Early Respiratory Mechanics and Gas Exchange after Lung Transplantation: Associations with Severe Primary Graft Dysfunction.

Abstract

Primary graft dysfunction (PGD) is a major cause of early morbidity and mortality after lung transplantation (LUTX), with limited early predictive markers. This study aimed to determine whether early postoperative bedside respiratory pathophysiology can predict severe PGD at 72 h. In this prospective, single-center study, adult LUTX recipients underwent a decremental positive end-expiratory pressure (PEEP) trial (14, 10, 6 cm H 2 O) within 12 h after reperfusion. Gas exchange (venous admixture [Q s /Q T ], alveolar dead space), partitioned respiratory mechanics (respiratory system, chest wall, lung compliances-respiratory system compliance [Cpl RS ], chest wall compliance, lung compliance), and regional ventilation/perfusion ratio ( ) and collapse/overdistension ( via electrical impedance tomography) were assessed. Severe PGD was defined as Pa o2 /fraction of inspired oxygen ratio less than 200 mmHg at 72 h with bilateral infiltrates. Eight (17%) of 47 enrolled patients developed PGD. Compared to non-PGD patients, those with PGD exhibited significantly lower lung compliance (58 vs . 80 ml/cm H 2 O; P = 0.021) and Cpl RS (37 vs . 44 ml/cm H 2 O; P = 0.038), elevated Q s /Q T (21% vs . 5%; P < 0.001), higher alveolar dead space (15% vs . 12%; P = 0.010), and greater lung collapse ( P = 0.015). Non-PGD patients had more regions with high ( P = 0.036). In PGD, increasing PEEP reduced Q s /Q T (difference, -6.1%; 95% CI, -9.1 to -3.1; P = 0.001) and collapse (difference, -19.0%; 95% CI, -27.7 to -10.3; P = 0.002) without altering mechanics. In non-PGD, higher PEEP induced hyperinflation (difference 16.2%; 95% CI, 13.6 to 18.8; P < 0.001) and reduced Cpl RS (difference, -2.9 ml/cm H 2 O; 95% CI, -4.8 to -1.0; P = 0.008) and chest wall compliance (difference, -25.3 ml/cm H 2 O; 95% CI, -41.9 to -8.7; P = 0.024) while increasing physiologic dead space (difference, 2.9%; 95% CI, 1.2 to 4.6; P = 0.010). Q s /Q T showed the highest discriminative performance (area under the receiver operating characteristics curve, 0.92; 95% CI, 0.88 to 0.96) in predicting PGD development. Severe PGD is associated with early increases in venous admixture, reduced lung compliance, increased dead space, and patterns of collapse. These findings provide the rationale for studies exploring early pathophysiology-guided ventilatory management after LUTX.