 per 4-week interval (95% CI, -$2853 to $2266; P = 0.81). Hypothesis 3 was rejected. The average amount of residual sevoflurane per bottle was 0.67 ± 0.06 mL (95% CI, 0.54 to 0.81 mL per bottle; P < 10 vs 2.5 mL). Hypothesis 4 was accepted. Once the PICO2 reached 3 mm Hg for at least 3 consecutive minutes, the absorbent became exhausted within 95 minutes in most (i.e., >50%) canisters. We showed that an anesthesia department can transition to a premium, nonreactive carbon dioxide absorbent in a manner that is at least cost neutral by reducing FGF below the lower flow limits recommended in the sevoflurane package insert. This was achieved, in part, by electronically monitoring PICO2, automatically notifying the anesthesia technicians when to change the absorbent, and by providing personalized feedback via e-mail to the anesthesia providers.

Measuring the concentrations of volatile anesthetic sevoflurane in the air during operation

Aim. To define concentrations of sevoflurane at the anesthetist working area during the operation. To compare the changes of the sevoflurane concentration depending on the anesthetic vaporizer design. Changes of the sevoflurane concentration in operating room air during operations on the abdominal organs duration 2:30–3:00 hours, depending on the vaporizer design (group 1–3 patients, vaporizer system “Quick Fill”; group 2–3 patients, the vaporizer that have a “direct casting”) were studied. Determination of the anesthetic air concentration in the working area has been provided (1–1.5 m from the anesthesiologist and the patient’s head) at the following stages: 1. Before filling the anesthetic vaporizer. 2. After filling the vaporizer (sevoflurane vial 250 ml) . 3. After the induction of anesthesia and tracheal intubation. 4. After sevoflurane saturation of the patient (fresh gas flow 1 l\min). 5 . After a patient extubation. Determination of the sevoflurane concentration was carried out by gas chromatography. Results. The sevoflurane concentration in air in group 2 was higher than the standard recommended concentration of the EU and the United States (2 ppm).

Is the Pressure Control Mode for Pediatric Anesthesia Machines Really Required?

Dear Editor, Choosing an appropriate anesthesia machine for mechanical ventilation of pediatric patients is of paramount importance because small changes in the fractions of the delivered tidal volume can cause a significant difference from the desired tidal volume. The anesthesia machines have classically been divided up into pressure or volume controlled modes, with two main characteristics; the limit (what determines the size of the breath), and the cycle (what actually ends the breath). The traditional anesthesia machines with volume controlled mode are not able to deliver precisely small tidal volumes to the pediatric patients. In the traditional anesthesia machines, fresh gas directly streams to the breathing circuit, so if 6 L/min of fresh gas is added to the previous setting (6 liters/60 seconds) 100 mL/s will be added to the delivered tidal volume, and if the inspiratory time is 2 seconds, 200 mL will be added to the tidal volume. These differences significantly increase the desired tidal volume. Therefore, the conventional anesthesia machines with the volume-controlled ventilation mode are not suitable to deliver a tidal volume less than 200 mL. During ventilation of neonates or children (in which tidal volume is less than 200 cc, respiratory rate is at least 16 - 20/minute and with a 1:2 I/E ratio, inspiratory time is less than 1 second), these differences are not acceptable. Thus, anesthesiologists usually use pressure-controlled ventilation rather than volume-controlled ventilation for pediatric anesthesia. A pressure-limited, time-cycled pulmonary ventilator includes a pressurized gas system that supplies respiratory gas to a patient at a selected inspiratory flow rate; an exhalation valve that opens an expiratory flow path in response to the elapsing of a selected inspiratory time period, and maintains a selected proximal pressure limit during the inspiratory time period. The tidal volume that results from a pressure-targeted machine is attributable to the set inspiratory pressure and patient’s lung-thorax compliance. Circuit compliance, fresh gas flow changes, and even small leaks around an un-cuffed endotracheal tube do not modify the delivered tidal volume (1). Pressure-controlled ventilation offers the advantage of limiting barotrauma in the condition of changing lung compliance, but a decrease in tidal volume will occur in the pressure-controlled ventilation mode, when the compliance of the lung is decreased or a pressure against the abdomen is created (e.g. in laparoscopic surgeries) (2). There are also some pediatric ventilators that deliver the breath by setting the inspiratory and expiratory duration and setting the flow of gas, but management of patients with these ventilators can lead to hypoventilation in the circumstance of increasing of the pulmonary resistance or reversal of muscle relaxants. To deliver a precise tidal volume, some new anesthesia machines have equipped with fresh gas decoupling valves. In these machines, the fresh gas (FGF) is not delivered to the inspiratory limb during inspiration. Practically, it means that FGF does not increase the tidal volume. The function of the fresh gas decoupling valve is to provide a precise delivery of the set tidal volume unaffected by varying fresh gas flow rates. During the inspiratory phase of ventilation, the valve closes, allowing only gas from the ventilator piston chamber to be delivered through the inspiratory branch to the patient. During the expiratory phase, the valve opens, allowing the ventilator piston chamber to fill with a mixture of the exhaled gas that has passed through the absorber and fresh gas (3). A second method for accurate delivery of desired tidal volume is compliance compensation, to replace volume lost to the breathing tubes. A potentially large percentage of the bellows volume is lost into the breathing circuit, secondary to compliance and compression. Leaks and sampled gas flow will further reduce desired tidal volume (4). To ensure that the set tidal volume will be delivered to the patients, new anesthesia machines involve a preuse leak and compliance test during which the end of the circuit must be occluded. The total compliance will be measured and the machine use this data to adjust piston or bellows movement, according to desired pressure airway setting (5). The anesthesiologist can use volume-controlled ventilation by a modern anesthesia machine that equipped with fresh gas decoupling valves and compliance and fresh gas compensation technology with confidence. Minimal tidal volume as low as 30 mL can be delivered precisely (5). The anesthesiologist should not persist in ordering a ventilator with multiple ventilation modes. Rather, choosing a ventilator with a unique mode that delivers a precise tidal volume would be suitable.

A survey on the use of low flow anaesthesia and the choice of inhalational anaesthetic agents among anaesthesiologists of India.

Background and Aims:With the availability of modern workstations and heightened awareness on the environmental effects of waste anaesthesia gases, anaesthesiologists worldwide are practicing low flow anaesthesia (LFA). Although LFA is being practiced in India, hard evidence on the current practice of the same from anaesthesiologists practicing in India is lacking and hence, we conducted this survey.Methods:A questionnaire containing 16 questions was distributed among a subgroup of anaesthesiologists who attended the 2014 National Conference of Indian Society of Anaesthesiologists. The filled-in questionnaires were computed and analysed with SPSS version 11.Results:The response rate to the survey was 82%. About 73% of the respondents practiced LFA routinely, with 65% having workstations. Most of the anaesthesiologists used fresh gas flows <1.5 L/min with 45.1% using O2 concentrations at a range of 30–40%. ETCO2 monitoring was used routinely by most whereas use of agent analysers and bispectral index monitoring were restricted. The availability of scavenging system was also limited to only 33.5%. Majority preferred N2 O as carrier gas and sevoflurane as volatile agent of their choice.Conclusion:Our survey revealed that practice of LFA in India has numerous lacunae. Provision of better monitoring facilities, workstations as well as awareness regarding the environmental issues of waste anaesthetic gases need to be addressed.

Effects of Low-Flow Sevoflurane Anesthesia on Pulmonary Functions in Patients Undergoing Laparoscopic Abdominal Surgery

Objective. The aim of this prospective, randomized study was to investigate the effects of low-flow sevoflurane anesthesia on the pulmonary functions in patients undergoing laparoscopic cholecystectomy. Methods. Sixty American Society of Anesthesiologists (ASA) physical status classes I and II patients scheduled for elective laparoscopic cholecystectomy were included in the study. Patients were randomly allocated to two study groups: high-flow sevoflurane anesthesia group (Group H, n = 30) and low-flow sevoflurane anesthesia group (Group L, n = 30). The fresh gas flow rate was of 4 L/min in high-flow sevoflurane anesthesia group and 1 L/min in low-flow sevoflurane anesthesia group. Heart rate (HR), mean arterial blood pressure (MABP), peripheral oxygen saturation (SpO2), and end-tidal carbon dioxide concentration (ETCO2) were recorded. Pulmonary function tests were performed before and 2, 8, and 24 hours after surgery. Results. There was no significant difference between the two groups in terms of HR, MABP, SpO2, and ETCO2. Pulmonary function test results were similar in both groups at all measurement times. Conclusions. The effects of low-flow sevoflurane anesthesia on pulmonary functions are comparable to high-flow sevoflurane anesthesia in patients undergoing laparoscopic cholecystectomy.

Comparison of Two Isoflurane Delivery Systems for Maintaining Anesthesia in Horses: End-Tidal Closed-Loop Target-Controlled Versus Out-Of-Circuit Vaporizer

The purpose of this study was to compare two different isoflurane (Iso) delivery systems: (1) end-tidal closed-loop target-controlled infusion (ETCLo-TCI) system and (2) out-of-circuit vaporizer (VOC)—in horses undergoing surgery. Twenty-four horses undergoing scheduled surgery were enrolled in this study. Anesthesia was maintained using Iso delivered either by a calibrated TEC 4 VOC (group V, n = 14) or an ETCLo-TCI system (group I, n = 10). Data were collected within the first hour of anesthesia on the consumption of Iso, the number of anesthetist drug delivery adjustments (modifing the vaporizer setting or the FE'Iso target in the software), the number of fresh gas flow changes, and the time taken to reach the first FE'Iso target (1.5%) after induction. The median consumption of Iso and the median consumption of Iso per kilogram of body weight during the first hour of anesthesia were significantly lower in group I compared with group V (20.5 [9.3–31.4] vs. 29.1 [21.5–43.0]) mL (P = .003) and 0.042 (0.028–0.052) versus 0.062 (0.037–0.094) mL kg−1 (P = .009). The median number of anesthetist drug delivery adjustments was significantly lower in group I compared with group V (1.5 [0–3] vs. 4 [3–9]; P = .0002). No significant difference was found in FGF changes and in the time taken by both systems to reach the end-tidal target.