[EEG effects of sodium nitroprusside and hemodynamic references]

A study was performed on baboons (Papio papio) of various hemodynamic and EEG effects of sodium nitroprussiate (SNP), substance with powerful vasodilator action. Three different procedures of drug injection were used: (1) in isolation, either in doses close to those used in clinical practice or in high doses; (2) after neuroleptanalgesia (NLA); (3) after causing vasospasm. With isolated SNP, effects on blood pressure were unstable; in certain cases hypotension could be maintained only with toxic doses. Hypotension was facilitated when NLA had been previously induced. At low doses the cerebral blood flow (CBF) was practically unmodified, whereas at toxic doses it first increased then decreased. In animals under NLA, the CBF drop was only moderate, suggesting persistence of adequate spasm, CBF was significantly improved through SNP. The EEG did not undergo sizeable change at low SNP doses given in isolation; toxic doses always induced alterations with peculiar morphology, but developing only tardily after SNP perfusion was begun. This lag may indicate that hypotensive and toxic SNP effects are dissociated. These alterations suggest that screening of the EEG is necessary during prolonged administration of SNP, e.g., in surgical procedures. Combining NLA and SNP (at low doses) causes EEG deceleration, but no great alteration of the rhythms, as observed during other types of controlled experimental hypotension. Hence, cerebral circulation may be relatively well protected during SNP hypotension.