A 28-year-old woman with type 1 diabetes mellitus presents to the emergency department with a 2-day history of polyuria, polydipsia, and malaise. On examination, she is tachypneic (RR 28/min) with Kussmaul breathing. Arterial blood gas shows pH 7.15, PaCO₂ 22 mmHg, HCO₃⁻ 8 mEq/L, and PaO₂ 95 mmHg on room air. Blood glucose is 420 mg/dL. What is the most appropriate immediate next step in management?

Explanation

## Clinical Diagnosis This patient has **diabetic ketoacidosis (DKA)** with severe metabolic acidosis and respiratory compensation. ### ABG Interpretation **Key Point:** The pH is 7.15 (severe acidemia), HCO₃⁻ is 8 (primary metabolic acidosis), and PaCO₂ is 22 (appropriate respiratory compensation via hyperventilation). The low PaCO₂ confirms this is NOT respiratory acidosis — the lungs are appropriately hyperventilating to blow off CO₂. ### Management Algorithm for DKA ```mermaid flowchart TD A[DKA Confirmed]:::outcome --> B{Assess severity}:::decision B -->|Mild-Moderate| C[IV insulin + fluids + K+ monitoring]:::action B -->|Severe| D[IV insulin + aggressive fluid resuscitation + K+ monitoring]:::action C --> E[Recheck ABG, glucose, electrolytes q1-2h]:::action D --> E E --> F{Anion gap closing?}:::decision F -->|Yes| G[Continue insulin, transition to SC when eating]:::action F -->|No| H[Increase insulin rate, reassess]:::action ``` ### Immediate Management Priorities 1. **Insulin infusion** — stops ketone production and allows cellular glucose uptake - Dose: 0.1 unit/kg/hr IV (typical range 5–10 units/hr) - Do NOT give bolus; use continuous infusion 2. **IV fluid resuscitation** — restores intravascular volume and improves renal perfusion - Start with 0.9% normal saline (1–1.5 L in first hour if hemodynamically unstable) - Reduces serum osmolality and promotes ketone clearance 3. **Electrolyte monitoring** — especially K⁺ - Insulin drives K⁺ intracellularly; risk of hypokalemia - Add KCl once K⁺ < 5.5 mEq/L and urine output confirmed **High-Yield:** The respiratory compensation (Kussmaul breathing) is a protective mechanism — do NOT suppress it with sedation or mechanical ventilation unless respiratory failure develops. ### Why NOT Bicarbonate? **Warning:** Sodium bicarbonate is **contraindicated in DKA** unless pH < 6.9 (which this patient does not have). Bicarbonate: - Paradoxically worsens intracellular acidosis (CO₂ crosses BBB freely; HCO₃⁻ does not) - Delays ketone clearance - Increases risk of hypokalemia - Increases risk of cerebral edema **Clinical Pearl:** Correction of acidemia occurs naturally as insulin suppresses ketone production and the anion gap closes. The pH will rise as ketones are cleared, not from exogenous bicarbonate. [cite:Harrison 21e Ch 297]