Variation in cerebral blood flow velocity with cerebral perfusion pressure >40 mm Hg in 42 children with severe traumatic brain injury

Objective: To determine the prevalence of low, normal, and high mean middle cerebral artery flow velocity when cerebral perfusion pressure is >40 mm Hg in children with severe traumatic brain injury. There is no information regarding the relationship between middle cerebral artery flow velocity and cerebral perfusion pressure in pediatric traumatic brain injury. Design: Prospective, observational study. Setting: Level I pediatric trauma center. Patients: A total of 42 children <17 yrs of age with an admission diagnosis of severe traumatic brain injury (admission Glasgow Coma Scale score of <9), traumatic brain injury on computed-tomography scan, tracheal intubation/mechanical ventilation, and intracranial pressure monitoring. Interventions: None. Measurements and Main Results: Bilateral middle cerebral arteries were insonated using transcranial Doppler ultrasonography to calculate mean middle cerebral artery flow velocity after traumatic brain injury. Low mean middle cerebral artery flow velocity was defined as middle cerebral artery flow velocity <2 standard deviation and high was defined as mean middle cerebral artery flow velocity >2 standard deviation. Patients were grouped by age (0.8-2.9, 3-5.9, 6-9.9, and 10-16.9 yrs) and gender to examine the relationship between cerebral perfusion pressure and low, high, or normal mean middle cerebral artery flow velocity. Potential confounders of the relationship between cerebral perfusion pressure and mean middle cerebral artery flow velocity (intracranial pressure, PaCO2, hematocrit, sedation, fever,and impaired autoregulation were examined). Most children (n = 33; 79%) had normal mean middle cerebral artery flow velocity but four patients (9%) had low mean middle cerebral artery flow velocity and five children (12%) had high mean middle cerebral artery flow velocity despite cerebral perfusion pressure >40 mm Hg. There was no difference in potential confounders of the relationship between cerebral perfusion pressure and mean middle cerebral artery flow velocity except for hematocrit, which was lower (25 +/- 4%; range = 21-30%) in children with high mean middle cerebral artery flow velocity. An inverse relationship between mean middle cerebral artery flow velocity and hematocrit was also found in boys aged 10 to 16.9 yrs. Conclusions: Both low and/or high mean middle cerebral artery flow velocity occur with cerebral perfusion pressure >40 mm Hg in severe pediatric traumatic brain injury. Of the potential confounders considered, only lower hematocrit was associated with high mean middle cerebral artery flow velocity. (Crit Care Med 2009; 37:2973-2978)