How to manage increased end-tidal CO2 (etco2) during a Peroral Endoscopic Myotomy (POEM) procedure?

Management of Increased End-Tidal CO2 During POEM Procedures

When ETCO2 rises during Peroral Endoscopic Myotomy (POEM), immediately optimize ventilation by increasing minute ventilation through higher respiratory rate or tidal volume adjustments, ensure adequate CO2 elimination, and verify there is no CO2 retention from pneumomediastinum or subcutaneous emphysema. 1

Understanding the Problem

During POEM procedures, increased ETCO2 occurs primarily from:

• CO2 insufflation into the submucosal tunnel and mediastinum, which gets absorbed systemically and must be eliminated through ventilation 2
• Pneumomediastinum or pneumoperitoneum from CO2 tracking into tissue planes, increasing total body CO2 load 2
• Inadequate minute ventilation relative to the increased CO2 production/absorption during the procedure 3, 2

Normal ETCO2 is 35-40 mmHg; values >50 mmHg indicate hypoventilation and potential respiratory compromise requiring immediate intervention. 1, 4

Immediate Ventilatory Management Algorithm

Step 1: Increase Minute Ventilation

• Increase respiratory rate first (typically to 14-16 breaths/minute or higher as needed) while maintaining protective tidal volumes 3
• If ETCO2 remains >50 mmHg, cautiously increase tidal volume while monitoring peak airway pressures to avoid barotrauma 3
• Target ETCO2 of 40-45 mmHg (normocapnia) during the procedure 5

Step 2: Optimize Ventilation Mode

• Pressure-controlled ventilation may be superior to volume-controlled ventilation during procedures with CO2 insufflation, as it reduces the arterial-to-end-tidal CO2 gradient and improves dynamic compliance 3
• Consider switching to pressure-controlled mode if peak airway pressures are elevated and ETCO2 control is difficult 3

Step 3: Monitor Arterial-to-End-Tidal Gradient

• ETCO2 may underestimate actual PaCO2 during POEM procedures due to ventilation-perfusion mismatch from pneumomediastinum 6
• The median difference between PaCO2 and ETCO2 can exceed 12.9 mmHg in critically managed patients, with 61.4% having differences >10 mmHg 6
• Obtain arterial blood gas if ETCO2 >50 mmHg persists despite ventilatory adjustments to assess true PaCO2 and guide further management 6

Intraoperative Monitoring Strategy

• Continuous waveform capnography is mandatory to detect trends and ensure endotracheal tube patency 1
• An absolute change from baseline ETCO2 >10 mmHg is clinically significant and requires immediate assessment 1, 4
• Monitor for sudden increases in ETCO2 that may indicate massive CO2 absorption or ventilatory failure 7

Communication with Endoscopist

• Request temporary cessation of CO2 insufflation if ETCO2 exceeds 60 mmHg despite maximal ventilatory adjustments 2
• Allow time for systemic CO2 elimination before resuming insufflation 2
• Consider using lower insufflation pressures or intermittent insufflation techniques 2

Technical Troubleshooting

Before assuming the problem is purely from CO2 absorption, verify:

• ETT patency - check for kinking, mucous plugging, or bronchospasm 8
• Circuit integrity - ensure no disconnections or leaks 8
• Sampling line patency - confirm capnography is reading accurately 8

Post-Procedure Considerations

• Continue monitoring ETCO2 closely in recovery as absorbed CO2 from tissue planes continues to be eliminated 2
• Expect gradual normalization of ETCO2 over 30-60 minutes after procedure completion 2
• Maintain supplemental oxygen and monitor SpO2, as oxygenation is typically well-maintained even with elevated CO2 2

Critical Pitfall to Avoid

Do not rely solely on ETCO2 to guide ventilation during POEM procedures. The correlation between ETCO2 and PaCO2 becomes unreliable with significant CO2 absorption and ventilation-perfusion mismatch. 6 Obtain arterial blood gas measurements if there is any concern about adequacy of ventilation or if ETCO2 remains persistently elevated despite aggressive ventilatory management. 6