Which clinical feature best distinguishes diabetic ketoacidosis (DKA) from hyperglycemic hyperosmolar state (HHS)?

Explanation

## Distinguishing DKA from HHS ### Key Discriminating Feature **Key Point:** Kussmaul respiration (deep, rapid, labored breathing) is the hallmark of metabolic acidosis and is present in DKA but absent in HHS. This reflects the respiratory compensation for severe metabolic acidosis (pH < 7.3) in DKA. ### Comparative Table | Feature | DKA | HHS | | --- | --- | --- | | **Kussmaul respiration** | Present (hallmark) | Absent | | **Arterial pH** | < 7.3 (severe acidosis) | > 7.30 (normal or mild alkalosis) | | **Serum ketones** | Marked elevation (β-hydroxybutyrate) | Minimal or absent | | **Anion gap** | High (> 12) | Normal | | **Osmolality** | Usually < 320 mOsm/kg | Often > 320 mOsm/kg | | **Altered mental status** | Mild to moderate | Severe (common) | | **Glucose level** | Usually 250–600 mg/dL | Often > 600 mg/dL | ### Why Kussmaul is the Discriminator **High-Yield:** DKA is fundamentally an **acidotic** crisis (pH < 7.3 with high anion gap), whereas HHS is an **osmotic** crisis (very high glucose and osmolality with preserved pH). The respiratory system compensates for DKA's acidosis by hyperventilating (Kussmaul breathing), a phenomenon absent in HHS. **Clinical Pearl:** A patient with severe hyperglycemia and Kussmaul respiration = DKA until proven otherwise. If you see severe hyperglycemia WITHOUT Kussmaul but WITH profound altered mental status, think HHS. ### Pathophysiology 1. **DKA:** Insulin deficiency → lipolysis → free fatty acids → ketone bodies (acetoacetate, β-hydroxybutyrate) → metabolic acidosis → respiratory compensation (Kussmaul). 2. **HHS:** Insulin deficiency is partial → glucose accumulates but ketogenesis is suppressed by residual insulin → no acidosis → no respiratory drive → severe osmotic dehydration and neurological symptoms dominate. **Mnemonic:** **KUSSMAUL = KETOACIDOSIS** — if you see Kussmaul breathing, the diagnosis is DKA.