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Abstract

Introduction: Cerebral salt wasting (CSW) and the syndrome of inappropriate antidiuretic hormone release (SIADH) are two causes of hyponatremia in neurosurgical patients. CSW presents with decreased plasma volume (PV); SIADH presents with normal or increased PV. Clinical exam and CVP are unreliable for assessing circulating volume. Bedside Isotopic blood volume analysis (BVA) can accurately measure PV and total blood volume (TBV). Hypothesis: The objective of this study was to evaluate the use of bedside BVA to distinguish SIADH from CSW in hyponatremic pts with neurocritical illness. Methods: The records of pts admitted between 2010 and 2012 who underwent a BVA were reviewed. Pts with neurocritical illness were grouped by BVA and Na+ levels. Data collected included: Age, Ht, Wt, Sex, Serum Na+, K+, BUN, Crt, HCT, & Urine SG, Na+, Osmo. Additionally I & O, Na+ balance, BVA, & outcome were recorded. The incidence of CSW and SIADH based on BVA was determined. Results: 72 pts had a BVA and an acute neurocritical illness. The group was 47.2% male with a mean age of 60.6 +/- 18.1 years. Mortality was 16.7% (11/72). Overall, 51.4% (37/72) of pts were hyponatremic, 36.1% (26/72) were normal, and 12.5% (9/72) were hypernatremic. Of the 37 patients with hyponatremia, 5.4% (2/37) had decreased PV, while 40.5% (15/37) and 54.1% (20/37) had normal or increased PV. All hyponatremic pts had normal or low red cell volume. In the hyponatremic group, TBV was decreased in 40.6% (15/37), normal in 37.8% (14/37), and increased in 21.6% (8/37). Neither serum Na+, K+, BUN, Crt, HCT, nor Urine SG, Na+, Osmo were predictive of PV or TBV status. Treatment was similar for all volume statuses. Mortality was higher in pts who failed to recover from hyponatremia 28.6% (2/7) versus those who normalized 17.9% (5/28) (p=NS). Conclusions: Using PV as a standard, CSW was present in only 5.4% of hyponatremic pts. Traditional markers of volume status are not useful in these pts. Measurement of TBV may incorrectly identify CSW in 40.6% of hyponatremic pts. Management of hyponatremia can be improved with BVA data and contraindicated interventions avoided. A prospective evaluation of BVA in neurocritical illness is warranted.