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Editorials: Point and Counterpoint |

Rebuttal From Dr Schmidt FREE TO VIEW

Gregory A. Schmidt, MD, FCCP
Author and Funding Information

FINANCIAL/NONFINANCIAL DISCLOSURES: None declared.

Division of Pulmonary Diseases, Critical Care, and Occupational Medicine, Department of Internal Medicine, University of Iowa, Iowa City, IA

CORRESPONDENCE TO: Gregory A. Schmidt, MD, FCCP, Division of Pulmonary Diseases, Critical Care, and Occupational Medicine, Department of Internal Medicine, University of Iowa, 200 Hawkins Dr, C33-GH, Iowa City, IA 52246


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


Chest. 2017;151(3):536-537. doi:10.1016/j.chest.2016.11.019
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Published online

For a patient in shock, ultrasound of the IVC is a fundamental component of the intensivist’s assessment. Dr Kory argues that IVC diameter and its variation cannot be reliably assessed, but most intensivists find that the longitudinal, subcostal examination is easily learned. Interrater reliability is known to be high,, and, with careful attention to methodology, errors are uncommon. Facility with trans-hepatic (and occasionally trans-splenic) sonographic windows makes the examination applicable for nearly every critically ill patient.

Respiratory variation in IVC diameter (ΔIVC) represents far more than a static filling pressure: ΔIVC is no CVP. For spontaneously breathing patients, the theory that links ΔIVC to FR is the physiology of the cardiac function curve. Inspiration lowers the pleural pressure, drawing the cardiac function curve to the left. If the patient’s circulation is operating on the flat portion of the cardiac function curve, right atrial pressure will not fall on inspiration, and the IVC will not collapse (Fig 1). Conversely, when operating on the steep limb of the cardiac function curve, inspiration shifts the point at which the cardiac function and venous return function curves intersect, right atrial pressure falls, and the IVC tends to collapse. As long as inspiratory effort is sufficient and the patient is not recruiting accessory muscles at end-expiration, this signal is physiologically sound.

Figure Jump LinkFigure 1 A, Represents a fluid-responsive circulation and shows the intersection of the venous return and cardiac function curves at end-expiration (solid cardiac function curve) and end-inspiration (dotted curve). The inspiratory drop in pleural pressure shifts the cardiac function curve to the left, moving the intersection point to a lower right atrial pressure. The IVC tends to collapse accordingly. B, The circulation is characterized by depressed cardiac function and high intravascular volume and would not respond to further fluid loading. Inspiration shifts the cardiac function curve to the left as in A but, because the circulation is operating on its flat portion, the intersection with the venous return function line shifts imperceptibly. Right atrial pressure will not fall measurably, and the IVC will not collapse. SV = stroke volume.Grahic Jump Location

The need to infuse fluid when hypovolemia contributes to shock is not always obvious. Tachycardia may signal pain, ventilator dyssynchrony, systemic inflammation, hypercapnia, pulmonary edema, or a hundred other ills. As a guide to fluid therapy in the bleeding patient, hemoglobin concentration is nearly useless. After all, the exsanguinating patient has similar values at the point of injury and the moment of death. In my own practice, both incomplete and excessive resuscitation are seen regularly; IVC ultrasound often clarifies a hazy picture.

The preconditions for validity of ΔIVC deserve attention. Perhaps I would agree with Dr Kory that a simple snapshot of the IVC could be misleading, especially when devoid of the clinical presentation, examination findings, patient-ventilator interaction, echocardiography, ultrasound interrogation of the lungs, and the clinical trajectory. However, the alert intensivist is attuned to inspiratory effort, abdominal muscle recruitment, intraabdominal pressure, ventricular function, cor pulmonale, and the ventilator tidal volume. Indeed, IVC ultrasound demands an intensivist at the bedside, hand on the belly, in intimate contact with the patient, which is right where he or she belongs.

References

Kory P. . Counterpoint: should acute fluid resuscitation be guided primarily by inferior vena cava ultrasound for patients in shock? No. Chest. 2017;151:533-536 [PubMed]journal
 
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]
 
Fields J.M. .Lee P.A. .Jeng 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. Acad Emerg Med. 2011;18:98-101 [PubMed]journal. [CrossRef] [PubMed]
 
Schmidt G.A. . Point: should acute fluid resuscitation be guided primarily by inferior vena caval ultrasound for patients in shock? Yes. Chest. 2017;151:531-532 [PubMed]journal
 
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. Crit Care. 2012;16:181- [PubMed]journal. [CrossRef] [PubMed]
 
Magder S. .Georgiadis G. .Cheong T. . Respiratory variations in right atrial pressure predict response to fluid challenge. J Crit Care. 1992;7:76-85 [PubMed]journal. [CrossRef]
 
Magder S. . Predicting volume responsiveness in spontaneously breathing patients: still a challenging problem. Crit Care. 2006;10:165- [PubMed]journal. [CrossRef] [PubMed]
 

Figures

Figure Jump LinkFigure 1 A, Represents a fluid-responsive circulation and shows the intersection of the venous return and cardiac function curves at end-expiration (solid cardiac function curve) and end-inspiration (dotted curve). The inspiratory drop in pleural pressure shifts the cardiac function curve to the left, moving the intersection point to a lower right atrial pressure. The IVC tends to collapse accordingly. B, The circulation is characterized by depressed cardiac function and high intravascular volume and would not respond to further fluid loading. Inspiration shifts the cardiac function curve to the left as in A but, because the circulation is operating on its flat portion, the intersection with the venous return function line shifts imperceptibly. Right atrial pressure will not fall measurably, and the IVC will not collapse. SV = stroke volume.Grahic Jump Location

Tables

References

Kory P. . Counterpoint: should acute fluid resuscitation be guided primarily by inferior vena cava ultrasound for patients in shock? No. Chest. 2017;151:533-536 [PubMed]journal
 
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]
 
Fields J.M. .Lee P.A. .Jeng 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. Acad Emerg Med. 2011;18:98-101 [PubMed]journal. [CrossRef] [PubMed]
 
Schmidt G.A. . Point: should acute fluid resuscitation be guided primarily by inferior vena caval ultrasound for patients in shock? Yes. Chest. 2017;151:531-532 [PubMed]journal
 
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. Crit Care. 2012;16:181- [PubMed]journal. [CrossRef] [PubMed]
 
Magder S. .Georgiadis G. .Cheong T. . Respiratory variations in right atrial pressure predict response to fluid challenge. J Crit Care. 1992;7:76-85 [PubMed]journal. [CrossRef]
 
Magder S. . Predicting volume responsiveness in spontaneously breathing patients: still a challenging problem. Crit Care. 2006;10:165- [PubMed]journal. [CrossRef] [PubMed]
 
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