The pathophysiology of brain swelling produced by mechanical trauma and hypertension

The effect of Routine nursing care procedures on the ICP in severe head injuries

The intracranial pressure (ICP) was monitored in a number of patients who were being treated by mechanical ventilation for head injury. The effect on the pressure of routine nursing procedures was studied. Fourteen out of thirty-three cases (group 1) showed small reversible rises in ICP during suction, insertion of a N/G tube, or i.m. injections. These were associated with similar small increases in intrathoracic pressure and small fluctuations in arterial blood pressure. These rises were effectively treated with additional doses of relaxants. In a small group of patients (group 2) irreversible intracranial hypertension was induced by some of these stimuli, but did not respond to the administration of more relaxants, although sedatives such as papaveretum reduced it in some cases, but only slightly.

Hyperventilation and cerebral blood flow

Hypocapnic-hyperventilation has a profound, but probably temporary, effect on CBF, producing approximately a 2% decline in CBF for each 1 torr decline in P co co2 . This effect appears to be mediated through changes in perivascular pH of the cerebral resistance vessels acting directly on the vessel wall. At low P co co2 the vasoconstrictor effect of short-term hypocapnic-hyperventilation is attenuated by resultant cerebral hypoxia. During prolonged hyperventilation CBF returns toward normal as the pH in the CSF is restored.

Short-term hypocapnic-hyperventilation can be lifesaving in the treatment of acute intracranial hypertension. On the other hand, prolonged hyperventilation has not been convincingly shown to benefit patients, whether with severe head injury or cerebral infarction, or during carotid endarterectomy without bypass.