A comparison of the ultrasound measurement of the inferior vena cava obtained with cardiac and convex transducers

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Journal of Ultrasonography

Polish Ultrasound Society (Polskie Towarzystwo Ultrasonograficzne)

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VOLUME 17 , ISSUE 71 (March 2017) > List of articles

A comparison of the ultrasound measurement of the inferior vena cava obtained with cardiac and convex transducers

Paweł Andruszkiewicz / Dorota Sobczyk / Krzysztof Nycz / Izabela Górkiewicz-Kot / Mirosław Ziętkiewicz / Karol Wierzbicki / Jacek Wojtczak / Ilona Kowalik

Keywords : point-of-care ultrasound, fluid responsiveness, inferior vena cava diameter, collapsibility index

Citation Information : Journal of Ultrasonography. Volume 17, Issue 71, Pages 241-245, DOI: https://doi.org/10.15557/JoU.2017.0035

License : (CC BY-NC-ND 4.0)

Received Date : 22-August-2017 / Accepted: 17-November-2017 / Published Online: 29-December-2017

ARTICLE

ABSTRACT

Background

Ultrasound measurement of the inferior vena cava diameter and its respiratory variability are amongst the predictors of fluid volume status. The primary purpose of the present study was to compare the consistency of inferior vena cava diameter measurements and the collapsibility index, obtained with convex and cardiac transducers. A secondary aim was to assess the agreement of the patient’s allocation to one of the two groups: “fluid responder” or “fluid non-responder”, based on inferior vena cava collapsibility index calculation made with two different probes.

Methods

20 experienced clinicians blinded to the purpose of the study analysed forty anonymized digital clips of images obtained during ultrasound examination of 20 patients. For each patient, one digital loop was recorded with a cardiac and the second with a convex probe. The participants were asked to determine the maximal and minimal diameters of the inferior vena cava in all presented films. An independent researcher performed a comparative analysis of the measurements conducted with both probes by all participants. The calculation of the collapsibility index and allocation to “fluid responder” or “fluid non-responder” group was performed at this stage of the study.

Results

The comparison of measurements obtained with cardiac and convex probes showed no statistically significant differences in the measurements of the maximal and minimal dimensions and in the collapsibility index. We also noticed that the decision of allocation to the “fluid responder” or “non-responder” group was not probe-dependent.

Conclusion

Both transducers can be used interchangeably for the estimation of the studied dimensions.

Graphical ABSTRACT

Introduction

Quick and adequate intravenous fluid resuscitation is crucial in the management of critically ill patients, however excessive fluid administration has been shown to contribute to mortality(1,2).

It has been established that clinical examination alone is unreliable; therefore, more objective means of intravascular volume assessment have arisen(35). Ultrasound measurement of the inferior vena cava (IVC) diameter and its respiratory variability have been proposed as a simple, non-invasive tool to estimate the fluid volume status and predict fluid responsiveness(68). This vital clinical information may determine the choice of critical treatment, and have a decisive impact on patients’ outcome.

In many studies, IVC collapsibility index (IVC-CI) over 40% was acknowledged as the cut-off value to differentiate “fluid responders (FR)” and “non- responders (FNR)” in spontaneously breathing patients(9,10).

IVC diameter assessment has been implemented into various simplified protocols used during evaluation of patients in a critical condition(11), and is thus often performed by clinicians in life-threatening scenarios. There is, however, an inconsistency in reporting, describing and determination of the recommended acquisition technique, including the methodology of performing IVC measurement(12). Although both cardiac and convex transducers are used for IVC diameter assessment in clinical practice, we are not aware of any study comparing the consistency and accuracy of measurements performed with both probes.

The primary objective of the present study was to compare the consistency in IVC diameter measurements and the dynamic IVC-derived collapsibility index, obtained with convex and cardiac transducers. A secondary aim was to assess the agreement of patient allocation to one of the two groups: “fluid responder” or “fluid non-responder”, based on IVC-CI calculation with two different probes.

Methods

A prospective observational study was performed in compliance with Helsinki declaration. Written informed consent was obtained from all patients. Institutional Bioethics Committee of the John Paul II Hospital in Kraków, Poland approved the study protocol (Ref. No.: DW-0700-017/14).

The methodology was consistent with international guidelines for observational studies(13). The study was conducted in February 2015 in the Emergency Department (ED) of a tertiary care centre. The inclusion criteria were: consecutive patients aged >18 years old, spontaneously breathing, admitted to the cardiac ED with chest pain. Exclusion criteria were: atrial fibrillation, dyspnoea, inability to lie down in a supine position, and difficulty to obtain interpretable ultrasound images from the subcostal acoustic window.

All bedside ultrasound examinations were performed by two certified sonographers, both with at least 5-year experience in echocardiography and emergency ultrasound. Each patient was examined twice. The first examination was conducted with a cardiac and the second one with a convex probe. All examinations were performed with a portable ultrasound system equipped with a 1–5 MHz transthoracic phased-array (cardiac) and a 3.5–5 MHz curvilinear (convex) transducers (CX 50 Philips, Eindhoven, Netherlands).

All IVC views were obtained in a supine position. The inferior vena cava was visualized longitudinally in a sub-xiphoid view. The infrahepatic segment of the IVC was imaged as it entered the right atrium. At that stage, the images were stored as 5-second digital loops on the machine’s hard drive.

During the second stage of the study, all digital loops (half performed with a cardiac, and half with a convex probe) stored in the ultrasound machine memory were reviewed by 20 clinicians with experience in focused cardiac ultrasound (at least 200 POCUS examinations’ experience). All participants were blinded to the study allocation, and not aware they assessed twice IVC diameter of the same patient examined with two different transducers. To minimize the possible inconsistencies in the measurement technique, all participating physicians underwent a 30-minutes didactic course focused on relevant sonographic details of the study. Maximal and minimal IVC diameters (IVC max and IVC min, retrospectively) were measured in two dimensional (2D) mode, distally to the hepatic vein-IVC junction, over a single respiratory cycle, by tracking the distance between anterior and posterior walls perpendicular to the long axis of the vessel.

In the final stage of the study, reports and measurements performed by the participating clinicians were analysed by an independent researcher. Comparisons of the measurements were conducted for each pair of transducers (cardiac vs convex) for each patient. IVC-CI was calculated for each of the digital loops. The IVC collapsibility index (IVC-CI) was defined as: IVC-CI = (IVC max – IVC min) / IVC max and expressed as percentage. Based on IVC-CI calculation, patients were categorized to “fluid responder” (if IVC-CI ≥ 40%) or “fluid non-responder” (if IVC-CI <40%) group.

Statistical analysis

The study sample size resulted from logistic reasons, primarily the number of clinicians with experience in POCUS, which determined the number of patients enrolled in the study. As modelling of balanced systems is more efficient and tolerant of deviations from the assumptions of testing, we assumed the same number of physicians-evaluators and patients enrolled in the study (n = 20). Continuous variables are presented as mean values and standard deviation. Differences between measurements were assessed by repeated-measure two-way analysis of variances (ANOVA), in which the first main factor was the type of transducer, and the second main factor was the sonographer evaluating the image. The statistical significance of the interaction between the two main factors was also examined, but multiple comparisons were excluded because of the 2 levels of the first factor (type of transducer) and the lack of interest in comparisons between physicians’ evaluations.

Categorical data are reported as number and percentages. Proportions were compared by Pearson’s chi2 test.

All tests were two-sided. A p-value of <0.05 was considered as statistically significant. SAS 9.2 software was used for the statistical analysis. Figures were made with STATISTICA 8 software.

Results

Twenty patients (13 male, aged 45–74 years old, median 59 years old) were included in the study. In all studied patients (n = 20) the ultrasound examination rendered an interpretable view of IVC, and enabled measurements of its diameters with cardiac and convex transducers.

Thus, two digital loops of each of 20 patients were stored on the machine’s hard drive. The whole analysed set comprised 800 elements (400 pairs). The participating clinicians represented the five following groups: 9 cardiology consultants, 2 internal medicine consultants, 2 anaesthesiology consultants, 5 cardiology residents and 2 internal medicine residents (with a minimum of four years of training completed). No differences were found between the two levels of the first main factor-type of transducer: in IVC min (p = 0.4127), IVC max (p = 0.1785), IVC delta (p = 0.6411) and IVC-CI (p = 0.9746). In the case of the second main factor (clinicians evaluating) there were statistically significant differences in IVC min (p = 0.0355), IVC max (p = 0.0272), IVC delta (p = 0.0262), and IVC-CI (p = 0.0069). No differences were observed in the interaction: type of the transducer* clinician. It means the differences between clinicians’ assessments did not depend on the type of transducer. The results are summarized in Tab. 1. Figures 1, 2, 3 and 4 show interaction: type of the transducer*clinician.

Tab. 1

The results of inferior vena cava diameters and ANOVA analysis of the assessed factors

ParameterFactor: transducerFactor: clinician *Interaction: transducer * clinician
Cardiac transducerConvex transducerRelative Delta [%]ppp
IVCmin (mm)12.6 ± 7.2512.1 ± 7.374.10.41270.03550.6557
IVCmax (mm)17.9 ± 6.3017.3 ± 6.553.50.17850.02720.6946
IVC delta (mm)5.3 ± 2.855.2 ± 3.112.70.64110.02620.4222
IVC CI (%)35.4 ± 24.535.3 ± 23.790.30.97460.00690.7062

IVCmin – minimal inferior vena cava diameter; IVCmax – maximal inferior vena cava diameter; IVC delta – maximal-minimal vena cava diameter ; IVC-CI – inferior vena cava collapsibility index

Fig. 1

Interaction: type of the transducer* clinician. IVCmin – minimal inferior vena cava diameter; IVCmax – maximal inferior vena cava diameter; IVC delta – maximal-minimal inferior vena cava diameter; IVC CI – inferior vena cava collapsibility index

JoU-2017-0035-g001.jpg

We also did not notice a significant difference in the decision of allocation to one of the two groups: “fluid responder” [(cardiac (n = 151; 37.7%) vs convex (n = 168; 42%); p = 0.2196] or “fluid non-responder” that was probe-dependent. This means that the type of the probe used by the physician during examination did not determine the allocation to FR or FNR category.

Discussion

Our study shows a good agreement between IVC diameter measurements and IVC collapsibility index when imaging was performed with convex and cardiac ultrasound probes. A novel finding in this study is the observation that allocation to one of the groups: “fluid responders” or “fluid non-responder” was not probe-dependent. Thus, both transducers can be used interchangeably to predict fluid responsiveness. This is important information in POC practice, since both transducers are used commonly during IVC assessment.

Although current American and European guidelines do not recommend any particular probe for IVC measurements, it has not been entirely clear whether the results obtained with these two transducers are equal, or at least similar(14). Although we did not observe it in our study, there are potentially few reasons for considerable discrepancies between measurements performed with these two probes. Both transducers have different characteristics and physical properties, such as operating at different centre frequencies (with bandwidth for cardiac 1–5 Mz vs convex 3.5–5 Mz), have different dimensions, footprints and shapes, and provide different image formats(15). All mentioned technical differences might translate into different imaging angles and planes when using convex or cardiac probes. Differences in imaging angulations, in turn, may cause significant differences in IVC diameters measured with these two transducers. Although in numerous studies various aspects of IVC measurements were assessed(6,15,16), we did not find any study comparing the consistency of measurements performed with cardiac and convex probes.

Many studies have shown that the potential source of discrepancies in measurement of IVC might be the image acquisition modality, methodology and the patient’s position during the assessment(17,18). Finnerty et al.(12) showed that inter-rater reliability of IVC measurement was the highest for B-mode long axis sub-xiphoid view, compared with transabdominal short axis and right lateral coronal long axis view. The poorest reliability was related to motion-mode (M-mode) modalities. Another study, however, showed no significant difference between M-mode and 2-D measurements, and between long and short-axis IVC diameter measurements(10). Wallace et al.(19) demonstrated equivalence in two anatomical approaches, namely, at the level of the left renal vein and 2 cm caudal to the hepatic vein inlet, both of which differ from measurements taken at the junction of the right atrium. Since we wanted to focus on the impact of the type of the probe on the measurements, minimizing the influence of other factors, we standardized the method of IVC diameter evaluation by the participants, holding the refreshing training prior to the study. Although we believed that this approach significantly reduced inter-observer variability resulting from various measurement techniques, we noticed significant differences in measurements between participants in minimal and maximal IVC dimensions.

There are some limitations of our study. The generalizability of our findings to other sonographers is limited by the relatively few numbers of examinations that obtained images for this study. All ultrasound examinations were performed by fairly experienced sonographers. It cannot be ruled out that results obtained by less competent physicians, especially in a life-threatening scenario, would have been different.

Conclusions

Cardiac and convex transducers can be used interchangeably for the estimation of dimensions of IVC and its respiratory variability.

Conflict of interest

The authors do not report any financial or personal connections with other persons or organizations, which might negatively affect the contents of this publication and/or claim authorship rights to this publication.

References


  1. Boyd JH,Forbes J,Nakada TA,Walley KR,Russell JA,Fluid resuscitation in septic shock: a positive fluid balance and elevated central venous pressure are associated with increased mortality Crit Care Med 2011 39 259 265
    [CROSSREF]
  2. Vincent JL,Sakr Y,Sprung CL,Ranieri VM,Reinhart K,Gerlach H,Sepsis in European intensive care units: results of the SOAP study Crit Care Med 2006 34 344 353
    [CROSSREF]
  3. Brennan JM,Blair JE,Goonewardena S,Ronan A,Shah D,Vasaiwala S,Reappraisal of the use of inferior vena cava for estimating right atrial pressure J Am Soc Echocardiogr 2007 20 857 861
    [CROSSREF]
  4. Eisenberg PR,Jaffe AS,Schuster DP,Clinical evaluation compared to pulmonary artery catheterization in the hemodynamic assessment of critically ill patients Crit Care Med 1984 12 549 553
    [CROSSREF]
  5. Marik PE,Monnet X,Teboul JL,Hemodynamic parameters to guide fluid therapy Ann Intensive Care 2011 1 1
    [CROSSREF]
  6. Preau S,Bortolotti P,Colling D,Dewavrin F,Colas V,Voisin B,Diagnostic accuracy of the inferior vena cava collapsibility to predict fluid responsiveness in spontaneously breathing patients with sepsis and acute circulatory failure Crit Care Med 2017 45 e290 e297
    [CROSSREF]
  7. Ciozda W,Kedan I,Kehl DW,Zimmer R,Khandwalla R,Kimchi A,The efficacy of sonographic measurement of inferior vena cava diameter as an estimate of central venous pressure Cardiovasc Ultrasound 2016 14 33
    [CROSSREF]
  8. Feissel M,Michard F,Faller JP,Teboul JL,The respiratory variation in inferior vena cava diameter as a guide to fluid therapy Intensive Care Med 2004 30 1834 1837
    [CROSSREF]
  9. Muller L,Bobbia X,Toumi M,Louart G,Molinari N,Ragonnet B,Respiratory variations of inferior vena cava diameter to predict fluid responsiveness in spontaneously breathing patients with acute circulatory failure: need for a cautious use Crit Care 2012 16 R 188
  10. Moreno FL,Hagan AD,Holmen JR,Pryor TA,Strickland RD,Castle CH,Evaluation of size and dynamics of the inferior vena cava as an index of right-sided cardiac function Am J Cardiol 1984 53 579 585
    [CROSSREF]
  11. Lanctôt JF,Valois M,Beaulieu Y,EGLS: Echo-guided life support. An algorithmic approach to undifferentiated shock Crit Ultrasound J 2011 3 123 129
    [CROSSREF]
  12. Finnerty NM,Panchal AR,Boulger C,Vira A,Bischof JJ,Amick C,Inferior vena cava measurement with ultrasound: What is the best view and best mode? West J Emerg Med 2017 18 496 501
    [CROSSREF]
  13. von Elm E,Altman DG,Egger M,Pocock SJ,Gøtzsche PC,Vandenbroucke JP,STROBE Initiative: The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement: guidelines for reporting observational studies Int J Surg 2014 12 1495 1499
    [CROSSREF]
  14. Lang RM,Badano LP,Mor-Avi V,Afilalo J,Armstrong A,Ernande L,Recommendations for cardiac chamber quantification by echocardiography in adults: an update from American Society of Echocardiography and the European Association of Cardiovascular Imaging J Am Soc Echocardiogr 2015 28 1 39
    [CROSSREF]
  15. Szabo TL,Lewin PA,Ultrasound transducer selection in clinical image practice J Ultrasound Med 2013 32 573 582
    [CROSSREF]
  16. Sobczyk D,Nycz K,Andruszkiewicz P,Bedside ultrasonographic measurement of the inferior vena cava fails to predict fluid responsiveness in the first 6 hours after cardiac surgery: A prospective case series observational study J Cardiothorac Vasc Anesth 2015 29 663 669
    [CROSSREF]
  17. Abu-Zidan FM,Optimizing the value of measuring inferior vena cava diameter in shocked patients World J Crit Care Med 2016 5 7 11
    [CROSSREF]
  18. Mookadam F,Warsame TA,Yang HS,Emani UR,Appleton P,Raslan SF,Effect of positional changes on inferior vena cava size Eur J Echocardiogr 2011 12 322 325
    [CROSSREF]
  19. 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 17 96 99
    [CROSSREF]
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FIGURES & TABLES

Fig. 1

Interaction: type of the transducer* clinician. IVCmin – minimal inferior vena cava diameter; IVCmax – maximal inferior vena cava diameter; IVC delta – maximal-minimal inferior vena cava diameter; IVC CI – inferior vena cava collapsibility index

Full Size   |   Slide (.pptx)

REFERENCES

  1. Boyd JH,Forbes J,Nakada TA,Walley KR,Russell JA,Fluid resuscitation in septic shock: a positive fluid balance and elevated central venous pressure are associated with increased mortality Crit Care Med 2011 39 259 265
    [CROSSREF]
  2. Vincent JL,Sakr Y,Sprung CL,Ranieri VM,Reinhart K,Gerlach H,Sepsis in European intensive care units: results of the SOAP study Crit Care Med 2006 34 344 353
    [CROSSREF]
  3. Brennan JM,Blair JE,Goonewardena S,Ronan A,Shah D,Vasaiwala S,Reappraisal of the use of inferior vena cava for estimating right atrial pressure J Am Soc Echocardiogr 2007 20 857 861
    [CROSSREF]
  4. Eisenberg PR,Jaffe AS,Schuster DP,Clinical evaluation compared to pulmonary artery catheterization in the hemodynamic assessment of critically ill patients Crit Care Med 1984 12 549 553
    [CROSSREF]
  5. Marik PE,Monnet X,Teboul JL,Hemodynamic parameters to guide fluid therapy Ann Intensive Care 2011 1 1
    [CROSSREF]
  6. Preau S,Bortolotti P,Colling D,Dewavrin F,Colas V,Voisin B,Diagnostic accuracy of the inferior vena cava collapsibility to predict fluid responsiveness in spontaneously breathing patients with sepsis and acute circulatory failure Crit Care Med 2017 45 e290 e297
    [CROSSREF]
  7. Ciozda W,Kedan I,Kehl DW,Zimmer R,Khandwalla R,Kimchi A,The efficacy of sonographic measurement of inferior vena cava diameter as an estimate of central venous pressure Cardiovasc Ultrasound 2016 14 33
    [CROSSREF]
  8. Feissel M,Michard F,Faller JP,Teboul JL,The respiratory variation in inferior vena cava diameter as a guide to fluid therapy Intensive Care Med 2004 30 1834 1837
    [CROSSREF]
  9. Muller L,Bobbia X,Toumi M,Louart G,Molinari N,Ragonnet B,Respiratory variations of inferior vena cava diameter to predict fluid responsiveness in spontaneously breathing patients with acute circulatory failure: need for a cautious use Crit Care 2012 16 R 188
  10. Moreno FL,Hagan AD,Holmen JR,Pryor TA,Strickland RD,Castle CH,Evaluation of size and dynamics of the inferior vena cava as an index of right-sided cardiac function Am J Cardiol 1984 53 579 585
    [CROSSREF]
  11. Lanctôt JF,Valois M,Beaulieu Y,EGLS: Echo-guided life support. An algorithmic approach to undifferentiated shock Crit Ultrasound J 2011 3 123 129
    [CROSSREF]
  12. Finnerty NM,Panchal AR,Boulger C,Vira A,Bischof JJ,Amick C,Inferior vena cava measurement with ultrasound: What is the best view and best mode? West J Emerg Med 2017 18 496 501
    [CROSSREF]
  13. von Elm E,Altman DG,Egger M,Pocock SJ,Gøtzsche PC,Vandenbroucke JP,STROBE Initiative: The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement: guidelines for reporting observational studies Int J Surg 2014 12 1495 1499
    [CROSSREF]
  14. Lang RM,Badano LP,Mor-Avi V,Afilalo J,Armstrong A,Ernande L,Recommendations for cardiac chamber quantification by echocardiography in adults: an update from American Society of Echocardiography and the European Association of Cardiovascular Imaging J Am Soc Echocardiogr 2015 28 1 39
    [CROSSREF]
  15. Szabo TL,Lewin PA,Ultrasound transducer selection in clinical image practice J Ultrasound Med 2013 32 573 582
    [CROSSREF]
  16. Sobczyk D,Nycz K,Andruszkiewicz P,Bedside ultrasonographic measurement of the inferior vena cava fails to predict fluid responsiveness in the first 6 hours after cardiac surgery: A prospective case series observational study J Cardiothorac Vasc Anesth 2015 29 663 669
    [CROSSREF]
  17. Abu-Zidan FM,Optimizing the value of measuring inferior vena cava diameter in shocked patients World J Crit Care Med 2016 5 7 11
    [CROSSREF]
  18. Mookadam F,Warsame TA,Yang HS,Emani UR,Appleton P,Raslan SF,Effect of positional changes on inferior vena cava size Eur J Echocardiogr 2011 12 322 325
    [CROSSREF]
  19. 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 17 96 99
    [CROSSREF]

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