Acute decompensated heart failure (ADHF) is associated with an increasing number of hospital admission for volume overload. The volume overload can be attributed to medication noncompliance, comorbidities, diet, modifiable risk factors, disease progression, and/or treatment failure. The standard treatment is usually pharmacologic involving intravenous (IV) diuresis, mainly with loop diuretics. Often, patients with ADHF will need chronic diuretic therapy. However, chronic diuretic therapy use is associated with negative neuro-hormonal effects which may lead to diuretic resistance which in turn can lead to increased morbidity and mortality in ADHF patients. The American College of Cardiology Foundation (ACCF) and the American Heart Association (AHA) guidelines recommend pharmacological and non-pharmacological interventions to treat volume overload. Extracorporeal ultrafiltration (UF) is, therefore, an emerging alternative therapy of interest for treating volume overload in ADHF patients.
The kidneys are bean-shaped structures that are located bilaterally and lateral to the spine in the retroperitoneal space. The left kidney is anatomically oriented around the T12 and L3 vertebrae. On the right, the kidney is displaced by the liver, orienting it anatomically lower than the left kidney. The male kidney typically weighs 125-175 g while the female kidney weighs 115-155 g. They are typically 10-12 cm in length, 5-7 cm in width, and 2-3 cm in thickness. The ribs, muscles, and renal fat pad located in the retroperitoneal space protect the kidneys. The renal hilum serves as a hub, allowing the entry and exit of blood vessels, nerves, lymph vessels, and the ureters. The aorta gives rise to the renal arteries and the renal veins drain into the inferior vena cava. The glomerulus is a capillary bed that filters blood and the Bowman’s capsule captures the filtrate. After leaving the glomerulus, there is a second capillary bed through which blood flows. This proximal convoluted tubule, distal convoluted tubule, and loop of Henle are surrounded by this capillary bed forming a portal system. This capillary bed serves to recover a majority of solutes and water. After the filtrate is processed, the collecting duct collects it, and from there it drains into the minor calyces. The minor calyces join and forms major calyces. The filtrate then moves on through the renal pelvis and finally through the ureters.
In patients with refractory ADHF, which is severe in nature, who do not respond to standard pharmacological treatment including the use of IV diuretics, volume overload can be reversed through the use of UF. UF has been shown to produce an overall positive nitrogen balance and may also be indicated in patients with the fluid overload that need to increase their caloric intake. In patients undergoing cardiopulmonary bypass with evidence of excess body water, UF may be used to prevent the additional accumulation of fluid.
UF is contraindicated in any patient with evidence of hemodynamically instability. It is also contraindicated in patients with acute coronary syndrome including myocardial infarction or unstable angina. Patients with serum creatinine greater than 3.0 mg/dL should not undergo UF. UF is also contraindicated in patients with hematocrit over 45%. Lastly, adequate venous access is necessary for UF, and inadequate venous access is therefore contraindicated.
UF equipment includes various setups used for aquapheresis, intermittent hemodialysis, and continuous hemodialysis. Components that are necessary for an optimal function includes monitoring devices, a blood pump to transports blood between the patient and the dialyzer, and a delivery system for transportation of dialysis solution.
Ultrafiltration requires a careful assessment of the patient to determine the goal of fluid removal. Vital signs must be monitored closely and periodically. A team of extensively trained hemodialysis nurses is required.
There are studies evaluating the differences among methods of vascular access for ultrafiltration that is done long term and intermittently. Issues related to cost and technical difficulty should be considered when choosing the access site. A central venous access is required with a preference for internal jugular access. Access, especially long-term, for UF patients increases the risks for adverse events. An arteriovenous communication is usually used in chronic dialysis patients but is also used in UF and can be associated with an increased risk of high output HF and right ventricular HF. Peritoneal dialysis access is also an option, but can cause a rare complication of peritonitis.
UF therapy is a mechanical modality of fluid removal. It reduces central venous pressure (CVP) without impacting circulating volume. This is accomplished by the creation of a hydrostatic pressure gradient that triggers a mechanical extraction of fluid across a filter which subsequently results in separation and removal of isotonic plasma water. Studies show that it can be used effectively to reduce volume overload in patients resistant to conventional diuretic therapy. The UNLOAD (UF versus Intravenous Diuretics for Patients Hospitalized for ADHF) trial found that UF is not only an effective alternative therapy for refractory HF, but also safely produces greater weight and fluid loss than intravenous diuretics and reduces 90-day HF readmissions and cumulative hospital readmissions. Three recent meta-analyses evaluating the comparative outcomes of UF versus conventional diuretic therapy in reducing volume overload in patients with ADHF found that patients that were able to tolerate UF had a significant reduction in volume overload and weight in comparison to conventional diuretics alone.
Adverse events associated with UF include clotting of UF filters, transient discomfort at the venous access site, central venous catheter infection, catheter malfunction, hypotension, bleeding events, and renal injury. A very small percentage of patients had volume overload refractory to UF. Early studies suggest that UF is unsafe. A recent systematic review and meta-analysis by Siddiqui et al. concluded that UF is safe and effective in ADHF and that there were no significant adverse events in UF in comparison to IV diuretics. There were fewer bleeding events with UF than with standard therapy. The increased events of hypotension in UF noted in the studies were clinically insignificant. In addition, the incidence of acute kidney injury in UF and diuretic therapy were comparable. The Cardiorenal Rescue Study in Acute Decompensated Heart Failure (CARRESS-HF) trial by Bart et al. compared the effect of UF with diuretic therapy on renal function in patients with heart failure who have persistent volume overload and renal function that is declining. The study found that, although UF is associated with a higher increase in serum creatine initially, long-term the serum creatinine is lower when compared to patients on standard diuretic therapy.
UF can show great benefit for patients in ADHF refractory to standard therapy with diuretics. It also causes iso-osmotic volume loss without changing or creating any electrolyte abnormalities. It can lead to maximum sodium loss per unit of volume removal compared to IV diuretics. UF can also lead to change in the neurohormonal milieu which may have clinical significance in heart disease, and it has also been shown to restore diuretic sensitivity.
The use of UF to manage CHF patients is done with a multidisciplinary team that includes a cardiologist, nephrologist, intensivist, hemodialysis nurses, an internist, and a vascular surgeon. Ultrafiltration requires a careful assessment of the patient to determine the goal of fluid removal. Vital signs must be monitored closely and periodically. A team of extensively trained hemodialysis nurses is required. While acutely the treatment can reduce the fluid in the body, the long term outcomes remain unknown. UF is also an expensive endeavor and not everyone benefits from it- hence patient selection is the key. 
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