3.1 Advanced Airway Assessment and Difficult Airway Algorithms

Advanced Airway Assessment and Difficult Airway Algorithms

Effective airway management in critical care transport (CCT) demands a systematic, proactive approach. Unlike controlled hospital environments, flight paramedics must secure airways in confined spaces, moving vehicles, and under extreme environmental conditions. The foundation of a successful airway intervention is a comprehensive pre-intubation assessment, allowing the transport clinician to anticipate difficulties and prepare appropriate backup strategies before administering induction medications.

The LEMON Assessment Framework

The LEMON mnemonic is the gold standard for predicting difficult laryngoscopy and intubation in the prehospital and critical care environments. Each letter represents a key anatomical or clinical assessment point:

• L – Look Externally: Perform a rapid visual inspection of the patient. Identify factors predicting difficult bag-valve-mask (BVM) ventilation, laryngoscopy, or surgical airway placement. Key markers include facial trauma, thick or short neck, retrognathia (receding chin), macroglossia (large tongue), facial hair (impeding BVM seal), and prominent incisors.
• E – Evaluate the 3-3-2 Rule: This rule uses finger breadths to assess anatomical geometry and airway access:
  • 3 Fingers (Mouth Opening): The patient should accommodate three finger breadths between their upper and lower incisors. Less than three predicts poor visualization and difficulty inserting the laryngoscope blade.
  • 3 Fingers (Hyoid-to-Mentum Distance): Three finger breadths should fit between the hyoid bone and the chin tip (mentum). A shorter distance suggests an anterior larynx, which makes visual alignment of the airway axes difficult.
  • 2 Fingers (Thyroid-to-Hyoid Distance): Two finger breadths should fit between the thyroid notch and the hyoid bone. Less than two fingers indicates a high, anterior larynx hidden behind the tongue base.
• M – Mallampati Classification: This score correlates the visibility of pharyngeal structures with the difficulty of intubation:
  • Class I: Full visualization of the soft palate, uvula, fauces, and tonsillar pillars.
  • Class II: Visualization of the soft palate, fauces, and uvula.
  • Class III: Visualization of the soft palate and only the base of the uvula.
  • Class IV: Only the hard palate is visible; the soft palate is completely obscured. Classes III and IV are strong predictors of a difficult intubation.
• O – Obstruction and Obesity: Assess for epiglottitis, Ludwig's angina, peritonsillar abscess, neck hematoma, or foreign bodies. Obesity (BMI > 30 kg/m²) increases redundant upper airway tissue that collapses during induction, making BVM ventilation and laryngoscopy challenging. Obese patients also experience rapid desaturation due to reduced functional residual capacity.
• N – Neck Mobility: The ability to place the patient in the optimal "sniffing position" is critical. Cervical spine immobilization in trauma patients completely restricts neck mobility, automatically classifying the patient as a difficult airway. Other restrictive conditions include ankylosing spondylitis and severe arthritis.

Cormack-Lehane Laryngoscopic View

During laryngoscopy, the clinician grades the visual field using the Cormack-Lehane classification:

• Grade I: Full view of the glottic opening, including the vocal cords and commissures.
• Grade II: Partial view of the glottic opening; the posterior commissure is visible, but the anterior portion is obscured.
• Grade III: Only the epiglottis is visible; no part of the glottic opening or vocal cords can be seen.
• Grade IV: Neither the epiglottis nor the glottic opening is visible.

Difficult Airway Algorithms in Critical Care Transport

When the assessment reveals a difficult airway, or when primary intubation attempts fail, the transport team must execute a structured algorithm:

Preparation and Setup: The SOAP ME Mnemonic

Before attempting intubation, the team must prepare using the SOAP ME checklist:

• S – Suction: Ensure at least one working suction unit is on, with a Yankauer tip under the patient's right shoulder.
• O – Oxygen: Set up high-flow oxygen for pre-oxygenation. Maintain nasal cannula at flush rate (> 15 L/min) for apneic oxygenation during the attempt.
• A – Airway Equipment: Select primary and backup blades, endotracheal tubes (ETTs) with stylets/bougies, and video laryngoscopy equipment.
• P – Pharmacy: Draw up induction, paralytic, and post-intubation sedation medications based on patient weight and hemodynamics.
• M – Monitoring: Confirm continuous waveform capnography (EtCO2), pulse oximetry, ECG, and non-invasive blood pressure.
• E – Escort / Extra Hands: Delegate specific roles to transport partners, ensuring a dedicated person is assigned to manual in-line stabilization if indicated.

The Rescue Pathway: Plans A through D

• Plan A: Primary Intubation: The goal is first-pass success. Optimize patient positioning. Choose video laryngoscopy (VL) as the primary modality if available, as it improves the Cormack-Lehane view. If the glottis is poorly visualized, apply external laryngeal manipulation or the BURP maneuver. Limit intubation attempts to a maximum of two before moving down the algorithm.
• Plan B: Secondary Airway (Rescue Supraglottic Devices): If primary intubation fails, insert a supraglottic airway rescue device such as an i-gel or LMA. The i-gel is highly favored in CCT due to its non-inflatable elastomer cuff, which is unaffected by altitude-induced pressure changes.
• Plan C: Bag-Valve-Mask (BVM) Ventilation: If the SGA fails, perform optimized mask ventilation. Use a two-person, two-handed VE-mask seal technique with oral and nasopharyngeal airway adjuncts. Ensure a PEEP valve is attached to the BVM and set between 5 and 10 cm H2O.
• Plan D: Surgical Airway (CICO): If the patient cannot be intubated and cannot be oxygenated, the clinician must immediately perform an emergency surgical cricothyroidotomy. The preferred approach in CCT is the scalpel-bougie technique:
  1. Identify the cricothyroid membrane.
  2. Stabilize the larynx with the non-dominant hand.
  3. Make a horizontal incision through the skin and cricothyroid membrane.
  4. Insert a gloved finger or the scalpel handle to dilate the incision.
  5. Pass a gum elastic bougie through the incision into the trachea.
  6. Advance a size 6.0 mm cuffed ETT over the bougie, inflate the cuff, confirm placement with waveform capnography, and secure the tube.

CAMTS and Transport Quality Standards

The Commission on Accreditation of Medical Transport Systems (CAMTS) mandates strict guidelines for airway management. Transport agencies must continuously monitor first-pass success rates, adverse events, and compliance with confirmation protocols. Standard CAMTS criteria require that ETT placement be confirmed using at least three distinct modalities:

1. Continuous Waveform Capnography (EtCO2): The absolute gold standard. A continuous, four-phase capnography waveform must be present to verify tracheal placement.
2. Auscultation: Bilateral breath sounds must be heard in the mid-axillary lines, and the epigastrium must be silent.
3. Visual Confirmation: Direct visualization of the ETT passing through the vocal cords, or secondary confirmation via a colorimetric detector if capnography is temporarily unavailable.