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.     

Effects of temperature gradient correction of carbon dioxide absorbent on carbon dioxide absorption

Background. The effects of temperature gradients in CO₂ absorbentson water content and CO₂ absorption are not clear. We constructeda novel temperature gradient correction (TGC) canister, andinvestigated the effects of temperature gradient correctionon the water content and longevity (time to exhaustion) of CO₂absorbent using a simulated anaesthesia circuit. Methods. Experiments were divided into two groups accordingto the type of canister used: the TGC canister (n=6) or theconventional canister (n=6). One kilogram of fresh CO₂ absorbentwas placed into the canister. The anaesthetic ventilator wasconnected to a 3 litre bag and 300 ml min^–1 of CO₂ wasintroduced. Oxygen (500 ml min^–1) was used as fresh gas.The anaesthetic ventilator was set at a ventilatory frequencyof 12 bpm, and tidal volume was adjusted to 700 ml. Results. Before the experiment, the water content of the freshCO₂ absorbent in the conventional canister and TGC canisterwas 16.1 (0.9)% and 15.7 (1.1)%, respectively. After the experiment,the water content of CO₂ absorbent near the upper outer rimof the canister increased to 32.4 (0.7)% in the conventionalcanister, but increased to only 20.6 (1.3)% in the TGC canister(P<0.01). The longevity of CO₂ absorbent in the conventionalcanister and TGC canister was 434 (9) min and 563 (13) min (P<0.01). Conclusions. Temperature gradient correction prevented a localexcessive increase in water content and improved the longevityof CO₂ absorbent.      

Cerebrovascular carbon dioxide reactivity in children anaesthetized with sevoflurane

Background. To determine the effects of sevoflurane on cerebrovascularcarbon dioxide reactivity (CCO₂R), middle cerebral artery bloodflow velocity (CBFV) was measured at different levels of PE'_CO2by transcranial Doppler sonography in 16 ASA I or II children,aged 18 months to 7 yr undergoing elective urological surgery. Methods. Anaesthesia comprised 1.0 MAC sevoflurane and air in30% oxygen delivered through an Ayre’s T piece by intermittentpositive-pressure ventilation, and a caudal epidural block with0.25% bupivacaine 1.0 ml kg^–1 without epinephrine.PE'_CO2 was randomly adjusted to 25, 35, 45 and 55 mm Hg(3.3, 4.6, 5.9 and 7.2 kPa) with an exogenous source ofCO₂, while maintaining ventilation variables constant. Results. CBFV increased as PE'_CO2 increased from 25 to 35, andto 45 mm Hg (P<0.001), but did not increase significantlywith an increase in PE'_CO2 from 45 to 55 mm Hg. Meanheart rate and arterial pressure remained constant. Conclusion. CCO₂R is preserved in healthy children anaesthetizedwith 1.0 MAC sevoflurane. Br J Anaesth 2002; 88: 357–61     

Quantification of the degradation products of sevoflurane using four brands of CO2 absorbent in a standard anesthetic circuit

Purpose. CO₂ absorbents convert sevoflurane to fluoromethyl-2,2-difluoro-1-(trifluoromethyl) vinyl ether (compound A), whose toxicity in rats raises concern regarding the safety of sevoflurane in a low-flow system. The type of CO₂ absorbent is one of factors that affect compound A concentration in the anesthetic circuit. The aim of the present study was to investigate the concentration of compound A in an anesthetic model circuit following the use of different brands of soda lime and Baralyme. Methods. We measured the concentrations of compound A in four different brands of CO₂ absorbent using a low-flow (1 l·min⁻¹ fresh gas) model circuit in which 2% sevoflurane was circulated. Sodasorb II, Baralyme, Sofnolime and Wakolime-A were used as CO₂ absorbents. The concentration of compound A was measured hourly, and the temperature of the CO₂ absorbent was monitored. Results. The maximum concentration of compound A in the circuit was highest for Baralyme (25.5 ± 0.6 ppm) (mean ± SD), followed by Sodasorb II (18.9 ± 1.6 ppm), Wakolime-A (16.1 ± 0.7 ppm), and Sofnolime (15.8 ± 1.4 ppm). The maximum temperature was 50.8 ± 1.3°C for Baralyme, 48.8 ± 1.3°C for Wakolime-A, 47.0 ± 1.4°C for Sodasorb II, and 43.5 ± 3.9°C for Sofnolime. Conclusion. The relative concentrations of compound A in the low-flow circuit were Baralyme > Sodasorb II > Wakolime-A = Sofnolime. Received: August 27, 1999 / Accepted: January 13, 2000     

国内麻醉科医师应用二氧化碳吸收剂的现状调查

目的 调查国内麻醉科医师应用二氧化碳(CO2)吸收剂的现状,为统一CO2吸收剂更换的指标、限值和流程提供参考.方法 采用自主设计调查问卷开展网络问卷调查,主要内容包括麻醉科医师的基本情况、对CO2吸收剂应用理论的理解和CO2吸收剂临床应用的现状.结果 本次调查发放并回收有效问卷475份,其中49.9％来自华南地区,其他...     

The carbon dioxide rate of rise in awake apneic humans

Currently available estimates of the PaCO2 rate of rise in resting humans with resting lung volume were gathered during general anesthesia. The PaCO2 rate of rise during apnea in awake subjects was determined to acquire a value that may be more applicable to awake, ventilator-dependent, critically ill patients. Clinically, apnea occurs at functional residual capacity. With FiO2 = 1.0, 20 volunteers held their breaths at functional residual capacity for 0, 10, and 20 seconds, and then for as long as possible. They exhaled through an infrared CO2 analyzer after each interval to determine end-tidal pCO2. An estimate of the logarithmic PaCO2 rise during breath holding at functional residual capacity was 7 mmHg during the first 10 seconds (43 mmHg/minute), 2 mmHg during the next 10 seconds (13 mmHg/minute), and 6 mmHg/minute thereafter. In conclusion, PaCO2 increases more rapidly in awake apneic humans than earlier thought. The values reported herein probably are better for estimating duration of apnea in conscious, critically ill patients than are values obtained during general anesthesia.     

Cerebrovascular carbon dioxide reactivity during general anesthesia: a comparison between sevoflurane and isoflurane

We compared cerebrovascular carbon dioxide reactivity during the administration of sevoflurane and isoflurane anesthesia by measuring cerebral blood flow velocity (CBFV) as an indirect measurement of cerebral blood flow. Thirty patients, 20-70 yr old, undergoing lower abdominal surgery and without known cerebral or cardiovascular system disease, were randomly assigned to either sevoflurane or isoflurane treatment groups. Anesthesia was induced with thiopental 5 mg/kg IV and maintained with either sevoflurane or isoflurane in 67% nitrous oxide and oxygen. The CBFV and pulsatility index (PI) of the left middle cerebral artery were monitored with transcranial Doppler. The P(ETCO)2 was increased stepwise from 20 to 50 mm Hg by changing the respiratory rate with a constant tidal volume. At every 5-mm Hg stepwise change in P(ETCO)2, CBFV and PI were recorded. CBFV increased with increasing P(ETCO)2. CBFV was significantly smaller in the isoflurane group at P(ETCO)2 = 20-40 mm Hg than in the sevoflurane group. The rate of change of CBFV with changes in CO2 was larger in the isoflurane group than in the sevoflurane group. PI was constant over time and was not different between groups. In conclusion, hypocapnia-induced reduction of intracranial pressure might be more effective during the administration of isoflurane than sevoflurane. IMPLICATIONS: Changes in cerebral blood flow caused by the changes of carbon dioxide tension are greater during the administration of isoflurane anesthesia compared with sevoflurane anesthesia. Attempts to decrease intracranial pressure by decreasing carbon dioxide tension may be more successful during isoflurane than sevoflurane anesthesia administration.     

七氟醚对室间隔缺损患儿脑血管CO2反应性的影响

目的使用经颅多普勒超声监测脑血流,比较静脉麻醉药与七氟醚对室间隔缺损患儿脑血管二氧化碳反应性(cerebrovascular carbon dioxide reactivity,CO_2R)的影响。方法纳入3～12月龄患儿32例,随机分为两组。静脉组静注哌库溴铵0.2 mg/kg、咪达唑仑0.2 mg/kg及舒芬太尼1μg/kg,肌松满意后行气管插管,全凭静脉维持麻醉。吸入组持续吸入七氟醚1.5 MAC,静注哌库溴铵0.2 mg/kg,自主呼吸消失后行气管插管,七氟醚1.0 MAC维持麻醉。调整机械通气条件,使P_(ET)CO_2依次维持在30 mmHg(T_1)、35 mmHg(T_2)、40 mmHg(T_3)、45 mmHg(T_4),使用经颅多普勒超声测量右侧大脑中动脉血流平均速度(V_(MCA)),同时记录HR、心脏指数(CI)及BIS,计算CO_2R。结果T_1—T_4时两组V_(MCA)明显增加,HR明显减慢(P0.01);吸入组BIS值和CO_2R明显下降(P0.01或P0.05)。与静脉组比较,吸入组T_3和T_4时V_(MCA),T_1—T_4时HR、T_1—T_2时段CO_2R明显增高(P0.01或P0.05)。结论 1.0 MAC七氟醚麻醉下,在低P_(ET)CO_2范围内CO_2R更高,且高于使用静脉麻醉药物。     

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.     

Reactivity of sevoflurane with carbon dioxide absorbents--comparison of soda lime and Baralyme

The reactivity of sevoflurane with carbon dioxide absorbents, soda lime and Baralyme which are commercially available carbon dioxide absorbents, was studied. A closed circuit system which was made only for this investigation was set up without rubber. Sevoflurane 5% was circulated for 17 hours. The circulated gas was analyzed by gas chromatography (GC) and degradation products were identified by a gas chromatography-mass spectroscopy (GC-MS) as fluoromethyl 2-methoxy-2, 2-difluoro-1-(trifluoromethyl) ethyl ether, fluoromethyl 2-methoxy-2-fluoro-1-(trifluoromethyl) vinyl ether, and its isomer. These degradation products of sevoflurane from soda lime and Baralyme were the same substances. The rate of degradation by soda lime was 0.88% +/- 0.306, while that by Baralyme was 3.40% +/- 0.501. Baralyme decomposed sevoflurane about four times more than soda lime. There are two possible explanations for these results. One is the Baralyme contains more potassium hydroxide than soda lime. The other is that soda lime absorbs sevoflurane more because it contains more silica.     

七氟醚紧闭循环麻醉时二氧化碳吸收剂对环路中compound A浓度的影响

目的比较七氟醚紧闭循环麻醉时二氧化碳吸收剂对环路中compound A浓度的影响。方法 42例神经外科择期手术患者随机分为Sofnolime组(S组)和Sodasorb LF组(LF组),每组21例。采用七氟醚紧闭循环麻醉,呼气末七氟醚的浓度保持在2.7%～3.5%。监测呼吸环路内compound A的浓度;采集术前、术毕、术后24、72h的血样,检测血清丙氨酸氨基转移酶(ALT)、天门冬氨酸氨基转移酶(AST)、总胆红素(TBIL)、肌酐(Cr)和尿素氮(BUN)的水平。留取术前、术毕、术后24、48、72h的尿样,检测总蛋白(TP)、β2微球蛋白(β2-MG)和β-N-乙酰氨基葡萄糖苷酶(NAG)。结果 LF组未检测出compound A,S组compound A平均最高浓度为(37.6±10.2)ppm。两组ALT、AST、TBIL、Cr和BUN水平组间、组内比较差异均无统计学意义。两组尿TP/Cr、β2-MG/Cr在术后增加(P0.05),但各时间点组间比较差异均无统计学意义。两组尿NAG/Cr无变化,组间比较差异无统计学意义。结论七氟醚紧闭循环麻醉时,呼吸环路中compound A的最大浓度低于50ppm,对肝、肾功能无明显影响。     

二氧化碳吸收剂中水分对七氟醚分解反应的影响

目的　研究模拟紧闭反应器内干燥的二氧化碳 (CO2 )吸收剂及自身含水对七氟醚分解的影响。方法　在紧闭反应器 (1 6 0ml)内 ,分别装钠石灰、钡石灰、干燥钠石灰和干燥钡石灰 (各 2 5g)。在密闭状态下注入液态的七氟醚 4 0 0 μl,放入 5 0℃水浴内反应 6h ,分别在 5、1 5、30、4 5、6 0min、以后每 30分钟至 36 0分钟采样 ,用气相色谱法分析。测定七氟醚的分解产物。结果　钠石灰组出现复合物A、B ,在其他组七氟醚产生 5种分解产物。复合物A∶干燥钡石灰 >干燥钠石灰 >钡石灰和钠石灰组。干燥钡石灰组明显高于其他两组 (P <0 0 5 )。复合物B∶干燥钡石灰组 <钡石灰组 <干燥钠石灰组 (P <0 0 5 )。复合物C、D、E ,以干燥钡石灰组最为明显 (P <0 0 5 )。各组均未检测到CO。结论　在 5 0℃的紧闭反应器内 ,七氟醚与干燥的CO2 吸收剂反应剧烈 ,未产生CO ;国产钠石灰优于钡石灰 ,在紧闭容器内自身含水可以抑制分解反应     

Comparison of hemodynamic and respiratory effects of propofol and sevoflurane during carbon dioxide pneumoperitoneum in a swine model

The aim of this study was to compare intraoperative hemodynamic and respiratory parameters using propofol and sevoflurane during laparoscopic surgery in a porcine model. After induction of general anaesthesia in 16 pigs with fentanyl (0.005 mg kg(-1)) followed by propofol (6 mg Kg(-1)), it was maintained with fentanyl (0.01 mg kg(-1)h(-1)) and sevoflurane in O2 in group 1 (G1, n = 8) and fentanyl and propofol (12 mg kg(-1)h(-1)) in group 2 (G2, n = 8). The parameters monitored were heart rate, airway pressure (PAW), arterial and venous blood pressures and arterial blood gas analysis. The carbon dioxide pneumoperitoneum was maintained at 12 mmHg for 2 hours. Data were expressed as mean +/- standard deviation and were analysed using the Wilcoxon test (p < 0.05). G1 showed significantly higher PAW values than G2 at T60, T90 and T120. The heart rate values were significantly higher in G1 at T90 and T120. Middle arterial pressure was significantly lower in G1 than G2 at T30 and T60. The base deficit was significantly greater in G1 at T60, T90, T120 and Tpost. In this study propofol assured better hemodynamic and respiratory conditions than sevoflurane during laparoscopy in a porcine model.     

Oxygen uptake and carbon dioxide elimination during epinephrine-induced arrhythmias in humans

Key words  cardiac arrhythmias - oxygen uptake - carbon dioxide elimination