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.     

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.     

Low-flow anesthesia and reduced animal size increase carboxyhemoglobin levels in swine during desflurane and isoflurane breakdown in dried soda lime

After institutional approval, we studied the effect of animal size, anesthetic concentration, and fresh gas flow (FGF) rate on inspired carbon monoxide (CO) and carboxyhemoglobin (COHb) during anesthesia in swine, using soda lime previously dried to 1 +/- 0.1% water content. To ascertain the effect of anesthesia, eight adult pigs were anesthetized with either 1 minimum alveolar anesthetic concentration (MAC) desflurane or isoflurane and, to characterize the effect of the FGF rate, it was doubled in four pigs. To determine the effect of animal size, four small and four large pigs received 1 MAC desflurane or isoflurane, and to determine the effect of the anesthetic concentration, a group of four swine was exposed to 0.5 MAC. CO and COHb concentrations were larger with desflurane (5500 +/- 980 ppm and 57.90% +/- 0.50%, respectively) than with isoflurane (800 ppm and 17.8% +/- 2.14%, respectively), especially in the small animals. Increasing the FGF rate significantly reduced peak CO and COHb concentrations resulting from both anesthetics; however, when each anesthetic was reduced to 0.5 MAC, the concentrations obtained were similar. We conclude that CO intoxication is more severe with desflurane than with isoflurane, that small animals are at higher risk for CO poisoning, and that low FGF can increase COHb concentrations. IMPLICATIONS: The present study shows that the use of desflurane with desiccated carbon dioxide absorbents in pediatric anesthesia can produce a dangerous carbon dioxide intoxication, especially with low-flow anesthesia.     

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.     

Zur Temperaturentwicklung von Inhalationsanästhetika auf trockenem Atemkalk

There are some case reports about excessive heat production in the absorbent canister when sevoflurane or enflurane are washed into a circle containing dried soda lime. This observation was often made in the DRÄGER ISO 8 circle system with the gas inlet upstream of the soda lime canister with the gas-flow from bottom to top. Methods: The temperature in the center of an absorbent canister was measured 3.0?cm and 7.5?cm above the bottom. Soda lime (DRÄGERSORB 800) was dried in an O₂ stream for 2–3 days until there was no further loss in weight. 5 Vol% of desflurane, enflurane, isoflurane and sevoflurane in 2?l/min O₂ or 4 Vol% of halothane in 2.5?l/min O₂ were continuously fed into the canister. The concentration of the respective inhalational agents were measured after the soda lime canister using a DATEX Capnomac. Experiments were performed at ambient temperatures of 20–22?°C. Results: A considerable temperature increase was achieved with all anaesthetics. The highest temperatures were measured at the upper sensor with 56–58?°C for desflurane, 76–80?°C for enflurane and isoflurane, 84–88?°C for halothane and 126–130?°C for sevoflurane. IR-detection for some agents was considerably delayed or the time course indicated that other compounds might have formed which absorb at the wavelength monitored. Discussion: The high temperatures indicate the degradation rather than absorption of the volatile anaesthetics. CO is known to be degradation product of all currently used volatile anaesthetics except sevoflurane. Sevoflurane, however, produced the highest temperatures passing through dried soda lime. There are no reports about new specific breakdown products for sevoflurane on dried soda lime.     

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.     

Stability of sevoflurane in soda lime

Stability of halogenated volatile anesthetic is important because of the potential toxicity associated with the breakdown products. The authors enclosed 100 ml of gas containing sevoflurane with 100 g of soda lime in a 581-ml flask for periods up to 24 h. The rate of degradation of sevoflurane by soda lime was several-fold greater than previously reported, and the degradation was temperature-dependent. At 22 degrees C, soda lime degraded 6.5% of the sevoflurane per hour. The rate increased by 1.6% per hour per degree rise in temperature, reaching 57.4% degradation per hour at 54 degrees C. In contrast, isoflurane was not degraded by soda lime. Halothane did not degrade at 22 degrees C or 37 degrees C, but did degrade (2.2% per hour) at 54 degrees C.     

Stability of I-653 in soda lime

Stability is an important characteristic of a halogenated volatile anesthetic because breakdown may produce toxic compounds. The resistance to breakdown by soda lime of a new halogenated volatile anesthetic, I-653, was compared with the resistances found for halothane, isoflurane, and sevoflurane. The four anesthetics were injected concurrently into flasks containing 500 ml of gas and 100 g of soda lime maintained at 40, 60, and 80 degrees C. Four or five flasks were tested at each temperature. The rate of anesthetic degradation increased as temperature increased. Degradation was greatest with sevoflurane and least with I-653. At 80 degrees C, the rate of degradation per hr was 92.2 +/- 5% with sevoflurane; 16.0 +/- 1.6% with halothane; 13.1 +/- 3.7% with isoflurane; and 0.44 +/- 0.26% with I-653 (means +/- SD). The in vitro stability of I-653 suggests that it may strongly resist biodegradation.     

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.     

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.     

Dry soda lime markedly degrades sevoflurane during simulated inhalation induction

We have investigated gas composition during simulated inhalation induction with sevoflurane to elucidate possible mechanisms of incidental prolonged induction times and airway irritation. Using a circle system, 8% sevoflurane in oxygen 6 litre min-1 was washed into an absorbing canister filled with fresh soda lime containing 2.9% KOH (Draegersorb, 'D') or no KOH (< 0.01%, Sofnolime, 'S'). The absorbent was dried by oxygen 20,000 litre before every second experiment. Maximum soda lime temperatures attained after 4-6 min were 107 degrees C using dry D and 62 degrees C (61 degrees C) with dry S. Temperature did not increase with fresh soda lime. With dry soda lime, sevoflurane was not detected at the T-piece for 3 min and reached 6-7% within 6-10 min. After 1 min, we detected methanol and compound A (CH2F-O-C(= CF2) (CF3)). Total amounts over 20 min were: methanol 1125 mg (D dry), 334 mg (S dry) and < 5 mg (fresh soda lime); compound A 148 mg (D dry), 13 mg (S dry) and 3-8 mg (fresh); and fluoride 8.5 mg (D dry), 3.3 mg (S dry) and 1 mg (fresh). Formaldehyde was detected only with dry lime (D > 2.5 mg, S > 0.6 mg). In summary, the use of moist soda lime is of crucial importance during inhalation induction. With dry soda lime, the patient may inhale potentially toxic degradation products in significant amounts. Sevoflurane degradation is aggravated by a high KOH content of the lime. The observed airway irritation may be caused by formic acid, which is generated in isomolar concentrations with methanol (Cannizzaro reaction). The amount of compound A found with dry KOH-containing lime is unlikely to be noxious.      

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 Drager absorber canister (bottom to top) filled with dried soda lime (Dragersorb 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).     

High Carboxyhemoglobin Concentrations Occur in Swine during Desflurane Anesthesia in the Presence of Partially Dried Carbon Dioxide Absorbents

Background: Increased carboxyhemoglobin concentrations in patients receiving inhalation anesthetics (desflurane, enflurane, and isoflurane) have been reported. Recent in vitro studies suggest that dry carbon dioxide absorbents may allow the production of carbon monoxide.

Methods: The authors used high fresh oxygen flow (5 or 10 l/min) through a conventional circle breathing system of an anesthesia machine for 24 or 48 h to produce absorbent drying. Initial studies used 10 l/min oxygen flow with the reservoir bag removed or with the reservoir bag left in place during absorbent drying (this increases resistance to gas flow through the canister). A third investigation evaluated a lower flow rate (5 l/min) for absorbent drying. Water content of the absorbent and temperature were measured. Pigs received a 1.0 (human) minimum alveolar concentration desflurane anesthetic (7.5%) for 240 min using a 1 l/min oxygen flow rate with dried absorbent. Carbon monoxide concentrations in the circuit and carboxyhemoglobin concentrations in the pigs were measured.

Results: Pigs anesthetized with desflurane using Baralyme exposed to 48 h of 10 l/min oxygen flow (reservoir bag removed) had extremely high carboxyhemoglobin concentrations (more than 80%). Circuit carbon monoxide concentrations during desflurane anesthesia using absorbents exposed to 10 l/min oxygen flow (reservoir bag, 24 h) reached peak values of 8,800 to 13,600 ppm, depending on the absorbent used. Carboxyhemoglobin concentrations reached peak values of 73% (Baralyme) and 53% (soda lime). The water content of Baralyme decreased from 12.1 +/- 0.3% (mean +/- SEM) to as low as 1.9 +/- 0.4% at the bottom of the lower canister (oxygen flow direction during drying was from bottom to top). Absorbent temperatures in the bottom canister increased to temperatures as high as 50 [degree sign] Celsius. With the reservoir bag in place during drying (10 l/min oxygen flow), water removal from Baralyme was insufficient to produce carbon monoxide (lowest water content = 5.5%). Use of 5 l/min oxygen flow (reservoir bag removed) for 24 h did not reduce water content sufficiently to produce carbon dioxide with desflurane.     

The carbon dioxide absorption capacity of Amsorb is half that of soda lime.

A new CO(2) absorbent, Amsorb (A), which does not contain monovalent bases, is ideal because it does not degrade volatile anesthetics to either Compound A (from sevoflurane) or carbon monoxide (from desflurane, enflurane, or isoflurane). The CO(2) absorption capacity of A, however, has not been investigated under clinical conditions. In this study, we compared the longevity (time to exhaustion) and CO(2) absorption capacity (the volume of CO(2) absorbed before CO(2) rebreathing occurs) of A under low-flow anesthesia (1 L/min) with those of two soda lime absorbents-Medisorb (M) and Sodasorb (S)-by using a 750-mL ADU canister and a 1350-mL Aestiva 3000 canister. In the study with the ADU canister, the longevity of A was 213 +/- 71 min, significantly less than those of M (445 +/- 125; P < 0.01) and S (503 +/- 89; P < 0.001). The CO(2) absorption capacity (L/100 g absorbent) of A was 5.5 +/- 1.2, significantly less than those of M (10.7 +/- 1.7) and S (12.1 +/- 1.8; P < 0.001). In the study with the Aestiva 3000 canister, the longevity of A was 218 +/- 61 min, significantly less than those of M (538 +/- 136) and S (528 +/- 103; P < 0.001). The CO(2) absorption capacity (L/100 g absorbent) of A was 7.6 +/- 1.6, significantly less than those of M (14.4 +/- 1.8) and S (14.8 +/- 2.3; P < 0.001). These results indicate that the CO(2) absorption capacity of A is half that of M or S and that the difference in the CO(2) absorption capacity between A and M or S is almost constant, regardless of the canister design. Implications: The CO(2) absorption capacity of Amsorb is half that of Medisorb and Sodasorb under clinical low-flow (1 L/min) anesthesia with either a 750-mL Ohmeda ADU compact or a 1350-mL Ohmeda Aestiva 3000 canister.     

Absorption and degradation of sevoflurane and isoflurane in a conventional anesthetic circuit

Soda lime and Baralyme degrade sevoflurane, the rate of degradation being a direct function of temperature. We tested whether this degradation would impede the development of an anesthetizing concentration of sevoflurane (compared with isoflurane, a compound that is not degraded) in a circle-absorption system having an increased temperature consequent to (a) carbon dioxide production (200 mL/min) and absorption; and (b) a low inflow rate (70 mL/min). We also measured the temperatures reached in various parts of the absorption system when used in clinical practice, finding that peak temperatures usually reached 37 degrees - 46 degrees C when low inflow rates (500 mL/min) were applied. The tests in the model system demonstrated that soda lime and Baralyme absorbed both sevoflurane and isoflurane, and that both absorbants degraded sevoflurane but not isoflurane. Baralyme produced a fourfold greater degradation of sevoflurane vapor than did soda lime (0.66 mL/min compared with 0.17 mL/min). However, except for a slight delay at the start of anesthesia, neither absorption nor degradation should noticeably affect the requirement for anesthetic delivery in clinical practice, even in low-flow systems.     

Partly exhausted soda lime or soda lime with water added, inhibits the increase in compound A concentration in the circle system during low- flow sevoflurane anaesthesia

We performed low-flow sevoflurane anaesthesia at a flow rate of 1 litre min-1 in three groups (n = 8 each) using 600 g of fresh soda lime (control group), 600 g of soda lime with 60 ml of water added (water group) or 600 g of soda lime saturated with carbon dioxide, that is partly exhausted soda lime (carbon dioxide group). Degradation products in the system were measured hourly. Inspired and end-tidal carbon dioxide and sevoflurane concentrations, carbon dioxide and temperature of the soda lime were monitored. CF2 = C(CF3)-O-CH2F (compound A) was the only sevoflurane degradation product detected. The mean maximum concentration of compound A was significantly higher in the control group (mean 16.0 (SD 5.0) ppm) than in the water (1.4 (1.0) ppm) or carbon dioxide (4.0 (1.8) ppm) group, and the maximum temperature of the soda lime was significantly lower in the carbon dioxide group (30.7 (3.5) degrees C) than in the control (43.4 (1.8) degrees C) or water (40.8 (1.8) degrees C) group (P < 0.05). The use of partly exhausted soda lime or soda lime with water added reduced compound A concentrations in the system during low-flow sevoflurane anaesthesia.      

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.     

Decomposition of enflurane in soda lime

The stability of enflurane in soda lime was examined. A product of enflurane decomposition was detected after the reaction of enflurane with soda lime, but not in the absence of soda lime. The production of this compound, identified as 1-chloro-1,2-difluorovinyl difluoromethyl ether by gas chromatography-mass spectrometry, increased with time and temperature. The same decomposition product was produced by the reaction of enflurane with potassium, sodium, or calcium hydroxides, and it was also detected in the gas phase at a maximum concentration of 1.29 ppm at 420 min after 5% enflurane circulated with 200 ml/min carbon dioxide gas in a closed anesthesia circle system with a soda lime canister and a model lung. We concluded that enflurane was decomposed to 1-chloro-1,2-difluorovinyl difluoromethyl ether by soda lime.     

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.     

Soda lime temperatures during low-flow sevoflurane anaesthesia and differences in dead-space

BACKGROUND: Sevoflurane degrades during low-flow anaesthesia to compound A, and high carbon dioxide absorbent temperatures cause increased degradation. The purpose of this investigation was to determine if larger tidal volumes, without increasing alveolar ventilation, decrease the temperature in the carbon dioxide absorber during low- and minimal-flow sevoflurane anaesthesia. METHODS: Prospective, randomized study, including 45 patients (ASA 1-2), scheduled for elective general or urology surgery. The patients were randomly assigned to one of three treatments. Patients in group 1 (NDS) received fresh gas flow of 1 litre/min without using additional dead-space volumes. In group 2 (DS + 1.0), the patients received fresh gas flow of 1 litre/min using additional dead-space volumes, placed between the Y-piece and the HME, and patients in group 3 (DS + 0.5) received the same technique with a fresh gas flow of 0.5 litre/min. The soda lime temperatures, dead-space volumes, end-tidal carbon dioxide, sevoflurane concentrations, ventilation volumes and pressures, absorbent weight and ear temperatures were measured. RESULTS: The maximum temperature of the soda lime was 44.1 +/- 1.1 degrees C in the NDS group, 37.8 +/- 0.8 degrees C in the DS + 1.0 group and 38.5 +/- 2.7 degrees C in the DS + 0.5 group (P<0.0001). The dead-space volume between the Y-piece the tracheal tube was 164 +/- 69 ml in the DS + 1.0 group and 196 +/- 15 ml in the DS + 0.5 group (P<0.05). The ventilator pressure were higher in the DS groups compared with the NDS group (P<0.001). Soda lime weight increased in all groups. End-tidal carbon dioxide, sevoflurane concentrations and ear temperatures were similar between the groups. CONCLUSION: Increasing dead-space volumes can reduce carbon dioxide absorber temperature during low- and minimal-flow sevoflurane anaesthesia.