An "oncometer" of clinical measurement of colloid osmotic pressure of plasma.

Measurement of colloid osmotic pressure complements measurements of pulmonary artery wedge pressure for assessing the risks of pulmonary edema and constitutes an increasingly important reference for purposes of guiding selection of colloid or crystalloid fluids in patients with acute cardiac disease. We describe a simple device for its routine clinical measurement. A membrane, selectively impermeable to molecules of relative molecular mass (Mr) greater than 30000, is rigidly mounted between a sample chamber and a reference chamber filled with isotonic saline. A pressure transducer measures the negative pressure developed in the reference chamber and displays it on a digital panel meter. The sensor chamber accommodates samples of 50 to 300 microliter. Equilibration is completed within 2 min. A control solution of human serum albumin (50 g/liter) is measured to confirm the accuracy of calibration of the system, with reproducible readings of 25.9 g/cm2 within one SD (equivalent to 0.4 g/cm2). Technical simplicity of operation and modest costs of disposables have made feasible the routine measurement of colloid osmotic pressure.