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The uptake of ISO-flurane by the foetal lamb in utero: Effect on regional blood flow

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Because isoflurane has recently been approved for clinical use in anaesthesia, we have studied the effect of this agent in the foetus using the pregnant ewe as an animal model.

Eight pregnant ewes of 120–125 days gestation were surgically prepared with indwelling catheters and tracke-ostonty. Prior to anaesthesia, labelled microspheres were injected into the foetal circulation to determine cardiac output and regional blood flows to all organs. The ewes were anaesthetized with a constant inspired concentration of 2 .0 per cent isoflurane in oxygen. Blood samples were drawn to construct an uptake curve for both mother and foetus. At 60 and 96 minutes of anaesthesia, microspheres were injected into the foetal circulation to measure changes in organ blood flow from the control period.

Isoflurane crossed the placenta and appeared in the foetal circulation within two minutes. By 96 minutes, maternal and foetal arterial levels were 116.3 ± 9.9 and 99.3 ± 9.1 mEqIL (0.98 vol% and 0.75 vol%). There were no significant changes in foetal blood pressure or pulserate but foetal pH decreased significantly from 7,39 ± 0.02 to 7.26 ± 0.2 (mean ± SEM) and base excess decreased from -1.1 ± 1.5 to -6.2 ± 0.7. Foetal cardiac index decreased from 390.8 ± 26 9ml-kg-1 min-1 to 292.0 ± 13.8 after 96 minutes of anaesthesia. There were no significant changes in any of the maternal cardiovascular or acid-base parameters. In the foetal lamb, isoflurane anaesthesia produces foetal acidosis and decreases foetal cardiac index after 96 minutes of anaesthesia.


L’ttpprobalion récente de F isoflurane pour usage clinique en anesthésie nécessitait une étude de ses effets sur te fœtus; elle fut réalisée sur la brebis gravide. Des sondes à demeure ont été installées par manœuvres chirurgicales sur huit brebis gravides de 120 à 125 jours qui furent aussi trachéotomisées. Avant l’ anesthésie, des microsphères marquées ont été injectées dans la circulation fœtale pour mesurer le débit cardiaque et les débits sanguins régionaux, Les brebis furent anesthésiée.s par inhalation d’une concentration inspirée constante de 2 pour cent d’ isoflurane dans l’ oxygène. Des échantillons furent prélevés pour tracer une courbe de capture tant pour la mère que pour le foetus. Après 60 et 96 minutes d’anesthésie, des microsphères furent injectées dans la circulation fœtale pour mesurer les changements de débits régionaux comparatifs à la période de contrôle. L’isoflurane a traversé le placenta et est apparu dans le sang fœtal en moins de deux minutes. A ta 96ième minute, les niveaux artériels maternels et fœtaux étaient respectivement de 116.3 ± 9.9etde99.3 ± 9.1 (0.98 vol pour cent et 0.75 vol. pour cent). ll n’y a pas eu de changements significatifs de la pression sanguine et du pouls fœtaux mais le pH a baissé de façon significative de 7.39 ± 0.02 à 7.26 ± 0.2 et l’ excès de base est passé de-1.1 ± 1.5 à -6.2 ± 0.7. L’index cardiaque fœtal a diminuéae390.8 ± 26.9mlkg-’ min-1 à292.0± 13.8 après 96 minutes d’ anesthésie, On n’a pas trouvé de changements significatifs dans les paramètres maternels cardiovasculaires et acido-basiques.

L’anesthésie à l’isofiurane produit chez le fœtus de la brebis de l’ acidose et diminue l’index cardiaque après 96 minutes d’anesthésie.


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Author information

Correspondence to D. R. Biehl or R. Yarnell or J. G. Wade or D. Sitar.

Additional information

Supported in part by the St. Boniface Research Foundation, Grant no. RF-79-3 and the Medical Research Council of Canada, Grant No. MA-6735.

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Biehl, D.R., Yarnell, R., Wade, J.G. et al. The uptake of ISO-flurane by the foetal lamb in utero: Effect on regional blood flow. Can Anaesth Soc J 30, 581–586 (1983). https://doi.org/10.1007/BF03015226

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Key words

  • anaesthetics
  • volatile
  • isoflurane
  • anaesthesia
  • obstetric
  • uterus
  • blood flow