Circulation 80,350 • Volume 21, No. 1 • Spring 2006   Issue PDF

Channeling Causes Concern

Michael A. Olympio, MD; Dr. Ciarán Magee

The APSF has received a report of a hypercarbic patient condition during the use of AMSORB¨ PLUS (Armstrong Medical Limited, Northern Ireland), detected through capnography and confirmed by arterial blood gas monitoring. After inspection, the clinician noted an outward completely white coloration of the absorbent, but a violet coloration of the absorbent channeled through the inner core. After exchange of the absorbent for a fresh container, the hypercarbia reportedly resolved. The clinician further believed that the product literature recommended that the canister be changed when the AMSORB® PLUS indicator completely turns to violet.

APSF recently reported the proceedings of a conference on absorbent desiccation,1 and there were no such reports of this situation at that conference. Considering the potential significance of this issue, we respectfully ask that Armstrong Medical Limited provide commentary on this report, for the benefit of our readership.

Michael A. Olympio, MD
Chair, Committee on Technology

1. Olympio, MA. APSF convenes conference on safety concerns of carbon dioxide absorbent desiccation. APSF Newsletter 2005;20:25, 27-29.


In Response:

As the manufacturer of AMSORB® PLUS and as a corporate member of APSF, we need to clarify certain performance characteristics and conditions of use of our product. The Instructions for Use (IFU) state that capnography is the primary measurement of exhaustive state, and color is there for indication purposes only. Routine anesthetic monitoring should include FiCO2 and expired CO2, as we consider this standard practice of anesthetic monitoring. Audio-visual alarms on the monitor, if enabled, will alert the clinician if FiCO2 exceeds 5 mmHg and ETCO2 exceeds 45 mmHg, for example.

We are not aware of any published literature (our own or independently published) that states that the canister be changed when the color has completely changed to violet. This would not make sense, as a completely color-changed canister of AMSORB¨ PLUS would be desiccated and be incapable of further absorption of CO2. It appears that since no coloration was observed on the exterior, then that material must have become too moist, preventing a color change or perhaps never had sufficient contact with CO2 to cause the desiccation necessary for coloration. The reasons for this can be many and we would like an opportunity to look into this.

The IFU states that the canister should be changed when CO2 breakthrough has reached FiCO2 of 0.5% (or 5 mmHg), which may be associated with color penetrating to two-thirds the depth of the canister. AMSORB® PLUS has a unique color indicator which is intended to give a gradual and permanent color change, unlike soda limes which have a transient and reversible color change which depends on continuous contact with CO2. With soda lime you will see the color reverting back to white during periods of non-use; this material can become inadvertently desiccated and potentially dangerous when next exposed to anesthetic vapor. This issue is widely published and accepted.

The fact that a clinician experienced color coring/channeling with a completely white exterior is not something that we have come across before, as center coring is normally associated with some level of coloration on the exterior. AMSORB® PLUS color change is gradual and permanent and is intended to be visible throughout the material to a depth of two-thirds the height of the absorber canister before FiCO2 exceeds 0.5% volume or 5 mmHg. What is described by the user may be related to fresh gas flow or particular absorber or user set-up, perhaps from retrograde gas flow during periods of non-use, which is known to cause irregular coloration of AMSORB® PLUS. This would need more investigation and we would appreciate the opportunity to work on this.

If one uses soda lime, the coloration that you see is not related to desiccation. Conversely, there would be no color change to indicate desiccation, and this material could be sufficiently desiccated to degrade the anesthetic whilst simultaneously absorbing CO2. A common misconception of soda limes is that users believe that they will be alerted to desiccation by failure to absorb CO2; however, we have done extensive work in our own laboratory, showing that a jumbo canister (2 x 1 kg trays) of completely desiccated soda lime will absorb a clinical loading of CO2 for at least 1 hour. Published literature would support the contention that this material, once desiccated (inadvertently by fresh gas flow or as part of the normal dehydrating effects of CO2 absorption) could degrade the anesthetic agent to carbon monoxide, formaldehyde, and other toxic chemicals.

Armstrong Medical Limited has offered AMSORB® PLUS as an absorbent that is incapable of degrading the anesthetic agent, in any state of use.

If any clinician with similar findings is willing to let us look into their channeling claims, then we can arrange for someone to discuss this more fully. In terms of performance problems in other hospitals, we keep in close contact with our distributors worldwide and, in respect to the United States, we are working through some user-specific and machine-specific characteristics in a small number of hospitals. Many of the issues are training related. Given our extensive experience with the characteristics of all commercially available absorbents, we suggest that capnography be used, regardless of which brand of absorbent is chosen.

Please feel free to contact us. Thank you.

Dr. Ciarán Magee
Technical Director
Armstrong Medical Limited
Wattstown Business Park
Newbridge Road
Coleraine BT52 1BS
Northern Ireland
T: 00 44 28 70356029
F: 00 44 28 70356875
e: [email protected]

The information provided is for safety-related educational purposes only, and does not constitute medical or legal advice. Individual or group responses are only commentary, provided for purposes of education or discussion, and are not statements of advice or the opinions of the APSF. It is not the intention of the APSF to provide specific medical or legal advice or to endorse any specific views or recommendations in response to the inquiries posted. In no event shall the APSF be responsible or liable, directly or indirectly, for any damage or loss caused or alleged to be caused by or in connection with the reliance on any such information.