Experiments have been done to determine the effect of hypothermia on dogs previously subjected to hypotension induced by hæmorrhage. After 1 hr. of hypotension two groups of dogs were cooled to 28° C. and 31° C. respectively and then left for 2 hr. at room temperature (24° C.). Seven out of nineteen died of ventricular fibrillation. On rewarming six more died after some hours. The E.C.G. (Lead II) changes during hypothermia were much the same as those found in cooled normal dogs. The E.C.G. changes due to hæmorrhage were similar to those found in dogs subjected to hæmorrhage at normal temperatures superimposed on the hypothermic E.C.G. patterns. Below 25° C. it was sometimes difficult to decide on the relative preponderance of the two effects. The only difference between survivors and those dogs which died was the greater incidence of the “Osborn wave” in the E.C.Gs. of the latter. However, there is no evidence that the appearance and behaviour of this wave can be taken either as a sign of a poor prognosis or as a warning of impending ventricular fibrillation.
E.C.G. changes were recorded in the course of twenty‐nine experiments on dogs which were bled during either light (30–32° C.) or deep (26–28° C.) hypothermia. After being maintained with a blood pressure of 40 mm. Hg for 2 hr., sixteen dogs received a 6 per cent solution of dextran in amounts equal to the total blood loss. The survival rate in this group was 87·5 per cent. The majority of dogs in the control group without administration of dextran died some hours after termination of the bleeding.
It was impossible to pick out any E.C.G. changes which are characteristic for the state of prolonged posthæmorrhagic hypotension in hypothermia. In fact, excluding the effects of hypothermia itself, the E.C.G. changes were very similar to that described for dogs bled at normal body temperature. The less the hypothermia, the greater was the similarity.
It is our opinion that the described E.C.G. changes do not explain the greater tolerance of cooled dogs to the posthæmorrhagic hypotension. Also, none of the described E.C.G. changes, including “Osborn's” wave, in the course of cooling and during posthæmorrhagic hypotension could be taken as a bad prognostic sign.
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