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.

Table 2 Electrolyte imbalance combinations and prognostic implications in traumatic brain injury

Electrolyte pattern	Prognostic signal	Evidence strength	Remarks
Hypernatremia + hypocalcemia	↑ Mortality (univariate)	Limited	Not confirmed in multivariate analysis[45]
Hypernatremia + hypokalemia + metabolic acidosis	Hypoperfusion marker	Limited	Triad not validated in TBI studies[5,8,9]
Hypernatremia + hypokalemia + hypophosphatemia	Cellular derangement	Theoretical	Not studied; potential "danger triad"[8]
Hypocalcemia alone	Strong adverse prognostic marker	High	Independently predicts mortality[9,46]
Hypernatremia alone	Linked with mortality and DI	High	Especially with high ICP or osmotherapy[6,46]
Hypokalemia alone	Associated with poor outcomes	High	Early TBI marker[8,9]

TBI: Traumatic brain injury; ICP: Intracranial pressure; DI: Diabetes insipidus.

Table 3 Electrolyte correction formulas in traumatic brain injury

Correction	Formula	Use case	Importance
Corrected sodium (mg/dL glucose)[50,51]	Na+ + 0.016 × (glucose − 100)	Hyperglycemia	Prevents misdiagnosis of hyponatremia
Corrected sodium (mmol/L glucose)[50,51]	Na+ + 0.024 × (glucose − 5.6)	Hyperglycemia (SI units)	Same as above
Corrected calcium (g/dL albumin)[51]	Ca + 0.8 × (4 − albumin)	Hypoalbuminemia	Prevents under-treatment of hypocalcemia
Corrected calcium (g/L albumin)[51]	Ca + 0.02 × (40 − albumin)	Hypoalbuminemia (SI units)	Same as above

SI: Standard international.