The upper limit of cerebral blood flow autoregulation is decreased with elevations in intracranial pressure

BACKGROUND: The upper limit of cerebrovascular pressure autoregulation (ULA) is inadequately characterized. OBJECTIVE: To delineate the ULA in an infant swine model. METHODS: Neonatal piglets with sham surgery (n = 9), interventricular fluid infusion (INF) (n = 10), controlled cortical impact (CCI) (n = 10), or CCI + INF (n = 11) had intracranial pressure monitoring and bilateral cortical laser-Doppler flowmetry recordings during arterial hypertension to lethality using an aortic balloon catheter. An increase of red cell flux as a function of cerebral perfusion pressure was determined by piecewise linear regression, and static rates of autoregulation were determined above and below this inflection. The ULA was rendered as the first instance of an upward deflection of Doppler flux causing a static rate of autoregulation decrease greater than 0.5. RESULTS: ULA was identified in 55% of piglets after sham surgery, 70% after INF, 70% after CCI, and 91% after CCI with INF (P = .36). When identified, the median (interquartile range) ULA was as follows: sham group, 102 mm Hg (97-109 mm Hg); INF group, 75 mm Hg (52-84 mm Hg); CCI group, 81 mm Hg (69-101 mm Hg); and CCI + INF group, 61 mm Hg (52-57 mm Hg) (P = .01). In post hoc analysis, both groups with interventricular INF had significantly lower ULA than that observed in the sham group. CONCLUSION: Neonatal piglets without intracranial pathology tolerated acute hypertension with minimal perturbation of cerebral blood flow. Piglets with acutely increased intracranial pressure with or without trauma demonstrated loss of autoregulation when subjected to arterial hypertension.