What are the indications for intubation in critically ill patients, including those with severe respiratory distress, cardiac arrest, or inability to protect their airway, such as acute respiratory distress syndrome (ARDS), severe pneumonia, or chronic obstructive pulmonary disease (COPD) exacerbation?

Indications for Intubation in Critically Ill Patients

Endotracheal intubation is indicated when respiratory failure leads to hypoxemia, hypercapnia, and acidosis, or when patients cannot maintain or protect their airway due to diminished consciousness, physical exhaustion, or airway obstruction. 1

Primary Indications

Respiratory Failure

• Hypoxemia, hypercapnia, and acidosis are the primary respiratory indications for intubation 1
• Refractory hypoxemia (PaO₂/FiO₂ <150 mmHg) despite supplemental oxygen warrants intubation 2
• Progressive hypercapnia with acidosis (pH <7.25, especially <7.15) after initial resuscitation is an indication for intubation 2
• Respiratory rate >30 breaths/min with acute respiratory distress that does not improve with high-flow oxygen therapy indicates need for intubation 2
• Severe tachypnea (respiratory rate >40 breaths/min), use of accessory muscles, or muscular respiratory failure are indications for mechanical ventilation 1

Airway Protection

• Inability to maintain or protect the airway is a fundamental indication for intubation 1
• Glasgow Coma Score <8 indicates inability to protect the airway 2
• Diminished consciousness with inability to maintain airway patency requires intubation 1, 2
• Unconscious patients unable to protect their airway require immediate intubation regardless of other vital parameters 2, 3

Airway Obstruction

• Upper airway obstruction with stridor, dyspnea, or desaturation from facial burns, anaphylaxis, or angioedema requires intubation 2
• Inability to manage secretions with oropharyngeal accumulation and aspiration risk is an indication 2

Cardiac Arrest

• Cardiac arrest during cardiopulmonary resuscitation is an indication for intubation, though interruptions should be limited to <10 seconds 1, 3
• During CPR, intubation should only interrupt compressions for the time needed to visualize vocal cords and insert the tube, ideally <10 seconds 1

Specific Clinical Scenarios

Acute Pulmonary Edema

• Cardiac-related pulmonary edema that deteriorates despite optimal pharmacological treatment and non-invasive ventilation requires intubation 1, 2
• Non-invasive ventilation (CPAP/NIPPV) may be used first to relieve dyspnea, but intubation is indicated if patients fail to improve with pharmacological therapy 1

COPD Exacerbation

• Non-invasive positive-pressure ventilation (NPPV) should be the initial approach in acute COPD exacerbations unless specific exclusion criteria exist 4
• Exclusion criteria for NPPV include cardiovascular instability, severely impaired mental status, or failure after 2 hours of optimal CPAP/BiPAP treatment 2, 4
• Patients with severe COPD requiring intubation have better outcomes when admitted for COPD exacerbation (9% ICU mortality) versus other causes of respiratory failure (27% ICU mortality) 5

ARDS and Severe Pneumonia

• ARDS and acute lung injury generally require intubation, as NPPV has not been shown to be beneficial in these settings 1, 4
• Severe pneumonia with progressive respiratory failure requires intubation 2

Decision Algorithm

Step 1: Assess Airway Protection

• Can the patient protect their airway? (GCS <8 = cannot) 2
• Is there airway obstruction? 2
• If YES to either → Intubate immediately 2

Step 2: Assess Respiratory Failure

• Is there apnea or respiratory arrest? → Intubate immediately 2, 3
• Respiratory rate >40 breaths/min with accessory muscle use? 1
• PaO₂/FiO₂ <150 mmHg despite oxygen? 2
• pH <7.25 with progressive hypercapnia? 2
• If YES to any → Consider immediate intubation or trial of NPPV if COPD 2, 4

Step 3: Trial of Non-Invasive Support (Selected Patients)

• COPD exacerbation: Trial NPPV unless contraindicated 4
• Cardiogenic pulmonary edema: Trial CPAP/NIPPV with pharmacotherapy 1
• Early hypoxemic respiratory failure in immunocompromised: May trial NPPV 4
• Monitor for failure indicators:
  • Under standard oxygen: RR ≥30 breaths/min predicts intubation need 6
  • Under NPPV: PaO₂/FiO₂ ≤200 mmHg or tidal volume >9 mL/kg after 1 hour predicts intubation need 6
  • Failure after 2 hours of optimal NPPV → Intubate 2

Critical Pitfalls to Avoid

Do Not Delay

• Do not delay intubation waiting for arterial blood gas or radiography if there are clear clinical signs of respiratory failure 2
• Do not delay intubation in COPD patients if indicated, despite concerns about hypercapnia 2
• In unconscious non-trauma patients, many regain consciousness quickly; however, those remaining unconscious during transport have a 19% intubation rate in the emergency department, suggesting selective rather than universal intubation is appropriate 7

Technical Considerations

• Waveform capnography is mandatory to confirm tube placement, with 100% sensitivity and specificity in cardiac arrest 1, 3
• Limit laryngoscopy attempts to three maximum; after one failed attempt, ensure front-of-neck access equipment is immediately available 1
• Avoid hyperventilation post-intubation (maintain 10 breaths/min) as it compromises venous return and cerebral blood flow 2, 3

High-Risk Populations

• Obesity (BMI >30 kg/m²) doubles complication risk; BMI >40 kg/m² quadruples it, with 22-fold increased life-threatening complications versus non-obese 1
• In obese patients, use head-up positioning, thorough preoxygenation with CPAP/NIV/HFNO, and have low threshold for front-of-neck access 1
• Cervical spine injury: Use manual in-line stabilization with rapid sequence intubation; videolaryngoscopy increases success with minimal cervical movement 1

When NPPV is Contraindicated

• Contraindications to non-invasive ventilation include hypotension, vomiting, possible pneumothorax, and depressed consciousness 1
• NPPV should be avoided in sepsis-related ALI/ARDS as patients are more likely to fail this therapy 1