ABSTRACT
Hypotension is the most common side effect from spinal anesthesia, and studies in rats suggest that this side effect could be abolished by the coadministration of neostigmine with spinal local anesthetics. Therefore, the aim of the present work was to study the hemodynamic effects of spinal neostigmine and to test whether neostigmine would prevent spinal bupivacaine-induced hypotension in dogs. Fifteen dogs were included in this study. They were anesthetized with i.v. pentobarbital. Polyvinyl cannulas were inserted into a femoral artery and vein. The femoral artery cannula was connected to the Super Speed Kymograph via heparinized tubing for arterial blood pressure [BP] monitoring. ECG electrodes were connected to the dog via special needles for decubitus, a polyvinyl [epidural] catheter was inserted intrathecally [IT] via a Tuohy needle inserted in L 4-5 space. After a period of 30 mm, baseline values for HR and BP were recorded. The dogs were divided into three groups of five each. In the first group, 1 ml 0.5% bupivacaine in 8.33% dextrose was injected via the IT catheter. In the second group, 1mg [lml] neostigmine was injected via the IT catheter and followed by 1 ml 0.5% bupivacaine in 8.33% dextrose after 30 min. HR and BP were recorded at 10-min intervals. The third group was the control one in which l ml normal saline was injected via the IT catheter. Transverse sections were taken from the spinal cord at the lumbar region from neostigmine-treated dogs and from the control ones for histopathological examination by light and electron heart rate [HR] recording. In the lateral microscopes. Spinal neostigmine alone increased [non significantly] arterial BP by 5% with a latency of 15 min, but it had no effect on HR. Compared with spinal bupivacaine alone, pretreatment with neostigmine resulted in hypotension of slower onset [15 vs 5 min] shorter duration [60 vs 90 min] and smaller magnitude [-11% vs - 19%]. Light and electron microscope examination did not reveal any change between control and neostigmine treated dogs. In conclusion, spinal bupivacaine-induced hypotension was partially counteracted by spinal neostigmine in dogs