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LETTER TO THE EDITOR

Exhausted Amsorb Plus CO₂ Absorbent Recognized only by Inspired CO₂

Department of Anesthesiology and Critical Care Medicine, University of New Mexico, Albuquerque, New Mexico, nealgerstein{at}pol.net

To the Editor:

The manufacturers of Amsorb® Plus state that it is "designed for low- and minimal-flow anesthesia. Its absorption capacity, intensity and uniformity of color change have been improved from the original Amsorb" (1). A letter in the most recent Anesthesia Patient Safety Foundation Newsletter comments on an episode of hypercarbia due to channeling with Amsorb Plus (2). Amsorb and Amsorb Plus are two newer generation carbon dioxide (CO₂) absorbents that have been developed for their ability to produce less Compound A and carbon monoxide than do older absorbents, especially when desiccated. Neither Amsorb nor Amsorb Plus contain a strong base or cause anesthetic degradation. The disadvantage of Amsorb is that its CO₂ absorption capacity is 40%–90% less than that of soda lime or Baralyme (3). This led to the development of Amsorb Plus, which compared to Amsorb, supposedly has a greater CO₂ absorption capacity (4).

We recently had 10 cases involving Amsorb Plus with low-flow anesthesia (1 L total fresh gas flow) that led to significant rebreathing of expired CO₂ with virtually no color change of the absorbent. These cases occurred in the operating rooms at both a large tertiary care academic hospital and its associated ambulatory surgery center. Five cases were performed using a Dräger Narkomed-2C, and the other five cases were performed using a Dräger Narkomed-GS. In all of these cases, the anesthesiologist noted an inappropriate inspired CO₂ level or failure of the capnograph to return to baseline completely during the inspiratory phase or both circumstances, as shown in Figure 1. All the cases we report occurred with the administration of a low-flow anesthetic. In each case, the absorbent was examined for channeling. In eight of these cases, the absorbent remained white throughout, as shown in Figure 2. In two cases, there was scant purple speckling of the absorbent. No patient was harmed from CO₂ rebreathing.

View larger version (124K): [in this window] [in a new window]   Figure 1. Anesthesia machine monitor showing inspired CO2 level, capnograph not returning to baseline upon inspiration.

View larger version (154K): [in this window] [in a new window]   Figure 2. Exhausted Amsorb® Plus showing minimal to no color change.

Our experience suggests there is an indicator problem in Amsorb Plus that leads to unrecognized absorbent exhaustion. A heightened level of vigilance for inspired CO₂ is required when using Amsorb Plus.

REFERENCES

1. http://www.armstrongmedical.com.
2. Olympio MA. Dear SIRS—channeling causes concern [letter]. Anesthesia Patient Safety Foundation Newsletter 2006;21:14.
3. Higuchi H, Adachi Y, Arisuma S, et al. The carbon dioxide absorption capacity ofAmsorb is half that of soda lime. Anesth Analg 2001;93:221–5.[Abstract/Free Full Text]
4. Kobayashi S, Hiromichi B, Morita K, et al. Amsorb® Plus and Dragersorb Free, two new-generation carbon dioxide absorbents that produce a low Compound A concentration while providing sufficient CO₂ absorption capacity in simulated sevoflurane anesthesia. J Anesth 2004;18:277–81.[Medline]

This article has been cited by other articles:

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				C. Magee Carbon Dioxide Rebreathing Due to Unrecognized Amsorb Plus Exhaustion Anesth. Analg., July 1, 2007; 105(1): 289 - 290. [Full Text] [PDF]

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