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Hemodialysis



AUTHOR: THIERRY. FRANCEY




SYNONYMS


Blood purification, renal replacement therapy



OVERVIEW AND GOALS


Hemodialysis is a blood purification procedure used for correcting azotemia and normalizing the fluid, electrolyte, and acid-base imbalances resulting from kidney disease. In this procedure, the animal’s anticoagulated blood circulates through an artificial kidney (hemodialyzer) and is exposed to an electrolyte solution (dialysate) across a semipermeable membrane. Metabolic waste products, exogenous toxins, and excess water are removed from the bloodstream by diffusion (concentration gradient) and convection (hydrostatic gradient) through the dialysis membrane. The combination of these two basic blood purification principles define different treatment modalities, including hemodialysis (HD: diffusion), hemofiltration (HF: convection), and hemodiafiltration (HDF: combined diffusion and convection).


In acute uremia, hemodialysis restores metabolic stability and is provided for a finite period of time to allow animals to use their potential of recovery from acute kidney injury. Hemodialysis itself has no direct effect on renal recovery. Although hemodialysis can also be used for indefinite renal replacement in end-stage chronic kidney disease, chronic kidney disease is rarely a true indication because of the associated costs and the limited availability.



INDICATIONS



• Acute uremia: worsening azotemia and clinical signs of uremia despite adequate conventional therapy, anuria, fluid overload, severe refractory hyperkalemia, severe azotemia (blood urea nitrogen [BUN] > 100 mg/dL, creatinine > 10 mg/dL)

• Chronic kidney disease: acute decompensation, preanesthetic stabilization, pretransplant conditioning, chronic renal replacement

• Miscellaneous: fluid overload, acute poisoning, drug overdose (small-molecular-weight toxins or drugs with minimal protein binding capacity)


CONTRAINDICATIONS



• Small animal size (<2 kg) (relative contraindication)

• Severe pulmonary or cerebral hemorrhage (due to required anticoagulation)

• Cardiovascular instability and hypovolemia (should be corrected first)


EQUIPMENT, ANESTHESIA


Sedation/anesthesia: required for the placement of a vascular access but not for the hemodialysis procedure itself.



• Vascular access: short-term, temporary large-bore double-lumen catheter (7 Fr for cats and small dogs; up to 14 Fr for larger dogs); long-term, permanent double-lumen or twin-lumen catheter with subcutaneous tunneling; typically placed surgically in the external jugular vein

• Hemodialysis delivery system (hemodialysis machine)

• Disposable extracorporeal circuit and dialyzer (artificial kidney)

• Water purification system: particulate filter, carbon sorbent, water softener, deionization bed, and reverse osmosis

• Dialysate concentrates

• Replacement fluids for convective therapies (HF, HDF): on-line preparation or specific hemofiltration replacement fluids

• Monitoring equipment: blood pressure (BP) monitor, coagulation timer (e.g., activated clotting time [ACT]), in-line blood volume and oxygen saturation monitor (e.g., Critline), electrocardiogram (ECG)

• Emergency cart: cardiopulmonary resuscitation drugs, oxygen, endotracheal tube

• Protamine (for excessive heparinization and active hemorrhage)

• Physical restraint (i.e., harness and table straps)


ANTICIPATED TIME



• Acute treatments: depending on the degree of azotemia and the selected therapeutic schedule, initial treatments can be provided as intermittent (treatment of 1-8 h) or continuous therapy; treatments are provided daily until normalization of azotemia; a schedule of three times a week is then maintained until recovery of renal function.

• Chronic treatments: 4-5 hours, three times a week

• Every treatment necessitates 2 additional hours for setup, animal preparation, and completion.


PREPARATION: IMPORTANT CHECKPOINTS



• Initial database for animal evaluation and formulation of the dialysis prescription: body weight, physical exam, body temperature, heart rate, BP, hematocrit/total solids, serum chemistry profile (especially BUN, creatinine, electrolytes, Tco2 [Hco3−]), coagulation time (e.g., ACT)

• Adequacy of vascular access: should deliver between 15 and 50 mL/min in cats and very small dogs and 200-500 mL/min in large-breed dogs

• Preparation of the dialysis system: alarm testing, priming and refreshing of the extracorporeal circuit

• Dialysis prescription: type and size of dialyzer and extracorporeal circuit, total volume of blood to be processed, duration of the treatment, ultrafiltration (fluid removal), dialysate composition and profiling (Na+, K+, bicarbonate, additives), dialysate flow rate and temperature, anticoagulation (type, prime, infusion rate), type of fluid used to prime the extracorporeal circuit (crystalloid, colloid, blood), and special procedures (e.g., single-needle operation, bypass time)


POSSIBLE COMPLICATIONS AND COMMON ERRORS TO AVOID



• Intradialytic complications: hemorrhage, hypotension, vomiting (hypovolemia, dialyzer reaction), dialysis disequilibrium (osmotic fluid shift into the intracellular compartment due to rapid correction of the azotemia; cellular edema can progress to cerebral edema and death), malfunction of vascular access, clotting of the extracorporeal circulation.

• Interdialytic complications: hemorrhage, delayed dialysis disequilibrium, catheter complications (thrombosis, vascular stenosis, infection, chylothorax)

• Other complications: related to severe uremia (i.e., uremic pneumonitis, encephalopathy, ulcers), its treatment (i.e., fluid overload, drug toxicity), or to the underlying etiology precipitating the renal failure (i.e., sepsis, hypovolemic shock)


PROCEDURE


Establishment of vascular access:


• A temporary or permanent dialysis catheter is placed aseptically in the external jugular vein, with the tip reaching the cranial vena cava or the right atrium. Permanent catheter placement requires general anesthesia for venotomy and subcutaneous tunneling. Proper placement is confirmed by adequate blood flow and thoracic radiographs. The dialysis catheter is strictly dedicated to dialysis therapy, and it is never used for other indications. It is prepared and handled aseptically for each use.

Anticoagulation:


• Animals require anticoagulation for extracorporeal circulation, typically with unfractionated heparin (initial bolus of 50 U/kg IV, followed by a constant rate infusion [CRI] of 50 IU/kg/h). Target: doubling of coagulation time (e.g., ACT 160-190 seconds).

• Alternative protocols have been established for animals with hemorrhagic risk: regional anticoagulation with citrate, special filters with anticoagulant membrane, and other modifications to provide low-heparin or heparin-free therapy.

Initiation of dialysis therapy:


• The dialysis machine is equipped with appropriate disposables (extracorporeal circuit, hemodialyzer), and its function is tested according to the manufacturer’s protocols. Animals are equipped with a harness and strapped to the table to loosely restrain their activity.

• The catheter is connected to the extracorporeal circuit using aseptic techniques, and the extension lines are secured to the animal’s body to avoid accidental catheter removal. The extracorporeal circulation is established under close monitoring of cardiovascular and respiratory status, and it is progressively increased to reach the prescribed blood flow.

Monitoring:


• Cardiovascular parameters (heart rate, BP, venous oxygen saturation, relative blood volume change), general condition (mentation, pupillary light reflexes), anticoagulation (ACT), and machine function (extracorporeal blood flow, dialyzer clearance) are monitored and recorded every 15-30 minutes for the duration of the treatment.

• Initial dialysis treatments commonly necessitate additional monitoring, including ECG and pulse oximetry.
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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on H

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