A 72-year-old woman with COPD (FEV₁ 35% predicted) and sleep apnea undergoes emergency repair of a perforated peptic ulcer. During induction with thiopental 3 mg/kg, she develops stridor and cyanosis within 30 seconds. SpO₂ drops from 94% (on room air) to 78%. Breath sounds are audible bilaterally. Capnography shows a plateau waveform. What is the most likely cause of hypoxia, and what is the immediate next step?

Explanation

## Diagnosis: Laryngospasm with Hypoxia **Key Point:** Laryngospasm is an involuntary reflex closure of the vocal cords in response to airway irritation (secretions, blood, light touch, or inadequate anesthesia). It is the most common cause of acute hypoxia in the immediate perioperative period, especially in patients with reactive airways (COPD, asthma, sleep apnea). **Clinical Pearl:** The classic triad of laryngospasm is: 1. **Stridor** (high-pitched breathing sound, audible without stethoscope). 2. **Cyanosis** (within 10–30 seconds due to apnea). 3. **Plateau capnography waveform** (absence of CO₂ exhalation because no air reaches the lungs). In this case, all three are present. The patient is at high risk: COPD (reactive airway), sleep apnea (upper airway collapse tendency), and emergency surgery (stress, inadequate fasting, higher aspiration risk). **High-Yield:** Differential diagnosis of acute perioperative hypoxia: | Cause | Stridor | Cyanosis Onset | Capnography | Breath Sounds | Management | |-------|---------|----------------|-------------|---------------|-------------| | **Laryngospasm** | Yes (high-pitched) | 10–30 sec | Plateau | Bilateral present | PPV + 100% O₂, prepare intubation | | Aspiration | No | 30–60 sec | Decreased CO₂ | Crackles/wheezes | Rigid bronchoscopy, suction, ICU | | Anaphylaxis | No (angioedema possible) | 10–30 sec | Normal initially | Wheezes ± stridor | Epinephrine IM, IV fluids, antihistamine | | Pulmonary edema | No | Gradual (minutes) | Normal | Crackles | Diuretics, reduce fluids, CPAP | | Bronchospasm | No | 30–60 sec | Decreased CO₂ | Wheezes bilaterally | Albuterol nebulized, IV steroids | ### Management Algorithm ```mermaid flowchart TD A[Acute hypoxia with stridor]:::outcome --> B{Laryngospasm suspected?}:::decision B -->|Yes: plateau capnography + stridor| C[STOP all stimulation]:::action C --> D[Apply positive pressure ventilation<br/>100% O₂, gentle mask pressure]:::action D --> E{SpO₂ recovery?}:::decision E -->|Yes| F[Maintain PPV, deepen anesthesia<br/>with IV propofol or volatile]:::action E -->|No after 30 sec| G[Prepare for emergency intubation<br/>Succinylcholine 1-2 mg/kg IV]:::urgent G --> H[Intubate under apnea]:::action H --> I[Confirm tube placement<br/>Resume surgery]:::outcome B -->|No: consider aspiration| J[Rigid bronchoscopy]:::action ``` **Mnemonic: STOP-LARYNGOSPASM** - **S**top all stimulation (light, suctioning, intubation attempts). - **T**urn off volatile anesthetic (if running). - **O**xygen 100% via positive pressure. - **P**repare for intubation (have succinylcholine ready). - **L**aryngeal mask airway (LMA) as backup if intubation fails. - **A**void repeated intubation attempts (worsen laryngeal edema). - **R**emember: most laryngospasms resolve with PPV + O₂ + deeper anesthesia. - **Y**ield to intubation only if PPV fails after 30 seconds. - **N**o aspiration precautions needed (airway is closed). - **G**entle technique always (avoid trauma). - **O**bserve post-op for recurrence (especially in COPD/sleep apnea). - **S**uccinylcholine 1–2 mg/kg if intubation required (fastest onset, shortest duration). - **P**ost-intubation: confirm tube, resume anesthesia, monitor for laryngeal edema. - **A**void extubation until fully awake and able to protect airway. - **S**teroids (dexamethasone 4–8 mg IV) reduce post-op stridor risk. - **M**onitor in ICU if severe (risk of re-intubation). **Why Positive Pressure Ventilation Works:** Laryngospasm is a reflex that can be overcome by applying gentle positive pressure (5–10 cm H₂O) via mask, which: 1. Recruits collapsed alveoli and improves oxygenation. 2. Provides sensory feedback that inhibits the spasm reflex. 3. Allows deeper anesthesia to be administered IV (propofol 0.5–1 mg/kg or volatile deepening), which abolishes the reflex. **Tip:** Do NOT attempt forceful intubation or aggressive suctioning during active laryngospasm — this worsens the reflex and causes laryngeal edema. Patience with PPV + O₂ resolves 90% of cases within 30–60 seconds. [cite:Morgan & Mikhail Clinical Anesthesiology 6e Ch 5; Gupta & Singh Essentials of Anesthesia Ch 10]