BODY FLUID DISTURBANCES - due to injury to the supraoptic nucleus and paraventricular nucleus of the hypothalamus and neurohypophyseal stalk

  • Syndrome of Inappropriate Antidiuretic Hormone (SIADH)
    • Signs: hyponatremia, lethargy, nausea, and possibly seizures
    • Diagnosis:
      • Eliminate adrenal insufficiency (glucocorticoid deficiency may mimic SIADH) and drug-related SIADH (e.g. carbamazepine). Approximately 50% of patients with moderate or severe TBI have at least transient adrenal insufficiency (AI). Younger age, greater injury severity, early ischemic insults, and the use of etomidate and metabolic suppressive agents are associated with AI. Because lower cortisol levels were associated with lower blood pressure and higher vasopressor use, consideration should be given to monitoring cortisol levels in intubated TBI patients, particularly those receiving high-dose pentobarbital or propofol (Cohan, et al 2005).
      • Following an oral water load of 20ml/kg body weight given over 15-20 minutes, hourly collection of urine for 5 hours will result in the patient with SIADH:
        • excreting <40% of the water (as opposed to >80% by normal individuals)
        • failing to dilute urine maximally
        • having hypertonic urine osmolality compared with plasma osmolality
    • Treatment:
      • Fluid restriction is the usual treatment, or, if fluid restriction is difficult to maintain
      • Drug therapy has been limited, but has included oxilorphan (a narcotic antagonist), Dilantin (diphenylhydantoin), and demethylchlortetracycline, the latter in some patients with SIADH due to liver cancer
      • Repeated assessment of serum and urine sodium and osmolality

  • Diabetes Insipidus
    • Signs:
      • Polydipsia and polyuria, without concomitant hyperglycemia
      • Associated with hypernatremia, normal or high serum osmolality, and dilute urine
      • Sometimes accompanied by fatigue and/or changes in mental status
    • Diagnosis - If urine osmolality reaches a plateau after 12-18 hours of fluid deprivation, but then increases after a subcutaneous injection of aqueous vasopressin
    • Treatment:
      • DDAVP (1-d-amino-8-D-arginine-vasopressin) is the drug of choice
      • Carbamazepine has been shown to be effective

Based on information in Medical Rehabilitation of Traumatic Brain Injury, L.J. Horn and N.D. Zasler, eds. St. Louis, MO, Mosby, 1996, except for information where other papers are cited.