Brief Report
The role of inferior vena cava diameter in volume status monitoring; the best sonographic measurement method?

https://doi.org/10.1016/j.ajem.2014.12.014Get rights and content

Abstract

Objectives

This study aims to determine the site of and the best sonographic method for measurement of inferior vena cava (IVC) diameter in volume status monitoring.

Methods

This observational before-and-after study was performed at the intensive care unit of the emergency department. It included hypotensive adult patients with suspected sepsis who were recommended to receive at least 20 mg/kg fluid replacement by the emergency physician. The patients were fluid replaced at a rate of 1000 mL/h, and maximum and minimum IVC diameters were measured and the Caval index calculated sonographically via both B-mode and M-mode. Hence, IVC’s volume response was assessed by a total of 6 parameters, 3 each in M-mode and B-mode. Freidman test was used to assess the change in IVC diameter with fluid replacement. Wilcoxon test with Bonferroni correction was used to determine which measurement method more sensitively measured IVC diameter change.

Results

Twenty-eight patients with a mean age of 71.3 were included in the final analysis.The IVC diameter change was significant with all 6 methods (P < .001). The IVC minimum diameter change measured on M-mode during inspiration (M-mode i) was the only measurement method that significantly showed diameter change with each 500-mL fluid replacements. The initial and the subsequent M-mode i values after each 500 mL of fluid were 5.65 ± 3.34; 8.05 ± 3.66; 10.16 ± 3.61, and 11.21 ± 2.94, respectively (P < .001, P < .002, and P < .003, respectively).

Conclusion

Inferior vena cava diameter was changed by fluid administration. The M-mode i method that most sensitively measures that change may be the most successful method in volume status monitoring.

Introduction

Assessing and monitoring intravascular volume status are critical parts of the management of critically ill patients. Currently, the volume status is assessed by physical examination, vital sign assessment, measurement of biochemical markers, tissue perfusion, and central venous pressure (CVP), and sonographic assessment of inferior vena cava (IVC) diameter [1]. Physical examination, one of the simplest and most rapid methods among them, is not reliable for assessment of intravascular volume status [2], [3]. Blood pressure, on the other hand, may remain relatively normal until 30% of total body water is lost, which is sufficient for multiple-organ dysfunction [4]. Therefore, various advanced methods including CVP monitorization, pulmonary artery catheterization, esophageal catheterization, transesophageal echocardiography, and transthoracic echocardiography (TTE) are sometimes needed. Unfortunately, most of these methods require special knowledge and skills, and they cause significant time loss for the patients in the emergency department. Moreover, there is no consensus for the indications of the traditional invasive monitorization methods [5], [6]. All these invasive methods are a source of potential morbidity and mortality. Noninvasive methods have thus recently become more popular [7]. Among them, IVC diameter ultrasound measurement (IVC-USG) has been reported to reliably reflect volume status [8], [9], [10], [11], [12], [13], [14], although there have also been studies suggesting otherwise [15], [16], [17]. Most important of all, CVP is considered as gold standard when the relationship between the IVC diameter and intravascular volume is studied [18], [19], [20], [21]. However, the accuracy of CVP measurement in reflecting volume status is controversial [22], [23], [24]. A total of 803 patient meta-analyses containing 24 studies demonstrated that there is only a weak correlation between CVP and volume status [23]. This has caused the value of CVP to be debated. Studies on the relationship between IVC diameter and volume status in volunteer blood donors without taking CVP into account have yielded varying results [8], [16]. These data suggest that there is an ongoing need for studies that examine the relationship between IVC and volume status.

The first objective of the present study was to determine whether there was a relationship between sonographically measured IVC diameter and intravascular volume status. The second objective was to find out which of the IVC measurement methods was most successful in reflecting the accurate volume status.

Section snippets

Study design and setting

We designed a prospective, observational, single-center study with a before-and-after design to determine the relationship between fluid replacement and IVC diameter. The study design dictated repeated measurements of IVC diameter after each 500-mL saline replacement. This study was conducted after it was approved by the education planning committee of the hospital. Each study subject gave a written informed consent.

The study was conducted in the emergency department of a training and research

Results

This study included 35 consecutive patients in total who presented to the emergency department within the specified time window. Four patients (11.4 %) were excluded because they lacked the required optimal echogenity for IVC-USG and TTE. Three patients (8.5 %) were excluded from the final data analysis owing to severe TR on TTE. The remaining 28 patients were included in the final statistical analysis. None of the patients were intubated and received vasoactive treatment. The demographic

Discussion

Inferior vena cava is a high compliance vessel whose dimensions and dynamics are altered by total body water and respiration [26]. Nett et al administered norepinephrine to patients with low total body fluid and blood pressure. They observed that IVC size remained constant despite increased blood pressure, suggesting that IVC diameter was more related to volume status than SBP [28]. However, a meta-analysis dated 2011 indicated a moderate level of evidence for measuring IVC diameter in

Limitation

This study is a single-center study with a relatively small sample size.

B-mode and M-mode measurements might have been affected by each other since they were carried out in a successive manner. To minimize this bias, video recordings were made first in both modes, followed by carrying out measurements from the video recordings.

This study excluded patients with severe TR. Therefore, this method is not applicable to patients with severe TR.

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    Prior presentations: Poster Presentation at the 1. International Critical Care and Emergency Medicine Congress, Novenber 2013, Istanbul.

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