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Activated Charcoal Effectively Removes Inhaled Anesthetics from Modern Anesthesia Machines

Birgenheier, Nathaniel, MD; Stoker, Robert, BA; Westenskow, Dwayne, PhD; Orr, Joseph, PhD

doi: 10.1213/ANE.0b013e318213fad7
Patient Safety: Technical Communication
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INTRODUCTION: If a malignant hyperthermia–susceptible patient is to receive an anesthetic, an anesthesia machine that has been used previously to deliver volatile anesthetics should be flushed with a high fresh gas flow. Conflicting results from previous studies recommend flush times that vary from 10 to 104 minutes. In a previously proposed alternative decontamination technique, other investigators placed an activated charcoal filter in the inspired limb of the breathing circuit.

METHODS: We placed activated charcoal filters on both the inspired and expired limbs of several contaminated anesthesia machines and measured the time needed to flush the machine so that the delivered concentrations of isoflurane, sevoflurane, and desflurane would be <5 parts per million (ppm). We next simulated the case for which malignant hyperthermia is diagnosed 90 minutes after induction of anesthesia and measured how well activated charcoal filters limit further exposure.

RESULTS: Activated charcoal filters decrease the concentration of volatile anesthetic delivered by a contaminated machine to an acceptable level in <2 minutes. The concentrations remained well below 5 ppm for at least 60 minutes. When malignant hyperthermia is diagnosed after induction of anesthesia, we found that with charcoal filters in place, the current anesthesia machine may be used for at least 67 minutes before the inspired concentration exceeds 5 ppm.

CONCLUSIONS: Activated charcoal filters provide an alternative approach to the 10 to 104 minutes of flushing that are normally required to prepare a machine that has been used previously to deliver a volatile anesthetic.

Published ahead of print May 4, 2011

From the Department of Anesthesiology, University of Utah, Salt Lake City, Utah.

Funding: Departments of Anesthesiology and Bioengineering.

Conflict of Interest: See Disclosures at the end of the article.

Reprints will not be available from the authors.

Address correspondence to Nathaniel Birgenheier, MD, University of Utah, 30 N. 1900 E., Room 3C-444, Salt Lake City, UT 84132. Address e-mail to nathaniel.birgenheier@hsc.utah.edu.

Accepted February 1, 2011

Published ahead of print May 4, 2011

Malignant hyperthermia is a life-threatening complication of general anesthesia, triggered by halogenated volatile anesthetics in susceptible patients.15 From 2000 to 2005, the number of cases increased from 372 to 521 per year in the United States.6 The incidence is between 1:5000 and 1:100,000.7,8 Since the advent of dantrolene, mortality has decreased from 70%–80% to 6.5%–16.9%.3

If a susceptible patient is to receive an anesthetic, it is recommended that a “clean” dedicated anesthesia machine be used. The machine needs to be one from which the vaporizers can be switched off or removed and all parts of the machine that absorb significant amounts of volatile anesthetics can be exchanged. If a dedicated machine is not available, a machine that has been used previously to deliver volatile anesthetics can be flushed with a high-flow fresh gas for 10 to 104 minutes so that an acceptable concentration of <5 parts per million (ppm) is reached.2,5,8 Machines of the current generation must be flushed longer because of their internal elastomeric and plastic parts that capture and release volatile anesthetic molecules.9 In a previously proposed alternative decontamination technique the authors placed an activated charcoal filter in the inspired limb of the breathing circuit. Using a Fabius anesthesia machine, the authors found that the inspired sevoflurane concentration decreased to <5 ppm after a 10-minute flush when a charcoal filter was used.8

We placed activated charcoal filters on both the inspired and expired limbs of several contaminated anesthesia machines and measured the time needed to flush the machine so that the delivered concentrations of isoflurane, sevoflurane, and desflurane would be <5 ppm. We next simulated the case during which malignant hyperthermia is diagnosed 90 minutes after induction of anesthesia and measured how well activated charcoal filters limit further exposure.

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METHODS

To measure how effectively activated charcoal decontaminates current-generation anesthesia machines, we first contaminated an Apollo anesthesia machine (Draeger, Luebeck, Germany) by using the machine to deliver 1.5% isoflurane to a test lung for 90 minutes (Single Lung TTL, Model 4600, Michigan Instruments, Grand Rapids, MI). We set the oxygen flow to 3 L/min and ventilated the test lung through a plastic breathing circuit (Anesthesia Circ Extendaflex-LF 90′′ parallel Wye, Medline Industries, Mundelein, IL) with a tidal volume of 600 mL and a respiratory rate of 10 breaths/min using an inspired to expired time ratio of 1:2. To enhance the fidelity of the simulation, we added expired CO2 (200 mL/min) and humidity (ConchaTherm III, Hudson RCI, Durham, NC) to the expiratory limb.

We placed Vapor-Clean activated charcoal filters (Dynasthetics LLC, Salt Lake City, UT) on both the inspired and expired limbs of the contaminated anesthesia machine, as shown in Figure 1. Each filter contained 50 cc of granular activated carbon between spun-bond polypropylene filter mesh. We replaced the breathing circuit and rebreathing bag, turned off the vaporizer, and set the fresh oxygen flow to 10 L/min. We measured the concentration of the volatile anesthetic delivered to the test lung every 45 seconds by connecting the sampling wand of a Miran ambient air analyzer (SapphIRe XL, Thermo-Fisher Scientific, Waltham, MA) between the filter and the breathing circuit's inspiratory limb, as shown in Figure 2. The Miran analyzer was zeroed in room air. It has a sensitivity of 0.04 ppm. After 45 minutes we reduced the oxygen flow from 10 L/min to 3 L/min and recorded readings for another 45 minutes to show the value of maintaining a high fresh gas flow. After 90 minutes we removed the charcoal filters to show the value of keeping the filters in place. We repeated the above procedure with 2.0% sevoflurane and with 6.0% desflurane, using a different Apollo machine for each anesthetic gas. We repeated the complete set of tests using a different Aestiva anesthesia machine for each test condition (GE Medical, Madison, WI). To provide control data, we repeated the protocol without using charcoal filters for each machine and for each of the 3 anesthetic gasses. In the control study without charcoal filters, we reduced the oxygen flow from 10 L/min to 3 L/min when the delivered concentration decreased below 5 ppm, to show the value of maintaining a high fresh gas flow.

Figure 1

Figure 1

Figure 2

Figure 2

To simulate a case during which malignant hyperthermia is diagnosed 90 minutes after induction of anesthesia, we repeated the procedure outlined above using an Apollo machine, only this time we inserted a 2-L flask containing olive oil into the breathing circuit, so that the expired gas bubbled through the oil (Fig. 3). To simulate a 70-kg adult with a cardiac output of 5 L/min, we used 2.0 L of olive oil for isoflurane, 0.94 L for desflurane, and 0.65 L for sevoflurane.10 During the 90-minute “contamination” phase the oil absorbed the volatile anesthetic. After turning off the vaporizer and adding the charcoal filters, the oil released the anesthetic in a manner similar to that of an anesthetized patient.10

Figure 3

Figure 3

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RESULTS

Figure 4 shows the isoflurane, sevoflurane, and desflurane concentrations delivered by a contaminated Aestiva anesthesia machine after turning off the vaporizer, increasing the fresh gas flow to 10 L/min and replacing the breathing hoses. Table 1 lists the time it took before the inspired anesthetic concentration coming from the contaminated anesthesia machine decreased below 5 ppm. When the delivered concentration decreased below 5 ppm, the fresh gas flow was changed from 10 L/min to 3 L/min, showing the value of maintaining a high fresh gas flow.

Figure 4

Figure 4

Table 1

Table 1

Figure 5 shows the anesthetic concentrations delivered by a contaminated Apollo anesthesia machine when activated charcoal filters were placed on both the inspiratory and expiratory limbs of the breathing circuit. Table 1 lists the time it took before the inspired anesthetic concentration decreased below 5 ppm. After 45 minutes we reduced the fresh gas flow from 10 L/min to 3 L/min, and the concentration still remained below 1.0 ppm. After 90 minutes we removed the activated charcoal filters, and the residual isoflurane in the anesthesia machine caused the delivered concentration to increase to 24 ppm, showing the need to keep the charcoal filters in place.

Figure 5

Figure 5

Figures 6 and 7 show the results for a contaminated Apollo machine. Table 1 shows the times until the concentration of inspired vapor delivered by a contaminated Aestiva anesthesia machine decreased below 5 ppm, with and without the charcoal filters.

Figure 6

Figure 6

Figure 7

Figure 7

Figure 8 shows the delivered anesthetic concentrations when we used olive oil to simulate a case in which malignant hyperthermia was diagnosed 90 minutes after induction of anesthesia. After placing charcoal filters on the inspiratory and expiratory limbs of the breathing circuit, it took <2 minutes for the volatile anesthetic concentrations to decrease below 5 ppm. The delivered desflurane concentration remained below 5 ppm, even after reducing the fresh gas flow from 10 L/min to 3 L/min. The charcoal filters became saturated, and the inspired anesthetic concentration increased above 5 ppm 67 minutes after ending an isoflurane anesthetic, 83 minutes after sevoflurane, and 90 minutes after desflurane.

Figure 8

Figure 8

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DISCUSSION

Our results show that when activated charcoal filters are used to decontaminate an Aestiva or Apollo anesthesia machine, activated charcoal filters decrease the concentration of volatile anesthetic delivered by the machine to an acceptable level in <2 minutes. The concentrations remained well below the 5 ppm threshold for at least 60 minutes. Activated charcoal filters provide an alternative approach to the 10 to 104 minutes of flushing that are normally required to prepare a contaminated machine for use with a malignant hyperthermia–susceptible patient.2,5,8

We found that it took 27 to 84 minutes to flush residual anesthetic vapor from the Apollo and Aestiva anesthesia machines. Whereas a 10 L/min fresh gas flow will clear the residual vapor from an older generation machine in 10 minutes, we found, as did Shinkaruk and Crossan, that it takes 55 minutes to flush sevoflurane from a contaminated Aestiva machine.11 We found that it took only 46 minutes to flush sevoflurane from the Apollo machine, suggesting that the Apollo may have fewer internal elastomeric and plastic parts to capture and release volatile anesthetic molecules. Gunter et al. reported 104 minutes to flush sevoflurane from the Fabius machine.12 This suggests that the Fabius may be the most difficult machine to decontaminate. However, many new anesthesia machines have not yet been studied. The data needed to formulate a recommendation regarding the minimum flush time for all anesthesia machines are not yet available.

The data in Figures 4 and 6 show that it took longer to remove isoflurane from a contaminated machine than it took to remove sevoflurane or desflurane. It is no surprise that isoflurane is the most difficult vapor to remove, because isoflurane has a higher rubber/plastic partition coefficient when compared with sevoflurane or desflurane.13

An alternative decontamination technique is to place an activated charcoal filter in the inspired limb of the breathing circuit. Activated charcoal captures and holds volatile anesthetic molecules on its porous surface.1420 Charcoal has been used by closed-circuit anesthesia enthusiasts to remove the volatile anesthetic from closed breathing circuits at the end of a case to shorten emergence time and to prevent pollution of the operating room.2123

In 1986, Greene used activated charcoal to remove “all traces” of the volatile anesthetic.24 He reported that “[O]ne of these charcoal absorption units is a worthwhile addition to the store of emergency supplies reserved for malignant hyperthermia.” His findings were confirmed in 1989 by Jatzen et al.25 In 2008 Gunter et al. placed a commercially available activated charcoal filter (QED-100, Anecare Inc., Salt Lake City, UT) on the inspiratory limb of the Draeger Fabius anesthesia machine and found that the inspired concentration decreased below 5 ppm within 10 minutes.12 He concluded that it is safe to use the Fabius machine with malignant hyperthermia–susceptible patients after a 10-minute flush with 10 L/min oxygen if a charcoal filter is used.12

In our study we used Food and Drug Administration– approved activated charcoal filters that were designed specifically for the purpose of removing anesthetic vapor from the breathing circuit (Vapor-Clean, Dynasthetics LLC, Salt Lake City, UT). The QED-100 charcoal filter used by Gunter et al. was designed for use during recovery from anesthesia, not for machine decontamination.12 When used to decontaminate a machine, the QED must be installed on the inspiratory limb of the breathing circuit, contrary to the QED's instructions for use. The QED should not be installed at the breathing circuit Y piece, as specified in the instructions for use. The QED's on/off switch, 2 internal 1-way valves, and rebreathing hose are not needed to decontaminate a machine. The on/off switch may not seal completely and may let some anesthetic bypass the charcoal filter during inspiration. The 1-way valves may not be 100% competent; reverse flow through the device would allow trace amounts of residual anesthetic to pass to the patient. As a result, the QED product specifications specify only 90% efficiency in removing volatile anesthetics. Because the Dynasthetics filters we tested contain a simple charcoal-filled disk, it has 99% efficiency; the flush time needed to reach 5 ppm is <2 minutes rather than the 10 minutes reported by Gunter et al.12

Our study explored, for the first time, whether activated charcoal filters can be used to reduce further exposure when malignant hyperthermia is diagnosed intraoperatively. Our results show that by adding charcoal filters to an Apollo machine after a 70-kg patient has been exposed to 1.5% isoflurane for 90 minutes, the filters kept the inspired concentration coming from the machine below 5 ppm for 67 minutes (Fig. 8). Filters kept the inspired concentration below 5 ppm for 90 minutes after a 90-minute exposure to 6.0% desflurane. We simulated these conditions by placing a flask of olive oil in the expiratory limb of the breathing circuit. Loughlin used olive oil in his lung simulator and showed that it faithfully reproduced the uptake and elimination of volatile anesthetic vapor. Loughlin et al. used 3 oil-filled chambers to simulate the fast vessel-rich tissue group, the muscle group, and the slow poorly perfused tissue group. They set the air flow through each oil-filled reservoir to simulate the bloodflow to that compartment.10 We used a single flask filled with enough oil to simulate the total amount of drug taken up by a 70-kg patient but did not reproduce the time constants for fast and slow compartments.

When malignant hyperthermia is diagnosed intraoperatively, the amount of anesthetic taken up will be highly variable because it depends on the length of exposure, muscle and fat tissue volumes, tissue bloodflow, and anesthetic solubility.26 In a North American malignant hyperthermia registry study of the presentation of malignant hyperthermia, Larach et al. found in younger patients that the median time from induction to volatile anesthetic discontinuation was 45 minutes (range 19 to 90 minutes). Patients older than 19 years had a median time of 112 minutes (range = 60.0 to 180 minutes).27Figure 8 shows the filter's lifetime after a 90-minute exposure in a 70-kg patient. Clinical judgment must be exercised when an episode of malignant hyperthermia triggers in the operating room. The charcoal filters should be replaced after a shorter period of use if the period of exposure is longer than 90 minutes, if the anesthetic concentration is higher than 1 minimum alveolar concentration, or if the patient is 19 years or older.

When malignant hyperthermia is diagnosed during a case, the recommended action is to turn off the vaporizer, increase the fresh gas flow to at least 10 L/min of oxygen and hyperventilate the patient.a In May 2008 the Malignant Hyperthermia Association of the United States further recommended, “Don't waste time changing the circle system and CO2 absorbent.” The immediate need is dantrolene, followed by cooling and other medical treatment. At some point it might then be reasonable to change the breathing circuit and add charcoal filters, to thereby reduce further exposure to inhaled vapor. Installing charcoal filters would reduce the urgency to switch to a nonrebreathing method of providing ventilation or to find an extra person to provide mechanical ventilation, thereby maintaining focus on delivering dantrolene, cooling, and other medical treatment.

When using activated charcoal to decontaminate an anesthesia machine, the time to reach the 5-ppm threshold may be shorter than reported in our results because the Miran gas analyzer's response time may be longer than the time it takes for charcoal to remove anesthetic vapor. The Miran was designed for environmental measurements in which time response is not critical. The plastic and elastomeric components inside the Miran analyzer's sampling chamber may retain and release anesthetics over a several-minute time period.12,13,28

In our study we used 4 different Apollo machines and 3 Aestiva machines. Our results show that charcoal is equally effective when used to decontaminate all 7 machines after exposure to 1 of the 3 volatile anesthetics. However, the data we report for the time needed to flush a machine with fresh gas do not have the number of repetitions to characterize the flush times adequately for the Apollo and Aestiva machines. One reason for recommending charcoal is to eliminate the uncertainty regarding the flush time needed for a particular machine and a particular drug.

The lowest concentration of volatile anesthetic that can potentially trigger malignant hyperthermia in humans is unknown and will remain unknown because it is unethical to expose susceptible patients to inhalation anesthetics. Malignant hyperthermia–susceptible swine have been exposed to 10 ppm of halothane without triggering a reaction.7 Operating room personnel were commonly exposed to 1 to 5 ppm of halogenated anesthetics before waste gas scavenging systems were installed, without triggering any known cases of spontaneous malignant hyperthermia.1,2,5 Although it is prudent to avoid volatile anesthetic exposure altogether, exposure to concentrations <5 ppm is considered below the triggering threshold.1,2,5,8

Activated charcoal should be tested in malignant hyperthermia–susceptible swine before claims can be made regarding its safety in malignant hyperthermia–susceptible patients. However, our results verify that charcoal removes all but trace concentrations from contaminated machines. Delivered concentrations are well below the accepted trigger threshold of 5 ppm.

We recommend placing activated charcoal filters on both the expiratory and inspiratory limbs of a contaminated anesthesia machine:

  1. Many modern anesthesia machines have either subtle or obscure markings identifying the inspiratory and expiratory limbs of the circuit. Placing filters on both limbs avoids altogether the issue of incorrectly placing the filter on the expiratory limb rather than on the inspiratory limb.
  2. If the expiratory nonrebreathing valve were to fail and become incompetent, a filter on the expiratory limb would prevent volatile anesthetic from reaching the patient through the expiratory limb.
  3. If the fresh gas flow is less than the minute ventilation, a filter on the expiratory limb would remove anesthetic from the expiratory gas before it is rebreathed.
  4. If malignant hyperthermia is detected intraoperatively, placing filters on both limbs of the breathing circuit doubles the amount of charcoal available to absorb the anesthetic as minute volume increases.

In conclusion, we found that placing activated charcoal filters on the inspiratory and expiratory limbs of the new-generation Aestiva and Apollo anesthesia machines immediately reduced the inhaled anesthetic below the 5-ppm threshold. Activated charcoal filters may offer a means to safely, effectively, and quickly make contaminated machines available for clinical use without the need to keep a “clean” machine in reserve or the cumbersome task of flushing a machine for nearly an hour before use.

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RECUSE NOTE

Dwayne Westenskow is section Editor of Technology, Computing, and Simulation for the Journal. This manuscript was handled by Sorin J. Brull, section Editor of patient Safety, and Dr. Westenskow was not involved in any way with the editorial process or decision.

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DISCLOSURES

Name: Nathaniel Birgenheier, MD.

Contribution: This author wrote the original manuscript, helped design the study, conduct the study, and analyze the data.

Attestation: Nathaniel Birgenheier has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.

Conflict of Interest: Nathaniel Birgenheier reported no conflict of interest.

Name: Robert Stoker, BA.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Robert Stoker has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflict of Interest: Robert Stoker reported no conflict of interest.

Name: Dwayne Westenskow, PhD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Dwayne Westenskow has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflict of Interest: Dwayne Westenskow received royalties from Dynasthetics, LLC.

Name: Joseph Orr, PhD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Joseph Orr has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflict of Interest: Joseph Orr received royalties from Dynasthetics, LLC.

a Available at http://medical.mhaus.org/PubData/PDFs/treatmentposter.pdf. Last accessed February 2, 2011.
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