Integrating Left Ventricular Outflow Tract Velocity Time via Point-of-Care Ultrasonography (POCUS) for Volume Assessment and Tailored Management of Hyponatremia: A Case Series

Introduction: Hyponatremia is a prevalent electrolyte disturbance that requires accurate volume status assessment for appropriate management. Traditional clinical signs and laboratory markers often provide conflicting or ambiguous information. Point-of-care ultrasound (POCUS), particularly using left ventricular outflow tract velocity-time integral (LVOT VTI), offers a noninvasive, reproducible surrogate for cardiac output (CO). VTI <16 cm suggests hypovolemia; >18 cm is considered normal. We report four cases where VTI-guided evaluation aided in the diagnosis and treatment of hyponatremia. Case Description: Case 1: A 70-year-old man with malignancy and encephalitis developed new-onset hyponatremia(Na 131)despite hydration. VTI was high (25.48 cm,CO 4.3 L/min), indicating euvolemia. IV fluid was stopped, and tolvaptan was initiated, normalizing sodium to 137. Case 2: A 30-year-old HIV-positive male on cotrimoxazole presented with Na 125. Initial VTI was <13.43 cm. Patient was hydrated with saline at 1.2cc/kg/hr then to 3cc/kg/hr when repeat VTI and Na was still low (14cmand 126). VTI guided fluid escalation ensued. Sodium normalized with increased VTI and CO. Case 3: An 80-year-old woman on diuretics had a Na of 126 and appeared volume-depleted. But VTI ranged from 20–32 cm. Tolvaptan was started and up titrated. Sodium improved to 136. Case 4: A 55-year-old woman with Guillain-Barré syndrome presented with Na 120. Initial sodium rose with fluids but later dropped to 116. VTI was high(23.69 cm,CO 5.37 L/min),indicating euvolemia. Fluids were discontinued, and tolvaptan was started, resulting in stable sodium recovery. Discussion: In all four cases, clinical exam and standard labs were inadequate to confirm true volume status. POCUS-derived VTI enabled precise assessment, revealing cases of euvolemia that might have been misclassified. This real-time, noninvasive method guided effective management decisions leading to improved and sustained correction of hyponatremia. LVOT VTI should be considered a valuable bedside tool to supplement clinical judgment, particularly in patients with confounding signs, unreliable intake/output monitoring, or ongoing gastrointestinal and diuretic losses.