Methods to Reduce Intracranial Pressure.
- Hyperventilation – in the short term, hyperventilation to a PaCO2 of 25 mmHg can reduce cerebral blood flow, reducing ICP. This must be balanced, however, against the increased intrathoracic pressure required to hyperventilate the patient’s lungs, which can reduce venous return causing hypotension. Meanwhile vasoconstriction in the areas under carbon dioxide control might decrease compensatory blood flow.
- Mannitol – bolus administration of this 6-carbon sugar has three effects: (i) it expands the blood volume and decreases viscosity, improving cerebral blood flow; (ii) it generates an osmotic gradient in the brain, drawing water out of brain tissue; and (iii) it scavenges oxygen free radicals. The net effect – an acute reduction in ICP. However, the subsequent diuresis can exacerbate hypovolemia, and in the presence of poor renal perfusion the high osmolality can trigger acute tubular necrosis.
- Elevating the head of the bed and keeping the neck in a neutral position – these simple maneuvers can reduce ICP. Head elevation can also impair venous return from the lower extremities. Trauma patients are often placed in Trendelenburg position (with the head below the level of the legs) to increase venous return, a maneuver best avoided in patients with high ICP.
- Fluid management – hypotonic solutions and those containing glucose clearly worsen neurologic outcome by encouraging brain swelling. With an intact blood–brain barrier, hypertonic solutions might provide an advantage by reducing brain swelling.
- Glucocorticoids – these drugs reduce edema associated with brain tumors and are also used by many for the treatment of acute spinal cord injury; but steroids do not reduce edema from traumatic brain injuries.
- Hypothermia – oxygen consumption depends on temperature (in the absence of shivering, basal metabolic rate falls by 7% per 1°C of temperature reduction). But hypothermia raises other problems: the patient might shiver, which dramatically raises oxygen consumption; coagulation is profoundly disturbed, which can worsen intracerebral hemorrhage; arrhythmias can be triggered with temperatures below 30°C; and wound infections become slightly more likely.
- Barbiturate coma – reserved for the most severely injured who have failed to respond to more conservative therapy; high barbiturate plasma levels reduce cerebral metabolic rate and cerebral blood flow thus lowering ICP until the injury can heal. Unfortunately, barbiturates depress the cardiovascular system.
- CSF drainage – after a ventriculostomy has been placed, we can readily reduce the CSF volume. Care must be taken in the presence of brain swelling and elevated ICP, however, as draining CSF from a lumbar tap can result in brain herniation into the foramen magnum. Hence the admonition to look for clinical signs and symptoms of elevated ICP before performing a lumbar puncture or neuraxial anesthetic.