Pulsatility index, patent ductus arteriosus, and brain damage

The study of CBF velocity by external Doppler method appears to offer the clinician a noninvasive tool with which to gather information related to changes in cerebral hemodynamics. Inasmuch as the clinical condition of sick preemature infants is different from that of adults with obstructive vascular disease, and as the arteries under study are deeper than those for which the technique originally was intended, we suggest that absolute values for the frequency shift and the mean velocity observed be reported rather than the pulsatility index. Obviously, this will require calibration of each instrument (to obtain an appraisal of the blood velocity) and an estimate of the experimental error, using the actual measurements of blood velocities. Finally, we believe that the mechanisms by which PDA can cause IVH or ischemic damage remain to be solved. It is conceivable that the worsening of respiratory distress syndrome associated with a severe PDA, with significant hypercapnea, hypoxemia, and shock, requiring vigorous ventilatory assistance, could play a more important role in the pathogenesis of brain damage than the hemodynamic alterations in the brain circulation as estimated by measuring only changes in the PI.