Demystifying Volume Status: An Ultrasound-Guided Physiologic Framework.

Topic Importance: Accurate assessment of a patient's volume status is crucial in many conditions, informing decisions on fluid prescribing, vasoactive agents, and decongestive therapies. Determining a patient's volume status is challenging, due to limitations in examination and investigations and the complexities of fluid homeostasis in disease states. Point-of-care ultrasound (POCUS) is useful in assessing hemodynamic parameters related to volume status, fluid responsiveness, and fluid tolerance. It requires understanding several physiologic concepts to accurately interpret and integrate POCUS findings into volume-related clinical decision-making.

Review Findings: The following concepts serve as a scaffold for a comprehensive volume status assessment: central venous pressure, right heart function, left heart assessment, extravascular volume, and venous congestion. POCUS allows us access to these hemodynamic and structural data points as an extension and refinement of the physical exam. Often, multiple POCUS applications are employed, and findings must be integrated with the rest of the clinical evaluation. We illustrate this using three common scenarios: hypotension, hypoxia, and acute kidney injury. Clinicians must be aware of the strengths and weaknesses of findings in different physiologic states, and potential pitfalls of image acquisition and interpretation. Further studies are necessary to determine the benefits and clinical outcomes of a POCUS-directed volume status assessment.

Summary: Volume status assessment is ubiquitous, yet challenging to perform. This review summarizes foundational physiologic concepts relevant to volume status evaluation, and highlights how multiorgan POCUS informs on hemodynamic parameters that can be combined with the conventional clinical assessment to make fluid-related decisions.