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Editorials: Point and Counterpoint |

COUNTERPOINT: Should Acute Fluid Resuscitation Be Guided Primarily by Inferior Vena Cava Ultrasound for Patients in Shock? No FREE TO VIEW

Pierre Kory, MD
Author and Funding Information

FINANCIAL/NONFINANCIAL DISCLOSURE: The author has reported to CHEST the following: P. K. received a stipend from SonoSite/Fujifilm to provide a video-based tutorial based on how to diagnose a DVT using ultrasound.

Trauma and Life Support Center, Critical Care Service, University of Wisconsin School of Medicine and Public Health, Madison, WI

CORRESPONDENCE TO: Pierre Kory, MD, Trauma and Life Support Center, Critical Care Service, University of Wisconsin School of Medicine and Public Health, 600 Highland Ave, Centennial Bldg, Room 5245, Madison, WI, 53792


Copyright 2016, American College of Chest Physicians. All Rights Reserved.


Chest. 2017;151(3):533-536. doi:10.1016/j.chest.2016.11.017
Text Size: A A A
Published online

The goal of fluid resuscitation in shock is to improve organ perfusion while avoiding the harms of excess fluid administration. Fluids lead to harm unless: (1) the tissue hypoxia results from inadequate oxygen delivery rather than mitochondrial or microvascular dysfunction; and (2) fluid administration leads to an increase in tissue oxygen delivery.,, Previous debates and investigations have focused on optimal methods for differentiating between states of inadequate oxygen delivery and mitochondrial dysfunction.,, The role of IVC ultrasound in fluid resuscitation focuses on its ability to predict whether fluids will increase cardiac output, a condition known as fluid responsiveness (FR).

Decades of investigations on tools to identify FR have led to several oft-cited conclusions: (1) only 50% of critically ill patients believed to benefit from fluids actually have FR; (2) traditional clinical and static hemodynamic parameters are poor predictors of FR; and (3) the most accurate predictors are “dynamic measures” (ie, tests that measure changes in cardiac output in response to transient fluid boluses such as pulse pressure variation and PLR).,, Publications regarding these dynamic measures have dominated fluid resuscitation literature since pulse pressure variation was first described > 15 years ago. So why are we debating the utility of IVC ultrasound rather than one of these more established tools? The answer likely has more to do with perceived convenience than diagnostic accuracy. Dynamic measures typically require invasive or sophisticated equipment to insert and calibrate, advanced echocardiographic skills to perform, or unique patient clinical conditions to be met (eg, lack of spontaneous respiratory effort). These limitations render such approaches more difficult for clinicians, particularly in acute care settings such as the ED. In contrast, IVC ultrasound is seen as the “holy grail” of FR predictors: immediately available, easy to learn, quick to perform, and applicable in a wide range of patients. However, diagnostic accuracy must not be sacrificed on the altar of convenience; what good is a convenient tool if it misleads us?

The arguments against IVC ultrasound can be grouped into three categories: (1) technical measurement challenges; (2) inability of filling pressures to predict FR; and (3) difficulties interpreting effects of intrathoracic pressure changes.

Measuring the IVC is confounded by a host of technical factors, including obesity, abdominal distension, surgical dressings, and intraabdominal hypertension. The abdominal aorta may be mistaken for the IVC. The IVC may be measured at a point that is not the true maximum diameter. IVC measurements have suboptimal interoperator reliability., Translational artifacts during inspiration may be incorrectly interpreted as IVC variation. Some of these well-known technical challenges were ignored in studies validating IVC ultrasound.

Two parameters of the IVC have been studied to predict FR: (1) diameter; and (2) variation in diameter during inspiration. In healthy adult subjects, the IVC diameter averages 1.7 ± 0.4 cm and decreases by approximately 50% during tidal breathing.,

The IVC diameter is determined by the difference between the internal (ie, central venous pressure [CVP]) and external pressure (intraabdominal pressure). When intraabdominal pressure is negligible, a curvilinear positive relationship between CVP and IVC diameter is observed.,, Consequently, “the IVC is the CVP.” However, static filling pressures, such as CVP, cannot accurately identify FR in a heterogeneous ICU population composed of significant proportions of patients with septic shock.,

Why do we still equate low filling pressures with hypovolemia and/or a need for fluids in septic shock? We forget that low filling pressures are: (1) most often caused by factors other than volume loss in these patients, namely vasodilation and hyperdynamic cardiac function; (2) the normal state of health; and (3) necessary to promote venous return. Although the two main types of hypotensive insults seen in ICUs (bleeding and sepsis) both produce low filling pressures, they require different fluid resuscitation approaches. Blood loss leads to a pure hypovolemic state and requires (and clinically responds to) aggressive repletion of intravascular volume. Sepsis is more complex but, in general, benefits most from initial, modest fluid administration followed by treatment of the associated vasoplegia and/or myocardial dysfunction.

When clinicians do not explicitly identify these disparate clinical contexts, the low filling pressures “seen” on goal-directed echocardiograms (or measured via internal jugular catheters) of patients with sepsis in the ICU after initial fluid resuscitation leads to a conditioned response. This response comprises continued aggressive fluid resuscitation and fluid overload in the > 50% of ICU patients with low filling pressures who do not have FR.

Clearly, in overt hypovolemic insults (eg, after blood donation, after fluid removal during dialysis, bleeding trauma patients), low filling pressures identified by using IVC ultrasound reflect volume loss.,, Is IVC ultrasound really needed to guide our management in these cases, however? Probably not. Assessing and targeting heart rate, blood pressure, or hemoglobin levels during resuscitation represents a sound clinical approach to such cases.

It is when faced with the complex physiology of the patient with septic (or multifactorial) shock that we desire equally robust, simple guides to direct and balance the multiple therapies required. Unfortunately, it is precisely these patients for whom the evidence does not support the use of IVC ultrasound: “where it is useful, it is not needed, and where it is needed, it is not useful.” There are two ways to argue why IVC diameter cannot predict FR in critically ill patients: directly and indirectly. The direct argument relies on citing the two studies that report the poor predictive accuracy of IVC diameter in a heterogeneous ICU population. Airapetian et al reported an area under the receiver operating characteristic curve of 0.62 in 58 critically ill shock patients, similar to that of CVP (0.56) and the tossing of a coin, and nowhere near the accuracy of PLR (0.95). Similarly, Feissel et al reported a very weak correlation (r = 0.46) of IVC diameter with FR. The indirect argument relies on simply citing the extensive literature demonstrating the near complete inability of the CVP (which largely determines IVC diameter) to predict FR.

There are two types of IVC variation: (1) “collapse” (during inspiration in spontaneously breathing patients); and (2) “distention” (during inspiration in paralyzed patients who are mechanically ventilated).

IVC “Collapsibility”

During inspiration in a spontaneously breathing patient, intrathoracic pressure decreases, the right heart chambers expand, and CVP falls., Intraabdominal pressure rises due to descent of the diaphragm and contraction of abdominal muscles. This combination of forces “collapses” the IVC. The amount of collapse observed is thus driven by CVP and the magnitude of inspiratory effort.

To my knowledge, no theory or study has proposed a correlation between the magnitude of inspiratory efforts and presence of FR. Even if we could standardize inspiratory effort among critically ill patients (ie, similar to the “sniff” tests used in the quiet of an echocardiography laboratory), the amount of collapse seen would simply reflect baseline CVP. This fact has not prevented multiple groups from assessing the ability of IVC collapse to predict FR, with predictably and uniformly poor results (Table 1).,,,, To support the assertion that both IVC collapse and IVC diameter are determined according to CVP, the one study that reported on their predictive accuracy for FR found them to have identical area under the receiver operating characteristic curves of 0.62, similar to that of CVP., Of note, the two studies in Table 1 that found even a modest predictive ability of IVC collapse included 38% and 50% of patients, respectively,, with baseline, overt hypovolemic insults.

Table Graphic Jump Location
Table 1 Predictive Accuracy of IVC Collapse for Fluid Responsivenessa
a Published studies with ≥ 15 patients.
b 38% of patients with dehydration.
c 50% of patients with bleeding, dehydration or trauma.

AUC = area under receiver operating characteristics curve; CO= cardiac output; CTICU = cardiothoracic surgery ICU; IC = impedance cardiography; IVC = inferior vena cava; R = correlation coefficient; SBP = systolic blood pressure; SV = stroke volume; VTI = velocity time integral.

IVC “Distensibility”

During insufflation of a paralyzed, intubated patient, the IVC will distend but only in patients whose IVCs are not yet maximally distended. This increase in diameter indicates a “preload reserve” within the vein and has a high correlation with FR (r = 0.82). Unfortunately, only 2% of patients in ICUs at a given time will possess the entire set of clinical conditions required to perform this test reliably, making it one of the least generalizable measures described.

Routine use of IVC ultrasound parameters to guide fluid therapy should be abandoned because they are rarely reliably assessed, are unnecessary in managing patients with overt hypovolemic insults, and are almost completely determined by filling pressures that cannot predict FR in heterogeneous critically ill patient populations. For those who have abandoned CVP in favor of the IVC as a guide to fluid resuscitation, beware of the “wolf in sheep’s clothing.”

Boyd J. .Forbes J. .Taka-aki N. .et al Fluid resuscitation in septic shock: a positive fluid balance and elevated central venous pressure are associated with increased mortality. Crit Care Med. 2011;39:259-265 [PubMed]journal. [CrossRef] [PubMed]
 
Garzotto F. .Ostermann M. .Martín-Langerwerf D. .et al The Dose Response Multicentre Investigation on Fluid Assessment (DoReMIFA) in critically ill patients. Crit Care. 2016;20:196- [PubMed]journal. [CrossRef] [PubMed]
 
Alsous F. .Khamiees M. .DeGirolamo A. .et al Negative fluid balance predicts survival in patients with septic shock: a retrospective pilot study. Chest. 2000;117:1749-1754 [PubMed]journal. [CrossRef] [PubMed]
 
Monnet X. .Julien F. .Ait-Hamou N. .et al Lactate and venoarterial carbon dioxide difference/arterial-venous oxygen difference ratio, but not central venous oxygen saturation, predict increase in oxygen consumption in fluid responders. Crit Care Med. 2013;41:1412-1420 [PubMed]journal. [CrossRef] [PubMed]
 
Mekontso-Dessap A. .Castelain V. .Anguel N. .et al Combination of venoarterial PCO2 difference with arteriovenous O2 content difference to detect anaerobic metabolism in patients. Intensive Care Med. 2002;28:272-277 [PubMed]journal. [CrossRef] [PubMed]
 
Jones A.E. .Elkin R. .Cannon C.M. .et al Should lactate clearance be substituted for central venous oxygen saturation as goals of early severe sepsis and septic shock therapy? Chest. 2011;140:6- [PubMed]journal. [CrossRef] [PubMed]
 
Osman D. .Ridel C. .Ray P. .et al Cardiac filling pressures are not appropriate to predict hemodynamic response to volume challenge. Crit Care Med. 2007;35:64-68 [PubMed]journal. [CrossRef] [PubMed]
 
Michard F. .Teboul J.L. . Predicting fluid responsiveness in ICU patients: a critical analysis of the evidence. Chest. 2002;121:2000-2008 [PubMed]journal. [CrossRef] [PubMed]
 
Marik P.E. .Cavallazzi R. .Vasu T. .et al Dynamic changes in arterial waveform derived variables and fluid responsiveness in mechanically ventilated patients: a systematic review of the literature. Crit Care Med. 2009;37:2642-2647 [PubMed]journal. [CrossRef] [PubMed]
 
Bowra J. .Uwagboe V. .Goudie A. .et al Interrater agreement between expert and novice in measuring inferior vena cava diameter and collapsibility index. Emerg Med Australas. 2015;27:295-299 [PubMed]journal. [CrossRef] [PubMed]
 
Akkaya A. .Yesilaras M. .Aksay E. .et al The interrater reliability of ultrasound imaging of the inferior vena cava performed by emergency residents. Am J Emerg Med. 2013;31:1509-1511 [PubMed]journal. [CrossRef] [PubMed]
 
Blehar D.J. .Resop D. .Chin B. .Dayno M. .Gaspari R. . Inferior vena cava displacement during respirophasic ultrasound imaging. Crit Ultrasound J. 2012;4:18- [PubMed]journal. [CrossRef] [PubMed]
 
Duwat A. .Zogheib E. .Guinot P. .et al The gray zone of the qualitative assessment of respiratory changes in inferior vena cava diameter in ICU patients. Crit Care. 2014;18:R14- [PubMed]journal. [CrossRef] [PubMed]
 
Mintz G. .Kotler M. .Parry W. .Iskandrian A. .Kane S. . Real-time inferior vena caval ultrasonography: normal and abnormal findings and its use in assessing right heart function. Circulation. 1981;64:1018-1025 [PubMed]journal. [CrossRef] [PubMed]
 
Mookadam F. .Warsame T.A. .Yang H.S. .et al Effect of positional changes on inferior vena cava size. Eur J Echocardiography. 2011;12:322-325 [PubMed]journal. [CrossRef]
 
Vieillard-Baron A. .Jardin F. . Ultrasonographic examination of the venae cavae. Intensive Care Med. 2006;32:203-206 [PubMed]journal. [CrossRef] [PubMed]
 
Prekker M.E. .Scott N.L. .Hart D. .et al Point-of-care ultrasound to estimate central venous pressure: a comparison of three techniques. Crit Care Med. 2013;41:833-841 [PubMed]journal. [CrossRef] [PubMed]
 
Nagdev A.D. .Merchant R.C. .Tirado-Gonzalez A. .Sisson C.A. .Murphy M.C. . Emergency department bedside ultrasonographic measurement of the caval index for noninvasive determination of low central venous pressure. Ann Emerg Med. 2010;55:290-295 [PubMed]journal. [CrossRef] [PubMed]
 
Marik P.E. .Cavallazzi R. . Does the central venous pressure (CVP) predict fluid responsiveness? An update meta-analysis and a plea for some common sense. Crit Care Med. 2013;41:1774-1781 [PubMed]journal. [CrossRef] [PubMed]
 
Dipti A. .Soucy Z. .Surana A. .et al Role of inferior vena cava diameter in assessment of volume status: a meta-analysis. Am J Emerg Med. 2012;30:1414-1419 [PubMed]journal. [CrossRef] [PubMed]
 
Lyon M. .Blaivas M. .Brannam L. .et al Sonographic measurement of the inferior vena cava as a marker of blood loss. Am J Emerg Med. 2005;23:45-50 [PubMed]journal. [CrossRef] [PubMed]
 
Guiotto G. .Masarone M. .Paladino F. .et al Inferior vena cava collapsibility to guide fluid removal in slow continuous ultrafiltration: a pilot study. Intensive Care Med. 2010;36:692-696 [PubMed]journal. [CrossRef] [PubMed]
 
Airapetian A. .Maizel J. .Alyamani O. .et al Does inferior vena cava respiratory variability predict fluid responsiveness in critically ill patients? Crit Care. 2015;19:400- [PubMed]journal. [CrossRef] [PubMed]
 
Monnet X. .Teboul J.L. . Passive leg raising for predicting fluid responsiveness: a systematic review and meta-analysis. Intensive Care Med Experimental. 2015;3:A587- [PubMed]journal. [CrossRef]
 
Feissel M. .Michard F. .Faller J.P. .et al The respiratory variation in inferior vena cava diameter as a guide to fluid therapy. Intensive Care Med. 2004;30:1834-1837 [PubMed]journal. [PubMed]
 
Bodson L. .Vieillard-Baron A. . Respiratory variation in inferior vena cava diameter: surrogate of central venous pressure or parameter of fluid responsiveness? Let the physiology reply. Critical Care. 2012;16:181- [PubMed]journal. [CrossRef] [PubMed]
 
Kircher B.J. .Himelman R.B. .Schiller N.B. . Noninvasive estimation of right atrial pressure from the inspiratory collapse of the inferior vena cava. Am J Cardiol. 1990;96:493-496 [PubMed]journal
 
Sobczyk D. .Nycz K. .Andruszki P. .et al Ultrasonographic caval indices do not significantly contribute to predicting fluid responsiveness immediately after coronary artery bypass grafting when compared to passive leg raising. Cardiovascular Ultrasound. 2016;14:23- [PubMed]journal. [PubMed]
 
De Valk S. .Olgers T.J. .Holman M. .et al The caval index: an adequate non-invasive ultrasound parameter to predict fluid responsiveness in the emergency department? BMC Anesthesiology. 2014;14:114- [PubMed]journal. [CrossRef] [PubMed]
 
Corl K. .Napoli A.M. .Gardiner F. . Bedside sonographic measurement of the inferior vena cava caval index is a poor predictor of fluid responsiveness in emergency department patients. Emergency Medicine Australasia. 2012;24:534-539 [PubMed]journal. [CrossRef] [PubMed]
 
Muller L. .Bobbia X. .Toumi M. .et al Respiratory variations of inferior vena cava diameter to predict fluid responsiveness in spontaneously breathing patients with acute circulatory failure: need for a cautious use. Critical Care. 2012;16:R188- [PubMed]journal. [CrossRef] [PubMed]
 
Williams K, Ablordeppey E, Theodoro D, et al. The diagnostic accuracy of inferior vena cava collapsibility versus passive leg raise testing in determining volume responsiveness in emergency department patients with shock. In: Proceedings of the 40th Critical Care Congress, Society of Critical Care Medicine. 2011;39:8.
 
Mahjoub Y. .Lejeune V. .Muller L. .et al Evaluation of pulse pressure variation validity criteria in critically ill patients: a prospective observational multicentre point-prevalence study. Br J Anaesthesia. 2014;112:681-685 [PubMed]journal. [CrossRef]
 

Figures

Tables

Table Graphic Jump Location
Table 1 Predictive Accuracy of IVC Collapse for Fluid Responsivenessa
a Published studies with ≥ 15 patients.
b 38% of patients with dehydration.
c 50% of patients with bleeding, dehydration or trauma.

AUC = area under receiver operating characteristics curve; CO= cardiac output; CTICU = cardiothoracic surgery ICU; IC = impedance cardiography; IVC = inferior vena cava; R = correlation coefficient; SBP = systolic blood pressure; SV = stroke volume; VTI = velocity time integral.

References

Boyd J. .Forbes J. .Taka-aki N. .et al Fluid resuscitation in septic shock: a positive fluid balance and elevated central venous pressure are associated with increased mortality. Crit Care Med. 2011;39:259-265 [PubMed]journal. [CrossRef] [PubMed]
 
Garzotto F. .Ostermann M. .Martín-Langerwerf D. .et al The Dose Response Multicentre Investigation on Fluid Assessment (DoReMIFA) in critically ill patients. Crit Care. 2016;20:196- [PubMed]journal. [CrossRef] [PubMed]
 
Alsous F. .Khamiees M. .DeGirolamo A. .et al Negative fluid balance predicts survival in patients with septic shock: a retrospective pilot study. Chest. 2000;117:1749-1754 [PubMed]journal. [CrossRef] [PubMed]
 
Monnet X. .Julien F. .Ait-Hamou N. .et al Lactate and venoarterial carbon dioxide difference/arterial-venous oxygen difference ratio, but not central venous oxygen saturation, predict increase in oxygen consumption in fluid responders. Crit Care Med. 2013;41:1412-1420 [PubMed]journal. [CrossRef] [PubMed]
 
Mekontso-Dessap A. .Castelain V. .Anguel N. .et al Combination of venoarterial PCO2 difference with arteriovenous O2 content difference to detect anaerobic metabolism in patients. Intensive Care Med. 2002;28:272-277 [PubMed]journal. [CrossRef] [PubMed]
 
Jones A.E. .Elkin R. .Cannon C.M. .et al Should lactate clearance be substituted for central venous oxygen saturation as goals of early severe sepsis and septic shock therapy? Chest. 2011;140:6- [PubMed]journal. [CrossRef] [PubMed]
 
Osman D. .Ridel C. .Ray P. .et al Cardiac filling pressures are not appropriate to predict hemodynamic response to volume challenge. Crit Care Med. 2007;35:64-68 [PubMed]journal. [CrossRef] [PubMed]
 
Michard F. .Teboul J.L. . Predicting fluid responsiveness in ICU patients: a critical analysis of the evidence. Chest. 2002;121:2000-2008 [PubMed]journal. [CrossRef] [PubMed]
 
Marik P.E. .Cavallazzi R. .Vasu T. .et al Dynamic changes in arterial waveform derived variables and fluid responsiveness in mechanically ventilated patients: a systematic review of the literature. Crit Care Med. 2009;37:2642-2647 [PubMed]journal. [CrossRef] [PubMed]
 
Bowra J. .Uwagboe V. .Goudie A. .et al Interrater agreement between expert and novice in measuring inferior vena cava diameter and collapsibility index. Emerg Med Australas. 2015;27:295-299 [PubMed]journal. [CrossRef] [PubMed]
 
Akkaya A. .Yesilaras M. .Aksay E. .et al The interrater reliability of ultrasound imaging of the inferior vena cava performed by emergency residents. Am J Emerg Med. 2013;31:1509-1511 [PubMed]journal. [CrossRef] [PubMed]
 
Blehar D.J. .Resop D. .Chin B. .Dayno M. .Gaspari R. . Inferior vena cava displacement during respirophasic ultrasound imaging. Crit Ultrasound J. 2012;4:18- [PubMed]journal. [CrossRef] [PubMed]
 
Duwat A. .Zogheib E. .Guinot P. .et al The gray zone of the qualitative assessment of respiratory changes in inferior vena cava diameter in ICU patients. Crit Care. 2014;18:R14- [PubMed]journal. [CrossRef] [PubMed]
 
Mintz G. .Kotler M. .Parry W. .Iskandrian A. .Kane S. . Real-time inferior vena caval ultrasonography: normal and abnormal findings and its use in assessing right heart function. Circulation. 1981;64:1018-1025 [PubMed]journal. [CrossRef] [PubMed]
 
Mookadam F. .Warsame T.A. .Yang H.S. .et al Effect of positional changes on inferior vena cava size. Eur J Echocardiography. 2011;12:322-325 [PubMed]journal. [CrossRef]
 
Vieillard-Baron A. .Jardin F. . Ultrasonographic examination of the venae cavae. Intensive Care Med. 2006;32:203-206 [PubMed]journal. [CrossRef] [PubMed]
 
Prekker M.E. .Scott N.L. .Hart D. .et al Point-of-care ultrasound to estimate central venous pressure: a comparison of three techniques. Crit Care Med. 2013;41:833-841 [PubMed]journal. [CrossRef] [PubMed]
 
Nagdev A.D. .Merchant R.C. .Tirado-Gonzalez A. .Sisson C.A. .Murphy M.C. . Emergency department bedside ultrasonographic measurement of the caval index for noninvasive determination of low central venous pressure. Ann Emerg Med. 2010;55:290-295 [PubMed]journal. [CrossRef] [PubMed]
 
Marik P.E. .Cavallazzi R. . Does the central venous pressure (CVP) predict fluid responsiveness? An update meta-analysis and a plea for some common sense. Crit Care Med. 2013;41:1774-1781 [PubMed]journal. [CrossRef] [PubMed]
 
Dipti A. .Soucy Z. .Surana A. .et al Role of inferior vena cava diameter in assessment of volume status: a meta-analysis. Am J Emerg Med. 2012;30:1414-1419 [PubMed]journal. [CrossRef] [PubMed]
 
Lyon M. .Blaivas M. .Brannam L. .et al Sonographic measurement of the inferior vena cava as a marker of blood loss. Am J Emerg Med. 2005;23:45-50 [PubMed]journal. [CrossRef] [PubMed]
 
Guiotto G. .Masarone M. .Paladino F. .et al Inferior vena cava collapsibility to guide fluid removal in slow continuous ultrafiltration: a pilot study. Intensive Care Med. 2010;36:692-696 [PubMed]journal. [CrossRef] [PubMed]
 
Airapetian A. .Maizel J. .Alyamani O. .et al Does inferior vena cava respiratory variability predict fluid responsiveness in critically ill patients? Crit Care. 2015;19:400- [PubMed]journal. [CrossRef] [PubMed]
 
Monnet X. .Teboul J.L. . Passive leg raising for predicting fluid responsiveness: a systematic review and meta-analysis. Intensive Care Med Experimental. 2015;3:A587- [PubMed]journal. [CrossRef]
 
Feissel M. .Michard F. .Faller J.P. .et al The respiratory variation in inferior vena cava diameter as a guide to fluid therapy. Intensive Care Med. 2004;30:1834-1837 [PubMed]journal. [PubMed]
 
Bodson L. .Vieillard-Baron A. . Respiratory variation in inferior vena cava diameter: surrogate of central venous pressure or parameter of fluid responsiveness? Let the physiology reply. Critical Care. 2012;16:181- [PubMed]journal. [CrossRef] [PubMed]
 
Kircher B.J. .Himelman R.B. .Schiller N.B. . Noninvasive estimation of right atrial pressure from the inspiratory collapse of the inferior vena cava. Am J Cardiol. 1990;96:493-496 [PubMed]journal
 
Sobczyk D. .Nycz K. .Andruszki P. .et al Ultrasonographic caval indices do not significantly contribute to predicting fluid responsiveness immediately after coronary artery bypass grafting when compared to passive leg raising. Cardiovascular Ultrasound. 2016;14:23- [PubMed]journal. [PubMed]
 
De Valk S. .Olgers T.J. .Holman M. .et al The caval index: an adequate non-invasive ultrasound parameter to predict fluid responsiveness in the emergency department? BMC Anesthesiology. 2014;14:114- [PubMed]journal. [CrossRef] [PubMed]
 
Corl K. .Napoli A.M. .Gardiner F. . Bedside sonographic measurement of the inferior vena cava caval index is a poor predictor of fluid responsiveness in emergency department patients. Emergency Medicine Australasia. 2012;24:534-539 [PubMed]journal. [CrossRef] [PubMed]
 
Muller L. .Bobbia X. .Toumi M. .et al Respiratory variations of inferior vena cava diameter to predict fluid responsiveness in spontaneously breathing patients with acute circulatory failure: need for a cautious use. Critical Care. 2012;16:R188- [PubMed]journal. [CrossRef] [PubMed]
 
Williams K, Ablordeppey E, Theodoro D, et al. The diagnostic accuracy of inferior vena cava collapsibility versus passive leg raise testing in determining volume responsiveness in emergency department patients with shock. In: Proceedings of the 40th Critical Care Congress, Society of Critical Care Medicine. 2011;39:8.
 
Mahjoub Y. .Lejeune V. .Muller L. .et al Evaluation of pulse pressure variation validity criteria in critically ill patients: a prospective observational multicentre point-prevalence study. Br J Anaesthesia. 2014;112:681-685 [PubMed]journal. [CrossRef]
 
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