Respiratory and cardiovascular changes during asphyxia and resuscitation of foetal and newborn rabbits.

Abstract

A study has been made of the respiratory and circulatory responses to asphyxia and resuscitation of fœtal and newborn rabbits. Fœtuses were both delivered and maintained under isotonic saline, while newborn animals were asphyxiated in an atmosphere of N2 after light ether anæsthesia. Both groups were resuscitated by intermittent positive pressure ventilation with 02, begun after the last spontaneous gasp of asphyxia.The response to asphyxia was very similar in the two groups. There was a short initial period of (primary) apnœa, accompanied by a sudden fall in heart rate and blood pressure. This hypotension and bradycardia during the early part of asphyxia was reduced by vagotomy. Following primary apnœa, the animals gasped for some 15–20 min. and then again became apnœic (secondary apnœa). The heart rate and blood pressure fell further and, in the absence of external interference, the animals died. Resuscitation was successful, provided the blood pressure was above 5 mm. Hg at the start of I.P.P. ventilation. The heart rate and blood pressure invariably rose before the return of respiration in the successful cases. The Hering‐Breuer and paradoxical reflexes were fully active in the newborn rabbit, but were abolished by asphyxia due to a central nervous block. They did not return for several minutes after resuscitation.