A 28-year-old man with type 1 diabetes mellitus presents to the emergency department with a 2-day history of polyuria, polydipsia, and progressive lethargy. He had stopped taking insulin 3 days ago due to financial constraints. On examination: BP 110/70 mmHg, HR 118/min, RR 28/min, temperature 37.2°C. Breath has a fruity odour. Laboratory findings: blood glucose 520 mg/dL, arterial pH 7.18, HCO₃⁻ 12 mEq/L, anion gap 18 mEq/L, serum osmolality 310 mOsm/kg, serum sodium 128 mEq/L, serum potassium 5.8 mEq/L. Urine ketones are strongly positive. What is the most appropriate immediate management step?

Explanation

## Diagnosis and Immediate Management of DKA **Key Point:** This patient has diabetic ketoacidosis (DKA) with hyponatremia, hyperkalemia, and severe metabolic acidosis. The initial management sequence is critical. ### Diagnostic Criteria Met - Blood glucose >250 mg/dL (520 mg/dL) ✓ - Arterial pH <7.35 (7.18) ✓ - HCO₃⁻ <18 mEq/L (12 mEq/L) ✓ - Positive serum and urine ketones ✓ - Anion gap metabolic acidosis (18 mEq/L) ✓ ### Fluid Resuscitation Strategy **High-Yield:** The choice of saline concentration depends on serum osmolality and sodium status. - **Serum osmolality 310 mOsm/kg** (normal 280–295): hyperosmolar state → use **0.9% saline** initially - **Hyponatremia (128 mEq/L)** is *pseudohyponatremia* due to hyperglycemia and hyperosmolality; it corrects as glucose falls - 0.45% saline is reserved for hyperosmolar hyperglycemic state (HHS) or when osmolality >320 mOsm/kg ### Insulin Timing and Potassium Monitoring | Parameter | Action | Rationale | |-----------|--------|----------| | **Serum K⁺ >5.5 mEq/L** | Hold insulin, give IV fluids only | Insulin drives K⁺ intracellularly; premature insulin worsens hyperkalemia and risk of arrhythmia | | **Serum K⁺ 4.5–5.5 mEq/L** | Start insulin after K⁺ check | Safe to initiate insulin infusion | | **Serum K⁺ <4.5 mEq/L** | Add KCl to IV fluids before insulin | Prevent severe hypokalemia during treatment | **Clinical Pearl:** In this case, K⁺ = 5.8 mEq/L (elevated). Insulin must be withheld until potassium drops below 5.5 mEq/L, even though acidosis is severe. Fluids alone will lower K⁺ through dilution and improved renal perfusion. ### Fluid Rate and Type - **0.9% saline at 1 L/hr** for the first 1–2 hours (aggressive rehydration) - Deficit is typically 5–8 L; replace over 24–48 hours - Switch to 0.45% saline once osmolality falls below 320 mOsm/kg **Warning:** Do NOT give insulin before K⁺ is safe, and do NOT use hypertonic saline or sodium bicarbonate as first-line agents in DKA management. ### Why NOT the Other Options - **0.45% saline too early:** osmolality is only 310; not yet indication for hypotonic fluid - **Bicarbonate:** reserved for pH <6.9 with severe shock; not standard DKA management and delays insulin initiation - **3% saline:** hyponatremia is pseudohyponatremia and will correct with glucose normalization; hypertonic saline risks hyperchloremic acidosis [cite:Harrison 21e Ch 397]