A 28-year-old woman from Delhi presents to the emergency department with acute onset polyuria, polydipsia, and fatigue for 3 days. On examination, she is tachypneic (RR 28/min), has fruity-smelling breath, and appears dehydrated. Capillary blood glucose is 480 mg/dL. Arterial blood gas shows pH 7.18 with HCO₃⁻ of 12 mEq/L. Serum beta-hydroxybutyrate is markedly elevated. Which of the following best explains the pathophysiology of her metabolic acidosis?

Question

Accepted Answer

D. Unopposed lipolysis due to severe insulin deficiency leading to excess ketone body production. ## Pathophysiology of Diabetic Ketoacidosis (DKA)

### Mechanism of Metabolic Acidosis in DKA

**Key Point:** In DKA, severe insulin deficiency removes the inhibitory effect of insulin on hormone-sensitive lipase, leading to uncontrolled lipolysis and excessive free fatty acid (FFA) mobilization from adipose tissue.

### Sequential Events

1. **Insulin deficiency** → Loss of anti-lipolytic effect
2. **Unopposed lipolysis** → Massive FFA release into bloodstream
3. **Hepatic beta-oxidation** → Ketone body production (acetoacetate, beta-hydroxybutyrate, acetone)
4. **Ketone accumulation** → High anion-gap metabolic acidosis
5. **Respiratory compensation** → Kussmaul respiration (fruity breath from acetone)

### Why This Patient Has Severe Acidosis

| Feature | Role in Acidosis |
|---------|------------------|
| Insulin deficiency | Removes brake on lipolysis |
| Elevated glucagon | Stimulates hepatic ketogenesis |
| High FFAs | Substrate for ketone production |
| Impaired ketone clearance | Ketones accumulate faster than utilization |

**High-Yield:** The anion gap in DKA is due to **ketone bodies (beta-hydroxybutyrate and acetoacetate)**, not lactate. Serum beta-hydroxybutyrate >3 mmol/L confirms ketosis.

**Clinical Pearl:** Fruity breath (acetone) and Kussmaul respiration are compensatory mechanisms — the body attempts to blow off CO₂ to raise pH, but ketone production outpaces respiratory compensation.

### Distinction from Other Causes

- ~~Impaired renal H⁺ excretion~~ — Osmotic diuresis actually *increases* renal H⁺ loss; acidosis is from ketones, not H⁺ retention
- ~~Gluconeogenesis inhibition~~ — Hyperglycemia is caused by *unopposed* gluconeogenesis and glycogenolysis, not inhibition
- ~~Glucose utilization~~ — Cells cannot use glucose (insulin-dependent); glucose accumulates while cells starve

[cite:Harrison 21e Ch 397]

Answer

A. Increased peripheral glucose utilization overwhelming the buffering capacity of bicarbonate

Answer

B. Direct inhibition of hepatic gluconeogenesis by elevated blood glucose

Answer

C. Impaired renal excretion of hydrogen ions due to hyperglycemia-induced osmotic diuresis

Explanation

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