The impact of acute hyponatraemia on severe traumatic brain injury in rats

The effect of experimental acute hyponatraemia on severe traumatic brain injury (TBI) was studied in a modified impact-acceleration model. The cortical contusional volume was quantified by image analysis on serial sections, injured axons were visualized and quantified by beta-Amyloid Precursor Protein (beta-APP) immunohistochemical staining. Regional brain water content was estimated by the wet-dry weight method. The experiment was conducted in Group I (injury only) and Group II (injury followed by acute hyponatraemia). Comparison between the two groups showed that acute hyponatraemia significantly increased contusional volume (3.24 +/- 0.70 mm3 vs. 1.80 +/- 0.65 mm3, P = 0.009) and the number of injured axons (128.7 +/- 44.3 vs. 41.7 +/- 50.1, P = 0.04) in the right thalamus & basal ganglia region. Water content of the brain stem region was also significantly increased by acute hyponatraemia (73.71 +/- 0.14% vs. 72.28 +/- 0.93%, P = 0.004). These results suggest that acute hyponatraemia potentiates secondary brain damage in severe TBI by augmentation of both focal contusion and diffuse axonal injury. The injured brain stem region is more susceptible to edema formation induced by experimental acute hyponatraemia.