Intensivist use of hand-carried ultrasonography to measure IVC collapsibility in estimating intravascular volume status: correlations with CVP

Authors: Stawicki SP, Braslow BM, Panebianco NL, et alJournal: J American College of Surgeons 2009; 209: 55–61Centre: University of Pennsylvania School of Medicine, Philadelphia, PA, USA

BACKGROUND

Clinical examination is known to be unreliable in the evaluation of intravascular volume, leading to the need for more objective means of assessment. Recent technological advances have made ultrasonography equipment compact, mobile, easy to use, and inexpensive. Clinician-performed bedside ultrasonography examinations have become popular methods of round-the-clock, rapidly deployed strategies for initial assessment and guide to subsequent therapy in a wide range of acute clinical situations. Intensivist-performed bedside ultrasonography (INBU) has been used in evaluation of the circulating volume status in critically ill patients. One widely used parameter in IVC assessment of intravascular volume is the IVC collapsibility index (IVC-CI).

IN SUMMARY IVC collapsibility index (IVC - CI) versus CVP

Number Mean CVP (mm Hg)

IVC-CI group

High (> 0.6) 13 7.40

Intermediate (0.2 - 0.6) 41 9.75

Low (< 0.2) 29 12.0An IVC-CI in the intermediate range (0.20 - 0.60) was not helpful in

discriminating CVP

Authors' claim(s): “...Measurements of IVC-CI by INBU can provide a useful guide to noninvasive volume status assessment in SICU patients. ... Additional studies are needed to confirm and expand on findings of this study.”

THE TISSUE REPORT Let's first set aside the flaws in this study; there are many and are easily spotted. The authors are quick to state that "large-scale prospective studies will be needed to confirm and expand on the findings of the present study". This study enlarges the growing list of physician-performed, bedside ultrasound assessments that add value to the process of decision making in acute situations. Future reports on this matter will clarify the value of this study.

The devil is in the details (more on the paper) ...

© Dr Arjun Rajagopalan

EBM-O-METER

Evidence level Overall rating Bias levelsDouble blind RCT

TrashLife's too

short for this

Swiss cheese

Full of holes

SafeHolds water

News-worthy

“Just do it”

Sampling

Randomized controlled trial (RCT) Comparison

Prospective cohort study - not randomized Measurement

Case controlled study Interesting l | Novel l | Feasible l Ethical l | Resource saving lCase series - retrospective

RESEARCH QUESTION

Population

Adult patients admitted to a high-acuity, surgical intensive care unit.

Indicator variable

IVC collapsibility index (IVC-CI) measured by intensivist-performed bedside ultrasonography (INBU) using a hand-carried ultrasonography unit.

Outcome variable

Primary: circulating volume status

Comparison

CVP measurement.

DIAGNOSIS

19 August 2009DissectionsDissectionsEvidence-based Medicine for Surgeons

IVC-CI consists of the difference between the end-expiratory (IVCD-exp) and end-inspiratory IVC diameter (IVCD-insp) divided by IVCD-exp. IVC diameter measurement is obtained using M-mode ultrasonography. Studies have shown an inverse relationship between IVC-CI and right atrial (RA) pressure or CVP, where higher IVC-CI values correlate with low RA filling pressures (low CVP) and lower IVC-CI values correlate with higher RA filling pressures.

For eg. if IVCD-exp = 18.3 mm and IVCD-insp = 3.8mm, the IVC-CI would be (18.3 - 3.8)/18.3, or 0.792.

SAMPLING Sample type Inclusion criteria Exclusion criteria Final score card

Simple random Adult (older than 18) patients admitted to an SICU who had a CVP catheter placed

Not stated IVC-CI vs CVP study

Stratified random Target ?

Cluster Accessible 124

Consecutive Intended 101

Convenience Drop outs 18

Judgmental Study 83

= Reasonable | ? = Arguable | = QuestionableDuration of the study: October 2006 and April 2007

Sampling bias: The drop off between accessible patients and the study group is very large. This is a single centre experience.

© Dr Arjun Rajagopalan

COMPARISON Randomized Case-control Non-random Historical None

Controls - detailsAllocation details The INBU-derived measurements of IVC-CI were compared with invasively measured CVP.

After completion of the ultrasonography examination, members of the SICU team caring for the patient, blinded to ultrasonography findings, provided data on a standardized form about patient demographics, vital signs, and invasive hemodynamic monitoring variables obtained at the time of the examination.

Comparability -

Disparity -

Comparison bias: -

MEASUREMENT Measurement error

Device used Device error Observer error

Device suited to task

Y ? N

Rep

etitio

n

Gol

d st

d.

Trai

ning

Prot

ocol

s

Sco

ring

Blin

ding

1.IVC-CI by INBU ? N ? Y Y N Y

All intensivists had earlier ultrasonography experience in general bedside sonography (including focused assessment with sonography for trauma, gallbladder, aorta, and first-trimester pregnancy evaluations) and an additional 3 hours of didactic review of the techniques of acquisition and interpretation of sonographic images of the heart and IVC.

A record of each examination was stored in the form of static images and 6-second digital video clips. Sonographers recorded their interpretation of each examination and completion times on a standardized form blinded to the results of all invasive and noninvasive monitoring data.

IVC-CI was defined in one of two ways, depending on whether or not the patient was intubated.

IVC-CI measurements were grouped by range (<.20, 0.20 to 0.60, and >0.60). CVP values were also grouped into three ranges: <7 mmHg, 7 to 12 mmHg, and >12 mmHg.

Measurement bias: There was no attempt to measure observer variability: a critical element of bias in these studies. The grouping of CVP by three ranges is arbitrary. CVP is well known to have no standardizable normal ranges.