Abstract
We measured ventilation, PetC02 and the ventilatory response to added carbon dioxide before and at intervals up to six hours after epidural morphine 3.5 mg and 7.0 mg, and before and after subcutaneous injections of the same dose in volunteers. Subcutaneous morphine increased PetCO.2 slightly, but did not alter the sensitivity of the response to added carbon dioxide. Epidural morphine reduced ventilation and increased PetC02 progressively with lime and, six hours after injection, reduced the ventilatory response to carbon dioxide considerably. In two subjects tested, these ventilatory effects persisted for twenty-four hours. The added effects of epidural morphine were due primarily to reductions in tidal volume and the tidal volume response to added carbon dioxide. We conclude that epidural morphine causes delayed and very prolonged ventilatory depression, which is of a greater magnitude and a different ventilatory pattern than that which follows the same dose of morphine given subcutaneously. Ventilatory depression after lumbar epidural morphine develops slowly, as the lower limb analgesic effect is waning.
Résumé
La ventilation, la Pco2 de fin d’expiration et la réponse respiratoire à l’inhalation de CO2 ont été étudiées chez des volontaires avant et à intervalles allant jusqu’à six heures, après l’administration par voie péridurale de morphine aux doses de 3.5 et de 7mg. Les mêmes paramètres ont été étudiés après l’administration par voie sous-cutanée des mêmes doses de cet agent. L’administration de morphine par voie souscutanée a été suivie d’une élévation légère de la Pco2 de fin d’expiration mais n’a pas modifié la réponse à l’addition de co2. La morphine administrée par voie péridurale amenait une diminution de la ventilation et une augmentation, croissante avec le temps, de la Pco2 de fin d’expiration; six heures après l’administration péridurale, la réponse respiratoire à l’inhalation de co2 était diminuée de façon considérable. Ces effets respiratoires ont persisté durant 24 heures chez deux des sujets étudiés. Les effets additionnels de la morphine administrée par voie péridurale étaient dus principalement à une diminution du volume courant et de la réponse en volume courant à l’inhalation de co2. Nous concluons que la morphine par voie péridurale produit une dépression tardive et très prolongée de la ventilation et que celte dépression est plus importante (et différente) que celle qui suit l’adminsitration de la même dose de cet agent par voie sous-cutanée. La dépression respiratoire après administration de morphine par voie péridurale s’installe lentement alors que les effets d’analgésie aux membres inférieurs s’atténuent.
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This study was supported by The Medical Research Council of Canada, Grant MA 6443.
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Knill, R.L., Clement, J.L. & Thompson, W.R. Epidural morphine causes delayed and prolonged ventilatory depression. Canad. Anaesth. Soc. J. 28, 537–543 (1981). https://doi.org/10.1007/BF03007149
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DOI: https://doi.org/10.1007/BF03007149