A 35-year-old woman with type 1 diabetes mellitus presents with fruity-smelling breath, rapid deep breathing, and altered mental status. Arterial blood gas shows: pH 7.15, PaCO₂ 22 mmHg, HCO₃⁻ 8 mEq/L, PaO₂ 95 mmHg. What is the most common precipitating cause of this acid-base disturbance?

Explanation

## Interpretation of the Acid-Base Disorder **Key Point:** The arterial blood gas shows pH < 7.35 (severe acidemia), low PaCO₂ (22 mmHg), and low HCO₃⁻ (8 mEq/L). This is **primary metabolic acidosis with respiratory compensation (Kussmaul respiration)**. ### Clinical Diagnosis: Diabetic Ketoacidosis (DKA) The constellation of: - Type 1 diabetes - Fruity-smelling breath (acetone) - Rapid deep breathing (Kussmaul respiration) - Altered mental status - Severe metabolic acidosis with low HCO₃⁻ ...confirms **diabetic ketoacidosis**. ### Most Common Precipitating Cause **High-Yield:** Infection or sepsis is the **most common precipitating cause of DKA** in clinical practice, accounting for 30–50% of cases. Common infections include: - Urinary tract infection (UTI) / pyelonephritis - Pneumonia - Gastroenteritis - Skin/soft tissue infections - Meningitis **Clinical Pearl:** Infections trigger DKA through: 1. Increased counter-regulatory hormones (cortisol, glucagon, catecholamines) 2. Increased insulin resistance 3. Accelerated lipolysis → free fatty acid mobilization 4. Hepatic ketone body production → metabolic acidosis ### Verification of Respiratory Compensation **Key Point:** In metabolic acidosis, the respiratory system compensates by hyperventilating to eliminate CO₂. Winter's formula predicts expected PaCO₂: $$\text{Expected PaCO}_2 = 1.5 \times [\text{HCO}_3^-] + 8 \pm 2$$ $$\text{Expected PaCO}_2 = 1.5 \times 8 + 8 \pm 2 = 20 \pm 2 = 18\text{–}22 \text{ mmHg}$$ Observed PaCO₂ = 22 mmHg → **appropriate respiratory compensation** (confirms primary metabolic acidosis). ### Why Other Options Are Less Common | Precipitant | Frequency | Why It's Less Common | |-------------|-----------|----------------------| | **Infection/Sepsis** | 30–50% | **Most common** — correct answer | | **Acute MI** | 5–10% | Cardiac stress can trigger DKA but is less frequent than infection | | **Hyperthyroidism** | < 5% | Rare precipitant; thyroid storm is distinct | | **Acute pancreatitis** | < 5% | Can coexist but is not a primary trigger of DKA | **Mnemonic — DKA Precipitants: SICK** - **S**epsis / Infection - **I**schemia (MI, stroke) - **C**eased insulin (non-compliance, pump failure) - **K**etogenic diet / Medication (SGLT2 inhibitors) Infection is the **S** — the single most common trigger.