An observational study in Perioperative Fluid Management, Hemodynamic Monitoring and Inferior Vena Cava Collapsibility Index, sponsored by Sunnybrook Health Sciences Centre. Not yet recruiting at 1 site in Canada. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2025-12-26.
Sponsored by Sunnybrook Health Sciences Centre · Observational
This research study will compare two ultrasound methods for assessing the inferior vena cava (IVC), a major vein that reflects intravascular fluid status and cardiac function before and after surgery. The standard method uses a subcostal ultrasound view obtained below the breastbone, but this approach may be limited in patients with obesity, surgical dressings, or postoperative discomfort. An alternative approach, the transhepatic view, uses the liver as an acoustic window and may provide improved feasibility in these situations.
The study will evaluate whether the transhepatic view provides measurements comparable to the standard subcostal view and whether operators with different levels of ultrasound experience obtain consistent results using both methods. Adult patients who are awake and scheduled for cardiac surgery at Sunnybrook Health Sciences Centre will undergo a brief ultrasound examination before surgery. The scan takes less than 10 minutes, involves no discomfort, and does not alter clinical care. This is a minimal-risk observational study with no therapeutic interventions. Participation is voluntary, and all personal health information will remain confidential. Findings may inform future approaches to ultrasound-guided assessment and training in perioperative care.
Respiratory variation in inferior vena cava (IVC) diameter is a widely accepted non-invasive marker of intravascular volume status and fluid responsiveness, particularly in spontaneously breathing patients. Among transthoracic echocardiographic windows, this variation is most commonly assessed using the subcostal (SC) view, which is considered the clinical reference standard due to its direct acoustic pathway and extensive validation in research and clinical practice. The physiologic basis for this measure is strongest in the context of spontaneous respiration, where negative intrathoracic pressure significantly influences venous return dynamics. For this reason, the study population is limited to spontaneously breathing patients to ensure physiologic consistency and interpretive validity.
The SC view, however, may be limited by factors such as body habitus, postoperative dressings, or an obstructed subxiphoid window. The transhepatic (TH) view has been proposed as a complementary or alternative approach, providing an oblique acoustic window through the liver that facilitates visualization of the IVC long axis. Several observational studies have reported strong correlation and agreement between TH and SC measurements of IVC diameter and collapsibility, including in both spontaneously breathing and mechanically ventilated patients. Despite these promising findings, prior studies have been constrained by small sample sizes, heterogeneous methodologies, and limited assessment of reproducibility-particularly across operators with different levels of ultrasound experience. These gaps underscore the need for a larger, methodologically rigorous validation study.
The primary objective of this prospective, single-center observational study is to evaluate agreement between the SC and TH views using methodological standards aligned with diagnostic accuracy frameworks such as QUADAS-2, in a larger cohort of patients scheduled for cardiac surgery. The secondary objective is to assess interrater reliability of TH and SC IVC measurements obtained by novice and expert sonographers. The results are intended to strengthen the evidence base supporting the use of the transhepatic view in perioperative care and to inform future training, competency assessment, and quality-assurance processes in point-of-care ultrasound.
Sunnybrook Health Sciences Centre is the lead sponsor of 566 studies on the registry; 134 are open to participants now.
Of its 6 completed or terminated interventional studies of FDA-regulated products, 2 (33%) have results posted.
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The study population consists of adult patients scheduled to undergo elective cardiac surgery at Sunnybrook Health Sciences Centre. Eligible participants will be spontaneously breathing and able to lie supine during ultrasound assessment. The study will include male and female patients aged eighteen years or older, with no upper age limit. Exclusion criteria focus on conditions that impair accurate visualization of the inferior vena cava, including right heart failure, significant tricuspid regurgitation, portal hypertension, end-stage renal disease, obstructive dressings, or inadequate acoustic windows despite optimization maneuvers. This population reflects typical perioperative cardiac surgery patients in whom reliable non-invasive assessment of fluid status is clinically relevant.
Exclusion Criteria:
This group includes adult patients (Age ≥ 18) who are awake, spontaneously breathing, and scheduled to undergo cardiac surgery at Sunnybrook Health Sciences Centre. They must also be able to lie supine and provide informed consent.
Agreement for collapsibility index (cIVC) between transhepatic and subcostal views
Outcome Metric: Intraclass correlation coefficient (ICC) for the collapsibility index (unitless). Rationale: To determine agreement between transhepatic and subcostal cIVC measurements.
Time frame: Preoperative period, within twenty-four to forty-eight hours before cardiac surgery.
Inter-rater reliability for transhepatic collapsibility index (cIVC)
Metric: ICC(2,1) for cIVC (unitless). Rationale: To assess reproducibility between novice and expert sonographers.
Time frame: Preoperative period, during the same imaging session.
Agreement for IVC maximum diameter (IVCmax)
Metrics: ICC for IVC maximum diameter (millimetres). Rationale: To determine whether transhepatic and subcostal measurements of IVC maximum diameter demonstrate sufficient agreement to support interchangeable use of the two ultrasound views for this parameter.
Time frame: Preoperative period, during the same imaging session.
Bland-Altman analysis for IVC diameter ratio (IVCmax:IVCmin)
Outcome Metric: Bland-Altman bias and limits of agreement for the IVC diameter ratio (unitless). Rationale: To assess systematic bias and variability in the ratio of IVC maximum to minimum diameter across the two ultrasound views, offering an additional perspective on agreement in dynamic IVC behavior.
Time frame: Preoperative period, during the same imaging session.
Agreement for IVC minimum diameter (IVCmin)
Outcome Metric: Intraclass correlation coefficient (ICC) for IVC minimum diameter (millimetres). Rationale: To evaluate the agreement between transhepatic and subcostal measurements of IVC minimum diameter, which contributes to understanding the consistency of static diameter assessment across imaging windows.
Time frame: Preoperative period, during the same imaging session.
Agreement for IVC diameter ratio (IVCmax:IVCmin)
Outcome Metric: Intraclass correlation coefficient (ICC) for the ratio of IVC maximum to IVC minimum diameter (unitless). Rationale: To assess agreement for the proportional relationship between maximum and minimum IVC diameters, providing additional information on dynamic venous diameter behavior across ultrasound views.
Time frame: Preoperative period, during the same imaging session.
Bland-Altman analysis for collapsibility index (cIVC)
Outcome Metric: Bland-Altman bias and limits of agreement for the collapsibility index (unitless). Rationale: To quantify systematic bias and random variation between transhepatic and subcostal collapsibility index measurements, complementing correlation-based agreement metrics.
Time frame: Preoperative period, during the same imaging session.
Bland-Altman analysis for IVC maximum diameter
Outcome Metric: Bland-Altman bias and limits of agreement for IVC maximum diameter (millimeters). Rationale: To characterize systematic differences and dispersion between transhepatic and subcostal measurements of IVC maximum diameter, informing clinical interpretability of any observed discrepancies.
Time frame: Preoperative period, during the same imaging session.
Bland-Altman analysis for IVC minimum diameter
Outcome Metric: Bland-Altman bias and limits of agreement for IVC minimum diameter (millimeters). Rationale: To evaluate the magnitude and spread of measurement differences in IVC minimum diameter between transhepatic and subcostal views, providing a detailed assessment of potential measurement error.
Time frame: Preoperative period, during the same imaging session.
Plan to share: Yes — De-identified individual participant data (IPD) underlying published results (including ultrasound measurements and basic demographic variables) will be made available to qualified researchers upon reasonable request to the Principal Investigator, following publication of the primary manuscript. Data will be stored on secure institutional servers at Sunnybrook Research Institute.
Supporting information: Study protocol, Sap, Analytic code
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