Identification of the hydration state in emergency patients: correlation between caval index and BUN/creatinine ratio

Dehydration is a frequent clinical problem. No single laboratory value has been found to be accurate; however, the BUN/Creatinine Ratio appears the most sensitive parameter. The respiratory variation (Caval Index, CIn) in the diameter of the inferior vena cava has been investigated as a non-invasive marker for the intravascular volume status.

The present study is performed with the aim to explore the relationship between CIn and BUN/creatinine ratio.

This prospective, observational study was conducted at Emergency Department (ED) of San Paolo Hospital (Savona, Italy), in October 2011.

113 patients were considered eligible (mean age of 63 years). We found a good correlation between CIn and BUN/Cr Ratio (Pearson Index 0.76, p < 0.001). Receiver operator characteristic curve (ROC) analyses indicated that the maximum value was 0.884 (p < 0.0001) and corresponded to CIn 60.7%, (sensitivity 79%, specificity 89%). CIn was a good predictor for patients with BUN/Cr ratio greater than 20, and was particularly strong in determining patients with lower BUN/Cr ratio.

Our study suggests that inferior vena cava could provide indications on the state of hydration of the patients: we found that a caval index greater than or equal to 60% was associated with a BUN/Cr Ratio over 20, which is considered an important marker for dehydration. Therefore, bedside sonography can give emergency physicians immediate information on patient volume status long before obtaining laboratory findings.

Our study seems to support the hypothesis that CIn can be a useful bedside marker to predict dehydration in Emergency Department (ED) patients.