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The effect of ketamine anaesthesia on the acidotic fetal lamb

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The following study in pregnant ewes was done to examine the effects of ketamine—oxygen anaesthesia on the fetal lamb made acidotic by partial occlusion of the umbilical cord.

Fifteen pregnant ewes were instrumented under general anaesthesia to allow continuous measurement of maternal and fetal mean arterial pressure and pulse rate and for withdrawal of arterial blood samples for blood gas analysis. An occlusion loop was loosely secured around the umbilical cord.

Following a recovery period of 48 hours, a tracheostomy was performed on each ewe. After a control period, the umbilical occlusion loop was slowly inflated until fetal pH had decreased to 7.12-7.15. Following inflation the animals were divided into groups A and B. Group A received no anaesthesia. In Group B, the ewes received ketamine 3mg·kg-1 intravenously and controlled ventilation with F1O2 of 1.0. After ten minutes ketamine 1 mg·kg-1 was given. In both groups radioactive microspheres were injected into the fetus at 0, 5, and 15 minutes.

Ketamine anaesthesia in the pregnant ewe abolished the fetal hypertension and bradycardia produced by partial cord occlusion. All fetuses survived the 15 minutes of ketamine anaesthesia and there were no significant changes in arterial blood gases or pH. Blood flows determined by the microsphere method to the brain, heart, and kidneys were not significantly altered by ketamine. We conclude that ketamine-oxygen anaesthesia does not cause further deterioration in the acidotic fetal lamb.


La présente étude fut faite sur des brebis pleines afin ďexaminer les effets de ľanesthésie à la kétamine—oxygène sur le f œtus de la brebis rendu acidotique par occlusion partielle du cordon ombilical.

Quinze brebis pleines étaient instrumentées sous anesthésie générale afin de permettre la mesure continuelle de la pression artérielle moyenne maternelle et f œtale ainsi que la mesure du pouls et ľétude de la gazométrie. Un tourniquet pouvant permettre ľocclusion fut installé autour du cordon ombilical.

Après une période de recouvrement de 48 heures une trachéostomie fut faite pour chaque brebis. Après une période de contrôle ľocclusion du cordon ombilical fut accomplie lentement jusqu’à la diminution du pH fœtal à 7.12-7.15. Après ľocclusion les animaux furent divisés en deux groupes A et B. Le groupe A n’a reçu aucune anesthésie. Dans le groupe B, les brebis ont reçu de la kétamine 3 mg·kg-1 par voie intraveineuse et leur ventilation fut contrôlée avec une F1O2 de 1.0. Dix minutes plus tard de la kétamine 1 mg·kg-1 fut donnée. Dans les deux groupes des microsphères radioactifs furent injectés dans le f œtus à 0, 5, et 15 minutes.

Lanesthésie à la kétamine chez les brebis pleines a aboli ľhypertension et la bradycardie produite par ľocclusion partielle du cordon ombilical chez les fœtus. Tous les fœtus ont survécu les 15 minutes de ľanesthésie à la kétamine et il n’y avait aucun changement significatif des gaz sanguins artériels ou du pH. Les flots sanguins déterminés par la méthodes des microsphères pour le cerveau, cœur et reins ne furent pas significativement altérés par la kétamine. On conclue que ľanesthésie à la kétamine-oxygène n’amène pas ľavantage de détérioration chez le f œtus acidotique des brebis.


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Correspondence to J. Swartz or M. Cumming or D. Biehl.

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Swartz, J., Cumming, M. & Biehl, D. The effect of ketamine anaesthesia on the acidotic fetal lamb. Can J Anaesth 34, 233–237 (1987). https://doi.org/10.1007/BF03015158

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Key words

  • anaesthesia
  • obstetric
  • anaesthetics
  • intravenous
  • ketamine
  • fetus
  • acidosis