Intravenous dexmedetomidine decreases lung permeability induced by intracranial hypertension in rats.

Background: Intracisternal dexmedetomidine (Dex) attenuates cardiac dysfunction in rats with intracranial hypertension (ICH). However, the effects of IV Dex on cardiac function and lung permeability during ICH have not been evaluated. We tested the hypothesis that IV Dex attenuates hemodynamic changes and decreases lung permeability induced by ICH in rats.

Methods: Halothane-anesthetized and mechanically ventilated rats were divided into four groups. In two groups, a subdural balloon catheter was inflated for 60 s to produce ICH. Arterial blood gas analysis was performed before and 30 min after ICH. Mean arterial blood pressure, heart rate (HR) and intracranial pressure were monitored for 30 min. The Dex group (n = 8) received IV Dex 80 microg/kg, followed by 6 microg.kg(-1).min(-1) (40 microg/mL) for 10 min and the control group (n = 8) received IV saline 2 mL/kg, followed by at 0.15 mL.kg(-1).min(-1) for 10 min. Surgery was performed without ICH with Dex (Sham-Dex group, n = 5) and without Dex (Sham-control, n = 5). In all groups, pulmonary permeability was measured using a modification of the Evans blue dye extravasation technique. IV Evans blue dye 20 mg/kg was administered 2 h before being killed and Evans blue dye in plasma and lung tissue was quantified by dual-wavelength spectrophotometric analysis.

Results: There were no significant differences in basal arterial blood pressure, HR, and Pao(2) among groups. In the control group, ICH resulted in transient increases in mean arterial blood pressure and HR, followed by a rapid decline and a plateau. In the Dex group, mean arterial blood pressure showed a transient increase and subsequent, rapid decrease to baseline, whereas HR did not change during ICH. Pao2 was higher in the Dex group than in the control group after ICH [138 (127-169) vs 78 (59-124) mm Hg, median (range), P < 0.01]. The pulmonary permeability index was lower in the Dex group than the control group [430 (182-450) vs 570 (427-1170), P < 0.01]. It was however, higher in the Sham-Dex group than the Sham-Control group [25 (24-35) vs 6 (4-7), P < 0.01].

Conclusions: Prophylactic IV Dex decreases lung permeability as well as hemodynamic changes induced by ICH in rats.