Introduction

The growing prevalence of class III obesity (BMI ≥ 40 kg/m²) is transforming perioperative care worldwide. Patients with obesity present unique respiratory and cardiovascular challenges, particularly during general anesthesia and mechanical ventilation. A 2026 narrative review by Boesing et al. (BJA) highlights the critical role of positive end-expiratory pressure (PEEP) in optimizing outcomes for this high-risk population.

Understanding obesity-related respiratory physiology

Key physiological changes

Obesity significantly alters pulmonary mechanics, increasing the risk of complications during surgery.

• reduced functional residual capacity (FRC)
• increased pleural pressure
• decreased lung compliance
• increased airway resistance
• ventilation–perfusion mismatch

According to the review by Boesing et al., FRC decreases by 5–15% for every 5 kg/m² increase in BMI, leading to early airway closure and alveolar collapse.

Why PEEP matters in obese surgical patients

Role of PEEP in lung protection

PEEP is a cornerstone of lung-protective ventilation. It works by:

• preventing alveolar collapse (atelectasis)
• increasing end-expiratory lung volume (EELV)
• improving oxygenation
• enhancing ventilation–perfusion matching

When applied correctly, PEEP counteracts elevated pleural pressures seen in obesity.

Risks of improper PEEP

However, inappropriate PEEP levels can lead to:

• alveolar overdistension
• increased lung stress and strain
• reduced venous return
• cardiovascular instability

Atelectasis: a major perioperative risk

Why obese patients are vulnerable

Up to 90% of patients under general anesthesia develop atelectasis, with higher rates in obesity.

Contributing factors include:

• increased abdominal pressure pushing the diaphragm upward
• reduced lung volumes
• impaired surfactant function
• high pleural pressures

Clinical consequences

• hypoxemia
• pneumonia
• respiratory failure
• prolonged hospital stay
• increased mortality (up to 5-fold)

Personalized PEEP: the emerging standard

Why fixed PEEP is insufficient

Traditional fixed PEEP strategies (e.g., 4–12 cm H₂O) often fail to address individual variability.

Studies show:

• many obese patients require PEEP > 15 cm H₂O
• some cases (BMI > 50) may require 20–25 cm H₂O

Benefits of personalized PEEP

• improved respiratory compliance
• reduced driving pressure
• better oxygenation
• decreased atelectasis

Step-by-step PEEP optimization strategy

Clinical indicators for PEEP adjustment

• driving pressure > 14 cm H₂O
• decreasing lung compliance
• worsening oxygenation
• increasing FiO₂ requirements

Cardiovascular effects of PEEP

Positive effects

• reduced left ventricular afterload
• improved oxygenation
• decreased pulmonary vascular resistance (with proper use)

Potential adverse effects

• reduced venous return
• hypotension
• bradycardia (especially during recruitment maneuvers)

Interestingly, in obese patients:

• elevated pleural pressures may protect against hemodynamic compromise
• cardiac output often remains stable even at higher PEEP levels

Interplay between lung and heart

PEEP influences:

• cardiac preload
• right ventricular afterload
• pulmonary circulation

Key takeaway:

• balance is essential. Optimize lung function without impairing circulation

Postoperative challenges

Even with optimal intraoperative PEEP:

• benefits may disappear within hours after extubation
• atelectasis can recur quickly

This highlights the need for:

• postoperative respiratory support
• continued lung recruitment strategies

Practical recommendations

Core clinical principles

• anticipate obesity-related physiology
• identify atelectasis risk early
• use recruitment maneuvers cautiously
• personalize PEEP settings
• monitor continuously for complications

Conclusion

PEEP optimization in obese patients undergoing general anesthesia is complex but essential. A personalized, physiology-driven approach offers the best balance between improving respiratory function and maintaining cardiovascular stability.

While current evidence supports individualized strategies, further large-scale studies are needed to confirm their impact on patient-centered outcomes.

Reference: Boesing C et al. Positive end-expiratory pressure optimisation during general anaesthesia in patients with obesity: a narrative review of respiratory and cardiovascular outcomes. Br J Anaesth. 2026;136:970-982.

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