Influence of anaesthetic agent on limb abnormalities observed following amniotic sac puncture

In all of our previous studies into the effect of amniotic sac puncture (AS P) carried out on day 13 of pregnancy in mice, we have used intraperitoneal Avertin (tribromoethanol) as the general anaesthetic. In the present study , we used an inhalational anaesthetic (a mixture of halothane, oxygen and n itrous oxide in a ratio of 2:3:3). The principal difference between these t wo regimens is that even under optimal post-operative conditions when Avert in is used it can take between 45 and 90 min before complete recovery is ac hieved; when the inhalational anaesthetic is used, complete recovery is usu ally achieved within about 3-5 min. Because the experimental conditions wer e otherwise identical, this allowed the influence of the anaesthetic employ ed during ASP and the incidence of abnormalities induced on survival rate t o day 19 of pregnancy to be studied. The survival rate was slightly higher when the inhalational anaesthetic was used, as was the incidence of limb ab normalities, although the overall incidence of gross abnormalities involvin g the palate, limbs and tail was not significantly different. The most mark ed difference, however, was in the incidence of syndactyly, which was signi ficantly lower when the inhalational compared to the intraperitoneal anaest hetic was used: 26.6% v. 70.2% of the abnormal limbs analysed. A possible h ypothesis is presented to explain this difference.