Monitoring and modifying brain oxygenation in patients at risk of hypoxic ischaemic brain injury after cardiac arrest

Occult cerebral ischemia is one likely contributor to the development of hypoxic ischemic brain injury in patients after cardiac arrest. Local brain hypoxia may occur, irrespective of significant hypotension, especially if autoregulation of cerebral blood flow (CBF) is impaired. The regional brain saturation of oxygen (rSO2) may be estimated non-invasively, using near infrared spectroscopy (NIRS). The rSO2 also offers a surrogate measure of CBF and makes it possible to estimate the efficacy and limits of cerebrovascular autoregulation by calculating the moving correlation in the time domain between arterial pressure and rSO2. The advantage of NIRS is its easy implementation, providing continuous data. Studies have not, thus far, shown unequivocal associations between the rSO2 estimates of autoregulation and the magnitude of hypoxic ischemic brain injury or the clinical neurological outcome. With the use of invasive catheters inserted through a cranial burr hole, the partial pressure of oxygen in brain tissue (PbtO2) can be measured directly—as can intracranial pressure (ICP), local blood flow and markers of metabolism. Such catheters are commonly used in neurointensive care, but less so in the management of cardiac arrest patients. This is due to the risk of bleeding complications associated with anticoagulation and antiplatelet therapy, which is standard practice in cases where the cause of the arrest is myocardial ischemia. Pilot studies have shown promise—both for the use of PbtO2 and for its potentially superior precision over NIRS in detecting brain ischemia. The means available for treating cerebral ischemia include manipulating the arterial blood pressure with vasopressors, as well as modifying blood oxygen and carbon dioxide levels by adjusting ventilatory management. Thus far, no conclusive evidence exists supporting these interventions to alleviate hypoxic ischemic brain injury and improve outcome. One possible strategy is the adoption of a multimodal treatment strategy to detect and treat cerebral ischemia—similar to the management of patients with TBI.