What are the lung‑protective mechanical ventilation settings for adult patients undergoing general anesthesia, including tidal volume, respiratory rate, FiO₂, PEEP, plateau pressure limits, monitoring, and adjustments for obesity, COPD, asthma, and emergence?

Lung-Protective Mechanical Ventilation Settings for General Anesthesia

Use low tidal volume ventilation (6-8 mL/kg predicted body weight), PEEP of 5 cmH₂O minimum, FiO₂ 0.4 targeting SpO₂ ≥94%, and maintain plateau pressure <30 cmH₂O with driving pressure <15 cmH₂O for all patients undergoing general anesthesia. 1

Core Ventilator Settings

Tidal Volume

• Set tidal volume at 6-8 mL/kg predicted body weight (PBW), not actual body weight. 1, 2
• Calculate PBW using: Males = 50 + 0.91[height (cm) - 152.4] kg; Females = 45.5 + 0.91[height (cm) - 152.4] kg 3
• Target the lower end (6 mL/kg PBW) for high-risk patients or those with established lung disease 2
• Never use high tidal volumes (>8 mL/kg) as they significantly increase postoperative pulmonary complications 1, 4

PEEP (Positive End-Expiratory Pressure)

• Start with PEEP of 5 cmH₂O immediately after intubation—zero PEEP (ZEEP) is explicitly contraindicated. 1, 2
• ZEEP causes reduction in end-expiratory lung volume and promotes atelectasis formation in approximately 90% of patients 1, 5
• Individualize PEEP upward (6-10 cmH₂O) to prevent increases in driving pressure while maintaining low tidal volume 1
• PEEP maintains functional residual capacity but does not restore it—recruitment maneuvers must precede PEEP increases 5

FiO₂ (Fraction of Inspired Oxygen)

• Set FiO₂ to 0.4 (40%) after intubation, then titrate to the lowest level achieving SpO₂ ≥94%. 1
• Avoid high FiO₂ (>0.8) during emergence as it significantly increases atelectasis formation due to rapid oxygen absorption 5
• Use FiO₂ <0.4 during emergence when clinically appropriate to reduce atelectasis 5

Plateau Pressure and Driving Pressure

• Monitor plateau pressure (Pplat) continuously and maintain <30 cmH₂O in non-obese patients. 1, 2, 3
• In obese patients, accept Pplat up to 40-50 cmH₂O if necessary 1
• Monitor driving pressure (Pplat - PEEP) and keep <15 cmH₂O—this is strongly associated with mortality reduction. 1, 2
• Driving pressure may be a better predictor of outcomes than tidal volume or plateau pressure alone 3

Respiratory Rate

• Adjust respiratory rate to maintain normocapnia (PaCO₂ 35-45 mmHg) 2
• Accept permissive hypercapnia if necessary to maintain plateau pressure <30 cmH₂O 3

Ventilation Mode

• No specific mode (volume-controlled vs pressure-controlled) is recommended over another 1, 6
• Volume-controlled ventilation may provide more predictable tidal volumes and lower plateau pressures 1

Monitoring Requirements

Monitor dynamic compliance, driving pressure, and plateau pressure in all mechanically ventilated patients in addition to standard ASA/ESA monitoring. 1

• Assess respiratory system compliance continuously under constant tidal volume 1
• Decreasing compliance from surgical factors (pneumoperitoneum, positioning, circuit disconnect) requires immediate intervention 1
• Increasing FiO₂ improves oxygenation but does not improve compliance—address mechanical problems directly 1

Induction and Positioning

Pre-Induction

• Position patient with head of bed elevated 30 degrees ("beach chair" position)—avoid flat supine. 1, 2
• Apply NIPPV or CPAP during induction if not contraindicated (avoid in altered mental status, facial/nasal/esophageal surgery, emergencies) 1
• Head-up positioning combined with NIPPV/CPAP increases PaO₂ and duration of non-hypoxic apnea, particularly in obese patients 1

During Induction

• Monitor for obstructive breathing patterns 1
• Use positioning, NIPPV/CPAP, or nasopharyngeal airway to prevent upper airway obstruction 1

Recruitment Maneuvers

Routine recruitment maneuvers after intubation lack high-quality evidence, but consider them based on individual risk-benefit assessment. 1

When to Perform

• Consider recruitment when compliance decreases from surgical factors, positioning changes, or circuit disconnection 1, 5
• Particularly beneficial in hypoxic patients following intubation 5
• Recruitment maneuvers reverse alveolar collapse but have limited benefit without sufficient PEEP 1, 5

Technique

• Use ventilator-driven recruitment maneuvers—avoid bag-squeezing techniques. 1
• Apply lowest effective Pplat (30-40 cmH₂O in non-obese; 40-50 cmH₂O in obese) for shortest effective time 1
• Ensure hemodynamic stability with continuous blood pressure and oxygen saturation monitoring before and during recruitment 1, 5
• Avoid recruitment maneuvers in hemodynamically unstable patients or with pneumothorax 1, 5
• Always increase PEEP after recruitment to maintain alveolar patency—PEEP maintains but does not restore functional residual capacity. 5, 3

Special Population Adjustments

Obesity (BMI >40 kg/m²)

• Require higher PEEP levels (8-12 cmH₂O) to counteract increased chest wall weight and reduced functional residual capacity. 1
• Use predicted body weight (not actual weight) for tidal volume calculation 2, 3
• Head-up positioning and NIPPV/CPAP during induction are particularly beneficial 1
• Consider CPAP immediately post-extubation as obese patients develop larger atelectatic areas 5
• Accept higher plateau pressures (40-50 cmH₂O) during recruitment maneuvers 1

COPD

• Use standard lung-protective settings (6-8 mL/kg PBW, PEEP 5 cmH₂O minimum) 1
• Monitor for auto-PEEP and adjust respiratory rate to allow adequate expiratory time 7
• Avoid excessive PEEP that may worsen hyperinflation, but never use zero PEEP 1, 2

Asthma

• Apply standard lung-protective ventilation with careful attention to expiratory time 7
• Use PEEP 5 cmH₂O minimum despite concerns about air trapping—zero PEEP worsens atelectasis 1, 2
• Monitor plateau pressure closely and accept permissive hypercapnia if needed 3

Pneumoperitoneum, Prone, or Trendelenburg Positioning

• Increase PEEP (typically to 8-12 cmH₂O) to counteract increased intra-abdominal pressure and gravitational effects. 1
• Individualize PEEP to avoid increases in driving pressure 1
• Monitor compliance continuously as positioning changes can dramatically affect respiratory mechanics 1

Emergence and Extubation

Pre-Extubation

• Maintain positive pressure until extubation—never turn off ventilator to allow CO₂ accumulation as this causes alveolar collapse. 5
• Avoid routine suctioning of tracheal tube just before extubation as it reduces lung volume 5
• Use FiO₂ <0.4 during emergence when clinically appropriate to reduce atelectasis formation 5

Post-Extubation

• Consider CPAP (7.5-10 cmH₂O) immediately post-extubation, especially in obese patients 5
• Maintain head-of-bed elevation at 30 degrees 5, 2
• Apply CPAP/NIPPV liberally for patients with postoperative hypoxemia (SpO₂ <90%) despite supplemental oxygen 5

Critical Pitfalls to Avoid

• Never calculate tidal volumes based on actual body weight—always use predicted body weight to prevent volutrauma. 2, 3
• Never use zero PEEP (ZEEP)—minimum PEEP of 5 cmH₂O prevents atelectasis and maintains functional residual capacity. 1, 5, 2
• Never accept driving pressure >15 cmH₂O—reduce tidal volume further if necessary. 2, 3
• Do not increase FiO₂ as the primary intervention for hypoxemia from atelectasis—address mechanical problems with PEEP and recruitment. 1, 3
• Do not apply PEEP without first performing recruitment maneuvers when atelectasis is present—PEEP maintains but does not restore functional residual capacity. 5, 3
• Avoid high FiO₂ (>0.8) during emergence—this significantly increases atelectasis formation. 5
• Do not turn off the ventilator before extubation to allow CO₂ accumulation—this causes alveolar collapse. 5