What's the next step for a morbidly obese patient with a struvite partial staghorn kidney stone who developed increased airway pressure in the prone position during percutaneous nephrolithotomy (PCNL) access?

Management of Airway Pressure Increase in Morbidly Obese Patient During Prone PCNL

The next step for a morbidly obese patient who developed increased airway pressure in prone position during PCNL access is to modify the positioning with improved chest and abdominal support while maintaining prone position, and increase PEEP from 6 to 9-12 cmH2O to optimize ventilation. 1, 2

Assessment of the Situation

• The patient's airway pressure normalized after returning to supine position, indicating a positioning-related respiratory compromise rather than a primary airway issue 1
• Morbidly obese patients are at higher risk for rapid and potentially catastrophic airway complications during anesthesia, especially in prone position 3, 1
• Prone positioning can compromise pulmonary compliance by compressing the abdomen and restricting chest wall movement, particularly in obese patients 4

Immediate Management Steps

1. Optimize Positioning While Maintaining Prone Position

• Ensure adequate support under the chest and pelvis to allow free movement of the abdomen during ventilation 1, 4
• Use a frame that minimizes abdominal compression - the Jackson table has been shown to cause less reduction in pulmonary compliance compared to chest rolls or Wilson frame 4
• Maintain ramped position principles even in prone position, ensuring optimal positioning of the chest and abdomen to allow for maximum respiratory excursion 1

2. Optimize Ventilation Parameters

• Increase PEEP from typical 6 cmH2O to 9-12 cmH2O, which has been shown to improve respiratory mechanics and lung ventilation after prone positioning 2
• Consider switching to pressure-controlled ventilation rather than volume-controlled ventilation, as it often achieves greater tidal volumes for a given peak pressure 3, 1
• Use ideal body weight to calculate tidal volume (6-8 ml/kg) during controlled ventilation 3
• Ensure peak inspiratory pressure remains <35 cmH2O 1
• Perform recruitment maneuvers to reduce atelectasis 3, 1

3. Monitor Closely

• Continuously monitor airway pressures, oxygen saturation, and end-tidal CO2 3
• Be vigilant for signs of increasing airway pressure or decreasing oxygen saturation 3, 1
• Monitor for increases in intra-abdominal pressure, which can rise from baseline during prone positioning in obese patients 1

If Optimization Fails

• If airway pressures remain elevated despite optimization measures, return to supine position and consider alternative approaches 1
• Options include:
  • Modified lateral position for PCNL access 1
  • Complete supine PCNL, which has been shown to be effective and safe for staghorn stones 5
  • Consider regional anesthesia techniques where feasible 1

Common Pitfalls to Avoid

• Failing to recognize the severity of positioning-related airway compromise, which can lead to rapid desaturation 3, 1
• Attempting to force prone positioning without addressing the underlying cause of airway pressure increases 1
• Using inadequate PEEP levels - intratidal compliance analysis suggests that in most patients, a PEEP above commonly used settings is necessary to avoid alveolar collapse in the prone position 2
• Neglecting the importance of proper positioning - the type of frame used significantly impacts pulmonary mechanics in prone position 4