Superior Vena Cava (SVC) Diameter and Collapsibility Index and Its Relationship to Central Venous Pressure (CVP) Measurements in Patients Undergoing Liver Transplantation
Conditions: Liver Failure
Sponsor: The Cleveland Clinic

 
SVC diameter and Collapsibility Index and its Relationship to Central Venous Pressure Measurements in 
Patients undergoing Liver Transplantation 
Argalious et al 
 
 

SVC diameter and Collapsibility Index and its Relationship to Central Venous Pressure Measurements in 
Patients undergoing Liver Transplantation 
Argalious et al 
 
Introduction 
 
Central venous pressure (CVP) measured invasively through a central venous catheter in the internal 
jugular vein or through a right atrial port of a pulmonary artery catheter is commonly used during liver 
transplant surgery. CVP measurements at the SVC-RA junction are a function of circulating blood 
volume, right ventricle function, intrathoracic pressure. (1) CVP measurements can also be affected by 
the presence of tricuspid regurgitation. Because central venous pressure measurements are determined 
by several factors and do not predict the response to subsequent fluid bolus administration, they are 
considered “static measures” and are poor indicators of fluid responsiveness. (2) 
 
CVP measurements remain an important measurement during liver transplant surgery (3) since a rise in 
CVP especially during the postanhepatic phase can alert the perioperative team to worsening pulmonary 
artery elevations and/or a decline in RV function. (4)This in turn triggers several therapeutic 
interventions aimed at reducing an increasing afterload on the newly transplanted liver, which can 
otherwise result in disruption of liver anastomoses, increased bleeding and coagulopathy and liver 
failure of the transplanted liver.(5) 
 
In spontaneously breathing patients, transthoracic echocardiographic measurements of the inferior 
vena caval diameter and its change with inspiration (sniff) is routinely used to estimate right atrial 
pressure measurements (Size <2.1 cm; collapses >50% during sniff = RAP 0–5 mm H; g Size > 2.1 cm; 
collapses >50% during sniff = 5–10 mm Hg Size > 2.1; collapses <50% during sniff = 10–20 mm Hg. This 
echocardiographic measurement allows noninvasive estimation of pulmonary artery systolic pressure 
based on the modified Bernoulli equation (PASP=RVSP= 4v2 + RA pressure). (6) 
Due to its intraabdominal location, the IVC is less suited for estimation of right atrial pressure during 
mechanical ventilation; especially that positive pressure ventilation causes a dilation of IVC diameter. (7)  
Given the entirely intrathoracic location of the superior vena cava (SVC), its diameter and collapsibility 
with positive pressure ventilation it is a potentially attractive method of non-invasively estimating CVP. 
(8)  

SVC diameter and collapsibility index, dynamic measures of fluid responsiveness have been successfully 
utilized as echocardiographic indices for fluid responsiveness in ventilated septic patients. (9)Whether 
SVC collapsibility is correlated with CVP measurements in liver transplant patients is not known. 
 
Significance: 
 
While most centers utilize central venous catheters or pulmonary artery catheters during liver 
transplant surgery, (3) there are complications associated with central invasive catheter use. (10) 
If SVC collapsibility index is correlated with CVP measurements, it would allow: 
1- Less reliance on central invasive catheter use especially in select population of liver transplant 
recipients especially those with normal pulmonary artery pressures and normal right ventricle 
function. Large bore peripheral venous catheters that allow rapid administration of fluids and 
blood products would substitute central venous catheter use with transesophageal monitoring 
of SVC diameter and collapsibility for calculation of pulmonary artery systolic pressure (PASP). 
2- Noninvasive measurement of PASP in mechanically ventilated patients with no central venous 
monitoring (not just in patients undergoing liver transplantation) especially that IVC 
measurement in mechanically ventilated patients may be inaccurate in identifying CVP. (7) Since 
the SVC is entirely located  intrathoracic  its collapsibility with positive pressure ventilation 
makes it an attractive method of non-invasively estimating CVP.(8) 
3- There are no studies that identify the changes in SVC diameter and collapsibility index during IVC 
cross- clamping (during the anhepatic phase of liver transplant surgery). This study will provide 
insight to changes in SVC diameter and collapsibility index in response to IVC crossclamping 
during the anhepatic phase. 
 
 
 
 
Hypothesis: 
SVC diameter and SVC collapsibility index is correlated with CVP measurement in patients undergoing 
liver transplant surgery (liver transplant recipients) 
 
 

Aim of the study: 
1- To assess the correlation of SVC diameter and  SVC collapsibility index measurements obtained 
intraoperatively by Transesophageal echocardiography (TEE)  with simultaneous CVP 
measurements obtained and recorded electronically ( via an automated intraoperative record 
keeping system) through a centrally inserted central venous catheter or a right atrial port of a 
pulmonary artery catheter 
2- To identify the changes in SVC diameter and SVC collapsibility index that occur with inferior vena 
cava cross clamping  during  liver transplant cases performed using IVC cross clamping 
 
Inclusion criteria: 
Adult patients => 18 years of age undergoing liver transplantation surgery (cadaveric and living related) 
Exclusion criteria: 
Contraindication to Transesophageal echocardiography: Esophageal pathology (stricture, trauma, 
tumor, scleroderma, Mallory-Weiss tear, diverticulum), Active upper gastrointestinal bleed, perforated 
viscous, esophagogastrectomy, esophagectomy, recent upper gastrointestinal surgery. (11) 
Methods: 
 Following RAC and IRB approval, consecutive patients undergoing liver transplant surgery will be 
included in the study. We will ask the IRB for informed consent waiver since both TEE and central 
venous monitoring are used routinely in liver transplant recipients. 
Simultaneous measurements of SVC diameter, SVC collapsibility index, CVP (captured electronically 
through an automated record keeping system) will be recorded by experienced anesthesiologists with 
expertise and qualifications in Transesophageal Echocardiography. Simultaneous cardiac output 
measurements (thermodilution) will also be recorded.  
Measurements of the SVC will be taken in the midesophageal bicaval view (90-110 degrees) using M-
mode echocardiography, 1 to 2 cm away from the entry point into the right atrium. This technique is 
analogous to that recommended when measuring IVC diameter and collapsibility (7) and was previously 
described by Cowie et al. (8) 
The maximum and minimal diameter of the SVC will be measured and recorded.  
Collapsibility index of SVC, “SVC collapsibility index” which is a measure of the inspiratory decrease in 
SVC diameter will be determined based on the following formula 
 (Maximum diameter on expiration—minimum diameter on inspiration)/Maximum diameter on 
expiration, expressed as a percentage 
 

Patients will be ventilated using Pressure Control Ventilation with a tidal volume of 6 to 8 ml/kg with a 
respiratory rate of 10-12/min and a positive end expiratory pressure of 5 to 8 cmH20. 
Measurements will be recorded during the following time periods: 
1- Before surgical incision ( following induction of General Anesthesia and placement of invasive 
monitoring and TEE) 
2- Preanhepatic phase 
3- Anhepatic phase  
4- Postanhepatic phase ( following reperfusion) 
5- Following closure of the deep fascial layer of the anterior abdominal wall 
Simultaneously, CVP will recorded from the right atrial port of the pulmonary artery catheter or from 
the proximal port of a CVC inserted in the internal jugular vein 
Patients will be placed in the supine position with pressure transducers zeroed to atmospheric pressure 
and located at the mid-thoracic position, half-way between the sternum and bed, as recommended in 
recent guidelines. (12) 
 
Statistical methods 
Demographics and perioperative characteristics of this cohort will be summarized using the standard 
summary statistics. 
We will use a linear mixed effect model with repeated measures to estimate the correlation between (1) 
SVC diameter and (2) SVC collapsibility index and simultaneously measured CVP across over the five 
measurement times, including before surgical incision, start of preanhepatic phase, start of anhepatic 
phase, start of postanhepatic phase, and after closure of deep fascial layer of the anterior abdominal 
wall (13). In the mixed model, an unstructured covariance matrix will be used to account for within-
patient correlation. The significance criterion will be 0.025 for each analysis; thus 97.5% CI will be 
reported (i.e., 0.05/2, Bonferroni correction).  
In addition, we will assess whether the correlation between SVC diameter and SVC collapsibility index 
and CVP differs over measurement time (time interaction) using a separate linear mixed effect model 
with a time interaction term. Regardless of the significance of the interaction, we will repot the 
correlation coefficient at each of the five measurement times along with 99.5% confidence interval (i.e., 
0.025/5, Bonferroni correction) for information purpose. 
Secondly, we will also assess whether the correlation between SVC diameter and SVC collapsibility index 
and CVP differs between patients with and without normal pulmonary artery pressures and normal right 
ventricle function. If the above interaction exists, we will repot the correlation separately.  

The changes in SVC diameter and SVC collapsibility index that occur with inferior vena cava cross 
clamping during liver transplant will be summarized.  
 
Sample Size Considerations 
With 100 patients and 5 pairs of measurement per patients we will provide enough data to adequately 
study the accuracy. For example, the width of our 97.5% CI for Pearson correlation will range from 0.19 
to 0.15 for correlations ranging from 0.2 to 0.5, respectively, assuming a within-subject correlation of 0 
(i.e., equivalent to 500 independent patients). In the other of the extreme scenario (i.e., within-subject 
correlation of 1), the width of our 97.5% CI for Pearson correlation will range from 0.43 to 0.34 for 
correlations ranging from 0.2 to 0.5, respectively. Approximately 10 liver transplant cases per month are 
conducted at the Cleveland Clinic main campus. Thus, a plan of 100 patients is feasible within 1 year. 
SAS software version 9.4 for Windows (SAS Institute, Cary, NC, USA) will be used for all analyses.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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