Hyponatremia Clinical Update, August 9, 2011

A new study provides evidence that brain natriuretic peptide (BNP) plasma concentrations increase rapidly after traumatic brain injury (TBI). Plasma BNP concentrations are correlated with hyponatremia in severe TBI patients but not in mild and moderate TBI patients.

Furthermore, patients with elevated intracranial pressure (ICP) have a higher serum BNP level in the first four days after injury, according to Chinese researchers, who published the study in the Journal of Trauma.

The role of BNP after TBI remains unclear, and its relationship with hyponatremia is still controversial, the researchers noted. The aim of their study was to investigate the secretion pattern of N-terminal (NT)-proBNP in patients with TBI and to assess the relationship between NT-proBNP, sodium balance, and ICP.

For the study, the researchers measured serum NT-proBNP levels of 84 patients with isolated TBI on a daily basis from day one to day 14 after injury. On average, the peak of BNP level was measured at 703.9 pg/mL ± 179.1 pg/mL on day three after injury, which was correlated to the severity of TBI.

“Among patients with severe TBI, plasma NT-proBNP concentrations in patients with hyponatremia were statistically higher than those without hyponatremia (P< 0.05),” the researchers wrote in the study abstract. “In the hyponatremic group, the plasma NT-proBNP increased to a peak of 1001.16 pg/mL ± 131.52 pg/mL within 48 hours after injury and maintained at a high level for three days.”

In the normonatremic group, the plasma NT-proBNP reached a peak of 826.43 pg/mL ± 337.43 pg/mL on day five and quickly decreased thereafter. In addition, we found plasma NT-proBNP concentrations in patients with ICP >15 mm Hg were significantly higher than those in patients with ICP ≤15 mm Hg (P<0.01).

Cerebral Salt Wasting Syndrome in Post-Operative Pediatric Brain Tumor Patients

The diagnosis of (cerebral salt wasting syndrome) CSWS should be strongly considered in hyponatremic pediatric patients with significant natriuresis following brain tumor resection, and a treatment initiated promptly to prevent neurologic sequeleae, according to a study published recently in Neurocritical Care.

“CSWS and the syndrome of inappropriate antidiuretic hormone [SIADH] are both causes of hyponatremia in pediatric neurosurgical patients, often with similar presenting symptoms; however, despite similar clinical characteristics, the treatment for CSWS and SIADH can be drastically different, which makes the distinction critical for post-operative treatment,” the authors wrote in the study abstract. The researchers were led by Douglas A. Hardestry, MD, of the Department of Neurosurgery at Children’s Hospital of Philadelphia and the University of Pennsylvania Medical Center

“Further complicating matters are the exact mechanism for CSWS, which remains unclear, and the [fact that the] incidence and severity of CSWS is not well studied in pediatric neurosurgical patients. We hypothesized that CSWS occurs frequently in post-operative brain tumor patients and is an important cause of post-operative hyponatremia in these patients.”

The authors designed a single institution retrospective cohort study of all pediatric brain tumor patients undergoing craniotomy for tumor resection at their institution between January 2005 and December 2009.

According to the study abstract, of the 282 patients undergoing 291 operations, post-operative CSWS was identified in 15 cases (5%), and was more frequently observed than SIADH (nine cases, 3%).

“Median onset of CSWS was on post-operative day three, lasting a median of 2.5 days. Patients with CSWS were more likely to have suffered post-operative stroke (40 vs. 4.6%, P < 0.001), have chiasmatic/hypothalamic tumors (40 vs. 3.8%, P = 0.002), and be younger (mean age 5.9 vs. 9.7 years, P = 0.01) than eunatremic patients. In addition, nearly half of the patients with CSWS (47%) had post-operative hyponatremic seizures,” the authors concluded in the abstract.

SourcesTerminal Pro-B-Type Natriuretic Peptide in Patients With Isolated Traumatic Brain Injury: A Prospective Cohort Study [Journal of Trauma]Cerebral Salt Wasting Syndrome in Post-Operative Pediatric Brain Tumor Patients [Neurocritical Care]