Influence of dobutamine and norepinephrine and cerebral blood flow: preliminary data

Background

Severe head trauma patients are often deeply sedated and this can cause a myocardial depression with hypotension and low cardiac output. Hypotension is very dangerous, particularly in patients with cerebral oedema and high intracranial pressure. Dobutamine and/or norepinephrine are usually given to restore myocardial performance and increase blood pressure and, consequently, cerebral perfusion pressure (PPC). The effects of these two drugs on the cerebral blood flow (CBF) are unknown. The aim of this study is to measure CBF and central hemodynamics in a group of patients with severe head trauma (Glasgow Coma Scale < 8), first using dobutamine and then norepinephrine.

Methods

Five patients have been studied. The following parameters were monitored: intracranial pressure, jugular oxygen saturation (SjO₂), mean arterial pressure, central hemodynamic parameters (cardiac index, central venous pressure, systemic vascular resistances, intrathoracic blood volume, extravascular lung water) and CBF. The CBF was measured with the TCDI technique (COLD-system; Germany) [1]. Patients had two fiberoptic catheters provided with a thermistor: the first inserted in the femoral artery and the second in the bulb of the right jugular vein.

First patients had a dobutamine infusion (t1) to reach PPC > 70 mmHg (mean dosage 6.7 μg/kg/min), and then, after central hemodynamic and CBF measurements, dobutamine was changed with norepinephrine (0.12 μg/kg/min) (t2), trying to reach the same PPC achieved with dobutamine. Finally, measurements were performed with simultaneous infusion of dobutamine and norepinephrine (dobutamine 4.2 μg/kg/min and norepinephrine 0.05 μg/kg/min) (t3), always achieving the same PPC as t1.

Results

The CBF increased significantly with norepinephrine (median value 47.7 ml/100 g vs 72 ml/100 g; P < 0.05), but not with the association dobutamine-norepinephrine (median value 52.5 ml/100 g). No significantly changes were observed in central hemodynamic parameters.

Conclusions

From these preliminary data it seems that dobutamine causes a decrease of CBF compared with norepinephrine, with no changes in central hemodynamic parameters and PPC. The physiopathology of these results remains unknown.