Aim–  To study the relationship of pump flow and expired pump Co₂ (PepCo₂)  on  cardiopulmonary bypass (CPB).

Background – PepCo₂ (partial pressure of expired pump carbon dioxide) is a good correlator  of PaCo₂ during CPB. It is  established that PaCo₂ reflects cardiac output in a state of controlled ventilation.

Hence, it was hypothesized that  PepCo₂ is an indicator of changes in pump flow (cardiac output) during CPB where oxygenator acts as an ideal lung.

Methodology – An observational study was conducted in 30 patients of either sex undergoing open heart  surgeries under CPB to establish the relation between PepCo₂ and pump flow. 

Keeping  constant sweep flow rate and temperature  during CPB, PaCO₂ and PepCO₂ values were measured  at stable hypothermia  30^oC . The variations in PepCo₂ were observed by adjusting the pump flow within the permissible range of cardiac index for that patient. The adequacy of perfusion was also assessed by measuring  SvO₂, glucose, and lactate levels.

Results – It was observed that values of PepCO₂ correlated with the pump flow (p=0.011) and change in PepCO₂ has definite positive relationship with the change in  pump flow. One unit change in pump flow resulted in 0.97unit change in PepCO₂.

Conclusion – PepCo2 on cardiopulmonary bypass is a good continuous, non–invasive tool for monitoring adequacy of pump flow. Hence ,it is  recommended to  monitor PepCo₂ routinely during CPB.