EFFECTS OF RESPIRATORY STIMULANTS ON CEREBRAL METABOLISM AND BLOOD-FLOW

The cerebral metabolic and circulatory effects of the two main classes of respiratory stimulants used in the apnea of the newborn and premat ure infant, i.e. methylxanthines and doxapram, have not been studied i n great detail. In adult animals and humans, methylxanthines widely in crease cerebral metabolic rates and simultaneously decrease cerebral b lood flow levels. Thus, these compounds are able to reset the level of coupling between cerebral blood flow and energy metabolism inducing a relative hypoperfusion at a constant metabolic rate. In neonates, met hylxanthines induce no change in cerebral blood flow as long as the dr op in pCO(2) related to drug administration is prevented. Information on doxapram effects on cerebral blood flow and metabolism is very scar se and limited to adult animals. Doxapram does not induce any change i n cerebral energy metabolism and transiently decreases cerebral blood flow. In conclusion, it seems that the use of methylxanthines in apnei c newborn infants fulfils a good margin of safety with respect to cere bral blood flow as long as no other pathology such as marked hypoxia o r seizures is present. The use of doxapram also seems to stay in a goo d margin of safety in terms of cerebral blood flow and energy metaboli sm but many more studies are necessary to better understand the effect s of this respiratory stimulant on cerebral functional activity.