Intensivist Use Of Hand-carried Ultrasonography To Measure Ivc Collapsibility In Estimating Intravascular Volume Status: Correlations With Cvp

Dissections

DIAGNOSIS 19 August 2009

Evidence-based Medicine for Surgeons

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 al Journal: J American College of Surgeons 2009; 209: 55–61 Centre: 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

RESEARCH QUESTION

IVC collapsibility index (IVC - CI) versus CVP

Population Adult patients admitted to a highacuity, 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

SUMMARY Number

Mean CVP (mm Hg)

High (> 0.6)

13

7.40

Intermediate (0.2 - 0.6)

41

9.75

Low (< 0.2)

29

12.0

IVC-CI group

An 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.”

CVP measurement.

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 physicianperformed, 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.

IVC-CI consists of the difference between the end-expiratory (IVCDexp) and end-inspiratory IVC diameter (IVCD-insp) divided by IVCDexp. 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.

EBM-O-METER Evidence level

Overall rating

Bias levels

Double blind RCT

Sampling

Randomized controlled trial (RCT) Prospective cohort study - not randomized Case controlled study Case series - retrospective

Trash Life's too short for this

Swiss cheese Full of holes

Safe Holds water



Newsworthy “Just do it”

Comparison Measurement

l | Novel l | Feasible l Ethical l | Resource saving l

Interesting

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

© Dr Arjun Rajagopalan



SAMPLING Sample type

Inclusion criteria

Simple random

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

Stratified random Cluster Consecutive

Exclusion criteria

Final score card

Not stated

IVC-CI vs CVP study Target

?

Accessible

124

Intended

101

Convenience

Drop outs

18

Judgmental

Study

83



= Reasonable | ? = Arguable |  = Questionable Duration 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.

COMPARISON Randomized

Case-control

Non-random

Historical

None

Controls - details Allocation 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

1.IVC-CI by INBU

?

N

?

Y

Y

N

Blinding

N

Scoring

?

Protocols

Y

Training

Device suited to task

Observer error Gold std.

Device error Repetition

Device used

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.

© Dr Arjun Rajagopalan