Point-of-care ultrasound (POCUS) encompasses a broad spectrum of applications in nephrology, ranging from procedural guidance to diagnostic kidney ultrasound and comprehensive volume status assessment [1]. However, certain nuances must be considered for its effective adoption and utilization in patient care. As specialists dealing with intricate fluid and electrolyte disorders, nephrologists should be cautious about the misconception that inferior vena cava (IVC) ultrasound is synonymous with volume status assessment. Contrary to this belief, IVC POCUS is not a surrogate for intravascular volume; it just provides an estimate of central venous pressure (CVP), albeit with modest correlation, which in turn is a poor indicator of intravascular volume [2]. As such, equating IVC ultrasound with volume status can lead to management errors. For instance, a patient with a small collapsible IVC may be euvolemic, hypovolemic, or have a high cardiac output state (e.g., cirrhosis-related hyperdynamic circulation). Accurate differentiation relies on simultaneous cardiac output measurement, which can be performed at the bedside using Doppler ultrasound, albeit not foolproof. This consideration extends to managing hyponatremia, where misinterpreting euvolemia as hypovolemia based on IVC POCUS and administering normal saline may worsen serum sodium levels in some patients [3].

On the other hand, a plethoric IVC may indicate intravascular volume excess or conditions like pericardial effusion, pulmonary embolism, chronic pulmonary hypertension, or even a pneumothorax. Understanding these nuances is crucial, as optimal management strategies do not necessarily involve volume removal. For example, overzealous ultrafiltration in a dialysis patient solely relying on IVC assessment, without detecting pericardial effusion, can precipitate tamponade due to a decrease in intracardiac pressure in relation to pericardial pressure. Regarding the adverse effects of elevated CVP on organ function, it is important to recognize that assessing venous congestion extends beyond the capability of IVC ultrasound alone. Venous excess Doppler ultrasound serves as an additional tool in this context, facilitating the quantification of congestion and monitoring the efficacy of decongestive therapy, as elaborated elsewhere [4, 5].

Additionally, conditions like cirrhosis frequently render IVC ultrasound unreliable due to local structural and functional changes. In instances such as tense ascites causing intra-abdominal hypertension, the IVC might appear small and collapsed despite an elevated CVP [6]. Conversely, IVC dilation in these patients may result from factors unrelated to RAP, including portosystemic collaterals draining into the IVC, proximal constriction from an enlarged caudate lobe, or the extension of hepatic vein thromboses or hepatocellular carcinoma into the IVC [7].

Besides the numerous technical constraints of IVC ultrasound, a prevalent misconception among novice POCUS users is that the IVC is an effective tool for assessing fluid responsiveness. Contrary to this belief, CVP (and thereby IVC ultrasound) does not serve as a reliable surrogate for fluid responsiveness. While it may seem reasonable to infer that lower CVP values (small collapsible IVC) suggest a patient is on the steep segment of the Frank-Starling curve and, therefore, fluid-responsive and vice versa, this approach is of limited value. This is due to wide inter-patient variability in the slopes; also, in a patient operating in the intermediate portions of the Frank-Starling curve, CVP cannot predict fluid responsiveness [8, 9]. A more effective method for assessing fluid responsiveness involves measuring the change in cardiac output after a passive leg raise [10]. However, in the era of fluid tolerance, the significance of fluid responsiveness as a parameter to guide fluid management is diminishing because exhausting fluid responsiveness (a physiological state) is not the therapeutic goal [11].

Much like IVC ultrasound, lung ultrasound (LUS) is frequently misapplied to infer volume status. LUS is gaining popularity among nephrologists due to its technical simplicity and several studies in hemodialysis patients demonstrating its diagnostic superiority and prognostic significance [12]. Nevertheless, one must be aware that LUS only reflects left heart pressures, neglecting the other components of the hemodynamic circuit, that is, forward flow and right heart pressures. Therefore, relying solely on LUS provides incomplete information [13]. Additionally, the B-lines observed on LUS, generally indicative of extravascular lung water, are not specific to cardiogenic pulmonary edema and can appear in several other conditions causing interlobular septal thickening. Consequently, conditions such as viral pneumonia, pulmonary fibrosis, alveolar hemorrhage in a case of vasculitis can be misinterpreted as fluid overload, leading to inappropriate management and care delays. Furthermore, a patient exhibiting B-lines due to increased afterload from uncontrolled hypertension may benefit more from vasodilators than diuretics or ultrafiltration, indicating the need for holistic clinical decision-making as opposed to knee-jerk responses. Similarly, while A-lines in the lung, a normal finding, exclude pulmonary edema, they do not serve as a surrogate for volume depletion or ultrafiltration intolerance, a misconception that is prevalent [14]. We hereby advocate abandoning the term “volume status assessment,” urging the adoption of “hemodynamic assessment” through a multi-organ POCUS approach to prevent hasty management decisions (Fig. 1).

Fig. 1.

Pitfalls of excessive reliance on individual organ ultrasound and knee-jerk clinical decision-making. Comprehensive bedside hemodynamic evaluation should almost always involve focused cardiac ultrasound, interpreting all these observations in the relevant clinical context. This applies to both initial diagnosis and monitoring selected parameters during follow-up examinations. *In intra-abdominal hypertension, IVC is small irrespective of CVP and typically does not exhibit respiratory variation. IVC, inferior vena cava; CVP, central venous pressure.

Fig. 1.

Pitfalls of excessive reliance on individual organ ultrasound and knee-jerk clinical decision-making. Comprehensive bedside hemodynamic evaluation should almost always involve focused cardiac ultrasound, interpreting all these observations in the relevant clinical context. This applies to both initial diagnosis and monitoring selected parameters during follow-up examinations. *In intra-abdominal hypertension, IVC is small irrespective of CVP and typically does not exhibit respiratory variation. IVC, inferior vena cava; CVP, central venous pressure.

Close modal

We have observed that critics of POCUS in nephrology often highlight the lack of randomized controlled trials supporting superior outcomes for POCUS-assisted hemodynamic assessment but when it comes to traditional applications such as kidney ultrasound, they praise its ability to enhance patient care and expedite diagnosis. We attribute this, in part, to nephrologists’ lesser familiarity with the practical utility of advanced sonographic applications. It is noteworthy that diagnostic modalities such as POCUS do not improve patient outcomes unless coupled with an efficacious therapeutic intervention. For that matter, conventional examination parameters like auscultation lack such evidence as well but do remain the standard of care in clinical practice. POCUS, as a diagnostic tool, excels in accuracy compared to conventional methods, influencing outcomes such as timely diagnosis, imaging necessity, healthcare costs, and patient satisfaction [1]. Enhanced diagnostic capabilities such as POCUS should not be dismissed simply because optimal treatment approaches are currently unavailable. Instead, the focus should be on developing well-structured longitudinal training and competency-based certification [15]. Recent data indicate a strong desire for such programs among practicing nephrologists [16]. Nephrology professional societies should collaborate to form expert committees led by individuals with a proven track record in multi-organ POCUS performance and education. Guidelines addressing crucial aspects like maintenance of certification, image archiving, and quality assessment are imperative. Establishing superficial or “check mark” curricula by fellowship training programs, aimed solely at attracting applicants without investing in proper infrastructure and quality assessment, risks exacerbating the waning interest in nephrology as a career choice and may lead to patient harm through improper image acquisition, interpretation, or clinical integration.

The authors have no conflicts of interest to disclose. Abhilash Koratala reports research funding from KidneyCure and the American Society of Nephrology’s William and Sandra Bennett Clinical Scholars Grant.

No funding was received for this work.

All authors participated in conceptualizing the manuscript content, have seen the final version, and agreed for submission. A.Ko. and A.Kz. drafted the initial version. O.A.O. reviewed and revised the manuscript.

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