A 32-year-old woman with a BMI of 38 kg/m² presents to the emergency department with acute appendicitis requiring emergency surgery. She ate a full meal 2 hours ago. During pre-operative assessment, the anesthesiologist is concerned about difficult airway management and aspiration risk. Which investigation is most appropriate to assess the likelihood of difficult intubation before rapid sequence induction?

Explanation

## Assessment of Difficult Airway Before RSI **Key Point:** Pre-operative airway assessment using simple bedside tests is the investigation of choice to predict difficult intubation before rapid sequence induction. ### Mallampati Score and Thyromental Distance These are the **gold standard bedside investigations** for pre-operative airway assessment: | Parameter | Method | Interpretation | |-----------|--------|----------------| | **Mallampati Score** | Patient sitting upright, mouth open, tongue protruded | Class I–II: Easy; Class III–IV: Difficult | | **Thyromental Distance** | Measured from thyroid cartilage to mentum with neck extended | >6.5 cm: Easy; <6.5 cm: Difficult | | **Sternomental Distance** | Measured from sternal notch to mentum with neck extended | >12.5 cm: Easy; <12.5 cm: Difficult | | **Interincisor Gap** | Distance between upper and lower incisors when mouth fully open | >3 cm: Easy; <3 cm: Difficult | **High-Yield:** A combination of **abnormal Mallampati (Class III–IV) + thyromental distance <6.5 cm + BMI >30** significantly increases the risk of difficult intubation and should prompt consideration of awake fiberoptic intubation instead of RSI. ### Why These Tests Are Ideal for RSI Context 1. **Rapid and non-invasive** — can be performed in seconds at bedside 2. **No delay to emergency surgery** — critical in acute appendicitis 3. **Inform choice of induction technique** — if difficult airway predicted, modify approach (awake intubation, video laryngoscope, have backup plans) 4. **Reproducible and standardized** — part of every anesthesia curriculum **Clinical Pearl:** In obese patients (BMI >35), even with normal Mallampati scores, assume difficult airway due to reduced neck mobility and increased soft tissue bulk. Combine assessment with patient factors: age, dentition, neck mobility, jaw opening, and previous anesthetic history. **Mnemonic: LEMON** — **L**ips (can you see them?), **E**ye (external appearance), **M**allampati, **O**pen mouth (interincisor gap), **N**eck mobility. All five should be assessed before RSI. ## Why Other Investigations Are Not First-Line **Chest X-ray and ABG:** These assess pulmonary function and oxygenation status, not airway anatomy. Relevant for risk stratification but not for predicting intubation difficulty. **CT neck:** Invasive, time-consuming, exposes patient to radiation, and delays emergency surgery. Reserved only for suspected anatomical abnormalities (tumors, abscess, epiglottitis) when diagnosis is unclear. **Fiberoptic laryngoscopy under local anesthesia:** Gold standard for **confirming** difficult airway in awake patients, but NOT an investigation of choice for **prediction** before RSI. Used therapeutically (awake intubation) in predicted difficult airways, not for assessment.