Choosing the right carbon dioxide absorbent

Chemical reactions between inhalation anaesthetics and carbon dioxide absor bents are a well-known problem. Desflurane, enflurane and isoflurane are de graded to carbon monoxide by desiccated soda lime. Halothane and sevofluran e are decomposed to multiple gaseous compounds, some of which are harmful f or the patient, Both the last-named agents, however, do not only react with dry absorbents but are also degraded to haloalkenes by absorbents containi ng the normal amount of water, In recent years compound A, the degradation product of sevoflurane with carbon dioxide absorbents, became a matter of c oncern, and there is a still ongoing scientific discussion on its possibly nephrotoxic effect in humans. Besides correct handling of the carbon dioxide absorbent its judicious sele ction is an additional way to minimize any risk for the patient. As barium lime was found to react more eagerly with volatile agents than soda lime it s further use should be completely abandoned. Alkali metal hydroxides conta ined in soda lime, especially perhaps potassium hydroxide, are mainly respo nsible for degradation of inhalation anaesthetics. Potassium hydroxide free soda lime, possibly being less liable to degrade volatiles, became availab le and should be used consistently in routine clinical practice, Neverthele ss, all care should be taken, to avoid any accidental desiccation of the ca rbon dioxide absorbent. Recently, two carbon dioxide absorbents were introd uced which do not react with inhalation anaesthetics at all, neither in des iccated nor in normal wet condition. Calcium hydroxide lime, being already approved for clinical use and available in the countries of the European Un ion, has a somewhat lower absorption capacity than soda lime but meets all requirements for routine clinical use. The use of this absorbent should man datory if sevoflurane routinely is used in long lasting low-flow anaesthesi a, Lithium hydroxide also was found to be inert with respect to anaesthetic agent degradation. The basic substance, however, is more aggressive than e ither soda or barium lime, and it is quite expensive. Considering both alte rnatives, actually calcium hydroxide lime seems to be more promising. Thus, safety of inhalation anaesthesia can be improved not only by correct handl ing but also by a judicious selection of the carbon dioxide absorbent.