Cardiovascular and metabolic responses to severe head injury
The cardiovascular and metabolic responses to severe head injury were studied in the acute phase after severe head injury with the object of determining if a common response was present and, if so, its significance in the management of the patients' intracranial and systemic physiological states. The cardiovascular response to head injury was studied by measurement of cardiac output, pulmonary capillary wedge pressure, arterial blood pressure, arterial and mixed venous blood gases and arterial and mixed venous epinephrine and norepinephrine serially in 15 patients during the first three days after injury. A hyperdynamic state was found characterized by increased cardiac output and cardiac work, moderate hypertension, tachycardia, decreased or normal systemic and pulmonary vascular resistance, increased pulmonary shunting and increased oxygen delivery and utilisation. Arterial E and NE levels correlated well with the cardiac output, cardiac work, blood pressure, heart rate, oxygen delivery, and oxygen utilization but not with vascular resistance or pulmonary shunt. The magnitude of the hyperdynamic state did not correlate with intracranial pressure, Glasgow Coma Score, or findings on CT scan. The metabolic response to head injury was studied by measurement of resting metabolic expenditure (RME) in 14 comatose head-injured patients in the first nine days after injury. During this period patients were fed with a continuous parenteral infusion of a formula containing 2 Kcal/cc and 10 mg nitrogen/liter. Indirect calorimetry was carried out for 102 patient-days. The mean resting metabolic expenditure (RME) for nonsedated, nonparalyzed patients was 138 +/- 37% of that expected for a non-injured resting person of equivalent age, sex, and body surface area. Nitrogen excretion was measured for 109 patient-days. The mean excretion was 20.2 +/- 6.4 mg/day. The mean protein caloric contribution was 23.9 +/- 6.7% and was greater than 25% for six patients, compared to normal values of 10-15%. Despite hyperalimentation, positive nitrogen balance for any 3-day period was achieved in only seven patients, and required replacement of 161% to 240% of RME with the parenterally administered formula. Head-injured patients had a metabolic response similar to that reported for patients with burns of 20-40% of the body surface.