The nephrotic syndrome: pathogenesis and treatment of edema formation and secondary complications

IPNA clinical practice recommendations for the diagnosis and management of children with steroid-sensitive nephrotic syndrome

Idiopathic nephrotic syndrome is the most frequent pediatric glomerular disease, affecting from 1.15 to 16.9 per 100,000 children per year globally. It is characterized by massive proteinuria, hypoalbuminemia, and/or concomitant edema. Approximately 85-90% of patients attain complete remission of proteinuria within 4-6 weeks of treatment with glucocorticoids, and therefore, have steroid-sensitive nephrotic syndrome (SSNS). Among those patients who are steroid sensitive, 70-80% will have at least one relapse during follow-up, and up to 50% of these patients will experience frequent relapses or become dependent on glucocorticoids to maintain remission. The dose and duration of steroid treatment to prolong time between relapses remains a subject of much debate, and patients continue to experience a high prevalence of steroid-related morbidity. Various steroid-sparing immunosuppressive drugs have been used in clinical practice; however, there is marked practice variation in the selection of these drugs and timing of their introduction during the course of the disease. Therefore, international evidence-based clinical practice recommendations (CPRs) are needed to guide clinical practice and reduce practice variation. The International Pediatric Nephrology Association (IPNA) convened a team of experts including pediatric nephrologists, an adult nephrologist, and a patient representative to develop comprehensive CPRs on the diagnosis and management of SSNS in children. After performing a systematic literature review on 12 clinically relevant PICO (Patient or Population covered, Intervention, Comparator, Outcome) questions, recommendations were formulated and formally graded at several virtual consensus meetings. New definitions for treatment outcomes to help guide change of therapy and recommendations for important research questions are given.

Kinesin-5 Eg5 is essential for spindle assembly, chromosome stability and organogenesis in development

Chromosome stability relies on bipolar spindle assembly and faithful chromosome segregation during cell division. Kinesin-5 Eg5 is a plus-end-directed kinesin motor protein, which is essential for spindle pole separation and chromosome alignment in mitosis. Heterozygous Eg5 mutations cause autosomal-dominant microcephaly, primary lymphedema, and chorioretinal dysplasia syndrome in humans. However, the developmental roles and cellular mechanisms of Eg5 in organogenesis remain largely unknown. In this study, we have shown that Eg5 inhibition leads to the formation of the monopolar spindle, chromosome misalignment, polyploidy, and subsequent apoptosis. Strikingly, long-term inhibition of Eg5 stimulates the immune responses and the accumulation of lymphocytes in the mouse spleen through the innate and specific immunity pathways. Eg5 inhibition results in metaphase arrest and cell growth inhibition, and suppresses the formation of somite and retinal development in zebrafish embryos. Our data have revealed the essential roles of kinesin-5 Eg5 involved in cell proliferation, chromosome stability, and organogenesis during development. Our findings shed a light on the cellular basis and pathogenesis in microcephaly, primary lymphedema, and chorioretinal dysplasia syndrome of Eg5-mutation-positive patients.

Furosemide and albumin for the treatment of nephrotic edema: a systematic review

BACKGROUND

Edema is one of the cardinal clinical features of nephrotic syndrome (NS). It may vary from mild periorbital edema to severe generalized edema (anasarca). In patients where edema does not improve with prednisone therapy, the most common supportive medications are diuretics and albumin. However, due to the complex pathophysiology of edema formation in NS patients resulting in intravascular normovolemia or hypovolemia, optimal therapy for edema is still debated. We conducted a systematic review with the objective of evaluating the change in urine volume and urine sodium excretion after treatment with furosemide only versus furosemide with albumin in edematous patients with NS.

OBJECTIVES

(1) To evaluate efficacy of furosemide alone versus furosemide with albumin in the treatment of nephrotic edema in adults and children. (2) To compare the harms and benefits of different doses of furosemide for treating nephrotic edema.

SEARCH METHODS

The search included all randomized or quasi-randomized controlled trials in English and French using MEDLINE, Embase, and CENTRAL Trials Registry of the Cochrane Collaboration using the Ovid interface.

CLINICALTRIALS

gov and the International Clinical Trials Registry Platform were also searched.

SELECTION CRITERIA

We included all RCTs and randomized cross-over studies in which furosemide and furosemide plus albumin are used in the treatment of children or adults with nephrotic edema. We excluded patients with hypoalbuminemia of non-renal origin and severe chronic kidney disease (CKD) with a glomerular filtration rate below 30 ml/min/1.74 m2 and patients with congenital NS.

DATA COLLECTION AND ANALYSIS

All abstracts were independently assessed by at least two authors to determine which studies met the inclusion criteria. Information on study design, methodology, and outcome data (urine volume, urine sodium excretion, adverse effects) from each identified study was entered into a separate data sheet. The differences in outcomes between the types of therapy were expressed as standardized mean difference (SMD) with 95% confidence intervals (CI).

RESULTS

The search yielded 525 records, and after screening, five studies were included in the systematic review and four of those studies in the meta-analysis. One study had high risk of bias and the remaining three studies were deemed to have some concerns. Urine excretion was greater after treatment with furosemide and albumin versus furosemide (SMD 0.85, 95% CI = 0.33 to 1.38). Results for sodium excretion were inconclusive (SMD 0.37, 95%CI =  - 0.28 to 1.02).

AUTHORS' CONCLUSIONS

The current evidence is not sufficient to make definitive conclusions about the role of albumin in treating nephrotic edema. High-quality randomized studies with adequate samples sizes are needed. Including an assessment of intravascular volume status may be helpful.

TRIAL REGISTRATION

Prospero: CRD4201808979. https://www.crd.york.ac.uk/PROSPERO A higher resolution version of the Graphical abstract is available as Supplementary information.

The circulating renin-angiotensin-aldosterone system is down-regulated in dogs with glomerular diseases compared to other chronic kidney diseases with low-grade proteinuria

Glomerular diseases (GD) lead to a variety of disorders of the vascular and the total body water volumes. Various pathomechanisms, including vascular underfill and overfill, have been suggested to explain these disturbances. Accordingly, the circulating renin-angiotensin-aldosterone system (cRAAS) is expected to be activated as either a cause or a result of these fluid disorders. The aim of this study was to characterize the activity of the cRAAS in dogs with GD and to evaluate its relationship with the vascular volume status. In a prospective study, we evaluated the plasma renin activity and the serum aldosterone concentration in 15 dogs with GD. Their fluid volume status was estimated with clinical variables reflecting volemia and hydration, echocardiographic volume assessment, N-terminal pro B-type natriuretic peptide, blood urea nitrogen:creatinine ratio, and the urinary fractional excretion of sodium. Ten dogs with chronic kidney disease (CKD) with matching degree of azotemia were recruited as controls. The activity of the cRAAS was low in 10 dogs, normal in 3 dogs, high in 1 dog and equivocal (high renin—low aldosterone) in 1 dog with GD. These dogs had a lower cRAAS activity than dogs with CKD (p = 0.01). The clinical evaluation showed 8 hypovolemic and 7 non-hypovolemic dogs; 3 dehydrated, 9 euhydrated and 3 overhydrated dogs. The cRAAS activity was not different between hypovolemic and non-hypovolemic dogs. The down-regulated cRAAS without obvious association with the clinical volume status of these dogs with GD, suggests different mechanisms of fluid volume dysregulation in dogs with GD than previously assumed. This finding however should be confirmed in a focused larger scale study, as it may influence the use of cRAAS blockers as part of the standard therapy of GD in dogs.

OUP accepted manuscript

Podocytopathies are glomerular disorders in which podocyte injury drives proteinuria and progressive kidney disease. They encompass a broad spectrum of aetiologies, resulting in pathological pictures of minimal-changes, focal segmental glomerulosclerosis, diffuse mesangial sclerosis or collapsing glomerulopathy. Despite improvement in classifying podocytopathies as a distinct group of disorders, the histological definition fails to capture the relevant biological heterogeneity underlying each case, manifesting as extensive variability in disease progression and response to therapies. Increasing evidence suggests that podocytopathies can result from a single causative factor or a combination of multiple genetic and/or environmental risk factors with different relative contributions, identifying complex physiopathological mechanisms. Consequently, the diagnosis can still be challenging. In recent years, significant advances in genetic, microscopy and biological techniques revolutionized our understanding of the molecular mechanisms underlying podocytopathies, pushing nephrologists to integrate innovative information with more conventional data obtained from kidney biopsy in the diagnostic workflow. In this review, we will summarize current approaches in the diagnosis of podocytopathies, focusing on strategies aimed at elucidating the aetiology underlying the histological picture. We will provide several examples of an integrative view of traditional concepts and new data in patients with suspected podocytopathies, along with a perspective on how a reclassification could help to improve not only diagnostic pathways and therapeutic strategies, but also the management of disease recurrence after kidney transplantation. In the future, the advantages of precision medicine will probably allow diagnostic trajectories to be increasingly focused, maximizing therapeutic results and long-term prognosis.

Mechanisms and management of edema in pediatric nephrotic syndrome

Edema is the abnormal accumulation of fluid in the interstitial compartment of tissues within the body. In nephrotic syndrome, edema is often seen in dependent areas such as the legs, but it can progress to cause significant accumulation in other areas leading to pulmonary edema, ascites, and/or anasarca. In this review, we focus on mechanisms and management of edema in children with nephrotic syndrome. We review the common mechanisms of edema, its burden in pediatric patients, and then present our approach and algorithm for management of edema in pediatric patients. The extensive body of experience accumulated over the last 5 decades means that there are many options, and clinicians may choose among these options based on their experience and careful monitoring of responses in individual patients.

IPNA clinical practice recommendations for the diagnosis and management of children with steroid-resistant nephrotic syndrome

Idiopathic nephrotic syndrome newly affects 1-3 per 100,000 children per year. Approximately 85% of cases show complete remission of proteinuria following glucocorticoid treatment. Patients who do not achieve complete remission within 4-6 weeks of glucocorticoid treatment have steroid-resistant nephrotic syndrome (SRNS). In 10-30% of steroid-resistant patients, mutations in podocyte-associated genes can be detected, whereas an undefined circulating factor of immune origin is assumed in the remaining ones. Diagnosis and management of SRNS is a great challenge due to its heterogeneous etiology, frequent lack of remission by further immunosuppressive treatment, and severe complications including the development of end-stage kidney disease and recurrence after renal transplantation. A team of experts including pediatric nephrologists and renal geneticists from the International Pediatric Nephrology Association (IPNA), a renal pathologist, and an adult nephrologist have now developed comprehensive clinical practice recommendations on the diagnosis and management of SRNS in children. The team performed a systematic literature review on 9 clinically relevant PICO (Patient or Population covered, Intervention, Comparator, Outcome) questions, formulated recommendations and formally graded them at a consensus meeting, with input from patient representatives and a dietician acting as external advisors and a voting panel of pediatric nephrologists. Research recommendations are also given.

Augmentation index, a predictor of cardiovascular events, is increased in children and adolescents with primary nephrotic syndrome

BACKGROUND

Arterial stiffness is associated with an increased risk of cardiovascular diseases. Augmentation index (AIx@75), a measure of arterial stiffness and wave reflection, has not been evaluated in patients with primary nephrotic syndrome (PNS). We investigated whether central and peripheral vascular profiles, hemodynamic parameters, and biochemical tests are associated with AIx@75 in PNS patients.

METHODS

This observational study involved 38 children and adolescents with PNS (12.14 ± 3.65 years) and 37 healthy controls (13.28 ± 2.80 years). Arterial stiffness and vascular and hemodynamic parameters were measured noninvasively using the Mobil-O-Graph® (IEM, Stolberg, Germany). In the PNS group, biochemical tests and corticosteroid dosage/treatment time were analyzed.

RESULTS

Peripheral and central systolic blood pressure (SBPp, SBPc) Z-scores were significantly higher in the PNS patients. AIx@75 was significantly higher in the PNS patients (25.14 ± 9.93%) than in controls (20.84 ± 7.18%). In the control group, AIx@75 negatively correlated with weight (r = - 0.369; p = 0.025), height (r = - 0.370; p = 0.024), and systolic volume/body surface (r = - 0.448; p = 0.006). In the PNS group, a univariate linear correlation showed that AIx@75 negatively correlated with weight (r = - 0.360; p = 0.027), height (r = 0.381; p = 0.18), and systolic volume/body surface (r = - 0.447; p < 0.002) and positively with the Z-score of SBPp (r = 0.407; p = 0.011), peripheral diastolic blood pressure (DBPp, r = 0.452; p = 0.004), SBPc (r = 0.416; p = 0.009), DBPc (r = 0.407; p = 0.011), triglycerides (r = 0.525; p = 0.001), and cholesterol [total (r = 0.539; p < 0.001), LDLc (r = 0.420; p = 0.010), and non-HDLc (r = 0.511; p = 0.001)].

CONCLUSIONS

Early abnormalities of AIx@75 and vascular parameters suggest that patients with PNS, even in stable condition, present subclinical indicators for the development of cardiovascular disease.

Mechanisms in fluid retention - towards a mutual concept

Fluid retention is a common and challenging condition in daily clinical practice. The normal fluid homoeostasis in the human body is based on accurately counter-balanced physiological mechanisms. When compromised fluid retention occurs and is seen in pathophysiologically different conditions such as liver cirrhosis, heart and kidney failure, and in preeclampsia. These conditions may share pathophysiological mechanisms such as functional arterial underfilling, which seems to be a mutual element in cirrhosis, cardiac failure, cardiorenal and hepatorenal syndromes, and in pregnancy. However, there are also distinct differences and it is still unclear whether kidney dysfunction or arterial underfilling is the initiating factor of fluid retention or if they happen simultaneously. This review focuses on similarities and differences in water retaining conditions and points to areas where important knowledge is still needed.

Limited sampling strategy to predict mycophenolic acid area under the curve in pediatric patients with nephrotic syndrome: a retrospective cohort study

PURPOSE

Limited sampling strategy (LSS) is a precise and relatively convenient therapeutic drug monitoring method. We evaluated LSSs for mycophenolic acid (MPA) in children with nephrotic syndrome treated with mycophenolic mofetil (MMF) and validated the LSSs using two different approaches.

METHODS

We measured MPA plasma concentrations in 31 children using HPLC-UV method and received 37 MPA pharmacokinetic profiles (0-12 h). For six children, MPA profiles were estimated twice after two MMF doses. LSSs were developed using multilinear regression with STATISTICA and R software and validated using validation group and bootstrap method, respectively.

RESULTS

The best three time point equations included C₁, C₃, C₆ (good guess 83%, bias - 2.78%; 95% confidence interval (CI) - 9.85-0.46); C₁, C₂, C₆ (good guess 72%, bias 0.72%; 95% CI - 5.33-7.69); and C₁, C₂, C₄ (good guess 72%, bias 2.05%; 95% CI - 4.92-13.01) for STATISTICA software. For R software, the best equations consisted of C₁, C₃, C₆ (good guess 92%, bias - 2.69%; 95% CI - 27.18-33.75); C₀, C₁, C₃ (good guess 84%, bias - 2.11%; 95% CI - 24.19-22.29); and C₀, C₁, C₂ (good guess 84%, bias - 0.48%; 95% CI - 30.77-54.07). During validation, better results were obtained for R evaluations, i.e., bootstrap method.

CONCLUSIONS

The most useful equations included C₀, C₁, C₃ and C₀, C₁, C₂ time points; however, the most precise included C₁, C₃, C₆ time points because of MPA enterohepatic recirculation. Better results were obtained for bootstrap validation due to greater number of patients. Validated LSS should be used only in the population for which it was developed. As there is growing evidence that underexposure of MPA is associated with insufficient treatment response, we recommend the introduction of therapeutic drug monitoring for MPA in children with nephrotic syndrome.

Nephrotic Syndrome: Oedema Formation and Its Treatment With Diuretics

Oedema is a defining element of the nephrotic syndrome. Its' management varies considerably between clinicians, with no national or international clinical guidelines, and hence variable outcomes. Oedema may have serious sequelae such as immobility, skin breakdown and local or systemic infection. Treatment of nephrotic oedema is often of limited efficacy, with frequent side-effects and interactions with other pharmacotherapy. Here, we describe the current paradigms of oedema in nephrosis, including insights into emerging mechanisms such as the role of the abnormal activation of the epithelial sodium channel in the collecting duct. We then discuss the physiological basis for traditional and novel therapies for the treatment of nephrotic oedema. Despite being the cardinal symptom of nephrosis, few clinical studies guide clinicians to the rational use of therapy. This is reflected in the scarcity of publications in this field; it is time to undertake new clinical trials to direct clinical practice.

Safety and Efficacy of Pneumococcal Vaccination in Pediatric Nephrotic Syndrome

Nephrotic syndrome affects both children and adults. Idiopathic nephrotic syndrome is reported to be one of the most frequent renal pathologies in childhood. Nephrotic children are at high risk for severe pneumococcal infections as one of the life-threatening complications of nephrotic syndrome due to involvement of the immunosuppressive regimen and the acquired immune deficiency induced by nephrotic syndrome including decreased plasma IgG and low complement system components. Aiming to prevent pneumococcal infection is of paramount importance especially in this era of ever-increasing pneumococcal resistance to penicillins and cephalosporins. The pneumococcal vaccines currently available are inactivated vaccines-the two main forms in use are polysaccharide vaccines and conjugated vaccines. However, the data supporting the use of these vaccines and to guide the timing and dosage recommendations is still limited for nephrotic children. Thus, this review discusses the evidences of immunogenicity and safety profile of both vaccinations on nephrotic patients as well as the effect of nephrotic syndrome treatment on vaccine seroresponses.

Circadian blood pressure abnormalities in patients with primary nephrotic syndrome

BACKGROUND

Only a few studies have evaluated the abnormalities of ambulatory blood pressure (ABP) in patients with nephrotic syndrome (NS).

METHODS

The 24-h ABPs were measured in primary NS patients with acute onset of disease and analyzed in relation to the clinical variables.

RESULTS

Our subjects comprised 21 patients: 17 with minimal change disease and 4 with focal segmental glomerulosclerosis. Of these patients, 8 (38%) had daytime hypertension, 13 (62%) had nighttime hypertension, and 13 (62%) were non-dippers (nighttime-to-daytime ratio of ABP: NDR > 0.9). The serum sodium level was correlated with the average 24-h ABP and NDR, after adjustment for other clinical variables, such as the increase in body weight, serum albumin level, and urinary protein excretion. The data from repeated ABP measurements, before and after the achievement of remission, showed a marked decrease in the average 24-h ABP after remission. Furthermore, change in the serum sodium level was significantly correlated with the change in NDR.

CONCLUSION

These results suggest that alteration in renal handling of sodium and water, which might be reflected in serum sodium level, is involved in the abnormality of circadian blood pressure in primary NS patients.

Economic evaluation of human albumin use in patients with nephrotic syndrome in four Brazilian public hospitals: pharmacoeconomic study

CONTEXT AND OBJECTIVE:

In 2004, the Brazilian National Health Surveillance Agency (Agência Nacional de Vigilância Sanitária, ANVISA) published a resolution establishing guidelines for albumin use. Although the published data do not indicate any definitive conclusions about the benefits of albumin use in patients with nephrotic syndrome (NS), the guidelines recommend this procedure only in cases of edema that is refractory to use of diuretics. The aim here was to analyze albumin use among patients with nephrotic syndrome.

DESIGN AND SETTING:

Pharmacoeconomic study conducted in four large public referral hospitals for nephrology services in northeastern Brazil.

METHOD:

Cost-effectiveness and cost-utility economic evaluations were performed on a concurrent cohort of patients with nephrotic syndrome, who were divided into two groups according to compliance or noncompliance with the guidelines. Quality-of-life data were obtained from the SF36 and CHQ-PF50 questionnaires.

RESULTS:

This study enrolled 109 patients (60% adults and 56% women); 41.3% were using albumin in accordance with the guidelines. The weight, diuresis and fluid balance parameters were more cost-effective for patients who adhered to the guidelines. Regarding days of hospitalization avoided, the incremental ratio showed a daily cost of R$ 55.33, and guideline-compliant patients were hospitalized for five days or fewer. The quality of life improved by 8%, and savings of R$ 3,458.13/QALY (quality-adjusted life year) for the healthcare system were generated through guideline compliance.

CONCLUSION:

The economic analyses of this study demonstrated that there were greater cost benefits for patients whose treatment followed the guidelines.

Overall condition improvement in a rat model of nephrotic syndrome treated with CellCept nanoliposomes

Purpose To investigate the effect of CellCept nanoliposomes on Adriamycin-induced nephrotic syndrome in rats. Methods To model nephrotic syndrome, rats were injected with 6.5 mg/kg of Adriamycin in the tail vein. The rats were randomly divided into three groups, including a control group, a free mycophenolate mofetil (MMF)-treated group, and a liposome-encapsulated MMF-treated group. Five weeks after the Adriamycin treatment, the free MMF-treated group received CellCept while the liposome-encapsulated MMF-treated group received the CellCept nanoliposomes for 2 weeks. The general condition of the animals was observed, which included urine volume over 24 h, urine protein levels, and serum biochemical indexes. Renal morphology was also observed. Results The level of urine protein over 24 h was increased in the control group, while plasma albumin (ALB) was decreased. The total cholesterol (TC) and triacylglycerol (TG) levels increased significantly (P < 0.05, P < 0.01). The pathological examination of the kidneys showed some abnormalities. In contrast, these parameters were improved significantly in the free mycophenolate mofetil (MMF)-treated and liposome-contained mycophenolate mofetil (MMF)-treated groups. Conclusion The CellCept nanoliposomes have a good therapeutic effect on Adriamycin-induced nephrotic syndrome in rats.

The non-immunosuppressive management of childhood nephrotic syndrome

Idiopathic nephrotic syndrome (INS) is one of the most common renal diseases found in the paediatric population and is associated with significant complications, including infection and thrombosis. A high proportion of children enter sustained remission before adulthood, and therapy must therefore mitigate the childhood complications, while minimising the long-term risk to health. Here we address the main complications of INS and summarise the available evidence and guidance to aid the clinician in determining the appropriate treatment for children with INS under their care. Additionally, we highlight areas where no consensus regarding appropriate management has been reached. In this review, we detail the reasons why routine prophylactic antimicrobial and antithrombotic therapy are not warranted in INS and emphasise the conservative management of oedema. When pharmacological intervention is required for the treatment of oedema, we provide guidance to aid the clinician in determining the appropriate therapy. Additionally, we discuss obesity and growth, fracture risk, dyslipidaemia and thyroid dysfunction associated with INS. Where appropriate, we describe how recent developments in research have identified potential novel therapeutic targets.

Perspectives on edema in childhood nephrotic syndrome

There have been two major theories surrounding the development of edema in nephrotic syndrome (NS), namely, the under- and overfill hypotheses. Edema is one of the cardinal features of NS and remains one of the principal reasons for admission of children to the hospital. Recently, the discovery that proteases in the glomerular filtrate of patients with NS are activating the epithelial sodium channel (ENaC), resulting in intrarenal salt retention and thereby contributing to edema, might suggest that targeting ENaC with amiloride might be a suitable strategy to manage the edema of NS. Other potential agents, particularly urearetics and aquaretics, might also prove useful in NS. Recent evidence also suggests that there may be other areas involved in salt storage, especially the skin, and it will be intriguing to study the implications of this in NS.

Childhood nephrotic syndrome in the 21st century: What's new?

Childhood nephrotic syndrome is a condition managed by general paediatricians and paediatric nephrologists. Whether treating a first presentation or a relapse, the clinician requires expertise in order to minimise the risk of serious complications and optimise long-term care. Indeed, many children suffer a difficult relapsing course in their disease, warranting consideration of second-line therapies. The last two decades have witnessed a growing knowledge of the condition and increased complexity of diagnostic and therapeutic options, which poses a challenge for the general paediatrician, given the condition's relative rarity in daily practice. This review aims to familiarise the reader with some of the most important recent developments and particularly to provide an insight into what management options are available and when it may be appropriate to seek advice from a nephrologist.

Pathophysiology, Evaluation, and Management of Edema in Childhood Nephrotic Syndrome

Generalized edema is a major presenting clinical feature of children with nephrotic syndrome (NS) exemplified by such primary conditions as minimal change disease (MCD). In these children with classical NS and marked proteinuria and hypoalbuminemia, the ensuing tendency to hypovolemia triggers compensatory physiological mechanisms, which enhance renal sodium (Na(+)) and water retention; this is known as the "underfill hypothesis." Edema can also occur in secondary forms of NS and several other glomerulonephritides, in which the degree of proteinuria and hypoalbuminemia, are variable. In contrast to MCD, in these latter conditions, the predominant mechanism of edema formation is "primary" or "pathophysiological," Na(+) and water retention; this is known as the "overfill hypothesis." A major clinical challenge in children with these disorders is to distinguish the predominant mechanism of edema formation, identify other potential contributing factors, and prevent the deleterious effects of diuretic regimens in those with unsuspected reduced effective circulatory volume (i.e., underfill). This article reviews the Starling forces that become altered in NS so as to tip the balance of fluid movement in favor of edema formation. An understanding of these pathomechanisms then serves to formulate a more rational approach to prevention, evaluation, and management of such edema.