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Ask the Expert - Emergency Ultrasound Section Newsletter, December 2012

Robert M. Bramante MD RDMS

This edition’s featured expert is:
J Matthew Fields MD
Director, Ultrasound Fellowship
Thomas Jefferson University Hospital

“How do you use ultrasound in your evaluation of the IVC and what methods are most accurate or most helpful in the ongoing resuscitation of the critical patient?”

Personally I feel IVC ultrasound should be performed in all critically ill patients. It provides diagnostic information that can help define the etiology of shock and significantly change management. I still remember the first time IVC ultrasound significantly changed my management of a difficult to examine, obese patient. The patient was hypotensive and in respiratory distress initially thought to have sepsis and pneumonia. Ultrasound showed his IVC was actually plethoric and echo revealed a significant pericardial effusion and tamponade. Since then I have made IVC ultrasound a routine part of my evaluation.

IVC Interpretation:
The IVC is a highly compliant vessel that traverses the liver reflecting right atrial pressure. In low pressure states the IVC is small and tends to collapse during inspiration due to the negative intrathoracic pressure generated by by chest wall expansion. In high pressure states the IVC becomes large with little to no collapse.

The Small IVC [<2.5cm , >50% collapse]
A small, highly collapsible IVC is almost always indicative of a hypovolemic state in critically ill patients. Studies have suggested that when there is 50% or more collapse the patient will respond to fluids. These numbers are guidelines and smaller IVCs may be normal in some patients with smaller body habitus.

The Large IVC [>2.5cm, <50% collapse]
A large IVC is more difficult to interpret in a critically ill patient. It may be due to volume overload, in which case fluids should be avoided. Alternatively, a large IVC may be due to obstruction (valvular disease, pulmonary hypertension, tension pneumothorax, cardiac tamponade), which may require higher filling pressures to maintain cardiac output. A large IVC alone should not determine fluid needs, but should prompt the clinician to further investigate with cardiac and thoracic ultrasound for the underlying cause.

The Middle of the Road IVC
A mid-sized or mixed picture IVC with collapse of 40% in one respiratory cycle and 60% in the next is hard to interpret. In these cases I look for other indicators such as hepatic vein dilation, RV size and filling, LV function and EF. Serial examination after fluid bolus can be useful. If uncertain I fall back on other clinical parameters to help guide fluid resuscitation.

Technique
Subxiphoid is the most common approach, but in cases of bowel gas obstruction, abdominal dressing or a protuberant abdomen the alternative intercostal approach can be performed in the mid to anterior axillary line. Before measuring I scan longitudinally and transversely through the IVC to determine if there are any anatomic strictures or extrinsic masses that would compromise IVC assessment. Most of the literature describes measuring below the entry of the hepatic veins which is typically 1-3 cm below the caval-atrial junction. I recommend watching the IVC over a few respiratory cycles and visually estimating the collapse. Visual estimation has similar reliability to measurements. I have personally found M-mode measurements are difficult for novices especially when the machine does not permit simultaneous live M-mode and B-mode display. In video review of my residents I often see a B-mode clip of an IVC that is collapsing 50% and then get an M-mode still which shows 100% collapse. This is often due to cylinder tangential effect, which occurs when the sampling beam moves from the midline of the vessel towards the edge (either due to probe movement or patient movement) leading to overestimation of collapse. Another common error occurs if the hepatic or portal vein (or even aorta when using the intercostal approach) also crosses the M-mode sampling beam and the operator accidentally measures the wrong vessel. Visual estimation avoids these errors and is simpler and quicker.

Mechanical Ventilation
Use of IVC ultrasound in mechanically ventilated patients is a bit more challenging and depends on whether the patient is spontaneously breathing or not. In the non-spontaneous breather, mechanical insufflation leads to a greater intrathoracic than extrathoracic pressure and leads to an increase in IVC diameter. One study by Feissel et al found that if the tidal volume is set to 8-10ml/kg a delta IVC (dIVC) of >12% predicted a patient that would be fluid responsive. Another similar study by Barbier et al used a tidal volume of 8.5ml/kg and found dIVC of 18% to be predictive. Personally, changing ventilator settings and performing IVC ultrasound is a bit cumbersome in the ED and I make it more simple. If the IVC is small and the patient is hypotensive I think fluids, fluids, fluids with serial IVC assessments. If the IVC is large and the patient is hypotensive with good oxygenation, I still give a fluid challenge, but am quicker to move onto pressors.

Ongoing Resuscitation
The IVC can be reassessed after fluid boluses to assess change in collapse and diameter. I find that I trust IVC measurements more than its counterpart the CVP monitor. CVP monitors, despite being invasive, assume appropriate placement and calibration. They are frequently erratic and wrong. In contrast I know exactly what I am looking at when I perform IVC ultrasound. If a CVP monitor is placed I use IVC ultrasound to double check its readings.

Conclusion
In summary, when correctly used IVC ultrasound is extremely helpful in managing the critically ill. Below are some studies that I find have been useful in shaping my understanding of the IVC:

Critically Ill/Sepsis/Hypotension:
1. Jones AE, Tayal VS, Sullivan DM, et al. Randomized, controlled trial of immediate versus delayed goal-directed ultrasound to identify the cause of nontraumatic hypotension in emergency department patients. Crit Care Med. 2004 Aug;32(8):1703-8.
2. Ferrada P, Anand RJ, Whelan J, et al. Qualitative assessment of the inferior vena cava: useful tool for the evaluation of fluid status in critically ill patients. Am Surg. 2012 Apr;78(4):468-70.
3. Nagdev AD, Merchant RC, Tirado-Gonzalez A, et al. Emergency department bedside ultrasonographic measurement of the caval index for noninvasive determination of low central venous pressure. Ann Emerg Med. 2010 Mar;55(3):290-5. Epub 2009 Jun 25.
4. Perera P, Mailhot T, Riley D, et al. The RUSH exam: Rapid Ultrasound in SHock in the evaluation of the critically lll. Emerg Med Clin North Am. 2010 Feb;28(1):29-56, vii.
5. Weekes AJ, Tassone HM, 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. Acad Emerg Med. 2011 Sep;18(9):912-21
6. Haydar SA, Moore ET, Higgins GL 3rd, et al. Effect of Bedside Ultrasonography on the Certainty of Physician Clinical Decisionmaking for Septic Patients in the Emergency Department. Ann Emerg Med. 2012 May 23.

Mechanically Ventilated:
1. Jue J, Chung W, Schiller NB. Does inferior vena cava size predict right atrial pressures in patients receiving mechanical ventilation? J Am Soc Echocardiogr. 1992 Nov-Dec;5(6):613-9.
2. Feissel M, Michard F, Faller JP, et al. The respiratory variation in inferior vena cava diameter as a guide to fluid therapy. Intens Care Med. 2004 Sep;30(9):1834-7.
3. Barbier C, Loubières Y, Schmit C, et al. Respiratory changes in inferior vena cava diameter are helpful in predicting fluid responsiveness in ventilated septic patients. Intens Care Med. 2004 Sep;30(9):1740-6. Epub 2004 Mar 18.

Trauma:
1. Sefidbakht S, Assadsangabi R, Abbasi HR, et al. Sonographic measurement of the inferior vena cava as a predictor of shock in trauma patients. Emerg Radiol. 2007 Jul;14(3):181-5. Epub 2007 Jun 1.
2. Yanagawa Y, Sakamoto T, Okada Y. Hypovolemic shock evaluated by sonographic measurement of the inferior vena cava during resuscitation in trauma patients. J Trauma. 2007 Dec;63(6):1245-8; discussion 1248.
3. Akilli B, Bayir A, Kara F, Ak A, et al. Inferior vena cava diameter as a marker of early hemorrhagic shock: a comparative study. Ulus Travma Acil Cerrahi Derg. 2010 Mar;16(2):113-8.

Peds:
1. Kosiak W, Swieton D, Piskunowicz M. Sonographic inferior vena cava/aorta diameter index, a new approach to the body fluid status assessment in children and young adults in emergency ultrasound--preliminary study. Am J Emerg Med. 2008 Mar;26(3):320-5.
2. Chen L, Hsiao A, Langhan M, et al. Use of bedside ultrasound to assess degree of dehydration in children with gastroenteritis. Acad Emerg Med. 2010 Oct;17(10):1042-7.
3. Levine AC, Shah SP, Umulisa I, et al. Ultrasound assessment of severe dehydration in children with diarrhea and vomiting. Acad Emerg Med. 2010 Oct;17(10):1035-41

Technique:
1. Wallace DJ, Allison M, Stone MB. Inferior vena cava percentage collapse during respiration is affected by the sampling location: an ultrasound study in healthy volunteers. Acad Emerg Med. 2010 Jan;17(1):96-9. Epub 2009 Dec 9.
2. Fields JM, Lee PA, Jenq KY, et al. The interrater reliability of inferior vena cava ultrasound by bedside clinician sonographers in emergency department patients. Acad Emerg Med. 2011 Jan;18(1):98-101
3. Kimura BJ, Dalugdugan R, Gilcrease GW 3rd, et al. The effect of breathing manner on inferior vena caval diameter. Eur J Echocardiogr. 2011 Feb;12(2):120-3. Epub 2010 Oct 27.
4. Saul T, Lewiss RE, Langsfeld A, et al. Inter-rater reliability of sonographic measurements of the inferior vena cava. J Emerg Med. 2012 May;42(5):600-5. Epub 2012 Jan 12.

Volume Status:
1. Cheriex EC, Leunissen KM, Janssen JH, et al. Echography of the inferior vena cava is a simple and reliable tool for estimation of 'dry weight' in haemodialysis patients. Nephrol Dial Transplant. 1989;4(6):563-8.
2. Kircher BJ, Himelman RB, Schiller NB. Noninvasive estimation of right atrial pressure from the inspiratory collapse of the inferior vena cava. Am J Cardiol. 1990 Aug 15;66(4):493-6.
3. Lyon M, Blaivas M, Brannam L. Sonographic measurement of the inferior vena cava as a marker of blood loss. Am J Emerg Med. 2005 Jan;23(1):45-50.
4. Brennan JM, Ronan A, Goonewardena S, et al. Handcarried ultrasound measurement of the inferior vena cava for assessment of intravascular volume status in the outpatient hemodialysis clinic. Clin J Am Soc Nephrol. 2006 Jul;1(4):749-53. Epub 2006 May 24.
5. Carr BG, Dean AJ, Everett WW, et al. Intensivist bedside ultrasound (INBU) for volume assessment in the intensive care unit: a pilot study. J Trauma. 2007 Sep;63(3):495-500; discussion 500-2.
6. Brennan JM, Blair JE, Goonewardena S, et al. Reappraisal of the use of inferior vena cava for estimating right atrial pressure. J Am Soc Echocardiogr. 2007 Jul;20(7):857-61.
7. Blehar DJ, Dickman E, Gaspari R. Identification of congestive heart failure via respiratory variation of inferior vena cava diameter. Am J Emerg Med. 2009 Jan;27(1):71-5.
8. Stawicki SP, Braslow BM, Panebianco NL, et al. Intensivist use of hand-carried ultrasonography to measure IVC collapsibility in estimating intravascular volume status: correlations with CVP. J Am Coll Surg. 2009 Jul;209(1):55-61
9. Moretti R, Pizzi B. Inferior vena cava distensibility as a predictor of fluid responsiveness in patients with subarachnoid hemorrhage. Neurocrit Care. 2010 Aug;13(1):3-9.
10. Resnick J, Cydulka R, Platz E, et al. Ultrasound does not detect early blood loss in healthy volunteers donating blood. J Emerg Med. 2011 Sep;41(3):270-5. Epub 2011 Mar 21.
11. De Lorenzo RA, Morris MJ, Williams JB, et al. Does a simple bedside sonographic measurement of the inferior vena cava correlate to central venous pressure? J Emerg Med. 2012 Apr;42(4):429-36. Epub 2011 Dec 22.
12. 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 Jan 3.
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