RENAL SYSTEM
D. Continuous Renal Replacement Therapy 1. Indications for CRRT include ARF with hemo-
dynamic instability, azotemia, severe electrolyte imbalance, hypervolemia, and symptomatic met- abolic abnormalities. CRRT may also be initiated in patients who would otherwise not be able to receive adequate nutrition owing to fluid restriction.
CRRT is appropriate for hemodynamically unstable patients who are unable to tolerate hemodialysis and patients who are not candidates for PD. Other indications include sepsis for removal of inflamma- tory cytokines and those patients with acute renal failure in conjuction with brain injury and cerebral edema to avoid large fluctuations in cerebral perfu- sion pressure (Garzotto, Zanella, & Ronco, 2014).
2. Process
a. CRRT uses a double-lumen venous cath- eter or two single-lumen venous catheters. It offers a highly efficient circuit that is driven by
a roller-head pump and is the preferred method of renal replacement therapy for the hemody- namically unstable patient in many neonatal and pediatric intensive care units (PICUs) because it minimizes large shifts in metabolic and fluid sta- tus. A number of different pumps are commercially available for hemofiltration, but they all work in a similar fashion. A roller-head pump drives the blood through the hemofilter, and one or more other roller-head pumps control the ultrafiltration rate, replacement fluid, and dialysis rate. Several methods of CRRT can be used to accomplish the goal of fluid or solute removal. The method used is dictated by the patient’s condition as well as the institutional policies and preferences.
b. Continuous venovenous hemofiltration (CVVH) uses the principles of ultrafiltration and convec- tion to allow for fluid and solute removal. It is the most widely used method of CRRT (Lerma, 2009). Blood is drawn from one port of a venous catheter, propelled through a hemofilter using a roller-head pump, and returned to the other port of the venous catheter. Ultrafiltration and convection are accomplished as the blood moves through the semipermeable membrane of the hemofilter. The ultrafiltration rate is controlled by programming the hemofiltration pump’s fluid controller for an ordered amount each hour.
To obtain adequate clearance, large volumes of ultrafiltrate are removed and replacement fluid is infused to maintain the desired fluid balance.
The replacement rate is also controlled via the hemofiltration pump’s fluid-control module.
c. Continuous venovenous hemofiltration with dial- ysis (CVVH-D) is similar to CVVH but uses a dif- fusion gradient instead of convection to provide clearance. The process of blood removal is the same as with CVVH, but a dialysate solution is infused into the outside compartment of the hemofilter, countercurrent to the blood, to provide diffusive transport of solutes and water. As with CVVH, the ultrafiltration rate and the dialysate rate are both controlled by the hemofiltration pump’s fluid con- troller or additional infusion pumps. Little or no replacement fluid is used.
d. Continuous venovenous hemodiafiltration (CVVH-DF) uses the principles of ultrafiltra- tion, convection, and diffusion to remove fluid and solutes. The process is similar to CVVH-D, but it also utilizes high ultrafiltration rates with replacement fluid, as in CVVH. This method of CRRT may be used for patients in whom one of the other methods is not providing adequate clearance (Sutherland & Alexander, 2012).
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e. Slow continuous ultrafiltration (SCUF) may be used to remove a set amount of fluid from a patient each hour. This method of CRRT utilizes the principles of ultrafiltration and convection.
It is effective for fluid removal, but it does not utilize a high ultrafiltration rate or replacement fluid and therefore will not provide adequate clearance of solutes.
3. Methods for Measuring Filtration Capability or Performance of the Filter and Circuit
a. Clearance is removal of solutes from the plasma and is dependent on the filter’s capabil- ity for removing individual molecules, the size of the solute, the solute’s protein-binding capac- ity, and the rate of blood flow through the hemo- filter. Clearance for a particular molecule can be expressed by the ultrafiltrate-to-plasma ratio, known as the sieving coefficient
x x
x x
Sieving coefficient =
Concentration of in ultrafiltrate UF Concentration of in plasma plasma
1 = 100% Clearance
( )
( ) ( )
b. Another indicator of the efficiency of the system is the FF. The FF is reflective of the frac- tion of plasma water being removed by ultrafil- tration. Optimum FF is a percentage that is high enough to provide adequate solute and fluid removal needs but not so high that blood viscos- ity and increased oncotic pressure impact filter performance.
Filtration fraction % =
QF Ultrafiltration rate mL/min QP Plasma flow rate at the inlet mL/min
( )
( )
( ) ( ) ( )
4. Nursing implications for the hemodynamically unstable infant or child during CRRT
a. Limited vascular access sites and catheter diam- eter often limit blood pump speed and therefore impact circuit efficiency and solute clearance.
The challenges of vascular access are greatest in infants and small children because of the small size of the vessels in relation to the catheter.
Access may also be difficult in patients with an underlying coagulopathy because of concerns of bleeding during placement of these large- bore catheters. It may be necessary to attempt to correct the coagulopathy before access place- ment. Optimal placement in an infant or small
child would be an internal jugular or subclavian catheter with the tip at the junction of the right atrium, thus preventing “pulling of the ves- sel wall” and subsequent obstruction to flow.
A femoral catheter may be used, however, and the pump speed is adjusted accordingly. As with all indwelling lines, infection is also a risk factor.
b. Thermoregulation is a significant issue with infants and small children. Depending on the extracorporeal volume of the circuit compared with the child’s size, a significant amount of heat may be lost via the circuit. Fluid- and blood- warmer systems or external heat sources should be used to maintain normothermia. Many of the hemofiltration pumps now available have a blood- or fluid-warming device incorporated in them. Small-volume extracorporeal tubing sets are ideal if they are available for the pump that is being used.
c. Anticoagulation is often necessary to main- tain patency of the circuit. Heparinization or citrate regional anticoagulation are the two most commonly used methods of anticoagulation.
i. Heparinization involves infusing a hep- arin solution into the prefilter side of the cir- cuit with the goal of maintaining activated clotting times (ACTs) at 1.5 to two times normal. In the absence of a coagulopa- thy, a heparin bolus is given to the patient before initiation of therapy. In the presence of coagulopathy, heparin administration may be contraindicated, and the life span of the circuit may be decreased (Sutherland &
Alexander, 2012). Heparinization is an effec- tive method of anticoagulating the circuit, but precautions must be taken as the patient is also systemically anticoagulated.
ii. Citrate regional anticoagulation is gain- ing popularity as the circuit may be antico- agulated without systemic effects. Sodium citrate is infused via the “arterial limb” of the circuit to chelate calcium and prevent clotting. The goal of the therapy is to keep the ionized calcium level of the circuit below 0.5 mmol/L. A calcium infusion is given to the patient via a separate line or via the distal “venous return limb” to maintain the patient’s ionized calcium in the normal range (1.1–1.3 mmol/L). Citrate anticoagulation has certain inherent concerns in the pediat- ric population, the most common of which are the development of a metabolic alkalosis, hypocalcemia, hyperglycemia, and “citrate lock.” These problems are seen because
the blood flow rate per weight of the pedi- atric patient is greater than in adults; thus the citrate load is often significantly higher.
Citrate lock is a phenomenon in which the patient’s total calcium level rises as the ion- ized calcium level decreases. This is the result of infusing the citrate solution at a rate that exceeds the hepatic metabolism and CRRT clearance of citrate. Stopping the citrate infu- sion for a number of hours and restarting at a lower rate should remedy the situation.
Metabolic alkalosis results from the break- down of citrate to bicarbonate at a rate greater than it can be cleared. Hypocalcemia results from inadequate repletion of calcium to the patient and should be treated by increasing the calcium infusion. Hyperglycemia may result from the large infusion of citrate, which is in a glucose-based solution, or from the high flow of glucose containing dialysate solutions. Prompt recognition of these poten- tial complications can prevent untoward effects to the patient. Citrate regional anti- coagulation has generally been performed with diffusive clearance using a calcium-free dialysate solution to allow for the removal of the large citrate load; however, recent information in the literature suggests that ultrafiltration and convection alone might be adequate to clear citrate by-products (Davis, Neumayr, Geile, Doctor, & Hmeil, 2014).
iii. The benefit of routine flushes of normal saline, lactated Ringer’s, or filter replace- ment solution to maintain circuit patency and decrease clotting is debatable.
d. Hemodynamic stability. The CRRT circuit volume should be considered in relationship to the child’s circulating blood volume. In small infants and children, it may be necessary to prime the circuit with whole blood or another colloid substance. If the circuit is primed with a blood product preserved with citrate, assess the serum calcium level before CRRT initiation and treat if necessary to decrease the risk of hypo- tension secondary to hypocalcemia. Because of drug clearance by the hemofilter, it may be nec- essary to titrate the infusion of vasoactive agents just before or in the first few minutes after initi- ation of CRRT. If the preceding precautions are taken, the incidence of hemodynamic instability during initiation of CRRT is rare.
e. Fluid balance. Fluid management is an integral component of management for the critically ill patient. In the presence of shock and multiorgan
failure, replacment therapies are essential. Fluid overload may be an important independent factor associated with increased morbidity and mortal- ity as it results in vital organ dysfunction and isch- emia, especially if fluid overload is greater than 10% to 20% of baseline. The goal of fluid manage- ment would therefore be to remove excess fluid while maintaining cardiac output, hemodynamic stability, and optimizing pharmacological and nutritional support. Setting targets is vital in fluid management with CRRT (Lerma, 2009). It may be necessary to begin at an ordered zero fluid balance and slowly adjust the fluid removal as tolerated in order to minimize over- or underestimation of the patient’s need, which may result in worsen- ing volume overload or hypotension from intra- vascular volume depletion. Strict fluid intake and output are recorded hourly. In a child receiving multiple blood products or fluid boluses, it is important to determine what is to be included in the formula as fluid to be removed. The formula for determining the hourly fluid balance is:
(Total intake) – (Total output) ± (Desired hourly change) = Fluid to be removed
f. All pumps now available have slightly dif- ferent calculations for fluid removal and manu- facturer recommendations should be followed.
Example:
(Total intake) – (Total output) – (Desired hourly change) = Fluid to be removed
(100) – (10) – (–20) = 110mL to be removed g. The extracorporeal circuit. Plasma-free hemo- globin levels may be measured before initiation of CRRT and daily to monitor RBC destruction.
Elevated plasma-free hemoglobin levels indicate the necessity to change the circuit.
h. CRRT used in conjuction with extracorporeal membrane oxygenation (ECMO). Renal failure in patients on ECMO for respiratory or car- diac support is a challenge. CRRT has been used through the ECMO circuit to mediate the fluid overload and renal compromise that often occurs with this therapy. CRRT is attached to the ECMO circuit before the oxygenator, often at the venous bladder. This reduces the risk of air embolism reaching the patient. Anticoagulation of the ECMO circuit mitigates the need for anticoagultion in the CRRT circuit. This is a developing area of research in a very vulner- able population and further study is needed (Askenazi et al., 2012).
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RENAL TRANSPLANTATION A. Criteria for Transplantation
1. All candidates must have ESRD or rapidly approaching ESRD. Preemptive transplants, that is, those performed before dialysis is needed, have bet- ter long-term outcomes. CKD is stratified into five catagories, based on GFR. Stage 3b has a GFR 30 to 44 and is classified as moderate to severe kidney failure. Stage 4 has a GFR of 15 to 29 with severely decreased function, and Stage 5 has a GFR of <15 and kidney failure (Inker et al., 2014).
2. Common causes of ESRD requiring transplanta- tion include congenital renal disorder, glomerulone- phritis, and ESRD secondary to other disease states or treatment.
3. Pretransplantation Evaluation Criteria. Transplant is considered at the time of ESRD diagnosis. Urologic issues should be addressed before transplantation, and the patient should be free of any major multi- system complications (malignancy, advanced cardio- pulmonary disease) and active infection. Nutritional status should be optimized, and psychiatric and socioeconomic parameters should be viewed as appropriate (Chaudhuri, Gallo, & Grimm, 2015).
4. Donor considerations include a full health history of the donor with emphasis on diabetes and hypertension; drug use; HIV exposure; malignancies;
evaluation of infectious markers, including urine culture and urinalysis; renal mass size; human leu- kocyte antigen (HLA) matching; dose of vasopres- sors; and time of resuscitation if donor is deceased.
Exclusion criteria include intrinsic renal disease or parenchymal trauma (Chaudhuri et al., 2015).
5. Postoperative Management
a. Minimize the risk for infection by observ- ing strict handwashing and other institutional infection-control guidelines and by using strict aseptic techniques with all dressing changes.
b. Maintain pulmonary toilet.
c. Closely monitor urinary output and observe for signs and symptoms of infection.
d. Monitor and maintain metabolic and electro- lyte balance (BUN, creatinine, ionized calcium, phosphorus [low], magnesium, glucose, serum albumin [low if recurrence of disease], urinary protein–creatinine ratio).
e. Maintain comfort for the patient, and admin- ister medications as needed to decrease pain or anxiety.
f. Administer the daily immunosuppressive med- ication regimen as ordered, and monitor serum drug levels as necessary.
g. Potential complications include ATN, rejec- tion, infection, obstruction to urinary flow, hypovolemia, renal artery stenosis, renal vein thrombosis, and ureteral leaks.
h. Intermediate-term follow-up consists of mon- itoring for hyperparathyroid hormone and hypercalcemia. Parathyroid may still be “revved up” from pretransplant and parathyroid resec- tion may be required.
i. Long-term complications. Posttransplant lymphoproliferative disease and infections (par- ticularly Epstein–Barr virus [EBV], cytomegalo- virus [CMV], herpes simplex virus [HSV], BK virus, varicella, and Pneumocystis carinii pneu- monia [PCP]).
j. Outcomes. Long-term outcomes are better with living donated kidneys than with cadaveric kidneys. Kidney transplants in general have a 90% to 95% success rate at 5 years. However, graft-failure rates increase starting at 13 years of age and peak between 17 and 24 years of age.
Two factors that effect graft loss at this age are transition to adult care and noncompliance with medication regimens (Bertram et al., 2016).
RENAL TRAUMA