VALIDATION-STUDY OF A CENTRAL VENOUS PRESSURE-BASED PROTOCOL FOR THE MANAGEMENT OF NEUROSURGICAL PATIENTS WITH HYPONATREMIA AND NATRIURESIS

OBJECTIVE: We had previously suggested a protocol for the management o f neurosurgical patients with hyponatremia and natriuresis that was ba sed on their volume status as determined by actual blood volume measur ements. All patients in that study were found to be hypovolemic or nor movolemic and responded, within 72 hours, to salt and fluid replacemen t. In the present study, the validity of that protocol was tested usin g central venous pressure as the sole measure of volume status of pati ents with hyponatremia and natriuresis. METHOD: Twenty-five consecutiv e patients (26 cases) who fulfilled the inclusion criteria typically u sed to diagnose the syndrome of inappropriate secretion of antidiureti c hormone were included in the study. Central venous pressure was used to classify patients as hypovolemic (<5 cm of water) normovolemic (6- 10 cm of water), or hypervolemic (>11 cm of water). Hypovolemic patien ts were given fluids (50 ml/kg/d) and salt (12 g/d). Normovolemic pati ents were given normal fluid with 12 g of salt per day. In addition, p atients with anemia (hematocrit <27%) were administered whole blood. T he end point was a serum sodium of more than or equal to 130 mEq/L mea sured in two consecutive samples 12 hours apart or 72 hours after entr y into the study. If the serum sodium was less than 130 mEq/L at the e nd of 72 hours, the clinical condition of the patient determined furth er management. RESULTS: Nineteen of 25 patients (26 cases) were hypovo lemic, the rest were normovolemic. No patient was hypervolemic. Ninete en of 25 patients (26 cases) attained normal serum sodium values withi n 72 hours and an additional 3 responded within the next 36 hours (108 h after entry into the study). One patient who was discharged on requ est had normalized her serum sodium a week later. Among the three nonr esponders, two were severely hypovolemic, as revealed by blood volume measurement, and responded to increased fluid and salt administration. One was normovolemic and responded to increased salt administration. There were no complications related to the therapy. CONCLUSION: Hypona tremia with natriuresis in the neurosurgical setting responds to salt and fluid replacement guided by the patients' volume status as determi ned by the central venous pressure. This study also offers further ind irect evidence to suggest that the syndrome of hyponatremia with natri uresis is most often caused by ''cerebral salt wasting'' rather than b y the syndrome of inappropriate secretion of antidiuretic hormone.