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

Introduction

Traditionally invasive haemodynamic measurements of pulmonary artery occlusion pressures have been used to assess the volume status in critically ill patients. The vascular pedicle, as seen on chest X-ray scan, is the mediastinal silhouette of the great vessels. We hypothesized that the vascular pedicle width (VPW) on supine, portable chest X-ray scans could be used to predict intravascular volume overloaded status in critically ill patients.

Methods

We conducted a prospective, blinded observational trial where both pulmonary artery occlusion pressures (PAOP) and VPWs were measured in patients admitted to the ICU. We used measurements of PAOP ≥ 18 mmHg as indicative of a fluid overloaded state, and measurements of PAOP < 18 mmHg as normal or low volume states. Standardized, portable chest X-ray scans in the supine position were obtained within 1 hour of PAOP measurement. Receiver-operating characteristics (ROC) curves were constructed using different cutoffs of the VPW measurement to identify sensitivities and specificities for each value (see Figure 1).

Figure 1

Receiver-operating characteristics curve for vascular pedicle width. The curve shows the ability of the vascular pedicle width to differentiate between fluid overload and euvolemia at different cutoff points. The area under the curve is 0.724. Increased vascular volume is defined as pulmonary artery occlusion pressure ≥ 18 mmHg.

Results

Measurements were obtained from 50 patients. Using ROC-derived cutoffs, a VPW measurement of 74.5 mm was found to have a sensitivity of 83% and a specificity of 78% for correctly predicting a fluid overloaded state.

Conclusion

These results suggest that serial measurements of the VPW can reliably be used to predict intravascular volume overload in the ICU.