Cerebral blood flow in critically ill cardiac patients: effects of vasoactive drug therapy

The introduction of the thermodilution technique (TD) in measuring cardiac output (CO) and coronary sinus blood flow has suggested the application of the same technique into measuring CBF which has been validated by several methods using transcranial Doppler and Xenon inhalation clearance curves.

The present work is intended to assess the effect of two vasoactive drugs on CBF in 20 critically ill patients (12 males, 8 females, mean age: 5.86 ± 9.46) all having CHF due to dilated cardiomyopathy. Following clinical examination all patients were subjected to haemodynamic evaluation including central venous line, arterial cannulation and jugular vein catheterization. The latter was performed using Baim coronary sinus catheter directed towards the right jugular vein under fluroscopic guidance up to the bulb of internal jugular vein. Jugular blood flow (JBF) was measured by constant infusion of ice cold (5%) dextrose solution and recorded digitally on a Baim coronary sinus computer. Haemodynamic measurements including CBF were made at rest and repeated following infusion of noradrenaline (NA) in incremental doses sufficient to raise BP by one third of the basal reading. An average of three readings were taken. NA was discontinued and after 20 min the same method was repeated after dobutamine infusion given in a dose of 10 μg/kg/min for 20 min.

Compared to basic measurements, NA significantly reduced CBF by 22.4 ± 4.79% in 13 patients with simultaneous increase in CVR by 106.73 ± 29.0%, NA increased CBF by 40.46 ± 12.0% in seven patients with simultaneous decrease of CVR by 13.7 ± 6.2%. It also increased systemic vascular resistance by 24.9 ± 2.76%, P < 0.0001. On the other hand dobutamine has led to an increase in CBF by 56 ± 12% in 11 patients with simultaneous decrease in CVR by 22 ± 6.31%. It decreased the CBF by 38.1 ± 11.8% in four patients with simultaneous increase in CVR by 130.68 ± 70.01%, and a decrease SVR by 21 ± 5%, P < 0.0359.

In conclusion, vasoactive drugs commonly used in critically ill cardiac patients have different effects on cerebral blood flow. Despite the beneficial effects obtained from using NA in increasing perfusion pressure and cardiac output, the adverse effects on CBF are an obvious limitation to its use as a monotherapy, compared to dobutamine which besides augmenting CO improves dramatically CBF.