Reflection Versus Rebreathing for Administration of Sevoflurane During Minor Gynecological Surgery.

BACKGROUND: Contemporary anesthetic circle systems, when used at low fresh gas flows (FGF) to allow rebreathing of anesthetic, lack the ability for rapid dose titration. The small-scale anesthetic reflection device Anaesthetic Conserving Device (50mL Version; AnaConDa-S) permits administration of volatile anesthetics with high-flow ventilators. We compared washin, washout, and sevoflurane consumption using AnaConDa-S versus a circle system with low and minimal FGF. METHODS: Forty patients undergoing breast surgery were randomized to receive 0.5 minimal alveolar concentration (MAC) sevoflurane with AnaConDa-S (21 patients, reflection group) or with a circle system (low flow: FGF = 0.2 minute ventilation [V'E], 9 patients; or minimal flow: 0.1 V'E, 10 patients). In the reflection group, syringe pump boluses were given for priming and washin; to simulate an open system, the FGF of the anesthesia ventilator was set to 18 L·min-1 with the soda lime removed. In the other groups, the FGF was increased for washin (1 V'E for 8 minutes) and washout (3 V'E). For all patients, tidal volume was 7 mL·kg-1 and the respiratory rate adjusted to ensure normoventilation. Analgesia was attained with remifentanil 0.3 µg·kg-1·min-1. Sevoflurane consumption was compared between the reflection group and the low- and minimal-flow groups, respectively, using a post hoc test (Fisher Least Significant Difference). To compare washin and washout (half-life), the low- and minimal-flow groups were combined. RESULTS: Sevoflurane consumption was reduced in the reflection group (9.4 ± 2.0 vs 15.0 ± 3.5 [low flow, P < .001] vs 11.6 ± 2.3 mL·MAC h-1 [minimal flow, P = .02]); washin (33 ± 15 vs 49 ± 12 seconds, P = .001) and washout (28 ± 15 vs 55 ± 19 seconds, P < .001) times were also significantly shorter. CONCLUSIONS: In this clinical setting with short procedures, low anesthetic requirements, and low tidal volumes, AnaConDa-S decreased anesthetic consumption, washin, and washout times compared to a circle system.

Carbon Dioxide Absorption During Inhalation Anesthesia: A Modern Practice.

CO2 absorbents were introduced into anesthesia practice in 1924 and are essential when using a circle system to minimize waste by reducing fresh gas flow to allow exhaled anesthetic agents to be rebreathed. For many years, absorbent formulations consisted of calcium hydroxide combined with strong bases like sodium and potassium hydroxide. When Sevoflurane and Desflurane were introduced, the potential for toxicity (compound A and CO, respectively) due to the interaction of these agents with absorbents became apparent. Studies demonstrated that strong bases added to calcium hydroxide were the cause of the toxicity, but that by eliminating potassium hydroxide and reducing the concentration of sodium hydroxide to <2%, compound A and CO production is no longer a concern. As a result, CO2 absorbents have been developed that contain little or no sodium hydroxide. These CO2 absorbent formulations can be used safely to minimize anesthetic waste by reducing fresh gas flow to approach closed-circuit conditions. Although absorbent formulations have been improved, practices persist that result in unnecessary waste of both anesthetic agents and absorbents. While CO2 absorbents may seem like a commodity item, differences in CO2 absorbent formulations can translate into significant performance differences, and the choice of absorbent should not be based on unit price alone. A modern practice of inhalation anesthesia utilizing a circle system to greatest effect requires reducing fresh gas flow to approach closed-circuit conditions, thoughtful selection of CO2 absorbent, and changing absorbents based on inspired CO2.

Comparison of the use of AnaConDa® versus AnaConDa-S® during the post-operative period of cardiac surgery under standard conditions of practice.

Changes have been made to the AnaConDa device (Sedana Medical, Stockholm, Sweden), decreasing its size to reduce dead space and carbon dioxide (CO2) retention. However, this also involves a decrease in the surface area of the activated carbon filter. The CO2 elimination and sevoflurane (SEV) reflection of the old device (ACD-100) were thus compared with the new version (ACD-50) in patients sedated after coronary artery bypass graft surgery. After ERC approval and written informed consent, 23 patients were sedated with SEV, using first the ACD-100 and then the ACD-50 for 60 min each. With each device, patients were ventilated with tidal volumes (TV) of 5 ml/kg of ideal body weight for the first 30 min, and with 7 ml/kg for the next 30 min. Ventilation parameters, arterial blood gases, Bispectral-Index™ (BIS, Aspect Medical Systems Inc., Newton, MA, USA), SEV concentrations exhaled by the patient (SEV-exhaled) and from the expiratory hose (SEV-lost) were recorded every 30 min. A SEV reflection index was calculated: SRI [%] = 100 × (1 - (SEV-lost/SEV-exhaled)). Data were compared using ANOVA with repeated measurements and Student's T-tests for pairs. Respiratory rates, tidal and minute volumes were not significantly different between the two devices. End tidal and arterial CO2 partial pressures were significantly higher with the ACD-100 as compared with the ACD-50. SEV infusion rate remained constant. SEV reflection was higher (SRI: ACD-100 vs. ACD-50, TV 5 ml/kg: 95.29 ± 6.45 vs. 85.54 ± 11.15, p = 0.001; 7 ml/kg: 93.42 ± 6.55 vs. 88.77 ± 12.26, p = 0.003). BIS was significantly lower when using the higher TV (60.91 ± 9.99 vs. 66.57 ± 8.22, p = 0.012), although this difference was not clinically relevant. During postoperative sedation, the use of ACD-50 significantly reduced CO2 retention. SEV reflection was slightly reduced. However, patients remained sufficiently sedated without increasing SEV infusion.

Halving the Volume of AnaConDa: Evaluation of a New Small-Volume Anesthetic Reflector in a Test Lung Model.

BACKGROUND: Volatile anesthetics are increasingly used for sedation in intensive care units. The most common administration system is AnaConDa-100 mL (ACD-100; Sedana Medical, Uppsala, Sweden), which reflects volatile anesthetics in open ventilation circuits. AnaConDa-50 mL (ACD-50) is a new device with half the volumetric dead space. Carbon dioxide (CO2) can be retained with both devices. We therefore compared the CO2 elimination and isoflurane reflection efficiency of both devices. METHODS: A test lung constantly insufflated with CO2 was ventilated with a tidal volume of 500 mL at 10 breaths/min. End-tidal CO2 (EtCO2) partial pressure was measured using 3 different devices: a heat-and-moisture exchanger (HME, 35 mL), ACD-100, and ACD-50 under 4 different experimental conditions: ambient temperature pressure (ATP), body temperature pressure saturated (BTPS) conditions, BTPS with 0.4 Vol% isoflurane (ISO-0.4), and BTPS with 1.2 Vol% isoflurane. Fifty breaths were recorded at 3 time points (n = 150) for each device and each condition. To determine device dead space, we adjusted the tidal volume to maintain normocapnia (n = 3), for each device. Thereafter, we determined reflection efficiency by measuring isoflurane concentrations at infusion rates varying from 0.5 to 20 mL/h (n = 3), for each device. RESULTS: EtCO2 was consistently greater with ACD-100 than with ACD-50 and HME (ISO-0.4, mean ± standard deviations: ACD-100, 52.4 ± 0.8; ACD-50, 44.4 ± 0.8; HME, 40.1 ± 0.4 mm Hg; differences of means of EtCO2 [respective 95% confidence intervals]: ACD-100 - ACD-50, 8.0 [7.9-8.1] mm Hg, P < .001; ACD-100 - HME, 12.3 [12.2-12.4] mm Hg, P < .001; ACD-50 - HME, 4.3 [4.2-4.3] mm Hg, P < .001). It was greatest under ATP, less under BTPS, and least with ISO-0.4 and BTPS with 1.2 Vol% isoflurane. In addition to the 100 or 50 mL "volumetric dead space" of each AnaConDa, "reflective dead space" was 40 mL with ACD-100 and 25 mL with ACD-50 when using isoflurane. Isoflurane reflection was highest under ATP. Under BTPS with CO2 insufflation and isoflurane concentrations around 0.4 Vol%, reflection efficiency was 93% with ACD-100 and 80% with ACD-50. CONCLUSIONS: Isoflurane reflection remained sufficient with the ACD-50 at clinical anesthetic concentrations, while CO2 elimination was improved. The ACD-50 should be practical for tidal volumes as low as 200 mL, allowing lung-protective ventilation even in small patients.

Efficacy of Malignant Hyperthermia Association of the United States-Recommended Methods of Preparation for Malignant Hyperthermia-Susceptible Patients Using Dräger Zeus Anesthesia Workstations and Associated Costs.

BACKGROUND: The objective of this study was to assess the efficacy and cost of Malignant Hyperthermia Association of the United States-recommended methods for preparing Dräger Zeus anesthesia workstations (AWSs) for the malignant hyperthermia-susceptible patient. METHODS: We studied washout profiles of sevoflurane, isoflurane, and desflurane in 3 Zeus AWS following 3 preparation methods. AWS was primed with 1.2 minimum alveolar concentration anesthetic for 2 hours using 2 L/min fresh gas flow, 500 mL tidal volume, and 12/min respiratory rate. Two phases of washout were performed: high flow (10 L/min) until anesthetic concentration was <5 parts per million (ppm) for 20 minutes and then low flow (3 L/min) for 20 minutes to identify the rebound effect. Preparation methods are as follows: method 1 (M1), changing disposables (breathing circuit, soda lime, CO2 line, and water traps); method 2 (M2), M1 plus replacing the breathing system with an autoclaved one; and method 3 (M3), M1 plus mounting 2 activated charcoal filters on respiratory limbs. Primary outcomes are as follows: time to obtain anesthetic concentration <5 ppm in the high-flow phase, peak anesthetic concentrations in the low-flow phase, and for M3 only, peak anesthetic concentration after 70 minutes of low-flow phase, when activated charcoal filters are removed. Secondary outcomes are as follows: cost analysis of time and resources to obtain anesthetic concentration <5 ppm in each method and a vapor-free Zeus AWS. Sensitivity analyses were performed using alternative assumptions regarding the costs and the malignant hyperthermia-susceptible caseload per year. RESULTS: Primary outcomes were as follows: M3 instantaneously decreased anesthetic concentration to <1 ppm with minimal impact of low-flow phase. M1 (median, 88 minutes; 95% confidence interval [CI], 69-112 minutes) was greater than M2 (median, 11 minutes; 95% CI, 9-15 minutes). Means of peak rebound anesthetic concentrations in M1, M2, and M3 were 15, 6, and 1 ppm, respectively (P < .001). Anesthetic concentration increased 33-fold (95% CI, 21-50) after removing charcoal filters (from 0.7 to 20 ppm). The choice of anesthetic agents did not impact the results. Secondary outcomes were as follows: M3 was the lowest cost when the cost of lost operating room (OR) time due to washout was included, and M1 was the lowest cost when it was not included. When the cost of lost OR time due to washout was considered the estimated cost/case of M3 was US $360 (M1, US $2670; M2, US $969; and a "vapor-free" Zeus AWS was US $930). The OR time and equipment costs represent the largest differentiators among the methods. CONCLUSIONS: Institutions in which demand for OR time has exceeded capacity should consider M3, and institutions with surplus OR capacity should consider M1.

Environmental safety: Air pollution while using MIRUS™ for short-term sedation in the ICU.

BACKGROUND: MIRUS™ is a device for target-controlled inhalational sedation in the ICU in combination with use of isoflurane, or sevoflurane, or desflurane. The feasibility of this device has recently been proven; however, ICU staff exposure may restrict its application. We investigated ICU ambient room pollution during daily work to estimate ICU personnel exposure while using MIRUS™. METHODS: This observational study assessed pollution levels around 15 adult surgical patients who received volatile anaesthetics-based sedation for a median of 11 hours. Measurements were performed by photoacoustic gas monitoring in real-time at different positions near the patient and in the personnel's breathing zone. Additionally, the impact of the Clean Air™ open reservoir scavenging system on volatile agent pollution was evaluated. RESULTS: Baseline concentrations [ppm] during intervention and rest periods were isoflurane c¯mean = 0.58 ± 0.49, c¯max = 5.72; sevoflurane c¯mean = 0.22 ± 0.20, c¯max = 7.93; and desflurane c¯mean = 0.65 ± 0.57, c¯max = 6.65. Refilling MIRUS™ with liquid anaesthetic yielded gas concentrations of c¯mean = 2.18 ± 1.48 ppm and c¯max = 13.03 ± 9.37 ppm in the personnel's breathing zone. Air pollution in the patient's room was approximately five times higher without a scavenging system. CONCLUSION: Ambient room pollution was minimal in most cases, and the measured values were within or below the recommended exposure limits. Caution should be taken during refilling of the MIRUS™ system, as this was accompanied by higher pollution levels. The combined use of air-conditioning and gas scavenging systems is strongly recommended.

Randomized-controlled trial of parent-led exposure to anesthetic mask to prevent child preoperative anxiety.

PURPOSE: To examine the efficacy of parent-directed anesthetic mask exposure and shaping practice to prevent child preoperative anxiety, with a specific focus on timing of exposure. METHODS: This randomized-controlled trial included 110 children ages four to seven years undergoing day surgery dental procedures and their parents. Families were randomly assigned to one of three groups: 1) parent-directed mask exposure/shaping practice at least three times in the week prior to surgery (Group 1); 2) parent-directed mask exposure/shaping practice at least once on the day of surgery (Group 2); 3) no exposure prior to induction (Group 3). Child anxiety was observer-rated using the modified Yale Preoperative Anxiety Scale during the day surgery experience, and induction compliance was observer-rated using the Induction Compliance Checklist. RESULTS: Results demonstrated significant differences in observer-rated child anxiety at anesthetic induction across groups. Group 2 demonstrated significantly lower observer-rated anxiety than Group 3 with a medium effect, F(1, 71) = 4.524, P = 0.04, η p 2 = 0.06. A significant interaction was observed between these two groups over time (i.e., admission to anesthesia induction), F(1, 71) = 4.365, P = 0.04, η p 2 = 0.06 (i.e., small to medium effect). Group 2 demonstrated the best anesthesia induction compliance (i.e., significantly lower scores than Group 3, P = 0.04). CONCLUSION: Timing of the delivery of mask exposure (i.e., on the day of surgery) to address child preoperative anxiety and induction compliance in the day surgery setting may be an important consideration. The current results inform the integration of this simple, effective strategy into practice.

RéSUMé: OBJECTIF: Examiner l'efficacité d'une exposition au masque anesthésique menée par un parent et détermination d'une pratique visant à prévenir l'anxiété préopératoire de l'enfant en se concentrant spécifiquement sur le moment de l'exposition. MéTHODES: Cette étude randomisée contrôlée a inclus 110 enfants âges de quatre à sept ans subissant une procédure dentaire en chirurgie d'un jour et leurs parents. Après randomisation, les familles ont été assignées à l'un des trois groupes suivants : 1) exposition au masque/pratique de modelage comportemental dirigée par le parent au moins trois fois dans la semaine précédant l'intervention (Groupe 1); 2) exposition au masque/pratique de modelage comportemental dirigée par le parent au moins une fois le jour de la chirurgie (Groupe 2); 3) aucune exposition avant l'induction (Groupe 3). L'anxiété de l'enfant a été évaluée par un observateur utilisant l'échelle mYPAS (échelle modifiée d'anxiété préopératoire de Yale) au cours de l'expérience le jour de la chirurgie et la conformité de l'induction a été évaluée par un observateur utilisant l'ICC (liste de vérification de la conformité de l'induction). RéSULTATS: Les résultats ont mis en évidence des différences significatives entre les groupes sur l'anxiété de l'enfant évaluée par un observateur au moment de l'induction anesthésique. Le Groupe 2 a présenté une anxiété évaluée par l'observateur significativement inférieure à celle du Groupe 3 avec un effet médian F (1, 71) = 4,524, P = 0,04, η P 2 = 0,06. Une interaction significative a été observée entre ces deux groupes au fil du temps (c'est-à-dire entre l'admission et l'induction de l'anesthésie), F (1, 71) = 4,365, P = 0,04, η P 2 = 0,06 (soit un effet petit à moyen). Le Groupe 2 a manifesté la meilleure conformité de l'induction de l'anesthésie (c'est-à-dire, des scores significativement inférieurs au Groupe 3, P = 0,04). CONCLUSION: Il peut être important de tenir compte du moment de l'exposition au masque (c'est-à-dire le jour de l'intervention) pour répondre à l'anxiété préopératoire de l'enfant et à la conformité de l'induction dans le cadre de la chirurgie d'un jour. Les résultats actuels renseignent sur l'intégration de cette stratégie simple et efficace dans la pratique.

Saving sevoflurane: Automated gas control can reduce consumption of anesthetic vapor by one-third in pediatric anesthesia.

BACKGROUND: Many modern anesthetic machines offer automated control of anesthetic vapor. The user simply sets a desired end-tidal concentration and the machine will manipulate the vaporizer and gas flow rates to obtain and maintain the preset target. Greater efficiency, and more accurate delivery of anesthetic vapor have been documented across multiple machines within the adult setting however, there is little evidence for their use in children. AIMS: The aim of this study was to compare the consumption of sevoflurane using the Maquet Flow-i anesthesia machine (Maquet, Solna, Sweden) in automatic gas control mode vs manual mode in pediatric anesthesia. The primary outcome measure is rate of sevoflurane use. METHOD: Data logs were collected from our three Maquet Flow-i anesthesia machines over a 4-week period. We compared the rate of sevoflurane use when in manual mode vs cases where the automatic gas control mode was used. We also examined each automatic gas control case to determine whether percentage of anesthesia time in this mode correlated significantly with average rate of sevoflurane consumption. RESULTS: Sevoflurane was the primary anesthetic used in 220 cases, comprising over 230 hours of anesthesia time. Of these, 36 cases were identified as automatic gas control cases and 184 as manual cases. Consumption of sevoflurane liquid in mL/min was significantly lower in automatic gas control cases (median 0.46, IQR 0.32-0.72 mL/min for automatic gas control; median 0.82, IQR 0.62-1.17 mL/min for manual; P < 0.001 by Wilcoxon Rank Sum test). For a case of median duration (49 minutes), average rate of sevoflurane liquid consumption was 0.54 mL/min for automatic gas control cases vs 0.81 mL/min for manual cases, a reduction of 33% (bootstrapped 95% CI 0.21-0.61 mL/min, P < 0.001). CONCLUSION: Maquet's Flow-i automatic gas control mode reduced use of sevoflurane an average of one-third in a pediatric anesthesia setting.

Low-flow anaesthesia with a fixed fresh gas flow rate.

During the wash-in period in low flow anaesthesia (LFA), high fresh gas flow is used to achieve the desired agent concentration. In this study, we aimed to evaluate the safety of fixed 1 L/min fresh gas flow desflurane anaesthesia in both the wash-in and maintenance periods in patients including the obese ones. 104 patients undergoing surgery under general anaesthesia were included. After endotracheal intubation, fresh gas flow was reduced to 1 L/min and the desflurane vaporizer was set at 18%. The time from opening the vaporizer to end-tidal desflurane concentration reaching 0.7 MAC was recorded (MAC 0.7 time). Throughout the surgery, hemodynamic variables, FIO2, MAC and BIS values were observed. MAC 0.7 time, BIS and MAC values at the start of surgery, number of adjustments in vaporizer settings, desflurane consumption were recorded. The average MAC 0.7 time was 2.9 ± 0.5 min. MAC and BIS values at the start of the surgery were 0.7 (0.6-0.8) and 39 ± 8.5 respectively. No individual patient had a BIS value above 60 throughout the surgery. Hemodynamic variables were stable and FIO2 did not fall below 30% in any patient. The number of adjustments in vaporizer settings was 56. Average desflurane consumption was 0.33 ± 0.05 mL/min. We demonstrated that LFA without use of initial high fresh gas flow during the wash-in period is an effective, safe and economic method which is easy to perform.

The Ayre's T-piece turns 80: A 21st century review.

Ayre's T-piece, first introduced 80 years ago, continues to be widely used in pediatric anesthesia despite colossal advances in equipment and technology. We present a review of its history, advantages, and disadvantages, and place in modern-day clinical practice.

Delivery of sevoflurane using a neonatal ventilator.

BACKGROUND: Most anesthetic ventilators are designed to cope with a wide range of patient sizes and may lack precision at the lowest end of the minute volume scale. Neonatal intensive care ventilators on the other hand are designed specifically for this patient group, but are not able to deliver volatile anesthesia. AIMS: We aimed to adapt the neonatal ventilator currently in use in our institution to deliver sevoflurane by incorporating a vaporizer and a scavenging system. METHODS: We used a Diamedica draw-over vaporizer incorporated into the ventilator circuit and a custom designed open interface scavenging system. A number of safety measures are described to ensure that this equipment is correctly inserted into the circuit. RESULTS: Bench testing revealed that the vaporizer output is linear and stable within the circuit flow range 4-8 L/min in all modes except high frequency oscillation where concentrations are not predictable. The scavenging system was found to be effective and did not affect volumes, pressures or waveforms when ventilating a test lung over a wide range of flows and pressures. This remained the case over the full range of scavenger flow adjustment. CONCLUSION: The addition of a Diamedica vaporizer to a Fabian neonatal ventilator was shown in bench testing to provide stable, linear vapor concentrations without compromise of ventilator function. The system should not be used in high frequency oscillation mode because concentrations will exceed those expected and will not maintain a linear relationship with the vaporizer setting.

Evaluating the efficiency of desflurane reflection in two commercially available reflectors.

With the AnaConDa™ and the MIRUS™ system, volatile anesthetics can be administered for inhalation sedation in intensive care units. Instead of a circle system, both devices use anesthetic reflectors to save on the anesthetic agent. We studied the efficiency of desflurane reflection with both devices using different tidal volumes (VT), respiratory rates (RR), and 'patient' concentrations (CPat) in a bench study. A test lung was ventilated with four settings (volume control, RR × VT: 10 × 300 mL, 10 × 500 mL, 20 × 500 mL, 10 × 1000 mL). Two different methods for determination of reflection efficiency were established: First (steady state), a bypass flow carried desflurane into the test lung (flowin), the input concentration (Cin) was varied (1-17 vol%), and the same flow (flowex, Cex) was suctioned from the test lung. After equilibration, CPat was stored online and averaged; efficiency [%] was calculated [Formula: see text]. Second (washout), flowin and flowex were stopped, the decline of CPat was measured; efficiency was calculated from the decay constant of the exponential regression equation. Both measurement methods yielded similar results (Bland-Altman: bias: -0.9 %, accuracy: ±5.55 %). Efficiencies higher than 80 % (>80 % of molecules exhaled are reflected) could be demonstrated in the clinical range of CPat and VT. Efficiency inversely correlates with the product of CPat and VT which can be imagined as the volume of anesthetic vapor exhaled by the patient in one breath, but not with the respiratory frequency. Efficiency of the AnaConDa™ was higher for each setting compared with the MIRUS™. Desflurane is reflected by both reflectors with efficiencies high enough for clinical use.

Technology III: in-line vaporizer with reflector.

As the clinical advantages of vapor anesthesia (VA) for sedation of patients in ICU become more apparent, the ergonomics, economy and safety issues need to be better addressed. Here we describe the use of a new commercial digital in-line anesthetic vaporizer that can be attached to the inspiratory limb of a ventilator. If used with a simple, and easily assembled secondary circuit and anesthetic reflector, the circuit remains remote from the patient, the VA consumption approaches a physical minimum, VA level is controlled and monitored, and the tidal volume size is not limited.

Uncontrolled delivery of liquid volatile anaesthetic when using the anaesthetic conserving device.

During patient sedation with liquid volatile anaesthetic, some problems may occur through a process called auto-pumping, defined as an expansion of bubbles inside the syringe, which can lead to uncontrolled anaesthetic delivery. The study examined how the temperature of liquid volatile anaesthetics (sevoflurane and isoflurane) and the presence of gas bubbles in the syringe affect the occurrence of auto-pumping when using the anaesthetic conserving device (ACD, AnaConDa™, Sedana Medical, Uppsala, Sweden). Four different circumstances for each volatile anaesthetic were tested with a bench study: volatile anaesthetic at room temperature or precooled with and without the presence of gas bubbles in the syringe. Liquid volatile anaesthetic was infused into the ACD via a syringe pump at a fixed rate and heated gradually until the temperature of the syringe surface reached 50 °C. A main-stream gas monitor was used to measure the expired fraction of volatile anaesthetic (FE vol%). The occurrence of auto-pumping was observed only in the subgroups containing gas bubbles, with both anaesthetics. In these subgroups, the values of the expired anaesthetic gas fraction increased dramatically with the expansion of gas bubbles in the syringe (ΔFE ranged from +1.6 to 2.4 vol% for sevoflurane and +2.3 to 3.4 vol% for isoflurane). Furthermore, when the heat source was removed, a substantial decline in anaesthetic agent values below the baseline was observed with both anaesthetics. The presence of gas bubbles in the syringe, especially when exposed to a heat source, may provoke auto-pumping with uncontrolled excessive anaesthetic delivery. If auto-pumping is suspected, the syringe pump must be stopped and the ACD removed from the breathing circuit at once.

In vitro performance of prefilled CO2 absorbers with the Zeus®.

Low fresh gas flows (FGFs) decrease the use of anesthetic gases, but increase CO2 absorbent usage. CO2 absorbent usage remains poorly quantified. The goal of this study is to determine canister life of 8 commercially available CO2 absorbent prepacks with the Zeus®. Pre-packed CO2 canisters of 8 different brands were tested in vitro: Amsorb Plus, Spherasorb, LoFloSorb, LithoLyme, SpiraLith, SpheraSorb, Drägersorb 800+, Drägersorb Free, and CO2ntrol. CO2 (160 mL min- 1) flowed into the tip of a 2 L breathing bag that was ventilated with a tidal volume of 500 mL, a respiratory rate of 10/min, and an I:E ratio of 1:1 using the controlled mechanical ventilation mode of the Zeus® (Dräger, Lubeck, Germany). In part I, canister life of 5 canisters each of 2 different lots of each brand was determined with a 350 mL min- 1 FGF. Canister life is the time it takes for the inspired CO2 concentration (FICO2) to rise to 0.5%. In part II, canister life was measured accross a FGF range of 0.25 to 4 L min- 1 for Drägersorb 800+ (2 lots) and SpiraLith (1 lot). In part III, the calculated canister life per 100 g fresh granule content of the different brands was compared between the Zeus and (previously published data for) the Aisys. In vitro canister life of prefilled CO2 absorber canisters differed between brands, and depended on the amount of CO2 absorbent and chemical composition. Canister life expressed as FCU0.5 (the fraction of the canister used per hour) was proportional to FGF over 0.2-2 L min-1 range only, but was non-linear with higher FGF: FCU0.5 was larger than expected with FGF > 2 L min-1, and even with FGF > minute ventilation FCU0.5 did not become zero, indicating some CO2 was being absorbed. Canister life on a per weight basis of the same brand is higher with the Zeus than the Aisys. Canister life of prefilled CO2 absorber canisters differs between brands. The FCU0.5-FGF relationship is not linear across the entire FGF range. Canister life of prepacks of the same brand for the Zeus and Aisys differs, the exact etiology of which is probably multifactorial, and may include differences in the absolute amount of absorbent and different rebreathing characteristics of the machines.

Efficient application of volatile anaesthetics: total rebreathing or specific reflection?

The circle system has been in use for more than a 100 years, whereas the first clinical application of an anaesthetic reflector was reported just 15 years ago. Its functional basis relies on molecular sieves such as zeolite crystals or activated carbon. In a circle system, the breathing gas is rebreathed after carbon dioxide absorption; a reflector on the other hand specifically retains the anaesthetic during expiration and resupplies it during the next inspiration. Reflection systems can be used in conjunction with intensive care ventilators and do not need the permanent presence of trained qualified staff. Because of easy handling and better ventilatory capabilities of intensive care ventilators, reflection systems facilitate the routine use of volatile anaesthetics in intensive care units. Until now, there are three reflection systems commercially available: the established AnaConDa™ (Sedana Medical, Uppsala, Sweden), the new smaller AnaConDa-S™, and the Mirus™ (Pall Medical, Dreieich, Germany). The AnaConDa consists only of a reflector which is connected to a syringe pump for infusion of liquid sevoflurane or isoflurane. The Mirus represents a technical advancement; its control unit includes a gas and ventilation monitor as well as a gas dispensing unit. The functionality, specific features, advantages and disadvantages of both systems are discussed in the text.

Halving the volume of AnaConDa: initial clinical experience with a new small-volume anaesthetic reflector in critically ill patients-a quality improvement project.

AnaConDa-100 ml (ACD-100, Sedana Medical, Uppsala, Sweden) is well established for inhalation sedation in the intensive care unit. But because of its large dead space, the system can retain carbon dioxide (CO2) and increase ventilatory demands. We therefore evaluated whether AnaConDa-50 ml (ACD-50), a device with half the internal volume, reduces CO2 retention and ventilatory demands during sedation of invasively ventilated, critically ill patients. Ten patients participated in this cross-over protocol. After sedation with isoflurane via ACD-100 for 24 h, the 5-h observation period started. During the first hour, ACD-100 was used; for the next 2 h, ACD-50; and for the last 2 h, ACD-100 was used again. Sedation was titrated to Richmond Agitation and Sedation Scale (RASS) score - 3 to - 4 and a processed electroencephalogram (Narcotrend Index, Narcotrend-Gruppe, Hannover, Germany) was recorded. Minute ventilation, CO2 elimination, and isoflurane consumption were compared. All patients were deeply sedated (Narcotrend Index, mean ± SD: 38 ± 10; RASS scores - 3 to - 5) and breathed spontaneously with pressure support throughout the observation period. Infusion rates of isoflurane and opioid, either remifentanil or sufentanil, as well as ventilator settings were unchanged. Minute ventilation and end-tidal CO2 were significantly reduced with the ACD-50, respiratory rate remained unchanged, and tidal volume decreased by 66 ± 43 ml. End-tidal isoflurane concentrations were also slightly reduced while haemodynamic measures remained constant. The ACD-50 reduces the tidal volume needed to eliminate carbon dioxide without augmenting isoflurane consumption.

Use of the MIRUS™ system for general anaesthesia during surgery: a comparison of isoflurane, sevoflurane and desflurane.

The MIRUS™ system enables automated end-expired control of volatile anaesthetics. The device is positioned between the Y-piece of the breathing system and the patient's airway. The system has been tested in vitro and to provide sedation in the ICU with end-expired concentrations up to 0.5 MAC. We describe its performance in a clinical setting with concentrations up to 1.0 MAC. In 63 ASA II-III patients undergoing elective hip or knee replacement surgery, the MIRUS™ was set to keep the end-expired desflurane, sevoflurane, or isoflurane concentration at 1 MAC while ventilating the patient with the PB-840 ICU ventilator. After 1 h, the ventilation mode was switched from controlled to support mode. Time to 0.5 and 1 MAC, agent usage, and emergence times, work of breathing, and feasibility were assessed. In 60 out of 63 patients 1.0 MAC could be reached and remained constant during surgery. Gas consumption was as follows: desflurane (41.7 ± 7.9 ml h-1), sevoflurane (24.3 ± 4.8 ml h-1) and isoflurane (11.2 ± 3.3 ml h-1). Extubation was faster after desflurane use (min:sec): desflurane 5:27 ± 1:59; sevoflurane 6:19 ± 2:56; and isoflurane 9:31 ± 6:04. The support mode was well tolerated. The MIRUS™ system reliable delivers 1.0 MAC of the modern inhaled agents, both during mechanical ventilation and spontaneous (assisted) breathing. Agent usage is highest with desflurane (highest MAC) but results in the fastest emergence. Trial registry number: Clinical Trials Registry, ref.: NCT0234509.