The Relationship between Serum Sodium, Serum Osmolality, and Intracranial Pressure in Patients with Traumatic Brain Injury Treated with Hyperosmolar Therapy.

BACKGROUND: Treatment of elevated intracranial pressure (ICP) in traumatic brain injury (TBI) is controversial. Hyperosmolar therapy is used to prevent cerebral edema in these patients. Many intensivists measure direct correlates of these agents-serum sodium and osmolality. We seek to provide context on the utility of using these measures to estimate ICP in TBI patients. MATERIALS AND METHODS: Patients admitted with TBI who required ICP monitoring from 2008 to 2012 were included. Intracranial pressure, serum sodium, and serum osmolality were assessed prior to hyperosmotic therapy then at 6, 12, 18, 24, 48, and 72 hours after admission. A linear regression was performed on sodium, osmolality, and ICP at baseline and serum sodium and osmolality that corresponded with ICP for 6-72-hour time points. RESULTS: 136 patients were identified. Patients with initial measures were included in the baseline analysis (n = 29). Patients who underwent a craniectomy were excluded from the 6-72-hour analysis (n = 53). Initial ICP and serum sodium were not significantly correlated (R2 .00367, P = .696). Initial ICP and serum osmolality were not significantly correlated (R2 .00734, P = .665). Intracranial pressure and serum sodium 6-72 hours after presentation were poorly correlated (R2 .104, P < .0001), as were ICP and serum osmolality at 6-72 hours after presentation (R2 .116, P < .0001). DISCUSSION: Our results indicate initial ICP is not correlated with serum sodium or osmolality suggesting these are not useful initial clinical markers for ICP estimation. The association between ICP and serum sodium and osmolality after hyperosmolar therapy was poor, thus may not be useful as surrogates for direct ICP measurements.

Seasonal and geographical patterns of fin whale song in the western North Atlantic Ocean.

Male fin whales, Balaenoptera physalus, produce a song consisting of 20 Hz notes at regularly spaced time intervals. Previous studies identified regional differences in fin whale internote intervals (INI), but seasonal changes within populations have not been closely examined. To understand the patterns of fin whale song in the western North Atlantic, the seasonal abundance and acoustic features of fin whale song are measured from two years of archival passive acoustic recordings at two representative locations: Massachusetts Bay and New York Bight. Fin whale 20 Hz notes are detected on 99% of recorded days. In both regions, INI varies significantly throughout the year as two distinct periods: a "short-INI" season in September-January (9.6 s) and a "long-INI" season in March-May (15.1 s). February and June-August are transitional-INI months, with higher variability. Note abundance decreases with increasing INI, where note abundance is significantly lower in April-August than in September-January. Short-INI and high note abundance correspond to the fin whale reproductive season. The temporal variability of INI may be a mechanism by which fin whale individuals encode and communicate a variety of behaviorally relevant information.