Transvascular Transport of 67Ga in the Lungs After Cardiopulmonary Bypass Surgery

Abstract

To examine the effect of cardiac surgery with cardiopulmonary bypass (CPB) on pulmonary vascular permeability. A prospective, serial study. Department of nuclear medicine and intensive care units of a university hospital. Twelve consecutive patients were studied, before and immediately after elective cardiac surgery using CPB (group 1), and 4 consecutive, artificially ventilated patients with acute cardiogenic pulmonary edema (group 2). The kinetics in blood and over both lungs were measured, using two mobile probes at the bedside, of intravenously injected 67Ga, assumed to bind to circulating transferrin, and in vitro 99mTc-labeled red blood cells to account for pulmonary blood volume. From data recorded in time (1 h), a pulmonary leak index (PLI), the time constant of transport of 67Ga from the intravascular to the extravascular space of the lung, was calculated and values for both lungs were averaged. In group 1, the PLI (.10(-3).min-1, mean +/- SD) was 8.2 +/- 3.7 before and 17.0 +/- 13.5 after CPB surgery (p < 0.01) and changes directly related to the duration of CPB. In four patients with a CPB duration > or = 120 min, the PLI, 31.1 +/- 16.3.10(-3).min-1, exceeded 2 SD plus mean preoperative PLI. Changes in PLI tended to relate inversely to changes in arterial WBC, which, in turn, inversely related to CPB duration. The PaO2/FIO2 ratio decreased and tended to relate inversely to PLI after surgery. No patient developed alveolar pulmonary edema on chest radiograph. In group 2, the PLI was 11.1 +/- 3.1.10(-3).min-1 (NS from group 1 preoperative PLI). Cardiopulmonary bypass induces a pulmonary vascular leak, as assessed by 67Ga kinetics using a bedside detection technique, in some cardiac surgery patients with prolonged CPB. This leak may reflect pulmonary vascular injury and increased permeability, following activation of leukocytes by CPB and subsequent pulmonary sequestration, rather than increased filtration through pressure factors. It may contribute to impaired gas exchange, even in the absence of manifest alveolar edema of the lungs, after surgery.