Echographie pulmonaire et évaluation de la surcharge hydrique en dialyse péritonéale

Résumé

La gestion des fluides reste un défi majeur dans la dialyse péritonéale (DP), en particulier en raison de la difficulté à détecter l’hypervolémie subclinique. Cette étude transversale, menée dans un seul centre sur un échantillon de 22 patients ; nous avons examiné l’utilité de l’échographie pulmonaire (LUS) comme outil complémentaire pour l’évaluation de l’état volumique. À l’aide d’un protocole de balayage en 8 zones et d’un système de cotation des lignes B, l’échographie pulmonaire a été réalisée lors de visites de routine, parallèlement à l’évaluation de la veine cave inférieure (VCI) et à l’analyse par bioimpédance électrique (BIA). Les résultats ont montré une forte corrélation entre les scores des lignes B et l’hyperhydratation mesurée par la BIA (r = 0,625) et l’indice de collapsibilité de la VCI (r = –0,722). Il est à noter que la moitié des patients considérés comme cliniquement euvolémiques présentaient des signes d’hypervolémie selon les critères échographiques. Ces résultats suggèrent que la LUS est une méthode non invasive, pratique et efficace pour identifier une surcharge liquidienne non évidente lors d’une évaluation clinique standard, ce qui justifie son intégration dans les soins de routine des patients sous DP.

INTRODUCTION

Estimation of ideal volume status is a constant challenge in nephrology. This is usually based on clinical evaluation, along with other diagnostic tools such as natriuretic peptides and bioimpedance spectroscopy (BIS). Several methods have been developed to accurately assess fluid status in dialysis patients, including BIS, measurement of inferior vena cava (IVC) diameter by ultrasound, analysis of biomarkers such as natriuretic peptides, and, more recently, the observation of lung comets using chest ultrasound[1].

In 1996, Dr. Daniel Lichtenstein first described the comet tail artifact detected in lung ultrasound in a cohort of patients with both cardiogenic and noncardiogenic pulmonary edema[2]. This artifact is caused by micro-reflections at the subpleural interface, which the ultrasound interprets as distance, caused by the presence of extravascular lung water or small air-fluid interfaces, resulting in a narrow, laser-like ray on the screen. The artifact, now known as the B-line, has contributed to our ability to detect both clinical and, especially, subclinical pulmonary edema, offering a more precise and accessible alternative to traditional methods such as lung auscultation or chest radiography[3]. One of its main limitations is the lack of specificity. B-lines are a sonographic sign of lung interstitial syndrome, but they cannot differentiate between thickening of the interlobular septa caused by excess lung water and fibrotic thickening, as seen in pulmonary fibrosis (dry B-lines). Therefore, caution must be exercised when interpreting LUS findings in patients with known or suspected pulmonary fibrosis[4].

Many studies have demonstrated the clinical use of LUS. Studies such as LUS-HF and CLUSTER-HF have shown the use of LUS in guiding more intensive diuretic treatment in heart failure patients, leading to a reduction in B-lines and improved management of fluid overload[5][6]. While there are few studies on subclinical hypervolemia in chronic kidney disease (CKD) patients, one study by Baki et al. demonstrated that the combination of elevated natriuretic peptide levels and decreased inferior vena cava collapsibility index (IVCCI) increased the specificity and positive predictive value for detecting subclinical hypervolemia[7].

It is well known that the prevalence of hypervolemia in PD patients is considerable and is associated with increased mortality[8]. Persistent volume overload increases arterial stiffness, causes higher systolic BP, lower diastolic BP, and increased pulse pressure. This increases afterload to the left ventricle, resulting in left ventricular hypertrophy (LVH). All of these effects have been identified as independent risk factors for cardiovascular morbidity and mortality in end-stage kidney disease (ESKD)[9][10].

Asymptomatic lung congestion has been described in a significant proportion of dialysis patients[11]. In a multicenter study by Zoccali et al., moderate to severe lung congestion was present in 45% of hemodialysis patients, with 71% of these patients being asymptomatic or presenting only slight symptoms of heart failure[12]. Another study by Enia et al. reported that 58% of hemodialysis patients exhibited moderate to severe lung congestion, 38% of whom were asymptomatic (NYHA class I)[13]. Additionally, Mallamaci et al. demonstrated that 57% of asymptomatic dialysis patients exhibited moderate to severe lung congestion[14]. Thus, some dialysis patients are erroneously considered euvolemic.

Increased precision in volemia evaluation is an important unmet need in dialysis patients, particularly PD patients. Some studies suggest that PD patients may be more prone to overhydration compared to those undergoing hemodialysis (HD). Achieving euvolemia in PD patients is especially challenging because PD depends on self-treatment, daily ultrafiltration, and residual renal function, all of which can vary widely among individuals[8][15][16].

LUS has been validated as an effective method for evaluating extracellular lung water, particularly in heart failure and hemodialysis patients[1][16]. Although its role in PD patients remains uncertain, it may play an important role in evaluating volume status in PD patients. In hemodialysis, LUS has demonstrated a strong prognostic value, as the number of B-lines correlates with adverse cardiovascular outcomes and mortality, and LUS-guided ultrafiltration can safely reduce pulmonary congestion without increasing intradialytic complications. In peritoneal dialysis, LUS findings do not consistently correlate with bioimpedance or clinical signs. This suggests that LUS and other assessment methods evaluate different fluid compartments and are therefore complementary[1][11][15][17].

The technique itself is cost-effective and widely accessible, requiring only 3-5 minutes to perform. It can be efficiently carried out by trained technicians and demonstrates low interobserver variability[18]. The 8-point scoring system has shown excellent diagnostic performance in the evaluation of ESKD patients[19][20]. Measurement of IVCCI adds information about intravascular volume status[21].

Given these considerations, combining different methods and technologies may improve the detection of subclinical hypervolemia in PD patients. As such, we aimed to estimate its prevalence using LUS and to determine the concordance between LUS findings, IVCCI, and other clinical parameters and tools, such as BIS.

METHODS

Patient Selection and Recruitment

This study was approved by the local ethics committee. All participants were provided informed consent.

This was an opportunistic, cross-sectional study involving peritoneal dialysis (PD) patients during routine clinic visits. Patients were not pre-selected based on specific characteristics but were included if they met the following criteria: duration on PD greater than 3 months, absence of active infections, and willingness to participate. Recruitment occurred during routine outpatient visits in the first semester of 2023 and was dependent on the availability of both staff and equipment to perform the assessments.

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