Cerebral and systemic effects of hypotension induced by trimetaphan or nitroprusside in dogs

The effects of hypotension induced by trimetaphan (TMP) or nitroprusside (NTP) together with controlled haemorrhage on cerebral electrical activity, cerebrospinal fluid pressure (CSFP) and systemic circulatory and metabolic variables were measured in 10 mongrel dogs anaesthetized with halothane (end-tidal, 0.88 +/- 0.03%). Induced hypotension was maintained at cerebral perfusion pressure (CPP) of 45 mmHg for 45 min and then at 30 mmHg for 45 min. In five TMP dogs, there were significant decreases in EEG-power and slowing of peak power frequency from the frontal area, but not from the occipital area. The CSFP did not change significantly except for an increase during the induction stage of hypotension. In five NTP dogs, there were no significant changes in EEG-power and peak power frequency throughout the study from either frontal or occipital areas, but CSFP increased significantly. With both drugs, an increase in glucose, lactate and lactate pyruvate ratio (L/P), and a decrease in PaO2 were more pronounced at 30 mmHg than 45 mmHg. With NTP, there were sustained increases in lactate and L/P, even after restoration of arterial pressure. The same magnitude and duration of the decrease in CPP induced by either TMP or NTP produced different effects on cerebral and systemic function.