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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 neurocritical care 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). CSW and SIADH are the result of alterations in the hormonal regulation of plasma volume. Therefore plasma volume levels can be used to distinguish between CSW and SIADH. Methods: The records of patients admitted between 2007 and 2013 who underwent a BVA were reviewed. Patients with a neurointensive care diagnosis 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, BVA results & outcome were recorded. The incidence of CSW and SIADH based on BVA was determined. A normalized Hct was calculated based on the actual red cell volume and predicted normal plasma volume based on the BVA results. Results: The records of 95 patients with a neurointensive care diagnosis were reviewed. There were a total of 106 BVA performed on these 95 patients. The group consisted of 50 females and 45 males. The mean age was 59.8 + 18.5 years. Overall mortality was 22.1% (21/95). 53.7% (51/95) of patients experienced hyponatremic episodes (Serum Na+< 136 mEq/dl). The most common neurological diagnoses were intraparenchymal hemorrhage (IPH) (26.5%), subarachnoid hemorrhage (SAH) (26.5%), or subdural hematoma (SDH) (24.5%). BVA results in the hyponatremic group demonstrated that plasma volume (PV) was Decreased in 7.8% (4/51), Normal in 43.1% (22/51) and Increased in 49.0% (25/51). Regardless of volume status, all patients had normocytic anemia. Peripheral Hct was 33.0 (+ 4.6), 29.8 (+ 4.5), and 29.0 (+ 4.5) in the Decreased, Normal and Increased plasma volume patients, which was not significant. However, after correcting for plasma volume, the normalized Hct was 24.8 (+ 4.7), 25.5 (+ 5.5), and 30.4 (+ 6.6) in the Decreased, Normal and Increased plasma volume patients (p<0.05). No patient had increased Red Cell Volume (RCV), 3 had a normal RCV (5.9%). There was no significant difference in Hct based on the reason for neurocritical care. Total blood volume (TBV) was decreased in 45.1% (23/51), normal in 39.2% (20/51), and increased in 15.7% (8/51) of the patients. Serum Na+, K+, BUN, Crt, Hct and Urine SG, Na+, Osmolality were not associated with plasma or blood volume status. Among hyponatremic patients, mortality was 18.4%. Conclusions: Evaluation and treatment of hyponatremia in neurointensive care patients remains a challenge. Anemia is common in hyponatremic patients with neurocritical illness. Paradoxically, the normalized Hct is lowest in patients with decreased volume status. Peripheral Hct does not correlate with volume status and may be misleading in this group of patients. The mechanism for this anemia requires additional research. Based on plasma volume levels, CSW was present in only 7.8% of hyponatremic pts. SIADH appears to be more common than CSW in hyponatremic patients. Traditional markers of volume status are not useful in these pts. Measurement of TBV alone may incorrectly identify CSW in 45.1% of hyponatremic pts. Management of hyponatremia can be improved with BVA data and contraindicated interventions avoided. A prospective evaluation of BVA in neurointensive care patients is warranted.