Carbon monoxide production from five volatile anesthetics in dry sodalime in a patient model: halothane and sevoflurane do produce carbon monoxide; temperature is a poor predictor of carbon monoxide production

Knowledge Gaps in Anesthetic Gas Utilization in a Large Academic Hospital System: A Multicenter Survey

Inhaled anesthetics account for a significant portion of the greenhouse gases generated by perioperative services within the healthcare systems. This cross-sectional study aimed to identify knowledge gaps and practice patterns related to carbon dioxide (CO₂) absorbents and intraoperative delivery of fresh gas flows (FGF) for future sustainability endeavors. Secondary aims focused on differences in these knowledge gaps based on the level of training. Surveys were distributed at five large academic medical centers. In addition to site-specific CO₂ absorbent use and practice volume and experience, respondents at each institution were queried about individual practice with FGF rates during anesthetic maintenance as well as the cost-effectiveness and environmental impact of different volatile anesthetics. Results were stratified and analyzed by the level of training. In total, 368 (44% physicians, 30% residents, and 26% nurse anesthetists) respondents completed surveys. Seventy-six percent of respondents were unaware or unsure about which type of CO₂ absorbent was in use at their hospital. Fifty-nine percent and 48% of respondents used sevoflurane and desflurane with FGF ≥1 L/min, respectively. Most participants identified desflurane as the agent with the greatest environmental impact (89.9%) and a greater proportion of anesthesiologists correctly identified isoflurane as a cost-effective anesthetic (78.3%, p=0.02). Knowledge gaps about in-use CO₂ absorbent and optimal FGF usage were identified within the anesthesia care team. Educational initiatives to increase awareness about the carbon emissions from anesthesia and newer CO₂ absorbents will impact the environmental and economic cost per case and align anesthesia providers toward healthcare decarbonization.

Determination of minimum alveolar concentration and cardiovascular effects of desflurane in positive-pressure ventilated sheep

OBJECTIVE To determine the minimum alveolar concentration of desflurane (MAC_DES) and effects on cardiovascular variables in positive-pressure ventilated sheep. ANIMALS 13 adult female sheep. PROCEDURES Anesthesia was induced with desflurane. After a 30-minute equilibration at an end-tidal concentration of desflurane (et_DES) of 10.5%, an electrical stimulus (5 Hz/ms and 50 mA) was applied for 1 minute or until gross purposeful movement occurred. The et_DES was then changed by 0.5% (modified up-down method), depending on whether a positive motor response had been elicited, and stimulation was repeated. The MAC_DES was the et_DES midway between a positive and negative response. After MAC_DES was determined, et_DES was increased to 1.3 and 1.6 MAC_DES. Animals were allowed to equilibrate for 15 minutes, and cardiovascular, blood gas, acid-base, and hematologic variables were measured. Times to induction of anesthesia, extubation, attainment of sternal position, and standing and duration of anesthesia were recorded. RESULTS Mean ± SD MAC_DES was 9.81 ± 0.79%. Times to intubation, extubation, and standing were 4.81 ± 2.21 minutes, 14.09 ± 4.05 minutes, and 32.4 ± 12.5 minutes, respectively. Duration of anesthesia was 226 ± 22 minutes. Heart rate increased significantly at induction of anesthesia but otherwise remained at preanesthetic rates. Arterial blood pressures progressively decreased with increasing et_DES; pressures increased slightly only in response to noxious stimulation. CONCLUSIONS AND CLINICAL RELEVANCE The MAC_DES determined here compared favorably with that determined for other sheep populations and indicated similar anesthetic potency as in other species. Desflurane caused dose-dependent arterial hypotension, which indicated the need for careful blood pressure monitoring.

Important role of calcium chloride in preventing carbon monoxide generation during desflurane degradation with alkali hydroxide-free carbon dioxide absorbents

We investigated whether calcium chloride (CaCl₂), a supplementary additive in carbon dioxide (CO₂) absorbents, could affect carbon monoxide (CO) production caused by desflurane degradation, using a Japanese alkali-free CO₂ absorbent Yabashi Lime^®-f (YL-f), its CaCl₂-free and 1% CaCl₂-added derivatives, and other commercially available alkali-free absorbents with or without CaCl₂. The reaction between 1 L of desflurane gas (3-10%) and 20 g of desiccated specimen was performed in an artificial closed-circuit anesthesia system for 3 min at 20 or 40 °C. The CO concentration was measured using a gas chromatograph equipped with a semiconductor sensor detector. The systems were validated by detecting dose-dependent CO production with an alkali hydroxide-containing CO₂ absorbent, Sodasorb^®. Compared with YL-f, the CaCl₂-free derivative caused the production of significantly more CO, while the 1% CaCl₂-added derivative caused the production of a comparable amount of CO. These phenomena were confirmed using commercially available absorbents AMSORB^® PLUS, an alkali-free absorbent with CaCl₂, and LoFloSorb™, an alkali-free absorbent without CaCl₂. These results suggest that CaCl₂ plays an important role in preventing CO generation caused by desflurane degradation with alkali hydroxide-free CO₂ absorbents like YL-f.

Anesthesia-Related Carbon Monoxide Exposure: Toxicity and Potential Therapy

Exposure to carbon monoxide (CO) during general anesthesia can result from volatile anesthetic degradation by carbon dioxide absorbents and rebreathing of endogenously produced CO. Although adherence to the Anesthesia Patient Safety Foundation guidelines reduces the risk of CO poisoning, patients may still experience subtoxic CO exposure during low-flow anesthesia. The consequences of such exposures are relatively unknown. In contrast to the widely recognized toxicity of high CO concentrations, the biologic activity of low concentration CO has recently been shown to be cytoprotective. As such, low-dose CO is being explored as a novel treatment for a variety of different diseases. Here, we review the concept of anesthesia-related CO exposure, identify the sources of production, detail the mechanisms of overt CO toxicity, highlight the cellular effects of low-dose CO, and discuss the potential therapeutic role for CO as part of routine anesthetic management.

Carbon monoxide and anesthesia-induced neurotoxicity

The majority of commonly used anesthetic agents induce widespread neuronal degeneration in the developing mammalian brain. Downstream, the process appears to involve activation of the oxidative stress-associated mitochondrial apoptosis pathway. Targeting this pathway could result in prevention of anesthetic toxicity in the immature brain. Carbon monoxide (CO) is a gas that exerts biological activity in the developing brain and low dose exposures have the potential to provide neuroprotection. In recent work, low concentration CO exposures limited isoflurane-induced neuronal apoptosis in a dose-dependent manner in newborn mice and modulated oxidative stress within forebrain mitochondria. Because infants and children are routinely exposed to low levels of CO during low-flow general endotracheal anesthesia, such anti-oxidant and pro-survival cellular effects are clinically relevant. Here we provide an overview of anesthesia-related CO exposure, discuss the biological activity of low concentration CO, detail the effects of CO in the brain during development, and provide evidence for CO-mediated inhibition of anesthesia-induced neurotoxicity.

Sevoflurane inside and outside the operating room

BACKGROUND

Sevoflurane is often presented as a near-perfect anaesthetic. After 10 years in the operating room, new uses are emerging outside.

OBJECTIVE

To remind readers of the principal characteristics of sevoflurane, to affirm its usefulness for day-case anaesthesia and to consider the recent new uses.

METHODS

The discussion of the physical properties, pharmacokinetics, metabolism, mechanisms of action and clinical effects is based on classic, essential papers. Recent literature concerning emerging utilizations of sevoflurane was analysed.

RESULTS

Sevoflurane presents many benefits with minimum inconvenience. It allows rapid inhalation induction, maintenance and rapid recovery. It has little toxicity and its haemodynamic and respiratory depressive effects are moderate and well tolerated. It is already widely use for sedation for magnetic resonance imaging in children. Its use in paediatric or adult intensive care could improve the management of pain and sedation.

Exhaled Carbon Monoxide Levels Change in Relation to Inspired Oxygen Fraction During General Anesthesia

BACKGROUND

Heme oxygenase produces carbon monoxide (CO) during the breakdown of heme molecules. A variety of stressors upregulate this enzymatic activity and can increase exhaled CO levels. Recently, exhaled CO levels have been reported to increase in critically ill patients and after anesthesia and surgery. To use this measurement during mechanical ventilation, it is important to clarify the effects of factors which interfere with exhaled CO levels. The fraction of inspired oxygen (Fio2) is often changed during artificial ventilation. To investigate the effect of changes of Fio2 on exhaled CO, we measured exhaled CO levels during general anesthesia.

METHODS

Thirty patients who underwent elective operations were enrolled in this study. Anesthesia was maintained with sevoflurane and fentanyl. All patients were tracheally intubated and ventilated with a non-rebreathing ventilator. Exhaled CO levels were measured in gas sampled from the expired limb of the respiration circuit using a CO monitor. The effects of sequential changes of Fio2 on exhaled CO levels, and the effects of long-term inhalation of Fio2 0.75 and Fio2 0.35 on exhaled CO levels and arterial carboxyhemoglobin concentrations were investigated.

RESULTS

Exhaled CO levels changed rapidly in response to changes of Fio2. Long-term inhalation of Fio2 0.75 initially increased and then gradually decreased exhaled CO to basal levels, concomitant with a decrease of arterial carboxyhemoglobin. Long-term inhalation of Fio2 0.35 did not elicit any significant change in the observed variables.

CONCLUSION

When monitoring exhaled CO levels during mechanical ventilation, it is important to consider the effects of Fio2.

Detection of carbon monoxide production as a result of the interaction of five volatile anesthetics and desiccated sodalime with an electrochemical carbon monoxide sensor in an anesthetic circuit compared to gas chromatography

OBJECTIVES

There is a continuing risk of production of toxic levels of carbon monoxide (CO) as a result of interaction of volatile anesthetics and desiccated strong base carbon dioxide absorbents like soda lime. The aim of this study is to establish the reliability of detection of CO levels by an electrochemical carbon monoxide sensor compared to gas chromatography.

METHODS

Completely desiccated sodalime was conducted through a circle anesthesia system connected to an artificial lung. For different rates of CO production, a low flow anesthesia with a oxygen/nitrous oxide mixture was maintained using five volatile anesthetics. For quantification of CO production, a portable gas chromatograph (GC) was connected to this setup, as well as a Bedfont EC40 electrochemical carbon monoxide sensor (ES) with a claimed reliable sensitivity of 0-200 parts per million (ppm) and a maximum detection range of more than 5500 ppm. To assess the agreement between the GC and ES measurements the intra class correlation coefficient (ICC) and the 95% limits of agreement were calculated. Bland and Altman scatterplots were made to visualize the difference between measurements.

RESULTS

For concentrations up to 200 ppm, no significant differences between the GC and ES mean CO measurements were found in the halothane experiments. However CO was not accurately measured at every moment during these experiments by the ES. For concentrations above 200 ppm the results of the two instruments differed significantly. The ES malfunctioned when exposed to sevoflurane and desiccated sodalime.

CONCLUSIONS

From these data we conclude that the ES can only be used as an indicator of CO production. When this sensor is used with sevoflurane and desiccated sodalime it is not capable of normal operation. The use of a strong base free carbon dioxide absorbent is therefore recommended.

Blood Concentrations of Enflurane Before, During, and After Hypothermic Cardiopulmonary Bypass

OBJECTIVE

The purpose of this study was to determine blood concentrations of enflurane delivered via a membrane oxygenator during hypothermic cardiopulmonary bypass (CPB) with changes in the input enflurane concentration and temperature and to characterize the pharmacokinetics of enflurane washout during and after CPB.

DESIGN

Blood enflurane concentrations were measured by gas chromatography before, during, and after CPB by using mean delivered enflurane concentrations of 0.5% v/v (group 1, n = 5), 0.8% (group 2, n = 7), and 1% (group 3, n = 14).

SETTING

The investigation was performed in a teaching hospital setting.

PARTICIPANTS

Twenty-six patients undergoing cardiac surgery requiring hypothermic CPB.

INTERVENTIONS

Variations in input enflurane concentration in different patients plus blood sampling from the arterial side of the circuit for enflurane assay.

MEASUREMENTS AND MAIN RESULTS

Median (25th and 75th percentiles) pre-CPB blood enflurane concentrations were 48 (25-50) mg/L, 52 (47-56) mg/L, and 115 (90-143) mg/L in groups 1 (0.5% v/v), 2 (0.8% v/v), and 3 (1% v/v), respectively. During hypothermia (28 degrees C) corresponding enflurane concentrations were 44 (31-53) mg/L, 56 (45-62) mg/L, and 145 (109-203) mg/L, respectively. For groups 1 and 2, there were no significant changes in blood enflurane compared with the corresponding pre-CPB value. However, for group 3, cooling resulted in a significant increase (p = 0.006) in blood enflurane. In all groups, enflurane concentrations after rewarming were similar to those in the pre-CPB period.

CONCLUSIONS

It is concluded that exposure to enflurane concentrations greater than 0.8% during CPB can result in high blood concentrations.

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.