Increase in plasma protein concentration for diagnosing weaning-induced pulmonary oedema

Objective: Weaning-induced cardiogenic pulmonary oedema is a cause of weaning failure that is classically diagnosed by an increase in pulmonary artery occlusion pressure during a spontaneous breathing trial. During cardiogenic pulmonary oedema, a hypo-oncotic fluid is filtered toward the interstitial space. Thus, we tested whether the changes in plasma protein concentration during a weaning trial could diagnose weaning-induced pulmonary oedema. Design: Prospective study. Setting: The 24-bed medical intensive care unit of a university hospital. Patients: Forty-six patients who had failed two weaning trials. Intervention: Weaning-induced pulmonary oedema was diagnosed if a respiratory failure associated with an increase in pulmonary artery occlusion pressure above 18 mmHg occurred during a third weaning trial on a T-tube. The plasma protein concentration was measured before and at the end of the spontaneous breathing trial. Measurements and results: During the weaning trial, pulmonary oedema was observed in 24 patients. In these patients, the plasma protein concentration increased by 11% (3-25%). The plasma protein concentration did not change significantly in patients who did not experience weaning-induced pulmonary oedema. An increase in the plasma protein concentration greater than 6% from baseline to the end of the weaning trial allowed detecting a weaning-induced pulmonary oedema with a sensitivity of 87% and a specificity of 95%. Conclusion: The acute changes in plasma protein concentration during a weaning trial represent an alternative method to right heart catheterisation for assessing weaning-induced pulmonary oedema.