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The effect of graded application of positive end-expiratory pressure (PEEP) was studied in 10 mongrel dogs with pulmonary edema induced by oleic acid infusion. Six animals received progressive increases in PEEP (5 cm H2O) 120 min after the injection of oleic acid. These animals were compared to 4 control animals who did not receive PEEP. We found no difference between the 2 groups in lung water measured by a double indicator dilution technique during PEEP application. Lung water determined by gravimetric analysis was also not different between groups at the end of the experiment. PEEP did result in significant reductions in shunt fraction and alveolar-arterial oxygen tension difference suggesting that PEEP improves gas exchange in pulmonary edema by increasing lung volume, but not by altering lung water accumulation.

The thermal dye double indicator dilution technique for estimating lung water was compared with gravimetric analyses in nine human subjects who were organ donors. As observed in animal studies, the thermal dye measurement of extravascular thermal volume (EVTV) consistently overestimated gravimetric extravascular lung water (EVLW), the mean (SEM) difference being 3.43 (0.59) ml/kg. In eight of the nine subjects the EVTV -3.43 ml/kg would yield an estimate of EVLW that would be from 3.23 ml/kg under to 3.37 ml/kg over the actual value EVLW at the 95% confidence limits. Reproducibility, assessed with the standard error of the mean percentage, suggested that a 15% change in EVTV can be reliably detected with repeated measurements. One subject was excluded from analysis because the EVTV measurement grossly underestimated its actual EVLW. This error was associated with regional injury observed on gross examination of the lung. Experimental and clinical evidence suggest that the thermal dye measurement provides a reliable estimate of lung water in diffuse pulmonary oedema states.

The diagnosis of pulmonary edema is frequently made from characteristic findings on the chest roentgenogram that suggest an increase in lung water. Optimal radiographic technique depends on a cooperative upright patient, which is not possible with most critically ill patients. These patients may also have multiple radiographic abnormalities that make interpretation of the chest roentgenogram difficult. The ability of portable chest roentgenograms to accurately identify the presence of excess lung water and monitor changes in lung water has not previously been evaluated in critically ill adults who are intubated and ventilated and in the supine position when the films are exposed. In 12 patients the pulmonary edema seen on portable chest roentgenograms was given a score (0 to 390 points), which was then compared with a determination of extravascular lung water using the thermal-dye indicator dilution technique. A linear correlation was observed (r = 0.51; p less than 0.05; n = 73). Evaluation of a change in radiographic score vs a change in lung water showed no linear correlation (r = 0.1; p greater than 0.05). While portable chest roentgenograms exposed under the conditions described were a useful technique for demonstrating pulmonary edema, they were not accurate in monitoring modest changes in lung water in critically ill patients.

The measurement of extravascular lung water by a double-indicator dilution technique using cold indocyanine green dye was evaluated in dogs. Pulmonary edema was induced in 11 animals by volume overload; 12 animals served as controls. For each measurement, the two indicators (cold dye) were injected into the superior vena cava and detected in the femoral artery. The extravascular thermal volume was calculated using the mean transit times of the two indicator curves. Pretermination measurements of extravascular thermal volume correlated closely with standard gravimetric analysis of pulmonary extravascular tissue weight (EVTV - 1.15 PEW + 2.1 ml/kg, n = 21, r = 0.97, P less than 0.001; where EVTV = extravascular thermal volume and PEW = pulmonary extravascular tissue weight). Throughout the experiment, the arterial oxygen tension and alveolar-arterial oxygen tension gradient, correlated poorly with EVTV (linear correlation: r = 0.47, 0.45, respectively). The intrapulmonary shunt correlated better with EVTV (r = 0.72). Nonlinear correlation of EVTV with intravascular pressures (left ventricular filling pressures, colloid oncotic pressures, and the pulmonary artery occlusion pressure-colloid oncotic pressure gradient) were more significant than linear relationships. The critical pressures at which lung water rapidly increased in this model occurred at left ventricular filling pressures of 22-27 mmHg and at pulmonary artery occlusion pressure-colloid oncotic pressure gradients of 25-30 mmHg. The thermal dye technique appears to provide an accurate measurement of lung water changes in this pressure edema model.