• Qing Zhang, Dawei Liu, Xiaoting Wang, Hongmin Zhang, Huaiwu He, Yangong Chao, Chunxian Wang, and China Critical Ultrasound Study Group (CCUSG).
• Department of Critical Care Medicine, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing 100730, China.
• Zhonghua Nei Ke Za Zhi. 2014 Nov 1;53(11):880-3.

ObjectiveTo investigate the inferior vena cava internal diameter (IVCID) and inferior vena cava variability (IVCV) on longitudinal plane measured from subcostal area and right mid-axillary line through ultrasonography and to find out if the measuring site and different respiratory status were related to the IVCID and IVCV.MethodsA total of 127 patients were enrolled successively in Critical Care Medical Department of Peking Union Medical Hospital from November to December, 2013. IVCID and IVCV of patients on mechanical ventilation or with spontaneous breathing were measured longitudinally from subcostal area and right mid-axillary line.Results(1) Totally 124 out of the 127 patients achieved measurement from right mid-axillary line, while only 83 patients achieved measurement from subcostal area. The difference was statistically significant (χ(2) = 74.42, P < 0.01) . Eighty-one patients can be measured from both sites, with 44 had spontaneous breathing and 37 on mechanical ventilation. (2)Whether in spontaneous or mechanically ventilated patients, IVCID measured from subcostal area was statistically different from right mid-axillary line measurement at both end expiration and end inspiration. (3) In mechanically ventilated patients with IVCID ≥ 2 cm measured from subcostal area at end expiration, no statistical difference was found between the IVCID from right mid-axillary line and from subcostal area[ (2.25 ± 0.32) cm vs (2.10 ± 0.12) cm, P = 0.083]. In spontaneous breathing patients with IVCID ≥ 2 cm measured from subcostal area at end expiration, there were significant differences between the IVCID from right mid-axillary line and from subcostal area at both end expiration and end inspiration. The IVCV between the two sites were also statistically different. In mechanically ventilated patients with IVCID ≤ 1.5 cm measured from subcostal area at end expiration, there were significant difference between the IVCID from right mid-axillary line and from subcostal area [ (1.58 ± 0.43) cm vs (1.09 ± 0.38) cm, P = 0.026]. In spontaneous breathing patients with IVCID ≤ 1.5 cm measured from subcostal area at end expiration, there were significant difference between the IVCID from right mid-axillary line and from subcostal area at both end expiration and end inspiration. The IVCV between the two sites were also statistically different. (4) Correlation analysis showed in mechanically ventilated patients, IVCID measured from right mid-axillary line at end expiration was correlated with the IVCID measured from subcostal area at end expiration(r = 0.565, P = 0.000). In spontaneous breathing patients, IVCID measured at end expiration from right mid-axillary line was correlated with the IVCID measured from subcostal area (r = 0.526, P = 0.000) . IVCID measured at end inspiration from right mid-axillary line was correlated with the IVCID measured from subcostal area (r = 0.454, P = 0.002). IVCV measured from right mid-axillary line was correlated with IVCV measured from subcostal area (r = 0.513, P = 0.000).ConclusionsInferior vena cava internal diameter and variability measured longitudinally through ultrasonography from subcostal area is different with measurements from right mid-axillary line. Measurements from the two sites are not replaceable with each other. Further studies are needed before the clinical use of inferior vena cava internal diameter and variability measured from right mid-axillary line.

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