Comparison of Amsorb, sodalime, and Baralyme degradation of volatile anesthetics and formation of carbon monoxide and compound a in swine in vivo.

BACKGROUND: Consequences of volatile anesthetic degradation by carbon dioxide absorbents that contain strong base include formation of compound A from sevoflurane, formation of carbon monoxide (CO) and CO toxicity from desflurane, enflurane and isoflurane, delayed inhalation induction, and increased anesthetic costs. Amsorb (Armstrong Ltd., Coleraine, Northern Ireland) is a new absorbent that does not contain strong base and does not form CO or compound A in vitro. This investigation compared Amsorb, Baralyme (Chemetron Medical Division, Allied Healthcare Products, St. Louis, MO), and sodalime effects on CO (from desflurane and isoflurane) and compound A formation, carboxyhemoglobin (COHb) concentrations, and anesthetic degradation in a clinically relevant porcine in vivo model. METHODS: Pigs were anesthetized with desflurane, isoflurane, or sevoflurane, using fresh or partially dehydrated Amsorb, Baralyme, and new and old formulations of sodalime. Anesthetic concentrations in the fresh (preabsorber), inspired (postabsorber), and end-tidal gas were measured, as were inspired CO and compound A concentrations and blood oxyhemoglobin and COHb concentrations. RESULTS: For desflurane and isoflurane, the order of inspired CO and COHb formation was dehydrated Baralyme > soda-lime > Amsorb. For desflurane and Baralyme, peak CO was 9,700 +/- 5,100 parts per million (ppm), and the increase in COHb was 37 +/- 14%. CO and COHb increases were undetectable with Amsorb. Oxyhemoglobin desaturation occurred with desflurane and Baralyme but not Amsorb or sodalime. The gap between inspired and end-tidal desflurane and isoflurane did not differ between the various dehydrated absorbents. Neither fresh nor dehydrated Amsorb caused compound A formation from sevoflurane. In contrast, Baralyme and sodalime caused 20-40 ppm compound A. The gap between inspired and end-tidal sevoflurane did not differ between fresh absorbents, but was Amsorb < sodalime < Baralyme with dehydrated absorbents. CONCLUSION: Amsorb caused minimal if any CO formation, minimal compound A formation regardless of absorbent hydration, and the least amount of sevoflurane degradation. An absorbent like Amsorb, which does not contain strong base or cause anesthetic degradation and formation of toxic products, may have benefit with respect to patient safety, inhalation induction, and anesthetic consumption (cost).     

Carbon monoxide production from sevoflurane breakdown: modeling of exposures under clinical conditions

Isoflurane, enflurane, sevoflurane, and especially desflurane produce carbon monoxide (CO) during reaction with desiccated absorbents. Of these, sevoflurane is the least studied. We investigated the dependence of CO production from sevoflurane on absorbent temperature, minute ventilation (VE), and fresh gas flow rates. We measured absorbent temperature and in vitro CO concentrations when desiccated Baralyme reacted with 1 minimum alveolar anesthetic concentration of (2.1%) sevoflurane at 2.3-, 5.0-, and 10.0-L VE. Mathematical modeling of carboxyhemoglobin concentrations was performed using an existing iterative method. Rapid breakdown of sevoflurane prevented the attainment of 1 minimum alveolar anesthetic concentration with low fresh gas flow rates. CO concentrations increased with VE and with absorbent temperatures exceeding 80 degrees C, but concentrations decreased with higher fresh gas flow rates. Average CO concentrations were 150 and 600 ppm at 2.3- and 5.0-L VE; however, at 10 L, over 11,000 ppm of CO were produced followed by an explosion and fire. Methanol and formaldehyde were present and may have contributed to the flammable mixture but were not quantitated. Mathematical modeling of exposures indicates that in average cases, only patients < or =25 kg, or severely anemic patients, are at risk of carboxyhemoglobin concentrations >10% during the first 60 min of anesthesia. IMPLICATIONS: Sevoflurane breakdown in desiccated absorbents is expected to result in only mild carbon monoxide (CO) exposure. Completely dry absorbent and high minute ventilation rates may degrade sevoflurane to extremely large CO concentrations. Serious CO poisoning or spontaneous ignition of flammable gases within the breathing circuit are possible in extreme circumstances.     

Physical Factors Affecting the Production of Carbon Monoxide from Anesthetic Breakdown

Background: Parameters determining carbon monoxide (CO) concentrations produced by anesthetic breakdown have not been adequately studied in clinical situations. The authors hypothesized that these data will identify modifiable risk factors.

Methods: Carbon monoxide concentrations were measured when partially desiccated barium hydroxide lime was reacted with isoflurane (1.5%) and desflurane (7.5%) in a Draeger Narkomed 2 anesthesia machine with a latex breathing bag substituting for a patient. Additional experiments determined the effects of carbon dioxide (0 or 350 ml/min), fresh gas flow rates (1 or 4 l/min), minute ventilation (6 or 18 l/min), or absorbent quantity (1 or 2 canisters). End-tidal anesthetic concentrations were adjusted according to a monochromatic infrared monitor.

Results: Desflurane produced approximately 20 times more CO than isoflurane when completely dried absorbents were used. Peak CO concentrations approached 100,000 ppm with desflurane. Traces of water remaining after a 66-h drying time (one weekend) markedly reduced the generation of CO compared with 2 weeks of drying. Reducing the quantity of desiccated absorbent by 50% reduced the total CO production by 40% in the first hour. Increasing the fresh gas flow rate from 1 to 4 l/min increased CO production by 67% in the first hour but simultaneously decreased average inspiratory concentrations by 53%. Carbon dioxide decreased CO production by 12% in completely desiccated absorbents.     

Comparison of Amsorb®, Sodalime, and Baralyme® Degradation of Volatile Anesthetics and Formation of Carbon Monoxide and Compound A in Swine In Vivo

Background: Consequences of volatile anesthetic degradation by carbon dioxide absorbents that contain strong base include formation of compound A from sevoflurane, formation of carbon monoxide (CO) and CO toxicity from desflurane, enflurane and isoflurane, delayed inhalation induction, and increased anesthetic costs. Amsorb(R) (Armstrong Ltd., Coleraine, Northern Ireland) is a new absorbent that does not contain strong base and does not form CO or compound A in vitro. This investigation compared Amsorb(R), Baralyme(R) (Chemetron Medical Division, Allied Healthcare Products, St. Louis, MO), and sodalime effects on CO (from desflurane and isoflurane) and compound A formation, carboxyhemoglobin (COHb) concentrations, and anesthetic degradation in a clinically relevant porcine in vivo model.

Methods: Pigs were anesthetized with desflurane, isoflurane, or sevoflurane, using fresh or partially dehydrated Amsorb(R), Baralyme(R), and new and old formulations of sodalime. Anesthetic concentrations in the fresh (preabsorber), inspired (postabsorber), and end-tidal gas were measured, as were inspired CO and compound A concentrations and blood oxyhemoglobin and COHb concentrations.

Results: For desflurane and isoflurane, the order of inspired CO and COHb formation was dehydrated Baralyme(R) >> soda-lime > Amsorb(R). For desflurane and Baralyme(R), peak CO was 9,700 +/- 5,100 parts per million (ppm), and the increase in COHb was 37 +/- 14%. CO and COHb increases were undetectable with Amsorb(R). Oxyhemoglobin desaturation occurred with desflurane and Baralyme(R) but not Amsorb(R) or sodalime. The gap between inspired and end-tidal desflurane and isoflurane did not differ between the various dehydrated absorbents. Neither fresh nor dehydrated Amsorb(R) caused compound A formation from sevoflurane. In contrast, Baralyme(R) and sodalime caused 20-40 ppm compound A. The gap between inspired and end-tidal sevoflurane did not differ between fresh absorbents, but was Amsorb(R) < sodalime < Baralyme(R) with dehydrated absorbents.     

Physical factors affecting the production of carbon monoxide from anesthetic breakdown

BACKGROUND: Parameters determining carbon monoxide (CO) concentrations produced by anesthetic breakdown have not been adequately studied in clinical situations. The authors hypothesized that these data will identify modifiable risk factors. METHODS: Carbon monoxide concentrations were measured when partially desiccated barium hydroxide lime was reacted with isoflurane (1.5%) and desflurane (7.5%) in a Draeger Narkomed 2 anesthesia machine with a latex breathing bag substituting for a patient. Additional experiments determined the effects of carbon dioxide (0 or 350 ml/min), fresh gas flow rates (1 or 4 l/min), minute ventilation (6 or 18 l/min), or absorbent quantity (1 or 2 canisters). End-tidal anesthetic concentrations were adjusted according to a monochromatic infrared monitor. RESULTS: Desflurane produced approximately 20 times more CO than isoflurane when completely dried absorbents were used. Peak CO concentrations approached 100,000 ppm with desflurane. Traces of water remaining after a 66-h drying time (one weekend) markedly reduced the generation of CO compared with 2 weeks of drying. Reducing the quantity of desiccated absorbent by 50% reduced the total CO production by 40% in the first hour. Increasing the fresh gas flow rate from 1 to 4 l/min increased CO production by 67% in the first hour but simultaneously decreased average inspiratory concentrations by 53%. Carbon dioxide decreased CO production by 12% in completely desiccated absorbents. CONCLUSION: Anesthetic identity, fresh gas flow rates, absorbent quantity, and water content are the most important factors determining patient exposures. Minute ventilation and carbon dioxide production by the patient are relatively unimportant.     

Rehydration of Desiccated Baralyme Prevents Carbon Monoxide Formation from Desflurane in an Anesthesia Machine

Background: Desiccated carbon dioxide absorbents degrade desflurane, enflurane, and isoflurane to carbon monoxide (CO) in vitro and in anesthesia machines, which can result in significant clinical CO exposure. Carbon monoxide formation is highest from desflurane, and greater with Baralyme than with soda lime. Degradation is inversely related to absorbent water content, and thus the greatest CO concentrations occur with desflurane and fully desiccated Baralyme. This investigation tested the hypothesis that rehydrating desiccated absorbent can diminish CO formation.

Methods: Baralyme was dried to constant weight. Carbon monoxide formation from desflurane and desiccated Baralyme was determined in sealed 20.7-ml vials without adding water, after adding 10% of the normal water content (1.3% water), and after adding 100% of the normal water content (13% water) to the dry absorbent. Similar measurements were made using an anesthesia machine and circle system. Carbon monoxide was measured by gas chromatography-mass spectrometry.

Results: Carbon monoxide formation from desflurane in vitro was decreased from 10,700 ppm with desiccated Baralyme to 715 ppm and less than 100 ppm, respectively, when 1.3% and 13% water were added. Complete rehydration also decreased CO formation from enflurane and isoflurane to undetectable concentrations. Desflurane degradation in an anesthesia machine produced 2,500 ppm CO in the circuit, which was reduced to less than 180 ppm when the full complement of water (13%) was added to the dried absorbent.     

Temperatures in soda lime during degradation of desflurane, isoflurane, and sevoflurane by desiccated soda lime

Rarely, fire and patient injury result from the degradation of sevoflurane by desiccated Baralyme. The present investigation sought to determine whether high temperatures also arose with sevoflurane use in the presence of desiccated soda lime. We desiccated soda lime by directing a 10 L/min flow of oxygen through fresh absorbent. Using 1140 +/- 30 g (mean +/- sd) of this desiccated absorbent, we filled a single standard absorber canister placed in a standard anesthetic circuit to which we directed a 6 L/min flow of oxygen containing 1.5 minimum alveolar concentration (MAC) desflurane or sevoflurane, or 3.0 MAC desflurane, isoflurane, or sevoflurane (with and without concurrent delivery of 200 mL/min carbon dioxide). In an additional test, 2 canisters (rather than a single canister) containing desiccated absorbent were used and 3.0 MAC sevoflurane was applied. A 3-L reservoir bag served as a surrogate lung, and we ventilated this lung with a minute ventilation of 10 L/min. With desflurane at 1.5 MAC or 3.0 MAC or isoflurane at 3.0 MAC temperatures increased in 20 to 40 min to a peak of 30 degrees C to 45 degrees C and then declined. With 1.5 or 3.0 MAC sevoflurane, temperatures increased to approximately 90 degrees C, after which temperatures declined. Concurrent delivery of carbon dioxide and sevoflurane did not increase the peak temperatures reached. The use of 2 canisters increased the duration but not the peak of increased temperature reached with 3.0 MAC sevoflurane. No fires resulted from degradation of any anesthetic.     

Mathematical Modeling of Carbon Monoxide Exposures from Anesthetic Breakdown: Effect of Subject Size, Hematocrit, Fraction of Inspired Oxygen, and Quantity of Carbon Monoxide

Background: Carbon monoxide (CO) is produced by reaction of isoflurane, enflurane, and desflurane in desiccated carbon dioxide absorbents. The inspiratory CO concentration depends on the dryness and identity of the absorbent and anesthetic. The adaptation of existing mathematical models to a rebreathing circuit allows identification of patient factors that predispose to more severe exposures, as identified by carboxyhemoglobin concentration.

Methods: From our companion study, the authors used quantitative in vitro CO production data for 60 min at 7.5% desflurane or 1.5% isoflurane at 1 l/min fresh gas flow. The carboxyhemoglobin concentration was calculated by iteratively solving the Coburn Forster Kane equation modified for a rebreathing system that incorporates the removal of CO by patient absorption. Demonstrating good fit of predicted carboxyhemoglobin concentrations to published data from animal and human exposures validated the model. Carboxyhemoglobin concentrations were predicted for exposures of various severity, patients of different sizes, hematocrit, and fraction of inspired oxygen.

Results: The calculated carboxyhemoglobin concentrations closely predicted the experimental results of other investigators, thereby validating the model. These equations indicate the severity of CO poisoning is inversely related to the hemoglobin quantity of a subject. Fraction of inspired oxygen had the greatest effect in patients of small size with low hematocrit values, where equilibrium and not the rate of uptake determined carboxyhemoglobin concentrations.     

Fires from the interaction of anesthetics with desiccated absorbent

Rarely, fire and patient injury have resulted from the degradation of sevoflurane by desiccated carbon dioxide absorbent. Desiccated absorbent also can degrade desflurane and isoflurane, and in the present investigation we sought to determine whether a danger of fire also arose with their use in the presence of desiccated absorbent. Baralyme was desiccated by heating and directing a 10 L/min flow of oxygen through the absorbent. Approximately 1200 g of this desiccated absorbent was used to fill a standard absorber placed in a standard anesthetic circuit to which we directed a 6 L/min flow of oxygen containing 1.5 or 3.0 MAC desflurane, isoflurane, or sevoflurane. A 3-L reservoir bag served as a surrogate lung, and we ventilated this lung with a minute ventilation of 10 L/min. With desflurane or isoflurane, at both 1.5 MAC and 3.0 MAC, temperatures increased in 30 to 70 min to a peak of approximately 100 degrees C and then decreased. With 1.5 MAC sevoflurane (3.0 MAC was not studied), temperatures increased to over 200 degrees C, and in 2 of 5 studies, flames appeared in the anesthetic circuit. In a separate study, we found that concurrent delivery of carbon dioxide and desflurane did not increase peak temperatures. We conclude that the interaction of desflurane or isoflurane with desiccated absorbent is not likely to produce the conflagrations possible with sevoflurane.     

模拟紧闭环路内不同的碱石灰对地氟烷分解反应的比较

目的 研究模拟紧闭环路内三种成分不同的十燥碱石灰与地氟烷发生分解反应生成一氧化碳(CO)的差异。方法 选用钡石灰、国产钠石灰及Sofnolime。在麻醉机的Y-piece端接一贮气囊做为模拟肺。二氧化碳(CO_2)以200ml·min~(-1)的流速通入环路。设定分钟通气量6L·min~(-1),呼吸频率(RR)12次/min,使P_(ET)CO_2在35～45 mm Hg。根据碱石灰的种类不同将实验分为三组,每组实验重复三次。向环路内通入二氧化碳及氧气的同时开启蒸发罐,洗入期开始,当呼气未地氟烷浓度达9％时关闭蒸发罐及新鲜气流,紧闭环路,继续机械通气直至180min。监测 P_(ET)CO_2、重复吸入CO_2分压、地氟烷的吸入、呼出浓度及上下罐反应温度。用气相色谱仪测定CO浓度。结果 三种碱石灰分解地氟烷生成CO的峰浓度及平均浓度由高到低的顺序依次是钡石灰、Sofnolime及国产钠石灰。钡石灰组CO达峰浓度时间明显快于其它两组(P<0.05)。与上罐相比下罐温度上升时间延迟。国产钠石灰组洗入时间较其余两组短。在温度上升期钠石灰组上罐温度上升速度快而钡石灰组下罐温度上升速度快。结论 在模拟紧闭环路内,使用钡石灰发生CO中毒的危险性要高于钠石灰。但仅仅去除钠石灰中的KOH,不能减少吸入全麻药的分解,相反生成CO的量可能增多。     

Mathematical modeling of carbon monoxide exposures from anesthetic breakdown: effect of subject size, hematocrit, fraction of inspired oxygen, and quantity of carbon monoxide

BACKGROUND: Carbon monoxide (CO) is produced by reaction of isoflurane, enflurane, and desflurane in desiccated carbon dioxide absorbents. The inspiratory CO concentration depends on the dryness and identity of the absorbent and anesthetic. The adaptation of existing mathematical models to a rebreathing circuit allows identification of patient factors that predispose to more severe exposures, as identified by carboxyhemoglobin concentration. METHODS: From our companion study, the authors used quantitative in vitro CO production data for 60 min at 7.5% desflurane or 1.5% isoflurane at 1 l/min fresh gas flow. The carboxyhemoglobin concentration was calculated by iteratively solving the Coburn Forster Kane equation modified for a rebreathing system that incorporates the removal of CO by patient absorption. Demonstrating good fit of predicted carboxyhemoglobin concentrations to published data from animal and human exposures validated the model. Carboxyhemoglobin concentrations were predicted for exposures of various severity, patients of different sizes, hematocrit, and fraction of inspired oxygen. RESULTS: The calculated carboxyhemoglobin concentrations closely predicted the experimental results of other investigators, thereby validating the model. These equations indicate the severity of CO poisoning is inversely related to the hemoglobin quantity of a subject. Fraction of inspired oxygen had the greatest effect in patients of small size with low hematocrit values, where equilibrium and not the rate of uptake determined carboxyhemoglobin concentrations. CONCLUSION: This model predicts that patients with low hemoglobin quantities will have more severe CO exposures based on the attainment of a higher carboxyhemoglobin concentration. This includes patients of small size (pediatric population) and patients with anemia.     

Reduction in the Incidence of Carbon Monoxide Exposures in Humans Undergoing General Anesthesia

Background: Carbon monoxide forms via reaction of isoflurane, enflurane, and desflurane with dried CO2 absorbents. The authors hypothesize that interventions by nonphysician support personnel to decrease absorbent drying will decrease the exposure rate of patients to carbon monoxide from anesthetic breakdown.

Methods: In the control group, all anesthetizing personnel were made aware of the factors enabling CO generation from anesthetic breakdown, and prevention techniques were left to the anesthetizing personnel. After data collection was complete, the following interventions were initiated to reduce absorbent drying: Anesthesia technicians and housekeeping personnel were instructed to turn off all anesthesia machines after the last case of the day in each room, and the CO2 absorbent was changed each morning if fresh gas was found flowing. Baralyme[registered sign] was used in all phases of this study.

Results: Five cases of intraoperative carbon monoxide exposure occurred among 1,085 (0.46%) first cases in the control group. Postintervention, patient carbon monoxide exposures decreased (P <0.05), with one exposure among 1,961 (0.051%) first cases in the main operating room. Two exposures among 68 (2.9%) first cases occurred in remote locations (P < 0.001) versus main operating room. Predisposing factors for absorbent drying include the prolonged use of anesthesia machines for monitored anesthesia care, inappropriate drying techniques for expiratory flowmeters, understaffing of support personnel, and anesthesia in remote locations.     

Small carbon monoxide formation in absorbents does not correlate with small carbon dioxide absorption

In this study we sought to determine whether an absorbent in which little carbon monoxide (CO) forms has a correspondingly small capacity to absorb carbon dioxide (CO(2)). Completely dried samples (600 g) of Baralyme (A), Dr?gersorb 800 (B), Dr?gersorb 800 Plus (C), Intersorb (D), Spherasorb (E), LoFloSorb (F), Superia (G), and Amsorb (H) were exposed to a flow of 0.5% (A-H; n = 4-5) and 4% isoflurane (F-H; n = 3) in pure oxygen at 5 L/min for 60 min. Downstream CO concentration, temperature, and isoflurane concentration were recorded every 60 s to calculate CO formation and isoflurane loss. The CO(2) absorption capacity of each brand was determined by passing 5.1% CO(2) in oxygen (flow, 250 mL/min) through untreated samples (30 g; n = 5) until the outlet CO(2) concentration reached 0.5%. CO formation was largest in absorbents containing potassium hydroxide (A and B) and negligible in absorbents not containing any alkali hydroxide (F-H). The outlet temperature correlated with CO formation, but the isoflurane loss did not. The duration of CO(2) absorption also did not correlate with CO formation. We conclude that absorbents that allow only very little CO formation are not necessarily poor CO(2) absorbents. IMPLICATIONS: In an in vitro study, carbon dioxide (CO(2)) absorption capacity and possible carbon monoxide (CO) formation were tested in different absorbent brands. Absorbents with very small CO formation are not necessarily poor CO(2) absorbents.     

Amsorb: a new carbon dioxide absorbent for use in anesthetic breathing systems.

BACKGROUND: This article describes a carbon dioxide absorbent for use in anesthesia. The absorbent consists of calcium hydroxide with a compatible humectant, namely, calcium chloride. The absorbent mixture does not contain sodium or potassium hydroxide but includes two setting agents (calcium sulphate and polyvinylpyrrolidine) to improve hardness and porosity. METHODS: The resultant mixture was formulated and subjected to standardized tests for hardness, porosity, and carbon dioxide absorption. Additionally, the new absorbent was exposed in vitro to sevoflurane, desflurane, isoflurane, and enflurane to determine whether these anesthetics were degraded to either compound A or carbon monoxide. The performance data and inertness of the absorbent were compared with two currently available brands of soda lime: Intersorb (Intersurgical Ltd., Berkshire, United Kingdom) and Dragersorb (Drager, Lubeck, Germany). RESULTS: The new carbon dioxide absorbent conformed to United States Pharmacopeia specifications in terms of carbon dioxide absorption, granule hardness, and porosity. When the new material was exposed to sevoflurane (2%) in oxygen at a flow rate of 1 l/min, concentrations of compound A did not increase above those found in the parent drug (1.3-3.3 ppm). In the same experiment, mean +/-SD concentrations of compound A (32.5 +/- 4.5 ppm) were observed when both traditional brands of soda lime were used. After dehydration of the traditional soda limes, immediate exposure to desflurane (60%), enflurane (2%), and isoflurane (2%) produced concentrations of carbon monoxide of 600.0 +/- 10.0 ppm, 580.0 +/- 9.8 ppm, and 620.0 +/-10.1 ppm, respectively. In contrast, concentrations of carbon monoxide were negligible (1-3 ppm) when the anhydrous new absorbent was exposed to the same anesthetics. CONCLUSIONS: The new material is an effective carbon dioxide absorbent and is chemically unreactive with sevoflurane, enflurane, isoflurane, and desflurane.     

Amsorb: A New Carbon Dioxide Absorbent for Use in Anesthetic Breathing Systems

Background: This article describes a carbon dioxide absorbent for use in anesthesia. The absorbent consists of calcium hydroxide with a compatible humectant, namely, calcium chloride. The absorbent mixture does not contain sodium or potassium hydroxide but includes two setting agents (calcium sulphate and polyvinylpyrrolidine) to improve hardness and porosity.

Methods: The resultant mixture was formulated and subjected to standardized tests for hardness, porosity, and carbon dioxide absorption. Additionally, the new absorbent was exposed in vitro to sevoflurane, desflurane, isoflurane, and enflurane to determine whether these anesthetics were degraded to either compound A or carbon monoxide. The performance data and inertness of the absorbent were compared with two currently available brands of soda lime: Intersorb (Intersurgical Ltd., Berkshire, United Kingdom) and Dragersorb (Drager, Lubeck, Germany).

Results: The new carbon dioxide absorbent conformed to United States Pharmacopeia specifications in terms of carbon dioxide absorption, granule hardness, and porosity. When the new material was exposed to sevoflurane (2%) in oxygen at a flow rate of 1 l/min, concentrations of compound A did not increase above those found in the parent drug (1.3-3.3 ppm). In the same experiment, mean +/-SD concentrations of compound A (32.5 +/- 4.5 ppm) were observed when both traditional brands of soda lime were used. After dehydration of the traditional soda limes, immediate exposure to desflurane (6%), enflurane (2%), and isoflurane (2%) produced concentrations of carbon monoxide of 600.0 +/- 10.0 ppm, 580.0 +/- 9.8 ppm, and 620.0 +/- 10.1 ppm, respectively. In contrast, concentrations of carbon monoxide were negligible (1-3 ppm) when the anhydrous new absorbent was exposed to the same anesthetics.     

Lack of degradation of sevoflurane by a new carbon dioxide absorbent in humans

BACKGROUND: Potent inhaled anesthetics degrade in the presence of the strong bases (sodium hydroxide or potassium hydroxide) in carbon dioxide (CO2) absorbents. A new absorbent, Amsorb (Armstrong Medical Ltd., Coleraine, Northern Ireland), does not employ these strong bases. This study compared the scavenging efficacy and compound A production of two commercially available absorbents (soda lime and barium hydroxide lime) with Amsorb in humans undergoing general anesthesia. METHODS: Four healthy volunteers were anesthetized on different days with desflurane, sevoflurane, enflurane, and isoflurane. End-tidal carbon dioxide (ETCO2) and anesthetic concentrations were measured with infrared spectroscopy; blood pressure and arterial blood gases were obtained from a radial artery catheter. Each anesthetic exposure lasted 3 h, during which the three fresh (normally hydrated) CO2 absorbents were used for a period of 1 h each. Anesthesia was administered with a fresh gas flow rate of 2 l/min of air:oxygen (50:50). Tidal volume was 10 ml/kg; respiratory rate was 8 breaths/min. Arterial blood gases were obtained at baseline and after each hour. Inspired concentrations of compound A were measured after 15, 30, and 60 min of anesthetic administration for each CO2 absorbent. RESULTS: Arterial blood gases and ETCO2 were not different among three CO2 absorbents. During sevoflurane, compound A formed with barium hydroxide lime and soda lime, but not with Amsorb. CONCLUSIONS: This new CO2 absorbent effectively scavenged CO2 and was not associated with compound A production.     

Carbon monoxide production from desflurane and six types of carbon dioxide absorbents in a patient model

BACKGROUND: Desflurane is known to produce high concentrations of carbon monoxide (CO) in desiccated sodalime or Baralyme (Allied Healthcare Products, St. Louis, MO). Desiccated absorbents without strong bases like potassium hydroxide or sodium hydroxide are reported to produce less or no CO at all. The purpose of this study is to compare the concentration of CO in an anesthesia circuit for desflurane with six different types of completely desiccated CO(2) absorbents with less strong bases than sodalime. METHODS: A patient model was simulated using a circle anesthesia system connected to an artificial lung. Completely desiccated CO(2) absorbent (950 g) was used in this system. A low flow anesthesia (500 ml min(-1)) was maintained using desflurane. For immediate quantification of CO production a portable gas chromatograph was used. RESULTS: Peak concentrations of CO were very high in Medisorb (Datex-Ohmeda, Hoevelaken, The Netherlands) and Spherasorb (Intersurgical, Uden, The Netherlands) (13317 and 9045 p.p.m., respectively). It was lower with Loflosorb (Intersurgical, Uden, The Netherlands) and Superia (Datex-Ohmeda, Hoevelaken, The Netherlands) (524 and 31 p.p.m., respectively). Amsorb (Armstrong, Coleraine, N. Ireland) and lithium hydroxide produced no CO at all. CONCLUSION: Medisorb and Spherasorb are capable of producing large concentrations of CO when desiccated. Loflosorb and Superia produce far less CO under the same conditions. Amsorb and lithium hydroxide should be considered safe when desiccated.     

Using amsorb to detect dehydration of CO2 absorbents containing strong base

BACKGROUND: Because Amsorb changes color when it dries, the authors investigated whether Amsorb combined with different strong base-containing carbon dioxide absorbents signals dehydration of such absorbents. METHODS: Five different carbon dioxide absorbents (1,330 g) each topped with 70 g of Amsorb were dried in an anesthesia machine (Modulus CD, Datex-Ohmeda, Madison, WI) with oxygen (Amsorb layer at the fresh gas inflow site). As soon as a color change was detected in the Amsorb, the authors tested the samples for a change in weight and carbon monoxide formation from 7.5% desflurane or 4% isoflurane. In a different experiment with the five absorbents, Amsorb was layered at the drying gas outflow site. In further experiments, the authors tested for a color change in Amsorb from drying and rehydrating and from drying with nitrogen. Finally, they dried a mixture of Amsorb and 1% NaOH and examined it for color change. RESULTS: In the experiments with Amsorb layered at the inflow, the Amsorb changed color when the water content of the samples was only marginally reduced (to a mean 13.6%), and no carbon monoxide formed. With Amsorb layered at the outflow, it changed color when the mean water content of the samples was reduced to 8.8%, and carbon monoxide formation was detected to varying degrees. The color change was independent of the drying gas and could be reversed by rehydrating. Adding NaOH to Amsorb prevented a color change. CONCLUSIONS: Dehydration in strong base-containing absorbents can reliably be indicated before carbon monoxide is formed when Amsorb is layered at the fresh gas inflow. The authors assume that the indicator dye in Amsorb changes color on drying because of the absence of strong base in this absorbent.     

Mass Spectrometry Provides Warning of Carbon Monoxide Exposure Via Trifluoromethane

Background: The chemical breakdown of isoflurane, enflurane, or desflurane in dried carbon dioxide absorbents may produce carbon monoxide. Some mass spectrometers can give false indications of enflurane during anesthetic breakdown.

Methods: During clinical anesthesia with isoflurane or desflurane, the presence of carbon monoxide in respiratory gas was confirmed when enflurane was inappropriately indicated by a clinical mass spectrometer that identified enflurane at mass to charge ratio = 69. In vitro, isoflurane, enflurane, or desflurane in oxygen was passed through dried carbon dioxide absorbents at 35, 45, and 55 degrees C. Gases were analyzed by gas chromatography and by mass spectrometry.

Results: Mass spectrometry identified several clinical incidents in which 30-410 ppm carbon monoxide was measured in respiratory gas. Trifluoromethane was produced during in vitro breakdown of isoflurane or desflurane. Although these inappropriately indicated quantities of "enflurane" correlated (r2 > 0.95) to carbon monoxide concentrations under a variety of conditions, this ratio varied with temperature, anesthetic agent, absorbent type, and water content.     

Lack of Degradation of Sevoflurane by a New Carbon Dioxide Absorbent in Humans

Background: Potent inhaled anesthetics degrade in the presence of the strong bases (sodium hydroxide or potassium hydroxide) in carbon dioxide (CO2) absorbents. A new absorbent, Amsorb (Armstrong Medical Ltd., Coleraine, Northern Ireland), does not employ these strong bases. This study compared the scavenging efficacy and compound A production of two commercially available absorbents (soda lime and barium hydroxide lime) with Amsorb in humans undergoing general anesthesia.

Methods: Four healthy volunteers were anesthetized on different days with desflurane, sevoflurane, enflurane, and isoflurane. End-tidal carbon dioxide (ETco2) and anesthetic concentrations were measured with infrared spectroscopy; blood pressure and arterial blood gases were obtained from a radial artery catheter. Each anesthetic exposure lasted 3 h, during which the three fresh (normally hydrated) CO2 absorbents were used for a period of 1 h each. Anesthesia was administered with a fresh gas flow rate of 2 l/min of air:oxygen (50:50). Tidal volume was 10 ml/kg; respiratory rate was 8 breaths/min. Arterial blood gases were obtained at baseline and after each hour. Inspired concentrations of compound A were measured after 15, 30, and 60 min of anesthetic administration for each CO2 absorbent.

Results: Arterial blood gases and ETco2 were not different among three CO2 absorbents. During sevoflurane, compound A formed with barium hydroxide lime and soda lime, but not with Amsorb.