Measurement of lung oxygen consumption in a patient after double-lung transplant

Abstract

A 48-year woman underwent double-lung transplantation for treatment of severe emphysema. She required venous-arterial extracorporeal membrane oxygenation (ECMO; Bio-Medicus pump, model 540T; Bio-Medicus, Inc., Eden Prairie, Minn.; Medtronic/Carmeda Bioactive Surface with Maxima Hollow Fiber oxygenator CB 1380; ECMO flow rate 5 L/min, Medtronic, Inc., Minneapolis, Minn.) to correct severe nonpulsatile arterial pressure hypoxemia and cardiovascular instability. A postoperative 12:39 30.1 38 chest radiograph demonstrated bilateral alveolar infil12:40 18.3 27 trates compatible with acute lung injury. 12:41 15.2 30 On the second postoperative day, we measured oxygen 12:42 12.8 21.6 consumption (Vo2) and carbon dioxide excretion (Vco2) 12:43 11.2 22.7 by means of respiratory gas analysis with a metabolic cart 12:44" 7.7 19.6 (Deltatrac; SensorMedics Corp., Yorba Linda, Calif.). 12:45" 8.2 18.4 Blood flow through the pulmonary circulation was varied 12:46" 9.7 18.3 by adjusting the ECMO flow rates during the study 12:47" 6.9 19.6 interval. The patient was ventilated with a Puritan-Ben12:48" 5.1 15.7 nett 7200e ventilator (Puritan-Bennett Corp., Portable Ventilator Division, Boulder, Colo.) set on a tidal volume ECMO flow rate 2 L/rain, of 600 ml with a respiratory rate of 4 breaths/rain, positive cardiac output 3.43 L/min end-expiratory pressure of 10 cm H20, and inspired 13:43 46.5 77,6 oxygen fraction of 0.5. With the ECMO flow at 5 L/rain, 13:44 41.5 75,9 there was a nonpulsatile pulmonary arterial tracing with a 13:45 43.4 76.1 mean pressure of 8 mm Hg, which was inferred to reflect 13:46 47.7 75.5 no flow in the pulmonary artery. The simultaneous non13:47 53.6 78.0 pulsatile radial arterial tracing confirmed the absence of 13:48" 67.2 83.4 aortic valve opening. These settings were maintained for 13:49" 65.9 80.5 10 minutes, during which time the readings stabilized to 13:50" 68.4 80.0 yield, during a 5-minute period: Vo2, 7.8 -+ 1.7 ml/min 13:51" 70.1 81.2 (mean + standard deviation); and Vc% 18.3 -+ 1.6 ml/min 13:52" 72.1 79.8 (Table I). Respiratory quotient (RQ) was 1.97 + 0.05. When the ECMO flow rate was reduced gradually to 2 L/min, there was a return of pulmonary artery flow. This was evidenced by the reappearance of pulsatile pulmonary arterial and radial arterial tracings. Furthermore, a thermodilution cardiac output was measured at 3.43 L/rain. V% increased progressively and stabilized (after 5 rain-