Abstract
We read with interest the study by Soret et al 1 examining the relationship between point-of-care ultrasound (POCUS), particularly lung ultrasound (LUS), and worsening renal function (WRF) in patients hospitalized with acute heart failure. Given that the journal’s audience is primarily nephrologists who may have limited experience with POCUS, we offer clarifications to help contextualize the findings.
The authors report a significant association between the number of B-lines on admission and WRF, while no such association was observed with tricuspid annular plane systolic excursion (TAPSE; a measure of RV systolic function) or inferior vena cava (IVC) diameter. We caution against interpreting this as causal. B-lines reflect left-sided filling pressures, while WRF in heart failure is more closely linked to right-sided pressures and venous congestion, which is more physiologically plausible. 2 Although renal injury can accompany acute lung injury, it is usually mediated by inflammatory pathways or mechanical ventilation, not directly by lung water. 3 The small sample size (43 patients; only eight developing WRF with mild elevations in serum creatinine) limits the strength of the conclusions. The statistical association between higher B-line burden and WRF is not robust, and the lack of associations for TAPSE and IVC diameter could reflect limited power rather than true absence of effect. The nonspecific nature of B-lines also warrants greater emphasis than was given in the discussion. B-lines are seen in various conditions such as pulmonary fibrosis, interstitial pneumonia, pneumonitis, ARDS, and postsurgical changes. 4 This is particularly important in heart failure exacerbations, which are often accompanied by pulmonary infections, 5 even more so in this cohort given the overlap with the COVID-19 pandemic. The lack of higher diuretic dosing in the highest B-line quartile, with clinicians blinded to POCUS, underscores the limitations of physical examination in assessing congestion. It also suggests that WRF in this subgroup may have been due to inadequate decongestion and worsening venous congestion rather than LUS findings, though a benign rise in creatinine during effective decongestion remains an alternative explanation.
Technically speaking, relying solely on IVC diameter without collapsibility is problematic, as it is influenced by factors like body surface area and tricuspid regurgitation. 6 While the authors mention IVC limitations, they overlook those of TAPSE, which is angle-dependent and error-prone depending on the underlying cardiac image quality. Alternative measures like mitral inflow Doppler or RV systolic pressure could have strengthened differentiation between cardiogenic and noncardiogenic B-lines. Notably, these parameters fall within the scope of nephrologists performing advanced POCUS. 7 Also, the 28-zone LUS protocol, though thorough, is impractical in routine care; abbreviated approaches like the 8-zone scan offer similar diagnostic and prognostic value. The mention of venous Doppler (VExUS) also felt abrupt and incomplete. VExUS is not equivalent to right atrial pressure; it integrates venous compliance, therefore correlating better with organ dysfunction. 8 This is of relevance in acute heart failure, where neurohormonal activation reduces venous compliance. Finally, while the study cites “expert sonographers,” it lacks details on training, validation, or interrater reliability—key considerations when interpreting POCUS studies, especially in specialties with limited adoption.
