Development of a piglet model for cerebrovascular autoregulation assessment with altered PaCO2

Introduction: Cerebrovascular autoregulation (CA) capacity can be impaired in the aftermath of acute brain injuries. Altered physiological states, such as hypo- and hypercapnia, affect CA. Although these effects have been demonstrated in several animal experiments, the exact effect of PaCO2 on the plateau of cerebral blood flow (CBF) across the spectrum of arterial blood pressures has not been fully disclosed. Research question: The aim was to explore pial vasodynamics in response to changing PaCO2 in a porcine cranial window model, as preparation for an experimental setup in which the CBF plateau position is investigated under different PaCO2 conditions. Material and methods: Five piglets were brought under anesthesia, intubated, ventilated and instrumented with a cranial window through which pial arteriolar diameters could be microscopically observed. By changing ventilation to either hyper- or hypoventilation we were able to investigate a range of PaCO2 from 25 till 90 mmHg. Results: Altering the respiratory rate to manipulate PaCO2 by ventilation appeared to be feasible and reliable. Discussion and conclusion: We found that ETCO2 reliably represents PaCO2 in our model. Pial arteriolar diameter changes followed the direction of PaCO2 changes, but the effect of PaCO2 on the diameters was not linear. Only in the hypercapnia setting did we observe a clear and consistent vasodilation of the pial arterioles.