Electrolyte-derived clinical indices in traumatic brain injury: A narrative review

Table 1 Summary of key electrolyte-based indices in traumatic brain injury

Index	Components	Clinical relevance	Prognostic use in TBI	Limitations
GPR[11-20]	Glucose/K+	Reflects neuroendocrine stress	Predicts mortality, poor outcomes (OR: 4.08-5.26); GPR > 50 linked to poor prognosis	Cutoffs vary and are affected by glucose/K+ fluctuations; there are few multicenter validations
Plasma osmolality[28-32]	2 × Na+ + glucose/18 + BUN/2.8	Indicates total osmotic load	Levels > 320 mOsm/kg associated with mortality, BBB disruption	BUN may overestimate osmolality
Effective osmolality[29,30-34]	2 × Na+ + Glucose/18	Reflects true water shifts across the BBB	Critical in managing ICP, preventing edema	Requires the exclusion of urea
Ion shift index[35,36]	(K+ + Mg2+ + PO43-)/Ca2+	Marker of cellular membrane failure	Promising in trauma and OHCA; not yet validated in TBI	Lack of prospective TBI studies
Anion gap[42-44]	Na+ – (Cl- + HCO3-)	Marker of metabolic acidosis	Suggests hypoperfusion, a potential prognostic tool	Not specific to brain injury; influenced by many variables
Corrected sodium	Na+ + 0.016 × (glucose-100)	Prevents pseudohyponatremia	Guides the osmotherapy decisions	Formula-specific interpretation
Corrected calcium	Ca + 0.8 × (4–albumin)	Accounts for hypoalbuminemia	Identifies true hypocalcemia	Ionized Ca is preferred, but not always available

OR: Odds ratio; mOsm: Milliosmoles; BUN: Blood urea nitrogen; BBB: Blood–brain barrier; ICP: Intracranial pressure; OHCA: Out-of-hospital cardiac arrest; TBI: Traumatic brain injury; GPR: Glucose-to-potassium ratio.