Hisamuddin, Nik, et al. “Ultrasonographic assessment of inferior vena cava/abdominal aorta diameter index: a new approach of assessing hypovolemic shock class 1.” International Journal of Emergency Medicine (2016) 9:8.
A cross-sectional, prospective, observational study of 52 healthy blood donors in Malaysia compared IVC to Aorta diameters using ultrasound pre- and post-blood donation to evaluate a potential marker of class 1 hypovolemic shock. Patients donated a mean of 450 cc of blood. The mean IVC/Aorta pre-donation was 1.21 ± 0.20 and IVC/Aorta post-donation was 1.14 ± 0.18. The study proposed that an IVC/Aorta proportion below 1.14 can be considered type 1 hypovolemic shock. The study was the first to use IVC:AA measurement to evaluate shock, however the study population was limited to healthy adults 18-55 years, over 45 kg, with no medical problems and on no medications.
Stawicki, Stanislaw, et al. “Prospective evaluation of intravascular volume status in critically ill patients: Does inferior vena cava collapsibility correlate with central venous pressure?” Journal of Trauma Acute Care Surgery (2013) 76:4.
A prospective, observational study of 79 surgical/medical intensive care unit patients in the United States and India compared the inferior vena cava collapsibility index (IVC-CI) and central venous pressure (CVP) to assess intravascular volume status. Results comparing IVC-CI to CVP correlated poorly and were loosely inversely proportional. Only those with the lowest (<25%) and highest collapsibility (>75%) were found to have significant differences in their mean CVP (6.51 vs. 4.63, respectively). Those with intermediate collapsibility did not have statistically different CVP measurements. The study was also limited by studying both intubated and non-intubated patients and difference in positioning amongst patients. The study was also rather difficult to read.
Blehar, David, et al. “Inferior vena cava displacement during respirophasic ultrasound imaging.” Critical Ultrasound Journal (2012) 4: 18.
A prospective study of 70 emergency department patients attempted to standardize IVC measurement technique to reduce error when evaluating for respiratory variation as a marker of volume status. The IVC was measured in both long axis and short axis and IVC movement was measured in both craniocaudal and mediolateral directions. Data showed that movement of the IVC was present in both craniocaudal (mean 21.7 mm) and mediolateral (mean 3.9 mm) directions. However, movement in either direction has limited evaluation based upon the transducer orientation. The study also found the axis of greatest collapse to be at 115°, not at the AP diameter of the vessel. Study was limited to healthy patients and not those in acute distress, so data is not easily generalizable to sicker populations.
Yamanoglu, Adnan, et al. “The role of inferior vena cava diameter in the differential diagnosis of dyspneic patients; best sonographic measurement method?” American Journal of Emergency Medicine (2015) 12: 32.
A prospective observational study conducted in the ICU in Turkey evaluated IVC diameter measurement suitability for differentiation of cardiac vs. pulmonary causes of dyspnea in 74 adult patients. IVC measurements during inspiration and exhalation were measured in B-mode and M-mode. These measurements were then compared with other data points that ultimately diagnosed patients with cardiac vs. pulmonary causes of dyspnea. The study found that B-mode measurements of the IVC during inspiration >9mm was 84.4% sensitive and 92.9% specific for cardiac dyspnea. The study was limited as it was single center study and had uneven gender populations (35.1% female, 64.9% male).
Fields, J. Matthew, et al. “The interrater reliability of inferior vena ultrasound by bedside clinician sonographers in emergency department patients.” Society for Academic Emergency Medicine (2011) 18: 1.
A prospective observational double-blinded study evaluated interrater reliability of emergency department physicians’ measurements of the IVC via ultrasound using visual estimation, M-mode and B-mode. 5 physicians evaluated 46 patients. 4 measurements were obtained: M-mode diameter, B-mode diameter, B-mode area, and visual estimation. No significant differences were found amongst all 4 measurements. Interrater agreement was strong between M-mode IVC diameter measurements and moderate between M-mode IVC collapsibility index. Improvements in interrater reliability was noted when assessing both hyper- and hypo-volemic patients (extremes of volume status) and when sonographers had performed 5 exams previously. The study was limited by Hawthorne effect as sonographers knew their measurements were being studied.
Feissel, Marc, et al. “The respiratory variation in inferior vena cava diameter as a guide to fluid therapy.” Intensive Care Med (2014) 30: 1834-1837.
A prospective study of 39 mechanically ventilated patients with septic shock evaluated respiratory variation in IVC diameter as a measure of fluid responsiveness. The IVC diameter variation (DDIVC) was measured by subtracting the minimum diameter from the maximum diameter over a single respiratory cycle. Cardiac output (CO) was also measured in each patient by the diameter of the aortic orifice and using velocity time integral. DDIVC and CO was measured in each patient pre- and post a standardized volume challenge. Volume expansion lead to significantly increased CO, maximum DIVC, minimum DIVC and significantly decrease in DDIVC. A higher DDIVC correlated strongly with greater increase in CO after volume loading (r2 = 0.68). This study was limited to a specific population of ventilated patients with septic shock so is not generalizable.
Prekker, Matthew E., et al. “Point-of-care ultrasound to estimate central venous pressure: A comparison of three techniques.” Journal of Critical Care Medicine (2013)
A cross-sectional study of 65 spontaneously breathing medical ICU patients with intrathoracic central venous catheters compared three different ultrasound parameters to determine which correlated best with CVP. Ultrasonographers in this study were blinded. The three ultrasound measurements were an internal jugular (IJ) aspect ratio (IJ height/IJ width), maximal IVC size, and IVC collapsibility with inspiration ([IVCdmax – IVCdmin]/IVCdmax x 100%. Of the three measurements, a maximal IVC diameter was found to have the best correlation with CVP. A measurement <2 cm predicted a CVP < 10 mm Hg with 85% sensitivity and 81% specificity. The study was limited by ICU patients who had already received resuscitation, most were in septic shock, and inter and intra-rater reliability were not compared between ultrasound techniques.
Schefold, Joerg C., et al. “Inferior vena cava diameter correlates with invasive hemodynamic measures in mechanically ventilated intensive care unit patients with sepsis.” The Journal of Emergency Medicine (2010) 38:5.
A prospective study of 30 mechanically ventilated ICU patients with severe sepsis or septic shock was studied to evaluate correlation between IVC diameter and central venous pressures. This study found a significant correlation between both inspiratory and expiratory IVC diameter with central venous pressure, extravascular lung water index, intrathoracic blood volume index, and intrathoracic blood volume index, intrathoracic thermal volume, and PaO2/FiO2 oxygenation index. The study controlled for BMI, body surface area, age, sex, and vasopressor dose. **This study may be difficult to read.
Ciozda, William, et al. “The efficacy of sonographic measurement of inferior vena cava diameter as an estimate of central venous pressure.” Cardiovascular Ultrasound (2016) 14:33.
This systematic review of 21 studies evaluated data in existing literature to look at clinical accuracy of IVC diameter as a measurement of central venous pressure (CVP) and right atrial pressure (RAP). A total of 1430 patients across studies were examined. This review found that all studies noted positive correlation between IVC size and CVP or RAP and negative correlations between IVC collapsibility index (IVCCI) and CVP or RAP with moderate to strong evidence. There was substantial heterogeneity in timing of IVC measurement, indicating that correlations between IVC diameter and CVP were similar regardless of timing of respiratory cycle during measurement. However, the study found that IVC and CVP correlated poorly in mechanically ventilated patients, young elite athletes, patients with vasovagal syncope, patients with atrial fibrillation, and patients with cardiac transplants. Finally, the study recommends serial IVC measurements as findings demonstrated increase in IVC diameter after fluid resuscitation correlated with increases in CVP.
Nagdev, Arun D., et al. “Emergency department bedside ultrasonographic measurement of the caval index for noninvasive determination of low central venous pressure.” Annals of Emergency Medicine (2010) 55:3.
A prospective, observational study of 73 patients undergoing central venous catheterization evaluated whether a caval index >50% correlated with a CVP <8 mm Hg. It also evaluated whether emergency physicians were equipped to make caval index measurements. Study staff were blinded to the patients they were scanning. Caval index was calculated as expiratory (IVC – inspiratory IVC) / expiratory IVC. Correlation between caval index and CVP was -0.74 and each 12.5% increase in IVC caval index predicted a 1 mm Hg decrease in CVP with R2 = 0.54, which was considered a strong predictor. Sensitivity was 91%, specificity was 94%, PPV was 87% and NPV was 96%. The study was limited as all ED physicians were ultrasound fellows and may be more experienced, no interrater reliability was measured, and the study selection of participants was a convenience sample, not random.
Ng, Lorraine, et al. “Does bedside sonographic measurement of the inferior vena cava diameter correlated with central venous pressure in the assessment of intravascular volume in children?” Pediatric Emergency Care (2013) 29: 3
A prospective observational study of 51 children aged <21 who required invasive hemodynamic monitoring examined whether the same strong correlation between IVC measurements and CVP measurements in adults applied to a pediatric population. They also evaluated whether a sagittal or transverse view was best to view a pediatric IVC. Study staff was blinded to CVP measurements. The study found no significant correlation between collapsibility index and CVP measurements. Sagittal view of IVC was visualized in 100% of patients whereas transverse view of IVC was visualized in only 84% of patients. Some differences between this study and a previous study evaluating adults (#10) were that in this study 67% of patients were intubated vs. 19% in the adult study. In addition, 65% of patients had a femoral venous catheter which limits CVP measurements.
Weeks, Anthony J., et al. “The effect of weight based volume loading on the inferior vena cava in fasting subjects: a prospective randomized double-blinded trial” Academic Emergency Medicine (2012) 19: 8.
A prospective, randomized, double-blinded trial of 42 healthy fasting adult patients examined differences in IVC measurements before and after receiving a 2 ml/kg (control), 10 mg/kg, or 30 mg/kg fluid bolus. The study hypothesized that larger fluid boluses would result in larger proportional IVC changes. No statistical significance between IVC measurements were found amongst groups, despite receiving different volumes of fluid. In addition, baseline IVC measurements were very variable. The study cautions employing IVC ultrasound to clinically determine fluid status. The study was limited by a small sample size.
Wallace, David et al. “Inferior vena cava percentage collapse during respiration is affected by the sampling location: An ultrasound study in healthy volunteers” Academic of Emergency Medicine (2010) 17: 1.
This prospective study in 39 healthy adults evaluated difference in percentage collapse in 3 different areas of the IVC: at the level of the diaphragm, hepatic vein inlet, and left renal vein. Results found significant differences between mean collapse at the diaphragm (20%) compared to the hepatic vein inlet (30%) or compared to the left renal vein (35%), but no significant differences between the latter two. The study thus recommends avoiding IVC measurements at level of the diaphragm. The study was limited by including healthy volunteers only.