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VASOPRESSORS TO MAINTAIN CEREBRAL PERFUSION PRESSURE IN HYPOTENSIVE RABBITS WITH RAISED INTRACRANIAL PRESSURE

Department of Anesthesia, London Health Sciences Centre, Univ Campus, 339 Windermere Road, London, Ontario, N6A 5A5

INTRODUCTION

Maintenance of cerebral perfusion pressure (CPP) is a primary goal in the management of patients with raised intracranial pressure (ICP). Elevation of mean arterial pressure (MAP) with a vasopressor is an effective means of modifying the CPP (ie. CPP=MAP-ICP). This study examined the use of phenylephrine (PE) or norepinephrine (NE) to increase MAP in hypotensive rabbits with elevated ICP. We hypothesized that both drugs would increase MAP but not ICP.

METHODS

IRB approval was obtained. 19 New Zealand White rabbits were anesthetized and maintained normothermic and normocapnic (BASELINE) . An extradural balloon was used to increase ICP to 25 mmHg while keeping CPP at 70 mmHg (RAISED ICP). The animal was then hemorrhaged to reduce MAP by 30% and CPP to 55 mmHg for a period of 15 minutes (HYPO). The rabbits were then randomized to receive either a 15 minute infusion of PE or NE, titrated to restore CPP to pre-hypotensive values. Subsequently the rabbits were subjected to another 15 minute hypotensive phase (HYPO) and then given the alternate vasopressor.

RESULTS

The results for PE and NE were pooled based on drug received (fig). Two rabbits died and were not included in the data. MAP increased from 74.0 ±8.68 to 96.2 ±8.34 mmHg during infusion of PE (p< 0.05) and from 76.2 ±8.66 to 98.2 ±8.29 mmHg during infusion with NE (p< 0.05). However, there were no significant changes in ICP with either drug (p>0.23).

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PE and NE can be used to increase CPP without adversely affecting ICP, when ICP is increased by a focal lesion.

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