A 32-year-old male patient is scheduled for emergency intubation in the ICU. He receives succinylcholine 1.5 mg/kg IV for rapid sequence induction. Within 2 minutes of administration, he develops severe hyperkalemia (K⁺ 7.2 mEq/L), followed by cardiac arrhythmias and cardiac arrest. The anesthesiologist suspects a genetic predisposition to abnormal succinylcholine metabolism. Which investigation is most appropriate to confirm the suspected diagnosis?

Explanation

## Clinical Context This patient has presented with a classic hyperkalemic response to succinylcholine, suggesting **pseudocholinesterase (butyrylcholinesterase) deficiency** or abnormal variants. The severe hyperkalemia and cardiac arrhythmia are hallmark features of prolonged succinylcholine apnea or exaggerated response. ## Investigation of Choice **Key Point:** Plasma cholinesterase activity (pseudocholinesterase) and the **dibucaine number** are the gold-standard screening and confirmatory tests for succinylcholine sensitivity. ### Dibucaine Number Interpretation | Dibucaine Number | Plasma Cholinesterase | Succinylcholine Duration | Genetic Status | |---|---|---|---| | 70–80 | Normal | 5–10 min | Homozygous normal (EE) | | 40–60 | Intermediate | 20–30 min | Heterozygous (Ea or Ef) | | 20–30 | Low | 30–60 min | Heterozygous (Ea or Ef) | | <20 | Very low/absent | >2 hours | Homozygous atypical (aa) | **High-Yield:** Dibucaine is a local anesthetic that normally inhibits plasma cholinesterase activity by 70%. In patients with abnormal enzyme variants, dibucaine inhibition is reduced, resulting in a low dibucaine number. ## Why This Investigation Works 1. **Rapid turnaround:** Results available within hours, allowing immediate clinical management. 2. **Phenotypic confirmation:** Directly measures enzyme activity and response to dibucaine. 3. **Guides family screening:** Identifies heterozygotes and homozygotes for genetic counseling. 4. **Cost-effective:** Cheaper than genetic sequencing for immediate clinical decision-making. ## Clinical Pearl **Warning:** Serum potassium levels and ABG are essential for acute management but do NOT diagnose the underlying enzyme deficiency—they only document the consequence. Genetic sequencing (BCHE gene mutations) is definitive but takes days to weeks and is typically done after phenotypic confirmation for family counseling, not for acute diagnosis. ## Mnemonic **DIBUCAINE = Diagnostic Investigation for Butyrylcholinesterase Abnormality Confirmation in Anesthesia Incidents Nationwide Emergencies** [cite:Gupta & Sharma Anesthesia Ch 12]