Background: Impairment of cerebrovascular autoregulation is a risk factor for ischemic damage following severe brain injury. Autoregulation can be assessed indirectly using intracranial pressure monitoring as a surrogate of cerebral blood volume, but this measure may not be applicable to patients following decompressive craniectomy. Here, we describe assessment of autoregulation using regional cerebral blood flow (rCBF).
Methods: In seven patients with severe brain trauma who underwent neurological surgery, a Hemedex® rCBF probe was placed intraoperatively in peri-lesional tissue. Autoregulation was assessed as a moving Pearson correlation between CPP and rCBF (rCBFx).
Results: Composite data from all patients showed relatively constant perfusion over a wide CPP range (50-90 mmHg) and a U-shaped autoregulation curve with maximal autoregulation (CPPopt) at 55-60 mmHg. All rCBF values fell below the ischemic threshold (<18 ml/100 g/min) when CPPs were <50 mmHg compared with 11 % ischemia when CPPs >50 mmHg (P < 0.05). We examined the percent time during which both autoregulation was intact and rCBF exceeded the ischemic threshold. In the composite data, this variable was maximal in the CPP range of 75-80 mmHg (CPPideal). In individual patients, the range of CPPs with intact autoregulation varied widely. Individual CPPopt values ranged between 60 and 100 mmHg and CPPideal ranged between 65 and 105 mmHg.
Conclusions: Assessment of autoregulation with Hemedex® rCBF monitor is feasible and could be used to guide CPP management strategies to optimize both autoregulation and perfusion. Autoregulatory impairment and CPPopt vary considerably between patients, and the addition of rCBF monitoring could help guide CPP targeting decisions.
Keywords: Blood flow velocity index (Mx); Neurocritical care; Oxygen reactivity index (ORx); Pressure reactivity index (PRx); Traumatic brain injury.