Brazilian Journal of Anesthesiology
https://bjan-sba.org/article/doi/10.1590/S0034-70942004000300015
Brazilian Journal of Anesthesiology
Miscellaneous

Como evitar a formação de substâncias tóxicas durante a absorção de dióxido de carbono pela cal sodada com uso de anestésicos halogenados

Preventing toxic substances production during carbon dioxide absorption by soda lime with halogenate anesthetics

Renato Ângelo Saraiva

http://dx.doi.org/10.1590/S0034-70942004000300015 Braz J Anesthesiol, vol.54, n3, p.431-437, 2004
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JUSTIFICATIVA E OBJETIVOS: A cal sodada desde o início do seu uso sempre apresentou algumas complicações que resultaram em dificuldade na sua aplicabilidade. No entanto, devido as grandes vantagens que oferecia em relação a redução do fluxo de gases frescos, despoluição da sala de cirurgia e umidificação do sistema de inalação e via aérea, fizeram com que continuassem as pesquisas para que pudesse ser melhorada e corrigida de forma que a continuidade da sua utilização fosse assegurada. Atualmente existe o problema da desidratação com elevação da temperatura e da degradação metabólica dos anestésicos halogenados que necessitam de cuidados especiais para evitar a formação de produtos tóxicos. CONTEÚDO: Existe uma reação em cadeia a partir da cal sodada desidratada ou ressecada com baixos volumes percentuais de água. Há aumento da temperatura, maior absorção de anestésico halogenado para o interior do granulo de cal em seguida maior degradação metabólica das moléculas destes agentes e conseqüentemente a produção de substâncias tóxicas como o Composto A pela reação dos hidróxidos com o sevoflurano. Há também formação de monóxido de carbono produzido da mesma forma pela reação entre os halogenados e as bases fortes da cal. O composto A é nefrotóxico e o monóxido de carbono leva a hipóxia e alterações graves da coagulação do sangue. Além dos cuidados para a hidratação da cal sodada é possível usá-la sem conter as bases fortes como os hidróxidos de potássio e de sódio, contendo apenas hidróxido de cálcio para evitar excessivo aumento da temperatura e grande degradação metabólica dos halogenados sem prejudicar a absorção do dióxido de carbono. CONCLUSÕES: Deve-se ter o cuidado em usar a cal sodada mais recente possível e quando ela fica exposta ao meio ambiente (ar seco) por muitas horas como por exemplo em um final de semana (mais de 48 horas) é recomendável colocar água, de preferência destilada, na relação de 25 ml para cada 500 g de cal. Atualmente a indústria está bem informada sobre o problema da composição da cal, então, deve-se preferir a cal sodada que tenha somente o hidróxido de cálcio e seja totalmente desprovida de hidróxido de potássio e hidróxido de sódio.

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Abstract

BACKGROUND AND OBJECTIVES: Since the beginning, soda lime use has presented some complications which resulted in its difficult application. However major advantages such as decreasing fresh gas flow, anesthetic consumption and operating room pollution, and improving breathing system and airway humidity, have pushed research forward to improve it and assure the continuity of its use. Currently, there are problems with dehydration, increased temperature and metabolic degradation of halogenate agents, which require special care to prevent toxic substances formation. CONTENTS: There is a chain reaction as from dehydrated or dried out soda lime with very low percent volume of water. There is increased temperature, more halogenate anesthetic absorption by lime granules, followed by higher metabolic degradation of these agents' molecules and, as a consequence, the production of toxic substances, such as Compound A by reaction of hydroxides with sevoflurane. There is also carbon monoxide production by reaction of halogenate anesthetics and strong lime bases. Compound A is nephrotoxic and carbon monoxide may lead to hypoxia and severe coagulation problems. In addition to care with soda lime hydration it is possible to use it without strong bases, such as potassium and sodium hydroxides, with just calcium hydroxide to prevent excessive temperature increase and major metabolic degradation of halogenate anesthetics without impairing carbon dioxide absorption. CONCLUSIONS: Care should be taken to use the newest possible soda lime; and when it is exposed to environment (dry air) for many hours, such as during weekends (more than 48 hours) it is recommended to add distilled water in the ratio of 25 mL to 500 g of soda lime. Industry is currently well aware of lime composition problems so, soda lime containing exclusively calcium hydroxide and totally potassium and sodium hydroxide-free should be preferred.

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References

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