What are the basics for initiating mechanical ventilation in patients with respiratory failure?

Initiating Mechanical Ventilation in Respiratory Failure

Indications for Intubation and Mechanical Ventilation

Intubate immediately when patients cannot protect their airway, have refractory hypoxemia (PaO2 < 60 mmHg despite high-flow oxygen), respiratory rate exceeding 35 breaths/min, or vital capacity below 15 ml/kg. 1

• Orotracheal intubation is the preferred route due to lower rates of nosocomial sinusitis and ventilator-associated pneumonia 1
• Use the largest endotracheal tube available (8-9 mm in adults) to minimize airway resistance 2
• Consider non-invasive ventilation first in patients with dyspnea and persistent hypoxemia if staff is adequately trained and the patient has no contraindications 1

Contraindications to Non-Invasive Ventilation

• Impaired consciousness or inability to protect airway 1
• Severe respiratory or cardiovascular failure 1
• Hemodynamic instability 1

Initial Ventilator Settings: The Core Protocol

Start with volume-cycled assist-control mode using tidal volumes of 4-8 ml/kg predicted body weight (PBW) and maintain plateau pressure ≤ 30 cmH2O. 1, 3, 4

Calculate Predicted Body Weight First

• Males: 50 + 0.91 × [height (cm) - 152.4] kg 3
• Females: 45.5 + 0.91 × [height (cm) - 152.4] kg 3

Tidal Volume Strategy

• Use 6 ml/kg PBW as the standard starting point for most patients 1, 3, 4
• This lung-protective approach is now recommended for ALL mechanically ventilated patients, not just ARDS 4, 5, 6
• Never exceed 8 ml/kg PBW 1, 3
• The strong recommendation for lower tidal volumes (4-8 ml/kg PBW) is based on moderate confidence evidence showing reduced mortality 1

Pressure Targets

• Plateau pressure must stay ≤ 30 cmH2O 1, 3, 4
• Monitor driving pressure (plateau pressure minus PEEP) as it may predict outcomes better than tidal volume alone 3
• Patients with stiff chest walls may tolerate plateau pressures up to 35 cmH2O 4

PEEP Settings

• Start with PEEP of 5 cmH2O minimum—zero PEEP is never recommended 3, 4
• For moderate to severe ARDS (PaO2/FiO2 < 200), use higher PEEP strategy (>12 cmH2O) 1, 3
• The conditional recommendation for higher PEEP in moderate/severe ARDS is based on individual patient data meta-analysis showing 10% mortality reduction 1

Respiratory Rate and Timing

• Set respiratory rate at 20-35 breaths/min for most patients 4
• Use standard inspiratory-to-expiratory (I:E) ratio of 1:2 3
• Inspiratory time should be 30-40% of the total respiratory cycle 3

Oxygenation Management

• Start with FiO2 of 0.4 after intubation 3
• Titrate to maintain SpO2 88-95%—avoid hyperoxia 3, 4
• Target arterial oxygen saturation of approximately 90% (PaO2 ~60 mmHg) 1

Ventilation Targets

• Maintain PaCO2 35-45 mmHg or PETCO2 35-40 mmHg 3
• Accept permissive hypercapnia when necessary to maintain lung-protective settings 1
• Hyperventilation with hypocapnia must be avoided as it causes cerebral vasoconstriction 3

Disease-Specific Modifications

For ARDS Patients

• Use tidal volumes at the lower end (4-6 ml/kg PBW) 1, 3
• Apply higher PEEP (>12 cmH2O) for moderate/severe ARDS 1, 3
• Consider recruitment maneuvers—conditional recommendation based on low-moderate confidence evidence showing mortality benefit 1
• Prone positioning for >12 hours/day is strongly recommended for severe ARDS based on moderate confidence evidence 1
• Never use high-frequency oscillatory ventilation routinely—strong recommendation against based on high confidence evidence 1

For Obstructive Disease (Asthma/COPD)

• Use tidal volumes of 6-8 ml/kg PBW 2, 3
• Reduce respiratory rate to 10-15 breaths/min to allow adequate expiratory time 2, 3
• Prolong expiratory time with I:E ratio of 1:4 or 1:5 to prevent auto-PEEP 2
• Set inspiratory flow rate at 80-100 L/min to minimize inspiratory time 2
• Accept permissive hypercapnia—do not attempt to normalize blood gases at the expense of lung protection 2

For Liver Disease/Cirrhosis

• Use lung-protective ventilation with 6 ml/kg PBW 3
• Consider low PEEP strategy (<10 cmH2O) for mild ARDS 3
• Monitor hemodynamics closely as high PEEP impedes venous return in vasodilated states 3

Critical Monitoring Parameters

Monitor plateau pressure, peak pressure, driving pressure, and auto-PEEP continuously. 3

• Assess patient-ventilator synchrony and adjust sedation as needed 3, 4
• Monitor for barotrauma, especially in obstructive disease 2, 3
• Check arterial blood gases to guide ventilation and oxygenation adjustments 1, 3
• Evaluate dynamic compliance as a marker of lung mechanics 3

Common Pitfalls and How to Avoid Them

Never Use High Tidal Volumes

• Historical practice of 10-12 ml/kg is harmful and increases mortality 1, 4, 5
• Even patients without ARDS benefit from lung-protective ventilation 4, 5, 6

Avoid Excessive Oxygen

• Hyperoxia provides no benefit and may cause harm 4
• Target SpO2 88-95%, not 100% 3, 4

Recognize Auto-PEEP Early

• In obstructive disease, delayed recognition of auto-PEEP causes hemodynamic collapse 2, 3
• If severe hypotension develops, immediately disconnect from ventilator and allow passive exhalation 2
• Press on chest wall to actively expel trapped air 2

Don't Delay Intubation

• Non-invasive ventilation should show improvement within 1-2 hours or proceed to intubation 7
• Clinical deterioration in severe respiratory failure can be rapid 2

Prioritize Ventilation Over Oxygenation

• Inadequate ventilation leads to rapid respiratory acidosis and cardiovascular collapse 7
• The body tolerates hypoxemia better than hypercapnia 7
• Always assess both parameters, but address ventilatory failure first 7

Adjunctive Measures

Fluid Management

• Use judicious fluid resuscitation in ARDS 1
• Consider albumin plus furosemide in hypo-oncotic patients to reduce duration of mechanical ventilation 1

Positioning

• Place patients in semi-recumbent position (head of bed 30-45°) unless hemodynamically unstable 1
• Unconscious patients should be in lateral position with airway maintained 1

Sedation Strategy

• Most patients tolerate lung-protective ventilation without excessive sedation 4
• Severe ARDS with ventilator asynchrony may require short-term neuromuscular blockade 4