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ORIGINAL ARTICLE - THORACIC IMAGING
Year : 2020  |  Volume : 69  |  Issue : 2  |  Page : 415-420

The relationship between inferior vena cava diameter measured by bedside ultrasonography and central venous pressure value


1 Professor of Pulmonary Medicine, Faculty of Medicine, Assuit University, Assuit, Egypt
2 Lecturer of Pulmonary Medicine, Faculty of Medicine, Assuit University, Assuit, Egypt

Date of Submission23-Mar-2019
Date of Decision10-Sep-2019
Date of Acceptance18-Sep-2019
Date of Web Publication14-May-2020

Correspondence Address:
MSc Mohamed Adam
Specialist of Pulmonary Medicine, Faculty of Medicine, Assuit University, 78 Mohafza Street 4th Floor, Assuit, 11711
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ejcdt.ejcdt_76_19

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  Abstract 


Background The exact evaluation of intravascular volume status is an essential parameter for assessing patients in critical conditions in ICUs. It is significant for both primary assessment and response to medical treatment and supportive measures.
Objective We are aiming for selecting a method to evaluate patients’ intravascular volume status by measuring inferior vena cava (IVC) diameter noninvasively by using transthoracic sonography and to evaluate if there is a relation between IVC and central venous pressure (CVP).
Patients and methods Patients were older than 18 years. All patients with a central venous catheter that was already inserted into internal jugular vein were involved in the study. IVC diameter records were estimated and assessed by the same physician with the help of chest sonography both at the end of inspiration and at the end of expiration. Measurements of CVP were done by water manometer.
Results A total of 50 patients were included in our study. The patients were diagnosed as having chronic obstructive pulmonary disease (84%), pneumonia (60%), and pleural effusion (12%). Overall, 48% of patients had spontaneous respiration and 52% required mechanical ventilation. Among respiratory phases of IVC diameter and the IVC caval index, we found an important negative correlation between CVP and caval index. Moreover, we can predict CVP measurement by IVC sonography.
Conclusion Measurements of IVC diameter by chest ultrasound can be used for estimation of the intravascular volume status of patients in critical conditions.

Keywords: critically ill, central venous pressure, inferior vena cava, ultrasonography


How to cite this article:
Agmy G, Wafy S, Adam M. The relationship between inferior vena cava diameter measured by bedside ultrasonography and central venous pressure value. Egypt J Chest Dis Tuberc 2020;69:415-20

How to cite this URL:
Agmy G, Wafy S, Adam M. The relationship between inferior vena cava diameter measured by bedside ultrasonography and central venous pressure value. Egypt J Chest Dis Tuberc [serial online] 2020 [cited 2020 Aug 4];69:415-20. Available from: http://www.ejcdt.eg.net/text.asp?2020/69/2/415/284332




  Introduction Top


The central venous pressure (CVP) is a key parameter for physiologic estimation of preload, which is helpful in assessing the state of intravascular volume [1]. In 1930, Sir Thomas Lewis performed an assessment of CVP by evaluating the height of the column of blood in the internal jugular veins (IJV) [2]. Chest sonography has been used as a method in the assessment of state of intravascular volume by evaluating the IJV height and inferior vena cava (IVC) diameters [3]. Ultrasound is being increasingly used for this purpose. Many methods have been described to estimate CVP using bedside ultrasound such as collapsibility and size of IVC, and size of IJV [4].


  Aims Top


The study aimed for the following;
  1. To support the role of chest sonography as a guidance for central venous catheter (CVC) insertion.
  2. To detect a relation between IVC diameters and measurements of the CVP.



  Patients and methods Top


Our study was done after approval of Faculty of Medicine Ethics Committee, Assuit University. Patients older than 18 years who had a CVP already introduced to IJV were included in our study. Patients were recommended for hemodynamic observation and were reserved to the respiratory ICU. Written and informed consent was taken before sonographic evaluation from the patient or relatives regarding his/her conscious level. Patients who did not accept participation in the study; patients with increased intra-abdominal tension, for example, pregnancy; patients in whom the sonographic evaluation would not be tolerated, for example, severe orthopnea; patients with obesity; and those with a history of neck trauma, radiotherapy, or surgery were excluded. A medical record was filled for gathering standard data. Patients’ age, sex, arterial blood pressure, heart rate, respiratory rate, temperature, CVP and IVC diameter measurements during the respiratory cycle, disease diagnosis, CVC type, oxygen therapy or not, and if the patient needed noninvasive or invasive mechanical ventilation. Medison Sonacer R3 color portable ultrasound machine (Korea) was used with its two transducers, i.e., (a) CN2-8 convex 2–8 MHz and (b) LNS 12/40 linear (40 mm) 5–12 MHz, for two purposes, (a) as a guidance for CVC insertion and (b) assessment of IVC diameters.

For central venous catheter introduction

The supine position with the head located in the Trendelenburg position was optimized for all cases ([Figure 1]). The skin was sterilized. Using neck ultrasound, IJV location was detected, and a needle was introduced through its guidance. After the needle insertion, evidenced by the ultrasound and the venous blood returning into the syringe, a guide wire was introduced through this needle to the IJV, and the needle removal was done. All CVCs used were Certofix (B. Braun Melsungen AG, Melsungen, Germany).
Figure 1 Transverse view of internal jugular vein. Left star: internal jugular vein, right star: common carotid artery.

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Assessment of inferior vena cava diameter

Location of the probe positionis at the right intercostal spaces in the mid-clavicular line at perpendicular to the body. The distance between outer limit of the vessel and inner limit of the border in long axis/subxiphoid view was taken to standardize the records. IVC was directly measured through a transhepatic view by a portable ultrasound machine, and a deep probe was used while supine position of the patient was optimized. The ultrasound cross-section was vertical to the IVC. B mode was used to assess the collapsibility of the IVC, and the M-mode ([Figure 2]) was used to measure variations in IVC diameter. Measurements were assessed at the end of inspiration and expiration by M-mode and were recorded in millimeters using the deep probe as shown in the following:
Figure 2 IVC diameter during inspiration and expiration by M-mode. IVC, inferior vena cava.

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  Results Top


During this 1-year prospective study, 50 critically ill cases from the respiratory ICU of Chest Department at Assiut University Hospital, who met the inclusion criteria, were included. Their mean age were 65.8±12.1 years, and 30% of them were males. CVC was already inserted for other purposes using ultrasound guidance. The catheter was easily inserted, decreased time was needed for the maneuver, correct and confirm site of insertion, with no complications were reported such as pneumothorax or local hematoma. Most patients were diagnosed as having chronic obstructive pulmonary disease (COPD) (42 patients, 84%), pneumonia (30 patients, 60%), and pleural effusion (six patients, 12%), as shown in [Table 1] and [Table 2].
Table 1 Diagnosis among studied group (N=50)

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Table 2 Comorbidities among studied group (N=50)

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The most common causes of fluid loss were vomiting and diarrhea (64 and 32%, respectively); moreover, there were clinical signs of dehydration such as dry tongue. Positive skin pinch test result was seen in 11 patients. Approximately 64% of patients needed fluid administration.

Among the studied group, 26 patients were mechanically ventilated. All of them were adjusted to positive end-expiratory pressure (PEEP) of 5 cmH2O (physiological PEEP). [Table 3] demonstrates classification of CVP among studied group; 60% of the studied group were more than 12 cmH2O. The mean measurement of the CVP was 13.1 cmH2O, mean minimum IVC diameter was 1.5 cm, and the mean maximum IVC diameter was 2 cm ([Table 4]). We found that CVP was negatively correlated well with caval index (r=−0.89, P<0.001) ([Figure 3]); when caval index was high (>38%), it is affirmed that CVP was less than 8 cmH2O, which indicated that the patient was mostly dehydrated. On the contrary, when caval index was low (<31%), the CVP was high more than 12 cmH2O, and the patient could be managed accordingly.
Table 3 Classification of central venous pressure among studied group

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Table 4 Inferior vena cava diameter measures (cm) and central venous pressure

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Figure 3 Correlation between CVP measures and caval index. CVP, central venous pressure.

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[Figure 3] shows test characteristics of caval index for prediction of elevated CVP more than 10 mmHg.

Regarding the receiver operating characteristic curve of caval index in predicting CVP of more than10 mmHg, a CVP of 10 mmHg was chosen as a clinically significant cutoff for high CVP. Mean and median values of caval index with a cutoff value of more than 31 had a sensitivity of 100.0%, specificity of 97.8%, a PPV of 83.3%, and an NPV of 100.0%. The area under the receiver operating characteristic curve was 0.99 (0.92–1) ([Table 4] and [Figure 4])
Figure 4 ROC curve of caval index in predicting central venous pressure more than 10 mmHg. A CVP of 10 mmHg was chosen as a clinically significant cutoff for high CVP. Mean and median values of caval index with a cutoff value of more than 31 had a sensitivity of 100.0%, specificity of 97.8%, a PPV of 83.3%, and an NPV of 100.0%. The area under the ROC curve was 0.99 (0.92–1). CVP, central venous pressure; NPV, negative predictive value; PPV, positive predictive value; ROC, receiver operating characteristic.

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  Discussion Top


CVP assessment is a useful method not only for hemodynamic monitoring but is also the key for care and management of shock [5]. However, CVP monitoring requires placement of a CVC, which is often difficult in an urgent situation and time consuming, and it is an invasive maneuver with multiple complications [6]. The frequency of mechanical complications ranges between 5 and 19% [7]. In our studied group, as CVC was inserted through sonar guidance, none of the patients developed any immediate complications. Bedside chest ultrasound is considered a useful tool that is present in a lot of ICUs. In addition, it is a nonharming, noninvasive, and portable device. Regarding the diagnosis among the studied group, it is evident that COPD and pneumonia were the most common concomitant diseases (84 and 60%, respectively) and the least one was interstitial lung disease. This is in agreement with Thanakitcharu et al. [8] and Sinan et al. [9] who found that COPD and pneumonia were the most common causes of admission to ICU in their study.

We found that clinical assessment of the dehydration signs was statistically significant (P<0.001) with CVP measurement (<8 cmH2O), whereas in another group of patients, CVP showed high pressure in spite of detection of some signs of dehydration. So, we cannot depend on clinical signs only for assessment of fluid status of patients. This in agreement with Charkoudian et al. [10] and Daniele and Nicola [11] who reported nearly the same findings.

According to the CVP measures, cases were divided into three groups: 11 (22%) patients were hypovolemic (CVP<8 cmH2O), nine (18%) patients were euvolemic (CVP 8–12 cmH2O), and 30 (60%) patients were hypervolemic (CVP>12). Among the three groups with respect to their intravascular volume status, complete blood count and kidney function test were not significantly different, and we found that no significant correlation could be detected between complete blood picture and kidney function test and CVP. These results are in agreement with that reported by Prasert et al. [9] who found that there was no significant relation between basic laboratory investigations and CVP measurements.

During mechanical ventilation with PEEP supported, it was thought that PEEP would affect the CVP by increasing the intrathoracic tension leading to decreased venous return and increased venous stasis. So, cardiac output would be decreased. Therefore, an increase in PEEP level would cause an increase in the measurements of IVC diameter and decrease in the caval index [12]. Actually, PEEP is not transferred directly to the venous system. Within respiration, less than 25% of the PEEP is transferred to the central veins, but PEEP levels more than 5 cmH2O might have an effect on IVC diameter. Manaligod et al. [13] reported that when using physiologic PEEP (3–5 cmH2O), there was no significant increase in CVP. In our study, although all the intubated patients received ventilator support with PEEP, the PEEP level was fixed (5 cmH2O) which was the normal physiologic PEEP. So, in our study, the PEEP support had not affected IVC diameter that much, as a result a relation between CVP and IVC diameter was applicable.

In 2008, the American College of Emergency Physicians published a policy statement on emergency ultrasound guidelines. This includes the evaluation of intravascular volume status and estimation of CVP based on the IVC diameter measurements [14]. IVC diameter could be measured by both B and M-mode of ultrasound and had a good reflection of intravascular volume status. Respiration could also affect the size and diameter of thin-walled IVC. During inspiration, the IVC diameter decreases owing to the negative intrathoracic pressure. The evaluation of IVC diameter changes during the respiratory cycle may lead to a more exact estimation of intravascular volume and predicting CVP [15].

Among different respiratory phases of IVC diameter and the IVC collapsibility index, we found that CVP was correlated well with caval index (r=−0.89, P<0.001) with negative significant correlation. This was in agreement with Thanakitcharu et al. [8], Wiryana et al. [16] and Prasert et al. [9] who found that calculation of caval index by detection of IVC diameter at different phases of respiratory cycle had a significant correlation with CVP. Moreover; there was a significant inverse relation between caval index and CVP measurement in cmH2O. On the contrary, Sinan et al. [9] found that IVC diameter (caval index) was not correlated with CVP measurements in all situations, which is not perform well in low CVP measurements but perform well in high CVP measurements. They explained these by the physiology of the venous structures; such structures can expand to certain point when the CVP increases and then the expansion ratio does not significantly change.

Limitations

There are a number of technical and pathophysiologic factors that limit the utility and accuracy of IVC-ultrasound.
  1. The subcostal view could be difficult in some cases, as some studies have failed to report the degree to which IVC visualization was technically difficult [17].
  2. Individual variations occur in measurements of CVP and IVC diameter.



  Conclusion Top


Ultrasound can be used as an alternative technique for estimating the intravascular volume such as measuring the IVC diameter and so the caval index. During different respiratory phases of IVC diameter and the IVC caval index, there was a significant negative correlation between CVP and caval index. Moreover, CVP values can be predicted by measurement of IVC diameter.

Recommendations

Based on our results, we recommend the following:
  1. Usage of neck ultrasound as a guidance for CVC insertion.
  2. Application of caval index calculation instead of using CVP measurement.
  3. Increase training on neck and chest ultrasound and help to improve the experience in using this maneuver.


Financial support and sponsorship

Nil.

Conflicts of interest

None declared.



 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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Abstract
Introduction
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Patients and methods
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