The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts


Authors Lisa Cracchiolo, RRT, Michael S. Avidan, MBBCh, Eric Jacobsohn, MBChB, MHPE, FRCPC, Charl J. DeWit, MBChB, Lauren L. Hill, MD, Syed Ali, MD, Michael Pasque, MD, Heidi Tymkaw, MHS, Mary Finayev, RRT, Barnes-Jewish Hospital and Washington University School of Medicine, St. Louis, MO

Objective To determine if administration of supplemental carbon dioxide results in improved cardiac index and peripheral tissue oxygenation in the post-operative cardiac surgery patient

Design Prospective, randomized, cross-over design of post-operative patients in the cardiothoracic intensive care unit at Barnes-Jewish Hospital; Study groups were randomized into a differing sequence of arterial CO2 tensions: Group 1=30®40®50 mmHg, Group 2= 40®50®30 mmHG, and Group 3=50®30®40 mmHg. The study goal is twenty-four patients following elective heart surgery; nine patients have been studied to date.

Method Patients were sedated with propofol and fentanyl, and paralyzed with rocuronium. All patients had a pulmonary artery catheter and an arterial line interfaced with an indwelling blood gas analyzer. Prior to the study, a transcutaneous monitor was placed close to the sternum to monitor oxygen tension. A Novametrics NICO2 monitor was placed inline with the ventilator circuit, utilizing a Capnostat CO2 sensor. Once patients were stable in the ICU, mechanical ventilator settings were adjusted to attain an initial PaCO2 of 30. Patients were randomized into Group 1, 2, or 3. Supplemental CO2 was bled into the inspiratory limb of the ventilator circuit to attain the desired PaCO2 levels. Patients were placed in A/C mode and tidal volume adjusted to compensate for additional CO2 flow and to maintain exhaled minute ventilation throughout the study. No other changes to the mechanical ventilator were made except in emergencies. No additional medical interventions (i.e., no changes in medications, fluids) were made. Upon achieving each desired PaCO2 level (± 3 mmHg), hemodynamic measurements, respiratory mechanics, and ABGs were recorded.

Results Data for nine patients (Mean ± SD):

Desired PaCO2®




MAP (mmHg)


CI (L/min)

SvO2 (%)


92 ± 16

94 ± 9

2.4 ± 0.6

72 ± 9

7.47 ± 0.02

85 ± 10

91 ± 8

2.7 ± 0.6

76 ± 7

7.37 ± 0.03

76 ± 12

95 ± 9

2.7 ± 0.6

77 ± 8

7.29 ± 0.04

There is a trend toward a decrease in SVR, but it is not yet statistically significant. There was no change in PaO2 values, potassium levels, no arrhythmias associated with supplemental CO2 administration, and no significant change in CVP, PVR, airway resistance, or compliance was noted. There is a statistically significant increase in CI when PaCO2 is increased from 30 to 40 or 50. Mean arterial pressure decreased significantly as PaCO2 increased. Interestingly, SVO2 increased with higher PaCO2.

CO2 administration appears to be well tolerated, may improve cardiac indices, and may not be associated with adverse effects or hemodynamic compromise in post-operative cardiac surgery patients. There is no clear indication that CO2 administration improves peripheral tissue oxygenation.

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