Renal replacement therapy hemodialysis

Chap. 43). When patients reach Stage 4, progression to Stage 5 is almost inevitable, although the process may be slowed if appropriate therapy is initiated. It is during Stage 4 CKD that plans for renal replacement therapy (hemodialysis or peritoneal dialysis) need to be made, and patients educated on dialysis modalities and options for transplantation if they are good candidates. 

Fluid restriction is generally unnecessary as long as sodium intake is controlled. The thirst mechanism remains intact in CKD to maintain total body water and plasma osmolality near normal levels. Fluid intake should be maintained at the rate of urine output to replace urine losses, usually fixed at approximately 2 L/day as urine concentrating ability is lost. Significant increases in free water intake orally or intravenously can precipitate volume overload and hyponatremia. Patients with stage 5 CKD require renal replacement therapy to maintain normal volume status. Fluid intake is often limited in patients receiving hemodialysis to prevent fluid overload between dialysis sessions. 

Renal replacement therapy (RRT), such as hemodialysis and peritoneal dialysis, maintains fluid and electrolyte balance while removing waste products. See Table 75-4 for indications for RRT in ARF. Intermittent and continuous options have different advantages (and disadvantages) but, after correcting for severity of illness, have similar outcomes. Consequently, hybrid approaches (e.g., sustained low-efficiency dialysis and extended daily dialysis) are being developed to provide the advantages of both. 

Five patients with metformin-associated severe lactic acidosis, seen between 1 September 1998 and 31 May 2001, have been reported (58). Two had attempted suicide. All had severe metabolic acidosis with a high anion gap and raised blood lactate concentrations. Four developed profound hypotension and three had acute respiratory failure. Three had normal preceding renal function. Three required conventional hemodialysis and two continuous renal replacement therapy. 

Hemofiltration is a prominent feature of many continuous renal replacement therapies (Table 6.2). How-ever continuous hemodialysis can also be employed to accelerate solute removal (16). The contribution of both processes to extracorporeal drug clearance will be considered separately in the context of continuous renal replacement therapy. 

Some of the renal replacement therapies listed in Table 6.2 incorporate continuous hemodialysis or a combination of continuous hemofiltration and hemodialysis. Continuous hemodialysis differs importantly from conventional intermittent hemodialysis in that the flow rate of dialysate is much lower than is countercurrent blood flow through the dialyzer. As a result/ concentrations of many solutes in dialysate leaving the dialyzer (Cd) will have nearly equilibrated with their plasma concentrations in blood entering the dialyzer (Cp) (16/31). The extent to which this equilibration is complete is referred to as the dialysate saturation (Sd) and is calculated as the following ratio ... 

In contrast with intermittent hemodialysis in which dialyzer blood flow is rate limiting/ diffusive drug clearance during continuous renal replacement therapy is limited by dialysate flow (Qd)/ which typically is only 25 mL/min. Accordingly/ diffusive drug clearance (CLd) is calculated from the equation ... 

Drug doses need to be increased or supplemented for patients requiring renal replacement therapy only if CLec/ representing extracorporeal clearance from either intermittent hemodialysis or continuous renal replacement therapy/ is substantial when compared to CLr + CLjVR (Equation 6.12). Levy (34) has proposed that supplementation is needed only when CLec is greater than 30% of CL + CLjvr- Several approaches will be considered that can be used to make appropriate drug dose adjustments for patients requiring renal replacement therapy. 

A second approach is to calculate supplemental doses to replace drug lost during hemodialysis or continuous renal replacement therapy by directly measuring drug loss by extracorporeal removal or by... 

The utility of continuous renal replacement therapies (CRRT) such as continuous venous-venous hemodialysis (CWHD) in the treatment of poisoning is uncertain. As CRRT provides slower clearance than conventional hemodialysis it may not be appropriate for drug removal in acute intoxications [25]. However, the lower blood flow rates and longer treatment times of continuous modalities may be desirable for vulnerable, hemodynamically unstable, patients who are not candidates for conventional hemodialysis [7]. Unlike hemodialysis, CRRT can give effective clearances in hypotensive patients. If the clinical condition of the patient requires a low intensity treatment that will necessarily decrease diffusive clearance, slow extended dialysis (SLED) or continuous treatment times with additional convective clearance (CVVHF and CVVHDF) can likely provide adequate total drug clearance [24]. 

Renal replacement therapies (RRTs) like hemodialysis, peritoneal dialysis, and other related treatments have been available for decades, but have not resulted in dramatic improvements in patient outcomes. RRT can help patient management by normalizing blood electrolyte values, augmenting waste product removal, and maintaining fluid balance. Despite the supportive care that RRT offers, development of ARF is frequently a catastrophic event. 

Renal replacement therapies are the most common nonpharma-cologic treatment that patients with ARF receive. Absolute indications for starting RRT in an ARF patient do not exist, but some general guidelines for therapy initiation do exist (Table 42-6). Renal replacement therapies come in two different forms, intermittent therapies like hemodialysis, and continuous RRTs like continuous hemofiltration or peritoneal dialysis. A more detailed explanation of these therapies appears in Chap. 45. The choice of whether continuous therapies or intermittent RRTs are used is a matter of debate and is usually determined by physician preference and the resources available at the hospital. 

Veltri MA, Neu AM, Fivush BA, et al. Drug dosing during intermittent hemodialysis and continuous renal replacement therapy special considerations in pediatric patients. Paediatr Drugs 2004 6 45-65. 

End-stage renal disease (ESRD) patients who present with severe hyperkalemia, or with cardiac manifestations of hyperkalemia, should undergo immediate hemodialysis. Dialysis is the most rapid means of lowering potassium compared to bicarbonate, epinephrine, or insulin plus glucose therapy. Other forms of dialysis can be performed (e.g., peritoneal dialysis or continuous renal replacement therapy), although they appear to be less effective means to acutely lower an elevated serum potassium. ... 

Indications for renal replacement therapy in the acute setting and for other disease processes are different from those for ESRD. A common mode of ESRD therapy in the outpatient setting is intermittent hemodialysis (IHD) where a patient receives intense treatment over the course of a few hours several times a week. Acute renal failure in the inpatient setting is often treated with continuous renal replacement therapy (CRRT), which is applied for the entire duration of the patient s clinical need and relies upon hemofiltration to a higher degree than IHD (Meyer, 2000). Other nonrenal indications for CRRT are based on the theoretical removal of inflammatory mediators or toxins and elimination of excess fluid (Schetz, 1999). These illnesses include sepsis and systemic inflammatory response syndrome, acute respiratory distress syndrome, congestive heart failure with volume overload, tumor lysis syndrome, crush injury, and genetic metabolic disturbances (Schetz, 1999). 

As of 1995, more than 30 different polymer blends were being used in the manufacture of membranes for hemodialysis and hemofiltration (Klinkmann and Vienken, 1995). The various membrane types used for renal replacement therapy can be divided into membranes derived from cellulose (83 percent of 1991 worldwide total) and from synthetic materials (the remaining 17 percent) (Klinkmann and Vienken, 1995). Synthetic membranes have been constructed from such materials as polyacrylonitrile (PAN), polysulfone, polyamide, polymethylmethacrylate, polycarbonate, and ethyl-vinylalchohol copolymer (Klinkmann and Vienken, 1995). In the United States, use of cellulosic materials for membrane construction predominates at around 95 percent of the total number of membranes used (Klinkmann and Vienken, 1995). 

Complications that occur during hemodialysis and hemofiltration can be divided into problems related to vascular access and those due to exposure of the blood to the exchange circuit Depending upon the method used, vascular access problems associated with renal replacement therapy are similar to those experienced in patients with vascular grafts or catheters and are covered in those respective sections. 

Advanced CKD may lead to end-stage renal failure that requires renal replacement therapy including hemodialysis, peritoneal dialysis and renal transplantation. 

Patients with less than 10% of normal kidney function require renal replacement therapy for removal of waste metabolites. In patients undergoing hemodialysis, the total clearance of a drug is equal to sum of the clearances due to nonrenal routes of elimination (C/rNu), residual renal function (OrRRp), and the dialyzer (CZrdiaiyzer) ... 

It is important to identify patients who may eventually require renal replacement therapy since adequate preparation can decrease morbidity and perhaps mortality. Early identification enables dialysis to be initiated at the optimal time with a functioning chronic access. The placement and adequate maturation of arteriovenous fistula (AVF) before the initiation of hemodialysis therapy requires timely patient education and counselling, selection of the preferred renal replacement modality, selection of an access type and location, and creation of the access at least several weeks to months in advance of its expected need. An early constructed AV fistula could also have a beneficial effect on the rapidity of worsening kidney failure. Reasons for this could be increased heart preload and consequently increased afterload or decreased peripheral resistance with increased renal perfusion. A simpler reason could be that patients after AV fistula construction become aware that situation is serious and they start to follow the therapy more accurately [11]. 

---