A 32-year-old male patient is scheduled for an emergency laparotomy under general anesthesia. The anesthesiologist administers a depolarising muscle relaxant for rapid sequence intubation. Which of the following is the most common serious adverse effect associated with depolarising muscle relaxants?

Explanation

## Most Common Adverse Effect of Depolarising Muscle Relaxants **Key Point:** Hyperkalemia is the most frequently encountered serious adverse effect of depolarising muscle relaxants (succinylcholine), occurring in nearly all patients to some degree. ### Mechanism of Hyperkalemia Depolarising agents cause sustained depolarisation of the muscle membrane, leading to: 1. Uncontrolled efflux of potassium from muscle cells 2. Typical increase of 0.5–1 mEq/L in healthy patients 3. Rise of 5–10 mEq/L or more in susceptible patients (burns, crush injuries, denervation, sepsis) ### Clinical Significance **High-Yield:** While mild hyperkalemia (0.5–1 mEq/L) is clinically insignificant in healthy individuals, severe hyperkalemia can precipitate: - Cardiac arrhythmias (peaked T waves, widened QRS, bradycardia, asystole) - Cardiac arrest, especially in children and high-risk patients ### Risk Factors for Severe Hyperkalemia | Risk Factor | Mechanism | |---|---| | Burn injury (>20% BSA) | Upregulation of extrajunctional acetylcholine receptors | | Crush injury / rhabdomyolysis | Massive potassium release from damaged muscle | | Spinal cord injury / paralysis | Denervation supersensitivity | | Sepsis / critical illness | Altered ion pump function | | Renal failure | Impaired potassium excretion | | Malignancy (especially hematologic) | Tumour lysis syndrome risk | ### Why Other Options Are Less Common **Malignant hyperthermia** — rare (1 in 10,000–15,000 exposures), genetic predisposition required, not the most common effect. **Prolonged apnea** — occurs only in patients with pseudocholinesterase deficiency (genetic variants); incidence ~1 in 3,500. **Anaphylaxis** — rare allergic reaction; depolarising agents have lower immunogenicity than non-depolarising agents. **Clinical Pearl:** In high-risk patients (burns, crush injuries, spinal cord injury), depolarising muscle relaxants should be **avoided entirely** due to the risk of life-threatening hyperkalemia. Non-depolarising agents are the safer choice. **Mnemonic: SHAKY** — Succinylcholine causes Hyperkalemia, Arrhythmias, Kick (fasciculations), Yawning (prolonged apnea in deficiency).