Lung ultrasound: a novel technique for detecting fluid overload in children on dialysis

Proceedings of the 2022 UAB CRRT Academy: Non-Invasive Hemodynamic Monitoring to Guide Fluid Removal with CRRT and Proliferation of Extracorporeal Blood Purification Devices

In 2022, we celebrated the 15th anniversary of the University of Alabama at Birmingham (UAB) Continuous Renal Replacement Therapy (CRRT) Academy, a 2-day conference attended yearly by an international audience of over 100 nephrology, critical care, and multidisciplinary trainees and practitioners. This year, we introduce the proceedings of the UAB CRRT Academy, a yearly review of select emerging topics in the field of critical care nephrology that feature prominently in the conference. First, we review the rapidly evolving field of non-invasive hemodynamic monitoring and its potential to guide fluid removal by renal replacement therapy (RRT). We begin by summarizing the accumulating data associating fluid overload with harm in critical illness and the potential for harm from end-organ hypoperfusion caused by excessive fluid removal with RRT, underscoring the importance of accurate, dynamic assessment of volume status. We describe four applications of point-of-care ultrasound used to identify patients in need of urgent fluid removal or likely to tolerate fluid removal: lung ultrasound, inferior vena cava ultrasound, venous excess ultrasonography, and Doppler of the left ventricular outflow track to estimate stroke volume. We briefly introduce other minimally invasive hemodynamic monitoring technologies before concluding that additional prospective data are urgently needed to adapt these technologies to the specific task of fluid removal by RRT and to learn how best to integrate them into practical fluid-management strategies. Second, we focus on the growth of novel extracorporeal blood purification devices, starting with brief reviews of the inflammatory underpinnings of multiorgan dysfunction and the specific applications of pathogen, endotoxin, and/or cytokine removal and immunomodulation. Finally, we review a series of specific adsorptive technologies, several of which have seen substantial clinical use during the COVID-19 pandemic, describing their mechanisms of target removal, the limited existing data supporting their efficacy, ongoing and future studies, and the need for additional prospective trials.

Assessment of fluid removal using ultrasound, bioimpedance and anthropometry in pediatric dialysis: a pilot study

BACKGROUND

Fluid overload is associated with morbidity and mortality in children receiving dialysis. Accurate clinical assessment is difficult, and using deuterium oxide (D₂O) to measure total body water (TBW) is impractical. We investigated the use of ultrasound (US), bioimpedance spectroscopy (BIS), and anthropometry to assess fluid removal in children receiving maintenance hemodialysis (HD).

METHODS

Participants completed US, BIS, and anthropometry immediately before and 1-2 h after HD for up to five sessions. US measured inferior vena cava (IVC) diameter, lung B-lines, muscle elastography, and dermal thickness. BIS measured the volume of extracellular (ECF) and intracellular (ICF) fluid. Anthropometry included mid-upper arm, calf and ankle circumferences, and triceps skinfold thickness. D₂O was performed once pre-HD. We assessed the change in study measures pre- versus post-HD, and the correlation of change in study measures with percent change in body weight (%∆BW). We also assessed the agreement between TBW measured by BIS and D₂O.

RESULTS

Eight participants aged 3.4-18.5 years were enrolled. Comparison of pre- and post-HD measures showed significant decrease in IVC diameters, lung B-lines, dermal thickness, BIS %ECF, mid-upper arm circumference, ankle, and calf circumference. Repeated measures correlation showed significant relationships between %∆BW and changes in BIS ECF (r_rm =0.51, 95% CI 0.04, 0.80) and calf circumference (r_rm=0.80, 95% CI 0.51, 0.92). BIS TBW correlated with D₂O TBW but overestimated TBW by 2.2 L (95% LOA, -4.75 to 0.42).

CONCLUSION

BIS and calf circumference may be helpful to assess changes in fluid status in children receiving maintenance HD. IVC diameter, lung B-lines and dermal thickness are potential candidates for future studies.

Evaluation of lung ultrasound to detect volume overload in children undergoing dialysis

BACKGROUND

Lung ultrasound is a well-established technique to assess extravascular lung water, a proxy for volume status, in the adult population. Despite its utility, the data are limited supporting the use of ultrasound to evaluate fluid volume status among pediatric patients. Our study uses a simplified ultrasound protocol to evaluate changes in extravascular lung water, represented by b-lines, among pediatric patients undergoing hemodialysis.

METHODS

This prospective single-center study included children from birth to 18 years of age. The number of b-lines per ml/kg of fluid removed was compared prior to, at the midpoint, and following termination of dialysis. An 8-zone protocol was utilized, and b-lines were correlated to hemoconcentration measured by the CRIT-LINE® hematocrit.

RESULTS

Six patients with a total of 26 hemodialysis sessions were included in this study. The b-line measurements post-dialysis were 2.27 (p < 0.001; 94%CI -3.31, -1.22) lower relative to pre-dialysis. The number of b-lines was reduced by 1.69 (p < 0.001; -2.58, -0.80) between pre-dialysis and at the midpoint of dialysis and by 0.58 (p = 0.001; -0.90, -0.24) between the midpoint of dialysis and post-dialysis. A 1 mL/kg fluid loss correlated to a decrease in the original b-lines by 0.079. An inverse relationship (r = -0.54; 95% CI: -0.72, -0.34; p < 0.001) was noted between the b-lines and the patients' hematocrit levels.

CONCLUSIONS

A simplified 8-zone ultrasound protocol can assess fluid volume change in real time and correlates with hematocrit levels obtained throughout dialysis. This provides a valuable method for monitoring fluid status in volume overloaded patient populations. A higher resolution version of the Graphical abstract is available as Supplementary information.

Bedside sonographic assessments for predicting predialysis fluid overload in children with end-stage kidney disease

Although the number of studies evaluating methods to predict fluid overload is increasing, the assessment of fluid status in children on dialysis is still fraught with inaccuracies. We aimed to evaluate the predictive capability of lung ultrasounds and the inferior vena cava collapsibility index (cIVC) in predialysis overhydration in children with end-stage kidney disease. Ten children with end-stage kidney disease who were on an intermittent hemodialysis program were included. The hydration status of the patients was clinically evaluated. Moreover, 30 predialysis and 30 postdialysis lung ultrasound, cIVC, and bioimpedance spectroscopy (BIS) measurements were performed. The median age of the participants was 14 (IQR, 13-15) years, and two (20%) were male. There was a strong positive correlation between the predialysis total number of B-lines and predialysis fluid overload (r=0.764, p<0.001). Additionally, there was a moderate negative correlation between predialysis cIVC and predialysis fluid overload (r=-0.599, p=0.002). Although the moderate correlation was determined between the postdialysis fluid overload and total number of B-lines, no correlation was determined using cIVC. Receiver operating characteristic curves demonstrated that the total number of B-lines and cIVC could successfully predict the predialysis fluid overload (relative hydration >7% derived from the BIS; AUROC 0.82 and 0.80, respectively). When both evaluations were combined, if either the total number of B-lines or the cIVC was outside the corresponding cutoff range (>10.5 and ≤23.5, respectively), it was detected in 16 out of 17 sessions (sensitivity 94%). If either one was outside the corresponding cutoff range (total number of B-lines >10.5 and cIVC ≤18.2), the severe predialysis fluid overload was predicted successfully in all eight (100%) sessions. Conclusion: Randomized controlled studies are needed to prove the reliability of the combined use of lung ultrasounds and cIVC in the assessment of predialysis fluid overload. What is Known: • The association of chronic fluid overload with increased morbidity and mortality raises the need for optimal determination of fluid overload in pediatric patients who are dialysis-dependent at a young age. • The linear correlation between the total number of B-lines on lung ultrasound images and fluid overload by weight has been shown. What is New: • This study evaluates the lung ultrasound and inferior vena cava collapsibility index combined in predicting fluid overload in dialytic children. • If either the total number of B-lines or the cIVC was outside the corresponding cutoff range (>10.5 and cIVC ≤18.2, respectively), the severe predialysis fluid overload was predicted successfully in all eight (100%) sessions.

Use of Point-of-Care Ultrasound for Evaluation of Extravascular and Intravascular Fluid Status in Pediatric Patients Maintained on Chronic Hemodialysis

AIMS

Traditional methods that use clinical parameters to determine dry weight in hemodialysis patients are inaccurate. This study aimed to compare clinical assessment of fluid status to sonographic parameters of fluid status in pediatric patients undergoing chronic hemodialysis.

METHODS

In a prospective observational study, pediatric patients maintained on chronic hemodialysis (ages 2.3-20 years) were evaluated clinically and sonographically before and after dialysis at 6 consecutive sessions. Sonographic parameters examined were number of lung B-lines as a measure of extravascular volume and inferior vena cava (IVC)/aorta ratio as a measure of intravascular volume. Clinical assessment of fluid status was compared to sonographic assessment.

RESULTS

Twelve patients were evaluated during 72 dialysis sessions. Sonographic parameters were significantly lower post-dialysis than pre-dialysis (B-lines number 4.5 ± 5 vs. 7.69 ± 7.46, p < 0.0001; IVC/aorta ratio 0.9 ± 0.2 vs. 1.1 ± 0.2, p < 0.0001, respectively). Ultrafiltration volume correlated with change in B-lines number during dialysis (r = 0.39, p < 0.01). Percent of blood volume drop correlated with post-dialysis IVC/aorta ratio (r = 0.48, p < 0.001). A higher percent of symptomatic episodes occurred with post-dialysis IVC/aorta ratio <0.8 versus ≥0.8 (39.1 vs. 15.2%, p = 0.036). Four patients were hypertensive, a clinical parameter implying fluid overload, in only one sonographic evaluation indicated fluid overload. Eight patients were clinically determined to be euvolemic, in three of them sonographic evaluation discovered covert fluids.

CONCLUSION

Bedside ultrasound is a single modality that can be used to assess both extravascular and intravascular fluid status. It may contribute to clinical decisions differentiating fluid-related versus fluid-unrelated hypertension and identifying patients with covert fluids.

Lung ultrasound methods for assessing fluid volume change and monitoring dry weight in pediatric hemodialysis patients

BACKGROUND

The value of lung ultrasound in adult hemodialysis has been confirmed. The determination of dry weight in children remains challenging. This study explores the usefulness of lung ultrasound in assessing fluid volume change and the possibility of pulmonary ultrasound as a method to monitor dry weight in pediatric dialysis patients.

METHODS

This was a prospective observational study. We compared the predialysis and postdialysis B-line scores of the dry-weight group and non-dry-weight group. Changes in body weight and B-line scores were recorded during the dialytic period and interdialytic period, and the correlation was analyzed. Lung ultrasound was performed after the dialysis session every Friday, and B-line score < 10 was considered to indicate that there was no volume overload; the weight was recorded as the target weight.

RESULTS

Fourteen patients were included. A total of 78 ultrasound assessments were performed: 30 in the dry-weight group and 48 in the non-dry-weight group. The B-line scores decreased after dialysis in all patients (p < 0.001). Thirty-three assessments were performed in the interdialytic period, and 40 assessments in the dialytic period were performed within 1 week. Linear regression showed that changes in B-line number were directly and positively correlated with interdialytic weight gain (r = 0.517, p = 0.002) and dialytic weight loss (r = 0.558, p < 0.001). The weight of the children increased gradually without volume overload in two patients during follow-up.

CONCLUSION

Lung ultrasound can assess the fluid volume change of pediatric dialysis patients in real time. Lung ultrasound could be a valuable method for monitoring dry weight in pediatric dialysis patients.

Clinical Relevance of Fluid Volume Status Assessment by Bioimpedance Spectroscopy in Children Receiving Maintenance Hemodialysis or Peritoneal Dialysis

Bioimpedance spectroscopy (BIS) is a noninvasive method used to evaluate body fluid volume status in dialysis patients, but reports on its effectiveness in pediatrics are scarce. We investigated the correlation between BIS and clinical characteristics and identified the changes in patients whose dialysis prescription was modified based on BIS. The medical records of children on maintenance dialysis who had undergone BIS between 2017 and 2019 were reviewed. Of the 49 patients, 14 were overhydrated, based on the >15% proportion of overhydration relative to extracellular water (OH/ECW) measured by BIS. Intake of ≥two antihypertensive medications was noted in the majority (85.7%) of children with fluid overload and only in 48.6% of those without fluid overload (p = 0.017). Elevated blood pressure despite medication use was significantly more common in patients with fluid overload than in those without fluid overload (78.6% vs. 45.7%, p = 0.037). Of the 14 overhydrated children, 13 (92.9%) had significant changes in body weight, OH/ECW, the number of antihypertensive drugs, left ventricular end-diastolic diameter, and cardiothoracic ratio after the change in dialysis prescription. BIS is a useful and noninvasive method to assess fluid status in dialysis children. Long-term follow-up and correlation with a more objective clinical indicator of fluid overload is necessary to verify the clinical effectiveness of BIS.

Evaluation of Hypervolemia in Children

Hypervolemia is a condition with an excess of total body water and when sodium (Na) intake exceeds output. It can have different causes, such as hypervolemic hyponatremia (often associated with decreased, effective circulating blood volume), hypervolemia associated with metabolic alkalosis, and end-stage renal disease. The degree of hypervolemia in critically ill children is a risk factor for mortality, regardless of disease severity. A child (under 18 years of age) with hypervolemia requires fluid removal and fluid restriction. Diuretics are able to increase or maintain urine output and thus improve fluid and nutrition management, but their benefit in preventing or treating acute kidney injury is questionable.

Effect of ultrafiltration on extravascular lung water assessed by lung ultrasound in children undergoing cardiac surgery: a randomized prospective study

Background

Increased lung water and the resultant atelectasis are significant pulmonary complications after cardiopulmonary bypass (CPB) in children undergoing cardiac surgery; these complications are observed after CPB than after anaesthesia alone. Ultrafiltration has been shown to decrease total body water and postoperative blood loss and improve the alveolar to arterial oxygen gradient and pulmonary compliance. This study investigated whether conventional ultrafiltration during CPB in paediatric heart surgeries influences post-bypass extravascular lung water (EVLW) assessed by lung ultrasound (LUS).

Methods

This randomized controlled study included 60 patients with congenital heart disease (ASA II-III), aged 1 to 48 months, with a body weight > 3 kg. Conventional ultrafiltration targeting a haematocrit (HCT) level of 28% was performed on the ultrafiltration group, while the control group did not receive ultrafiltration. LUS scores were recorded at baseline and at the end of surgery. The PaO2/FiO2 ratio (arterial oxygen tension divided by the fraction of inspired oxygen), urine output, and haemodynamic parameters were also recorded.

Results

LUS scores were comparable between the two groups both at baseline (p = 0.92) and at the end of surgery (p = 0.95); however, within the same group, the scores at the end of surgery significantly differed from their baseline values in both the ultrafiltration (p = 0.01) and non-ultrafiltration groups (p = 0.02).

The baseline PaO2/FiO2 ratio was comparable between both groups. at the end of surgery, The PaO2/FiO2 ratio increased in the ultrafiltration group compared to that in the non-ultrafiltration group, albeit insignificant (p = 0.16). no correlation between the PaO2/FiO2 ratio and LUS score was found at baseline (r = − 0.21, p = 0.31). On the other hand, post-surgical measurements were negatively correlated (r = − 0.41, p = 0.045).

Conclusion

Conventional ultrafiltration did not alter the EVLW when assessed by LUS and oxygenation state. Similarly, ultrafiltration did not affect the urea and creatinine levels, intensive care unit (ICU) stays, ventilation days, or mortality.

Trial registration

Clinicaltrials.gov Identifier: NCT03146143 registered on 29-April-2017.

Assessment and management of fluid overload in children on dialysis

Dysregulation of intravascular fluid leads to chronic volume overload in children with end-stage kidney disease (ESKD). Sequelae include left ventricular hypertrophy and remodeling and impaired cardiac function. As a result, cardiovascular complications are the commonest cause of mortality in the pediatric dialysis population. The clinical need to optimize intravascular volume in children with ESKD is clear; however, its assessment and management is the most challenging aspect of the pediatric dialysis prescription. Minimizing chronic fluid overload is a key priority; however, excessive ultrafiltration is toxic to the myocardium and can precipitate intradialytic symptoms. This review outlines emerging objective techniques to enhance the assessment of fluid overload in children on dialysis and outlines evidence for current management strategies to address this clinical problem.

The first hour refill index: a promising marker of volume overload in children and young adults on chronic hemodialysis

BACKGROUND

Volume overload is a known risk factor for cardiovascular complications in children on hemodialysis (HD), but a measurable index of volume overload is still lacking.

METHODS

We propose a novel index of pre-HD volume overload based on blood volume (BV) monitoring, the first hour refill index (RI), calculated as the ratio between the ultrafiltration rate indexed for body weight during the first HD hour and the percent BV change at the first hour of the treatment. This parameter was retrospectively calculated in 121 sessions in 11 oligoanuric children and young adults on chronic HD, with median age 14.3 years (range 5.4-22.4), and its association with left-ventricular mass index, pre-HD blood pressure, and number of antihypertensive medications was evaluated.

RESULTS

The median RI was 2.07 ml/kg/h/%. There was a significant correlation between RI and median LVMI (r 0.66, p = 0.028), which was 53.4 g/m^2.7 (45.7-64) in patients with a median RI > 2, and 36.6 g/m^2.7 (24.9-47) in those with a median RI < 2 ml/kg/h/% (p = 0.01). The number of antihypertensive drugs per patient was significantly higher in patients with a RI > 2 than in those with a RI < 2 ml/kg/h/% (three vs one per patient; p = 0.02) while blood pressure was not significantly different between the two groups.

CONCLUSIONS

The ratio between the ultrafiltration rate per body weight and the BV change during the first hour of a HD session could be a promising index of refill capacity and pre-HD volume overload in children and young adults on chronic HD.

Hypertension in Pediatric Dialysis Patients: Etiology, Evaluation, and Management

PURPOSE OF REVIEW

Review epidemiology, pathophysiology, and management of hypertension in the pediatric dialysis population.

RECENT FINDINGS

Interdialytic blood pressure measurement, especially with ambulatory blood pressure monitoring, is the gold standard to assess for hypertension. Tools to assess dry weight aid in achievement of euvolemia, the primary therapy for management of hypertension. Persistent hypertension should be treated with antihypertensive medications and potentially with native nephrectomies. Cardiovascular disease continues to be the primary cause of morbidity and mortality in the dialysis population with hypertension as an important modifiable factor. Achievement on dry weight and limiting both aggressiveness of interdialytic weight gain and ultrafiltration rate underlie the best approach. Tools to assess volume status beyond clinical assessment have shown promise in achieving euvolemia. When hypertension persists despite achievement of euvolemia, antihypertensive medications may be required and in some cases native nephrectomies. Future studies in children are needed to determine the best antihypertensive class and ideal rate of ultrafiltration on hemodialysis towards achievement of normotension and reduction of cardiovascular risk.

Blood pressure management in children on dialysis

Hypertension is a leading cause of cardiovascular complications in children on dialysis. Volume overload and activation of the renin-angiotensin-aldosterone system play a major role in the pathophysiology of hypertension. The first step in managing blood pressure (BP) is the careful assessment of ambulatory BP monitoring. Volume control is essential and should start with the accurate identification of dry weight, based on a comprehensive assessment, including bioimpedance analysis and intradialytic blood volume monitoring (BVM). Reduction of interdialytic weight gain (IDWG) is critical, as higher IDWG is associated with a worse left ventricular mass index and poorer BP control: it can be obtained by means of salt restriction, reduced fluid intake, and optimized sodium removal in dialysis. Optimization of peritoneal dialysis and intensified hemodialysis or hemodiafiltration have been shown to improve both fluid and sodium management, leading to better BP levels. Studies comparing different antihypertensive agents in children are lacking. The pharmacokinetic properties of each drug should be considered. At present, BP control remains suboptimal in many patients and efforts are needed to improve the long-term outcomes of children on dialysis.

Beyond playing games: nephrologist vs machine in pediatric dialysis prescribing

In a recent article in Pediatric Nephrology, Olivier Niel and colleagues applied an artificial intelligence algorithm to a clinical problem that continues to challenge experienced pediatric nephrologists: optimizing the target weight of children on dialysis. They compared blood pressure, antihypertensive medication and intradialytic symptoms in children whose target weight was prescribed firstly by a nephrologist, then subsequently using a machine learning algorithm. Improvements in all outcome measures are reported. Their innovative approach to tackling this important clinical problem appears promising. In this editorial, we discuss the strengths and weaknesses of their study and consider to what extent machine learning strategies are suited to optimizing pediatric dialysis outcomes.

Finding covert fluid: methods for detecting volume overload in children on dialysis

BACKGROUND

Lung ultrasound is a novel technique for detecting generalized fluid overload in children and adults with end-stage renal disease (ESRD). Echocardiography and bioimpedance spectroscopy are established methods, albeit variably adopted in clinical practice. We compared the practicality and accuracy of lung ultrasound with current objective techniques for detecting fluid overload in children with ESRD.

METHODS

A prospective observational study was performed to compare lung ultrasound B-lines, echocardiographic measurement of inferior vena cava parameters and bioimpedance spectroscopy in the assessment of fluid overload in children with ESRD on dialysis. The utility of each technique in predicting fluid overload, based on short-term weight gain, was assessed. Multiple linear regression models to predict fluid overload by weight were explored.

RESULTS

A total of 22 fluid assessments were performed in 13 children (8 on peritoneal dialysis, 5 on haemodialysis) with a median age of 4.0 (range 0.8-14.0) years. A significant linear correlation was observed between the number of B-lines detected by lung ultrasound and fluid overload by weight (r = 0.57, p = 0.005). A non-significant positive linear correlation was observed between fluid overload by weight and bioimpedance spectroscopy (r = 0.43, p = 0.2), systolic blood pressure (r = 0.19, p = 0.4) and physical examination measurements (r = 0.19, p = 0.4), while a non-significant negative linear relationship was found between the inferior vena cava collapsibility index and fluid overload by weight (r = -0.24, p = 0.3). In multiple linear regression models, a combination of three fluid parameters, namely lung ultrasound B-lines, clinical examination and systolic blood pressure, best predicted fluid overload (R ²  = 0.46, p = 0.05).

CONCLUSIONS

Lung ultrasound may be superior to echocardiographic methods and bioimpedance spectroscopy in detecting volume overload in children with ESRD. Given the practicality and sensitivity of this new technique, it can be adopted alongside clinical examination and blood pressure in the routine assessment of fluid status in children with ESRD.