Introduction

Cardiac output/pulmonary blood flow measurement is an important way to assess patients during the perioperative period, as well as patients who are critically ill. Current methods of assessing cardiac output have limitations. One indicator of cardiac output may be the expired carbon dioxide (CO₂) partial pressure response to intravenous sodium bicarbonate (IVSB), which is rapidly converted to CO₂.

Methods

We conducted an initial evaluation of the relationship between expired CO₂ partial pressure and blood flow after a bolus of IVSB. To assess this relationship, we used a cardiopulmonary bypass circuit with predetermined blood flows in a laboratory trial and then assessed 18 patients undergoing surgery requiring cardiopulmonary bypass.

Results

For the laboratory portion of this pilot study, higher peak expired CO₂, faster time to reach peak, higher area under the curve, and greater kurtosis of peak were observed at higher cardiac output flow rates, and higher mean expired CO₂ was significantly associated with higher flow rates (p < 0.001). In the human study, higher mean (p = 0.023) and peak expired CO₂ (p = 0.028) were both significantly associated with higher cardiac output flow rates.

Conclusions

This technique may be a way to intermittently assess cardiac output or improve accuracy when used in conjunction with other continuous output monitors.