Utility of Portable Chest X-ray

Abstract

To the Editor: The article by Dr. Halperin and colleagues1Halperin BD Feeley TW Mihm FG Chiles C Guthaner DF Blank NE Evaluation of the portable chest roentgenogram for quantitating extravascular lung water in critically ill patients.Chest. 1985; 88: 649-652Abstract Full Text Full Text PDF PubMed Scopus (119) Google Scholar assessing the estimation of extravascular lung water (EVLW) by portable chest x-ray examination (CXR) identifies the difficulty of managing patients with acute respiratory failure in the clinical intensive care setting. While there are certainly problems with anteroposterior CXR, in general, they appear to be less significant than the authors suggest. Sibbald et al,2Sibbald WJ Warshawski FG Short AK Harris J Lefcoe MS Holliday RL Clinical studies of measuring extravascular lung water by the dye technique in critically ill patients.Chest. 1983; 83: 725-731Abstract Full Text Full Text PDF PubMed Scopus (52) Google Scholar in their study comparing EVLW and CXR, used only the supine technique and made no mention of interpretive difficulties as a problem. Indeed, Bekemeyer3Bekemeyer WB Crapo RO Calhoon S Cannon CY Clayton PD Efficacy of chest radiography in a respiratory intensive care unit: a prospective study.Chest. 1985; 88: 691-696Abstract Full Text Full Text PDF PubMed Scopus (116) Google Scholar reported that, of 1,354 CXRs obtained in a respiratory intensive care unit, only 22 (9 percent) were technically inadequate, and these were simply repeated. The validity of using CXR to demonstrate pulmonary edema is well-documented. Snashall and colleagues4Snashall PD Keyes SJ Morgau BM et al.The radiographic detection of acute pulmonary edema. A comparison of radiographic appearances, densitometry and lung water in dogs.Br J Radiol. 1981; 54: 277Crossref PubMed Scopus (54) Google Scholar found that pulmonary edema was invariably recognized on CXR when lung water increased by more than 35 percent in canine models of cardiogenic and permeability pulmonary edema. There was a positive correlation between radiologic grade and gravimetric lung water measurement. This study confirmed previous observations by Pistolesi and Guintini,5Pistolesi M Guintini C Assessment of extravascular lung water.Radiol Clin N Am. 1978; 16: 551PubMed Google Scholar who found a linear relationship between double-indicator dilution lung water measurement and radiographic grade of pulmonary edema in patients with cardiogenic pulmonary edema. Sibbald et al2Sibbald WJ Warshawski FG Short AK Harris J Lefcoe MS Holliday RL Clinical studies of measuring extravascular lung water by the dye technique in critically ill patients.Chest. 1983; 83: 725-731Abstract Full Text Full Text PDF PubMed Scopus (52) Google Scholar also demonstrated a positive correlation between CXR and EVLW in patients with both cardiogenic and noncardiogenic pulmonary edema. Staub,6Staub NC Pulmonary edema.Physiol Rev. 1974; 54: 678Crossref PubMed Google Scholar and more recently Effros,7Effros RM Noninvasive measurements of pulmonary edema and epithelial permeability.Ann Intern Med. 1983; 99: 818Google Scholar endorsed CXR as a state-of-the-art method for evaluating pulmonary edema. In our own units, we find few patients in whom it is not feasible to use this technique, as described by Turner et al.8Turner AF Lav FYK Jacobson G A method for the estimation of pulmonary venous and arterial pressure from the routine chest roentgenogram.Am J Radiol. 1972; 116: 96Google Scholar In the present study, the poor correlation between EVLW and CXR may be due to factors other than just technically inadequate CXR. There is no mention of the hemodynamic characteristics of these patients. In a report by Goodwin and Pruitt9Goodwin CW Pruitt BA Underestimation of thermal lung water volume in patients with high cardiac output.Surgery. 1982; 92: 401-407PubMed Google Scholar of five thermally-injured patients, EVLW (as measured by the thermal dye technique) decreased slightly as cardiac index progressively increased. In this same group of patients, EVLW (as measured by the rebreathing technique) increased significantly as cardiac index increased. Fallon et al10Fallon KD Drake RE Laine GA Gabel JC Effect of cardiac output on extravascular lung water estimates made with the Edwards lung water computer.Anesthesiology. 1985; 62: 505-508Crossref PubMed Scopus (13) Google Scholar studied the effect of changes in cardiac output on estimates of EVLW by the thermal dye technique. They found that animals with decreases in cardiac output had marked increases of estimated EVLW, despite normal postmortem gravimetric lung water measurements. In addition, increases in cardiac output were associated with large decreases in EVLW.10Fallon KD Drake RE Laine GA Gabel JC Effect of cardiac output on extravascular lung water estimates made with the Edwards lung water computer.Anesthesiology. 1985; 62: 505-508Crossref PubMed Scopus (13) Google Scholar Clearly, the use of CXR in the bedside management of critically ill patients is not perfect. However, to minimize its usefulness based on a technique with its own inherent limitations would be unwise.