Difficult Airway Assessment and Failed Airway Algorithm

Decide the plan before induction. Once oxygenation is falling, every extra attempt costs more than the one before.

A difficult airway is one where a trained clinician has trouble with face-mask ventilation, laryngoscopy or tracheal intubation, or expects to. Prediction never rules it out. The point is the plan. Set it before induction, so a failed attempt does not become a hypoxic arrest.

How It Works

• Anticipate: screen the anatomy, the mask seal and the physiology before any induction drug goes in.
• Plan in three tiers: Plan A is the primary technique. Plan B is a supraglottic airway or bag-mask rescue. Plan C is front-of-neck access. It is a simplified scheme. DAS 2015 names front-of-neck access Plan D. Its Plan C is face-mask ventilation. So use your local plan letters.
• Oxygenation sets the clock: the time to desaturation limits each attempt. The number of attempts does not.
• Declare failure early: say the failed step out loud, call for help at the first failed attempt, and move to the next plan.

Where It Fits

The failed-airway sequence follows the Difficult Airway Society (DAS) 2015 and American Society of Anesthesiologists (ASA) 2022 guidelines. It starts with a limited number of optimized laryngoscopy attempts. Then comes a supraglottic airway or face mask. Surgical airway comes last, once the patient cannot be oxygenated. Intubation, RSI and cricothyrotomy each have their own technique. This page covers the decisions that connect them.

Indications

• Any airway where the LEMON, MOANS or HEAVEN screen is positive, or where the team expects difficulty
• Failed bag-mask ventilation or failed supraglottic airway: the next plan applies now
• Unexpected failure after induction, including a fall in SpO₂ during an attempt

Absolute Contraindications

None. A predicted difficult airway is a reason to plan. It is never a reason to delay an airway the patient needs.

Relative Contraindications & Cautions

• Cooperative patient with a predicted difficult airway: topical anesthesia with sedation may be safer than induction. Spontaneous breathing is kept. Choose per protocol.
• Unstable cervical spine: maintain manual in-line stabilization throughout.
• Surgical airway in a young child: age limits apply (see Special Populations).

Consider an Alternative

Awake intubation is the usual first choice for a cooperative patient with a predicted difficult airway or physiologic risk. Topical anesthesia with sedation keeps spontaneous breathing. Use noninvasive ventilation to bridge oxygenation when the patient can tolerate it. Use a supraglottic airway when ventilation works but the tube does not. Both belong to Plan B.

Abort / Stop Criteria

• SpO₂ falls below 90% during an attempt
• An attempt exceeds 30 s or makes no progress
• Three attempts have failed in total
• Hemodynamic collapse develops during laryngoscopy

Team Roles During the Procedure

• Operator: owns the plan and announces each attempt and each change of plan.
• Airway and oxygen manager: keeps the mask seal, PEEP and oxygen flow, and reports SpO₂ trends.
• Medication clinician: prepares and reads back drugs and doses, with a vasopressor drawn up.
• Monitor and recorder: times each attempt and records the device, EtCO₂ and SpO₂ nadir.

Three screens work at the bedside in the emergency setting. Each one predicts a different step, so write down which one is positive. A negative screen is not a clear airway. None of them rules out difficulty, and you still need a Plan B and a Plan C.

One emergency department study tested a LEMON-based score in a resuscitation room. Large incisors, a reduced inter-incisor distance and a reduced thyroid-to-floor-of-mouth distance were linked to a poorer laryngoscopic view. A 2021 emergency department cohort in Thailand reported that patients with positive LEMON criteria were less likely to receive neuromuscular blocking agents. The predictors did not track with first-pass success. In another emergency department study, only the anatomic HEAVEN criterion was associated with first-pass success. These studies are single-centre. This page reports no sensitivity or specificity for any of the three tools.

Anatomic Difficulty

Physiologic Risk

The thresholds below are examples. Use protocol values.

• Hypotension: SBP < 90 mmHg or shock index > 0.9. Correct before induction.
• Hypoxemia: An SpO₂ < 93% before laryngoscopy cuts the safe apnea time short.
• Acidosis: pH < 7.20 leans on high minute ventilation, and apnea takes that away.
• Low reserve: pregnancy, obesity, sepsis, low hemoglobin or ongoing bleeding.

These markers describe the physiologically difficult airway (see References). Think of them as examples, not guideline cut-offs. Severe ARDS, right heart failure and profound shock tolerate induction poorly. So resuscitate first. Get a vasopressor running, consider a reduced-dose induction agent, and consider awake intubation. Delayed sequence intubation suits an agitated, uncooperative hypoxemic patient who cannot be preoxygenated. It does not reduce the hemodynamic risk of induction.

Site / Device Check

Monitors first: SpO₂, ECG, blood pressure and EtCO₂ should all be running. Know where the bag-mask with PEEP valve, the supraglottic airways and the surgical airway kit are. Then name who opens each one.

Cricothyroid Membrane (CICO Plan)

1. Find the laryngeal prominence: move your fingers down the midline to the cricoid ring.
2. Palpate the membrane: it sits between the thyroid and cricoid cartilages.
3. Mark the midline: if the membrane is not palpable, plan a vertical midline incision.
4. Protect the neck: after trauma, keep manual in-line stabilization while you access the membrane, and do not extend the neck.

Equipment

Patient Positioning & Preparation

Preoxygenate with a tight mask seal and high-flow nasal oxygen or noninvasive ventilation until the protocol target is reached. Ramp the patient so the ear is level with the sternal notch.

No drug doses live on this page. Dosing, weight basis and drug-specific cautions sit on the Rapid Sequence Intubation and Endotracheal Intubation pages. They also sit on the medication pages for rocuronium, succinylcholine, ketamine and etomidate. Induction and paralytic agents are high-alert drugs. Read back the weight, dose and units.

Phase 1: Prepare

1. Screen before induction: record each positive LEMON, MOANS and HEAVEN item and the physiologic triggers.
2. Brief the team: name Plan A, Plan B and Plan C, the operator for each, the attempt limit, the SpO₂ abort value, and that the team will call for help at the first failed attempt.
3. Correct physiology: treat hypotension and acidosis per protocol before the first drug; have a vasopressor ready.
4. Preoxygenate fully: tight mask seal, high-flow nasal oxygen or noninvasive ventilation until the protocol target is reached (commonly SpO₂ 95% or higher, or about 3 minutes or 8 vital-capacity breaths, head up). Leave a nasal cannula at 15 L/min under the mask for apneic oxygenation and keep it running through laryngoscopy.
5. Position and suction: ramp the patient, suction on and the video laryngoscope in hand.

Phase 2: Perform

6. Attempt Plan A: start the timer, call for help at the first failed attempt, and use the best view available, with a bougie when only part of the glottis shows.
7. Stop at the limit: at 30 s, at SpO₂ below 90%, or with no progress, withdraw and resume bag-mask ventilation with PEEP.
8. Re-oxygenate between attempts: return to the protocol SpO₂ target before any new attempt.
9. Move to Plan B: after the failed attempts, place a supraglottic airway and confirm EtCO₂ before anything else.
10. Declare CICO: if neither mask nor supraglottic airway oxygenates, make a last optimized bag-mask attempt and release any cricoid pressure. Say "cannot intubate, cannot oxygenate" aloud and go to Plan C. While the front-of-neck kit is prepared, confirm full paralysis (give a paralytic if not yet given, per protocol); do not delay the incision.

11. Perform front-of-neck access: use the scalpel-bougie-tube technique on the Cricothyrotomy page, or a needle technique where the team is trained and protocol allows it.

Phase 3: Confirm & Secure

12. Confirm the airway: waveform EtCO₂ over 5–6 breaths, with chest rise and bilateral breath sounds.
13. Secure and record: fix the depth at the teeth or the cricothyrotomy mark, and record the time, attempts, device and EtCO₂ value.

Primary Confirmation

Waveform EtCO₂ is the one objective test of tracheal placement in a perfusing patient. Look for a sustained square waveform over at least 5–6 breaths. A typical value is 35–45 mmHg in a perfusing patient. Write down the time, the value and the waveform for every tube or device.

Cardiac Arrest (Low Flow)

In cardiac arrest, a low or absent waveform may mean low pulmonary blood flow. It doesn't have to mean a misplaced tube. Confirm with direct or video visualization of the tube passing the cords. Re-check EtCO₂ as perfusion changes. Don't remove a visualized tube on EtCO₂ alone. Airway attempts must not interrupt compressions for long. AHA 2025 Part 9 (Wigginton et al.) puts CPR quality first. It accepts bag-mask and advanced airway ventilation. It recommends continuous waveform capnography whenever an advanced airway is in place.

Secondary Confirmation

• Bilateral chest rise with each ventilation
• Symmetric breath sounds in both axillae, with no epigastric sounds or gurgling
• Improving SpO₂ in a hypoxemic patient

Ongoing Monitoring

• Continuous: waveform EtCO₂, SpO₂ and ECG, with trend review
• Blood pressure: continuous or every 1–2 minutes for the first 10–15 minutes after induction
• Each move: repeat the waveform check, depth and breath sounds

Pediatrics

Children desaturate faster. Vagal bradycardia can follow laryngoscopy. For tube size and depth, length-based tape or the pediatric protocol gives you the number. Confirm placement with waveform EtCO₂, exactly as in adults. Surgical cricothyrotomy generally stays off the table below about 8 years. The cut-off is contested, so go by local protocol. Under that age, the protocol names the needle or tracheotomy technique to use.

• Pediatric sizing: equipment sizing and Broselow
• Pediatric dosing: weight-based dosing
• Pediatric airway: pediatric airway
• Many pediatric protocols use cuffed tubes. Follow the protocol for cuff use and size.
• LEMON is less validated in children. Apply it with pediatric judgment.
• In children, a supraglottic airway is often the first rescue device.
• Infants and young children can develop bradycardia during laryngoscopy. Atropine or another response is per protocol.

Older Adults

• Reduced oxygen reserve: preoxygenate fully and expect fast desaturation
• Fragile dentition and mucosa: insert and laryngoscope gently

Obesity

• Ramp and use high-flow oxygen; the safe apnea time is shorter
• Video laryngoscopy is often the first device

Pregnancy

• Oxygen reserve is lower; preoxygenate thoroughly and expect rapid desaturation
• Left uterine displacement after about 20 weeks of gestation, to relieve aortocaval compression
• Aspiration risk is high: use a rapid-sequence approach with full preoxygenation
• Expect a smaller tube than for a nonpregnant adult of the same size
• Airway edema and aspiration risk both favor early video laryngoscopy. They also favor a smaller tube, per the obstetric airway protocol

Physiologically Difficult Patients

• Severe ARDS, right heart failure and profound shock tolerate induction poorly
• Resuscitate first: vasopressor running and a reduced-dose induction agent; consider awake intubation
• Use delayed sequence intubation only for an agitated hypoxemic patient who cannot be preoxygenated

Trauma and Cervical Spine

• Maintain manual in-line stabilization; remove an anterior collar only when the view requires it
• Expect blood and vomit; suction early and keep the bag-mask ready

Immediate Aftercare

• Recheck waveform EtCO₂, depth at the teeth or cricothyrotomy mark, and bilateral breath sounds
• Sedation and analgesia: paralytics stop breathing, not awareness. Start both once the tube is confirmed.

Ongoing Maintenance

• Cuff pressure 20–30 cm H₂O, checked after each move
• Recheck depth after every move and after any change in neck position

Transport Considerations

• Secure the tube and reassess after every move, including the stretcher and loading
• Altitude changes cuff pressure; check it during flights
• Rely on EtCO₂ and monitors in noise and vibration; a dislodged tube is a silent emergency

Pearls

• Plan before the first attempt: Once SpO₂ is falling, it is too late to make the plan.
• Oxygen is the timer: Desaturation sets the limit. The attempt count does not.
• A negative screen is not a clear airway: keep Plan B and Plan C ready.
• Chest rise is not placement: Confirm with waveform EtCO₂, or with direct visualization in arrest.

Common Pitfalls

• Repeating the same attempt → change the device or technique.
• Waiting for lower SpO₂ before declaring failure → declare at the limit.
• Trusting breath sounds or fogging → confirm with EtCO₂.
• Planning the surgical airway only after the SGA fails → name Plan C in the brief.

Skill Maintenance

• Rehearse the failed-airway sequence in simulation with a timer and a called plan change
• Practice the CICO declaration and the front-of-neck access steps on a task trainer
• Run the pre-procedure checklist before every simulated and real airway
• Debrief every attempt: time, SpO₂ nadir, device and the reason for each plan change