Correct Answer: C. Administration of 3% saline
This patient presents with diabetic ketoacidosis (DKA) with severe hyponatremia (Na+ 125 mEq/L). The hyponatremia is pseudohyponatremia — a spurious lab finding caused by severe hyperglycemia (700 mg/dL) and osmotic shift of water into the intravascular space, diluting serum sodium. The corrected sodium is actually much higher: for every 100 mg/dL glucose above 100, add 1.6 mEq/L to measured sodium. Corrected Na+ ≈ 125 + (6 × 1.6) ≈ 135–140 mEq/L — normal to high-normal. 3% hypertonic saline is contraindicated because it worsens hypernatremia and increases serum osmolality, which can precipitate cerebral edema as glucose is corrected. The standard of care in DKA is 0.9% isotonic saline (0.154 mEq/L Na+), which replaces volume deficit without worsening osmolality. As insulin lowers glucose and water shifts back into cells, sodium concentration naturally rises. Hypertonic saline is reserved for symptomatic hyponatremia (seizures, altered mental status from true hyponatremia), which this patient does not have. The fatigue and vomiting are from DKA and volume depletion, not from hyponatremia per se.
Why the other options are wrong
A. Initiation of 0.9% normal saline infusion — This is the gold standard initial fluid in DKA. Isotonic saline replaces the 5–10 L volume deficit, restores renal perfusion, and dilutes glucose without worsening osmolality. Initial bolus is 1 L over 1 hour, then 500 mL/h. This is mandatory, not contraindicated. B. Frequent monitoring of serum potassium levels — Essential in DKA management. Although K+ is 4.2 mEq/L (low-normal), total body K+ is depleted (1000–2000 mEq deficit). Insulin drives K+ intracellularly, causing life-threatening hypokalemia. Serial K+ monitoring every 2–4 hours initially guides K+ replacement. Omitting this monitoring risks fatal arrhythmias. D. Intravenous insulin therapy — Cornerstone of DKA treatment. Insulin (0.1 U/kg/h IV infusion) suppresses ketogenesis and lowers glucose. It is started after K+ is ≥3.5 mEq/L (to prevent hypokalemia). Withholding insulin prolongs DKA and risks mortality. This is absolutely indicated.
High-Yield Facts
- Pseudohyponatremia in DKA: Measured Na+ drops ~1.6 mEq/L per 100 mg/dL glucose rise; corrected Na+ is usually normal despite low measured value.
- 0.9% saline is first-line in DKA; 3% saline risks hypernatremia and cerebral edema during glucose correction.
- Total body K+ is depleted in DKA despite normal/low serum K+; insulin causes acute hypokalemia; K+ monitoring every 2–4 hours is mandatory.
- Insulin dosing in DKA: 0.1 U/kg/h IV infusion (not bolus); start only after K+ ≥3.5 mEq/L.
- Hypertonic saline (3%) is reserved for symptomatic hyponatremia (seizures, coma) with true low Na+, not pseudohyponatremia.
Mnemonics
DKA Fluid Rule: 'ISOTONIC First' Initial = 0.9% saline (isotonic), Start = 1 L/hour, Osmolality = avoid hypertonic, Then = switch to 0.45% when glucose <250 mg/dL. Use when deciding fluids in any DKA case. Pseudohyponatremia Trap: 'Glucose Dilutes, Not Depletes' High glucose pulls water out of cells → dilutes serum Na+ (pseudohyponatremia). Corrected Na+ = measured + (1.6 × [glucose − 100]/100). Hypertonic saline worsens this; isotonic saline fixes it. Use when seeing low Na+ + high glucose together.
NBE Trap
NBE pairs severe hyponatremia with DKA to trap students into choosing hypertonic saline, which is the classic treatment for true symptomatic hyponatremia. The trap: students forget that DKA causes pseudohyponatremia (osmotic, not true), and hypertonic saline is contraindicated here because it worsens osmolality and risks cerebral edema during insulin therapy.</trap> <parameter name="textbookRef">Harrison Ch. 296 (Diabetes Mellitus: DKA Management); KD Tripathi Ch. 23 (Insulin & Diabetes); Robbins Ch. 24 (Pancreatic Pathology)
Clinical Pearl
In Indian pediatric DKA cases (common in tier-2/3 hospitals with delayed diagnosis), the reflex to give hypertonic saline for "low sodium" is a leading cause of iatrogenic cerebral edema. Always calculate corrected sodium in hyperglycemia; pseudohyponatremia is the rule, not the exception, in DKA.