The effect of intermittant positive pressure ventilation (IPPV) on cerebral blood velocities in the newborn infancy

Abstract

We have used a pulsed bidirectional doppler ultrasound system to study the possible effects that IPPV may have on cerebral arterial and venous blood velocities in the newborn. The signal obtained from these vessels (usually the superior sagittal sinus and an intra-cerebral artery) is analysed by computer and the results are presented as velocity per consecutive heartbeat. 26 babies have been studied, several on more than one occasion and they represent a broad spectrum of babies requiring IPPV. The results indicate that the babies fall into 3 main groups:1.those in whom we could find no effect on cerebral blood velocities related either to the rate of ventilation or the peak inspiratory pressure(PIP),2.those in whom venous velocities diminished intermittantly in time with the rate of ventilation and 3.those in whom both arterial and venous velocties were influenced by the rate and the PIP. Most babies were in group 2 but a few showed large swings in arterial velocities related to IPPV and in general the higher the PIP the greater the beat to beat variation in the velocities. By lowering the PIP even by 1-3cm H2O the effect on venous velocities lessened and disappeared at a certain critical pressure. These findings could vary from day to day depending on lung disease and spontaneous respiratory effort. We have been able to show that it is possible to avoid some of the largest fluctuations in cerebral velocities by only small reductions in PIP whilst still adequately ventilating the infant.