Different measures of ventilatory efficiency in preoperative cardiopulmonary exercise testing are useful for predicting postoperative complications in abdominal cancer surgery

Background: Ventilation as a function of elimination of CO₂ during incremental exercise (VE/VCO₂ slope) has been shown to be a valuable predictor of complications and death after major non-cardiac surgery. VE/VCO₂ slope and partial pressure of end-tidal carbon dioxide (PetCO₂) are both affected by ventilation/perfusion mismatch, but research on the utility of PetCO₂ for risk stratification in major abdominal surgery is limited.

Aim: We aimed to determine the correlation between VE/VCO₂ slope and PetCO₂ measured during preoperative cardiopulmonary exercise testing (CPET) and its association with major cardiopulmonary complications (MCPCs) or death following oesophageal and other major abdominal cancer surgeries.

Method: In a retrospective cohort of 116 patients undergoing preoperative CPET 2008-2023, VE/VCO₂ slope and PetCO₂ (kPa) were recorded. The main outcome was MCPC during hospitalisation or death ≤90 days of surgery. We determined threshold values for each measure, corresponding to 90% specificity, using receiver operating characteristics analysis.

Results: A strong negative correlation was found between PetCO₂ after a 5-minute warm-up and VE/VCO₂ slope (Pearson r = -.88). In oesophagus cancer, VE/VCO₂ slope >38 and PetCO₂ < 4.1 kPa (30.8 mmHg) were both significant thresholds for the main outcome. For other major abdominal surgery patients, threshold analyses were non-significant. The area under the curve to predict outcome was similar using VE/VCO₂ slope (0.70, 95% confidence interval 0.51-0.89) as compared to PetCO₂ (0.71, 0.53-0-90).

Conclusion: Both preoperative VE/VCO₂ slope and PetCO₂ could identify subjects with a very high risk of complications following oesophageal resection, with similar prognostic utility. PetCO₂ can be measured with simpler equipment and could therefore be useful when CPET is not available.