**5. Extracorporeal ultrafiltration**

Extracorporeal UF is a mechanical pump-driven therapy that emerged as an option to overcome diuretic resistance. With this procedure, the volume and fluid removal rate is customized by clinicians to the needs and clinical characteristics of the patients.

#### *Advanced Treatment of Refractory Congestive Heart Failure by Peritoneal Ultrafiltration… DOI: http://dx.doi.org/10.5772/intechopen.114022*

Asymptomatic CHF patients have reduced sodium excretion in response to volume expansion compared to normal subjects. This abnormal fluid state leads to physiological abnormalities in multiple organ systems. Increased water in the myocardium can lead to ischemia and reduced contractility [35]. Hypervolemia may be related to a reduced excretion capacity or increased salt and water retention in the presence of decreased adequate circulating blood volume. The most common causes are endothelial damage, protein retention capacity, loss of plasma oncotic pressure, and reduced renal perfusion due to impaired cardiac function. Disturbed neurohormonal activation, excessive tubular sodium reabsorption, change in hemodynamics, oxidative stress, inflammation, and use of nephrotoxic drugs are essential factors of adverse cardiorenal interactions in CHF patients [36]. Diuretic agents remain the primary treatment for fluid overload. Although effective early in HF, diuretics become ineffective in the progression of the disease due to the development of unresponsiveness [37].

UF could safely improve hemodynamics in HF patients as an alternative sodium and water removal method. Some isolated schedules of UF may be too aggressive and result in severe hemodynamic instability. That is why continuous extracorporeal techniques have been applied to patients with excellent clinical outcomes. A stable hemodynamic state, good cardiovascular response, and adequate diuresis are the most common effects of continuous extracorporeal fluid removal methods. Hemodynamic instability is the driving factor behind the physician's decision to initiate extracorporeal UF, and the treatment was postponed until it became indispensable. This has been overcome with the development and availability of better-tolerated treatment modalities such as continuous RRT. Earlier intervention should always be considered because it is not justified to wait until the appearance of severe symptoms [38].

The UF process produces water from plasma in response to a transmembrane pressure gradient across a semipermeable membrane. The sieving capacity of UF membranes is responsible for the UF of crystalloids but not of cells or colloids. When hydrostatic pressure exceeds oncotic pressure, iso-osmotic ultrafiltrate is generated.

UF is performed from the patient's blood and then returned to the patient through separate access to the venous circulation. Adequate UF rates are needed for extracellular fluid to refill the intravascular space and gradually maintain sufficient blood volume. If the UF rate is too high, there is a decrease in intravascular volume, reflecting the reduction in total blood volume. Maintaining circulating blood volume, accurately determining the amount of fluid to be removed, and optimizing the fluid removal speed are essential for the success of the therapy [39]. Different techniques can be used for the hypervolemic patient to achieve an adequate fluid balance: UF, hemofiltration, and dialysis together with UF. Pure UF is only a fluid removal technique; others can simultaneously purify the blood. According to their frequency and duration, the treatments are classified as acute (single session up to 4 h), intermittent (single sessions up to 4 h repeated daily or three times a week), or continuous (24 h/ day or as required).

#### **5.1 Isolated intermittent ultrafiltration**

Intermittent isolated UF is carried out several hours daily to remove a desired amount of excess volume (1–2 L) [40]. The procedure can be repeated daily and uses standard hemodialysis (HD) equipment without dialysis fluid. Considering the short duration of the therapy, the effectiveness of this technique is in a higher UF rate. Sometimes, the UF rate may be too high, leading to significant hemodynamic instability. Many patients respond to diuretics again after one or more treatments with this method.

#### **5.2 Slow continuous ultrafiltration**

Its primary aim is to safely and effectively manage fluid overload in refractory edema without overt acute renal failure (ARF). This technique is mainly applied in patients with CHF NYHA IV. Slow continuous ultrafiltration (SCUF) can be performed with low blood flow rates (50–200 mL/min) in the veno-venous modality. The UF rate is usually 100–300 mL/h, according to fluid balance needs. The frequent complications from arterial cannulation are the primary reason the arterio-venous modality is rarely used. It is required to control the UF rate to maintain the desired volume status. Otherwise, higher UF rates would require fluid resuscitation. No fluids are administered as dialysate or replacement fluids, as the primary purpose of treatment is to achieve volume control. However, isolated UF is not a blood purification modality and solute clearance is irrelevant. UF in SCUF is iso-osmotic and isonatric, and water and sodium removal cannot be dissociated. That is possible because sodium elimination is linked to the sodium plasma water concentration. A small surface area filter can be used with reduced heparin doses to maintain the effectiveness of the therapy because low UF and blood flow rates are required. Removing myocardial depressant factors in the ultrafiltrate, reduction in preload, and modulation of the RAAS axis seem to be possible pathophysiological mechanisms underlying clinical improvement [41].

#### **5.3 Continuous veno-venous hemofiltration**

Continuous veno-venous hemofiltration (CVVH) produces a large ultrafiltrate volume across a high-permeability membrane. The advantages of CVVH include liberal fluid management, optimal clearance of uremic toxins, including middle molecules, and hemodynamic stability. The ultrafiltrate produced during CVVH is wholly or partly replaced with appropriate replacement solutions to achieve desired therapeutic goals. Replacement fluid can be infused before (predilution) and/or after (postdilution) the hemofilter. The decision on when to start CVVH should be based on the severity of organ failure and ARF. Early initiation should be considered at oliguric ARF and/or a steep rise in serum creatinine despite adequate fluid resuscitation. This method removes fluid with considerable solute clearance and blood purification [42]. The hemodynamic response is inimitable due to the possibility of dissociating water from sodium removal. In CVVH, the composition of ultrafiltrate is similar to plasma water, but sodium concentration in the replacement solution significantly affects the sodium balance.

#### **5.4 Continuous hemodialysis/hemodiafiltration**

The principal advantage of continuous hemodialysis/hemodiafiltration (CVVHD/ HDF) is the ability to remove large volumes of fluid, avoiding the hypotensive episodes caused by intermittent HD. It is indicated for managing patients with ARF who are hemodynamically unstable and/or must receive large volumes of fluid or both. UF volumes are optimized to exceed the desired volume of excess water. Solute removal is both diffusive and convective. To perform a successful CVVHD/HDF, optimal clinical tolerance to fluid removal is critical. In a setting of too aggressive UF, blood volume may decrease due to a too-slow intravascular refilling, leading to severe hemodynamic instability [43].

*Advanced Treatment of Refractory Congestive Heart Failure by Peritoneal Ultrafiltration… DOI: http://dx.doi.org/10.5772/intechopen.114022*
