Study Of Ultrasound Windows For Measuring Inferior Vena Cava Changes Before Cardiac Surgery

Official title

Comparison of Transhepatic and Subcostal Views for Assessing Inferior Vena Cava Diameter Variation in Cardiac Surgery Patients

Overview

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.

Detailed description

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.

Primary outcome measures

• Agreement for collapsibility index (cIVC) between transhepatic and subcostal views [Time frame: Preoperative period, within twenty-four to forty-eight hours before cardiac surgery.]

Secondary outcome measures (3)

• Inter-rater reliability for transhepatic collapsibility index (cIVC) [Time frame: Preoperative period, during the same imaging session.]
• Agreement for IVC maximum diameter (IVCmax) [Time frame: Preoperative period, during the same imaging session.]
• Bland-Altman analysis for IVC diameter ratio (IVCmax:IVCmin) [Time frame: Preoperative period, during the same imaging session.]

Eligibility criteria

Inclusion criteria

• 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
• Able to provide written informed consent

Exclusion criteria

• Inability to lie supine
• Known right heart failure
• Moderate to severe tricuspid regurgitation
• Portal hypertension
• End-stage renal disease
• Presence of abdominal dressings or conditions that preclude transhepatic imaging
• Poor acoustic windows that prevent adequate measurement from either the subcostal or transhepatic view, despite standard optimization techniques (positioning, breathing coaching, depth and gain adjustment, probe angulation)

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: No

Study design

Observational model

Cohort

Study locations

Canada · 1 center

• Sunnybrook Health Science Centre — Toronto

Publications

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• Koo TK, Li MY. A Guideline of Selecting and Reporting Intraclass Correlation Coefficients for Reliability Research. J Chiropr Med. 2016 Jun;15(2):155-63. doi: 10.1016/j.jcm.2016.02.012. Epub 2016 Mar 31. PMID 27330520
• McHorney CA, Tarlov AR. Individual-patient monitoring in clinical practice: are available health status surveys adequate? Qual Life Res. 1995 Aug;4(4):293-307. doi: 10.1007/BF01593882. PMID 7550178
• Whiting PF, Rutjes AW, Westwood ME, Mallett S, Deeks JJ, Reitsma JB, Leeflang MM, Sterne JA, Bossuyt PM; QUADAS-2 Group. QUADAS-2: a revised tool for the quality assessment of diagnostic accuracy studies. Ann Intern Med. 2011 Oct 18;155(8):529-36. doi: 10.7326/0003-4819-155-8-201110180-00009. PMID 22007046
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• Sites BD, Spence BC, Gallagher JD, Wiley CW, Bertrand ML, Blike GT. Characterizing novice behavior associated with learning ultrasound-guided peripheral regional anesthesia. Reg Anesth Pain Med. 2007 Mar-Apr;32(2):107-15. doi: 10.1016/j.rapm.2006.11.006. PMID 17350520
• Croskerry P. The importance of cognitive errors in diagnosis and strategies to minimize them. Acad Med. 2003 Aug;78(8):775-80. doi: 10.1097/00001888-200308000-00003. PMID 12915363

Identifiers

NCT: NCT07305051 · 6762

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗