General characteristics of the study population
Thirty-one patients were included between December 2016 and April 2017.
Characteristics of the study population are shown in Table 2. 83.9% of the patients were classified as hypertensive. Antihypertensive medications were prescribed to 67.8% of the study population. Most commonly prescribed were beta-blockers (32.3% of patients), followed by renin angiotensin system blockade (12.9% of patients), and calcium channel blockers (9.7% of patients). Loop diuretics were prescribed for 41.3% of patients. 19.3% of the patients had chronic heart failure, 41.9% had ischemic cardiopathy, 16.1% had atrial fibrillation, and 35.4% had diabetes mellitus. 61.3% of the patients had a residual diuresis.
Prevalence of fluid overload according to TTE
Volemic characteristics of the patients are presented in Table 2. At TTE, patients had a median E / A ratio of 0.82 [0.59–1.1], a median E / E’ ratio of 7.5 [5.7–10.6], a median IVC collapsibility of 17.4% [6.6–47.6], a median sPAP of 10.0 mmHg [5.0–28.2]. Five (16.1%) participants had FO according to the TTE score. In the TTE FO group, the median inter-dialytic weight variation was + 2.3% [1.6–3.0].
Clinical and lung ultrasound characteristics of patients with fluid overload
Ten out of 31 patients (32.3%) had FO according to the clinical score. The number of patients with clinical FO was significantly higher in patients with TTE FO: 100% versus 19.2%, P=0.0002. Five patients (19.2%) had clinical FO but no TTE FO (Table 3). Three clinical signs of FO were significantly associated with TTE FO: orthopnoea (60.0% versus 3.8%, P=0.0082, LR: 10.5); jugular turgor (100% versus 26.9%, P=0.0047, LR: 3.7); hepatic-jugular reflux (100% versus 30.8%, P=0.0076, LR: 3.24) (Table 4, Figure 1). There was no significant difference between the TTE overload and no TTE overload groups for all other clinical signs. There was no significant difference in terms of the occurrence of intra-dialytic hypotension between the two TTE groups (Table 3).
The proportion of patients with fistula was not different between the TTE overload and no TTE overload groups: 80.0% vs. 61.6%, respectively (P=0.63). The fistula flow rate was not different between the TTE overload and no TTE overload groups: 700 [500-950] ml/min vs. 900 [700-1060] ml/min, respectively (P=0.37). Serum albumin was not different between the TTE overload and no TTE overload groups: 37.8 [35.6-39.0] g/L vs 36.7 [34.4-41.3], respectively (p=0.89).
The diagnostic performances of the clinical FO score according to TTE FO were: Se: 100%; Sp: 77%; positive predictive value (PPV): 50%; negative predictive value (NPV): 100%, LR: 4.32 (Table 4, Figure 1). Inter-observer reliability test showed a substantial agreement with a κ of 0.77.
Fifteen out of 31 patients (48.4%) had pulmonary water on chest ultrasonography: one patient had mild pulmonary overload, two patients had moderate overload, and 12 patients had severe overload. The median ECS was 3 [0–42]. Among patients with pulmonary water on ultrasound, the median ECS was 44.5 [30.0–66.2]. The number of patients with lung water on ultrasonography was not different between the two TTE groups (80.0% versus 42.3%, P=0.11). The ECS was not significantly higher in patients with TTE overload: 51 [18–146] versus 0 [0–33.7], P=0.22 (Table 3). ECS were significantly correlated with E/E’ ratio (r=0.40, p=0.02, R² 0.40).The diagnostic performance of lung ultrasound according to TTE FO was Se: 80%; Sp: 58%; PPV: 26%; NPV: 94%, with a LR of 1.9 (Table 4, Figure 1). By considering only the patients with moderate to severe pulmonary overload (ECS > 15), lung ultrasound had a Se of 80%, a Sp of 62%, a PPV of 29%, a NPV of 94%, and a LR of 2.08 (Table 4). Finally, by considering only the patients with severe pulmonary overload (ECS > 30), lung ultrasound had a Se, Sp, PPV and NPV of 80%, 69%, 33%, and 95%, respectively, and a LR of 2.6 (Table 4).
Clinical and TTE characteristics of the patients based on the presence of pulmonary water at lung ultrasound
There were not significantly more patients in overload according to the clinical score in patients with overload on the pulmonary ultrasound than in patients without pulmonary overload: 35.7 versus 29.4%, P=0.50. Ten patients (32.3%) had pulmonary water without clinical overload. Pulmonary water ultrasonography was significantly associated with the presence of crackles: 28.6% versus 0.0%, P=0.03. There was no significant difference between the two lung ultrasound groups for all other clinical signs. There were not significantly more patients with TTE overload in patients with pulmonary ultrasound overload than in patients without lung overload: 5.8 versus 28.6%, P=0.11. Pulmonary water ultrasonography was significantly associated with a higher sPAP: 7.5 mmHg [5.0–11.5] versus 25.5 mmHg [5.0–39.7], P=0.012. There was no significant difference between the two lung ultrasound groups regarding other TTE data.