Absorbent Canister Research Articles

An unusual cause of intraoperative hypercarbia: Who's the boss:- Machine or The Man behind the machine?

Sir, Modern integrated anaesthesia workstations provide comprehensive facilities for patient ventilation, gas delivery and agent vapourisation, and allow seamless integration of patient monitoring and recording with anaesthesia information systems. American Society of Anesthesiologists (ASA) 2008 recommendations for pre-anaesthesia checkout advocate pre-use testing of anaesthesia machine before the conduct of anaesthesia.[1] Modern anaesthesia workstations including Dräger Perseus® A500 (Dräger, Germany) have integrated automatic self-testing to circumvent human errors and ensure administration of safe anaesthesia.[2] A 5 year-old boy with left hydrocele was posted for elective open herniotomy. Dräger Perseus® A500 anaesthesia workstation (Dräger, Germany) which had already passed an automated self-test was used to administer general anaesthesia with controlled ventilation using i-gel® supraglottic airway device (Intersurgical Limited, Wokingham) in-situ with ultrasound-guided left ilioinguinal and iliohypogastric nerve block. After obtaining valid informed parental consent, the child was pre-medicated with oral midazolam 0.5 mg/kg and wheeled into the operating room (OR). Standard ASA monitors were attached and incremental induction with sevoflurane (2-8%) was done. On achieving jaw relaxation and loss of purposeful movement, size 2 i-gel® was inserted and controlled ventilation using volume control auto-flow mode initiated. Anaesthesia was maintained using air-oxygen (50:50) and sevoflurane titrated to maintain age-adjusted minimum alveolar concentration (MAC) -1, with fresh gas flows (FGF) of 0.5 L/min. Following this, ultrasound-guided left-sided ilioinguinal and iliohypogastric nerve block using 0.15 ml/kg of 0.25% bupivacaine was given. A few minutes later, end-tidal carbon dioxide (ETCO2) and fraction of inspired carbon dioxide (FiCO2) values were observed to have risen from baseline values of 34 to 62 and 0 to 16 respectively. Switching over to the manual controlled mode of ventilation showed no increase in airway resistance (peak airway pressure <15 cm H2O) with bilaterally equal breath sounds. However, ETCO2 values continued to rise. At this point, we switched over to Jackson Rees (JR) circuit, to rule out the possibility of a faulty closed circuit. Simultaneously, a quick survey of the machine revealed an empty absorbent canister. The same was immediately refilled, following which ETCO2 values gradually normalised. Increased ETCO2 under anaesthesia is either due to decreased excretion or increased production [Table 1].[34] In accordance with our OR standard operating procedure (SOP), the canisters are refilled as required, which is usually on completion of the last case of the day. Visual inspection for exhausted carbon dioxide absorbent is a standard practice in the ASA checklist. We failed to identify the empty canister on visual inspection prior to beginning the case, which was a gross error irrespective of the high-end anaesthesia workstation. However, the machine passed the automated self-test and did not alert us regarding the same. Dräger Perseus® A500 workstation (Dräger, Germany) has two functional tools to support the safe conduct of low flow anaesthesia viz. the Low Flow Wizard and the Econometer.[5] Low Flow Wizard enables real-time analysis of data like patient uptake, breathing system leakage and the volume of carbon dioxide absorbed by the absorbent and compares the sum of these values with the actual FGF.[5] Econometer displays the FGF in a colour-coded bar graph based on filling of the manual breathing bag with each delivered breath, thus enabling a judicious and economical FGF set-up.[5] However, none of these tools are designed to identify the presence of an empty absorbent canister per se or indicate the time to complete exhaustion.Table 1: Causes of increased end-tidal carbon dioxide[4]We recommend that automated self-tests should include testing for presence of the absorbent to ensure patient safety. This assumes greater importance particularly in the context of increasing practice of paediatric low flow anaesthesia. Furthermore, an in-built alarm indicating the absorbent's functional capacity should be incorporated into the anaesthesia workstation to avert human errors and avoid hypercarbia. The advancements of the century may be leading us to an era of robotic anaesthesia and hi-tech workstations; nonetheless, “it is not the machine, but the man behind it that matters.” Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

Environmental and economic impact of using increased fresh gas flow to reduce carbon dioxide absorbent consumption in the absence of inhalational anaesthetics

BackgroundIncreasing fresh gas flow (FGF) to a circle breathing system reduces carbon dioxide (CO2) absorbent consumption. We assessed the environmental and economic impacts of this trade-off between gas flow and absorbent consumption when no inhalational anaesthetic agent is used. MethodsA test lung with fixed CO2 inflow was ventilated via a circle breathing system of an anaesthetic machine (Dräger Primus or GE Aisys CS2) using an FGF of 1, 2, 4, or 6 L min−1. We recorded the time to exhaustion of the CO2 absorbent canister, defined as when inspired partial pressure of CO2 exceeded 0.3 kPa. For each FGF, we calculated the economic costs and the environmental impact associated with the manufacture of the CO2 absorbent canister and the supply of medical air and oxygen. Environmental impact was measured in 100 yr global-warming potential, analysed using a life cycle assessment ‘cradle to grave’ approach. ResultsIncreasing FGF from 1 to 6 L min−1 was associated with up to 93% reduction in the combined running cost with minimal net change to the 100 yr global-warming potential. Most of the reduction in cost occurred between 4 and 6 L min−1. Removing the CO2 absorbent from the circle system, and further increasing FGF to control CO2 rebreathing, afforded minimal further economic benefit, but more than doubled the global-warming potential. ConclusionsIn the absence of inhalational anaesthetic agents, increasing FGF to 6 L min−1 reduces running cost compared with lower FGFs, with minimal impact to the environment.

Exhaustion by design

We would like to highlight a problem with the design of the carbon dioxide (CO2) absorber of a Maquet FLOW-i® Anaesthesia Delivery System machine (Maquet Cardiovascular, LLC, Wayne, NJ, USA) that results in elevated inspired CO2 levels. The FLOW-i anaesthesia machine is fitted with a disposable proprietary CO2 absorber canister containing enabling rapid change of an exhausted absorber. Sofnolime™ granules are coated with an indicator that changes from white to purple at exhaustion. During a recent case under general anaesthesia with mechanical ventilation through a circle circuit with a fresh gas flow of 2 l.min−1, the baseline inspired CO2 level was found to be 0.53 kPa, even though only approximately one-third of the Sofnolime granules were visibly exhausted (Fig. 2a). The absorber function was not bypassed and the inspiratory and expiratory valves were working correctly. Attempts to decrease the inspired CO2 levels by gentle knocking of the absorber canister to settle the granules were unsucessful. As the inspired CO2 level continued to rise, we changed the absorber canister and the inspired CO2 fell back to zero. Examination of the CO2 absorber canister revealed uneven exhaustion of the absorber granules preferentially towards the machine-facing aspect of the canister (Fig. 2b), where both the inflow and exit pipe channels are situated (Fig. 2c). We think that there may be preferential airflow between these, leading to the clinical problems and granule exhaustion pattern we found. We invite Maquet to comment on whether they are considering redesign of the inflow/exit channel positions relative to each other, or the incorporation of baffles, to overcome this problem.

Gas leak due to a damaged GE Disposable Multi Absorber Canister used with an EZchange Module following its reinstallation during anesthesia

Gas leak due to a damaged GE Disposable Multi Absorber Canister used with an EZchange Module following its reinstallation during anesthesia

Cases of carbon dioxide rebreathing without significant color change in the appearance of the carbon dioxide absorbent canisters

To the Editor: Three cases of carbon dioxide rebreathing without a significant color change in the appearance of the canisters were experienced during general anesthesia with the same model anesthesia machines; Aestiva/5 (Datex Ohmeda, Wisconsin, USA) with a fresh gas flow of 1–2 l/min. Carbon dioxide rebreathing was recognized because the inspiratory carbon dioxide baseline of the capnogram trace gradually rose. The inhalational carbon dioxide concentration decreased immediately after increasing the fresh gas flow, and rose again with decreasing the fresh gas flow. This indicates that carbon dioxide rebreathing was due to carbon dioxide accumulation in the semi-closed circuit system of the anesthesia machines. A color change in the appearance of the carbon dioxide absorbent was recognized only in the upper part of the canister (Fig. 1a). The top surface of the canister showed a significant color change limited to the middle part of it (Fig. 1b). The section image of the canister showed a significant columnar color change of the carbon dioxide absorbent along the full length of the center part of it (Fig. 1c). The observation of the canister bottom of Aestiva/5 revealed that only the center part of it had the mesh part for the exhaled gas, and the color change of the carbon dioxide absorbent seemed to accord with the mesh part of the bottom (Fig. 1d). As an experiment, when a transparent plastic partition wall was settled in the canister before filling with carbon dioxide absorbent, the columnar color change was no longer visible. This indicated that the flow of the exhaled gas was influenced by the wall in the canister. Considering these results, it is supposed that the structural characteristic of the canister bottom of the anesthesia machine; Aestiva/5, caused channeling and the inhomogeneity of the current of inhaled gas in the canister led to the columnar color change of the carbon dioxide absorbent. The role of the carbon dioxide absorbent canister becomes more important as the fresh gas flow quantity decreases. A technique of using a fresh gas flow of 1 l/min was reported first in 1952 [1]. The technique with the fresh gas flow less than 1 l/min subsequently became known as ‘‘low-flow anesthesia’’. Afterwards, a technique using a fresh gas flow of 500 ml/min was reported as ‘‘minimal flow anesthesia’’ [2]. These cases of carbon dioxide rebreathing without significant color change in the appearance of the canisters provide very important information not only for anesthesiologists, but also for all persons using anesthesia machines. When carbon dioxide rebreathing is recognized, carbon dioxide accumulation in the circuit system of the anesthesia machines should be suspected and exhaustion of the carbon dioxide absorbent should be immediately T. Yamamoto (&) Department of Pediatric Anesthesiology and Critical Care Medicine, Children’s Hospital Asklepios Klinik Sankt Augustin, Arnold-Janssen-Str. 29, 53757 Sankt Augustin, Germany e-mail: yamatomo270@hotmail.com; t.yamamoto@asklepios.com

Expiratory Limb Ventilation during Unique Failure of the Anesthesia Machine Breathing Circuit

Expiratory Limb Ventilation during Unique Failure of the Anesthesia Machine Breathing Circuit

High End-Expiratory Airway Pressures Caused by Internal Obstruction of the Draeger Apollo® Scavenger System That Is Not Detected by the Workstation Self-test and Visual Inspection

High End-Expiratory Airway Pressures Caused by Internal Obstruction of the Draeger Apollo® Scavenger System That Is Not Detected by the Workstation Self-test and Visual Inspection

Preparation of the Drager Fabius CE and Drager Zeus anaesthetic machines for patients susceptible to malignant hyperthermia

Malignant hyperthermia may follow exposure to trace quantities of inhalational anaesthetics. In susceptible patients, the complete avoidance of these triggers is advised when possible; however, failing this, it is essential to washout or purge the anaesthesia machine of residual inhalational anaesthetics. This study examined the washout profile of sevoflurane from the Drager Fabius CE and the Drager Zeus machines. The washout profile of sevoflurane was measured from the Fabius CE and Zeus anaesthesia machines following a standard period of exposure. The disposable tubing, CO2 absorber and other components of each machine were then replaced to examine their impact on the retention of sevoflurane. The effect of autoclaving the ventilator diaphragm and non-disposable ventilator tube or substituting for a new diaphragm and ventilation tube were examined in later parts of this study. University teaching hospital. Time taken to reach 5 parts per million of sevoflurane when machines underwent standard washout with fresh gas flush. The concentration of sevoflurane reached 5 parts per million in the Fabius CE machines after an mean (SD) of 140 min (46) at a fresh gas flow (FGF) of 10 l min(-1). The time taken for sevoflurane to reach 5 parts per million was significantly reduced when the ventilator diaphragm and non-disposable tube were replaced with either new or autoclaved components [14 or 22 min, respectively (P = 0.017, P = 0.031)]. The concentration of sevoflurane reached 5 parts per million in the Zeus machines after an mean (SD) of 85 min (6) at a fresh gas flow of 10 l min(-1). When the fresh gas flow was increased to 18 l min(-1) (the maximum allowable), the time to reach 5 parts per million was reduced to 16 min. When preparing the Fabius CE for the malignant hyperthermia susceptible patient, remove the vaporiser, replace the disposable tubing, the reservoir bag and the CO2 absorber. Replace the ventilator diaphragm and non-disposable ventilator tube with new or autoclaved components and flush the machine at 10 l min(-1) for at least 36 min. When preparing the Zeus, remove the vaporiser, replace the disposable tubing, the reservoir bag and CO2 absorber and flush at a fresh gas flow of 10 l min(-1) for at least 90 min. In both the Fabius and Zeus, continue at a fresh gas flow of 10 l min(-1) for the duration of the operation.

Setting standards for simulation in anesthesia: the role of safety criteria in accreditation standards

In this article, we describe a critical event which occurred in a simulation centre, and we also review possible safety issues for participants and staff involved in medical simulation training. The authors report an incident with the potential of harming trainees and staff which occurred during a full-scale simulation. The episode raised the question of training safety in simulation centres. In this instance, the computer program controlling the mannequin enabled a continuous and non-regulated outflow of carbon dioxide which led to an intense reaction in the soda lime canister. The absorbent canister became too hot to be touched (a temperature probe, later placed in the centre of the front canister, measured 53°C). All activities involving the mannequin and anesthesia machine were stopped immediately. Simulation in healthcare is a valuable educational tool to train for a variety of clinical encounters in a safe environment without harming a patient. Due to technological progress and the use of authentic equipment recreating near real environments, simulation training has become exceedingly realistic. The Society for Simulation in Healthcare (SSH) has published revised accreditation standards for simulation centres which incorporate training safety sub-criteria to address and manage. By highlighting recommendations of other high-risk industries on this issue, SSH proposes a possible approach to enhance safety in medical simulation.

Unusual Cause of Leak in Datex Aisys

To the Editor: We wish to report a serious incident encountered while using the Aisys Carestation (Datex-Ohmeda, GE Health Care, Finland, through GE India). While delivering anesthesia to a young male undergoing craniotomy, we noticed that the soda lime exhausted. The Aisys Reusable Multi Absorber canister was removed, refilled with fresh soda lime, and then replaced on the Carestation. The water trap was also drained at this time. After replacement of the canister on the Carestation, a large leak was noted in the circle breathing system. The canister was removed and refitted, but the leak persisted and it was impossible to ventilate the patient’s lungs manually or in ventilator mode, even with a high fresh gas flow. Changing the breathing system to a Bain coaxial circuit connected to the alternate common gas outlet of the Aisys eliminated the leak and allowed ventilation of the patient’s lungs. A subsequent thorough examination of the Carestation revealed a soda lime granule trapped in the flap valve of the water trap, rendering that valve incompetent (Fig. 1). Removal of the granule eliminated the leak when the Carestation was checked out with a circle system. It is unclear how the soda lime granule reached the drain valve of the water trap. One possible explanation is that some brands of soda lime have a high content of dust and flowing gas may have carried that dust through the breathing system, leading to deposits caking in the condenser reservoir. Despite following the manufacturer’s instructions for refilling absorber canisters and in particular replacing the filters, we have noticed clogged dust collecting in the condenser reservoir. Choosing a brand of soda lime with low dust content may prevent this mishap.Figure 1.: (a) Water trap of Aisys with granule stuck in rubber flap valve; (b) canister with water trap.As the anesthesia workstation evolves, it becomes more complicated and less intuitive for the user attempting to troubleshoot a malfunction. The circle breathing systems on many of the new anesthesia workstations have become more complex, and some of the components may be hidden or at least not obvious. The condenser and water trap are integral components of the Aisys circle system. Education and in service training when using a new anesthesia workstation will enable early recognition of system failure. Prashant Kummar, MD Grace Korula, MD, DA Sathish Kumar, MD, DA P. A. Saravanan, MD, DA Christian Medical College and Hospital Vellore, Tamil Nadu, India [email protected]

Inadvertent disconnection of the carbon dioxide absorber canister of a Blease Frontline anaesthetic machine

We wish to report the recurrent, accidental disengagement of the lever securing the carbon dioxide absorbing canister of a Blease Frontline 560 plus® anaesthetic machine (Blease UK, Chesham, UK) resulting in a leak. Appropriate immediate action and identification of the problem prevented any harm to the patient. On close examination it was found that minimal force was sufficient to disengage the lever from its locked position. We would like to emphasise that the design of the canister makes it very easy for the lever (Fig. 3) to be accidentally knocked from its normal position (securing the absorber canister). The slow, controlled way in which the lever moves from the locked to the fully open position means that the leak may initially be small (not triggering any alarms), before creating a larger leak some time after the lever was knocked – making the detection of the source of the leak more difficult. The locking lever for the carbon dioxide absorber canister assembly of the Blease Frontline 560 plus anaesthetic machine. There are a number of potential solutions to this problem, ranging from a screw type securing mechanism, to a catch securing the lever preventing its inadvertent displacement and subsequent release. However, the most elegant and reliable solutions tend to be the simplest, and a physical guard placed over the lever while in its locked position would prevent any inadvertent displacement. We believe that this should be combined with clear, unambiguous labelling indicating the locked and unlocked position of the lever; a notable absence from the current design. This incident has been reported to the MHRA.

Malfunction of the New Aisys® Anesthesia Machine

We recently replaced most of our anesthesia machine fleet with the newly available Aisys® Carestation (GE Healthcare, Waukesha, WI). In the course of using these second-generation electronic machines, we have encountered two clinically significant problems that have each occurred on more than one unit.The first problem relates to the EZchange absorber bracket. This component should create a gas-tight seal between the anesthesia machine and absorbent canister. It is also designed to automatically seal the circuit when the absorbent canister is removed, as during absorbent canister changes. We found instances in which a significant leak existed both with and without the canister in place (with one case even requiring patient ventilation with a manual resuscitator to achieve adequate tidal volumes.) The problem was localized to the interconnect valve between the canister and EZchange (fig. 1). The problem seemed to be intermittent and, in some instances, was not detected or appreciated during automated checkout. The exact cause of failure of this connection is still unclear and, according to a company representative, is under investigation by the manufacturer. A solution has been to remove the EZchange assembly and mount the canister directly to the machine.The second problem involves the built-in spirometry sensors. When this problem occurred, warning messages (e.g. , tidal volume not achieved, check flow sensors, system leak) appeared, and the calculated expired tidal volumes were well below those actually delivered. Further analysis revealed that excess moisture in the breathing system (suggested by the condensation seen in the expiratory valve assembly) may lead to such malfunction of the sensors, which are located near the inspiratory and expiratory valves. A solution to this has been to switch to the backup D-Lite spirometry module included on the machines, which uses separate pressure tubing and seems to be less vulnerable to the effects of moisture in the circuit. (The machine will still give an alarm indicating that the volume sensors disagree, but the flow volume loops will appear normal.) We are also adding expiratory limb filters to our circuits to help to protect the sensors.Users should be aware of these potential problems and solutions until the manufacturer offers definitive solutions.*Mount Sinai School of Medicine, New York, New York. david.wax@mssm.edu

Malfunction of the New Aisys® Anesthesia Machine

GE Healthcare, Life Support Solutions, Madison, Wisconsin. michael.mitton@med.ge.comGE Healthcare would like to thank Anesthesiology for the opportunity to respond to the Letter to the Editor by Drs. Wax and Neustein.In their letter, the authors discuss two issues pertaining to the Aisys® machine. The first concerns the function of the EZchange absorber manifold, the second concerns the effect of water on the inspiratory and expiratory flow sensors.We have been able to reproduce the leak described by the authors. The breathing circuit leaks experienced at Mt. Sinai (New York, NY) were the result of an inadequate seal between the manifold and the absorber canister; small frays on the drain port of the disposable absorber canister produced the inadequate seal. This issue may be identified during the Aisys® automatic system checkout procedure; we have verified this with affected canisters. Of course, if the canister is changed in the middle of a case, there would be no additional system checkout and a leak may result.We have not been able to reproduce a system leak when the EZchange manifold is in place without a disposable canister because the leak exists where the manifold and the disposable absorber canister connect, as suggested by the authors.We have taken a two-pronged approach to resolving this issue. First, we are addressing the root cause, the disposable absorber canister, by working with the third-party supplier to remedy the issue with the drain port flashing. Second, we are currently revising the drain seal on the EZchange module so this flashing, even if unchanged, will not affect the seal between the canister and the manifold.With respect to the moisture and flow sensor issue, the root cause was most likely the impact that moisture or water may have on the function of the flow sensor. Our flow sensors are a vital component of the Aisys® ventilator. Like anesthesia practice, these sensors have undergone extensive evolution since they were first introduced. As clinical anesthesia has moved toward lower and lower fresh gas flows, the impact of the increased humidity has necessitated a redesign of the basic flow sensor. At the time of the events, Mt. Sinai was using an earlier version of the flow sensor. The current flow sensor incorporates an offset in the area of the flow sensor flap that helps to overcome the issue associated with high moisture or water. This version can be readily recognized by the presence of grooves on the bezel of the flow sensor closest to the patient.The final issue the authors describe is the use of the D-Lite sensor to obtain spirometry instead of using the flow sensors. The D-Lite sensor and the direct patient monitoring of respiratory mechanics the use of the D-Lite may provide are a design feature of the Aisys®. Using the D-Lite will not resolve alarm issues produced by the inspiratory and expiratory flow sensor. The authors’ description of the ventilator alarms suggests that the old-style flow sensors they were using at the time may have either had some moisture on the inspiratory sensor or may not have been calibrated.The flow sensors should be calibrated daily simply by removing the flow sensor module, waiting for the “no insp flow sensor” and “no expiratory flow sensor” messages to appear, and then reattaching the flow sensor module. The alarm messages reported by Mt. Sinai would not have occurred with calibrated offset flow sensors.GE Healthcare commends the authors for their insightful and accurate Letter to the Editor.GE Healthcare, Life Support Solutions, Madison, Wisconsin. michael.mitton@med.ge.com

A Novel Leak from an Unfamiliar Component

To the Editor: New anesthesia machines may contain unfamiliar components, which may be difficult to troubleshoot (1). We report four cases of a novel type of leak in the Drager Fabius GS. Case 1. Preoperative checkout of the anesthesia machine, including the automated leak/compliance test, was performed and no defect was found. After endotracheal intubation, it was impossible to ventilate because of a large leak from a broken flow sensor. Case 2. During service between cases, an anesthesia technician bumped the absorbent canister into the sensor's electrical connector and fractured it, unbeknownst to the anesthesia team. Cases 3 and 4. An unexplained leak during ventilation after induction of general anesthesia was traced to a broken sensor. The mechanism of injury was not identified. The flow sensor consists of a plastic tube with a side port containing electronic components. A cable runs from the side port to the back of the machine (Fig. 1). Apparently, in case 1, the patient'sstretcher bumped an IV pole against the electrical connector and the sensor's side port was dislodged (Fig. 2).Figure 1.: View of the underside of the “Compact Breathing System.” The arrow indicates the position of the Flow Sensor.Figure 2.: The Flow Sensor and its electrical connector. The arrow indicates the site of the leak, an inappropriate dislodgement of the side port from the body of the sensor.The flow sensor's rigid electrical connector hangs near the exterior edge of the “Compact Breathing System.” Damage can occur when lateral force on the connector exerts torque upon the sensor's side arm. Personnel using the Fabius GS should be aware of this potential hazard and protect this vulnerable connection. The authors recommend performing a quick leak test by manually occluding the end of the circuit with the APL valve closed immediately before every induction, as this would have identified the defect in all of these cases. Drager Medical and the United States Food and Drug Administration have been contacted, and our department was informed that redesign is under consideration. Stephen O. Bader, MD Kirti K. Doshi, MD Zvi Grunwald, MD Department of Anesthesiology Thomas Jefferson University Hospital Philadelphia, PA [email protected]

Temperatures in Soda Lime During Degradation of Desflurane, Isoflurane, and Sevoflurane by Desiccated Soda Lime

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

Carbon Monoxide Production from Desflurane, Enflurane, Halothane, Isoflurane, and Sevoflurane with Dry Soda Lime

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. Each agent, 2.5 or 5% in 2 l/min oxygen, were passed for 2 h through a Dräger absorber canister (bottom to top) filled with dried soda lime (Drägersorb 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. 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). 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.

Carbon Monoxide Formation from Volatile Anesthetics Measured during Simulated Clinical Conditions

Carbon Monoxide Formation from Volatile Anesthetics Measured during Simulated Clinical Conditions. Wissing et al. (page 1205)Recent clinical reports of increased carbon monoxide (CO) hemoglobin concentrations in children anesthetized with sevoflurane that had passed through dry soda lime seem to contradict the laboratory experience with this anesthetic. To examine discrepancies between laboratory investigations and clinical experiences, Wissing et al. designed an experiment to measure CO formation from five different volatile anesthetics passed through an absorber system that permitted temperature changes.Experiments were conducted in triplicate. Either 2.5% or 5% of five inhalational anesthetics (desflurane, enflurane, isoflurane, halothane, and sevoflurane) were passed for 2 h through an absorber canister filled with dried soda lime. Baseline CO production was first determined using dry soda lime and a flow of 2 l/min O2with no volatile anesthetic and using fresh wet soda lime and a flow of 2 l/min with 5% anesthetic. CO concentrations were continuously measured at the absorber outlet. Additional experiments were conducted to confirm the sevoflurane results because the magnitude of CO production was unexpected and because of the potential of various breakdown products. CO was detected with all anesthetics passed through dry soda lime, but the time course and rate of CO production and the time course of temperature changes differed between the agents. Measurable amounts of CO were found immediately after desflurane, enflurane, or isoflurane came in contact with the soda lime; with sevoflurane, there was a time delay between contact and CO production. CO production peaked initially and was highest with desflurane, followed by enflurane, isoflurane, sevoflurane, and halothane. The temperature of the absorbent increased with all anesthetics, but was highest for sevoflurane. As a result of these experiments, the researchers caution that although CO production is clearly higher than with other agents, some CO—in possibly relevant amounts—is produced by sevoflurane. Adequate precautions should be taken to ensure that soda lime in absorbers does not become desiccated.

Heat production from reaction of inhalation anesthetics with dry soda lime

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 DRAGER ISO 8 circle system with the gas inlet upstream of the soda lime canister with the gas-flow from bottom to top. The temperature in the center of an absorbent canister was measured 3.0 cm and 7.5 cm above the bottom. Soda lime (DRAGERSORB 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 1/min O2 or 4 Vol% of halothane in 2.5 I/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 degrees C. A considerable temperature increase was achieved with all anaesthetics. The highest temperatures were measured at the upper sensor with 56-58 degrees C for desflurane, 76-80 degrees C for enflurane and isoflurane, 84-88 degrees C for halothane and 126-130 degrees 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. 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.

Food and Drug Administration Guidelines for Machine Checkout Need Modification

We would like to thank Drs. Dunn and Mushlin for taking the time to read our case report [1]. They appear to have missed the major problem we encountered, which was incomplete and possibly variable obstruction of the breathing circuit. Complete obstruction is easily detected by the current Food and Drug Administration checkout guidelines. As stated in our report, the most rational approach to correcting this problem is to redesign the packaging of the CO2 absorber canister so that a wrapped canister is either physically impossible to place into the absorber or so that it looks completely different from a canister with the wrapping removed. We apologize for puzzling Drs. Dunn and Mushlin with our preoxygenation methods. It is our standard practice to have all adult patients breathe 100% oxygen immediately upon entering the operating room while other preparations for induction are being performed. This is not meant to be a formal "denitrogenation" procedure, and we do not insist on a tight mask seal. In contrast, we certainly do require an appropriate mask seal in patients having a rapid sequence induction or significant respiratory disease. It is possible that even with a tight mask fit our patient may not have voiced any complaints due to the incomplete nature of the breathing circuit obstruction and/or the administration of preoperative sedation. The suggestion that a new Food and Drug Administration requirement for machine checkout require observation of CO2 waveforms and reservoir bag excursions generated by the patient before induction is interesting. While this may be a useful practice in many adults, difficulties would certainly arise in performing these procedures in uncooperative children or critically ill patients who have received muscle relaxants before entering the operating room. Although we agree that these procedures should be performed when possible, they should be considered primarily ancillary tests. With the busy operating room schedules present in most hospitals today, any procedures performed just before induction have the potential of being accomplished in a hurried and less than optimal manner. We thus believe that it is most prudent to ensure that the anesthesia apparatus is completely checked before the patient is brought into the operating room. To this end, an experienced anesthesiologist breathing through a circuit should be able to detect a faulty circuit by observing, among other things, the movements of the reservoir bag and the CO2 waveform. Peter H. Norman, MD, FRCPC M. Denise Daley, MD, FRCPC Department of Anesthesiology; Baylor College of Medicine; Houston, TX 77030

Obstruction Due to Retained Carbon Dioxide Absorber Canister Wrapping

Obstruction Due to Retained Carbon Dioxide Absorber Canister Wrapping