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.
Adults aged eighteen years or older
Scheduled to undergo cardiac surgery at Sunnybrook Health Sciences Centre
Spontaneously breathing at the time of ultrasound assessment
Able to lie supine for image acquisition
Inability to lie supine
Known right heart failure
Moderate to severe tricuspid regurgitation
Portal hypertension
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.
Cohort
Prospective
Not listed
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.
Inter-rater reliability for transhepatic collapsibility index (cIVC)
Metric: ICC(2,1) for cIVC (unitless). Rationale: To assess reproducibility between novice and expert sonographers.
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.
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.
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.
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.
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.
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.
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