EFFECTS OF PHENOBARBITAL ON CEREBRAL BLOOD-FLOW DURING HYPOXIA

Phenobarbital (PB), at anticonvulsant dosages, has been used in an att empt to reduce hypoxic brain injury in asphyxiated newborn infants. Th e effects of PB pretreatment on the cerebral blood flow (CBF) response in hypoxia were studied in 15 curarized and mechanically ventilated p iglets: 7 animals were pretreated with 20 mg/kg of PB (group 1) and 8 served as untreated controls (group 2). Successive aliquots (25 ml) of carbon monoxide were introduced into a closed ventilator circuit and CBF (measured with radiolabelled microspheres), arterial blood pressur e, blood gases, arterial pH and PaO2 were subsequently determined at d ifferent levels of hypoxia. The amount of hemoglobin available for oxy gen transport (i.e. total Hb - HbCO) was used to express hypoxic aggre ssion and decreased from grade I (>2 mmol/l) to grade II (1-2 mmol/l) to grade III (<1 mmol/l). In the control group, CBF increased during g rade-I hypoxia and continuously remained above baseline values during grade-II and grade-III hypoxia. In pretreated animals, however, only g rade-II hypoxia was associated with a significant increase in CBF abov e baseline. In addition during grade-III hypoxia, CBF decreased to the prehypoxic values despite a fall in cerebral oxygen delivery and card iac index. These data suggest that PB should be used with caution to p revent brain damage in the asphyxiated newborn infants.