Propofol versus isoflurane anesthesia under hypothermic conditions: effects on intracranial pressure and local cerebral blood flow after diffuse traumatic brain injury in the rat

Abstract

BACKGROUND The aim of this study was to compare the cerebral protective effects of two known protective anesthetics, isoflurane and propofol, when these were used in combination with moderate hypothermia (33–34°C) after diffuse traumatic brain injury (TBI) in the rat. We assessed cerebral protection by measuring local cerebral blood flow (LCBF), mean arterial blood pressure (MABP), cerebral perfusion pressure (CPP) and intracranial pressure (ICP). METHODS Sixteen female Wistar rats weighing 275 to 350 g were anesthetized and subjected to an accelerated-impact weight-drop model of diffuse TBI. Hypothermia (33–34°C) was induced 45 minutes after TBI (baseline), and was maintained for 180 minutes. The isoflurane group ( n = 8) received 70% N 2O in O 2, and isoflurane at 0.9 ± 0.04%. The propofol group ( n = 8) received 70% N 2O in O 2 and a propofol infusion (12 mg/kg/hr). LCBF was measured by laser Doppler flowmeter. MABP, ICP, and brain and rectal temperatures were measured every 15 minutes from baseline through 180 minutes. Blood gas and hematocrit testing was also done at baseline and every 60 minutes thereafter to assess the animals’ physiological state. RESULTS In the isoflurane group, MABP and CPP decreased significantly from baseline to 180 minutes ( p<0.05 and p<0.01, respectively), and MABP was significantly lower than the pressure in the propofol group from 45 minutes through 180 minutes ( p<0.05, p<0.01). ICP and LCBF remained unchanged in this group. In the propofol group, from baseline to 180 minutes, CPP increased to maximum 120 ± 8 mmHg at 75 minutes from 98 ± 5 mmHg ( p<0.05) and ICP fell from 18 ± 2 mmHg to 7 ± 1 mmHg ( p<0.01); and the latter was significantly lower than ICP in the isoflurane group ( p<0.05, p<0.01, p<0.001). LCBF in this group was significantly higher than LCBF in the isoflurane group in the last 30 minutes of the experiment ( p<0.05). The propofol group showed no change in MABP over the course of the experiment. CONCLUSION In the clinical setting, propofol anesthesia may be better for use in combination with hypothermia in cases of traumatic brain injury, as it reduces ICP and increases CPP under these conditions.