Removal of retained air during cardiac surgery with transesophageal echocardiography and capnography

Study Objective: To evaluate a new method for removal of retained air at the end of cardiopulmonary bypass (CPB) by end-tidal CO₂ pressure (P(ET)CO₂) and pulmonary arterial pressure (PAP) monitoring, and transesophageal two-dimensional echocardiogra phy (TEE). Design: Prospective study. Setting: Cardiac surgery unit at a university hospital. Patients: 36 ASA physical status I, II, and III patients for open heart surgery. Interventions: The CPB reservoir was gradually raised to decrease venous drainage. Accordingly, the right heart began to receive the venous blood and eject it to the pulmonary artery. The vent existing in the left ventricle or the left atrium then collected any whole blood containing aft bubbles that came from the pulmonary circulation. The air bubbles were confirmed by TEE to be removed and not to eject from the left ventricle to the systemic circulation. Measurements and Main Results: Levels of P(ET)CO₂, PaCO₂, PAP, and the duration of the removal procedure were measured when a sufficient pulmonary circulation was established and the removal of retained air was considered to be satisfactorily accomplished by the absence of air bubbles, confirmed by TEE for more than 30 seconds. P(ET)CO₂ reached 28 ± 4 mmHg during the removal of air, while PaCO₂ reached 35 ± 6 mmHg (p < 0.05). Mean PAP during removal of air reached 18 ± 4 mmHg, which was approximately 90% of that before CPB. The duration time of removal of air was 9 ± 2 min. Conclusions: P(ET)CO₂ and PAP are useful indicators of pulmonary circulation during this procedure for removal of air, P(ET)CO₂ of 25 to 30 mmHg and PAP of 90% of the prebypass level have been found to be necessary for the removal of air. Our technique for removal of air using P(ET)CO₂, PAP, and TEE enables us to satisfactorily eliminate residual air.