The Promising Role of Lung Ultrasound in Assessment of Volume Status for Patients Receiving Maintenance Renal Replacement Therapy Free

The key advantage of performing bedside LUS is its ability to diagnose pulmonary congestion before it is clinically evident [4]. It has been long recognized that conventional physical examination poorly reveals interstitial lung edema in ESRD. For instance, in a study including 79 patients treated with hemodialysis, the sensitivity of lung crackles, peripheral edema, and their combination were only 9, 3, and 13%, respectively, to detect congestion [5]. In another study, 57% of the patients treated with peritoneal dialysis who had severe lung congestion (>30 B-lines) presented with no dyspnea [6].

Both symptomatic and asymptomatic lung congestion have been associated with worse outcomes in patients with ESRD. In a multicenter study including 392 patients receiving hemodialysis, those with very severe congestion on 28-zone LUS had a 4-fold risk of death and a 3-fold risk of cardiac events. The relative risk of mortality was increased by 70% in patients with moderate-to-severe congestion as well. Of particular note, 71% of the patients in this group were asymptomatic or presented mild symptoms of heart failure [7]. Similarly, a prospective study reported that patients with presence of B-lines in ≥21.4% of the scan zones after 2 consecutive hemodialysis sessions were more likely to be hospitalized for cardiac causes [8].

Increased EVLW has also been shown to negatively affect the physical functioning of patients receiving hemodialysis or peritoneal dialysis [9, 10].

As the number of B-lines dynamically changes with ultrafiltration, the residual congestion at the end of dialysis treatment can be used to titrate dry weight [11, 12]. In a recent randomized controlled trial including 71 clinically euvolemic patients, Loutradis et al. [13] found that patients who underwent dry weight reduction guided by pre-hemodialysis LUS had greater weight reduction compared to those receiving standard care, correlating with the change in number of B-lines (–5.3 in active group vs. +2.2 in controls). Moreover, at 8 weeks, the magnitude of 48-h ambulatory blood pressure reduction was significantly greater in the active group (systolic –6.61 vs. –0.67 mm Hg and diastolic –3.85 vs. –0.55, p = 0.033). Furthermore, the active group demonstrated a significant reduction in left ventricular filling pressures at 8 weeks [14].

Evaluation of an air-rich organ such as lung is an inherent limitation of ultrasound technique because air scatters the ultrasound beam and does not allow proper visualization of the underlying structures. However, this limitation actually turns into a diagnostic advantage when performing LUS because of the characteristic artifacts (i.e., A- and B-lines). In normal aerated lung, A-lines are seen as hyperechoic, horizontal lines arising at regular intervals from the pleural line. These are reverberation artifacts formed due to multiple reflections of the ultrasound beam between the transducer and the pleura with air-filed lung underneath. B-lines are seen in the setting of interstitial edema or thickened interlobular septae, which are defined as discrete laser-like vertical hyperechoic artifacts that arise from the pleural line, extend to the end of the image without fading, and move synchronously with lung sliding [15]. The total number of B-lines provides an estimate of the amount of EVLW and aids in the determination of volume status as well as monitoring response to therapy [16]. Most studies in ESRD utilized a 28-zone scanning technique to obtain the total B-line count, which involves scanning of the anterior and lateral chest from the second to fourth (on the right side to the fifth) intercostal spaces and from the parasternal to midaxillary lines bilaterally [17] (Fig. 1). Description of other sonographic lung pathologies such as pleural effusion and consolidation is beyond the scope of this article.

LUS is a relatively easy-to-learn technique for physicians with basic understanding of the ultrasound physics. In fact, Gargani et al. [18] have demonstrated that nephrologists can be effectively trained to measure sonographic lung congestion by an entirely web-based program. However, like with any other skill, continued practice is the key to achieving mastery. Integration of point-of-care ultrasonography into nephrology fellowship curricula [19] with longitudinal training aids in long-term skill retention.

Current evidence clearly suggests that LUS is an -effective bedside tool to optimize the volume status in patients with ESRD. Nevertheless, the question whether targeting a certain B-line score on LUS improves the overall prognosis of these patients remains unanswered. A multicenter clinical trial currently in progress (Lung Water by Ultrasound Guided Treatment to -Prevent Death and Cardiovascular Complications in High-Risk ESRD Patients with Cardiomyopathy [LUST]) is expected to provide some valuable insights [20]. Future studies should also investigate the utility of simplified LUS protocols such as the 4-zone scanning technique [21] as an alternative to the traditional 28-zone method to possibly facilitate its more widespread acquisition.

None.

Human and animal rights: this article does not contain any studies with human participants or animals performed by any of the authors.

The authors have declared that no conflict of interest exists.

There is no funding to declare.

A. Koratala designed and drafted the manuscript. C.R. and A. Kazory revised the manuscript critically for important intellectual content. All authors have read and approved the manuscript prior to final submission.