A 28-year-old man with type 1 diabetes mellitus presents to the emergency department with a 3-day history of polyuria, polydipsia, and progressive lethargy. His mother reports he missed his insulin injections for 2 days due to illness. On examination, he is drowsy, respiratory rate 28/min with deep breathing, blood pressure 110/70 mmHg, and heart rate 110/min. Laboratory investigations reveal: blood glucose 450 mg/dL, arterial pH 7.25, HCO₃⁻ 12 mEq/L, PaCO₂ 28 mmHg, serum sodium 132 mEq/L, serum potassium 5.8 mEq/L, and serum osmolality 310 mOsm/kg. Urine ketones are strongly positive. What is the most appropriate immediate management step after establishing IV access and drawing blood for investigations?

Explanation

## Immediate Management of DKA: Fluid and Insulin Sequencing ### Clinical Context This patient has **severe DKA** (pH 7.25, HCO₃⁻ 12, respiratory rate 28) with **hyponatremia** (Na⁺ 132) and **hyperkalemia** (K⁺ 5.8). The hyponatremia is **pseudohyponatremia** (dilutional, due to high glucose osmotic effect), and the hyperkalemia reflects total body K⁺ depletion masked by acidosis-driven K⁺ shift out of cells. ### Why Option 3 is Correct **Key Point:** In DKA management, **fluid resuscitation precedes or runs parallel to insulin initiation**, and **insulin should be withheld if serum potassium is ≤3.5 mEq/L** to prevent life-threatening hypokalemia. 1. **Initial fluid bolus (0–60 min):** 15–20 mL/kg of **0.9% normal saline** (not hypotonic) to restore circulating volume, improve renal perfusion, and dilute serum osmolality. 2. **Insulin timing:** Insulin drives K⁺ intracellularly (via Na⁺-K⁺-ATPase), causing dangerous hypokalemia if serum K⁺ is already low. Although this patient's K⁺ is 5.8 (elevated), the **total body deficit is ~3–5 mEq/kg**. Rechecking K⁺ after initial fluid resuscitation ensures safe insulin initiation. 3. **Subsequent fluids:** 4–6 mL/kg/hr with 0.9% saline (isotonic, avoids worsening hyponatremia). **High-Yield:** The **0.9% saline** is preferred in early DKA because it: - Restores volume without exacerbating pseudohyponatremia - Provides Cl⁻ to correct hyperchloremic metabolic acidosis - Avoids hypotonic solutions that worsen cerebral edema risk ### Potassium Management Flowchart ```mermaid flowchart TD A[Serum K+ measured]:::outcome --> B{K+ level?}:::decision B -->|< 3.5 mEq/L| C[Add 20-40 mEq K+ to IV fluids]:::action C --> D[HOLD insulin]:::urgent B -->|3.5-5.5 mEq/L| E[Add 20 mEq K+ to IV fluids]:::action E --> F[Start insulin 0.1 units/kg/hr]:::action B -->|> 5.5 mEq/L| G[Recheck K+ after 1-2 hrs fluids]:::action G --> H[Then start insulin]:::action ``` **Clinical Pearl:** Hypokalemia is the **most common cause of death** in DKA if insulin is given without K⁺ repletion. Always check K⁺ before and frequently during insulin infusion. ### Why Not the Other Options | Option | Problem | |--------|----------| | Option 0 | Immediate insulin at 0.1 units/kg/hr without K⁺ recheck is dangerous; hyperkalemia may be masked by acidosis. | | Option 1 | Dextrose in early DKA worsens hyperglycemia and osmolality; insulin should never be deferred in severe acidosis (pH 7.25). | | Option 2 | Hypotonic saline (0.45%) worsens pseudohyponatremia and increases cerebral edema risk; insulin dose too low (0.05 units/kg/hr). |