Mechanical ventilation and the injured brain

Abstract

Ventilatory management of a brain-injured patient is challenging. Injury to the brain initiates an inflammatory cascade that may result in secondary brain injury and extracranial organ dysfunction. The lung is often the most compromised in this process, and at multiple stages of brain injury. Lung pathology can be part of the initial injury process, or result from sequelae of the brain injury and critical care course. Principles of lung protection and brain-directed therapies are often in direct conflict. There are limited randomised controlled trials from which clinicians can draw conclusions regarding management of this controversial cohort of patients. Physiological interactions between the brain and lung should be clearly understood. Injurious ventilation should be avoided. Secondary brain injury should be prevented. Risk factors for this must be identified early and treated promptly. Hypoxaemia should be avoided. Arterial CO₂ tension should be managed. Hyperventilation should be reserved for intractable intracranial hypertension. There is no role for prophylactic hyperventilation as primary therapy. Hypocarbia can precipitate cerebral ischaemia. Novel ventilatory strategies are in the infancy stages. By using these therapeutic modalities, more positive outcomes are hoped for.