Leon Bunegin

The effect of magnesium sulfate administration on cerebral and cardiac toxicity of bupivacaine in dogs

The effect of acutely elevated serum magnesium on the CNS and cardiac toxicity of bupivacaine was studied. Anesthesia was induced in mongrel dogs with thiopental, 25 mg/kg, and ventilation was controlled. Sedation was maintained with fentanyl (25 micrograms/kg bolus and 5 micrograms.kg-1h-1) and pancuronium (0.15 mg/kg bolus and 0.05 mg.kg-1h-1) provided paralysis. Two hours after the thiopental bolus, all animals received an intravenous (iv) infusion of bupivacaine (1 mg.kg-1 min-1). The control group (5 animals) received bupivacaine only. The Mg++ group (5 animals) received MgSO4 140 mg/kg iv and 80 mg.kg-1 h-1 15 min prior to beginning the bupivacaine infusion. Lead II ECG, cardiac hemodynamics, and two-channel EEG were continuously monitored. Serum magnesium concentrations in the Mg++ group rose from 0.67 mM (1.3 mEq/L) to 2.42 mM (4.8 mEq/L). The bupivacaine infusion caused PR and QRS interval prolongation in both groups, but QRS widening was greater in the control group. QT interval corrected for heart rate (QTIc) lengthened only in the control group. A depression of left ventricular stroke work index (LVSWI) occurred to an equal extent in both groups. The seizure dose of bupivacaine was not different between the two groups: 12.9 +/- 2.3 (SEM) mg/kg in the control group and 13.9 +/- 2.5 mg/kg in the Mg++ group.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracranial and spinal cord hemodynamics in the sitting position in dogs in the presence and absence of increased intracranial pressure

The effett of the sitting position on cerebral blood flow (CBF), spinal cord blood flow (SCBF), and cerebral metabolic rate for oqgen (CMRo2) was studied in anesthetized dogs with and without increased intracranial pressure. Blood flow measurements w e made at four time periods: (a) initial supine; (b) after 5 min in the sitting position; (c) after 60 min in the sitting position; and (d) 25 min after resuming the supine psition. Six dogs (group 1) serued as a control group with a normal intracranial pressure (ICP). In five dogs (group 2) ICP was elevated with a parietal epuiural balloon 1 h before the first measurements of blood flows were made. Saline was injected incrementally into the balloon so as to reach a steady-state ICP of 30 mm Hg for 1 h. Elevation o f ICP in group 2 resulted in significantly lower CBF, SCBF, and CMRo2 compared with group 1. Postural changes in group 2 did not result in any significant change in blood flow measurements whereas in group 2, after 1 h in the sitting position, there were significant decreases in CBF and SCBF compared with the initial supine measurements. There was, however, no corresponding decrease in CMRo2 in group 2 with change in psition. These data suggest that both the brain and spinal cord may be at risk for ischemia during sitting position procedures under general anesthesia in the presence o f elevated ICP.