Research synthesis of controlled studies evaluating the effect of hypocapnia and airway protection on cerebral outcome

Hyperventilation is a standard method of treating patients with intracranial hypertension. I reviewed all the relevant peer-reviewed literature to identify the documented benefits of hyperventilation as treatment for cerebral disease. Studies were identified by searches of the Medline database between 1966 and September 1996, interviews with experts, and reviews of reference Lists. Retained manuscripts reported results of a human or animal controlled trial that tested effect of hyperventilation and/or systemic hypocapnia on mortality, histopathology, or neurologic examination. Studies could be either randomized or observational and need not have been blinded. I found that for no clinical studies of cerebral disease, other than in acute head injury patients, was there any suggestion of a clinical benefit from hyperventilation. Three controlled, observational studies examined effects of airway management and ventilatory support in head-injured patients. These studies found that maintaining such patients hypocapnic, versus spontaneously breathing without ventilatory support, decreased mortality. However, by design the studies could not establish whether hypocapnia itself contributed to the decreased mortality. Two clinical studies examined the effect of PaCO2 itself in patients with head injury. In both, hypocapnic patients did not have better neurologic outcome. In conclusion, securing the airway and supporting ventilation probably reduces mortality in unconscious, neurosurgical patients. However, there are virtually no clinical data that hypocapnia improves outcome in patients with cerebral disease.