Determination of intravascular volume status in critically ill patients using portable chest X-rays: Measurement of the vascular pedicle width

Background and Aims: Traditionally, invasive hemodynamic pressure measurements have been used to assess the volume status in critically ill patients. The vascular pedicle, as seen on chest radiographs, is the mediastinal silhouette of the great vessels. It is measured by drawing a perpendicular line from the point at which the left subclavian artery emerges from the aortic arch and measured across to the point at which the superior vena cava crosses the right main stem bronchus. We carried out this study to establish a correlation between the width of the vascular pedicle as seen on chest radiographs and daily fluid balance or pulmonary capillary occlusion pressure in mechanically ventilated, critically ill patients.
Materials and Methods: In this prospective clinical study, 50 consecutive adult patients in a tertiary care, multidisciplinary intensive care unit underwent simultaneous measurements of the width of the vascular pedicle as seen on standardized, portable chest radiographs in the supine position and pulmonary capillary occlusion pressure measurements. Twenty-four hour fluid balance calculations were also recorded for each patient.
Results: Vascular pedicle width measurements correlated closely with positive fluid balance, r = + 0.88, P 0.000. A Receiver Operating Characteristic curve demonstrated that a vascular pedicle width of 86.5 mm had a 100% sensitivity and an 80% specificity (area under the curve 0.823, 95% confidence intervals 0.714-0.932) for predicting fluid overload equal to and greater than 1200 ml. The correlation between pulmonary capillary occlusion pressures and width of the vascular pedicle was poor, r = 0.41, P 0.02.
Conclusions: Our findings suggest that the vascular pedicle width on daily chest radiographs can be used to assess hypervolemia in the intensive care unit. Serial changes in the pedicle width could possibly be used to increase the accuracy of predictions.

Keywords
Intravascular volume, critically ill patients, chest X-rays, vascular pedicle