THE GRAVITY SHIFT TEST: A RADIOGRAPHIC METHOD FOR DETERMINING MOBILIZABLE LUNG WATER

Patients with acute respiratory failure (A.R.F.) often accumulate excess fluid in their lungs due to the A.R.F. or its treatment. Recognition is often difficult because of underlying lung disease, the difficulty of physical diagnosis and the limitations of portable radiography. A simple non-invasive test for excess lung water would be helpful for both diagnosis and management. Leeming (Chest 64, 1973) noted that A.R.F. patients often develop dependent pulmonary edema after lying on their sides for a few hours. Our study was designed to prospectively evaluate the use of a gravitational shift in distinguishing potentially mobilizable excess lung water (C.H.F. or fluid overload) from inflammatory or infectious infiltrates.Thirty-nine I.C.U. patients with diffuse pulmonary infiltrates of clearly defined etiology were studied. After an AP baseline chest film, the patient was placed in the decubitus position for 2 hrs. then sat up and re-x-rayed. Paired films were read blindly.A definite gravitational shift of the infiltrate to the dependent side was noted in 16 of the 19 patients with pulmonary edema. A positive shift test was noted in only 3 of the 14 patients who had no evidence of edema (as judged by other parameters). The predictive value of the shift test in detecting mobilizable lung water is .84 with a 15% false positive rate. The negative predictive value is .78. The therapeutic implications will be discussed.