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Inferior Vena Cava Collapsibility Index: Clinical Validation and Application for Assessment of Relative Intravascular Volume

      Accurate assessment of relative intravascular volume is critical to guide volume management of patients with acute or chronic kidney disorders, particularly those with complex comorbidities requiring hospitalization or intensive care. Inferior vena cava (IVC) diameter variability with respiration measured by ultrasound provides a dynamic noninvasive point-of-care estimate of relative intravascular volume. We present details of image acquisition, interpretation, and clinical scenarios to which IVC ultrasound can be applied. The variation in IVC diameter over the respiratory or ventilatory cycle is greater in patients who are volume responsive than those who are not volume responsive. When 2 recent prospective studies of spontaneously breathing patients (n = 214) are added to a prior meta-analysis of 181 patients, for a total of 7 studies of 395 spontaneously breathing patients, IVC collapsibility index (CI) had a pooled sensitivity of 71% and specificity of 81% for predicting volume responsiveness, which is similar to a pooled sensitivity of 75% and specificity of 82% for 9 studies of 284 mechanically ventilated patients. IVC maximum diameter <2.1 cm, that collapses >50% with or without a sniff is inconsistent with intravascular volume overload and suggests normal right atrial pressure (0-5 mmHg). Inferior vena cava collapsibility (IVC CI) < 20% with no sniff suggests increased right atrial pressure and is inconsistent with overt hypovolemia in spontaneously breathing or ventilated patients. These IVC CI cutoffs do not appear to vary greatly depending on whether patients are breathing spontaneously or are mechanically ventilated. Patients with lower IVC CI are more likely to tolerate ultrafiltration with hemodialysis or improve cardiac output with ultrafiltration. Our goal for IVC CI generally ranges from 20% to 50%, respecting potential biases to interpretation and overriding clinical considerations. IVC ultrasound may be limited by factors that affect IVC diameter or collapsibility, clinical interpretation, or optimal visualization, and must be interpreted in the context of the entire clinical situation.

      Keywords

      • A major utility of IVC ultrasound is to potentially decrease the likelihood of either overt relative intravascular hypervolemia or hypovolemia, in a given patient.
      • Recent data indicate that volume responsiveness can be predicted with similar accuracy for spontaneously breathing (pooled sensitivity 71%, specificity 81%) and for mechanically ventilated patients (pooled sensitivity 75%, specificity 82%).
      • IVC maximum diameter <2.1 cm, that collapses >50% with or without a sniff is inconsistent with intravascular volume overload and suggests normal mean RAP 0 to 5 mmHg, while IVC CI <20% (with moderate to large IVC diameter) with spontaneous inspiration or mechanical ventilation is inconsistent with intravascular volume depletion and suggests elevated mean RAP ≥15 mmHg.
      • The goal for IVC collapsibility index is in the range of 20% to 50%, respecting that there are many potential biases to interpretation and overriding clinical considerations.

      Background

      History, physical findings, and laboratory tests have limited sensitivity and specificity to assess relative intravascular volume or volume responsiveness.
      • Marik P.E.
      Fluid responsiveness and the Six guiding principles of fluid resuscitation.
      • Bentzer P.
      • Griesdale D.E.
      • Boyd J.
      • MacLean K.
      • Sirounis D.
      • Ayas N.T.
      Will this hemodynamically unstable patient respond to a Bolus of Intravenous Fluids?.
      • McGee S.
      • Abernethy 3rd, W.B.
      • Simel D.L.
      The rational clinical examination. Is this patient hypovolemic?.
      • Tuy T.
      • Peacock WFt
      Fluid overload assessment and management in heart failure patients.
      The clinical determination of relative intravascular volume and prediction of response to a volume intervention may be more difficult in hospitalized or critically ill patients because they are frequently not in a steady state, and may have mismatch between relative intravascular volume and blood pressure, or between intravascular and extravascular volume.
      • Kaptein M.J.
      • Kaptein E.M.
      Focused Real-time ultrasonography for Nephrologists.
      For example, severe vasoconstriction can elevate blood pressure in a volume-depleted patient. Patients may have low blood pressure and intravascular volume overload due to cardiac dysfunction, or vasodilation after volume resuscitation. Mismatch between intravascular and extravascular volume may occur due to delayed re-equilibration. IVC ultrasound provides a more direct assessment of relative intravascular volume status.

      Procedures and Technical Steps

      Subcostal View

      We begin by visualizing the heart using the subcostal approach in most supine patients, with a phased-array (cardiac) or curvilinear (abdominal) probe. The probe is then rotated vertically, with the orientation marker pointed cranially, and moved 1 to 2 cm to the right of the patient's midline, while maintaining visualization of the right atrium (RA), to view the inferior venal cava (IVC) in its long axis (Fig 1A).
      Figure thumbnail gr1
      Figure 1(A) Subcostal IVC window. Subcostal landmarks, position of ultrasound probe for visualization of the inferior vena cava (IVC) (also see A). The IVC is located to the right of midline and aorta (AO) as shown in the left panel. The corresponding ultrasound image of the IVC is shown in the right panel. It is recommended that the IVC be measured 3 to 4 cm from the right atrium (RA) or distal to the hepatic vein.
      • Caplan M.
      • Durand A.
      • Bortolotti P.
      • et al.
      Measurement site of inferior vena cava diameter affects the accuracy with which fluid responsiveness can be predicted in spontaneously breathing patients: a post hoc analysis of two prospective cohorts.
      The hepatic vein junction to the IVC and the IVC junction to right atrium are confirmatory landmarks. Reprinted with permission from Killu and colleagues.
      • Killu K.
      • Dulchavsky S.A.
      • Coba V.
      The ICU Ultrasound Pocket Book.
      (B, available at: http://doi.org/10.1053/j.ackd.2021.02.003.):Video of the relationship of the IVC to the aorta viewed from the subcostal view while fanning the probe from left to right.
      One must fan the probe to intentionally view the aorta to the left of the midline in every patient to be sure it is not mistaken for the IVC, and to visualize the junction of the IVC with the RA
      • Seif D.
      • Mailhot T.
      • Perera P.
      • Mandavia D.
      Caval sonography in shock: a noninvasive method for evaluating intravascular volume in critically ill patients.
      (Supplementary Fig 1B, available at: http://doi.org/10.1053/j.ackd.2021.02.003). There are very few instances in which the IVC can be seen but not the aorta, while if only the aorta is visualized, the IVC may be totally collapsed.
      The maximum and minimum diameters of the IVC with respiration/ventilation are most accurately measured 3 to 4 cm from the RA or approximately 1 cm distal to the hepatic vein inlet to the IVC
      • Caplan M.
      • Durand A.
      • Bortolotti P.
      • et al.
      Measurement site of inferior vena cava diameter affects the accuracy with which fluid responsiveness can be predicted in spontaneously breathing patients: a post hoc analysis of two prospective cohorts.
      ,
      • Seif D.
      • Mailhot T.
      • Perera P.
      • Mandavia D.
      Caval sonography in shock: a noninvasive method for evaluating intravascular volume in critically ill patients.
      ,
      • Beigel R.
      • Cercek B.
      • Luo H.
      • Siegel R.J.
      Noninvasive evaluation of right atrial pressure.
      (Fig 1A). In a large prospective study, inter-rater reliability was highest using the subcostal window long axis view in B-mode.
      • Finnerty N.M.
      • Panchal A.R.
      • Boulger C.
      • et al.
      Inferior vena cava measurement with ultrasound: what is the best view and best mode?.
      We find the subcostal window to be particularly useful in patients who are morbidly obese or otherwise have large body habitus because the needed depth may be much greater from the mid-axillary line than from the subcostal view.

      Midaxillary (Right Lateral Transabdominal Coronal Long Axis) View

      With the patient supine and the orientation marker pointed cranially, the probe is moved laterally to the patient's right in line with the sternal notch to over the lower ribs until your hand touches the bed (knuckles to the bed) (Fig 2A). The probe is then tilted anteriorly at an angle similar to the one used to visualize the kidney. It may be helpful to visualize aiming just anterior to the spine. The IVC crosses the diaphragm just inferior to the heart and traverses the liver. Traversing the abdomen, the aorta runs parallel to the IVC, farther from the probe (Fig 2B).
      Figure thumbnail gr2
      Figure 2(A) Ultrasound probe positions. Adapted from Perera and colleagues
      • Perera P.
      • Mailhot T.
      • Riley D.
      • Mandavia D.
      The RUSH exam: rapid Ultrasound in SHock in the evaluation of the critically lll.
      with permission. Parasternal long- and short-axis views (phased-array). Subcostal cardiac view (phased-array or curvilinear probe). IVC long-axis view subcostal (phased-array or curvilinear). IVC long-axis view from mid-axillary line (phased-array or curvilinear). (B) Ultrasound images corresponding to IVC long-axis from midaxillary line. The IVC is to the right of patient's midline and will be closer to the probe than the aorta.
      We find the midaxillary view to be particularly useful in patients with large anterior thoracic or abdominal surgical incisions, when the patient has anterior abdominal pain or distention, and in other instances when using the subcostal window is limited. In such difficult cases, the IVC may be visualized in the right midaxillary line and measured approximately 3 cm caudal to the RA (Fig 2).
      • Finnerty N.M.
      • Panchal A.R.
      • Boulger C.
      • et al.
      Inferior vena cava measurement with ultrasound: what is the best view and best mode?.
      Inter-rater reliability is reasonable for this approach.
      • Finnerty N.M.
      • Panchal A.R.
      • Boulger C.
      • et al.
      Inferior vena cava measurement with ultrasound: what is the best view and best mode?.

      B-Mode vs M-Mode

      Measuring IVC maximum and minimum diameters using M mode has not been shown to be superior to choosing maximum and minimum diameters viewed frame by frame in B-Mode.
      • Finnerty N.M.
      • Panchal A.R.
      • Boulger C.
      • et al.
      Inferior vena cava measurement with ultrasound: what is the best view and best mode?.
      ,
      • Fields J.M.
      • Lee P.A.
      • Jenq K.Y.
      • Mark D.G.
      • Panebianco N.L.
      • Dean A.J.
      The interrater reliability of inferior vena cava ultrasound by bedside clinician sonographers in emergency department patients.

      Calculation of Collapsibility Index vs Distensibility Index

      The physiology of spontaneous breathing is different from that of mechanical ventilation. During spontaneous inspiration, negative intrathoracic pressure increases venous flow to the heart and reduces the IVC diameter.
      • Natori H.
      • Tamaki S.
      • Kira S.
      Ultrasonographic evaluation of ventilatory effect on inferior vena caval configuration.
      At end expiration, the intrathoracic pressure increases to zero, decreasing the venous return and maximizing the IVC diameter.
      • Natori H.
      • Tamaki S.
      • Kira S.
      Ultrasonographic evaluation of ventilatory effect on inferior vena caval configuration.
      This has been defined as collapsibility index (CI).
      • Natori H.
      • Tamaki S.
      • Kira S.
      Ultrasonographic evaluation of ventilatory effect on inferior vena caval configuration.
      CI = (IVC max-IVC min)/IVC max.
      With mechanical ventilation, the cycle is inverted. Positive intrathoracic pressure during inspiration reduces the venous flow to the heart and increases the IVC diameter. At end expiration, the intrathoracic pressure decreases to zero, increasing the venous flow to the heart and minimizing IVC diameter.
      • Natori H.
      • Tamaki S.
      • Kira S.
      Ultrasonographic evaluation of ventilatory effect on inferior vena caval configuration.
      ,
      • Barbier C.
      • Loubieres Y.
      • Schmit C.
      • et al.
      Respiratory changes in inferior vena cava diameter are helpful in predicting fluid responsiveness in ventilated septic patients.
      This has been defined as distensibility index (DI).
      • Barbier C.
      • Loubieres Y.
      • Schmit C.
      • et al.
      Respiratory changes in inferior vena cava diameter are helpful in predicting fluid responsiveness in ventilated septic patients.
      DI = (IVC max-IVC min)/IVC min.
      Changes in IVC diameter do not appear to vary greatly depending on the mechanism by which intrathoracic pressure is changed.
      • Kaptein M.J.
      • Kaptein J.S.
      • Oo Z.
      • Kaptein E.M.
      Relationship of inferior vena cava collapsibility to ultrafiltration volume achieved in critically ill hemodialysis patients.
      The convention to normalize by end-expiratory diameter, using CI for spontaneous breathing and DI for ventilated breathing in some publications, does not readily allow comparison of data between ventilated and spontaneously breathing encounters. CI and DI can be interconverted: CI = DI/(1 + DI); DI = CI/(1-CI).
      Some authors normalize by the mean IVC diameter, which we term variability index: VI = (IVC max-IVC min)/IVC mean; CI = 2 ∗ VI/(2 + VI).
      For consistency and convenience, we calculate CI for all of our patients, both ventilated and nonventilated. As many patients cannot perform voluntary maneuvers such as a sniff, which can accentuate IVC collapse,
      • Seif D.
      • Mailhot T.
      • Perera P.
      • Mandavia D.
      Caval sonography in shock: a noninvasive method for evaluating intravascular volume in critically ill patients.
      ,
      • Laborda A.
      • Sierre S.
      • Malve M.
      • et al.
      Influence of breathing movements and Valsalva maneuver on vena caval dynamics.
      for consistency we do not routinely use a sniff. The IVC diameters are recorded over several respiratory cycles with spontaneous respiration or mechanical ventilation.
      • Seif D.
      • Perera P.
      • Mailhot T.
      • Riley D.
      • Mandavia D.
      Bedside ultrasound in resuscitation and the rapid ultrasound in shock protocol.

      Accuracy of Predicting Volume Responsiveness in Patients Who Are Mechanically Ventilated Compared with Those Who Are Spontaneously Breathing

      A current meta-analysis
      • Si X.
      • Cao D.
      • Xu H.
      • Guan X.
      Meta-analysis of ventilated versus spontaneously breathing patients in predicting fluid responsiveness by inferior vena cava variation.
      indicates that the reliability of IVC diameter variation with respiration to predict volume responsiveness is greater in mechanically ventilated patients than those with spontaneous breathing. In this comparison, 284 patients in 9 studies with mechanical ventilation had a pooled sensitivity of 75% and specificity of 82%, whereas 181 spontaneously breathing patients reported in 5 studies had a pooled sensitivity of 56% and specificity of 78%. The quality of these studies varied, with heterogeneity with respect to patient population, sample size, definition of index test such as change in cardiac output or stroke volume and in one study, change in blood pressure to define volume responsiveness, and method for determining optimal cutoff values for the IVC index which may favor sensitivity or specificity.
      • Bentzer P.
      • Griesdale D.E.
      • Boyd J.
      • MacLean K.
      • Sirounis D.
      • Ayas N.T.
      Will this hemodynamically unstable patient respond to a Bolus of Intravenous Fluids?.
      ,
      • Si X.
      • Cao D.
      • Xu H.
      • Guan X.
      Meta-analysis of ventilated versus spontaneously breathing patients in predicting fluid responsiveness by inferior vena cava variation.
      ,
      • Orso D.
      • Paoli I.
      • Piani T.
      • Cilenti F.L.
      • Cristiani L.
      • Guglielmo N.
      Accuracy of Ultrasonographic measurements of inferior vena cava to determine fluid responsiveness: a systematic review and meta-analysis.
      IVC CI cutoff values were not determined for equal sensitivity and specificity and varied widely among studies. Low sensitivity with spontaneous breathing was postulated to be due to shallow, nonstandardized breathing. However, if 2 large prospective studies of nonstandardized spontaneously breathing patients (n = 214)
      • Preau S.
      • Bortolotti P.
      • Colling D.
      • et al.
      Diagnostic accuracy of the inferior vena cava collapsibility to predict fluid responsiveness in spontaneously breathing patients with Sepsis and acute Circulatory failure.
      ,
      • Corl K.A.
      • George N.R.
      • Romanoff J.
      • et al.
      Inferior vena cava collapsibility detects fluid responsiveness among spontaneously breathing critically-ill patients.
      reported since that meta-analysis
      • Si X.
      • Cao D.
      • Xu H.
      • Guan X.
      Meta-analysis of ventilated versus spontaneously breathing patients in predicting fluid responsiveness by inferior vena cava variation.
      are included, the pooled sensitivity is 71% and pooled specificity is 81%, which is similar to that of mechanically ventilated patients. The sensitivity and specificity of IVC ultrasound to predict volume responsiveness has been shown to be further improved by using deep standardized inspiration (pooled sensitivity 87%, pooled specificity 89%) in 146 spontaneously breathing patients from 2 prospective studies.
      • Preau S.
      • Bortolotti P.
      • Colling D.
      • et al.
      Diagnostic accuracy of the inferior vena cava collapsibility to predict fluid responsiveness in spontaneously breathing patients with Sepsis and acute Circulatory failure.
      ,
      • Bortolotti P.
      • Colling D.
      • Colas V.
      • et al.
      Respiratory changes of the inferior vena cava diameter predict fluid responsiveness in spontaneously breathing patients with cardiac arrhythmias.

      Patient Positioning

      In contrast to jugular venous distention or measurement of collapsibility of more peripheral veins, which are highly position dependent,
      • Meyer T.E.
      Examination of the jugular venous pulse.
      similar values for IVC CI have been obtained with patients in the semisupine position from 0 to 45° head-of-bed elevation.
      • Bondarsky E.
      • Rothman A.
      • Ramesh N.
      • Love A.
      • Kory P.
      • Lee Y.I.
      Influence of head-of-bed elevation on the measurement of inferior vena cava diameter and collapsibility.
      ,
      • Panebianco N.L.
      • Shofer F.
      • Cheng A.
      • Fischer J.
      • Cody K.
      • Dean A.J.
      The effect of supine versus upright patient positioning on inferior vena cava metrics.
      Consequently, for assessment of IVC CI, time-consuming repositioning can often be avoided.

      Clinical Utility of Cardiac and IVC Ultrasound

      Both cardiac and IVC ultrasound may be useful for the daily assessment of relative intravascular volume; need for and response to volume resuscitation or volume removal by diuresis, paracentesis, or ultrafiltration; and management of hyponatremia, hypernatremia, and intradialytic hypotension.

      Assessment of Relative Intravascular Volume

      The major clinical value of IVC ultrasound findings is to potentially eliminate either the possibility of overt relative intravascular hypervolemia or hypovolemia in a given patient. A patient with a small IVC maximum diameter or large IVC CI may be “euvolemic”, but is unlikely to have elevated cardiac filling pressures, and a patient with a large IVC maximum diameter and small IVC CI may be “euvolemic”, but is unlikely to have reduced cardiac filling pressures.
      • Beigel R.
      • Cercek B.
      • Luo H.
      • Siegel R.J.
      Noninvasive evaluation of right atrial pressure.
      ,
      • Rudski L.G.
      • Lai W.W.
      • Afilalo J.
      • et al.
      Guidelines for the echocardiographic assessment of the right heart in adults: a report from the American Society of Echocardiography endorsed by the European Association of Echocardiography, a registered branch of the European Society of Cardiology, and the Canadian Society of Echocardiography.

      Differentiate Types of Shock

      The RUSH (Rapid Ultrasound in SHock) protocol, which includes ultrasound assessment of the IVC diameter and its variation with respiration, is routinely used for the immediate assessment and management of shock and hypotension (Table 1).
      • Perera P.
      • Mailhot T.
      • Riley D.
      • Mandavia D.
      The RUSH exam: rapid Ultrasound in SHock in the evaluation of the critically lll.
      ,
      • Seif D.
      • Perera P.
      • Mailhot T.
      • Riley D.
      • Mandavia D.
      Bedside ultrasound in resuscitation and the rapid ultrasound in shock protocol.
      ,
      • Bagheri-Hariri S.
      • Yekesadat M.
      • Farahmand S.
      • et al.
      The impact of using RUSH protocol for diagnosing the type of unknown shock in the emergency department.
      In a prospective study, the overall sensitivity of the RUSH examination for diagnosing the type of shock was 88% and specificity was 96%, compared with the final shock diagnosis.
      • Bagheri-Hariri S.
      • Yekesadat M.
      • Farahmand S.
      • et al.
      The impact of using RUSH protocol for diagnosing the type of unknown shock in the emergency department.
      Ultrasound findings influenced management
      • Perera P.
      • Mailhot T.
      • Riley D.
      • Mandavia D.
      The RUSH exam: rapid Ultrasound in SHock in the evaluation of the critically lll.
      ,
      • Ghane M.R.
      • Gharib M.H.
      • Ebrahimi A.
      • et al.
      Accuracy of rapid ultrasound in shock (RUSH) exam for diagnosis of shock in critically ill patients.
      • Jones A.E.
      • Tayal V.S.
      • Sullivan D.M.
      • Kline J.A.
      Randomized, controlled trial of immediate versus delayed goal-directed ultrasound to identify the cause of nontraumatic hypotension in emergency department patients.
      • Haydar S.A.
      • Moore E.T.
      • Higgins 3rd, G.L.
      • Irish C.B.
      • Owens W.B.
      • Strout T.D.
      Effect of bedside ultrasonography on the certainty of physician clinical decisionmaking for septic patients in the emergency department.
      and were useful in guiding volume administration or restriction and vasopressor therapy, which resulted in improved 28-day patient survival, a reduction in stage 3 acute kidney injury (AKI), and more days alive and free of kidney support.
      • Kanji H.D.
      • McCallum J.
      • Sirounis D.
      • MacRedmond R.
      • Moss R.
      • Boyd J.H.
      Limited echocardiography-guided therapy in subacute shock is associated with change in management and improved outcomes.
      Table 1Ultrasound Findings in Classic Shock States
      Adapted from Perera et al
      • Perera P.
      • Mailhot T.
      • Riley D.
      • Mandavia D.
      The RUSH exam: rapid Ultrasound in SHock in the evaluation of the critically lll.
      with permission.
      ShockHypovolemicDistributiveCardiogenicObstructive
      HeartHypercontractile

      Small chamber size
      Hypercontractile (early sepsis)

      Hypocontractile (late sepsis)
      Hypocontractile

      Dilated heart
      Hypercontractile

       Pericardial effusion

       Cardiac tamponade

       RV strain

       Cardiac thrombus
      IVCCollapsing IVCNormal or small IVC (early sepsis)Distended IVCDistended IVC
      Abbreviations: RV, right ventricle; IVC, inferior vena cava.

      Differentiate Types of AKI

      Patients assessed to have intravascular hypovolemia are at high risk for decreased kidney perfusion, which may cause a rapidly reversible prerenal state vs acute tubular necrosis. Patients with severe intravascular volume overload may also have decreased kidney perfusion, especially with accompanying heart failure (cardiorenal), and may benefit from volume removal. Nonsteroidal anti-inflammatory drugs, calcineurin inhibitors, angiotensin-converting enzyme inhibitors, and angiotensin receptor blockers decrease kidney perfusion and can exacerbate any prerenal state. Patients who do not appear to have severely deranged relative intravascular volume status may be considered “euvolemic”. Such patients may have decreased kidney perfusion (prerenal) from hepatorenal syndrome, which may be reversible or lead to acute tubular necrosis. “Euvolemic” patients may also have primary postrenal (obstruction or retention) or intrarenal causes of AKI (as may patients with severely deranged intravascular volume status).

      Assess Patients With Cirrhosis and AKI

      IVC ultrasound can be useful to more accurately diagnose the cause of AKI in patients with cirrhosis assumed to have hepatorenal syndrome (HRS), which in turn can improve volume management and potentially improve outcomes. In an observational study of 53 cirrhotic patients with AKI assumed to have HRS-AKI and deemed to be adequately volume repleted, IVCmax and IVC CI were used to estimate relative intravascular volume, followed by volume management.
      • Velez J.C.Q.
      • Petkovich B.
      • Karakala N.
      • Huggins J.T.
      Point-of-Care echocardiography Unveils Misclassification of acute kidney injury as hepatorenal syndrome.
      Twenty-three percent had a ≥20% decrease in serum creatinine at 48 to 72 h following ultrasound-guided therapeutic volume management,
      • Velez J.C.Q.
      • Petkovich B.
      • Karakala N.
      • Huggins J.T.
      Point-of-Care echocardiography Unveils Misclassification of acute kidney injury as hepatorenal syndrome.
      making the diagnosis of HRS-AKI highly unlikely.

      Guide Volume Management With Diuretics and Dialysis Prescription

      Repeated evaluations of IVC CI with volume administration or removal can guide ongoing volume management and optimize therapy,
      • Seif D.
      • Perera P.
      • Mailhot T.
      • Riley D.
      • Mandavia D.
      Bedside ultrasound in resuscitation and the rapid ultrasound in shock protocol.
      which in turn may improve morbidity and mortality.
      • Ronco C.
      • Kaushik M.
      • Valle R.
      • Aspromonte N.
      • Peacock WFt
      Diagnosis and management of fluid overload in heart failure and cardio-renal syndrome: the “5B” approach.
      IVC CI assessment may be useful to predict or avoid intradialytic hypotension.
      • Kaptein M.J.
      • Kaptein J.S.
      • Oo Z.
      • Kaptein E.M.
      Relationship of inferior vena cava collapsibility to ultrafiltration volume achieved in critically ill hemodialysis patients.
      ,
      • Kaptein M.J.
      • Kaptein J.S.
      • Nguyen C.D.
      • et al.
      Changes in cardiac output with hemodialysis relate to net volume balance and to inferior vena cava ultrasound collapsibility in critically ill patients.
      The goal for IVC CI is in the range of 20% to 50% respecting that there are many potential biases to interpretation and overriding clinical considerations which include, for example, acute respiratory distress syndrome, desire to extubate that may require volume removal, or preload dependent conditions that may require volume loading
      • Kaptein M.J.
      • Kaptein E.M.
      Focused Real-time ultrasonography for Nephrologists.
      (Table 2).
      Table 2Conditions Biasing Inferior Vena Cava Ultrasound Findings
      Adapted from Kaptein and Kaptein
      • Kaptein M.J.
      • Kaptein E.M.
      Focused Real-time ultrasonography for Nephrologists.
      with permission.
      IVC CIIVC maxComments
      Underestimate Intravascular Volume
      • Via G.
      • Tavazzi G.
      • Price S.
      Ten situations where inferior vena cava ultrasound may fail to accurately predict fluid responsiveness: a physiologically based point of view.
       Increased tidal volume (ventilated)Increased
      • Preau S.
      • Bortolotti P.
      • Colling D.
      • et al.
      Diagnostic accuracy of the inferior vena cava collapsibility to predict fluid responsiveness in spontaneously breathing patients with Sepsis and acute Circulatory failure.
      No change?
       Increased inspiratory effort moving probe “in & out” of field (diaphragmatic breathing)
      • Seif D.
      • Mailhot T.
      • Perera P.
      • Mandavia D.
      Caval sonography in shock: a noninvasive method for evaluating intravascular volume in critically ill patients.
      IncreasedNo changeMid-axillary views
      • Abu-Zidan F.M.
      Optimizing the value of measuring inferior vena cava diameter in shocked patients.


      Cross-sectional view
      • Seif D.
      • Mailhot T.
      • Perera P.
      • Mandavia D.
      Caval sonography in shock: a noninvasive method for evaluating intravascular volume in critically ill patients.
       Increased inspiratory effort/deep breathing (sniff)
      • Beigel R.
      • Cercek B.
      • Luo H.
      • Siegel R.J.
      Noninvasive evaluation of right atrial pressure.
      ,
      • Rudski L.G.
      • Lai W.W.
      • Afilalo J.
      • et al.
      Guidelines for the echocardiographic assessment of the right heart in adults: a report from the American Society of Echocardiography endorsed by the European Association of Echocardiography, a registered branch of the European Society of Cardiology, and the Canadian Society of Echocardiography.
      ,
      • Gignon L.
      • Roger C.
      • Bastide S.
      • et al.
      Influence of Diaphragmatic Motion on inferior vena cava diameter respiratory variations in healthy volunteers.
      Increased

      • Si X.
      • Cao D.
      • Xu H.
      • Guan X.
      Meta-analysis of ventilated versus spontaneously breathing patients in predicting fluid responsiveness by inferior vena cava variation.
      ,
      • Preau S.
      • Bortolotti P.
      • Colling D.
      • et al.
      Diagnostic accuracy of the inferior vena cava collapsibility to predict fluid responsiveness in spontaneously breathing patients with Sepsis and acute Circulatory failure.
      No changeLarge IVC max with no collapse indicates not hypovolemic.
       Valsalva maneuver
      • Laborda A.
      • Sierre S.
      • Malve M.
      • et al.
      Influence of breathing movements and Valsalva maneuver on vena caval dynamics.
      IncreasedDecreasedLarge IVC max with no collapse indicates not hypovolemic.
       Intra-abdominal hypertension
      • Abu-Zidan F.M.
      Optimizing the value of measuring inferior vena cava diameter in shocked patients.
      ,
      • Wachsberg R.H.
      Narrowing of the upper abdominal inferior vena cava in patients with elevated intraabdominal pressure: sonographic observations.
      Decreased? (No data)
      • Velez J.C.Q.
      • Petkovich B.
      • Karakala N.
      • Huggins J.T.
      Point-of-Care echocardiography Unveils Misclassification of acute kidney injury as hepatorenal syndrome.
      Decreased
      • Abu-Zidan F.M.
      • Idris K.
      Sonographic measurement of the IVC diameter as an indicator for fluid resuscitation: Beware of the intra-abdominal pressure.
      ,
      • Bauman Z.
      • Coba V.
      • Gassner M.
      • et al.
      Inferior vena cava collapsibility loses correlation with internal jugular vein collapsibility during increased thoracic or intra-abdominal pressure.
      Large IVC max with no collapse indicates not hypovolemic.
       Off-center scan (cylinder tangent effect)
      • Blehar D.J.
      • Resop D.
      • Chin B.
      • Dayno M.
      • Gaspari R.
      Inferior vena cava displacement during respirophasic ultrasound imaging.
      Minimal changesDecreasedAttempt to maximize IVC diameter. Cross-sectional view
      • Seif D.
      • Mailhot T.
      • Perera P.
      • Mandavia D.
      Caval sonography in shock: a noninvasive method for evaluating intravascular volume in critically ill patients.
       Hemodialysis (extracorporeal blood, steal from heart)Increased?Decreased?
      Overestimate Intravascular Volume
      • Via G.
      • Tavazzi G.
      • Price S.
      Ten situations where inferior vena cava ultrasound may fail to accurately predict fluid responsiveness: a physiologically based point of view.
       Cardiac tamponadeDecreasedIncreasedPreload dependent
       Severe valvular stenosisDecreasedIncreased
      • Altunbas G.
      • Yuce M.
      • Ozer H.O.
      • et al.
      Impact of chronic Rheumatic Valve diseases on large Vessels.
      Preload dependent
       Massive pulmonary embolism
      • Seif D.
      • Mailhot T.
      • Perera P.
      • Mandavia D.
      Caval sonography in shock: a noninvasive method for evaluating intravascular volume in critically ill patients.
      Decreased?IncreasedPreload dependent
       Right ventricular myocardial infarction
      • Goldstein J.A.
      Pathophysiology and management of right heart ischemia.
      DecreasedIncreasedPreload dependent

      Decreased venous return to left ventricle
       Severe tricuspid regurgitationDecreased
      • Shapira Y.
      • Porter A.
      • Wurzel M.
      • Vaturi M.
      • Sagie A.
      Evaluation of tricuspid regurgitation severity: echocardiographic and clinical correlation.
      ,
      • Nishimura R.A.
      • Otto C.M.
      • Bonow R.O.
      • et al.
      2014 AHA/ACC guideline for the management of patients with valvular heart disease: executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines.
      Increased
      • Nishimura R.A.
      • Otto C.M.
      • Bonow R.O.
      • et al.
      2014 AHA/ACC guideline for the management of patients with valvular heart disease: executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines.
      Preload dependent

      IVC CI varies with relative intravascular volume with severe TR.
      • Vaturi M.
      • Shapira Y.
      • Vaknin-Assa H.
      • Oron A.
      • Matesko R.
      • Sagie A.
      Echocardiographic markers of severe tricuspid regurgitation associated with right-sided congestive heart failure.
       High PEEP
      • Jellinek H.
      • Krenn H.
      • Oczenski W.
      • Veit F.
      • Schwarz S.
      • Fitzgerald R.D.
      Influence of positive airway pressure on the pressure gradient for venous return in humans.
      Minimal change
      • Saritas A.
      • Zincircioglu C.
      • Uzun Saritas P.
      • Uzun U.
      • Kose I.
      • Senoglu N.
      Comparison of inferior vena cava collapsibility, distensibility, and delta indices at different positive pressure supports and prediction values of indices for intravascular volume status.
      ,
      • Molokoane-Mokgoro K.
      • Goldstein L.N.
      • Wells M.
      Ultrasound evaluation of the respiratory changes of the inferior vena cava and axillary vein diameter at rest and during positive pressure ventilation in spontaneously breathing healthy volunteers.
      Increased
      • Saritas A.
      • Zincircioglu C.
      • Uzun Saritas P.
      • Uzun U.
      • Kose I.
      • Senoglu N.
      Comparison of inferior vena cava collapsibility, distensibility, and delta indices at different positive pressure supports and prediction values of indices for intravascular volume status.
      ,
      • Molokoane-Mokgoro K.
      • Goldstein L.N.
      • Wells M.
      Ultrasound evaluation of the respiratory changes of the inferior vena cava and axillary vein diameter at rest and during positive pressure ventilation in spontaneously breathing healthy volunteers.
      No difference between PEEP 0 and PEEP 5 cmH20
      • Jellinek H.
      • Krenn H.
      • Oczenski W.
      • Veit F.
      • Schwarz S.
      • Fitzgerald R.D.
      Influence of positive airway pressure on the pressure gradient for venous return in humans.


      Different with PEEP 15
      • Mitaka C.
      • Nagura T.
      • Sakanishi N.
      • Tsunoda Y.
      • Amaha K.
      Two-dimensional echocardiographic evaluation of inferior vena cava, right ventricle, and left ventricle during positive-pressure ventilation with varying levels of positive end-expiratory pressure.
       Decreased tidal volumeDecreased
      • Si X.
      • Cao D.
      • Xu H.
      • Guan X.
      Meta-analysis of ventilated versus spontaneously breathing patients in predicting fluid responsiveness by inferior vena cava variation.
      ,
      • Preau S.
      • Bortolotti P.
      • Colling D.
      • et al.
      Diagnostic accuracy of the inferior vena cava collapsibility to predict fluid responsiveness in spontaneously breathing patients with Sepsis and acute Circulatory failure.
      No change?
       Decreased inspiratory effort/shallow breathing
      • Gignon L.
      • Roger C.
      • Bastide S.
      • et al.
      Influence of Diaphragmatic Motion on inferior vena cava diameter respiratory variations in healthy volunteers.
      ,
      • Kimura B.J.
      • Dalugdugan R.
      • Gilcrease 3rd, G.W.
      • Phan J.N.
      • Showalter B.K.
      • Wolfson T.
      The effect of breathing manner on inferior vena caval diameter.
      Decreased
      • Si X.
      • Cao D.
      • Xu H.
      • Guan X.
      Meta-analysis of ventilated versus spontaneously breathing patients in predicting fluid responsiveness by inferior vena cava variation.
      ,
      • Preau S.
      • Bortolotti P.
      • Colling D.
      • et al.
      Diagnostic accuracy of the inferior vena cava collapsibility to predict fluid responsiveness in spontaneously breathing patients with Sepsis and acute Circulatory failure.
      No change?Highly collapsible IVC indicates not hypervolemic.
      Abbreviations: CI, collapsibility index; IVC, inferior vena cava; IVCmax, IVC maximum diameter; PEEP, positive end-expiratory pressure; TR, tricuspid regurgitation.

      Comparison of Techniques to Assess Relative Intravascular Volume and Response to Volume Administration or Removal

      The only purpose of a volume challenge is to increase stroke volume or cardiac output by at least 10% to 15%, which has become the “gold standard” for assessing response to volume administration or removal.
      • Marik P.E.
      Fluid responsiveness and the Six guiding principles of fluid resuscitation.
      ,
      • Bentzer P.
      • Griesdale D.E.
      • Boyd J.
      • MacLean K.
      • Sirounis D.
      • Ayas N.T.
      Will this hemodynamically unstable patient respond to a Bolus of Intravenous Fluids?.
      Passive leg raising is a reversible surrogate for volume administration with respect to changes in cardiac output to predict volume responsiveness.
      • Nikravan S.
      • Song P.
      • Bughrara N.
      • Díaz-Gómez J.L.
      Focused ultrasonography for septic shock resuscitation.
      ,
      • Monnet X.
      • Teboul J.L.
      Prediction of fluid responsiveness in spontaneously breathing patients.
      Passive leg raising is unsuitable in principle for predicting which patients may benefit from volume removal.
      Only 50% of hemodynamically unstable critically ill patients respond to volume expansion with a significant increase in stroke volume or cardiac output.
      • Marik P.E.
      Fluid responsiveness and the Six guiding principles of fluid resuscitation.
      ,
      • Bentzer P.
      • Griesdale D.E.
      • Boyd J.
      • MacLean K.
      • Sirounis D.
      • Ayas N.T.
      Will this hemodynamically unstable patient respond to a Bolus of Intravenous Fluids?.
      ,
      • Michard F.
      • Teboul J.L.
      Predicting fluid responsiveness in ICU patients: a critical analysis of the evidence.
      ,
      • Marik P.E.
      • Baram M.
      • Vahid B.
      Does central venous pressure predict fluid responsiveness? A systematic review of the literature and the tale of seven mares.
      There is a need for readily available techniques to help differentiate patients who will benefit from volume expansion from those who may benefit from inotropic or vasopressor support but not volume therapy
      • Marik P.E.
      Techniques for assessment of intravascular volume in critically ill patients.
      or those who may benefit from volume removal using diuretics or ultrafiltration.
      • Malbrain M.L.
      • Marik P.E.
      • Witters I.
      • et al.
      Fluid overload, de-resuscitation, and outcomes in critically ill or injured patients: a systematic review with suggestions for clinical practice.

      Comparison of “Dynamic” to “Static” Parameters to Predict Responsiveness to Volume Administration or Removal

      In contrast to “static” measures of cardiac preload such as mean values for central venous pressure, right atrial pressure (RAP), or pulmonary artery occlusion pressure, which have low sensitivity and specificity to predict volume responsiveness,
      • Michard F.
      • Teboul J.L.
      Predicting fluid responsiveness in ICU patients: a critical analysis of the evidence.
      ,
      • Marik P.E.
      Techniques for assessment of intravascular volume in critically ill patients.
      ,
      • Kalantari K.
      • Chang J.N.
      • Ronco C.
      • Rosner M.H.
      Assessment of intravascular volume status and volume responsiveness in critically ill patients.
      IVC CI is a “dynamic” parameter, in that it reflects the interaction between the respiratory and cardiac cycles,
      • Si X.
      • Cao D.
      • Xu H.
      • Guan X.
      Meta-analysis of ventilated versus spontaneously breathing patients in predicting fluid responsiveness by inferior vena cava variation.
      similar to dynamic respiratory variation of central venous pressure
      • Mohsenin V.
      Assessment of preload and fluid responsiveness in intensive care unit. How good are we?.
      or RAP,
      • Magder S.
      • Georgiadis G.
      • Cheong T.
      Respiratory variations in right artial pressure predict the response to fluid challenge.
      as long as no obstruction or restriction of the vena cava is present (Fig 3). One study of dynamic RAP in 33 patients, using threshold of RAP respiratory variation ≥1 mmHg to predict volume responsiveness, had sensitivity of 91% and specificity of 92% to predict an increase of cardiac output >250 mL/min after volume administration.
      • Kalantari K.
      • Chang J.N.
      • Ronco C.
      • Rosner M.H.
      Assessment of intravascular volume status and volume responsiveness in critically ill patients.
      These dynamic parameters are technologically refined versions of jugular venous waveform, in contrast to arterial parameters such as pulse pressure variation or stroke volume variation, which are refined versions of “pulsus paradoxus”. The variations in dynamic parameters are greater in volume responsive than volume nonresponsive patients. Change in cardiac output in response to a volume intervention is used as the “gold standard” by which to judge other dynamic and static parameters.
      • Marik P.E.
      Fluid responsiveness and the Six guiding principles of fluid resuscitation.
      ,
      • Bentzer P.
      • Griesdale D.E.
      • Boyd J.
      • MacLean K.
      • Sirounis D.
      • Ayas N.T.
      Will this hemodynamically unstable patient respond to a Bolus of Intravenous Fluids?.
      Figure thumbnail gr3
      Figure 3Changes in IVC CI corresponding to cardiac function curves and respiratory variations in CVP related to volume responsiveness and nonresponsiveness. IVC images (left panel, also in video format as , available at: http://doi.org/10.1053/j.ackd.2021.02.003), corresponding to cardiac function curves (middle panel) reprinted from Magder 2011
      • Magder S.
      Hemodynamic monitoring in the mechanically ventilated patient.
      with permission, and respiratory variation in CVP (right panel) reprinted from Mohsenin 2015
      • Mohsenin V.
      Assessment of preload and fluid responsiveness in intensive care unit. How good are we?.
      with permission. A distended hepatic vein (lower left panel) is consistent with relative intravascular volume overload.

      Clinical Interpretation of IVC Ultrasound Findings

      Following is a summary of the 2010 Guidelines for the echocardiographic assessment of the right heart in adults,
      • Beigel R.
      • Cercek B.
      • Luo H.
      • Siegel R.J.
      Noninvasive evaluation of right atrial pressure.
      ,
      • Rudski L.G.
      • Lai W.W.
      • Afilalo J.
      • et al.
      Guidelines for the echocardiographic assessment of the right heart in adults: a report from the American Society of Echocardiography endorsed by the European Association of Echocardiography, a registered branch of the European Society of Cardiology, and the Canadian Society of Echocardiography.
      which is a widely adopted method for interpreting measurement of IVC diameters to estimate relative intravascular volume status.
      • IVC diameter <2.1 cm, that collapses >50% with a sniff suggests normal mean RAP 0 to 5 mm Hg.
      • IVC diameter >2.1 cm that collapses <50% with a sniff suggests elevated mean RAP 10 to 20 mm Hg.
      • Intermediate cases may be assigned an intermediate mean RAP 5 to 10 mm Hg.
      • If there is minimal IVC collapse with a sniff (<35%), mean RA pressure may be upgraded to 15 mm Hg.
      • In patients who are unable to perform a sniff, IVC that collapses <20% with quiet inspiration suggest elevated mean RA pressure.

      Hypovolemia vs. Not-hypovolemia

      In a review of 4 publications with more than 50 extractable data points (total n = 298) of patients who did not sniff, optimal sensitivity (80%) and specificity (79%) for predicting a mean RAP <5 mmHg were obtained at a cutoff for IVC CI of ≥47.3% (approximately 50%).
      • Kaptein M.J.
      • Kaptein J.S.
      • Oo Z.
      • Kaptein E.M.
      Relationship of inferior vena cava collapsibility to ultrafiltration volume achieved in critically ill hemodialysis patients.
      ,
      • Kircher B.J.
      • Himelman R.B.
      • Schiller N.B.
      Noninvasive estimation of right atrial pressure from the inspiratory collapse of the inferior vena cava.
      • Nakao S.
      • Come P.C.
      • McKay R.G.
      • Ransil B.J.
      Effects of positional changes on inferior vena caval size and dynamics and correlations with right-sided cardiac pressure.
      • Moreno F.L.
      • Hagan A.D.
      • Holmen J.R.
      • Pryor T.A.
      • Strickland R.D.
      • Castle C.H.
      Evaluation of size and dynamics of the inferior vena cava as an index of right-sided cardiac function.
      • Capomolla S.
      • Febo O.
      • Caporotondi A.
      • et al.
      Non-invasive estimation of right atrial pressure by combinded Doppler echocardiographic measurements of the inferior vena cava in patients with congestive heart failure.
      This essentially agrees with the 50% cutoff value for IVC CI in the echocardiography guidelines presented by Rudski and colleagues.
      • Beigel R.
      • Cercek B.
      • Luo H.
      • Siegel R.J.
      Noninvasive evaluation of right atrial pressure.
      ,
      • Rudski L.G.
      • Lai W.W.
      • Afilalo J.
      • et al.
      Guidelines for the echocardiographic assessment of the right heart in adults: a report from the American Society of Echocardiography endorsed by the European Association of Echocardiography, a registered branch of the European Society of Cardiology, and the Canadian Society of Echocardiography.
      IVC CI is predictive of volume responsiveness with a pooled sensitivity of 75% and specificity of 82% in mechanically ventilated patients
      • Si X.
      • Cao D.
      • Xu H.
      • Guan X.
      Meta-analysis of ventilated versus spontaneously breathing patients in predicting fluid responsiveness by inferior vena cava variation.
      and a pooled sensitivity of 71% and specificity of 81% in spontaneously breathing patients as described previously.
      • Si X.
      • Cao D.
      • Xu H.
      • Guan X.
      Meta-analysis of ventilated versus spontaneously breathing patients in predicting fluid responsiveness by inferior vena cava variation.
      ,
      • Preau S.
      • Bortolotti P.
      • Colling D.
      • et al.
      Diagnostic accuracy of the inferior vena cava collapsibility to predict fluid responsiveness in spontaneously breathing patients with Sepsis and acute Circulatory failure.
      ,
      • Corl K.A.
      • George N.R.
      • Romanoff J.
      • et al.
      Inferior vena cava collapsibility detects fluid responsiveness among spontaneously breathing critically-ill patients.

      Hypervolemia vs Not-hypervolemia

      We use as default the 2010 echocardiography guideline that states that in patients who are unable to adequately perform a sniff, an IVC that collapses <20% with quiet inspiration suggests elevated mean RAP.
      • Beigel R.
      • Cercek B.
      • Luo H.
      • Siegel R.J.
      Noninvasive evaluation of right atrial pressure.
      ,
      • Rudski L.G.
      • Lai W.W.
      • Afilalo J.
      • et al.
      Guidelines for the echocardiographic assessment of the right heart in adults: a report from the American Society of Echocardiography endorsed by the European Association of Echocardiography, a registered branch of the European Society of Cardiology, and the Canadian Society of Echocardiography.
      Our data, showing that the ability to remove ≥0.5 L to ≥2 L of ultrafiltrate during dialysis could best be predicted using an IVC collapsibility cutoff of 23% to 18.5% (approximately 20%), are consistent with this.
      • Kaptein M.J.
      • Kaptein J.S.
      • Oo Z.
      • Kaptein E.M.
      Relationship of inferior vena cava collapsibility to ultrafiltration volume achieved in critically ill hemodialysis patients.
      Nephrologists may more frequently need to consider whether patients may benefit from volume removal than volume administration because of baseline population characteristics. For example, in a convenience sample of 658 encounters with 267 ICU patients with nephrology consults, of which a subset who received dialysis was formally analyzed and published,
      • Kaptein M.J.
      • Kaptein J.S.
      • Oo Z.
      • Kaptein E.M.
      Relationship of inferior vena cava collapsibility to ultrafiltration volume achieved in critically ill hemodialysis patients.
      we found that 47% of encounters had IVC CI ≤ 20%, 18% had IVC CI > 50%, and 35% had IVC CI 20 to 50%. IVC collapsibility may also predict ability to remove volume by ultrafiltration or to increase cardiac output with net volume removal in patients with intravascular volume overload.
      • Kaptein M.J.
      • Kaptein J.S.
      • Oo Z.
      • Kaptein E.M.
      Relationship of inferior vena cava collapsibility to ultrafiltration volume achieved in critically ill hemodialysis patients.
      ,
      • Kaptein M.J.
      • Kaptein J.S.
      • Nguyen C.D.
      • et al.
      Changes in cardiac output with hemodialysis relate to net volume balance and to inferior vena cava ultrasound collapsibility in critically ill patients.
      ,
      • Miller J.B.
      • Sen A.
      • Strote S.R.
      • et al.
      Inferior vena cava assessment in the bedside diagnosis of acute heart failure.
      ,
      • Blehar D.J.
      • Dickman E.
      • Gaspari R.
      Identification of congestive heart failure via respiratory variation of inferior vena cava diameter.
      Especially when at one extreme or the other, IVC ultrasound findings may influence the prediction of whether a patient would benefit from administration of volume, diuretics or ultrafiltration, or neither.

      Change in Cardiac Output vs IVC CI and Change in Volume

      Volume removal by ultrafiltration has been shown to increase cardiac output in patients with refractory congestive heart failure
      • Marenzi G.
      • Lauri G.
      • Grazi M.
      • Assanelli E.
      • Campodonico J.
      • Agostoni P.
      Circulatory response to fluid overload removal by extracorporeal ultrafiltration in refractory congestive heart failure.
      • Giglioli C.
      • Landi D.
      • Cecchi E.
      • et al.
      Effects of ULTRAfiltration vs. DIureticS on clinical, biohumoral and haemodynamic variables in patients with deCOmpensated heart failure: the ULTRADISCO study.
      • Giglioli C.
      • Landi D.
      • Gensini G.F.
      • et al.
      Cardiac efficiency improvement after slow continuous ultrafiltration is assessed by beat-to-beat minimally invasive monitoring in congestive heart failure patients: a preliminary report.
      and in volume overloaded patients with acute or chronic kidney failure.
      • Lauer A.
      • Alvis R.
      • Avram M.
      Hemodynamic consequences of continuous arteriovenous hemofiltration.
      • Del Greco F.
      • Simon N.M.
      • Roguska J.
      • Walker C.
      Hemodynamic studies in chronic uremia.
      • Jeong J.H.
      • Biruete A.
      • Fernhall B.
      • Wilund K.R.
      Effects of acute intradialytic exercise on cardiovascular responses in hemodialysis patients.
      We reported how changes in cardiac output determined by thermodilution in 22 critically ill patients receiving kidney replacement therapy during 58 encounters related to relative intravascular volume assessed by IVC CI and to changes in net volume.
      • Kaptein M.J.
      • Kaptein J.S.
      • Nguyen C.D.
      • et al.
      Changes in cardiac output with hemodialysis relate to net volume balance and to inferior vena cava ultrasound collapsibility in critically ill patients.
      In patient encounters with relative intravascular volume overload assessed by IVC CI < 20%, and net volume removal during continuous or intermittent dialysis, despite intradialytic hypotension in all cases, cardiac output increased > 10% in 36% of encounters, decreased ≥ 10% in 34% of encounters, and remained between −10% and +10% in 30% of encounters.

      Limitations of IVC Ultrasound

      Limitations to IVC ultrasound can be categorized as factors which affect the IVC diameter/collapsibility or its clinical interpretation
      • Via G.
      • Tavazzi G.
      • Price S.
      Ten situations where inferior vena cava ultrasound may fail to accurately predict fluid responsiveness: a physiologically based point of view.
      ,
      • Marik P.E.
      Techniques for assessment of intravascular volume in critically ill patients.
      and those which limit optimal visualization.
      • Weekes A.J.
      • Tassone H.M.
      • Babcock A.
      • et al.
      Comparison of serial qualitative and quantitative assessments of caval index and left ventricular systolic function during early fluid resuscitation of hypotensive emergency department patients.
      The former can be addressed by a systematic understanding of the direction of potential biases, and interpretation of results in clinical context for a specific patient
      • Kaptein M.J.
      • Kaptein E.M.
      Focused Real-time ultrasonography for Nephrologists.
      (Table 2).

      Factors That Affect IVC Diameter or Collapsibility

      Overestimation of relative intravascular volume may occur in conditions that impede flow to the right heart, including valvular abnormalities, pulmonary hypertension, heart failure,
      • Seif D.
      • Mailhot T.
      • Perera P.
      • Mandavia D.
      Caval sonography in shock: a noninvasive method for evaluating intravascular volume in critically ill patients.
      or poor respiratory excursions
      • Gignon L.
      • Roger C.
      • Bastide S.
      • et al.
      Influence of Diaphragmatic Motion on inferior vena cava diameter respiratory variations in healthy volunteers.
      ,
      • Kimura B.J.
      • Dalugdugan R.
      • Gilcrease 3rd, G.W.
      • Phan J.N.
      • Showalter B.K.
      • Wolfson T.
      The effect of breathing manner on inferior vena caval diameter.
      (Table 2). Severe tricuspid regurgitation decreases IVC CI
      • Shapira Y.
      • Porter A.
      • Wurzel M.
      • Vaturi M.
      • Sagie A.
      Evaluation of tricuspid regurgitation severity: echocardiographic and clinical correlation.
      ,
      • Nishimura R.A.
      • Otto C.M.
      • Bonow R.O.
      • et al.
      2014 AHA/ACC guideline for the management of patients with valvular heart disease: executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines.
      and may increase IVCmax.
      • Nishimura R.A.
      • Otto C.M.
      • Bonow R.O.
      • et al.
      2014 AHA/ACC guideline for the management of patients with valvular heart disease: executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines.
      Rheumatic valvular heart disease increases IVCmax.
      • Altunbas G.
      • Yuce M.
      • Ozer H.O.
      • et al.
      Impact of chronic Rheumatic Valve diseases on large Vessels.
      IVC CI may vary with relative intravascular volume with severe TR
      • Vaturi M.
      • Shapira Y.
      • Vaknin-Assa H.
      • Oron A.
      • Matesko R.
      • Sagie A.
      Echocardiographic markers of severe tricuspid regurgitation associated with right-sided congestive heart failure.
      and still may be useful if IVC CI increases with volume removal. In such circumstances, if the IVC is highly collapsible or totally collapsed, relative intravascular hypovolemia is likely present, and volume resuscitation may be indicated.
      Underestimation of intravascular volume may occur with intra-abdominal hypertension;
      • Wachsberg R.H.
      Narrowing of the upper abdominal inferior vena cava in patients with elevated intraabdominal pressure: sonographic observations.
      therefore, a distended IVC in this circumstance likely indicates intravascular hypervolemia.
      Interpretation of vena cava physiology may be hindered by conditions that restrict the physiologic variability of the IVC such as venous thrombosis, masses causing external compression, or large extracorporeal membrane oxygenation catheters.
      • Seif D.
      • Mailhot T.
      • Perera P.
      • Mandavia D.
      Caval sonography in shock: a noninvasive method for evaluating intravascular volume in critically ill patients.
      ,
      • Via G.
      • Tavazzi G.
      • Price S.
      Ten situations where inferior vena cava ultrasound may fail to accurately predict fluid responsiveness: a physiologically based point of view.
      The central venous anatomy is significantly altered in patients after liver transplant, and there are several possible surgical approaches. This has yet to be systematically investigated. Interpretation of the physiologic characteristics of the IVC should be done in context of the patient's clinical scenario and adjunctive data.
      • Seif D.
      • Mailhot T.
      • Perera P.
      • Mandavia D.
      Caval sonography in shock: a noninvasive method for evaluating intravascular volume in critically ill patients.

      Factors That Limit Visualization

      Adequate visualization may be compromised by morbid obesity, abdominal pain or distention, bowel gas, postoperative surgical dressings, an open chest or abdomen, subcutaneous emphysema, or talcum powder on the skin. Overcoming limitation of optimal visualization may be facilitated by expanding the repertoire of alternative ultrasound windows and techniques.

      Summary

      We use ultrasound of the inferior vena cava as an integral part of the evaluation of relative intravascular volume status and to guide volume management. This is particularly crucial in hospitalized patients who are not in steady state and frequently have mismatch between intravascular volume and blood pressure or between intravascular and extravascular volume, which may not otherwise be evident on physical examination.
      Recent data indicate that volume responsiveness can be predicted with similar accuracy for spontaneously breathing and for mechanically ventilated patients. The major benefit is to potentially eliminate one possibility of either overt relative intravascular hypervolemia or hypovolemia in a given patient. One must be mindful of the systematic direction of clinical biases that may affect IVC diameter/variation or the clinical interpretation, as well as overall clinical goals when making clinical decisions based on IVC ultrasound measurements.

      Acknowledgments

      The authors would like to thank John S. Kaptein, PhD, for reviewing the meta-analyses and calculating the pooled sensitivities and specificities, and Myint Bo Thu, MBBS, Zayar Oo, MBBS, and Phyu Phu Thwe, MBBS, for their invaluable assistance with image acquisition and literature review.

      Supplementary data

      References

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