Increased ICP and its cerebral haemodynamic sequelae

Objectives: Increased intracranial pressure (ICP) is a pathological feature of many neurological diseases; however, the local and systemic sequelae of raised ICP are incompletely understood. Using an experimental paradigm, we aimed to describe the cerebrovascular consequences of acute increases in ICP. Materials and methods: We assessed cerebral haemodynamics [mean arterial blood pressure (MAP), ICP, laser Doppler flowmetry (LDF), basilar artery Doppler flow velocity (Fv) and estimated vascular wall tension (WT)] in 27 basilar artery-dependent rabbits during experimental (artificial lumbar CSF infusion) intracranial hypertension. WT was estimated as the difference between critical closing pressure and ICP. Results: From baseline (~9 mmHg) to moderate increases in ICP (~41 mmHg), cortical LDF decreased (from 100 to 39.1%, p < 0.001), while mean global Fv was unchanged (from 47 to 45 cm/s, p = 0.38). In addition, MAP increased (from 88.8 to 94.2 mmHg, p < 0.01 and WT decreased (from 19.3 to 9.8 mmHg, p < 0.001). From moderate to high ICP (~75 mmHg), both global Fv and cortical LDF decreased (Fv, from 45 to 31.3 cm/s, p < 0.001; LDF, from 39.1 to 13.3%, p < 0.001) while MAP increased further (94.2 to 114.5 mmHg, p < 0.001) and estimated WT was unchanged (from 9.7 to 9.6 mmHg, p = 0.35). Conclusion: In this analysis, we demonstrate a cortical vulnerability to increases in ICP and two ICP-dependent cerebro-protective mechanisms: with moderate increases in ICP, WT decreases and MAP increases to buffer cerebral perfusion, while with severe increases of ICP, an increased MAP predominates.