A Study Of Monitoring Cerebral Blood Flow Using Laser Doppler Flowmetry And The Effect Of Mild Hypothermia On Cerebral Blood Flow In Patients With Severe Head Injury

Objective: To investigate the changes of local cerebral blood flow (CBF) at the early stage of trauma and the effect of mild hypothermia on CBF in patients with severe head injury.Methods: Cerebral blood flow (CBF) was measured in 24 patients with severe head injury using Laser Doppler flowmetry (LDF). The monitoring of CBF began at about 14 hours after trauma lasting for about 56 hours in average. 11 patients underwent treatment of mild hypothermia for 24 hours. The changes of CBF at the early stage of trauma was analysed, based on LDF data and correlation coefficient between LDF and cerebral perfusion pressure (CPP) as well as autoregulation of CBF, the effect of mild hypothermia on CBF and the relationship between CBF and prognosis in patients with severe head injury. Results: (1) The monitoring was divided into 3 stages: 0-12 hours, 12-24 hours, 24 hours later. Hypoperfusion was found in 11 cases (45.8%) in 0-12 hours, 6 cases (25%) in 12-24 hours and 4 cases (16.7%) in 24 hours later. There was statistically significant difference on hypoperfusion rate between within 12 hours (within 26 hours post trauma) and 12 hours later (after 26 hours post trauma), which indicates that hypoperfusion is the main change at the early stage (24 hours) of trauma. (2) The correlation coefficient between LDF and CPP wasused as an index of autoregulation. Impaired autoregulation was observed at least one time in 11 cases(45.8%), including 8 cases of GCS 3-5' and 3 cases of GCS 6-8'. It shows that many patients experienced transient loss of autoregulation during acute stage of severe head injury and the occurrence rate of impaired autoregulation in super severe head injury was higher than that in severe head injury with statistically significant difference. (3) Mild hypothermia can reduce CBF by analyzing range of LDF before and after mild hypothermia. The LDF range in patients with hypoperfusion in normal temperature group is lower than that in patients with normal perfusion, which shows that hypoperfusion can do harm to cerebrovascular function. (4) The outcome was evaluated 6 months post trauma. In 24 patients, 2 patients died, 5 patients were in persist vegetative state, 5 patients were severely disabled, 5 patients were moderately disabled, 7 patients had a good recovery. There was no relationship between early hypoperfusion after trauma and prognosis, while persistent hypoperfusion after trauma indicated poor outcome.Conclusions: (1) Hypoperfusion occurs frequently at the early stage of trauma in patients with severe head injury, hypoperfusion can do harm to cerebrovascular function while persistent hypoperfusion after trauma indicated poor outcome. (2) Many patients with severe head injury experienced transient impairment of autoregulation and the occurrence rate of impaired autoregulation in super severe head injury was higher than that in severe head injury. (3) Mild hypothermia can reduce CBF. (4) Laser Doppler Flowmetry, which is the method affording continuous, real-time, mini-invasive and sensitive way to monitor CBF, can be used to observe CBF changes dynamically and to estimate...