a b s t r a c t

Objectives: This study aims to determine the site of and the best sonographic method for measurement of inferior vena cava 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 param- eters, 3 each in M-mode and B-mode. Freidman test was used to assess the change in IVC diameter with fluid re- placement. 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 b .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 b .001, P b .002, and P b .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.

(C) 2014

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, mea- surement of biochemical markers, tissue perfusion, and central venous pressure , and sonographic assessment of inferior vena cava diameter [1]. Physical examination, one of the simplest and most rapid methods among them, is not reliable for assessment of intra- vascular volume status [2,3]. Blood pressure, on the other hand, may re- main relatively normal until 30% of total body water is lost, which is sufficient for multiple-organ dysfunction [4]. Therefore, various

? Prior presentations: Poster Presentation at the 1. International Critical Care and Emer- gency Medicine Congress, Novenber 2013, Istanbul.

* Corresponding author at: Department of Emergency Medicine, Haseki Training and Research Hospital, 34096 Istanbul, Turkey.

E-mail address: [email protected] (A. Yamanoglu).

advanced methods including CVP monitorization, pulmonary artery catheterization, esophageal catheterization, transesophageal echocardi- ography, and Transthoracic echocardiography are sometimes needed. Unfortunately, most of these methods require special knowl- edge and skills, and they cause significant time loss for the patients in the emergency department. Moreover, there is no consensus for the in- dications of the traditional invasive monitorization methods [5,6]. All these invasive methods are a source of potential morbidity and mortal- ity. 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 [8-14], although there have also been studies suggesting otherwise [15-17]. Most important of all, CVP is considered as gold standard when the relationship between the IVC diameter and intravascular volume is studied [18-21]. However, the accuracy of CVP measurement in reflecting volume status is contro- versial [22-24]. A total of 803 patient meta-analyses containing 24 stud- ies demonstrated that there is only a weak correlation between CVP and volume status [23]. This has caused the value of CVP to be debated.

http://dx.doi.org/10.1016/j.ajem.2014.12.014

0735-6757/(C) 2014

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 diam- eter 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.

Methods

Study design and setting

We designed a prospective, observational, single-center study with a before-and-after design to determine the relationship between fluid re- placement and IVC diameter. The study design dictated repeated measure- ments 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 hospital in Turkey. The emergency department in question annually serves 200000 patients, of whom 5% to 10% are treated at the intensive care unit located in the emergency department. All emergency medicine residents working at our hospital are certified by the emer- gency medicine societies for basic and advanced ultrasonography after attending basic and advanced ultrasonography courses. This study was conducted between December 1, 2012, and March 15, 2013.

The study included patients more than 18 years of age who present- ed to our emergency department with hypotension (systolic blood pressure [SBP] b 100 mm Hg or mean arterial pressure (MAP) b 65 mm Hg] and clinically suspected sepsis (Fig. 1) and were recommended to receive fluid replacement at an amount of 20 ml/kg or greater by the emergency physicians. Pregnancy, active trauma, cardiopulmonary ar- rest, intubation, severe tricuspid regurgitation (TR), or incalculable fluid losses (diarrhea, vomiting, and acute abdomen) were the reasons for exclusion from the study.

Study protocol

The IVC-USG measurement was performed by an emergency medi- cine resident having 2 years of experience in ultrasonography. That

resident received a 6-hour theoretical training followed by practice training on 20 patients.

The first measurement was made within 10 minutes of emergency department admission, once the initial physical examination was completed. The measurements were performed with a SonoScape (S6/ S6 Pro) branded portable ultrasonography device, using a 3.5- to 5- mHz convex transducer. The IVC-USG measurements were performed from the subxiphoid region with the patient being in the supine posi- tion. The measurements were made while the patient remained in the relaxed position, and the respiratory movements of the patients were not directed by the performer. As a first step of measurement, aorta and IVC were located transversely and their positions were confirmed by Doppler interrogation. Then, the view was shifted to the longitudinal line over IVC; the right atrial entry of IVC was spotted, and 2 cm distal to this point the IVC diameter was measured via a commonly utilized method recommended by the American College of Emergency Physi- cians (ACEP) and the measurement line perpendicular to both IVC walls [25-27]. A video recording was done during at least 3 respiratory cycles, first in B-mode and then in M-mode. The video recording was paused at the maximum diameter in expiration in B-mode (B-mode e), and a measurement was done (Fig. 2A). During the same respiratory cycle, the recording was again paused at the minimum diameter in in- spiration in B-mode (B-mode i), and a repeat measurement was done (Fig. 2B). The same measurements were made from the M-mode video recordings as well (M-mod e in expirium and M-mod i in inspirium; Fig. 2C). The IVC collapsibility index was calculated with the formula (IVCe - IVCi)/IVCe x 100 and recorded.

Once the initial measurement was done, fluid infusion at a rate of

1000 mL/h was commenced, and it was stopped after 500 mL of fluid was infused. After waiting for 1 cardiac cycle, the same measurements as above were done for the second time. The measurements were repeat- ed for a third and fourth time after 1000 and 1500 mL of fluid were ad- ministered, respectively. Pulse rate and blood pressure were also measured and recorded simultaneously with the IVC measurements.

All patients underwent a full transthoracic echocardiographic exami- nation (TTE) by a consulting cardiologist within 24 hours of admission. The IVC-USG measurements, TTE measurements, and clinical and labora- tory data obtained were recorded in Microsoft Office Excel 2007 software.

Primary data analysis

In complementary analyses, frequency numbers were used to pres- ent the continuous variables, and the frequency tables (marginal tables)

Fig. 1. Definitions of the terms Systemic Inflammatory Response Syndrome and sepsis.

a) B-Mode expiration (e) diameter b) B-Mode inspiration (i) diameter

c) M-Mode i, e diameters

Fig. 2. Inferior vena cava measurement methods.

were used for the categorical variables. The normality of the distribution of the continuous variables was tested with histogram and normality curves. None of the variables were distributed normally, and therefore, nonparametric tests were used to compare the continuous variables. Wilcoxon test was used for repeated paired comparisons of the median values of the dependent groups’ continuous variables. The statistical sig- nificance was set at P b .05. Freidman test was used for repeated multiple-sample comparisons of the median values of the dependent groups’ continuous variables, and the statistical significance was set at P b .05. Wilcoxon test with Bonferroni correction was used for post hoc analysis of the measurements found to be statistically significant in the Freidman test. The statistical significance was set at P b .008. Be- cause the continuous variables are not normally distributed, box plots were used for graphical display of these variables. All analyses were per- formed in SPSS 20.0 statistical software package.

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 opti- mal echogenity for IVC-USG and TTE. Three patients (8.5 %) were ex- cluded 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 characteristics of the study population were present- ed on Table 1. All measurements took less than 3 minutes to complete in each patient. The volume infusion lasted for a maximum of 120 minutes and an average of 102.6 minutes.

The values obtained via B-mode measurement of the IVC diameter change after intravenous fluid replacement were as follows: the initial

maximal expiratory IVC diameter (B-mode e0) was 13.47 +- 3.40 mm and became 15.68 +- 3.54 mm after 500 mL of fluid (B-mode e1);

16.70 +- 3.58 mm after 1000 mL of fluid (B-mode e2); and 16.9 +-

3.92 mm after 1500 mL of fluid (B-mode e3), which were found statisti- cally significant in the Freidman test (P b .001). The IVC minimum inspi- ratory diameter and Caval index measured with B-mode were also significantly changed by fluid replacement (P b .001). Similarly, IVC max- imum diameter, minimum diameter, and Caval index measured with M- mode were significantly changed by fluid administration (P b .001) (Table 2).

The initial pulse rate (PR0) and the subsequent pulse rates after ad- ministration of 500 (PR1), 1000 (PR2), and 1500 mL (PR3) fluid were

110.5 +- 20.9, 102.3 +- 15.6, 95.3 +- 12.7, and 90.3 +- 12.1 bpm, respec-

tively, which were found statistically significant in the Freidman test (P b .001).

The initial MAP (MAP0) was 61.71 +- 10.48 mm Hg, and it became

59.18 +- 12.51, 62.10 +- 13.84, and 63.90 +- 14.02 mm Hg after adminis- tration of 500 mL (MAP1), 1000 mL (MAP2), and 1500 mL (MAP3) of fluid, respectively, which were statistically nonsignificant (P N .05). Table 2 shows all measurements.

Table 1

Demographic characteristics of study subjects

Number 28

Sex (female: F, male: M) K:9 (% 32.1) E:19 (% 67.9)

Age 71.3 +- 11.7 (min: 51max: 92)

Pulse rate 110.57 +- 20.95/dk

Mean SBP 86 86.92 +- 11.69 mm Hg

MAP 61.71 +- 10.48 mm Hg

Table 2

Inferior vena cava diameter, pulse rate, and MAP values with fluid infusion

	Method	Initial IVC diameter (mm)	After 500 mL hydration (mm)	After 1000 mL hydration (mm)	After 1500 mL hydration (mm)	Friedman test P
B-mode	B-mod e	13.47 +- 3.40	15.68 +- 3.54	16.70 +- 3.58	16.97 +- 3.92	b.001
	B-mod i	5.35 +- 4.50	7.58 +- 3.95	9.45 +- 4.18	10.49 +- 3.94	b.001
	B-mod CI	63.54 +- 24.34	52.86 +- 18.54	45.00 +- 17.98	38.70 +- 15.27	b.001
M-mode	M-mod e	14.31 +- 3.56	16.72 +- 2.81	18.21 +- 3.80	18.20 +- 3.89	b.001
	M-mod i	5.65 +- 3.34	8.05 +- 3,66	10.16 +- 3.61	11.21 +- 2.94	b.001
	M-mod CI	61.57 +- 16.94	53.04 +- 16.67	45.88 +- 10.42	39.17 +- 7.60	b.001
Pulse rate and MAP	Pulse rate	110.5 +- 20.9/dk	102.3 +- 15.6/dk	95.3 +- 12.7/dk	90,3 +- 12,1/dk	b.001
	MAP	61.71 +- 10.48 mm Hg	59.18 +- 12.51 mm Hg	62.10 +- 13.84 mm Hg	63.90 +- 10.02 mm Hg	N.05

In the measurements with changes of statistical significance over volume infusion steps (500 vs 1000 vs 1500 mL), the Wilcoxon test with Bonferroni correction was used for post hoc analysis, and the sta- tistical significance was set at P b .008. Table 3 demonstrates the P values of the Wilcoxon test with Bonferroni correction for each 500-mL incre- ment of volume infusion.

The change elicited by each of 500-, 1000-, and 1500-mL hydration was calculated. The statistical significance of the IVC diameter change brought about by these liquid amounts was tested with the Wilcoxon test with a statistical significance set at P b .05. The corresponding P values were presented on Table 4.

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 relat- ed to volume status than SBP [28]. However, a meta-analysis dated 2011 indicated a moderate Level of evidence for measuring IVC diameter in differentiation of normovolemic and hypovolemic conditions, and stat- ed that more studies are needed to ascertain the exact role of measuring IVC diameter for this purpose [29]. We could not access any study that examined the role of IVC diameter in treatment monitoring, either. Moreover, various study groups used differing methods in measuring IVC diameter. Akilli et al [13], for instance, used B-mode while Sefidbakht et al [14] used M-mode for IVC diameter measurement. No studies to date have been conducted to determine which one of the IVC measurement methods, IVC diameter, or calculation method (inspiratory diameter, expiratory diameter, and Caval index) would be more suitable. Perhaps, each study reported so far evaluated a single dif- ferent method of measurement and thus reported the success or failure of that particular method. Thus, there is a need for determination of the ideal measurement method for IVC diameter change.

Recent studies have reported a weak correlation between CVP and Circulating blood volume [23]. We therefore designed our study to mea- sure IVC diameter serially while fluid infusion continues rather than using fluid replacement once: by using both B-mode and M-mode rath- er than a single method and by assessing the changes in minimum and maximum IVC diameter as well as in the Caval index rather than by assessing the Caval index only. By this way, we intended to reveal whether IVC diameter could be used in monitoring volume status and

find out which one among the multiple methods used in the same pa- tient would be more appropriate method.

In the patients deemed to be dehydrated, the maximal and minimal IVC diameters and the Caval index values are shown on Table 2. Accord- ing to ACEP, the IVC diameter and the Caval index indicating a normal CVP are 15 to 25 mm and greater than 50 %, respectively [25]. In patients with volume deficiency, the maximal IVC diameter is lower than 15 mm with complete compressibility. Therefore, our patients fell into the “dehydrated” category of ACEP guidelines, although the limits are not clearly defined.

In our study, serial measurements revealed that the response of the IVC diameter to liquid was significant in each of the 6 methods (B-mode i, e, CI, M-mode i, e, CI), as shown on Table 2 (P b .001). Pulse rate re- sponse to fluid was also significant (P b .001). However, the MAP re- sponse obtained in the blood Pressure measurements was not significant (P N .05). Yanagawa et al [10] reported that blood pressure failed to predict circulatory shock at an early stage in trauma patients. This subject was also studied by Nette et al who infused norepinephrine and found that IVC diameter was not affected by positive inotropes as norepinephrine, whereas pulse rate was affected by both positive inotropes and external factors (anxiety, fever) [28]. These reports sug- gest that IVC could be a more reliable indicator of volume status.

The IVC was changed significantly by the infused fluid, as measured by all methods. However, not all the 500-mL fluid infusions were equal- ly effective in eliciting this diameter response. To test this result, the contribution of the first, second, and third 500-mL fluid infusions to IVC change were individually calculated, and, to measure that difference more sensitively, Wilcoxon test with Bonferroni correction with a statis- tical significance set at P b .008 was used. As shown on Table 3, M-mod i measurement and pulse rate were the methods that showed the IVC di- ameter change produced by each 500-mL fluid administration.

The IVC diameter measured in 6 IVC measurement methods and pulse rate responded significantly to the first 500-mL fluide infusion. That is, in the dehydrated patients, the greatest amount of IVC diameter change occurred with the first 500-mL fluid infusion (greater than the second and third infusions). This is because at most 30% of the infused intravenous fluid remains intravascularly [30], and the rest is extrava- sated over time. The rate of the remaining intravascularly of the fluid is greatest with the firstly infused 500 mL when the dehydration rate of the patient is the greatest. As fluid infusion goes on, more fluid passes into extravascular space due to less dehydration. This causes the second and third fluid infusions to produce less IVC diameter change. Insensible losses via perspiration and respiration also contribute to this

Table 3

Wilcoxon test with Bonferroni correction P values (P b .008)

	B-mode				M-mode
	First 500-mL infusion	Second 500-mL infusion	Third 500-mL infusion		First 500-mL infusion	Second 500-mL infusion	Third 500-mL infusion
Expiration	b.001	b.041	b.168		b.001	b.009	b.003
Inspiration	b.001	b.003	b.042		b.001	b.002	b.003
Caval index Pulse rate	b.003 b.001	b.016 b.001	b.055 b.004		b.006	b.106	b.004

Table 4

Results of Wilcoxon test for the paired repeated measurements (P b .05)

	B-mode				M-mode
	500-mL	1000-mL	1500-mL		500-mL	1000-mL	1500-mL
	infusion	infusion	infusion		infusion	infusion	infusion
Expiration	b.001	b.001	b.001		b.001	b.001	b.001
Inspiration	b.001	b.001	b.001		b.001	b.001	b.001
Caval index Pulse rate	b.003 b.001	b.001 b.001	b.001 b.001		b.006	b.001	b.001

phenomenon. Furthermore, it is also probable that there is a greatest at- tainable IVC diameter beyond which IVC cannot be increased, and the infused volume is completely extravasated into third space. This may suggest that IVC diameter would have a less sensitivity in reflecting the real amount of body volume with further fluid replacements. How- ever, this decrease in IVC diameter change in the next amount of this re- placement may also indicate that the fluid deficit is now replaced. In our patients, the measurements were made after 20 mg/kg fluid replace- ment. Future studies may investigate whether a blunted or lost IVC di- ameter change response to volume replacement in patients with greater volume deficit might suggest that volume deficit is replaced.

As shown on Tables 3 and 4, the inspiration measurements revealed the most significant P value. Particularly M-mod i possessed the most significant P value, whereas the Caval index was associated with the greatest P value. Corl et al [17] used the B-mode CI method to measure the IVC response to fluid infusion and reported that the method was not successful. It is clear that methods used for evaluating IVC diameter re- sponse to the volume change are very important. The result of a study reflects the power of a particular method. We noted that the inspiratory and expiratory diameter measurements were more successful than the Caval index calculation. The inspiratory diameter change measurements were relatively more successful than the expiratory diameter change measurements. This was an expected finding since the inspiratory di- ameter is the minimum IVC diameter with inspiration, and IVC is ex- pected to shrink as much as possible allowed by blood inside its lumen. The expiratory diameter, on the other hand, is the maximum IVC diameter that is expected to be affected by conditions associated with forced expiration like chronic obstructive pulmonary disease or tachypnea to a greater extent. However, both inspiratory and expiratory measurements succeeded at monitoring IVC diameter change and deemed suitable for monitorization of IVC diameter. Sefidbakht et al used M-mode to predict shock in trauma patients and found both inspi- ratory and expiratory diameter measurements successful as we did [14]. Likewise, Lyon et al used B-mode for determining the relationship be- tween IVC diameter and blood loss and reported similar effectiveness of inspiratory and expiratory diameters [8].

In conclusion, all of the six IVC diameter measurement methods

were successful at monitoring volume status. The most effective meth- od was the M-mode i diameter measurement method. B-mode i mea- surements were more effective than B-mode e and CI measurements. We also found pulse rate monitoring as effective as M-mode i diameter measurement. However, it should be remembered that pulse rate is heavily affected by external factors. We concluded that MAP used for patient monitoring was not suitable for volume monitoring.

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 min- imize this bias, video recordings were made first in both modes, follow-

ed 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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