Compound A concentrations during low-flow sevoflurane anesthesia correlate directly with the concentration of monovalent bases in carbon dioxide absorbents

Sevoflurane degrades to Compound A, which is nephrotoxic in rats. Potassium hydroxide (KOH) and sodium hydroxide (NaOH) are primary determinants of this degradation reaction. To address this, new carbon dioxide absorbents, such as Amsorb((R)) (A; Armstrong Medical, Coleraine, Northern Ireland), which contains neither KOH nor NaOH, Dr?gersorb 800 Plus((R)) (D; Dr?ger, Luebeck, Germany), and Medisorb((R)) (M; Datex-Ohmeda, Bromma, Sweden), which contain some NaOH (1% to 2%) and only trace amounts of KOH (0.003%), were recently developed. We compared Compound A concentrations using these three CO(2) absorbents during low-flow (1 L/min) sevoflurane anesthesia in surgical patients, with those using a conventional CO(2) absorbent, Dr?gersorb 800 (C). The mean Compound A concentrations +/- SD using C, A, D, and M were 18.7 +/- 2.5, 1.8 +/- 0.7, 13.3 +/- 3.5, and 11.2 +/- 2.6 ppm, respectively, with significant differences (P < 0.001; A versus C, A versus D, A versus M, C versus D, C versus M). Amsorb prevented the degradation of sevoflurane to Compound A, whereas Dr?gersorb 800 Plus and Medisorb decreased the degradation to Compound A. Implications: Sevoflurane degradation to Compound A is decreased by lowering the concentration of monovalent bases in the carbon dioxide absorbent (Dr?gersorb 800 Plus) [Dr?ger, Luebeck, Germany] and Medisorb) [Datex-Ohmeda, Bromma, Sweden]) and is virtually eliminated in the absence of these bases (Amsorb) [Armstrong Medical, Coleraine, Northern Ireland]).     

The type of carbon dioxide absorbent has no relation to the concentration of carbon monoxide in the breathing circuit during low-flow isoflurane anaesthesia in smoking and non-smoking subjects

The present study was designed to investigate the concentrations of carbon monoxide (CO) in the anaesthetic circuit and of arterial carboxyhaemoglobin (COHb) during low-flow isoflurane anaesthesia in smoking and non-smoking subjects using three kinds of cardon dioxide (CO2) absorbent. Thirty smoking and 30 non-smoking subjects were selected for this study, and these two groups were each divided into three groups according to the type of CO2 absorbent used (Wakolime A, Dr?gersorb Free, and Amsorb). Anaesthesia was maintained with 1.0% isoflurane and nitrous oxide (1. 0 l min(-1))/oxygen (1.0 l min(-1)). Concentrations of CO in the inspired breathing circuit and concentrations of arterial COHb were measured at 0, 1, 2, 3, and 4 hours after exposure to isoflurane. In the smoking groups there were no significant differences in CO concentrations in the circuit between the groups and the CO concentrations did not change significantly during the study period. There were also no significant differences in the arterial COHb values between the groups and the COHb concentrations remained constant. There was a significant linear correlation between the concentrations of CO and COHb (r=0.86, n =30, P<0.001). In the non-smoking groups all of the parameters remained constant at low levels that were independent of the type of CO2 absorbents tested. The major source for increased intraoperative CO exposure is related to the patient's smoking status, and the type of CO2 absorbent used has no relation to an increase in CO concentration in the breathing circuit.     

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.     

Carbon dioxide absorbents containing potassium hydroxide produce much larger concentrations of compound A from sevoflurane in clinical practice

We investigated the concentrations of degraded sevoflurane Compound A during low-flow anesthesia with four carbon dioxide (CO(2)) absorbents. The concentrations of Compound A, obtained from the inspiratory limb of the circle system, were measured by using a gas chromatograph. In the groups administered 2 L/min fresh gas flow with 1% sevoflurane, when the conventional CO(2) absorbents, Wakolime(TM) (Wako, Tokyo, Japan) and Dr?gersorb(TM) (Dr?ger, Lübeck, Germany), were used, the concentrations of Compound A increased steadily from a baseline to 14.3 ppm (mean) and 13.2 ppm, respectively, at 2 h after exposure to sevoflurane. In contrast, when the other novel types of absorbents containing decreased or no potassium hydroxide/sodium hydroxide, Medisorb(TM) (Datex-Ohmeda, Louisville, CO) and Amsorb(TM) (Armstrong, Coleraine, Northern Ireland), were used, Compound A remained at baseline (<2 ppm) throughout the study. In the groups administered 1 L/min fresh gas flow with 2% sevoflurane, Wakolime(TM) and Dr?gersorb(TM) produced much larger concentrations of Compound A (35.4 ppm and 34.2 ppm, respectively) at 2 h after exposure to sevoflurane. Medisorb(TM) showed measurable concentrations of Compound A (8.6 ppm at 2 h), but they were significantly smaller than those produced by the two conventional absorbents. In contrast, when Amsorb(TM) was used, Compound A concentrations remained at baseline throughout the study period. IMPLICATIONS: Carbon dioxide absorbents containing potassium hydroxide/sodium hydroxide produce much larger concentrations of Compound A from sevoflurane in clinical practice. An absorbent containing neither potassium hydroxide nor sodium hydroxide produces the smallest concentrations of Compound A.     

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.     

低流量七氟烷吸入麻醉时不同二氧化碳吸收剂环路中化合物A浓度的比较及其对患者肝肾功能的影响

Objective To investigate the influence of different carbon dioxide (CO2) absorbents (Dr(a)gersorb 800 plus , Sodasorb,Sodasorb LF) on the production of compound A during low-flow sevoflurane anesthesia.Methods Twenty-seven ASA Ⅰ or Ⅱ patients aged 20-64 years were randomly assigned to three groups according to different CO2 absorbents: Dr(a)gersorb 800 plus' group (group D, n = 10), Sodasorb group (group S, n = 10) and Sodasorb LF group (group LF, n = 7). Anesthesia was maintained with low-flow (500 ml/min) sevoflurane inhalation (with the end-tidal sevoflurane concentration of approximately 2% ). At 2 h after low-flow sevoflurane anesthesia, gas samples were taken from the expiratory limb of the circuit. Compound A was detected by gas chromatography. Serum alanine transaminase (ALT), aspartate aminotransferase (AST), bilirubin (BR), urea nitrogen (BUN) and creatinine (Cr) levels were measured before (T0 ) and 24 h after operation (T1).Results The three groups were comparable with respect to age, body weight and height. After 2 h of low-flow sevoflurane anesthesia, compound A concentrations in the expiratory limb of the circuit were 11.6 ± 5.8 (group D), 2.1 ± 1.9 (group S)and ＜ 0.1 ppm (group LF), respectively. There were no significant changes in the serum ALT, AST, BR, BUN and Cr levels at 24 h after operation as compared with the preoperative baseline values in the three groups.Conclusion After 2 h of low-flow (500 ml/min) sevoflurane anesthesia, compound A concentrations within the circuit with different CO2 absorbents ( Dr(a)gersorb 800 plus' , Sodasorb, Sodasorb LF) are less than 50 ppm, with the lowest in Sodasorb LF.However, they have no significant effects on hepatic or renal function.     

Mechanistic Aspects of Carbon Monoxide Formation from Volatile Anesthetics

Background: Desflurane, enflurane and isoflurane can be degraded to carbon monoxide (CO) by carbon dioxide absorbents, whereas sevoflurane and halothane form negligible amounts of CO. Carbon monoxide formation is greater with drier absorbent, and with barium hydroxide, than with soda lime. The mechanism, role of absorbent composition and water, and anesthetic structures determining CO formation are unknown. This investigation examined sequential steps in anesthetic degradation to CO.

Methods: Carbon monoxide formation from anesthetics and desiccated barium hydroxide lime or soda lime was determined at equimole from deuterium-substituted anesthetics was also quantified. Proton abstraction from anesthetics by strong base was determined by deuterium isotope exchange. A reactive chemical intermediate was trapped and identified by gas chromatography-mass spectrometry. The source of the oxygen in CO was identified by18 O incorporation.

Results: Desflurane, enflurane, and isoflurane (difluoromethylethyl ethers), but not sevoflurane (monofluoromethyl ether), methoxyflurane (methyl-ethyl ether), or halothane (alkane) were degraded to CO. The amount of CO formed was desflurane >or= to enflurane > isoflurane at equiMAC and enflurane > desflurane > isoflurane at equimole concentrations. Proton abstraction from the difluoromethoxy carbon was greater with potassium than with sodium hydroxide, but unmeasurable with barium hydroxide. Carbon monoxide formation was correlated (r = 0.95-1.00) with difluoromethoxy (enflurane > desflurane > isoflurane >or= to methoxyflurane = sevoflurane = 0) but not ethyl carbon proton abstraction. Deuterium substitution on enflurane and desflurane diminished CO formation. Chemical trapping showed formation of a difluorocarbene intermediate from enflurane and desflurane. Incorporation of H218 O in barium hydroxide lime resulted in C18 O formation from unlabeled enflurane and desflurane.     

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.     

Absorbents differ enormously in their capacity to produce compound A and carbon monoxide

Concern persists regarding the production of carbon monoxide (CO) and Compound A from the action of carbon dioxide (CO(2)) absorbents on desflurane and sevoflurane, respectively. We tested the capacity of eight different absorbents with various base compositions to produce CO and Compound A. We delivered desflurane through desiccated absorbents, and sevoflurane through desiccated and moist absorbents, then measured the resulting concentrations of CO from the former and Compound A from the latter. We also tested the CO(2) absorbing capacity of each absorbent by using a model anesthetic system. We found that the presence of potassium hydroxide (KOH) and sodium hydroxide (NaOH) increased the production of CO from calcium hydroxide (Ca[OH](2)) but did not consistently affect production of Compound A. However, the effect of KOH versus NaOH was not consistent in its impact on CO production. Furthermore, the effect of KOH versus NaOH versus Ca(OH)(2) was inconsistent in its impact on Compound A production. Two absorbents (Amsorb) [Armstrong Medica, Ltd, Coleraine, Northern Ireland], composed of Ca(OH)(2) plus 0.7% polyvinylpyrrolidine, calcium chloride, and calcium sulfate; and lithium hydroxide) produced dramatically lower concentrations of both CO and Compound A. Both produced minimal to no CO and only small concentrations of Compound A. The presence of polyvinylpyrrolidine, calcium chloride, and calcium sulfate in Amsorb appears to have suppressed the production of toxic products. All absorbents had an adequate CO(2) absorbing capacity greatest with lithium hydroxide. Implications: Production of the toxic substances, carbon monoxide and Compound A, from anesthetic degradation by carbon dioxide absorbents, might be minimized by the use of one of two specific absorbents, Amsorb (Armstrong Medica, Ltd., Coleraine, Northern Ireland) (calcium hydroxide which also includes 0.7% polyvinylpyrrolidine, calcium chloride, and calcium sulfate) or lithium hydroxide.     

Carbon monoxide production from desflurane, enflurane, halothane, isoflurane, and sevoflurane with dry soda lime.

BACKGROUND: Previous studies in which volatile anesthetics were exposed to small amounts of dry soda lime, generally controlled at or close to ambient temperatures, have demonstrated a large carbon monoxide (CO) production from desflurane and enflurane, less from isoflurane, and none from halothane and sevoflurane. However, there is a report of increased CO hemoglobin in children who had been induced with sevoflurane that had passed through dry soda lime. Because this clinical report appears to be inconsistent with existing laboratory work, the authors investigated CO production from volatile anesthetics more realistically simulating conditions in clinical absorbers. METHODS: Each agent, 2.5 or 5% in 2 l/min oxygen, were passed for 2 h through a Dr?ger absorber canister (bottom to top) filled with dried soda lime (Dr?gersorb 800). CO concentrations were continuously measured at the absorber outlet. CO production was calculated. Experiments were performed in ambient air (19-20 degrees C). The absorbent temperature was not controlled. RESULTS: Carbon monoxide production peaked initially and was highest with desflurane (507 +/- 70, 656 +/- 59 ml CO), followed by enflurane (460 +/- 41, 475 +/- 99 ml CO), isoflurane (176 +/- 2.8, 227 +/- 21 ml CO), sevoflurane (34 +/- 1, 104 +/- 4 ml CO), and halothane (22 +/- 3, 20 +/- 1 ml CO) (mean +/- SD at 2.5 and 5%, respectively). CONCLUSIONS: The absorbent temperature increased with all anesthetics but was highest for sevoflurane. The reported magnitude of CO formation from desflurane, enflurane, and isoflurane was confirmed. In contrast, a smaller but significant CO formation from sevoflurane was found, which may account for the CO hemoglobin concentrations reported in infants. With all agents, CO formation appears to be self-limited.     

Compound A and carbon monoxide production from sevoflurane and seven different types of carbon dioxide absorbent in a patient model

Background: The degradation of sevoflurane can lead to the production of compound A (CA) and carbon monoxide (CO) and an increase in temperature of the absorbent. CA is known to be nephrotoxic in rats. These reactions depend on the strong base and water contents of the carbon dioxide absorbent used. The purpose of this study was to measure the maximum amounts of CA and CO produced, and the temperature increase, for seven different carbon dioxide absorbents for sevoflurane containing different contents of strong bases. Methods: Seven absorbents [some free of strong bases (f)] were employed in hydrated (h) and completely desiccated (d) conditions in a patient model, using a circle anesthesia system connected to an artificial lung. Low‐flow anesthesia with an oxygen–nitrous oxide mixture was maintained using 0.8% sevoflurane. For the quantification of CA and CO, a portable gas chromatograph was used. The temperature was measured inside the absorbent. Results: In consecutive order of CA‐producing potency, Amsorb^®(f)(d), Drägersorb(h), Medisorb^®(h), lithium hydroxide(f)(d), Drägersorb(d), Medisorb^®(d), Spherasorb^®(h) and Spherasorb^®(d) produced small amounts of CA. Loflosorb^® and Superia^®, which are free of strong bases, did not produce any CA or CO in hydrated or desiccated conditions. Only desiccated Drägersorb^®, Medisorb^® and Spherasorb^® demonstrated small amounts of CO accompanied by a significant temperature increase. Conclusion: In this patient model, we demonstrated that different types of absorbent produced small amounts of CA and CO or none at all. No relationship could be established between temperature and CA concentration.     

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.     

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.     

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).     

The elimination of sodium and potassium hydroxides from desiccated soda lime diminishes degradation of desflurane to carbon monoxide and sevoflurane to compound A but does not compromise carbon dioxide absorption.

Normal (hydrated) soda lime absorbent (approximately 95% calcium hydroxide [Ca(OH)2], the remaining 5% consisting of a mixture of sodium hydroxide [NaOH] and potassium hydroxide [KOH]) degrades sevoflurane to the nephrotoxin Compound A, and desiccated soda lime degrades desflurane, enflurane, and isoflurane to carbon monoxide (CO). We examined whether the bases in soda lime differed in their capacities to contribute to the production of these toxic substances by degradation of the inhaled anesthetics. Our results indicate that NaOH and KOH are the primary determinants of degradation of desflurane to CO and modestly augment production of Compound A from sevoflurane. Elimination of these bases decreases CO production 10-fold and decreases average inspired Compound A by up to 41%. These salutary effects can be achieved with only slight decreases in the capacity of the remaining Ca(OH)2 to absorb carbon dioxide. IMPLICATIONS: The soda lime bases used to absorb carbon dioxide from anesthetic circuits can degrade inhaled anesthetics to compounds such as carbon monoxide and the nephrotoxin, Compound A. Elimination of the bases sodium hydroxide and potassium hydroxide decreases production of these noxious compounds without materially decreasing the capacity of the remaining base, Ca(OH)2, to absorb carbon dioxide.     

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.     

Absorption of carbon dioxide by dry soda lime decreases carbon monoxide formation from isoflurane degradation

This study was performed to determine whether the absorption of carbon dioxide (CO(2)) influences the formation of carbon monoxide (CO) from degradation of isoflurane in dry soda lime. Isoflurane (0. 5%), CO(2) (5%), a combination of the two in oxygen, and pure oxygen were separately passed through samples of 600 g of completely dried soda lime (duration of exposure, 60 min; flow rate, 5 L/min). Downstream of the soda lime, we measured concentrations of CO, isoflurane, and CO(2) as well as the gas temperature. CO(2) increased the peaks of CO concentration (842 +/- 81 vs 738 +/- 28 ppm) and shortened the rise time of CO to maximum values (12 +/- 2 vs 19 +/- 4 min). However, CO(2) inhibited total CO formation (99 +/- 10 vs 145 +/- 6 mL). At the same time, CO(2) absorption by the soda lime decreased in the presence of CO formation (from 21.4 +/- 0. 8 to 19.4 +/- 0.9 g). The temperature of the gases increased during the passage of both isoflurane and CO(2) (to 32.6 +/- 2.0 degrees C and 39.4 +/- 4.0 degrees C, respectively), but the largest increase (to 41.5 +/- 2.1 degrees C) was recorded when isoflurane and CO(2) simultaneously passed through the dry soda lime. We assume that the simultaneous reduction in CO formation and CO(2) absorption is caused by the competition for the alkali hydroxides present in most of soda lime brands. Implications: We determined, in vitro, that carbon monoxide (CO) formation from isoflurane by dry soda lime is reduced by carbon dioxide (CO(2)). We believe that the potential for injury from CO is less in the clinical milieu than suggested by data from experiments without CO(2) because of an interdependence between CO formation and CO(2) absorption.     

Adsorption of carbon dioxide gas

OBJECTIVES: To analyse the various methods for carbon dioxide absorption in anaesthesia, the available absorbents and their modes of use. DATA SOURCES: We searched the Medline and Internet databases for papers using the key words: carbon dioxide absorption, soda-lime, zeolite. We also had correspondence and contacts with soda lime manufacturers. STUDY SELECTION: All types of articles containing data on CO2 absorption. DATA EXTRACTION: The articles were analysed for the benefits and adverse effects of the various absorbents. DATA SYNTHESIS: Carbon dioxide absorption enables the use of low flow anaesthesia, and a decreased consumption of medical gases and halogenated anaesthetics, as well as reduced pollution. Chemical absorbents (soda-lime and barium hydroxide lime (Baralyme) may produce toxic compounds: carbon monoxide with all halogenated anaesthetics and compound A with sevoflurane. Simple measures against desiccation of the lime prevent carbon monoxide production. The toxicity of compound A, shown in the rat, has not been proven in clinical anaesthesia. Recent improvements in manufacture processes have decreased the powdering of lime. Moreover, filters inserted between the anaesthesia circuit and the patient abolish the risk for powder inhalation.     

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.     

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.