Pulmonary sequestration of cardioplegia administered via the aortic root during aortocoronary bypass surgery

Abstract

A semi-quantitative method was devised of tracing blood flow through the heart and lungs at the time of cardioplegia delivery and circulatory arrest of the heart during coronary artery bypass graft surgery (CABG). There were no previous studies confirming or disputing an accepted 'observation' by cardiac surgeons that cardioplegia solution does enter the lung parenchyma during cardiopulmonary bypass (CPB). This study was conducted as part of a larger (n = 142) double-blind, randomised, controlled, clinical research study. The objective was initially to establish the efficacy of measures to prevent cardioplegia entering the lungs and, subsequently, to determine whether cardioplegia indeed circulates through the lung parenchyma or merely accumulates and 'pools'. A prospective study on 20 consecutive patients (5 per group) admitted for CABG was made. Technetium (Tc-99m), a radioactive isotope, was added to the cold blood cardioplegia solution prior to cardioplegia delivery in order to track flow of cardioplegia solution. An independent nuclear medicine radiographer measured the samples with the use of a 'Curimentor' dose calibrator for presence and quantity of radiation in the samples. Decay was factored into the results. The Tc-99m tracer samples were also analysed using Gamma Acquisition and Analysis on the Genie 2000vdm Well Counter to confirm the presence and quantity of Tc-99m. In the four groups, it was confirmed that the pulmonary artery (PA) vent is 90-100% effective in retrieving any cardioplegia solution not drained by the atriocaval cannulae. The PA vent is effective in preventing cold blood cardioplegia solution from entering the lungs. Any cardioplegia that does enter the lung parenchyma during CPB circulates through the lungs and can be retrieved by a vent in the left atrium. This method may be useful in other studies that require investigation.