Comment on “Diagnostic accuracy of subclavian vein versus inferior vena cava collapsibility index for predicting postinduction hypotension: An observational study”

Dear Editor, We read with great interest the study by Chaudhary et al.[1] comparing the diagnostic accuracy of the subclavian vein (SCV) versus the inferior vena cava (IVC) collapsibility index for predicting post-induction hypotension. We congratulate the authors for publishing this study and wish to present our comments on it. First, measurements of subclavian vein dimensions are highly position-dependent;[2] therefore, the position during measurement has a major impact on the assessment. Chaudhary et al.[1] have used the supine position for measurement. However, retrograde flow of blood may affect the measurements taken in the supine position even in normal individuals. Moderate to severe tricuspid regurgitation decreases IVC and SCV collapsibility index.[2] Indeed, SCV measurements taken with the patient reclining at 45° have been found to correlate better with IVC measurements than those taken with the patient supine.[3] Second, the study by Chaudhary et al.[1] predicts hypotension after induction of general anesthesia (GA). This depends on many factors such as the dose of the drugs used and their speed of injection. Also, the preinduction volume status of the patient would depend on factors such as bowel preparation and the presence of acute pain. Above all, Chaudhary et al.[1] included patients undergoing endotracheal intubation or laryngeal mask airway (LMA) insertion. LMA requires a lighter plane of anesthesia than intubation. The time taken to secure the airway, the agents used for the maintenance of anesthesia, and the surgical stimulation also determine the hemodynamics in the first 20 minutes after induction. Chaudhary et al.[1] have not accounted for the above confounding factors, which could affect the validity of the results. Last, we feel that hypotension after induction of GA in patients without significant comorbidities can be minimized by administering intravenous fluids before induction or by administering clear fluids orally until 2 h before induction. Future studies predicting hypotension after induction of GA in patients with significant comorbidities such as congestive heart failure or chronic renal failure would provide more valuable information for management of those difficult cases. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.