Detection and haemodilutive treatment of cerebral arterial vasospasm and delayed ischaemia after Aneurysmal Subarachnoid Haemorrhage

Abstract: This thesis deals with cerebral arterial vasospasm and ischaemia, a serious complication after aneurysmal subarachnoid haemorrhage. Firstly is the noninvasive transcranial Doppler ultrasound and transcranial cerebral oximetry techniques evaluated in detecting cerebral arterial vasospasm in clinical practice. Patients were examined during first 14 days after the bleed. Flow velocities in normo- versus hypertensive patients were also compared. Secondly is the effect in blood viscosity, cerebral blood flow and cerebral oxygen delivery rate evaluated during the commonly used haemodilutive therapy for vasospasm. Haematocrit after colloid infusion was compared with controls. Both global and regional cerebral blood flow was measured after iso- and hypervolaemic haemodilution. Transcranial Doppler ultrasound used daily is a valuable non-invasive bedside method to detect an increased risk for vasospasm. Especially when there is a rapid increase in mean flow velocity during 24 hours. However, in patients with verified arterial hypertension even a moderately increased mean flow velocity may indicate vasospasm. Transcranial cerebral oximetry may be useful as a complement to transcranial Doppler ultrasound as a correlation between reduced cerebral saturation and increased mean flow velocity seem to exist. There is a spontaneous haemodilution after subarachnoid haemorrhage as haematocrit is lowered irrespective of haemodilutive therapy or not. Haemodilutive therapy alone may therefore not be beneficial for SAH patients. Isovolaemic haemodilution does not improve cerebral oxygen delivery although global cerebral blood flow and transcranial Doppler mean flow velocity increases. Nor is hypervolaemic haemodilution beneficial for patients with vasospasm as the increased CBF is counteracted by a reduction in oxygen delivery to the brain.