Validity of cerebral blood flow measurements by the thermodilution technique in critically ill cardiac patients

Despite the importance of cerebral blood flow (CBF) in determining the natural history and hospital course of critically ill cardiac patients (pts), the qualitative determination of the CBF has been rarely resorted to, because of technical limitations with resultant lack of information about cerebral oxygen consumption and cerebral metabolic rate of oxygen when compared to other organs. The introduction of the thermodilution technique (TD) in measuring cardiac output (CO) and coronary sinus blood flow has led to the suggestion of applying the same technique in measuring CBF. The present work describes the use of TD to measure CBF in a group of critically ill cardiac patients in comparison with the golden standard technique of transcranial Doppler. The group studied included 20 critically ill cardiac pts (12 males, 8 females, mean age 58.6 ± 9.4 years), all having congestive heart failure due to dilated cardiomyopathy, and were candidates for inotropic treatment.

Following clinical examination, all pts were subjected to haemodynamic evaluation including central venous line insertion, arterial cannulation and internal jugular vein catheterization. The latter was performed using Baim coronary sinus catheter directed towards the right jugular vein under fluoroscopic guidance up to the bulb of internal jugular vein. Jugular blood flow (JBF) was measured by constant infusion of ice cold dextrose solution and JBF was recorded digitally on a Baim coronary sinus computer and CBF was calculated from the equation: (JBF × 2 × 100/Brain weight). Following the procedure CBF was measured by application of Doppler technique and expressed as middle cerebral artery flow velocity with the Doppler transducer over the zygomatic arch window. Doppler parameters included: mean velocity, maximum velocity, minimum velocity.. Assessed by TD, CBF averaged 22.32 ± 15.75 ml/min/100 g and was closely correlated in a linear relationship with middle cerebral artery flow velocity measured by the transcranial Doppler technique (45.9 ± 20.25 cm/s, r = 0.85, P < 0.0001).

In conclusion, CBF can be measured in critically ill cardiac patients by applying the TD principle. Our data have shown the validity of this technique for assessing the course of critical illness and effect of therapeutic interventions with the patient serving as a control for himself.