Abstract â–¡ 107

SIDS has been associated with winter climates, infection, and overwrapping of babies. The hypothesis has been tested in this laboratory that two different causes of increased metabolic rate, high core temperature (via the vant Hoff, or Q10, effect) and face cooling, might synergistically induce hyperthemia. This proved not to be the case, but we now report that if raised core temperature is made more like a febrile episode, by the intravenous administration of Salmonella abortus equi pyrogen, there is indeed a synergistic response. In the present investigation, 13 piglets aged 7-9 days were placed to sleep inside an air-tight chamber through which air was passed at a known, fixed rate, so as to allow calculation of oxygen consumption from inlet and outlet gas analysis. The animals were wrapped in an electric heating blanket, leaving the face exposed to air, and warmed until their core (rectal) temperature was 40.0 - 41.0 C (0.5 - 1.5 C above normal). Oxygen consumption, rectal, shin and ear surface temperatures were then recorded during warm face conditions, following which the air in the chamber was abruptly cooled from 32_C to 15 C, by surrounding with an ice-salt freezing mixture. Following recording under cold face conditions, the freezing mixture was removed and the chamber temperature restored to 32 C. Pyrogens (salmonella abortus equi lipopolysaccharide, 1 g stat then 4 g hr-1) were then administered intravenously and the cooling protocol repeated when a fall in ear temperature signalled the beginning of the thermogenic state. In a second group of 13 piglets the effect of the effect of pyrogens on oxygen consumption and temperatures without face cooling was recorded. Cooling of the face caused an average fall in oxygen consumption of 6.5% due to the van't Hoff effect. However, when the face cooling protocol was repeated with pyrogens 6 of the 13 piglets responded with an increase in oxygen consumption of between 18% and 78% (48% average), while the remaining 7 animals showed no response. Pyrogen administration in the absence of face cooling in the control group of animals caused no significant change in oxygen consumption. This piglet model of a human baby with a cold, warmly wrapped in a cold room clearly shows that the combination of a cold face and a febrile state can cause a dramatic rise in metabolic rate, suggesting there may be danger of life-threatening hyperthermia under such conditions.