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Sl'~DIA!n' III illfallts IIlld pz/;lets sulijected to periods of circulatory arrest at ;!()GC there u.'as close corrclatiol1 bet1£'eell duratioll of arrest alld de/a)' in return of c/ectroel1ceplza/ographic actit'ity. Post mortem studies demonstrated histological lTidelIce of brain damage in patients after circulatory arrest at 20°C. Similar histolor;ical changes lt'ere demonstrated in piglets, including some wlzo had complete I,'.E.(;. and clillical rcc07'ery fro/ll circl/latory arrest. In a pre\'ious stud~' of the effects of circulator~' arrest at :WcC in the infant pig (Fisk et al. ] 974), we found lesions in the cerebral cortex of pigs subjected to circulatory arrest for a period of one hour at 20°C and then allowed to survivc for 1 0 da~'s before being killed. These lesions were not found in pigs subjected to continuous perfusion at 20°C or at ;)72C. \\'e suggested tha~ the delay in return of electrocncephalogram (E.E.G.) activity after such circulatory arrest may be a useful index of the degree of ischaemic cerebral insult. BreclmtT et al. (HI;)~I) showed an eXjlonential relationship between the period of circulatory arrest at :~OcC in patients undergoing open-heart surgny and the time taken for return of continuous E.E.G. activity. They suggested that this provided a guide to the severity of the ischaemic insult of the brain. In this pillwr we report on E.E.G. activity and postmortem histological examination of the brain in infants SUbjected to circulatory arrest for open-heart surgery, and on the results of a study of infant pigs subjectcd to various periods of circulatory arrest at 20°C. \\'c have attempted to "correlate the period of arrE'st and the associated delay in return of E.E.C. activity with the presence of detectable histological changes in the cerebral cortex in surviving piglets.

Catheters for paediatric endotracheal suction were studied using an artificial lung with compliances in the range encountered in paediatric practice. With various combinations of" lung" compliance, size of endotracheal tube, endotracheal connector and catheter, "tracheal" pressure and air flow between endotracheal tube and catheter were measured. Recommendations for combinations of endotracheal tube, connector and catheter stze are made. The maximum negative pressure applied to the catheter should be limited.

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