CO2 production, body temperature, and ventilation in hypoxic newborn cats and dogs before and after body warming.

Many newborn mammals decrease metabolism and body temperature (Tb) during acute hypoxia. We asked what effects warming of the hypoxic newborn would have on these variables. In unanesthetized newborn cats and dogs, we measured the breathing pattern, CO2 production, Tb, and ambient temperature during normoxia at an ambient temperature of 28 degrees C, 30 min of hypoxia (10% O2), and an additional 30 min of hypoxia plus warming. During hypoxia, Tb and CO2 production decreased in both species, whereas the absolute value of ventilation did not change in kittens and increased in puppies. During hypoxia plus warming, Tb was gradually returned to the normoxic value by increasing ambient temperature by 3 to 4.5 degrees C. This increase did not modify CO2 production in either species, and it increased minute ventilation in kittens. We conclude that during hypoxia 1) warming the newborn can increase Tb, but not metabolism, to the normoxic value; 2) the decrease in Tb is not a causative prerequisite of the hypoxia-hypometabolism; and 3) an artificial increase in Tb to the normoxic value can stimulate minute ventilation, probably because it is perceived as an hyperthermic stimulus.