Abstract:Objective To inverstigate the changes of serum electrolytes and osmolality in the neonates with hypoxic ischaemic encephalophathy (HIE). Methods Serum levels of sodium [Na +], potassium [K +], chloride [Cl -], ionized calcium [Ca 2+ ], and osmolality were determined in 120 neonates with HIE and in 32 normal neonates. Results In all neonates with HIE (mild, moderate and severe), the serum levels of [Na +] ( 130.2 ± 6.0 ) mmol/L, ( 126.3 ± 9.1 ) mmol/L, ( 121.2 ± 12.2 ) mmol/L respectively; [Ca 2+ ] ( 1.0 ± 0.2 ) mmol/L, ( 0.9 ± 0.2 ) mmol/L, ( 0.8 ± 0.2 ) mmol/L respectively and osmolality ( 256.7 ± 11.2 ) mOsm/L, ( 248.7 ± 21.3 ) mOsm/L, ( 241.1 ± 22.2 ) mOsm/L respectively were lower than those in nomal neonates ( 136.1 ± 1.1 ) mmol/L, ( 1.2 ± 0.1 ) mmol/L, ( 262.6 ± 8.8 ) mOsm/L respectively, wheares serum [K +] levels were higher. Serum [Cl -] levels in the moderate and serere HIE neonates were lower compared with normal neonates. Serum levels of [Na +] and [Ca 2+ ] in the dead neonates were significantly decreased and obstinate; and osmolar gap was more than 10 mOsm/L. Conclusions Hyponatremia, hypocalcemia, and serum low osmolality occur in neonates with HIE and may be of prognostic significance.