General Critical Care Applied to Neurologic Patients
Ventilation and oxygen
Use lung-protective ventilation with tidal volumes around 6 mL/kg predicted body weight and plateau pressures at or below 30 cmH2O, but remember that permissive hypercapnia raises intracranial pressure. In a patient with a brain injury, target normocapnia (PaCO2 35-40 mmHg) while accepting the usual ARDS strategy only when ICP is not a concern.
Hemodynamics and fluids
Sepsis resuscitation begins with crystalloid and norepinephrine targeting a MAP of about 65 mmHg, higher if cerebral perfusion demands it. Avoid hypotonic fluids in brain-injured patients. In subarachnoid hemorrhage, differentiate cerebral salt wasting (hypovolemia, high urine output, low urine sodium is not reliable; treat with saline) from SIADH (euvolemic; fluid restriction), because fluid restriction in salt wasting worsens ischemia. Correct chronic hyponatremia by no more than 8-10 mmol/L per day to avoid osmotic demyelination.
Other supportive care
Target glucose 140-180 mg/dL, start enteral nutrition within 24-48 hours, treat fever aggressively because hyperthermia worsens brain injury, and provide VTE prophylaxis once bleeding risk is acceptable. Consider the hemodynamic and respiratory interactions of sedatives when titrating to neurologic exams.
Trap: applying permissive hypercapnia to a patient with elevated ICP, or fluid-restricting a patient with subarachnoid hemorrhage who actually has cerebral salt wasting.
Worked example: a patient with SAH and sodium 128 mmol/L, low central venous pressure, and high urine output needs isotonic saline and possibly hypertonic saline, not free water restriction.