What is the evidence and rationale for providing only oxygen therapy in patients undergoing general anesthesia with a laryngeal mask airway (LMA), allowing spontaneous breathing without positive end-expiratory pressure (PEEP) or inspiratory pressure, and its effect on emergence and atelectasis?

Spontaneous Ventilation with LMA and Zero PEEP: Evidence Against This Practice

Allowing spontaneous breathing with only oxygen therapy through an LMA without PEEP or inspiratory pressure support is not recommended and contradicts current lung-protective ventilation guidelines, as this approach promotes atelectasis formation and fails to maintain functional residual capacity. 1

Why Zero End-Expiratory Pressure (ZEEP) is Harmful

The British Journal of Anaesthesia expert consensus explicitly states that ZEEP is not recommended during general anesthesia. 1 The evidence demonstrates:

• ZEEP causes reduction in end-expiratory lung volume (EELV) and increased atelectasis formation after anesthesia induction 1
• Loss of EELV with ZEEP contributes to decreased respiratory system compliance in de-recruited lung areas and increases the propensity for overinflation of aerated lung tissue (volutrauma) 1
• Atelectasis occurs in approximately 90% of all patients undergoing general anesthesia and can persist for weeks postoperatively 1, 2
• The cyclic recruitment/de-recruitment injury from ZEEP increases driving pressure and is a key mediator of lung injury 1

Impact on Emergence and Atelectasis

During Emergence:

International guidelines provide 100% consensus (strong recommendation) to avoid ZEEP during emergence and to avoid apnea with ZEEP before extubation. 1

• Avoiding ZEEP during emergence is critical - the expert panel achieved 100% consensus on optimizing patient positioning and avoiding ZEEP during emergence 1
• Apnea with ZEEP before extubation must be avoided (100% consensus) as turning off the ventilator to allow CO2 accumulation causes alveolar collapse 1, 3

Atelectasis Formation:

The "oxygen-only" approach without positive pressure support significantly worsens atelectasis through multiple mechanisms:

• High FiO2 (>0.8) during emergence significantly increases atelectasis formation due to rapid oxygen absorption behind closed airways 1, 3, 4, 5
• Research demonstrates that ventilation with pure oxygen results in rapid reappearance of atelectasis, while moderate FiO2 (0.3-0.4) with PEEP reduces collapse 2
• When high FiO2 is used during emergence, low FiO2 (<0.3) CPAP immediately after extubation may reduce resorption atelectasis 1

Evidence from Spontaneous Ventilation Studies

A specific study examining spontaneous ventilation with LMA found that PEEP of +7 cm H2O in spontaneously breathing patients with LMA did not improve oxygen saturation 6. However, this study had critical limitations:

• Only included healthy patients (ASA I-II)
• Omitted pre-oxygenation which may have limited atelectasis development
• Used pulse oximetry rather than arterial blood gas measurements, which cannot detect subtle oxygenation changes 6
• This study does NOT support using ZEEP - it only shows that PEEP alone without other lung-protective measures may be insufficient 6

Recommended Approach Instead

The evidence-based alternative to spontaneous breathing with ZEEP includes: 1

1. Use PEEP of 5-10 cm H2O throughout anesthesia - even during spontaneous ventilation, some positive end-expiratory pressure should be maintained 1

2. Apply CPAP during induction - head-up positioning with CPAP/NIPPV before loss of spontaneous ventilation attenuates anesthesia-induced respiratory changes (100% consensus, strong recommendation) 1

3. Optimize FiO2 strategy:

   • Use FiO2 <0.4 during emergence when clinically appropriate (71% consensus) 1
   • Avoid routine high FiO2 without indication 3, 4

4. During emergence specifically:

   • Position patient with head elevated 30 degrees 1, 3, 4
   • Maintain positive pressure until extubation - avoid ZEEP (100% consensus) 1
   • Consider CPAP immediately post-extubation, especially in obese patients 3, 4

Common Pitfalls to Avoid

• Applying PEEP without first performing recruitment maneuvers - PEEP maintains but does not restore functional residual capacity 3
• Using high FiO2 during emergence - increases atelectasis formation 3, 7, 4
• Turning off ventilator before extubation - causes alveolar collapse 3
• Assuming adequate SpO2 means adequate lung recruitment - pulse oximetry during oxygen therapy cannot detect hyperoxia or atelectasis 1, 6

Clinical Bottom Line

There is no evidence supporting spontaneous ventilation with oxygen-only and ZEEP through an LMA. 1 This approach violates fundamental lung-protective ventilation principles by:

• Allowing progressive alveolar collapse 1
• Promoting atelectrauma from cyclic recruitment/de-recruitment 1
• Increasing postoperative pulmonary complications risk 1

Even in spontaneously breathing patients with LMA, some degree of positive end-expiratory pressure (minimum 5 cm H2O) combined with moderate FiO2 should be used to prevent atelectasis formation and maintain functional residual capacity throughout the anesthetic period. 1