CRITICAL CLOSING PRESSURE IN PRETERM NEONATES - TOWARDS A COMPREHENSIVE MODEL OF CEREBRAL AUTOREGULATION

In preterm neonates, intraventricular haemorrhage is linked to the dys function of cerebral autoregulation (AR). We aimed at tracing the crit ical closing pressure (CCP) in order to quantify AR and to reveal its inner workings. In an observational study, 10 preterm neonates (median , range: ga 28 weeks, 25 to 32 weeks; bw 1070, 685 to 1730 g; age 2d, 1 to 7 d) were continuously Doppler traced (a. carotis internal for > 10 min. Systemic blood pressure (BP, a. umbilicalis, a, radialis, a. t emporalis) was recorded simultaneously (> 1200 cardiac cycles each). S ystolic BP was on average 11 mmHg above CCP. There was a striking para llel between both variables, even in cases of sudden spontaneous BP fl uctuations > 30% (r=0.72, 0.41 to 0.99), while systolic cerebral blood flow velocity remained largely unaffected (r=-0.15, -0.75 to 0.53), i ndicating a properly functioning AR. CCP was 28 mmHg 74 to 38 mmHg. Ba sed on our data, a physiological model of AR is developed, integrating anatomy, metabolic and neuronal pathways with former physiologic find ings - including low frequency cycling of cerebral blood flow velocity . Tracing of CCP is thought to have the potential to identify infants with impaired AR. Since this method is noninvasive and independent of angle of insonation (thus rendering it uncritical in probe fixation), it is a promising tool for sustained monitoring of cerebral haemadynam ics in the clinical setting.