Rebreathing Used for Cardiac Output Monitoring Does Not Increase Heart Rate

The partial rebreathing method for cardiac output determination produces short periods of elevated arterial CO2 content. Because previous work had shown that elevated etCO2 levels increased cardiac output, mostly due to heart rate increases, a concern was raised that the rebreathing periods could be inducing an elevated heart rate. This could also raise the cardiac output (CO), since CO = (Heart Rate) X (Stroke Volume). We studied 93 patients in the OR and the ICU who had undergone a total of 5142 partial rebreathing measurements by the NICO2 monitor (Novametrix Medical Systems) to determine whether the heart rate was raised, even if transiently, during the monitored period. Our conclusion was that the rebreathing periods caused no detectable change in the heart rate