Ultrasound in Emergency Medicine
Does a Simple Bedside Sonographic Measurement of the Inferior Vena Cava Correlate to Central Venous Pressure?

Presented at: the 40th Annual Meeting, Society for Academic Emergency Medicine, Phoenix, AZ, June 3–6, 2010.
https://doi.org/10.1016/j.jemermed.2011.05.082Get rights and content

Abstract

Background

Bedside ultrasound has been suggested as a non-invasive modality to estimate central venous pressure (CVP).

Objective

Evaluate a simple bedside ultrasound technique to measure the diameter of the inferior vena cava (IVC) and correlate to simultaneously measured CVP. Secondary comparisons include anatomic location, probe orientation, and phase of respiration.

Methods

An unblinded prospective observation study was performed in an emergency department and critical care unit. Subjects were a convenience sample of adult patients with a central line at the superior venocaval-atrial junction. Ultrasound measured transverse and longitudinal diameters of the IVC at the subxiphoid, suprailiac, and mid-abdomen, each measured at end-inspiration and end-expiration. Correlation and regression analysis were used to relate CVP and IVC diameters.

Results

There were 72 subjects with a mean age of 67 years (range 21–94 years), 37 (53%) male, enrolled over 9 months. Seven subjects were excluded for tricuspid valvulopathy. Primary diagnoses were: respiratory failure 12 (18%), sepsis 11 (17%), and pancreatitis 3 (5%). There were 28 (43%) patients mechanically ventilated. Adequate measurements were obtainable in 57 (89%) using the subxiphoid, in 44 (68%) using the mid-abdomen, and in 28 (43%) using the suprailiac views. The correlation coefficients were statistically significant at 0.49 (95% confidence interval [CI] 0.26–0.66), 0.51 (95% CI 0.23–0.71), and 0.50 (95% CI 0.14–0.74) for end-inspiratory longitudinal subxiphoid, midpoint, and suprailiac views, respectively. Transverse values were statistically significant at 0.42 (95% CI 0.18–0.61), 0.38 (95% CI 0.09–0.61), and 0.67 (95% CI 0.40–0.84), respectively. End-expiratory measurements gave similar or slightly less significant values.

Conclusion

The subxiphoid was the most reliably viewed of the three anatomic locations; however, the suprailiac view produced superior correlations to the CVP. Longitudinal views generally outperformed transverse views. A simple ultrasound measure of the IVC yields weak correlation to the CVP.

Introduction

Central venous pressure (CVP) is a key physiologic estimate of preload, which in turn helps define the intravascular fluid status. It is a particularly important parameter to measure in critically ill and injured patients who may require fluid resuscitation. Unfortunately, measurement of the CVP requires invasive central venous catheters that can be difficult or time-consuming to insert and are associated with complications. A non-invasive means of inferring the CVP would provide clinicians with an acceptable alternative. Gosink was among the first to fully describe a relationship between the imaged diameter of the inferior vena cava (IVC) and CVP (1). Since then, ultrasonography has emerged as a reliable means to measure internal body structures, including the vena cava. Previous studies have shown various correlations between CVP or right atrial pressure and measurements of the IVC 2, 3, 4, 5, 6, 7.

There is considerable emergency and critical care relevance to non-invasive measurements of CVP. Care of emergency patients often requires resuscitation without the benefit of invasive monitoring. Ultrasound is a tool that potentially could provide a rapid and non-invasive means of gauging preload and the need for fluid resuscitation. Because ultrasound machines are relatively light and portable, and many clinicians are trained in their use (e.g., emergency physicians, anesthesiologists, intensivists, and surgeons), the ability to non-invasively measure CVPs could extend patient monitoring capabilities to a variety of settings where direct measurements of the CVP are unavailable or impractical.

This study examined the correlation between CVP and the IVC diameter as measured by a bedside ultrasonographic technique. In particular, this study evaluated several single-view images obtained at various abdominal locations using easily identified external and internal landmarks. The study used a focused bedside ultrasound examination that is simple to perform. In essence, images and measurements were made in real time and did not require elaborate or time-consuming procedures such as multiple views or complicated measurement techniques (e.g., review of cine images), the need for special equipment (e.g., transesophageal probes), or formal studies (e.g., echocardiography) that usually require a dedicated technician and specialist interpretation (8).

Section snippets

Study Design

The study was a prospective, cross-sectional observation that utilized a one-time assessment of IVC diameter to determine any correlation with CVP. Our primary hypothesis was that a single view technique using bedside ultrasound measurement of the diameter of the IVC correlates to simultaneously measured CVP in a variety of critical patients. Our secondary objectives included determining which combination of anatomic parameters (probe location and orientation) would demonstrate the highest

Results

Four operators enrolled 72 subjects with a mean age of 67.2 years (range 21–94 years), 37 (51%) male, over a period of 9 months. Seven subjects were excluded for tricuspid valvulopathy but had similar demographics to the subject population; there were no other exclusions. An analysis was conducted on 65 subjects, and it showed the leading primary diagnoses were: respiratory failure including pneumonia and congestive heart failure, 12 (18%); sepsis, 11 (17%); pancreatitis, 3 (5%); renal failure,

Discussion

Central venous pressure monitoring is a mainstay of estimating vascular fluid status and cardiac preload in critically ill and injured patients 10, 11. It is the preferred method in the ED and in other situations when a pulmonary artery catheter is not practical (12). Recent criticisms of using CVP to estimate fluid responsiveness notwithstanding, CVP measurements remain the standard of care in shock management (13). The advent of goal-directed therapy in sepsis and permissive-hypotension

Conclusion

The subxiphoid view was the most readily viewed of the three anatomic locations for obtaining adequate views of the IVC; however, the suprailiac view produced superior correlations to the CVP when compared to the subxiphoid and midpoint views. Longitudinal views generally outperformed transverse views at all levels except the suprailiac. Use of a single simple ultrasound measure of the IVC transverse diameter in end-inspiration yields weak correlation with the CVP.

Article Summary

1. Why is this topic important?

  1. Bedside sonographic

Acknowledgment

The authors thank John Ward, phd and Cristy Landt, ms for their biostatistical support.

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    The opinions or assertions are those of the author and do not necessarily reflect those of the Army Medical Department or the Department of Defense.

    This study was funded by a grant from the US Army Telemedicine and Advanced Technology Center, Fort Detrick, MD, with limited support from Sonosite, Inc., Bothell, WA.

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