Lund Concept for De-airing of the Left Heart. Clinical Evaluation

Abstract: Background: Residual air accumulated air in the pulmonary veins constitutes a challenge to achievment of complete de-airing in open left heart surgery. To adress this problem, a conceptual method for de-airing was developed in Lund comprising bilateral opening of the pleurae to induce pulmonary collapse and a strategy with gradual pulmonary reperfusion and ventilation at weaning from cardiopulmonary bypass (CPB). Aim: To evaluate effectiveness and safety aspects of the Lund concept for de-airing. Methods and results: In the first paper a randomized controlled study was conducted comparing the Lund method to a standardized carbon dioxide (CO2) insufflation technique in twenty patients undergoing open left heart surgery. The number of cerebral microembolic signals (MES) was monitored by transcranial Doppler sonography (TCD) during de-airing and in the first ten minutes after CPB. Residual intracardiac air during the first ten minutes after CPB was graded by transesophageal echocardiography (TEE). The frequency of reopenings of the left ventricular (LV) vent during the first ten minutes after CPB was registered as well as the duration of the de-airing procedure. Compared to the CO2 insufflation technique, the Lund method resulted in fewer MES during de-airing (p<0.001) and in the first ten minutes after CPB (p<0.001), lower grades of intracardiac air during the first three minutes after CPB (p<0.01) and shorter de-airing time, 9 vs 15 minutes, (p=0.001). In the second paper, systemic side-effects of CO2 insufflation were studied in the same twenty patients. Patients in the CO2 insufflation group developed hypercapnia (PaCO2>6 kPa) despite compensational higher gas flows in the oxygenator at 30 minutes of CPB (p<0.001) and acidosis (pH<7.35) already at 15 min of CPB, (p<0.01). CO2 production (VCO2 mL/min) increased during CPB as did the respiratory quotient (RQ; p<0.001) secondary to the extraneously supplied CO2. The mean blood flow velocities in both MCAs increased secondary to increasing PaCO2 (p<0.001 at 45 and 60 minutes of CPB). rSo2 measured by near-infrared spectroscopy (NIRS) were also found higher at 30, 45 and 60 minutes of CPB (p<0.05, p<0.01 and p<0.01, respectively). Scanning electron microscope imaging the cardiotomy suction and LV vent line tubing showed a higher fraction of morphologically changed red blood cells in the CO2 insufflation group. In the third paper we aimed to study the contribution of each component constituting the Lund concept. In a randomized controlled study of twenty patients undergoing open left heart surgery, we compared a group with open pleurae and conventional pulmonary reperfusion and ventilation to a group with intact pleurae combined with staged pulmonary reperfusion and ventilation. During de-airing and in the first ten minutes after CPB, there was a lower number of MES in the group with open pleurae (p<0.05, p<0.01, respectively). A lower amount of residual intracardiac air was also registered in the group with open pleurae in up to six minutes after CPB (p<0.01). The LV vent was reopened fewer times in the group with open pleurae (p<0.001). De-airing time was also shorter in the group with open pleurae, 9 vs 14 minutes (p<0.05). In the fourth paper we studied the impact of single right pulmonary collapse on effectiveness of the Lund method and the effectiveness of a right superior pulmonary vein vent (RSPV). Twenty patients in two prospective cohorts with right pleura open and RSPV respectively, were compared to a historical control cohort from the first paper with bilateral open pleurae and left ventricular apical vent (LVAV). We found a higher number of MES after CPB in the group with single right pulmonary collapse and in the group with RSPV compared to bilateral pulmonary collapse and LVAV (p<0.001, p<0.01, respectively) but no differences in residual intracardiac air graded by TEE or in de-airing times. Conclusion: The Lund concept for de-airing was demonstrated to be an effective and safe alternative to the CO2 insufflation technique. The effectiveness of the Lund method depends primarily on bilateral pulmonary collapse and it may preferably be combined with a left ventricular apical vent.