This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Laster, M. J. Articles by Eger, E. I. Search for Related Content PubMed PubMed Citation Articles by Laster, M. J. Articles by Eger, E. I., II

---

TECHNOLOGY, COMPUTING, AND SIMULATION

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

From the Department of Anesthesia and Perioperative Care, University of California, San Francisco, California

Address correspondence to Dr. Edmond I Eger II, Department of Anesthesia, S-455, University of California, San Francisco, California 94143-0464. Address electronic mail to: egere{at}anesthesia.ucsf.edu.

	Abstract

Top Abstract Introduction Methods Results Discussion References

 
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°C to 45°C and then declined. With 1.5 or 3.0 MAC sevoflurane, temperatures increased to approximately 90°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.

	Introduction

Top Abstract Introduction Methods Results Discussion References

 
The interaction of desiccated Baralyme® with sevoflurane can produce absorbent temperatures of several hundred degrees centigrade (1,2). The increase in temperature may cause anesthetic circuit fires and patient injury (3–5). The latest package label for sevoflurane (August, 2003) warns of this possibility. In addition, a communication to anesthesia practitioners from Abbott Laboratories (available at: www.fda.gov/medwatch/SAFETY/2003/ultane_deardoc.pdf) details several issues surrounding this concern. As indicated by the several-year delay between the introduction of sevoflurane and the reports of fires in clinical practice, fires from the interaction of sevoflurane with desiccated absorbents are extraordinarily rare—perhaps one case in tens of millions of sevoflurane anesthetics.

Results from a bench model that demonstrated the potential for temperatures exceeding 300°C and conflagrations consequent to the interaction of sevoflurane with desiccated Baralyme® confirmed these clinical findings (6). This model found much smaller temperatures (peak temperatures of approximately 100°C) from the interaction of desflurane or isoflurane with desiccated Baralyme®. No fires resulted from degradation of desflurane or isoflurane. These findings might have been predicted from reports that desflurane and isoflurane resist degradation more than sevoflurane (7) and from the absence of reports linking desflurane or isoflurane with fires.

These experiments did not examine whether other desiccated absorbents, particularly the widely used absorbent soda lime, might also produce great temperatures and fires from their interaction with potent inhaled anesthetics, particularly sevoflurane. All published reports (3–5) connected fires with the use of sevoflurane plus Baralyme®, and commercial distribution of Baralyme® has ceased. However, the 2003 letter from Abbott Laboratories noted that ". . . cases of extreme heat associated with desiccated soda lime have also been reported in Europe." Increased temperatures, but no fires, have been reported to occur during delivery of desflurane, isoflurane, or sevoflurane to desiccated soda lime (8–13). In the present study, we tested whether the interaction of potent inhaled anesthetics with desiccated soda lime might produce temperatures that resulted in fires in previous studies applying the same conditions with desiccated Baralyme®.

	Methods

Top Abstract Introduction Methods Results Discussion References

 
Anesthetics were obtained from commercial sources: desflurane and isoflurane from Baxter Healthcare Corp. (New Providence, NJ), and sevoflurane from Abbott Laboratories (Abbott Park, IL). The carbon dioxide absorbent, soda lime (Sodasorb®), was obtained from W.R. Grace (Atlanta, GA).

Approximately 3.5 kg of soda lime was placed in a 4-L flask capped with a rubber stopper. A plastic tube was directed through the stopper to the bottom of the flask. A second tube through the stopper ended at the top of the flask and allowed the exit of gases from the flask. A 10 L/min flow of oxygen was directed through the flask (i.e., through the soda lime). The flask plus stopper and tubes were weighed (Ohaus® Portable Navigator^TM with a scale accurate to 0.5 g and reading to 0.1 g; Ohaus Corporation, Pine Brook, NJ) before and after introduction of the soda lime and at intervals after initiating the 10 L/min flow of oxygen through the absorbent. Flow was continued until the weight of the flask containing the soda lime no longer changed (approximately 5–7 days). The prepared absorbent was only used once (for one study).

The lower of two absorbent canisters in a standard anesthetic circuit (OH Medical Products, Madison, WI) was modified to allow the introduction of 4 temperature probes (Model HH22 Microprocessor with thermocouple type K, having a temperature range of –200°C to 1,372°C and an accuracy of 0.6°C; Omega Engineering, Inc., Stamford, CT). A layer approximately 1 cm deep of desiccated soda lime was placed at the bottom of the canister, and the tip of one of the temperature probes was placed in the center of this layer ("bottom temperature"). Soda lime was added until the canister was half full. The tip of a second temperature probe was placed at the center of this layer ("middle temperature"), and the tip of a third probe was placed at the edge of this layer (i.e., near the wall of the canister; "side temperature"). Soda lime was added to complete the filling of the lower canister, and the fourth temperature probe was placed in the center of this layer approximately 1 cm from the surface ("top temperature"). Each canister (n = 19) was thus filled with 1140 ± 30 g of desiccated soda lime.

Except for one experiment with sevoflurane, the second, upper, canister was left empty. The lower and upper canisters then were arrayed as normally done, and the system was closed. The circuit then was assembled as it would be for anesthetic delivery. A 3-L reservoir bag served as a surrogate patient lung. The system was connected to a ventilator. A port at the Y-piece allowed the measurement of end-tidal anesthetic concentrations needed to certify the delivery of the target anesthetic concentrations.

Experiments were repeated 2-4 times except for the experiment in which 2 canisters filled with desiccated absorbent were placed concurrently. The study anesthetics (desflurane, isoflurane, sevoflurane) were delivered at 6 L/min in 100% oxygen at 3 MAC except for studies of desflurane and sevoflurane in which we also examined the effect of 1.5 MAC. We assumed the following MAC values: desflurane 6.0% (14,15), isoflurane 1.2% (15,16), and sevoflurane 1.9% (15). As in the study by Holak et al. (2), the ventilator delivered a tidal volume of approximately 660 mL at 15 breaths/min so as to produce a 10 L/min minute ventilation. At time zero, the vaporizer was set to deliver the predetermined target concentration of anesthetic in end-tidal gas. Temperatures were recorded at 5-minute intervals for the next 2 hours. Gas was drawn from the sampling port through an infrared analyzer (5250 RGM; Ohmeda, Louisville, CO), and the concentrations recorded concurrently with the temperature recordings.

To mimic the effect of patient metabolism and the production of carbon dioxide, in duplicate experiments with sevoflurane at 3.0 MAC, we added an inflow of 200 mL/min carbon dioxide to the tail of the bag that substituted for the patient's lungs. The experiment otherwise was conducted as described above.

In one experiment with 3.0 MAC sevoflurane, we filled both canisters with desiccated soda lime. As in the experiments described above, we measured temperatures only in the lower canister.

Peak temperatures achieved during the 2 hours of anesthetic delivery were compared by a one-way analysis of variance and a Student-Newman-Keuls test. We accepted P < 0.05 as indicative of statistical significance.

	Results

Top Abstract Introduction Methods Results Discussion References

 
Temperatures increased at all 4 measurement sites, reaching approximately 35°C to 50°C at the bottom and middle probes with desflurane and isoflurane and 80°C–100°C with sevoflurane (Figures 1–4; Table 1). All the studies with sevoflurane (1.5 MAC, 3.0 MAC with and without carbon dioxide, and 3.0 MAC with 2 canisters of desiccated absorbent) produced peak temperatures significantly greater than those produced with desflurane or isoflurane (P < 0.05). No other results differed significantly. Lower temperatures were attained with the top and side temperature probes (data not shown). Peak temperatures were reached after 15–55 min of anesthetic delivery and decreased thereafter. Times to peak temperatures were earlier with sevoflurane (P < 0.05). In studies with sevoflurane, addition of 200 mL/min of carbon dioxide did not affect these times or peak temperatures but did appear to delay the decay in temperature after the peak temperature had been reached (Figs. 1 and 3). Time to peak temperature was not affected by concentration with sevoflurane (Figs. 1 and 3) but the time to peak temperature was shorter with 3.0 MAC desflurane than with 1.5 MAC desflurane (P < 0.05). The use of 2 canisters, rather than 1 canister, containing desiccated soda lime tended to increase the peak temperature obtained in the middle of the canister, an increase of approximately 6°C (Figs. 1 and 3; Table 1). No conflagrations arose in any experiment.

View larger version (37K): [in this window] [in a new window]   Figure 1. Temperatures recorded from the bottom of desiccated soda lime exposed to sevoflurane peaked at 80°C–100°C, progressively decreasing thereafter. Peak temperatures in these experiments with sevoflurane did not change as a function of the concentration of sevoflurane (1.5 MAC versus 3.0 MAC) or the addition of 200 mL/min of carbon dioxide to the surrogate lung. However, the decrease in temperature from the peak temperatures reached occurred slower if carbon dioxide was added. Similarly, addition of a second canister of desiccated soda lime did not increase the temperatures reached although it prolonged the increase in temperature.

View larger version (31K): [in this window] [in a new window]   Figure 2. Temperature recorded from the bottom of the desiccated absorbent peaked at 30°C–45°C with 3.0 MAC desflurane and isoflurane, progressively decreasing thereafter. The temperature increases found with desflurane and isoflurane (approximately 20°C) were a third of the temperature increases found with sevoflurane (approximately 60°C).

View larger version (39K): [in this window] [in a new window]   Figure 3. As with temperatures recorded from the bottom of the desiccated soda lime, temperatures in the middle of desiccated soda lime exposed to sevoflurane peaked at 80°C–100°C, progressively decreasing thereafter. Peak temperatures in these experiments with sevoflurane did not change as a function of the concentration of sevoflurane (1.5 MAC versus 3.0 MAC) or the addition of 200 mL/min of carbon dioxide to the surrogate lung. However, the decrease in temperature from the peak temperatures reached occurred slower if carbon dioxide was added. Similarly, addition of a second canister of desiccated soda lime tended to increase the temperatures reached (approximately 6°C, not a significant increase) and prolonged the increase in temperature.

View larger version (33K): [in this window] [in a new window]   Figure 4. As with temperatures recorded from the bottom of the desiccated soda lime, temperature recorded from the middle of the desiccated absorbent peaked at 40°C–50°C with 3.0 MAC desflurane and isoflurane, progressively decreasing thereafter. That is, the temperature increases found with desflurane and isoflurane (approximately 20°C) were approximately one third of the temperature increases found with sevoflurane (approximately 60°C).

	Discussion

Top Abstract Introduction Methods Results Discussion References

 
Our findings are consistent with the suggestion in the 2003 letter from Abbott Laboratories that ". . . cases of extreme heat associated with desiccated soda lime have also been reported in Europe." We found that degradation of sevoflurane by desiccated soda lime could produce peak temperatures of 100°C (increases in temperature of 60°C–70°C). Under comparable conditions, degradation of desflurane and isoflurane increased peak temperatures one third as much (increases of approximately 20°C). The increase with sevoflurane approaches the 107°C found by Funk et al. (11) during induction of anesthesia in patients. Their soda lime contained 3.1% potassium hydroxide rather than sodium hydroxide. A greater temperature (126°C –130°C) was found by Wissing et al. in a bench model (12).

Although temperatures of 100°C (the greatest temperature found was 101.2°C) could result from the degradation of sevoflurane, no conflagrations were observed in 9 experiments. Unlike the findings with Baralyme®, the degradation of sevoflurane did not progressively increase temperature. Instead, having reached a peak temperature of 80°C–100°C, the temperature in the absorbent decreased thereafter. Doubling the available desiccated absorbent slightly (not significantly) increased the temperature produced or delayed the decay in the temperature (Figs. 1 and 3; Table 1). The temperatures reached with sevoflurane were comparable to those reached in studies of the degradation of desflurane and isoflurane by desiccated Baralyme® (6). These observations suggest that sevoflurane degradation by desiccated soda lime is unlikely to produce fires. The risk of fires with desflurane and isoflurane would be still less.

Other investigations suggest that anesthetic degradation by desiccated absorbent results from the action of a minor component of the bases in the absorbent, namely the monovalent bases sodium hydroxide and potassium hydroxide (17–19). In the case of the soda lime used in the present study, 3% of the base is sodium hydroxide. Neither potassium hydroxide nor barium hydroxide are present; the remaining base consists of calcium hydroxide. These differences from Baralyme® (5.3% potassium hydroxide as well as barium and calcium hydroxides) (18) probably explain the smaller increases in temperature resulting from the action of desiccated soda lime on all three test anesthetics. Other desiccated absorbents such as Amsorb®, which have fewer or no monovalent bases, produce still less degradation, and temperature increases are therefore likely to be smaller than with soda lime (18). Whether the greater safety (not only fires but also the production of toxic degradation products) that might accrue to the use of such absorbents merits their greater expense cannot be determined from present information.

We conclude that the use of soda lime rather than Baralyme® decreases the danger of increased temperatures from degradation of potent inhaled anesthetics by desiccated absorbents. Perhaps the issue should be moot because ensuring hydration of the absorbent (by replacing desiccated absorbent with fresh absorbent or by pouring water into the desiccated absorbent) (20). minimizes or avoids degradation. As anesthesia clinicians extend their care outside of the traditional operating room setting into remote hospital and office locations, greater vigilance and care is needed to ensure that the moisture content of absorbents is adequate.

	Footnotes

 
Accepted for publication February 22, 2005.

Dr. Eger is a paid consultant to Baxter Healthcare Corp. Baxter Healthcare Corp. donated the desflurane and isoflurane used in these studies

	References

Top Abstract Introduction Methods Results Discussion References

 

1. Eger EI II, Ionescu P, Laster MJ, Weiskopf RB. Baralyme® dehydration increases and soda lime dehydration decreases the concentration of compound A resulting from sevoflurane degradation in a standard anesthetic circuit. Anesth Analg 1997;85:892–8.[Abstract]
2. Holak EJ, Mei DA, Dunning MB 3rd, et al. Carbon monoxide production from sevoflurane breakdown: modeling of exposures under clinical conditions. Anesth Analg 2003;96:757–64.[Abstract/Free Full Text]
3. Wu J, Previte JP, Adler E, et al. Spontaneous ignition, explosion, and fire with sevoflurane and barium hydroxide lime. Anesthesiology 2004;101:534–7.[Web of Science][Medline]
4. Castro BA, Freedman LA, Craig WL, Lynch C III. Explosion within an anesthesia machine: Baralyme, high fresh gas flows and sevoflurane concentration. Anesthesiology 2004;101:537–9.[Medline]
5. Fatheree RS, Leighton BL. Acute respiratory distress syndrome after an exothermic Baralyme-sevoflurane reaction. Anesthesiology 2004;101:531–3.[Medline]
6. Laster M, Roth P, Eger EI II. Fires from the interaction of anesthetics with desiccated absorbent. Anesth Analg 2004;99:769–74.[Abstract/Free Full Text]
7. Eger EI II. Stability of I-653 in soda lime. Anesth Analg 1987;66:983–5.[Abstract/Free Full Text]
8. Wissing H, Kuhn I, Warnken U, Dudziak R. Carbon monoxide production from desflurane, enflurane, halothane, isoflurane, and sevoflurane with dry soda lime. Anesthesiology 2001;95:1205–12.[Web of Science][Medline]
9. Knolle E, Heinze G, Gilly H. Carbon monoxide formation in dry soda lime is prolonged at low gas flow. Anesth Analg 2001;93:488–93.[Abstract/Free Full Text]
10. Knolle E, Gilly H. Absorption of carbon dioxide by dry soda lime decreases carbon monoxide formation from isoflurane degradation. Anesth Analg 2000;91:446–51.[Abstract/Free Full Text]
11. Funk W, Gruber M, Wild K, Hobbhahn J. Dry soda lime markedly degrades sevoflurane during simulated inhalation induction. Br J Anaesth 1999;82:193–8.[Abstract]
12. Wissing H, Kuhn I, Dudziak R. Zur Temperaturentwicklung von Inhalationsanästhetika auf trockenem Atemkalk. Anaesthesist 1997;46:1064–70.[Web of Science][Medline]
13. Strauss JM, Baum J, Sumpelmann R, et al. Degradation of halothane, enflurane, and isoflurane by dry soda lime to give carbon monoxide [in German]. Anaesthesist 1996;45:798–801.[Medline]
14. Rampil IJ, Lockhart S, Zwass M, et al. Clinical characteristics of desflurane in surgical patients: Minimum alveolar concentration. Anesthesiology 1991;74:429–33.[Web of Science][Medline]
15. Eger EI II. Age, minimum alveolar anesthetic concentration, and minimum alveolar anesthetic concentration-awake. Anesth Analg 2001;93:947–53.[Abstract/Free Full Text]
16. Stevens WC, Dolan WM, Gibbons RT, et al. Minimum alveolar concentrations (MAC) of isoflurane with and without nitrous oxide in patients of various ages. Anesthesiology 1975;42:197–200.[Web of Science][Medline]
17. Neumann MA, Laster MJ, Weiskopf RB, et al. The elimination of sodium and potassium hydroxides from desiccated soda lime diminishes degradation of desflurane to carbon monoxide and sevoflurane to compound A but does not compromise carbon dioxide absorption. Anesth Analg 1999;89:768–73.[Abstract/Free Full Text]
18. Stabernack CR, Brown R, Laster MJ, et al. Absorbents differ enormously in their capacity to produce compound A and carbon monoxide. Anesth Analg 2000;90:1428–35.[Abstract/Free Full Text]
19. Murray JM, Renfrew CW, Bedi A, et al. Amsorb: a new carbon dioxide absorbent for use in anesthetic breathing systems. Anesthesiology 1999;91:1342–8.[Web of Science][Medline]
20. Baxter PJ, Kharasch ED. Rehydration of desiccated Baralyme prevents carbon monoxide formation from desflurane in an anesthesia machine. Anesthesiology 1997;86:1061–5.[Web of Science][Medline]

This article has been cited by other articles:

				L. S. Coleman Should soda lime be abolished? Anesth. Analg., April 1, 2006; 102(4): 1290 - 1291. [Full Text] [PDF]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Laster, M. J. Articles by Eger, E. I. Search for Related Content PubMed PubMed Citation Articles by Laster, M. J. Articles by Eger, E. I., II