Article, Sonography

Role of inferior vena cava and right ventricular diameter in assessment of volume status: a comparative study

a b s t r a c t

Objective: Ultrasonography has been suggested as a useful Noninvasive tool for the detection and follow-up for hypovolemia. Two possible sonographic markers as a surrogate for hypovolemia are the diameters of the inferior vena cava (dIVC) and the right ventricle (dRV). The goal of this study was to evaluate IVC and RV diameters and diameter changes in patients treated for hypovolemia and compare these findings with healthy volunteers.

Methods: Fifty healthy volunteers and 50 consecutive hypovolemic patients were enrolled in the study. The dIVC, both during inspiration (IVCi) and expiration (IVCe), was measured in hypovolemic patients both before and after fluid resuscitation, and they were also measured in healthy volunteers during the time they participated in the study. The dIVC, in hypovolemic patients both before and after fluid resuscitation, was measured ultrasonographically by M-mode in the subxiphoid area. The dRV was measured ultrasonogra- phically by B-mode in the third and fourth intercostals spaces.

Results: The average diameters of the IVCe, IVCi, and dRV in hypovolemic patients upon arrival were significantly lower compared with healthy volunteers (P = .001). After fluid resuscitation, there was a significant increase in the mean diameters of the IVCe, IVCi, and RV in hypovolemic patients (P = .001).

Conclusions: The results indicate that the dIVC and dRV are consistently low in hypovolemic subjects when compared with euvolemic subjects. Bedside serial measurements of dIVC and dRV could be a useful noninvasive tool for the detection and follow-up of patients with hypovolemia and evaluation of the response to the treatment.

(C) 2013

Introduction

Hypovolemic shock is a state that results in multiorgan failure related to insufficient tissue perfusion and frequently caused by rapid- onset hypovolemia [1]. The primary cause of death is hypovolemic shock in many conditions such as gastrointestinal bleeding, postpar- tum hemorrhage, and major trauma [2]. Thus, early detection of hypovolemia and prompt institution of therapy may save lives. There are many parameters that could be of help in identifying patients with suspected hypovolemia. Physical examination findings, Hematocrit levels, biochemical markers, and central venous pressure are the conventional parameters used to detect hypovolemia [3].

* Corresponding author. Emergency Department of Medicine Faculty, Gaziantep University, Gaziantep, Turkey. Tel.: +90 342 360 60 60/77122, +90 533 640 83

61(Mobile); fax: 90 342.360 22 44.

E-mail address: [email protected] (S. Zengin).

Measurement of CVP cannot be practically used for hypovolemic patients admitting to the emergency department (ED) because it is performed via central venous catheterization, which is an invasive procedure. Moreover, physical examination findings, hematocrit levels, and biochemical markers are not specific indicators [4]. Thus, we need methods to diagnose hypovolemia early and at a high rate of accuracy. Ultrasonography may be used as an effective tool in the detection and management of hypovolemia because it does not use radiation and is fast, repeatable, and applicable at the bedside. Recently, the ultrasonographic measurement of the diameter of inferior vena cava (dIVC) to detect hypovolemia has become popular [5-8]. These former studies were designed as case control or pretreatment and posttreat- ment. In this study, we investigated the efficacy of the ultrasono- graphic evaluation of IVC and right ventricle (RV) diameters in the diagnosis and treatment of hypovolemia. With this aim, we used both case-control and pretreatment/posttreatment group comparisons

that were different from former studies.

0735-6757/$ – see front matter (C) 2013 http://dx.doi.org/10.1016/j.ajem.2012.10.013

Materials and methods

This study was performed at Gaziantep University Medical Faculty Academic ED with the approval of the local ethics committee. The study protocol complies with the Declaration of Helsinki. Patients with dry mucosa, reduced skin elasticity, cool extremities, lengthened capillary refill times, tachycardia, reduced urine output, orthostatic hypotension, and fatigue; patients in whom hypovolemia is antici- pated (such as abnormal uterine bleeding, gastrointestinal bleeding, diarrhea, and vomiting); and patients in whom study criteria were met were enrolled in the study.

The control group consisted of healthy volunteers such as patient relatives and medical personnel. This study was performed without sex discrimination on adult patients older than 16 years. Patients whose ultrasonographic measurements could not be performed because of technical and anatomical reasons such as obesity and excessive abdominal gas were excluded from the study. Patients who had tricuspid failure, right-sided heart disease, portal hypertension, and obstructive lung disease were excluded from the study. Intubated patients were also excluded from the study.

Before enrolling patients in the study, 8 hours of theoretical and applied focused echocardiography training and 8 hours of basic emergency ultrasonography training were given to the physicians who would perform ultrasonography. Moreover, before the treat- ment, IVC and RV diameters were measured in 15 hypovolemic patients and 15 healthy volunteers in the presence of a lecturer experienced in emergent ultrasonography and echocardiography. Logiq P6 (GE Healthcare, USA, 2008) equipment was used in all ultrasonographical examinations. inferior vena cava diameters were checked in the supine position at 5-MHz frequency with a 4C convex probe and an M-mode. The probe was placed in the subxiphoid location, and the sagittal section of the IVC was imaged. To standardize the measurements, measuring of the dIVC was performed at 2 cm caudal of the junction point of the hepatic vein and IVC. The inspiratory (dIVCi) and expiratory (dIVCe) diameters of the VCI were detected by measuring the vein lumen at a single respiratory cycle from one interior wall to the opposite interior wall (Fig. 1). The Caval index (CI) (CI = dIVCe – dIVCi/dIVCe) was calculated as the IVC provided respiratory variance. The diameter of the RV (dRV) of the patients was measured at supine Left lateral decubitus position with a 3S probe and a B-mode at 3.2-MHz frequency. The probe was placed between the third and fourth intercostals spaces, and long-axis views

of the heart were obtained. Ten seconds of image records was taken during the evaluation. While examining these records, the first moment the mitral valve started to close was considered as the end of diastole, and measurements of dRV were performed at this time point. Measuring RV lumen under the Tricuspid valve from the interior wall to the opposite interior wall is recorded as dRV (Fig. 2).

The patients who were enrolled in the study were monitored. After the 2-minute relaxation period, their pulse and blood pressures were measured in the supine position, and Ultrasonographic evaluations were performed. These measurements were performed by a physician different from the physicians who performed follow-up and treat- ment for the patients. One thousand cubic centimeters of 0.9% isotonic NaCl solution was administered to hypovolemic patients as intrave- nous fluid. After the intravenous fluid, all measurements (pulse and blood pressure measuring at supine position, dIVCi, dIVCe, and dRV) were repeated.

Individuals in the control group were monitored in the supine position. After the 2-minute relaxation period, their pulse and blood pressures were measured, and ultrasonographic evaluations were performed. In this group, liquid therapy and further measurements were not performed. Demographic data and measurement data of both groups and the recent diagnosis of patient groups were recorded on the prepared forms.

SPSS 18.0 for Windows was used for statistical analyses (SPSS, Chicago, IL). All data were expressed as mean +- SD and minimum- maximum values. An independent-samples t test was used to compare the variables that gave a normal distribution between the patient group and the control group, whereas a paired t test was used to compare the variables that gave normal distribution pretreatment and posttreatment in the patient group. The relationship between variables was analyzed using the Pearson correlation test. In all comparisons, P b .05 was considered statistically significant.

Results

Fifty-two percent (26/50) of hypovolemic patients were male and 48% (n = 24) were female, whereas 52% (n = 26) of individuals in the control group (50) were male and 48% (n = 24) were female. No statistical difference existed between the mean ages of the patient (57.1 +- 16.8 [16-84] years) and control (56.3 +- 16.8 [16-81] years ) groups. In the preliminary evaluation of hypovolemic patients, dIVCe, dIVCi, and dRV were lower compared with the control group (1.27 +-

Fig. 1. Measurement of the dIVC in a patient in the control group. The dIVCe and dIVCi are 2.06 and 1.48 cm.

3.5

3

2.5

2

1.5

1

0.5

0

dIVCi

dIVCe

CI

dRV

Fig. 2. Measurement of the dRV in a patient in the control group. The dRV is 3.89 cm.

0.43, 0.73 +- 0.37, and 2.83 +- 0.37 cm vs 1.81 +- 0.38, 1.32 +- 0.35, and

3.11 +- 0.41 cm) (P = .001, independent-samples t test), and pulse count and CI were higher (104 +- 15.1 pulse/min and 0.44 +- 0.17 cm vs 80.8 +- 11.6 pulse/min and 0.27 +- 0.12 cm) (P = .001, independent-samples t test) (Table 1; Fig. 3). In hypovolemic patients, although posttreatment IVCe, IVCi, and RV diameters significantly increased (1.55 +- 0.41, 1.01 +- 0.44, and 3.09 +- 0.33 cm) (P = .001,

paired t test), pulse count and CI decreased (93.4 +- 12.2 pulse/min and 0.36 +- 0.14 cm) (P = .001, paired t test) (Table 1). The correlation of parameters obtained from both the patient and control groups are given in Table 2. The most frequent reason for hypovolemia in the study was gastrointestinal bleeding (Fig. 4).

Discussion

Hypovolemia and hypovolemic shock must be diagnosed and treated promptly in the EDs. In both conditions, it is important to identify intravascular volume status of the patient. In EDs, it is sometimes difficult to detect the intravascular volume status. For this purpose, CVP measurement is a frequently used method. However, measurement of CVP is an invasive procedure. Its use is limited because of the invasive nature of the procedure and Possible complications (Arterial puncture, venous thrombosis, infection, etc) during or after the process. Recent publications indicate that CVP is not an ideal method, and Clinical decisions regarding volume management should not be made based on CVP because of its poor Predictive role [9]. Physical examination findings, vital signs, and laboratory results are other parameters used to estimate the

Fig. 3. Comparison of dIVCi, dIVCe, CI, and dRV measurements in the hypovolemic group (pretreatment/posttreatment) and the control group.

of these parameters may be found normal as the compensatory mechanisms of the body initiate; thus, this may result in delays in the detection of volume loss. For instance, in some patients, a 30% loss of total body liquid would be compensated by the body, and blood pressure may be held at normal levels, whereas this amount of loss is sufficient to initiate multiple-organ failure [10].

pretreatment posttreatment control

The basal cardiac rate of many patients admitted to the ED is unknown. Although tachycardia is an indicator of acute liquid loss, it is not sufficiently specific and sensitive for a diagnosis or follow-up because it may be influenced by different inner and outer signals [11,12]. Serum lactate level is a biochemical parameter used as an indicator of tissue hypoperfusion; however, it is insufficient for the early diagnosis of hemodynamic instability and in the guidance of liquid resuscitation [3].

To determine the status of intravascular volume, the dIVC ultrasonographic measurement is another method [4]. The IVC is a highly collapsible major vein, and its diameter closely correlates with right-sided Cardiac functions. The dIVC has not been found to be affected by the body’s compensatory vasoconstrictor response to volume loss [4]. Hence, it reflects volume status more closely than other parameters based on the arterial system, such as blood pressure, pulse rate, and others.

Wallace et al [13] found that the CI differs according to the place of measurement and suggested that the most reliable measurement for the dIVC can be performed at 2 cm caudal from the junction of the hepatic vein and the IVC.

In another study performed on blood donors, Lyon et al [14] detected about a 5-mm decrease with 450 mL of blood loss when comparing levels of both the dIVCi and dIVCe, and the authors suggested that the serial measurement of IVC diameters may be used to follow ongoing blood loss and evaluate the response to the

Table 2

Correlation of parameters obtained from patient and control groups

intravascular volume status. These parameters are not reliable

because they are influenced by various clinical conditions [9]. Some

Study group, pretreatment

r

Table 1

P

P

r

P?

Comparison of parameters measured of the patient and control groups

dIVCi and SBP

0.508

.000

0.245

.086

-0.044

.761

Patient group, Patient group, Control group Pa?/Pb??

pretreatment posttreatment

dIVCe and SBP

CI and SBP

0.467 .000 0.218 .129 -0.015

.919

.569

dRV and SBP

0.237

.017

-0.019

.896

0.073

.631

Age (y)

57.1 +- 16.8

56.3 +- 16.8

.821

dIVCi and DBP

0.376

.000

0.070

.630

0.078

.589

SBP (mm Hg)

94.30 +- 13.2

113.3 +- 9.6

123.9 +- 15.6

.000/.000

dIVCe and DBP

0.274

.006

0.084

.562

-0.107

.458

DBP (mm Hg)

55.7 +- 12.2

66.6 +- 8.7

69.3 +- 11.1

.000/.000

CI and DBP

-0.409

.000

-0.056

.701

-0.272

.058

Pulse (pulse/min)

104 +- 15.1

93.4 +- 12.2

80.8 +- 11.6

.000/.000

dRV and DBP

0.177

.077

-0.140

.333

0.044

.762

dIVCi (cm)

0.73 +- 0.37

1.01 +- 0.44

1.32 +- 0.35

.000/.000

dIVCi and pulse

-0.594

.000

-0.264

.064

-0.184

.234

dIVCe (cm)

1.27 +- 0.43

1.55 +- 0.41

1.81 +- 0.38

.000/.000

dIVCe and pulse

-0.629

.000

-0.307

.031

-0.261

.067

CI (cm)

0.44 +- 0.17

0.36 +- 0.14

0.27 +- 0.12

.000/.000

CI and pulse

0.390

.000

0.199

.165

-0.081

.582

dRV (cm)

2.83 +- 0.37

3.09 +- 0.33

3.11 +- 0.41

.000/.000

dRV and pulse

-0.318

.001

0.017

.905

-0.276

.052

Study group, posttreatment

r

Control group

-0.416 .000 -0.231 .097 0.082

Pa/Pb, Patient group pretreatment vs posttreatment/control group.

* Paired t test.

?? Independent samples t test.

SBP and pulse -0.500 .000 -0.345 .014 0.223 .119

DBP and pulse -0.280 .005 -0.199 .166 0.361 .106

* Pearson correlation test.

Fig. 4. Recent diagnosis of hypovolemic patients.

treatment. On the other hand, Resnick et al [15] compared the dIVC with cardiac rate and the mean arterial pressure in a similar study. In this study by Resnick et al, no significant difference was observed in cardiac rate and mean arterial pressure after Blood donation. Although a minor decrease was detected in the dIVC, no difference was observed for respiratory CI. In this study [15], it was concluded that the dIVC was not sensitive enough to detect hemorrhage at an early phase. The difference in the results of these 2 studies may originate from the different techniques used in the dIVC measurement.

In our study, we performed dIVC measurements from 2 cm caudal to the junction point of the hepatic vein and the vena cava inferior. Our study was not a controlled hemorrhage model, but we detected that the mean diameter for the dIVCi in hypovolemic patients was 6.9 mm (P b .001) and the mean for the dIVCe was 5.4 mm lower (P b

.001) than that of healthy volunteers. These differences correspond to the results obtained by Lyon et al [14]. On the other hand, although a correlation existed between blood pressure and pulse in the hypovolemic group, none existed in the control group (Table 2). These results are partially similar to the results of Resnick et al.

Yanagawa et al [16] used the dIVCe in the early diagnosis of hypovolemic shock using ultrasonography in patients with trauma. In this study, the threshold level of the dIVCe for the diagnosis of hemorrhagic shock was 9 mm. The dIVCe (7.7 +- 0.3 mm) measured in the shock group was significantly lower than the level (13.4 +- 0.7 mm) measured in the control group. A similar study was performed by Sefidbakht et al [17] in patients with trauma. In this study, dIVCe and dIVCi levels (5.6 +- 0.8 and 4 +- 0.7 mm) of the shock group were significantly lower than those of the control group (11.9 +- 2.2 and 9.6

+- 2 mm), and the CI was higher. With this study, the dIVC was considered a reliable indicator of shock, although blood pressure is at normal limits because of sympathetic activation.

Akilli et al [6] compared the dIVCe and dIVCi with other shock parameters such as cardiac rate, systolic blood pressure (SBP)/ diastolic blood pressure , Shock Index, urine discharge, hemoglobin level, leukocyte count, and excessive base in the patients admitted to the ED with hemorrhagic shock. It was concluded in this study that the dIVC in hemorrhagic shock is more valuable than in conventional shock parameters.

Yanagawa et al [7] evaluated the response to volume replacement in patients experiencing hypovolemic shock due to trauma. Systolic blood pressure, cardiac rate, hemoglobin, and arterial base excess were not significantly different among 2 groups (a transient responder group in which a second episode of shock occurred after leaving the ED and a responder group in which the blood pressure remained stable) that received liquid therapy, but a significant difference was observed in the dIVC. When an insufficient extension occurs in the dIVC with liquid replacement, it is concluded that the hemorrhage continues. These results revealed that the dIVC mea- surement is more sensitive than other parameters in detecting hypovolemia and following the efficacy of the treatment. In this

study, an increase of 3.1 +- 0.5 mm in the dIVC after liquid therapy was similar to the results from our study (dIVCi/dIVCe, 2.8 +- 0.7/2.8 +- 0.2 mm). The RV preload represents filling before RV contraction. Right ventricular filling may be influenced by factors such as intravascular volume status, ventricular relaxation, and compliance. The compli- ance of the RV is higher than that of the left ventricle [18]. Right ventricular end-diastolic pressure may be monitored using right cardiac catheterization and measured ultrasonographically with the detection of the dIVC and CI. [19]. Normal RV diameter ranges between 18 and 33 mm according to a summary of 12 studies involving 405 patients [20]. Resnick et al [15] evaluated the left ventricular diameter in blood donors but were unable to obtain a significant result. In our study, the dRV was significantly lower (P b

.001) in the patient group (2.83 +- 0.37 cm) compared with the control group (3.1 +- 0.41cm) (Fig. 3). We observed that with administration of 1000 cc isotonic NaCl to hypovolemic patients, the dRV increased to levels (3.09 +- 0.33 cm) close to that of the control group (3.1 +- 0.41 cm). To our knowledge, no previous study exists in this topic, but according to us, the dRV may be used as a useful parameter in evaluating the response to Fluid replacement.

The results we obtained in this study reveal that the IVC and RV diameters may be beneficial for the early detection of hypovolemia and in the follow of fluid replacement. The dIVC and dRV are more sensitive than conventional parameters (such as blood pressure and pulse) in diagnosing hypovolemia.

Limitations

Some diseases (tricuspid failure, right cardiac diseases, portal hypertension, and obstructive lung disease) that impact the RV and IVC diameter and conditions when ultrasonography cannot be technically performed are the limiting factors of our study and the use of this application. The important limitation of the study is also the definition of hypovolemia using conventional clinical findings such as the skin elasticity loss; the mount, nose, and other mucous membranes being dry; and increased capillary refill time. Measure- ments of the RV diameters were performed by B-mode imaging rather than M-mode because of investigators’ own decision. This could be regarded as a limitation because M-mode measurements could have been more accurate in determining the end of the diastole. However, the end of the diastole was precisely determined as the point in which the mitral valve starts closing by B-mode. All measurements in each patient were done by the same physician. There may be intraobserver variability in these measurements. However, this possible variability was not evaluated. Differences in the mean measurements would be more accurate if they could be corrected for intraobserver variability. In addition, single measurement of the RV dimension may lead to defective insight for recognizing and evaluating of the volume status because of dynamic variability; thus, it would be better to have serial measurements to evaluate volume status more precisely.

Conclusion

In conclusion, bedside serial ultrasonographic measure of RV and IVC diameters, which is a noninvasive method for emergency physicians, may be a useful tool to detect and follow-up hypovolemia and evaluate the adequacy of volume replacement.

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