Physiological Difficult Airway and Awake Intubation

1. Introduction

A physiological difficult airway (PDA) refers to airway management in a critically ill patient where physiological derangements increase the risk of hypoxia, hypotension, and cardiac arrest during intubation. Unlike an anatomically difficult airway, where structural abnormalities make intubation challenging, a physiological difficult airway involves underlying medical conditions that complicate airway management.

Key Challenges:

  • Severe hypoxia
  • Hemodynamic instability (hypotension, shock)
  • Metabolic or respiratory acidosis
  • Right heart strain or failure
  • Raised intracranial pressure (ICP)


2. Causes of Physiological Difficult Airway

Physiological Factor

Impact on Airway Management

Hypoxia (e.g., ARDS, pneumonia, pulmonary edema)

Increased risk of oxygen desaturation, rapid progression to hypoxemia.

Hypotension/Shock (e.g., septic shock, hemorrhage, cardiogenic shock)

Prone to peri-intubation cardiac arrest due to loss of sympathetic tone.

Acidosis (e.g., DKA, lactic acidosis, renal failure)

Hypoventilation post-intubation worsens respiratory acidosis.

Right Heart Failure (e.g., PE, severe COPD, pulmonary hypertension)

Positive pressure ventilation increases RV afterload, leading to hemodynamic collapse.

Raised ICP (e.g., trauma, stroke, TBI)

Intubation-induced hypertension or hypotension worsens secondary brain injury.


3. Preoxygenation Strategies for Physiological Difficult Airway

To prevent rapid desaturation, preoxygenation is critical. The goal is to achieve Denitrogenation and Maximal Oxygenation.

✅ Best Preoxygenation Methods:

  • Non-rebreather mask (NRM) at 15 L/min for 3 minutes
  • Bag-mask ventilation with PEEP (5-10 cm Hâ‚‚O) if needed
  • High-flow nasal cannula (HFNC) for ongoing oxygenation
  • Noninvasive ventilation (NIV, CPAP/BiPAP) for patients with shunt physiology (e.g., pulmonary edema, ARDS)


4. Approaches to Avoid Physiological Collapse

  1. Resuscitate Before Intubation (“Resuscitation Sequence Intubation”)
    • Fluid bolus for hypovolemia/hypotension
    • Vasopressors (noradrenaline, phenylephrine) before induction if shock present
    • Oxygenation with apneic oxygenation (nasal cannula at 15 L/min during apnea phase)
    • Gentle ventilation to avoid acidosis worsening
  1. Use of Ketamine for Induction in Hypotensive Patients
    • Ketamine (1–2 mg/kg IV) preserves airway reflexes and supports blood pressure
    • Avoid propofol in unstable patients due to risk of severe hypotension
  1. Titrated Paralysis with Rocuronium
    • Rocuronium (1.2 mg/kg IV) preferred over succinylcholine in shock/ICU patients



Awake Intubation: Indications, Techniques, and Considerations

1. Indications for Awake Intubation

Awake intubation is preferred when there is a high risk of airway obstruction or decompensation under anesthesia.

✅ When to Choose Awake Intubation:

  • Anticipated difficult airway (anatomical abnormalities, tumors, airway edema, Ludwig’s angina, severe RA)
  • Patients with severe hypoxia (who may not tolerate apnea)
  • Severe hemodynamic instability (shock, cardiac failure)
  • Raised ICP where RSI may worsen brain perfusion


2. Preparation for Awake Intubation

✅ Key Steps:

  • Topical Anesthesia:
    • Nebulized 4% lidocaine or atomized lidocaine to airway
    • Spray-as-you-go (SAYGO) lidocaine via bronchoscope
    • Superior laryngeal nerve and transtracheal block if needed
  • Sedation Protocol (“Dissociated Awake Intubation”)
    • Dexmedetomidine (1 mcg/kg bolus over 10 min, then 0.2–0.7 mcg/kg/hr) – maintains respiratory drive
    • Ketamine (0.5–1 mg/kg IV push, then infusion if needed) – dissociative analgesia
    • Avoid benzodiazepines (risk of hypoventilation)
  • Patient Positioning:
    • Head-elevated (ramp position)
    • Oxygen via nasal cannula (for apneic oxygenation if needed)


3. Techniques for Awake Intubation

✅ Best Methods:

  1. Flexible Fiberoptic Intubation (Gold Standard)
    • Visualizes vocal cords and trachea directly
    • Allows precise tube placement
    • Ideal for airway tumors, obesity, and cervical spine issues
  1. Video Laryngoscopy (VL) with Nasal or Oral Approach
    • Useful if fiberoptic scope is unavailable
    • Provides good glottic visualization
  1. Cricothyrotomy as Last Resort
    • If all methods fail, surgical airway should be ready


Delayed Sequence Intubation (DSI)

1. Introduction

Delayed Sequence Intubation (DSI) is a technique used for critically ill patients who cannot tolerate preoxygenation or preparation for intubation due to agitation, respiratory distress, or altered mental status. It involves administering a sedative first to facilitate preoxygenation and resuscitation before paralysis, improving safety during intubation.

🔹 Key Difference from RSI (Rapid Sequence Intubation)

  • RSI: Induction agent + paralytic given together → Immediate intubation
  • DSI: Sedation first → Preoxygenation & Resuscitation → Paralytic given → Intubation

2. Indications for Delayed Sequence Intubation

DSI is useful in patients who cannot tolerate preoxygenation due to agitation but are at high risk for desaturation during intubation.

✅ Ideal Candidates for DSI:

  • Hypoxic patients requiring preoxygenation but unable to cooperate (e.g., severe ARDS, pneumonia, COVID-19, CHF)
  • Combative or altered mental status patients with inadequate oxygenation
  • Critically ill trauma patients where optimizing oxygenation and hemodynamics is essential
  • Severe metabolic acidosis (e.g., DKA, sepsis, renal failure) where ventilatory drive must be maintained

🚫 Avoid DSI if:

  • Patient already apneic or near apnea (needs immediate intubation)
  • Anatomically difficult airway requiring immediate intervention
  • Hemodynamically unstable patients requiring immediate RSI


3. Steps of Delayed Sequence Intubation (DSI)

Step 1: Preoxygenation Preparation

  • Goal: Maximize oxygen reserves (Denitrogenation)
  • Use: High-flow nasal cannula (HFNC), non-rebreather mask (NRM) at 15 L/min, or noninvasive ventilation (NIV)
  • Ensure proper positioning: Head-elevated position (ramping)

Step 2: Sedation with Ketamine (“Facilitated Preoxygenation”)

  • Ketamine 1 mg/kg IV push → Provides dissociative sedation while maintaining spontaneous breathing
  • Alternative: Dexmedetomidine infusion (if longer-term control needed)

✅ Why Ketamine?

  • Preserves respiratory drive (Unlike propofol or fentanyl)
  • Increases catecholamines, maintaining BP
  • Provides analgesia and amnesia

🚫 Avoid benzodiazepines (risk of respiratory depression)

Step 3: Preoxygenation & Resuscitation (2–3 minutes minimum)

  • Apply HFNC or NIV (BiPAP/CPAP)
  • Titrate PEEP if needed (5-10 cm Hâ‚‚O)
  • Fluid resuscitation or vasopressors if hypotensive

Step 4: Administration of Paralytic Agent

  • Once optimal oxygenation is achieved:
    • Rocuronium (1.2 mg/kg IV) or Succinylcholine (1.5 mg/kg IV)


4. Advantages of Delayed Sequence Intubation

✅ Improves oxygenation & reduces desaturation risk
✅ Prevents peri-intubation hypotension & cardiac arrest
✅ Maintains airway reflexes while optimizing preoxygenation
✅ Avoids unnecessary physical restraint or excessive sedation

🔹 Evidence: Studies have shown that DSI reduces desaturation rates in hypoxic patients and improves peri-intubation outcomes in ICU settings.


5. Summary Table: RSI vs. DSI

Feature

RSI (Rapid Sequence Intubation)

DSI (Delayed Sequence Intubation)

Induction & Paralysis

Given together

Sedation first → Preoxygenation → Paralysis

Indications

Immediate airway compromise

Hypoxia, agitation, metabolic acidosis

Preoxygenation

Brief (if tolerated)

Prolonged (using HFNC/NIV)

Ideal Patient

Apneic, GCS < 8, or severe distress

Agitated, hypoxic, or with high-risk physiology

Medications

Propofol, Etomidate + Paralytic

Ketamine, Dexmedetomidine → Paralytic

Ventilatory Drive

Lost immediately

Maintained during preoxygenation