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IVC ultrasound:The Ultimate Myth

Dr Justin BowraSydney Adventist & Royal North Shore Hospitals

SMACC 2013

Thanks esp to Drs Kylie Baker & Adrian Goudie

IVC ultrasound:

Holy Grail…

…or Wholly Nonsense?

TheIVC

The IVC

TThe inferior vena cava (IVC)he inferior vena cava (IVC)

Largest vein in the body.Largest vein in the body. BBreathe in: diameter decreasesreathe in: diameter decreases NB oNB opposite if ventilatedpposite if ventilated DDehydration: ehydration: ‘flattens out’.‘flattens out’. DDownstream occlusion (eg tamponade) or ownstream occlusion (eg tamponade) or

fluid overload (eg CCF): fluid overload (eg CCF): ‘fattens up’.‘fattens up’.

Subxiphoid longitudinal: shocked & drySubxiphoid longitudinal: shocked & dry

Subxiphoid transverse: massive PESubxiphoid transverse: massive PE

MMaybe the IVC can help me in the resus room.aybe the IVC can help me in the resus room.

1.1.IIs there fluid overload or a downstream s there fluid overload or a downstream occlusion (eg PE, tamponade)?occlusion (eg PE, tamponade)?

2.2.Should I give more IV fluids to this shocked Should I give more IV fluids to this shocked patient?patient?

WWhy is this an attractive idea?hy is this an attractive idea?

CheapCheap

EEasy to find & measureasy to find & measure

NNoninvasiveoninvasive

RRapidapid

RRepeatableepeatable

ParametersParameters

SShape (fat or flat?)hape (fat or flat?)

MMaximum IVC diameter (IVCD)aximum IVC diameter (IVCD)

IVC collapsibility index (IVCCI) = (max IVC collapsibility index (IVCCI) = (max –– min)/max min)/max x100x100

RResponse to ‘sniff test’esponse to ‘sniff test’

IVCCI (hypovolaemia) = 69%IVCCI (hypovolaemia) = 69%

IVCCI (CCF) = 10%IVCCI (CCF) = 10%

Critical care drs are now very, very Critical care drs are now very, very iinterested in the IVC nterested in the IVC

SStatementstatements

TTextbooksextbooks

Clinical aClinical algorithmslgorithms

EExperts xperts

PPapers apers

TTalks (like this one)alks (like this one)

WWishful thinkingishful thinking

I WANT TO BELIEVE

I WANT TO BELIEVE

I WANT TO BELIEVE

IVC MYTHS

Myth 1:The IVC

correlates with

volume Status

MEDSCAPE

Maximum IVC diameter (IVCD)

Dipti A et al. AJEM 2012

IVC diameter (not IVCCI)

140 papers 5 prospective trials

Gold standard = clinical Dx shock

IVCD lower in shocked patients

All 5 studies agreed

‘Moderate level of evidence suggests that the IVC diameter is consistently low in hypovolemic status when

compared with euvolemic.’

But wait a minute!

IVC 14-15mm = shocked (2 studies)

IVC 14-15mm = normal (3 studies)

Why?

Different ethnicity [Asian versus US/Turkish populations]?

Weekes and Yanagawa’s cases & ‘controls’ were the same patients

The IVCD improved after a fluid bolus and only when it was clinically obvious that the patient had improved!

So:

IVCD <0.9cm correlates with haemorrhagic shock… in patients you can already tell are shocked.

(Sefidbakht 2007, Yanagawa 2005, Weekes 2011)

Serial IVCDs get bigger with fluids… in patients you can already tell are getting better.

And if it stays <0.9cm after IVT, shock recurs in these patients. (Yanagawa 2007)

What about a big IVCD in the spontaneously breathing shocked

patient?

What a big IVCD in the spontaneously breathing shocked

patient?

No-one knows.

What about ventilated patients?

Do you like CVP as a surrogate for fluid status?

Small IVCDSmall IVCD

IVCD <1.2cm suggests RAP <10mmHg.

( Jue J et al 1992)

What about a large IVCD?

IVCD >2.5cm and minimal collapse (<10%)

correlates with raised RAP (>15mmHg)

= ‘the tank is full’.

…probably.

(Charron 2006: 100 patients)

So, in shocked patients:

IVCD Correlation

Spontaneously breathing

<0.9cm Empty

Anything else

Dunno

Ventilated <1.2cm Probably empty

>2.5cm Probably full

Or… PE/PTX/tamponade

Or… Other stuff that raises CVP

Okay, what about IVCcollapsibility index? (IVCCI)

IVCCI in ventilated patients

A minimal collapse (<10%) = raised RAP (>15mmHg)

= ‘the tank is full’… maybe.

(Charron 2006: 100 patients)

What about IVCCI in the patient sitting up?

In breathless patients at 45 degrees:

Low IVCCI <15% suggested clinical diagnosis of CCF.

(Blehar et al, 2009)

…and a high IVCCI? No-one knows.

What about shocked, spontaneously What about shocked, spontaneously breathing, supine patients?breathing, supine patients?

IVCCI > 50% … CVP <8mm (Nagdev 2010)

IVCCI <50% … CVP >10mm Hg (Kircher et al 1990)

Gold standard?

BUT

IVCCI Correlation

Kircher <50% full

Nagdev >50% empty

Sefidbakht 27% shock

20% euvolaemic

Weekes 16-72% shock

7-33% euvolaemic

So, in shocked patients:IVCCI Correlation

Spontaneously breathing

>72% Probably empty

<16% Probably full

Anything else

Dunno

Ventilated >10% Dunno

<10% Probably full

Or… PE/PTX/tamponade

Or… Other stuff that raises CVP

WHAT’S GOING ON?

Big statements…

From small studies.

(Maybe IVC just isn’t that precise)(Maybe IVC just isn’t that precise)

MMaybe CVP ≠ fluid statusaybe CVP ≠ fluid status

MMaybe ‘fluid status’ = the wrong question.aybe ‘fluid status’ = the wrong question.

So let’s try a new question!So let’s try a new question!

Why is this so?

Myth 2:IVC ultrasound

Can predictFluid

responsiveness

LOTS OF AUTHORITIES

‘‘The IVC can predict fluid responsiveness’The IVC can predict fluid responsiveness’

Empty IVC IV fluids improved end-organ perfusion

Full IVC IV fluids won’t help

Logic: It makes sense.

Let’s look at the evidence

Low IVCD that stays low is usefulLow IVCD that stays low is useful

Yanagawa 2007

So what about IVCCI?

Lanspa M et al. Shock 2013

Small study: 14 spontaneously breathing patients in septic shock, who had all received 2-5L IVT.

Intervention: 10ml/kg fluid challenge.

Gold standard: >15% increase in CI using TTE.

An IVCCI <15% ruled out fluid responsiveness.

Muller L et al. Critical Care 2012

Small study: 40 spontaneously breathing patients with clinical signs of shock.

Intervention: 500ml fluid challenge.

Gold standard: >15% increase in CI using TTE.

Their conclusion?

‘IVCCI cannot reliably predict fluid responsiveness in spontaneously breathing patients with ACF.’

IVCCI >40% often associated with fluid responsiveness.

Positive predictive value 72%.

In spontaneously breathing patients with shock:

An IVCCI <15% seems to rule out fluid responsiveness (in a small study).

IVCCI >40% often predicts fluid responsiveness (72% of the time)… in a small study.

What about ventilated patients?

3 small studies in ventilated patients:

Barbier 2004: 23 patients: IVCCI >18% predicted fluid responsiveness (90% sens 90% spec)

Feissel 2004: 39 patients: IVCCI >12% predicted fluid responsiveness (93% PPV and 92% NPV)

Moretti 2010: 29 patients: IVCCI >16% was only 70% sensitive for fluid responsiveness!

So, can IVCCI predict fluid responsiveness in shocked patients?

If spontaneously breathing:

IVCCI <15% seems to rule out fluid responsiveness (in a small study).

If ventilated:

IVCCI >18% might predict fluid responsiveness

(in 3 small studies).

Not great!

So let’s change the question (again).

Myth 3:IVC ultrasound

Can predictFluid

tolerance

WEINGART, ULTRASOUNDPODCAST,

LOTS OF OTHERS

Surely it’s SAFE to give fluids if the IVC is flat? And maybe it’s BAD to give fluids if the IVC is

distended?

Well, it seems to make sense. And most of us follow this approach.

Surely it’s SAFE to give fluids if the IVC is flat? And maybe it’s BAD to give fluids if the IVC is

distended?

Well, it seems to make sense. And most of us follow this approach.

But there’s no evidence for these statements.

Surely it’s SAFE to give fluids if the IVC is flat? And maybe it’s BAD to give fluids if the IVC is

distended?

Well, it seems to make sense. And most of us follow this approach.

But there’s no evidence for these statements.

And there’s evidence that IVC is affected by a number of other factors.

What else can splint the IVC open?

Not just XS fluids

Obstructive shock: tamponade, tension PTX, massive PE

Raised intrathoracic pressure: e.g. status asthmaticus

Chronic comorbidities: eg right heart disease

Even probe position: too close to the diaphragm may ‘artificially reduce’ IVC collapse (Wallace 2010)

What else can cause the IVC to collapse?

1. Ventilation:Mechanical ventilation ≠ spontaneous ventilation‘Diaphragmatic breathing’ (using abdominal wall muscles as well as the chest wall): (Kimura 2011)

2. Raised intra-abdominal pressure (in animal studies: Takata 1990)

3. Even pressure from the probe! (anecdotally)

Just because the IVC collapses, it doesn’t mean it’s safe to give fluids.

Most of us do, but that’s not evidence.

IVCultrasound

commandments

IVC diameter (cm)

IVCCI Estimated RA

pressure (mm Hg)

<1.7 >50% 0-5

>1.7 >50% 6-10

>1.7 <50% 11-15

‘dilated’

none >15

Commandment 1. THOU SHALT

USE THIS TABLE

ASE, ACEP, RUSH

IVC diameter

(cm)

IVCCI Estimated RA pressure

(mm Hg)

<1.7 >50% 0-5

>1.7 >50% 6-10

>1.7 <50% 11-15

‘dilated’ none >15

ASE guidelines 2005

Not validated in critically ill patients.Not validated in critically ill patients.

IVCD changes with patient position.IVCD changes with patient position.

ED patients are either sitting up (SOB) or supine ED patients are either sitting up (SOB) or supine (shock).(shock).

ASE guidelines are based on patients in the ASE guidelines are based on patients in the left left decubitus decubitus position.position.

And it’s based on sonographers’ measurements.And it’s based on sonographers’ measurements.

So?So?

IVC dimensions measured by clinicians don’t correlate IVC dimensions measured by clinicians don’t correlate with those measured by cardiac sonographers!with those measured by cardiac sonographers!

Randazzo et al: 70.2% overall raw agreement in IVC measurements between EP (trained for 3h in focused cardiac US) and formal echocardiograms performed

within 4h.

IVC diameter

(cm)

IVCCI Estimated RA pressure

(mm Hg)

<1.7 >50% 0-5

>1.7 >50% 6-10

>1.7 <50% 11-15

‘dilated’ none >15

ASE guidelines 2005

IVC diameter

(cm)

IVCCI Estimated RA pressure

(mm Hg)

<1.7 >50% 0-5

>1.7 >50% 6-10

>1.7 <50% 11-15

‘dilated’ none >15

ASE guidelines 2005

Commandment 2. Thou shalt Place the

probeIn subcostal

long axisAboutHere.AboutHere.

ASE, ACEP, stanford uni, ultrasoundpodcast

Or in the mid-Axillary line

Just likeA fast exam

ACEP

What probe?What probe?

What preset?What preset?

Where?Where?

Long or short axis?Long or short axis?

What probe should we use?What probe should we use?No-one knows.No-one knows.

What preset?What preset?No-one knows.No-one knows.

Where should we put the probe? Where should we put the probe?

How should we align it?How should we align it?

Where should we put the probe? Where should we put the probe?

How should we align it?How should we align it?

NO-ONE KNOWS!NO-ONE KNOWS!

Where Where can can we put the probe?we put the probe?

Subxiphoid long axis Subxiphoid transverse Midaxillary line long axis Midaxillary line transverse Transpyloric long axis Transpyloric transverse

Subxiphoid long axis: most studies & experts measure here.

Subxiphoid short axis: RUSH, Akilli.

MID-AXILLARY LINEAs for EFAST

Midaxillary long axis: ACEP website recommends as an alternative.

Subcostal trans: MAX & MIN.Subcostal trans: MAX & MIN.

Watch Watch howhow the IVC collapses (subcostal) the IVC collapses (subcostal)

Watch Watch howhow the IVC collapses (RUQ) the IVC collapses (RUQ)

Short axis or long axis?Short axis or long axis?

Short axis pitfall:Short axis pitfall:IVC slides craniocaudally!IVC slides craniocaudally!

Long axis pitfall #1Long axis pitfall #1 cylinder effect cylinder effect

Long axis pitfall #1Long axis pitfall #1 cylinder effect cylinder effect

Long axis pitfall #2Long axis pitfall #2IVC lateral movementIVC lateral movement

Subcostal long axis approach: probably OK Subcostal long axis approach: probably OK (if you’re careful).(if you’re careful).

Midaxillary longitudinal approach: probably Midaxillary longitudinal approach: probably not OK.not OK.

Any transverse view: dunno.Any transverse view: dunno.

But no-one’s really sure.But no-one’s really sure.

Commandment 3. Thou shalt

Measure at the HVC confluence

(JUST ABOUT EVERYONE)

Where should we measure the IVC?Where should we measure the IVC?

TThe IVC collapses non-uniformlyhe IVC collapses non-uniformly

Site IVCCI

At level of diaphragm

20% (+/-16%)

At hepatic vein inlet

30% (+/-21%)

At left renal vein

35% (+/-22%)

In supine healthy volunteersIn supine healthy volunteersWallace et al, 2010Wallace et al, 2010

The IVC collapses non-uniformlyThe IVC collapses non-uniformly

The IVC collapses non-uniformlyThe IVC collapses non-uniformly

Which site is best?Which site is best?

IVCCI measured above hepatic confluence does not IVCCI measured above hepatic confluence does not correlate with IVCCI measured at other sites.correlate with IVCCI measured at other sites.

Wallace’s conclusion:Wallace’s conclusion:‘‘Clinicians should avoid Clinicians should avoid measuring IVCCI measuring IVCCI at the junction of at the junction of

the right atrium and IVC’the right atrium and IVC’

But there was no gold standard in that But there was no gold standard in that study.study.

SSo how did Wallace know which site o how did Wallace know which site was the right one?was the right one?

And it gets murkier:And it gets murkier:

ASE recommends measuring 1-2cm from RA

Yanagawa found a correlation (IVCD & RAP) just below diaphragm

Charron found a correlation (IVCD & RAP) measured <2cm from RA

Akilli (IVCD) & Blehar (IVCCI) found a correlation

at / distal to hepatic veins

Corl found no correlation (IVCI & CO) measured 3cm distal to the RA

So…So…

We don’t even know where best to measure the IVC.

Should we avoid measuring above the hepatic confluence?

Should we insist on it?

Commandment 4. Try

M-mode (RUSH, stanford university)

Should I measure in M-mode?Should I measure in M-mode?

It’s lots of fun and displays both max & min diameter It’s lots of fun and displays both max & min diameter on the same image.on the same image.

Many experts (eg RUSH exam & Stanford Uni website) Many experts (eg RUSH exam & Stanford Uni website) recommend it.recommend it.

I like it. I like it.

But even experienced users can get the angles But even experienced users can get the angles wrong…wrong…

M-mode pitfalls:M-mode pitfalls:wrong angle, and IVC moveswrong angle, and IVC moves

TTop tip:op tip:

When starting out, aWhen starting out, avoid M-mode. void M-mode.

Commandment 5. Try

A sniff test(ASE, RUSH)

SSniff test (great in healthy niff test (great in healthy volunteers)volunteers)

Should I perform a sniff test?Should I perform a sniff test?

RUSH exam & American Society of Echo recommends RUSH exam & American Society of Echo recommends it.it.

But I can’t find any evidence for it.But I can’t find any evidence for it.

And half the time I lose sight of the IVC when the And half the time I lose sight of the IVC when the patient sniffs!patient sniffs!

And I can’t help thinking…And I can’t help thinking…

If the patient is well enough to perform a If the patient is well enough to perform a sniff test, I probably donsniff test, I probably don’’t need to be t need to be

looking at their IVC.looking at their IVC.

IVC ultrasound: what do we really know?IVC ultrasound: what do we really know?

IVC ultrasound: what do we really know?IVC ultrasound: what do we really know?

WWe e don’tdon’t know where to measure it know where to measure it……

IVC ultrasound: what do we really know?IVC ultrasound: what do we really know?

WWe e don’tdon’t know where to measure it know where to measure it … … or or even even howhow to measure it! to measure it!

IVC ultrasound: what do we really know?IVC ultrasound: what do we really know?

WWe e don’tdon’t know where to measure it, or even know where to measure it, or even how to measure it!how to measure it!

WWe e dondon’’tt know if a sniff test helps.know if a sniff test helps.

IVC ultrasound: what do we really know?IVC ultrasound: what do we really know?

WWe e don’tdon’t know where to measure it, or even know where to measure it, or even how to measure it!how to measure it!

WWe e dondon’’tt know if a sniff test helps.know if a sniff test helps. WWe know that ASE table is probably useless.e know that ASE table is probably useless.

IVC ultrasound: what do we really know?IVC ultrasound: what do we really know?

WWe e don’tdon’t know where to measure it, or even know where to measure it, or even how to measure it!how to measure it!

WWe e dondon’’tt know if a sniff test helps.know if a sniff test helps. WWe know that ASE table is probably useless.e know that ASE table is probably useless. WWe know everyone’s IVC is different, and that e know everyone’s IVC is different, and that

there are plenty of confounding factorsthere are plenty of confounding factors……

IVC ultrasound: what do we really know?IVC ultrasound: what do we really know?

WWe e don’tdon’t know where to measure it, or how know where to measure it, or how to measure it.to measure it.

WWe e dondon’’tt know if a sniff test helps.know if a sniff test helps. WWe know that ASE table is probably useless.e know that ASE table is probably useless. WWe know everyone’s IVC is different, and that e know everyone’s IVC is different, and that

there are plenty of confounding factorsthere are plenty of confounding factors……

Patient size & positionPatient size & position

Manner of breathingManner of breathing

Measurement siteMeasurement site

Etc Etc

IVC ultrasound: what do we really know?IVC ultrasound: what do we really know?

Shock + flat collapsing IVC = give fluid.Shock + flat collapsing IVC = give fluid.

<0.9cm (spontaneous breathing)<0.9cm (spontaneous breathing)

<1.2cm IVCD, IVCCI >18% (ventilated)<1.2cm IVCD, IVCCI >18% (ventilated)

Shock + distended IVC = don’t give fluid.Shock + distended IVC = don’t give fluid.

>2.5cm, IVCCI <10% (ventilated)>2.5cm, IVCCI <10% (ventilated)

SSerial IVC measurements seem useful.erial IVC measurements seem useful.

IVC ultrasound: what do we really know?IVC ultrasound: what do we really know?

Shock + flat collapsing IVC = give fluid.Shock + flat collapsing IVC = give fluid.

<0.9cm (spontaneous breathing)<0.9cm (spontaneous breathing)

<1.2cm IVCD, IVCCI >18% (ventilated)<1.2cm IVCD, IVCCI >18% (ventilated)

Shock + distended IVC = don’t give fluid.Shock + distended IVC = don’t give fluid.

>2.5cm, IVCCI <10% (ventilated)>2.5cm, IVCCI <10% (ventilated)

SSerial IVC measurements seem useful.erial IVC measurements seem useful.MAYBE

‘The IVC is the answer’

But I tried itAnd it didn’t

workAnd the sniff

Test seems likeA waste of

time

You mustn’t bedoing it

right

Or maybe it’sa load ofcobblers

The dark art of IVC measurement.

‘Give a bolus of fluid’

…I think

Take-home message

Check the evidence Check the evidence yourselfyourself before you change before you change your practice.your practice.

Be a doctor. Clinical context is more important than Be a doctor. Clinical context is more important than IVC ultrasound.IVC ultrasound.

IVC probably does help at extremes (fat & full IVC probably does help at extremes (fat & full versus flat & collapsing).versus flat & collapsing).

Thanks to Thanks to

Dr Kylie Baker (for that literature review)

Dr Adrian Goudie (for that IVC long axis image)

Drs Mike Blaivas, Matt Dawson, Cliff Reid & Scott Weingart (for their advice & input)

References References

ACEP http://www.acep.org/Content.aspx?id=80791 Akilli B, Bayir A et al. Inferior vena cava diameter as a marker of early

hemorrhagic shock: a comparative study. Ulus Travma Acil Cerrahi Derg 2010;16(2):113-8.

Baker, K. Review of Bedside Sonography for Guidance of Fluid Therapy in the Emergency Department. (unpublished)

Barbier C, Loubières Y, Schmit C, Hayon J, Ricôme JL, Jardin F, Vieillard-Baron A. Respiratory changes in inferior vena cava diameter are helpful in predicting fluid respon- siveness in ventilated septic patients. Intensive Care Med 2004; 30:1740–1746

Blehar DJ, Dickman E, Gaspari R. Identification of congestive heart failure via respiratory variation of inferior vena cava. Am J Em Med 2009;27:71–5.

Blehar et al. Inferior vena cava displacement during respirophasic ultrasound imaging. Critical Ultrasound Journal 2012, 4:18

References References

Charron C, Caille V, Jardin F, Viellard-Baron A. Echocardiographic measurement of fluid responsiveness. Curr Op Crit Care 2006; 12(3): 249-54.

Corl K, Napoli A, 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

Dipti A et al. Role of inferior vena cava diameter in assessment of volume status: a meta-analysis. AJEM 2012 (30). 1414 -19.

Feissel M, Michard F, Faller JP, Teboul JL (2004) The respiratory variation in inferior vena cava diameter as a guide to fluid therapy. Intensive Care Med 30:1834–1837

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; 5: 613-9.

References References

Kimura BJ, Dalugdugan R, Gilcrease GW 3rd, Phan JN, Showalter BK, Wolfson T. The effect of breathing manner on inferior vena caval diameter. Eur J Echocardiogr. 2011 Feb;12(2):120-3

Kircher B, Himelman R, Schiller N. Noninvasive estimation of right atrial pressure from the inspiratory collapse of the inferior vena cava. AM J Cardiol 1990; 66: 493-6.

Lang RM, Bierig M, Devereux F et al Recommendations for chamber quantification: a report from the American Society of Echocardiography’s guidelines and standards committee and the chamber quantification writing group, developed in conjunction with the European Association of Echocardiography, ad branch of the European Society of Cardiology. J Am Soc Echocardiogr 2005; 18: 1440-63.

Lanspa MJ, Grissom CK et al. Applying dynamic parameters to predict hemodynamic response to volume expansion in spontaneously breathing patients with septic shock. Shock 2013. 39(2). pp. 155-160

References References

Medscape http://www.medscape.com/viewarticle/727097 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.

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Nagdev AD, Merchant RC, Tirado-Gonzalez A, Sisson CA, Murphy MC. 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

Perera P et al. The RUSH Exam 2012: Rapid Ultrasound in Shock in the Evaluation of the Critically Ill Patient. Em Med Clinics. Ultrasound Clin 7 (2012) 255–278

References References

Randazzo MR, Snoey ER, Levitt MA, et al. Accuracy of emergency physician assessment of left ventricular ejection fraction and central venous pressure using echocardiography. Acad Emerg Med 2003;10:973–7.

Sefidbakht S, Assadsangabi R, Abbasi HR, Nabavizadeh A. Sonographic measurement of the inferior vena cava as a predictor of shock in trauma patients. Emerg Radiol 2007; 14(3): 181-185.

Stanford University. http://www.stanford.edu/group/ccm_echocardio/cgi-bin/mediawiki/index.php/IVC

Takata M, Wise RA, Robotham JL. Effect of abdominal pressure on venous return: abdominal vascular zone conditions. J Appl Physiol 1990 (69):1961– 1972

ultrasoundpodcast http://www.ultrasoundpodcast.com/?s=ivc )ultrasoundpodcast http://www.ultrasoundpodcast.com/?s=ivc )

References References

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Weekes A, Tassone HM, Tayal VS, Babcok AJ, Norton J. Sonodynamic Comparison of Systolic Blood Pressure to Aortic Velocity Time Integral Measurements as a Measure of Fluid Responsiveness In Non-Traumatic Symptomatic Hypotensive Emergency Department Patients. Annals of Emergency Medicine 2010. Volume 56, Issue 3 Suppl, pS76

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References References

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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; 63(6): 1245-1248.