|Year : 2008 | Volume
| Issue : 6 | Page : 753
Renal Replacement Therapy
Editor, IJA, India
|Date of Web Publication||19-Mar-2010|
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Bajaj P. Renal Replacement Therapy. Indian J Anaesth 2008;52:753
The general term renal replacement therapy (RRT) is used to describe all of the currently available approaches to “artificial” mechanical support of renal function,. RRT includes traditional intermittent hemodialysis (IHD), peritoneal dialysis (PD) and a variety of other intermittent and continuous therapies. Most anaesthesiologists are familiar with intermittent hemodialysis and peritoneal dialysis and the implications of both to perioperative care.
A variety of other therapies are available that provide continuous therapy to support the patient with renal failure. The term CRRT refers to a number of continuous renal replacement therapies used to optimize fluid and solute management,. In general these therapies provide better control of intravascular volume, electrolyte balance, and uremia depending on the characteristics of the renal replacement therapy.
CRRT refers to any mechanical approach to providing continuous solute or fluid removal. Although the specific method of delivering the therapy varies, all forms of CRRT include an extracorporeal circuit with a hemofilter and semipermeable membrane connected to the patient via a catheter in either the arterial or venous circuit. Fluid removal is determined by the hydrostatic pressure gradient across the hemofilter. Large volumes of fluid can be removed using this approach. Fluid balance is controlled by providing replacement fluid through the system; electrolytes and acid base balance are controlled by the electrolyte and bicarbonate concentration in the replacement fluid.
CRRT is used most commonly to manage the critically ill patient with acute renal failure. The therapy can be very helpful in addressing the uremia associated with renal failure but can also be helpful in managing hyperkalemia, controlling metabolic acidosis in the patient with either a renal tubular acidosis or lactic acidosis, and in optimizing fluid balance,. CRRT also has a role in the management of patients with other clinical problems whether associated with renal failure or not. For example, it has been advocated as a therapy for the patient with pulmonary edema or congestive heart failure to facilitate acute fluid management in the septic patient and the patient with multisystem failure because of its ability to optimize cytokine clearance and in patients with severe respiratory failure for whom mechanical ventilatory support alone does not provide optimum gas exchange and control acid base balance. CRRT has also been used in patients with cerebral edema to optimize overall fluid balance without compromising cerebral blood flow.
The anaesthesiologist must be aware of the implications of CRRT on anaesthetic and perioperative management. For the patient who is receiving CRRT preoperatively, the anaesthetic plan will be affected by the therapy. When CRRT is contemplated for use in the operating room, resources must be available to ensure that the therapy is safely administered. Finally, the transition of the patient receiving CRRT to and from the operating room requires more attention to the logistics of the transfer than is usually required.
For the patient who is receiving CRRT, the preoperative assessment has some specific elements that must be ensured. First, the anaesthesiologist should understand why the patient is receiving CRRT. Although the list of indications is lengthy, the primary concern for the anaesthesiologist is the patient's fluid, electrolyte, and acid base balance. Most, but not all, of the patients receiving CRRT will have multi-system failure. Many are receiving mechanical ventilatory support, are hemodynamically unstable, and many require vasopressor or inotropic therapy. In addition to the usual considerations for the management of the critically ill patient, the preoperative assessment of the patient receiving CRRT should clarify the indications for the therapy, the goals, and whether the goals have been met.
In addition to assessing the metabolic implications of the CRRT, the evaluation should include an evaluation of the coagulation status of the patient, in part because of the implications of renal failure on coagulation (e.g., platelet function) and whether the patient is receiving anticoagulants through the CRRT circuit to prevent filter and circuit clotting,. Although, when heparin is used as an anticoagulant, it is generally administered before the filter to minimize the systemic effects, the impact on clotting can be unpredictable. For some patients, alternative anticoagulants are used, including citrate. For every patient receiving CRRT, coagulation parameters must be carefully monitored.
Finally, the patient's temperature trend must be interpreted with caution. Considerable heat is lost through the extensive extracorporeal circuit. As a result, most patients receiving CRRT are hypothermic; some require rewarming with a warming blanket. It is rare that a patient receiving CRRT has a fever, so if the temperature is normal (or elevated), the likelihood of infection is high and may require evaluation before elective surgery.
Although CRRT has become a common mode of therapy for critically ill patients, the therapy will be discontinued before transfer to the operating room for most of these patients who require surgery. To facilitate the transition from CRRT requires an understanding of the process and careful planning regarding the management of the patient once the therapy has been stopped. The actual discontinuation of CRRT is straightforward. The CRRT pump and filter are separated from the access catheter and the circuit discarded. Once the system is disconnected, the catheter should be flushed with heparinized solution before capping it to ensure that it remains patent unless heparin is contraindicated. Before using the catheter again, the heparin should be aspirated from it.
When CRRT is discontinued, either for transport or for the duration of the surgical procedures, the anesthesiologist must have a plan for managing both fluid balance and electrolytes. To determine how best to manage the patient, the anesthesiologist should review the CRRT orders to clarify the fluid goals for the therapy, the amount of replacement fluid provided each hour and to clarify the electrolytes and bicarbonate that has been included in the replacement fluid. Based on the review, a plan for managing fluids, electrolytes and acid-base balance can be developed for the intraoperative period.
Although CRRT systems have become much easier to use, the technology is not familiar to most anesthesiologists. If the CRRT is to be initiated or continued intraoperatively, therefore, the anaesthesiologist either must be familiar with the equipment and have the ability to “troubleshoot” any problems that arise or must have resources available to support the system. In some institutions CRRT will be managed by an intensive care or dialysis nurse who is physically present in the OR for the duration of the procedure. In other cases someone familiar with the equipment and therapy will be available on call to provide advice and assistance to the anaesthesiologist.
One of the primary advantages of using CRRT during surgery is related to overall fluid management. Although the long-term benefits have not been objectively demonstrated, CRRT does minimize extravascular fluid accumulation and edema. Most patients who receive CRRT during surgery are less edematous and have smaller fluid shifts after major surgical procedures than do patients who receive conventional fluid management.
One additional feature of the system warrants additional comment. If CRRT is used during the surgical procedure, the cannula used for the therapy must be easily accessible to the anaesthesiologist. Although femoral catheters are occasionally used for CRRT, it is more common to use internal jugular catheters because they provide good flow characteristics and are on site in the operating room. Jugular catheters are easily monitored for evidence of kinking and malpositioning, so the risk of circuit clotting can be minimized.
When CRRT is used in the postoperative period, the clinicians managing the therapy in the postoperative period must be cognizant of the intraoperative course6. The flows and replacement fluid composition must be carefully titrated to account for intraoperative fluid shifts or blood loss and changes in intravascular volume. The patient must be closely monitored for evidence of postoperative coagulopathy or electrolyte abnormalities.
CRRT should also be considered as a therapeutic option in the postoperative period for the patient with progressive renal dysfunction or fluid overload that compromises gas exchange or pulmonary function.
Renal replacement therapies include a number of treatments to support the patient with renal failure or fluid and electrolyte abnormalities. Although most anaesthesiologists are familiar with intermittent renal replacement therapies, such as intermittent hemodialysis and peritoneal dialysis, the availability of CRRT now offers another approach to perioperative management that has significant potential clinical value. As a result, although CRRT is now most commonly used in the management of the unstable patient in the ICU, anaesthesiologists should understand the clinical indications for CRRT, the approaches that are available, and the potential value of the technique in optimizing perioperative care.
| References|| |
|1.||Bellomo R, Ronco C, Mehta R. Nomenclature for continuous renal replacement therapies. Am J Kidney Dis 1996;28:S2-S7. |
|2.||Teehan GS, Liangos O, Jaber BL. Update on dialytic management of acute renal failure. J. Intensive Care Med 2003;18:130-8. |
|3.||Kellum JA, Angus DC, Jonhson JP, et al. Continuous versus intermittent renal replacement therapy : a meta - analysis. Intensive Care Med 2002;28:29-37. |
|4.||Ronco C, Bellomo R, Ricci Z. Continuous renal replacement therapy in critically ill patients. Nephrol Dial Transplant 2001;16:67-72. [PUBMED] [FULLTEXT] |
|5.||van Bommel EFH, Leunissen KML, Weimar W. Continuous renal replacement therapy for critically ill patients : an update. J Intensive Care Med 1994;9:265-80. |
|6.||Petroni K, Cohen NH. Continuous renal replacement therapy : anesthetic implications. Anesth Analg 2002; 94:1288-97. |
|7.||Morabito S, Guzzo I, Solazzo A, et al. Continuous renal replacement therapies : anticoagulation in the critically ill at high risk of bleeding. J Nephrology 2003;16:566-71. |
|8.||Tan HK, Baldwin I, Bellomo R. Continuous veno-venous hemofiltration without anticoagulation in high risk patients. Int Care Med 2000;26:1652-7. |
|9.||Palsson R, Niles JL, Regional citrate anticoagulation in contiuous venovenous hemofiltration in critically ill patients with a high risk of bleeding. Kidney Int 1999;55:1991-7. |