Ultrasound reference values for inferior vena cava diameter and collapsibility index among adult Nigerians

Background: Correct estimation of intravascular volume is crucial in critically ill and traumatized patients. Measurement of the central venous pressure (CVP) is invasive and time consuming. Studies have shown that inferior vena cava diameter (IVCD) correlates with CVP. Sonographic assessment of IVCD and its respirophasic changes (collapsibility index; CI) is a non-invasive, quick and reliable means of estimating CVP and hence, intravascular fluid volume. Data on such studies are scanty among adult Nigerians. Aim: To establish normograms of IVCD and CI for healthy adults in Benin City, Nigeria as well as determine the relationship of IVCD and CI with height, weight, body mass index (BMI), age and gender. Method: Four hundred apparently healthy adult volunteers were prospectively studied by means of ultrasound. Demographic data and BMI were obtained. The IVCD was measured during inspiration, expiration and sniff. The CI was subsequently calculated for each subject. Statistical Package for the Social Sciences (SPSS) version 17.0 was used for data analysis including tests of significance. Probability values less than or equal to 0.05 were considered significant. Results: The mean IVCD in this study was 6.1±2.2mm and 13.0±4.0 mm for inspiration and expiration respectively. The mean CI was 49.7±0.5%. There was no statistically significant correlation between IVCD and CI with height and BMI. Conclusion: This study has determined normal IVCD and CI reference range for healthy Nigerian adults. The CI is independent of height, weight, BMI and gender. Since the CI is not dependent on physical attributes and gender, it may serve as an objective tool for monitoring the fluid status of patient