Received 02/02/2017
Review began 02/06/2017
Review ended 02/06/2017
Published 02/12/2017
© Copyright 2017
Ilyas et al. This is an open access
article distributed under the terms of
the Creative Commons Attribution
License CC-BY 3.0., which permits
unrestricted use, distribution, and
reproduction in any medium, provided
the original author and source are
credited.
Correlation of IVC Diameter and
Collapsibility Index With Central Venous
Pressure in the Assessment of Intravascular
Volume in Critically Ill Patients
Abid Ilyas , Wasib Ishtiaq , Salman Assad , Haider Ghazanfar , Salman Mansoor ,
Muhammad Haris , Aayesha Qadeer , Aftab Akhtar
1. Internal Medicine, Shifa International Hospital, Islamabad, Pakistan 2. Internal Medicine, Shifa
International Hospital, Islamabad, PAK 3. Internal Medicine, Marshall University School of Medicine,
Huntington, USA 4. Internal Medicine, Shifa College of Medicine, Islamabad, PAK 5. Department of
Neurology, Shifa International Hospital, Islamabad, Pakistan 6. Department of Cardiology, Shifa
International Hospital, Islamabad, Pakistan
Corresponding author: Haider Ghazanfar, haidergh@gmail.com
Disclosures can be found in Additional Information at the end of the article
Abstract
Objective
The objective of our study is to assess the correlation between inferior vena cava (IVC)
diameters, central venous pressure (CVP) and the IVC collapsibility index for estimating the
volume status in critically ill patients.
Methods
This cross-sectional study used the convenient sampling of 100 adult medical intensive care
unit (ICU) patients for a period of three months. Patients ≥ 18 years of age with an intrathoracic
central venous catheter terminating in the distal superior vena cava connected to the
transducer to produce a CVP waveform were included in the study. A Mindray diagnostic
ultrasound system model Z6 ultrasound machine (Mindray, NJ, USA) was used for all
examinations. An Ultrasonic Transducer model 3C5P (Mindray, NJ, USA) for IVC imaging was
utilized. A paired sampled t-test was used to compute the p-values.
Results
A total of 32/100 (32%) females and 68/100 (68%) males were included in the study with a mean
age of 50.4 ± 19.3 years. The mean central venous pressure maintained was 10.38 ± 4.14 cmH2O
with an inferior vena cava collapsibility index of 30.68 ± 10.93. There was a statistically
significant relation among the mean CVP pressure, the IVC collapsibility index, the mean
maximum and minimum IVC between groups as determined by one-way analysis of variance
(ANOVA) (p < 0.001). There was a strong negative correlation between CVP and IVC
collapsibility index (%), which was statistically significant (r = -0.827, n = 100, p < 0.0005). A
strong positive correlation between CVP and maximum IVC diameter (r = 0.371, n = 100, p <
0.0005) and minimum IVC diameter (r = 0.572, n = 100, p < 0.0005) was found.
Conclusion
There is a positive relationship of CVP with minimum and maximum IVC diameters but an
inverse relationship with the IVC collapsibility index.
1 2 3 4 5
6 2 2
Open Access Original
Article DOI: 10.7759/cureus.1025
How to cite this article
Ilyas A, Ishtiaq W, Assad S, et al. (February 12, 2017) Correlation of IVC Diameter and Collapsibility Index
With Central Venous Pressure in the Assessment of Intravascular Volume in Critically Ill Patients. Cureus
9(2): e1025. DOI 10.7759/cureus.1025
Categories: Internal Medicine
Keywords: collapsibility index, intensive care units, ultrasonography, inferior vena cava, central
venous pressure, critical care
Introduction
Bedside assessment of intravascular volume status in critically ill patients is challenging. Fluid
management impacts systemic perfusion and may influence the risk of organ failure and
mortality [1]. Clinicians often use invasive hemodynamic monitoring as an adjunct to
information gathered from the physical examination and laboratory evaluation to arrive at a
fluid management strategy. Central venous pressure (CVP) is a hemodynamic parameter that is
extensively used. A non-invasive and economical technique like ultrasound in the ICU helps to
approach diagnosis and treatment of the critically ill patients [2]. A survey carried out in
Canada concluded that 90% of the intensivists use CVP to monitor fluid resuscitation in septic
shock patients [3]. High CVP is known to be associated with volume overload states while low
CVP is associated with volume depleted states. CVP is a good approximation of right atrial
pressure (RAP) which in turn is a major determinant to right ventricular filling. Therefore CVP
is a good indicator of right ventricular preload. The complication associated with CVP insertion
includes failure to place the catheter, arterial puncture, catheter malposition, pneumothorax,
subcutaneous hematoma, hemothorax, asystolic cardiac arrest and catheter-related infection
[4-5]. Bedside ultrasound is potentially a useful non-invasive adjunct to estimate the
intravascular status by measuring IVC diameter [6-8]. One technique uses the size and
collapsibility of the inferior vena cava (IVC), similar to the method used by echocardiographers
to estimate right atrial pressure (RAP) in non-acute care settings. Cyclic changes in thoracic
pressure in a healthy person may result in the collapse of approximately 50% of the IVC
diameter [9]. Collapsibility of the inferior vena cava has been found to be useful in monitoring
an acute heart failure patient’s response to therapy as well as assisting in ongoing resuscitation
by providing means to measure CVP non-invasively [10-11].
In previous studies a head-to-head comparison has been made in spontaneously breathing
patients to evaluate how well CVP was predicted by maximal IVC diameter and collapsibility
with inspiration, hypothesizing that the IVC collapsibility index would have a superior
predictive value for a CVP > 10 mmHg than the maximal IVC diameter. The diameter variations
of the vena cava can be of range 13–28 mm and mean 20 mm. There was no significant relation
of vena cava diameters to height, weight, or body surface area based on previous studies. Vena
cava diameters are well reproducible, with an interobserver error, estimated as the coefficient
of variation of 2.2% (r = 0.98, p < 0.05) [12]. The rationale of our study is to assess correlation
between the inferior vena cava (IVC) diameters, central venous pressure (CVP) and inferior
vena cava collapsibility index for estimating the volume status in critically-ill patients.
Materials And Methods
This cross-sectional analysis used a convenient sampling of 100 adult medical intensive care
unit (ICU) patients over a period of three months. Patients ≥ 18 years of age with an
intrathoracic central venous catheter terminating in the distal superior vena cava connected to
the transducer to produce a CVP waveform were included in the study. Patients with clinical
signs of elevated abdominal pressure, moderate to severe tricuspid regurgitation, CVP inserted
for more than 24 hours, and patients in whom the supine position was contraindicated were not
included in the study.
The study was performed from January 2016 to May 2016 with a total duration of five months.
Using the World health Organization (WHO) sample size calculator, keeping 95% confidence
level and a prevalence of hypovolemia at 12.36%, a sample size of 85 was calculated. Informed
2017 Ilyas et al. Cureus 9(2): e1025. DOI 10.7759/cureus.1025 2 of 9
consent was obtained from all the participants, and they were assured that the identity of the
respondents will be kept anonymous. Ethical approval was obtained from the Shifa
International Hospital ethical review board. Three critical care fellows prospectively enrolled
eligible patients and completed the ultrasound examination of the IVC diameter. All three
ultrasonographers had familiarity with bedside vascular ultrasound. Before the study began,
they completed two hours of standardized training in image acquisition according to the study
protocol. It was followed by five practice examinations under the critical care consultant and
the supervisors.
During enrollment and collection of ultrasound data, study ultrasonographers were blinded to
CVP monitoring. Bedside ultrasound images were obtained in a systematic fashion with the
patient supine to determine the dimensions and collapsibility of the IVC. A Mindray diagnostic
ultrasound system model Z6 ultrasound machine (Mindray, NJ, USA) was used for all
examinations. Ultrasonographers used an Ultrasonic Transducer model 3C5P for IVC imaging
(Mindray, NJ, USA). First, ultrasound gel was applied to the subxiphoid region. The IVC was
imaged in a longitudinal plane with the transducer in the subxiphoid position. The intrahepatic
segment of the IVC was visualized as it entered the right atrium. The IVC diameter was
measured 2 cm caudal to the hepatic vein-IVC junction, or approximately 3–4 cm from the
junction of the IVC and right atrium. This measurement location was preferred as IVC
collapsibility in the intrahepatic segment was not influenced by the activity of the muscular
diaphragm compared to one at the IVC-right atrial junction. 15 M-mode was used to capture a
10-s cine loop of the IVC over two or three respiratory cycles. The maximum IVC diameter
(IVCdmax) was measured as the maximum anterior-posterior dimension at end-expiration
using the leading edge technique (inner edge to inner edge of the vessel wall). In addition, the
minimum IVC diameter was measured at end-inspiration (IVCdmin). The IVC collapsibility
index was the difference between the maximum and minimum IVC diameters divided by the
maximum IVC diameter, expressed as a percentage ([IVCdmax – IVCdmin] / IVCdmax × 100%).
Immediately following the ultrasound image acquisition, study personnel obtained a
simultaneous recording of the CVP waveform from the distal lumen of the central venous
catheter and a single-lead electrocardiogram rhythm strip. The CVP was uniformly measured
from a recording at end expiration with the patient supine and the pressure transducer having
been zeroed at the mid-thoracic position. A patient with CVP of less than 8 cmH2O was
considered as hypovolemic. The patients with CVP between 8–12 cmH2O were considered as
euvolemic and patients having CVP > 12 cmH2O were considered as hypervolemic. The data
was entered and analyzed on SPSS version 21 (IBM, NY, USA). Descriptive statistics were
calculated for both qualitative variables. One-way analysis of variance (ANOVA) was used for
comparison between the three groups of patients with different intravascular volume status and
Tukey's method was used for multiple comparisons. Pearson correlation coefficient was used to
assess the significance between CVP and IVC collapsibility index (%) and the maximum and
minimum IVC diameter. A p-value less than 0.05 was considered to be significant.
Results
A total of 32/100 (32%) females and 68/100 (68%) males were included in the study with a mean
age of 50.4 ± 19.3 years. This is presented in Table 1.
2017 Ilyas et al. Cureus 9(2): e1025. DOI 10.7759/cureus.1025 3 of 9
Age of the Patient (Mean ± Standard Deviation) 50.4±19.3 Years
Male Participants 68/100 (68%)
Female Participants 32/100 (32%)
On Invasive Ventilation 47/100 (47%)
Hypovolemic Group 26/100 (26%)
Euvolemic Group 46/100 (48%)
Hypervolemic Group 26/100 (26%)
TABLE 1: Demographics
The mean arterial pressure maintained was 82.6 ± 21.1 mmHg and mean positive end-
expiratory pressure (PEEP) was 5.3 ± 1.3 cmH2O. The mean heart rate was 95.2 ± 21.1 per
minute. The mean central venous pressure maintained was 10.38 ± 4.14 cmH2O with the
inferior vena cava collapsibility index of 30.68 ± 10.93. The central venous pressure (CVP) was
found to be less than 8 cmH2O among 26/100 (26%) patients, while 46/100 (48%) had CVP
between 8–12 cmH2O and 26/100 (26%) patients had CVP greater than 12 cmH20. Invasive
ventilation was done among 47/100 (47%) patients. The mean inferior vena cava (IVC)
minimum diameter was 1.17 ± 0.27 cm and maximum diameter was 1.75 ± 0.27 cm.
One-way ANOVA test was used for comparison between the three groups of patients with
different intravascular volume status. Tukey's method was used for multi-comparison. There
was a statistically significant correlation in the mean CVP pressure and the IVC collapsibility
index and the CVP with mean maximum and mean minimum IVC diameters between groups as
determined by one-way ANOVA (p < 0.001). This is presented in Table 2.
2017 Ilyas et al. Cureus 9(2): e1025. DOI 10.7759/cureus.1025 4 of 9
Parameters
Hypovolemia*
n=26
Euvolemia**
n=48
Hypervolemia***
n=26
Anova (p-
value)
Mean Arterial Pressure (mmHg) 80.12±16.06 84.00±16.23 82.63±16.60 0.625
Heart Rate (per minute) 87.77±12.89 99.06±24.09 95.70±21.50 0.095
IVC Collapsibility Index 44.39± 8.05 30.21± 4.14 17.78± 2.69 0.001
Mean CVP Pressure (cmH2O) 5.42±1.63 10.06±1.48 15.73±2.11 0.001
IVC (Maximum Diameter)
(centimeters)
1.63±0.19 1.68±0.16 1.78±0.16 0.006
IVC (Minimum Diameter)
(centimeters)
0.94±0.17 1.15±0.21 1.42±0.24 0.001
TABLE 2: Parameter assessment with volume status
*Hypovolemia CVP < 8 cmH2O, **Euvolemia CVP 8-12 cmH2O, ***Hypervolemia CVP > 12 cm H2O.
A Tukey post hoc test revealed that the CVP and IVC minimum diameters were statistically
lower in the hypovolemic group (p < 0.001) and statistically higher in the hypervolemia group
(p < 0.001). It also revealed that IVC collapsibility index was statistically higher in the
hypovolemic group and statistically lower in the hypervolemic group (p < 0.001). There was a
significant difference in IVC (maximum diameter) between the hypovolemic and hypervolemic
group (p = 0.004), as well as between the hypervolemic and euvolemic group (p = 0.025). There
was no significant difference in IVC (maximum diameter) between the euvolemic and
hypovolemic group (p=0.536). The IVC (minimum diameter) was statistically higher in the
hypervolemic group (p < 0.001) and statistically lower in the hypovolemic group (p < 0.001).
This is presented in Table 3.
2017 Ilyas et al. Cureus 9(2): e1025. DOI 10.7759/cureus.1025 5 of 9