ATLANTA—Many physicians are concerned about using pulmonary artery catheters to monitor fluid balance in the critically ill because catheters may increase mortality. However, it now appears possible to accurately monitor fluid balance using the serial chest x-ray that most critically ill patients routinely undergo.

In a study by Greg S. Martin, MD, and colleagues, daily chest films enabled them to track the fluid balance of 36 mechanically ventilated patients with acute lung injury.[1] In particular, the films identified significant treatment-related changes in vascular pedicle width (VPW), which correlates well with a number of intravascular volume indicators.

“Most important, radiographic changes in vascular pedicle width were highly correlated with measures of intravascular volume obtained invasively by a pulmonary artery catheter,” stressed Dr. Martin, Associate Professor of Pulmonary and Critical Care Medicine at Emory University in Atlanta. If these findings are confirmed, clinicians may be able to make chest films their primary method of monitoring fluid balance in the critically ill.

The patients in the study were part of a prospective, randomized trial of albumin plus furosemide or dual placebo for the treatment of acute lung injury.[2] Portable, supine, anteroposterior chest films for each patient were examined at baseline and on study days 1, 3, and 5 (the final treatment day) by observers blinded to the patients’ conditions. A total of 133 films were interpreted.

On average, the treatment group experienced a 3.3-L net diuresis and a 10-kg decline in weight, while the placebo group showed a 0.5-L fluid gain and a 4.7-kg weight loss. Ventilator management and mortality were the same in the two groups.

No between-group differences in VPW, cardiothoracic ratio (CTR), or other radiographic measures of fluid balance were observed at baseline. However, VPW was lower in the treatment group once treatment began; this finding was statistically significant on days 3 and 5. No significant changes in CTR or in subjective measures of fluid balance (such as edema score and pleural effusion) occurred during the study.

Among the subset of patients with a pulmonary artery catheter, intravascular volume as estimated from the pulmonary artery occlusion pressure correlated strongly with changes in VPW from baseline to day 5. During that time, there was also a strong relationship between changes in VPW and central venous pressure; in all patients, changes in VPW were significantly correlated with net intake/output or weight.

If the study findings are prospectively confirmed in a more varied group of critically ill patients, they may help eliminate the need for a pulmonary artery catheter and thereby reduce the risk of iatrogenic events. However, physicians who want to use chest films to monitor fluid balance will have to be carefully trained in the use of objective radiographic measures, such as VPW. Based on this study’s results, it appears that these objective measures are probably better than the current subjective methods, Dr. Martin said.

—Timothy Begany

References
1. Martin GS, Ely EW, Carroll FE, Bernard GR. Findings on the portable chest radiograph correlate with fluid balance in critically ill patients. Chest. 2002;122:2087-2095.
2. Martin GS, Mangialardi RJ, Wheeler AP, et al. Albumin and furosemide therapy in hypoproteinemic patients with acute lung injury. Crit Care Med. 2002;30:2175-2182.

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