Introduction
A capnodynamic method continuously calculates non-shunted pulmonary blood flow (COEPBF) using an automatic expiratory hold in three out of nine breaths during mechanical ventilation. In a porcine model, the method has performed well during different respiratory and circulatory challenges1, although as expected, transiently affected during swift changes in mixed venous CO2 and at high shunt levels2. Concordance during large CO changes has been preserved throughout the animal studies. The aim of the current study was to evaluate COEPBF clinically for the first time during abdominal surgery. 

Methods
Effective pulmonary blood flow was calculated and compared to trans-pulmonary thermodilution (TPTD) in 25 patients undergoing elective open abdominal surgery. Three measurements were performed at baseline (BLPEEP5) at five minutes interval and subsequently before and after changes in PEEP (5-15-5 cmH2O) and epidural activation with bolus mepivacaine. Events such as hypovolemia and low cardiac output were captured during surgery and values before and after installation of treatment were recorded. 

Results
Mean CO was 4.4 (1.0) and 4.8 (1.1) L/min for EPBF and TPTD in patients with a mean age 68 (9) years and weight 76 (16) kg.  Bias (levels of agreement) for all 233 paired values was -0.3 L/min and improved after ΔPEEP 15 without affecting LoA (-2.1 to 1.4 L/min) and percentage error (37%). Concordance with a 15% exclusion zone (0.7 L/min) was 81 and 95% after PEEP increase and decrease respectively, 86% after epidural activation and 100% after volume infusion.  

Conclusion
COEPBF performed acceptably during open abdominal surgery tracking small but recognizable hemodynamic changes. Further clinical studies are warranted to establish its role as a continuous and simple alternative for monitoring and tracking changes in CO in the operating theatre.


08 / A capnodynamic method delivers continuous hemodynamic monitoring during abdominal surgery