Cerebral blood flow during experimental epidural bleeding in swine

Abstract

Regional cerebral blood flow (rCBF) was studied during an aggressive epidural bleed, using a ventilated swine model. rCBF, regional organ blood flow and cardiac output were measured using the radioactive microsphere technique. Blood flows were measured prior to the start of bleeding (Stage 1), when intracranial pressures had reached a plateau and supratentorial perfusion pressure was reduced by about 50% (Stage 2), and at isoelectric EEG (Stage 3). Supratentorial rCBF did not change significantly between stages 1 and 2 while rCVR decreased, implying autoregulatory activity. Cerebral ischaemia developed between stages 2 and 3 when rCBF values fell to levels between 20 and 50% of control values. Infratentorial rCBF changes were similar but less marked, so that adequate brain stem perfusion was maintained below the upper mesencephalon. The left temporal and left parietal cortex and upper mesencephalon suffered a greater reduction in rCBF than other regions, due to proximity to the haematoma and tentorial herniation. The supratentorial perfusion pressure at stage 2 was 60 mm Hg associated with a haematoma volume of 6% of the intracranial volume (ICV). The infratentorial perfusion pressure never fell below 60 mm Hg. The Cushing response was absent when the EEG became isoelectric. This is tentatively ascribed to the absence of hypoxia, because mechanical ventilation was used. Instead systemic arterial hypotension accompanied bleeding in this ventilated model. This hypotension was due to falling cardiac output and peripheral vasodilation.

Different Compartments of Intracranial Pressure and Its Relationship to Cerebral Blood Flow

“…11 In a swine-model of epidural bleeding, ICP gradients was found between the pressure measurement in the lateral ventricles and in the cisterna magna. 12 In this animal model, supra-was higher than infratentorial ICP level, with a pressure gradient ranging from 15 to 33 mm Hg depending on the final mass volume. 12 Supraand infratentorial ICP gradients were also observed in animal models that simulated subdural bleeding.…”

“…12 In this animal model, supra-was higher than infratentorial ICP level, with a pressure gradient ranging from 15 to 33 mm Hg depending on the final mass volume. 12 Supraand infratentorial ICP gradients were also observed in animal models that simulated subdural bleeding. 13 In addition, it could be demonstrated a failure of free communication between the two hemispheres of increased epidural pressure resulting from focal epidural mass lesion as well as incomplete ICP transmission from an intracerebral mass lesion to the overlying subarachnoid space.…”

Effects of cerebrospinal fluid loss and epidural blood patch on cerebral blood flow in swine

“…It is of note, however, that Griffiths et al 18 demonstrated significant subarachnoid spread of blood following EBP by MRI studies. Therefore, the question arises as to whether EBP, and possibly also subarachnoid leakage of the injectate, 17 does not merely reverse the vasodilatation (due to CSF leak) that causes PDPH. Yucel et al 6 recently suggested that this might well be the case.…”

Interhemispheric supratentorial intracranial pressure gradients in head-injured patients: are they clinically important?

“…Using an extradural balloon as a model of mass lesion in monkeys, Langfitt, et al, 17 demonstrated the existence of gradients and their dependency on the patency of the basal cisterns surrounding the brainstem at the level of the tentorial incisura. In a model of epidural bleeding in swine, Ganz, et al, 13 also demonstrated ICP gradients between the pressures measured in the lateral ventricles and in the cisterna magna. In this model, supratentorial was higher than infratentorial ICP, with a pressure gradient ranging from 15 to 33 mm Hg J. Neurosurg.…”