The Anesthesia Gas Machine
Michael P. Dosch CRNA PhD, Darin Tharp CRNA MS
University of Detroit Mercy Graduate Program in Nurse Anesthesiology
This site is http://healthprofessions.udmercy.edu/programs/crna/agm/.
Revised March 2016
ANESTHESIA GAS MACHINE> COMPONENTS & SYSTEMS> DELIVERY> CARBON DIOXIDE ABSORPTION
Function- makes rebreathing possible, thus conserving gases and volatile agents, decreasing OR pollution, and avoiding hazards of carbon dioxide rebreathing. Soda lime- Activator is NaOH or KOH. Silica and kieselguhr added as hardeners. Indicators for soda lime (such as ethyl violet) are colorless when fresh, and purple when exhausted, because of pH changes in the granules. Problems:
The strong bases (NaOH, KOH which function as activators) have been convincingly implicated in the carbon monoxide problem with the ethyl-methyl ethers, and the generation of Compound A by sevoflurane. Two more definitive approaches to dealing with these problems have surfaced:
Lithium hydroxide lime (LitholymeTM) (Allied Healthcare Products, Inc.) is an effective carbon dioxide absorbent, and is free of the strong bases (NaOH, KOH). "Litholyme contains: LiCl as the catalyst to accelerate the formation of CaCO3; ethyl violet as the indicator; and does not contain KOH or NaOH." The CO2 absorbing capacity is similar to Sodasorb- and more than Amsorb (Dahms et al. 2010, Abstract A717). Litholyme does not produce carbon monoxide from breakdown of desflurane or other methyl-ethyl ethers under any circumstances- even when it is dessicated Dahms et al 2010, Abstract A718. The manufacturer shows data here that indicate that Litholyme:
Spiralith has lithium hydroxide (rather than calcium hydroxide) as its main constituent. Spirolith is a unique absorbent which is efficient, and does not degrade volatile agents. It does not desiccate since its water content is chemically bound. Spirolith is a powder enclosed in a polymer sheet, making the absorbent recyclable, and also limiting the danger to eyes and skin posed by dust in traditional absorbents. Since it lacks a color indicator, it may only be used with FICO2 monitoring.
Both Litholyme and Spiralith were found to be quite efficient in Aisys canisters (J Clin Monit Comput. 2016;30:193). Lithium hydroxide is a mature technology with a long history of use in space and submarine environments (though somewhat new in anesthesia applications).
Eliminating the activators entirely produces an absorbent which has similar physical characteristics (but perhaps less carbon dioxide absorption efficiency), as compared to soda lime: Amsorb (Armstrong Medical Ltd., Coleraine Northern Ireland).
Drägersorb 800 granules in CLIC absorber on Apollo. Click on the thumbnail, or on the underlined text, to see the larger version.
New "house brand" absorbents have been created to help deal with the problems of modern volatile anesthetic (desflurane, sevoflurane) breakdown. "House brand" absorbents made by GE and Dräger have less activator currently; especially less KOH. Dräger makes an absorbent with decreased amounts of NaOH, and no KOH (Drägersorb 800 Plus) and an absorbent which (it is stated) will not generate Compound A under any circumstances (Dragersorb Free). GE makes Medisorb, which also has decreased amounts of strong bases. The canisters which fit on the Aisys and Avance are filled with Medisorb.
Baralyme (Allied Healthcare Products Inc, St Louis MO) was withdrawn from the market worldwide in 2005. The - activator was Ba(OH)2 octahydrate; no hardeners, slightly less efficient. Colorless or pink changing to blue-gray with exhaustion.
Numbers are approximations which may not sum to 100%. Data assembled from APSF Newsl 2005;2:25; Anesth Analg 2001;93:221; Anesthesiology 2001; 95:1205; Anesth Analg. 2000;91:220; www.spiralith.com; http://www.litholyme.com/images/Litholyme_MSDS.pdf; and http://www.microporeinc.com/media/docs/MSDS_ExtendAir_Lithium.pdf
|Component||Soda lime||Medisorb||Dragersorb 800+||Amsorb||Litholyme||Spiralith|
|NaOH % (activator)||2-4||1-2||2||-||-||-|
|KOH % (activator)||1-3||0.003||2||-||-||-|
|Lithium chloride % (catalyst)||-||-||-||-||< 3||-|
|Water Content %||14-19||16-20||~14||14.5||12-19||Unknown*|
#1 is called the first neutralization reaction. In #3 the second neutralization reaction and the regeneration of activator take place. CaCO3 is an insoluble precipitate.
If present, KOH participates in the reactions above in the same manner as NaOH.
While it is possible to change canisters mid-case, it is safer to wait until the end of the case to do so. There are many case reports of inability to ventilate due to leaks after canisters could not be fit back together (Br J Anaesth 2011. Available at: http://bja.oxfordjournals.org/forum/topic/brjana_el%3B7463. J Clin Monit Comput. 2010;24:143. Anesth Analg 2009;109:1350. Anesthesiology 2013;118:751.)
Canister Change in Aisys. Click on the thumbnail, or on the underlined text, to see the larger version.
To change the absorbent granule canister on Aisys, press the latch release (arrow at left). The canister will pivot, and may then be slid off its rails (right). A new canister is then slid on, and pivoted upwards to latch.
CLIC canister Change on Apollo. Click on the thumbnail, or on the underlined text, to see the larger version.
The CLIC canister is changed in a similar way on the Apollo.
|Steps for changing Aestiva canisters. Click on the thumbnail, or on the underlined text, to see the larger version (23 KB).|
To change canisters in an Aestiva dual-canister setup, follow the procedure below.
Newer gas machines which measure inspired carbon dioxide (often with alarms) allow us to change canisters when inspired carbon dioxide exceeds a known threshold (2-3 cm H2O).