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Difficult Airway Algorithm

Definition

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Step 1 — Pre-procedure Assessment

1. Awake intubation vs. intubation after induction of general anesthesia
2. Non-invasive vs. invasive initial approach
3. Video-assisted laryngoscopy as the initial approach
4. Preservation vs. ablation of spontaneous ventilation

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ASA Difficult Airway Algorithm (2022)

Arm 1 — Predicted Difficult Airway → Awake Intubation

• Airway approached by noninvasive intubation (fiberoptic, video laryngoscopy)
• If fails → Cancel case or consider other options or invasive airway access
• Invasive airway access (a) is always an option

Arm 2 — Intubation After Induction (Non-emergency Pathway)

1. Call for help; consider returning to spontaneous ventilation; consider awakening the patient
2. Alternative approaches to intubation (see note c below)
3. If multiple attempts fail → Invasive airway access OR consider other options OR awaken patient

Arm 3 — Emergency Pathway (CICV)

1. Face mask ventilation NOT adequate → Attempt SGA
2. SGA adequate → "Stop and Think" (nonemergency pathway)
3. SGA NOT adequate → Emergency pathway: call for help → Emergency noninvasive airway ventilation (SGA attempt) → If fails → Emergency invasive airway access

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DAS Algorithm 2015 — Unanticipated Difficult Intubation in Adults

• Palpable CTM: transverse stab incision → turn blade 90° → bougie via blade → railroad 6-mm cuffed tube → confirm with capnography
• Impalpable CTM: 8–10 cm vertical skin incision → blunt dissection → identify larynx → proceed as above

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Algorithm Notes (Footnotes)

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Oxygen Delivery — Continuously Throughout

• Preoxygenation with 100% O₂ (8 breaths of VC or 3–5 min tidal breathing)
• Apneic oxygenation (high-flow nasal O₂ at 15 L/min) to extend safe apnea time
• Confirm ventilation/intubation/SGA placement with exhaled CO₂ at every step

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Emergency Department Context (Rosen's)

• Patient is rapidly deteriorating (anaphylaxis with angioedema, severe status asthmaticus, premature extubation)
• Impending arrest or complete obstruction within seconds to minutes
• No time for awake intubation preparation

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Other International Algorithms

• Do not repeat the same failed technique
• Awake intubation for the anticipated difficult airway
• SGA as rescue for difficult mask ventilation
• Emergency invasive access (FONA) for CICO
• Limit intubation attempts (typically ≤3 + 1 by a senior colleague)

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Post-incident Follow-up

• Document clearly in the medical record
• Complete an airway alert form
• Explain to the patient in person and in writing
• Send written report to the primary care provider and local database
• Urgent review of any cricothyrotomy site

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DAS 2025 Guidelines — Summary

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What's Retained from 2015

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Key Changes / New Emphases in 2025

1. Shift in Philosophy — "Maximise Success, Not Just Manage Failure"

2. Plan A — Videolaryngoscopy as the Default

• Videolaryngoscopy (VL) is now integrated early in Plan A, not just as an alternative — reflecting strong evidence that it improves glottic view and reduces failed intubation rates vs. direct laryngoscopy.
• Emphasis on: optimised patient positioning, adequate neuromuscular blockade, bougie use, and skilled VL technique.

3. Continuous Oxygenation / "Peroxygenation"

• High-flow nasal oxygen (HFNO) now explicitly recommended throughout airway management to extend safe apnoea time.
• Term "peroxygenation" used to describe oxygen delivery throughout the procedure (pre-, during, and post-attempt), not just pre-oxygenation.

4. The Physiologically Difficult Airway — New Dedicated Section

• Explicit recognition that physiological derangement (haemodynamic instability, severe hypoxaemia, metabolic acidosis, right heart failure) increases airway risk as much as anatomical difficulty.
• Specific guidance on how to optimise physiology before intubation in these patients.
• Awake tracheal intubation (ATI) is a priority in the physiologically compromised patient.

5. Obesity — Specific Recommendations

• Obesity elevated from a footnote to a distinct clinical phenotype with dedicated guidance.
• Early use of a second-generation SAD (better seal, intubation conduit option).
• ATI considered a physiological priority in complex obese patients.

6. Plan D — eFONA (Emergency Front-of-Neck Airway)

• Scalpel cricothyrotomy remains the preferred technique (over needle/cannula) for adults.
• Updated technical details: scalpel held in dominant hand, incisions made away from non-dominant hand.
• The vertical eFONA technique is largely unchanged from 2015; alternative scalpel–bougie–tube techniques also acceptable.
• Acknowledges ongoing debate around impalpable cricothyroid membrane management.

7. New Topic Areas (Not in 2015)

8. Waveform Capnography — Mandatory at Every Step

9. Team-Based Approach Formalised

• Pre-procedure team briefing mandatory.
• Airway strategy must be communicated with the anaesthetic assistant.
• History of previous difficulty must guide planning.

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Other Current DAS Guidelines (Full Suite)

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Extubation Criteria

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The Two Core Questions

1. Can the patient maintain a patent upper airway and protect it?
2. Can the patient sustain adequate oxygenation and ventilation independently?

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I. Criteria for Extubation — Post-operative / Routine Anesthesia

Neurological / Level of Consciousness

Respiratory

Haemodynamic / Systemic

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II. ICU Extubation — Weaning & Liberation Protocol

Step 1 — Daily Screening (Pass all of the following)

Step 2 — Spontaneous Breathing Trial (SBT)

• PSV 5–8 cmH₂O + PEEP 5 cmH₂O, or
• T-piece (CPAP 5 cmH₂O), or
• Pressure support 7 cmH₂O / PEEP 5 cmH₂O

Note: Any level of pressure support underestimates the resistance a patient will encounter after extubation, because post-extubation supraglottic work is approximately equal to endotracheal tube resistance. For borderline patients, a brief T-piece trial with zero support is more stringent. — Fishman's Pulmonary Diseases, p. 2617

Rapid Shallow Breathing Index (RSBI)

• RSBI = RR (breaths/min) ÷ Tidal Volume (litres)
• RSBI < 105 is classically used as a predictor of successful extubation
• Caution: recent meta-analyses show only moderate sensitivity and poor specificity — do not use in isolation — Sabiston Textbook of Surgery

Other Respiratory Mechanics (ancillary)

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III. Cuff Leak Test

• Deflate ETT cuff → measure volume/audible leak on ventilation
• Expected leak: 10–20% of ventilated tidal volume
• No cuff leak → suggests airway oedema → risk of post-extubation stridor/obstruction
• Management if no leak: IV dexamethasone (e.g. 0.1–0.2 mg/kg), reassess in 24 hours
• A persistent absent cuff leak over multiple days is not an absolute contraindication — extubation can proceed with preparations for reintubation in place

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IV. Awake vs Deep Extubation

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V. DAS Extubation Guidelines (2012, under revision)

1. Optimise the patient before extubation
2. Formulate a plan for failure (airway exchange catheter, senior backup present)
3. Perform extubation in a controlled, senior-supervised environment
4. Have a post-extubation management plan ready

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VI. Post-Extubation Management

10–20% of patients who pass an SBT fail extubation. Mortality among reintubated patients is >6 times higher than those who tolerate extubation — likely reflecting underlying severity of illness, not the reintubation itself. — Fishman's Pulmonary Diseases

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VII. Failure to Wean — Causes to Exclude

• Residual neuromuscular blockade
• Critical illness myopathy/polyneuropathy
• Acid-base disturbance (metabolic alkalosis → blunted drive; non-AG acidosis → compensatory tachypnoea)
• Delirium, anxiety, PTSD
• Unresolved sepsis or infection
• Nutritional depletion (diaphragm weakness)
• Small ETT (increased resistance)

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Extubation — Miller's Anesthesia, 10e

General Preparations for Extubation

• Adequate reversal or recovery from neuromuscular blockade
• Haemodynamic stability
• Normothermia
• Adequate analgesia
• Preoxygenate with 100% FiO₂
• Consider alveolar recruitment manoeuvres
• Suction the pharynx (and trachea if indicated)
• Remove throat packs
• Place a bite block (rolled gauze between molars — not an OPA)
• Inspect pilot balloon to confirm complete cuff deflation before removal (inflated cuff can cause vocal cord injury or arytenoid dislocation)
• If high-pressure mask ventilation was used → pass orogastric tube and suction to reduce aspiration risk

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Box 62.11 — Criteria for OR or PACU Extubation of the Trauma Patient

Mental Status

• Resolution of intoxication
• Able to follow commands
• Non-combative
• Pain adequately controlled

Airway Anatomy and Reflexes

• Appropriate cough and gag
• Ability to protect airway from aspiration
• No excessive airway oedema or instability

Respiratory Mechanics

• Adequate tidal volume and respiratory rate
• Normal motor strength
• Required FiO₂ < 0.50

Systemic Stability

• Adequately resuscitated
• Small likelihood of urgent return to OR
• Normothermic, without signs of sepsis

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Complications Associated with Extubation (Box 40.5)

• Laryngospasm and bronchospasm
• Upper airway obstruction
• Hypoventilation
• Respiratory drive failure (residual anaesthetic, decreased CO₂/O₂ response)
• Hypoxia (atelectasis)
• Vocal fold obstruction (laryngospasm, oedema, paralysis)
• Tracheal obstruction (subglottic oedema, tracheomalacia)
• Aspiration
• Hypertension, tachycardia
• Increased ICP / IOP / pulmonary artery pressure
• Increased bronchial stump pressure (post-pulmonary resection)

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Awake vs Deep Extubation

• Stage II anaesthesia (excitatory phase) must be avoided — highest risk of laryngospasm
• The Bailey manoeuvre (exchange ETT for SGA under deep anaesthesia) is an alternative

Position for extubation:

• Sniffing position — standard; optimal for airway rescue if needed
• Head-up — preferred in morbid obesity and high aspiration risk
• Lateral decubitus — when aspiration risk is high

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Extubation of the Difficult Airway (Box 40.6)

• Known difficult airway
• Airway deterioration (bleeding, oedema, trauma)
• Restricted airway access
• Obesity and obstructive sleep apnoea
• Aspiration risk

• Cardiovascular disease
• Respiratory disease

• Preferred technique: Airway Exchange Catheter (AEC)
  • Placed through ETT before extubation, kept in situ until reintubation risk has passed
  • Can connect to capnograph for respiratory monitoring
  • Oxygen insufflation is possible but carries significant barotrauma risk — if used in emergency, limit to 2 L/min as a temporising measure only
  • Smaller AECs (11 Fr) are well-tolerated by awake patients — secure with tape, label clearly
• Extubation plan must always include a reintubation strategy formulated in advance

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"Although considerable emphasis is placed on the problems that can arise during induction and intubation, the risk of complications can potentially be higher during extubation of the trachea." — Miller's Anesthesia, 10e, p. 5962

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Commands & Clinical Tests for Extubation Readiness — Miller's Anesthesia, 10e

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Commands / Clinical Tests (in an Awake Patient)

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Important Caveats from Miller's

• None of these tests alone are sufficient to confirm adequate NMB reversal. Objective quantitative TOF monitoring is required:
  • TOF ratio ≥ 0.9 (MMG/EMG) or ≥ 1.0 (AMG) to exclude residual block
• The 5-second head lift, despite being the "gold standard," is remarkably insensitive — patients can perform it at a TOF ratio as low as 0.60, at which point pharyngeal and upper oesophageal function remains impaired
• Opposing incisor teeth against a tongue depressor correlates with a TOF ~0.85 and is a more reliable indicator of airway-protective muscle tone than the head lift
• At TOF ≤ 0.4: patient is unable to lift the head or arm at all
• At TOF ~0.6: patient can open eyes, stick out tongue, and lift head for 3 seconds — but vital capacity and inspiratory force are still reduced
• At TOF 0.7–0.75: can cough and sustain head lift for 5 seconds, but grip strength still ~60% of normal
• At TOF ≥ 0.8: vital capacity and inspiratory force return to normal — but diplopia, blurred vision, and facial weakness may persist

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"The ability to strongly oppose the incisor teeth against a tongue depressor is a more reliable indicator of pharyngeal muscle tone... correlating with an average TOF ratio of 0.85 as opposed to 0.60 for the sustained head lift." — Miller's Anesthesia, 10e, p. 11569