• Celso A Hernandez, Kathryn L Reed, Elizabeth B Juneman, and Wayne R Cohen.
• Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology (C.A.H., K.L.R., W.R.C.), and Division of Cardiovascular Medicine, Department of Medicine, (E.B.J.) University of Arizona College of Medicine, Tucson, Arizona USA. celsohernandezmd@gmail.com.
• J Ultrasound Med. 2016 Feb 1; 35 (2): 389-94.

ObjectivesThe purpose of this study was to determine whether the inferior vena caval (IVC) diameter is influenced by intravascular volume changes in pregnancy.MethodsA prospective observational study was done on 2 groups of normal term gravidas. In 24 patients, we measured the IVC diameter, blood pressure, and heart rate (HR) before and after a 1-L fluid infusion in preparation for regional anesthesia, after initiation of an epidural block, and within 24 hours postpartum. In a second group of 15 women, we measured the IVC diameter sequentially during a 1-L crystalloid infusion.ResultsIn the first group, the mean baseline IVC diameter ± SD at end-inspiration was 1.45 ± 0.32 cm, which was 19% smaller than at end-expiration (1.73 ± 0.31 cm; P= .003). This respiratory cycle variation remained significant at each measurement epoch. The mean caval diameter at end-inspiration increased by 23% after the fluid bolus (P = .012). Hydration was not, however, accompanied by any significant change in the HR, mean arterial pressure, or collapsibility index of the inferior vena cava. With epidural anesthesia, the mean arterial pressure decreased from 88 ± 9 to 80 ± 7 mm Hg (P= .018), but the HR and collapsibility index remained unchanged. Postpartum values were not significantly different from their baseline measurements, except for the mean arterial pressure, which was lower by about 6 mm Hg (P = .042). In the second group, the IVC diameter at end-inspiration increased by 31% after the 1-L infusion, and there was a positive correlation between the volume infused and the IVC diameter (r= 0.67; P< .0001).ConclusionsMeasurable variations in the IVC diameter occur in response to volume changes in normal term pregnancy and postpartum.© 2016 by the American Institute of Ultrasound in Medicine.

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