Inferior Vena Cava Collapsibility for Fluid Responsiveness

IVC byte


Inferior vena cava collapsibility detects fluid responsiveness among spontaneously breathing critically-ill patients

Journal of Critical Care May 2017 (Epub) - Pubmed Link


Take Home Points

1. In spontaneously breathing patients, an IVC collapsibility index >25% may have some predictability of volume responsiveness, but this data is not sturdy enough to rely on it definitely.

2. This study did not show improved predictability with dynamic measurements or passive leg raise which is contrary to prior literature.


Background

Every patient has an optimal balance where they have just the right amount of volume in their system. It can often be difficult to determine where patients are in that balance based on physical exam and history alone. You don’t want to give a patient too little volume such that their body is not functioning properly, but you also don’t want to drown them by pouring too much fluids through their veins. This especially comes into play with critically-ill patients. Often times, these patients are hypotensive and the question is how much fluids to give. There are certainly invasive and expensive ways that you can try to find this out, but in order to make quick bedside decisions - it would be ideal if ultrasound could help out. We know that ultrasound of the IVC is pretty good in mechanically ventilated patients with regulated tidal volumes, but IVC measurements for fluid responsiveness in the spontaneously breathing has gone back and forth. First it was thought to be useful, then useless, maybe only useful at the extremes - well this paper seeks to figure out exactly how it might be used.

For a good understanding of the terms used and the important distinction between volume status, volume responsiveness, and volume tolerance - check out this great post by @thinkingcc

Volume status vs Volume responsiveness vs Volume tolerance


Questions

Can POCUS of the IVC detect fluid responsiveness in spontaneously breathing critically ill patients?

What is the optimum cutoff for the collapsibility of the IVC?

Does incorporating a passive leg raise help in determining fluid responsiveness?


Population

Enrolled from August 2014 to July 2016 at two adult academic hospitals in the US


Inclusion

Acute circulatory failures as defined by

A) systolic blood pressure <90 mhg, or MAP <65 for ≥30 minutes

B) decreased urine output (<0.5ml/kg/h)

C) tachycardia >120 bpm ≥30 minutes

D) serum markers suggesting hypoperfusion (pH <7.3 or lactic acid >2 meq/L)


Exclusion

  • Primary traumatic, cardiogenic, obstructive, or neurogenic shock (not clear how this was determined)

  • Age <18 yo

  • Incarceration

  • Pregnancy

  • Hospitalization for >36 hours [prior to enrollment]

  • If receiving NIPPV

  • If clinical team thought they had active pulmonary edema

  • If clinical team believed that IVF might “pose clinical risk”


Design

Prospective, observational, convenience sample

IVC ultrasound was compared to NICOM (non-invasive measurement of cardiac index) to determine correlation

Fluid responsiveness defined as ≥10% increase in cardiac index as measured by NICOM

90% power estimate determined sample size of 124 patients to detect difference in AUC (area under the receiver operating characteristic curve) of 0.88 and AUC of 0.70

Clinical and demographic characteristics summarized and assessed for significant differences

Intra and interrater reliability calculated from baseline IVC calculations.

Examined baseline IVC measurement compared to change in cardiac index

Also looked at IVC inspiratory and expiratory diameter or change in cIVC after PLR or 500 mL bolus

First checked fluid responsiveness of cIVC and PLR separately then checked if a 5% change in cIVC after PLR would identify fluid responders


Intervention

Following enrollment the patients had NICOM device leads placed which records cardiac index at 1 minute intervals

Placed supine for three minute NICOM calibration period

Then two baseline 10 second videos of IVC, 1 minute apart (#1 and 2)

Then 3 minutes passive leg raise (I believe that classic straight leg raise goes from sitting to supine with legs up)

Then 1 more IVC video (#3)

Then returned to supine for 3 minutes minimum.

Then 500 mL normal saline bolus administered through pressure bag through largest gauge IV

After bolus completed, single IVC video (#4)

Vasopressors (if patient was requiring) were held at constant rate throughout study

During review, images were frozen during maximum expiratory and minimum inspiratory diameter. Measured 3 cm caudal to IVC right atrium junction.

Calculated cIVC (collapsibility of IVC or caval index)

cIVC = (IVC expiratory diameter - IVC inspiratory diameter)/IVC expiratory diameter

Reviewer were blinded to NICOM results


Who did the ultrasounds?

3 study physicians (from departments of emergency medicine and pulmonary critical care medicine)

Training included POCUS (but does not specify to what degree, only mentioning they did not have ultrasound fellowship training)


The Scan

Phased array probe (1-5 MHz - actually says Hz in this paper - really low!)

phased array probe

Subcostal long axis view

Study participants not asked to take deep inspiratory breath

IVC identified by junction with right atrium and/or presence of hepatic veins

M-mode not used, only B mode clips slowed to identify maximum and minimum diameter


Learn how to scan the IVC! 5 Minute Sono IVC

Recent article on what is the best way to measure and scan IVC (it was the way they did in this study)

Article on technical pitfalls of IVC scanning


Results

79 excluded due to various criteria

  • 30 because IVF contraindicated

  • 23 due to altered mental status

  • 19 excluded from analysis because could not get images

N = 124

49.2% (61) were fluid responders

Differences between responders and nonresponders in demographics:

  • more COPD in fluid responders

  • more pulmonary HTN in nonresponders

Mean IVF of 4060mL prior to enrollment


Primary Results

Baseline cIVC had AUC 0.84

Optimal cIVC was 24.6%, rounded to 25%

sensitivity 87%

specificity 81%

+LR 4.56

-LR 0.16


Secondary Outcomes

Max or min baseline IVC did not detect fluid responsiveness

Change in cIVC with PLR did not detect fluid responsiveness

PLR + baseline cIVC did not help predict fluid responsiveness


Other Findings

PLR produced smaller change in cIVC in fluid responders compared to fluid nonresponders (opposite of what you would expect) → perhaps PLR did not stimulate the bolus or perhaps cIVC is just not a good measure of fluid responsiveness

False Positive (cIVC >25% but did not respond to IVF) - 4 patients with low EF or pulm HTN (authors states they have the capacitance for fluid but are not able to use it to augment stroke volume)

cIVC baseline:

Intrarater reliability: 0.92

Interrater reliability: 0.67

Supplemental Data:

  • Baseline IVC inspiratory diameter - best cut off was ≥0.81 cm, yielding 71.4% sensitivity, and 16.4% specificity

  • Baseline expiratory diameter was even worse.


Limitations

Is NICOM reliable gold standard?

Retrospectively derived cutoff of >25%

Although decent AUC, not sufficiently sensitive or specific to rule out or rule in

Exclusions! Many causes of shock were excluded, unclear how this would perform in undifferentiated shock population

Poor interrater reliability 0.67 - maybe this is hard to reproduce

Measured with clips and scrolling - not as easy as visual estimation

Patients got mean of over 4 liters of fluid prior to intervention - this shouldn’t affect the test itself but changes population to potentially have less fluid responders (affect external validity)

No patient centered outcomes - does it matter if cIVC predicts changes in cardiac index?


Take Home Points

1. In spontaneously breathing patients, an IVC collapsibility index >25% may have some predictability of volume responsiveness, but this data is not sturdy enough to rely on it definitely.

2. This study did not show improved predictability with dynamic measurements or passive leg raise which is contrary to prior literature.


Our score

3 Probes


More Recent Articles on IVC Collapsibility

Does Respiratory Variation in Inferior Vena Cava Diameter Predict Fluid Responsiveness: A Systematic Review and Meta-Analysis.

Diagnostic Accuracy of the Inferior Vena Cava Collapsibility to Predict Fluid Responsiveness in Spontaneously Breathing Patients With Sepsis and Acute Circulatory Failure


Other Recent FOAMed On this Topic

EMNerd Post

EMCrit physiology of IVC

The Bottom Line review


Published on 07/31/17 02:00 AM
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