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 impact + infusion (CCI + INF; n=11) had intracranial pressure monitoring and bilateral cortical laser-Doppler flux 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 (SRoR) were determined above and below this inflection. The ULA was rendered as the first instance of an upward deflection of Doppler flux causing an SRoR 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=0.36). When identified, the ULA was as follows: sham group: 102 mmHg [97-109], INF group: 75 mmHg [52-84], CCI group: 81 mmHg [69-101], and CCI + INF group: 61 mmHg [52-57] (median, IQR, p=0.01). In post-hoc analysis, both groups with interventricular infusion had significantly lower ULA than were observed in the sham group.
Conclusion: Neonatal piglets without intracranial pathology tolerated acute hypertension with minimal perturbation of cerebral blood flow. Piglets with acutely elevated intracranial pressure with or without trauma demonstrated loss of autoregulation when subjected to arterial hypertension.
From: The Upper Limit of Cerebral Blood Flow Autoregulation is Decreased With Elevations in Intracranial Pressure by Pesek et al.