Effect of fluid loading with saline or colloids on pulmonary permeability, oedema and lung injury score after cardiac and major vascular surgery

Background. The optimal type of fluid for treating hypovolaemia without evoking pulmonary oedema is still unclear, particularly in the presence of pulmonary vascular injury, as may occur after cardiac and major vascular surgery. Methods. In a single-centre, prospective, single-blinded clinical trial 67 mechanically ventilated patients were randomly assigned to receive saline, gelatin 4%, HES 6% or albumin 5%, according to a 90 min fluid loading protocol with target central venous pressure of 13 and pulmonary capillary wedge pressure of 15 mm Hg, within 3 h after cardiac or major vascular surgery. Before and after the protocol, we recorded haemodynamics and ventilatory variables and took chest radiographs. The pulmonary vascular injury was evaluated using the Ga-67-transferrin pulmonary leak index (PLI) and extravascular lung water (EVLW). Plasma colloid osmotic pressure (COP) was determined and the lung injury score (LIS) was calculated. Results. More saline was infused than colloid solutions (P < 0.005). The COP increased in the colloid groups and decreased in patients receiving saline. Cardiac output increased more in the colloid groups. At baseline, PLI and EVLW were above normal in 60 and 30% of the patients, with no changes after fluid loading, except for a greater PLI decrease in HES than in gelatin-loaded patients. The oxygenation ratio improved in all groups. In the colloid groups, the LIS increased, because of a decrease in total respiratory compliance, probably associated with an increase in intrathoracic plasma volume. Conclusions. Provided that fluid overloading is prevented, the type of fluid used for volume loading does not affect pulmonary permeability and oedema, in patients with acute lung injury after cardiac or major vascular surgery, except for HES that may ameliorate increased permeability. During fluid loading, changes in LIS (and respiratory compliance) do not represent changes in pulmonary permeability or oedema.