What are the guidelines for choosing ventilator settings?

How to Choose Ventilator Settings

For all mechanically ventilated patients, start with lung-protective ventilation using tidal volumes of 4-8 ml/kg predicted body weight (never actual body weight), plateau pressure ≤30 cmH2O, PEEP ≥5 cmH2O, initial FiO2 of 40%, and respiratory rate 20-35 breaths/min. 1, 2, 3

Calculate Predicted Body Weight First

Before setting any ventilator parameters, calculate predicted body weight (PBW) using these formulas 2:

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

Initial Ventilator Settings Algorithm

Step 1: Set Tidal Volume

• Start with 6-8 ml/kg PBW for most patients 1, 2, 3
• Use 4-6 ml/kg PBW if ARDS is present or suspected 1, 2
• Never exceed 8 ml/kg PBW—this dramatically increases ventilator-induced lung injury risk 2, 3

Step 2: Set Plateau Pressure Limit

• Keep plateau pressure strictly <30 cmH2O for all patients 1, 2, 3
• Patients with increased chest wall elastance may tolerate up to 29-32 cmH2O 1
• Monitor plateau pressure continuously to ensure lung-protective ventilation 4

Step 3: Set PEEP

• Start with PEEP of 5 cmH2O minimum—never use zero PEEP 2, 3
• For moderate-to-severe ARDS (PaO2/FiO2 <200), use higher PEEP of 10-15 cmH2O 1, 5, 6
• In obstructive disease, add PEEP when air-trapping is present to facilitate triggering 1
• Titrate PEEP using recruitment maneuvers when atelectasis is evident 2, 5

Step 4: Set FiO2

• Start with FiO2 of 0.4 (40%) after intubation 2
• Titrate to achieve SpO2 88-95% (or 88-92% in most ICU patients) 2, 5, 3
• Never target SpO2 >95-97% to avoid oxygen toxicity 2, 5

Step 5: Set Respiratory Rate

• Set rate between 20-35 breaths/minute for most adults 2, 3
• For children: 20-30 breaths/min; for neonates: 30 breaths/min 1
• Adjust to maintain PaCO2 35-45 mmHg in patients without lung disease 1
• Accept higher PaCO2 (permissive hypercapnia) with target pH >7.20 in ARDS 1, 7

Step 6: Set Inspiratory:Expiratory Ratio

• Use standard I:E ratio of 1:2 for most patients 2
• For obstructive disease (COPD, asthma), use 1:2 to 1:4 to allow sufficient expiratory time and prevent auto-PEEP 1, 5

Ventilator Mode Selection

No specific mode is universally superior, but consider these options 2, 3:

• Pressure-controlled ventilation offers advantages including constant pressure delivery and compensation for air leaks 2
• Volume-controlled ventilation ensures consistent tidal volume delivery 2
• Either pressure or volume control is acceptable if tidal volume and plateau pressure targets are met 1

Disease-Specific Modifications

For ARDS (PaO2/FiO2 ≤300)

• Use tidal volume 4-8 ml/kg PBW (lower end preferred) 1, 2
• Maintain plateau pressure <30 cmH2O strictly 1, 2
• Apply higher PEEP (≥10 cmH2O) for moderate-severe ARDS 1, 5
• For severe ARDS (PaO2/FiO2 <150), implement prone positioning >12 hours/day (preferably 16 hours) 1, 2, 5, 6
• Consider recruitment maneuvers when atelectasis is present 1, 2
• Strongly avoid routine high-frequency oscillatory ventilation 1, 5

For Obstructive Disease (COPD, Asthma)

• Use tidal volume 6-8 ml/kg PBW 1, 5
• Set I:E ratio 1:2 to 1:4 to prevent air-trapping 1, 5
• Add PEEP (4-8 cmH2O) to offset intrinsic PEEP and improve triggering 1, 5
• Monitor for auto-PEEP development 5, 4
• Allow adequate expiratory time to prevent dynamic hyperinflation 5

For Cardiac Patients

• Apply the same principles as for non-cardiac patients 1
• Use sufficient PEEP to maintain end-expiratory lung volume 1
• PEEP ≤15 cmH2O does not impair venous return or cardiac output 1
• Titrate settings more carefully due to cardiopulmonary interactions 1

Critical Monitoring Parameters

Obtain arterial blood gas within 1-2 hours of initiating mechanical ventilation 2:

• Measure plateau pressure, peak inspiratory pressure, mean airway pressure, and PEEP near the Y-piece in children <10 kg 1, 4
• Monitor dynamic compliance and driving pressure (plateau pressure - PEEP) 2, 4
• Assess for auto-PEEP, especially in obstructive disease 1, 4
• Monitor pressure-time and flow-time scalars 1
• Check SpO2 continuously in all ventilated patients 1

Common Pitfalls to Avoid

• Never use tidal volumes >8 ml/kg PBW—this is the single most important error to avoid 2, 3
• Never calculate tidal volume based on actual body weight; always use predicted body weight 2, 3
• Avoid excessive FiO2 (hyperoxia) causing oxygen toxicity 2
• Do not set zero PEEP—minimum 5 cmH2O is required to prevent atelectasis 2, 3
• In obstructive disease, setting PEEP greater than intrinsic PEEP can worsen air-trapping 7
• Avoid inadequate expiratory time in obstructive diseases, which causes dynamic hyperinflation 5
• Do not delay intubation when non-invasive ventilation is failing 7

Special Considerations for Cardiac Arrest Patients

If the patient is already intubated before cardiac arrest 1:

• Increase FiO2 to 1.0 1
• Use tidal volume 4-6 ml/kg ideal body weight for adults and neonates, 5-8 ml/kg for children 1
• Set respiratory rate to 10 breaths/min for adults, 20-30 breaths/min for children, 30 breaths/min for neonates 1
• Adjust trigger settings to prevent auto-triggering with chest compressions 1
• Ensure circuit continuity to prevent disconnections 1