Certified Hemodialysis Nurse (CHN) Exam

The hemodialysis machine is the primary equipment used to perform dialysis treatments. Understanding machine components, functions, and maintenance requirements is essential for safe and effective treatment delivery.

The dialysis machine consists of the blood pump, dialysate delivery system, monitoring systems, and user interface. The blood pump moves blood from the patient through the dialyzer and back to the patient. The dialysate delivery system mixes, heats, and delivers dialysate to the dialyzer.

The extracorporeal blood circuit includes arterial and venous bloodlines, the dialyzer, pressure monitors, air detectors, and blood leak detectors. The arterial line carries blood from the patient to the dialyzer; the venous line returns blood to the patient.

The dialysate circuit includes the proportioning system, heating system, conductivity monitors, and flow controls. The proportioning system mixes concentrated dialysate with treated water to achieve the prescribed dialysate composition.

The dialyzer, or artificial kidney, contains thousands of hollow fibers made of semipermeable membrane material. Blood flows through the hollow fibers while dialysate flows around them, allowing waste removal and electrolyte exchange across the membrane.

Common membrane materials include cellulose-based, modified cellulose, and synthetic polymers. Synthetic membranes such as polysulfone, polyethersulfone, and polyamide offer improved biocompatibility and clearance characteristics compared to older cellulose membranes.

When the unit evaluates new equipment or supplies, it checks the product against current AAMI standards for hemodialysis systems, the manufacturer's validated instructions, safety alarms and fail-safes, staff training needs, and cost. A trial with defined evaluation criteria and staff feedback comes before unit-wide adoption.

Dialyzers are characterized by surface area, ultrafiltration coefficient (KUf), clearance rates, and membrane flux. High-flux dialyzers have larger pore sizes and remove middle molecules more effectively than low-flux dialyzers. Selection depends on patient size, treatment goals, and physician prescription.

High-efficiency dialysis uses large surface area dialyzers to maximize small solute clearance. High-flux dialysis uses membranes with increased permeability to middle molecules. Many facilities use high-flux dialyzers as standard practice.

The arteriovenous fistula (AVF) is created surgically by joining an artery to a vein. It needs time to mature, at least about 6 weeks and often 2 to 4 months, before cannulation. Once mature, an AVF has the lowest infection and thrombosis rates of any access. Current guidance chooses the access that fits each patient's life plan rather than a fistula-for-everyone rule.

The arteriovenous graft (AVG) uses synthetic tubing, usually polytetrafluoroethylene (PTFE), to connect an artery to a vein. Most grafts can be cannulated about 2 to 3 weeks after placement (some early-cannulation grafts within 24 to 72 hours), but grafts have higher rates of stenosis, thrombosis, and infection than fistulas.

Central venous catheters (CVCs) provide immediate vascular access for patients requiring urgent dialysis or those unable to maintain permanent access. Catheter types include non-tunneled catheters for short-term use and tunneled catheters for longer-term access. CVCs have the highest infection and complication rates.

Regular assessment of vascular access includes inspection for signs of infection, palpation for thrill, auscultation for bruit, and monitoring for adequate blood flow. Early detection of access problems enables timely intervention and preserves access function.

Fistula needles are available in various gauges, with 15-gauge and 16-gauge being most common for hemodialysis. Larger gauge numbers indicate smaller needle diameters. Needle selection depends on access maturity, blood flow requirements, and patient comfort.

Three cannulation techniques are used. Rope ladder rotates insertion sites along the whole length of the access. Area puncture repeatedly uses a small area and leads to aneurysm formation, so it is avoided. Buttonhole uses the same sites at the same angle, with blunt needles once a tunnel track has formed; it is used only in fistulas and requires strict scab removal and skin antisepsis because of a higher infection risk.

Skin antisepsis before cannulation reduces infection risk. Common antiseptic agents include chlorhexidine, povidone-iodine, and alcohol. Chlorhexidine-based preparations are preferred for their persistent antimicrobial activity.

Dialysis patients are exposed to large volumes of water during treatment, making water quality critical for patient safety. Contaminants in dialysis water can cause serious complications including hemolysis, sepsis, and chemical toxicity.

Pretreatment removes particles, chlorine, and chloramine from incoming water. Components include sediment filters, carbon tanks, and water softeners. Sediment filters remove particulate matter; carbon tanks remove chlorine and chloramine; water softeners remove calcium and magnesium.

Reverse osmosis (RO) removes dissolved contaminants by forcing water through semipermeable membranes. RO systems are the primary purification method for dialysis water. Monitoring parameters include percent rejection, conductivity, and flow rates.

Deionization removes remaining ionic contaminants through ion exchange resins. Some facilities use deionization as a polishing step after reverse osmosis. Regular regeneration or replacement of deionization tanks maintains effectiveness.

The water distribution system delivers purified water to dialysis machines. Distribution loops should be designed to minimize stagnant water and bacterial growth. Regular disinfection and biofilm prevention maintain water quality throughout the system.

Regular preventive maintenance ensures equipment reliability and patient safety. Maintenance schedules should follow manufacturer recommendations and regulatory requirements. Documentation of maintenance activities demonstrates compliance.

Staff perform daily checks before patient use, including verification of alarms, calibration confirmation, and visual inspection. Any abnormalities must be addressed before treatment initiation.

Dialysis machines require disinfection between patients to prevent cross-contamination. Disinfection methods include heat disinfection, chemical disinfection, or combination approaches. Complete rinsing after chemical disinfection prevents patient exposure to residual disinfectants.

Water quality monitoring includes testing for bacteria, endotoxin, and chemical contaminants. AAMI standards establish maximum allowable levels for dialysis water contaminants. Testing frequency depends on contaminant type and regulatory requirements.

Effective inventory management ensures adequate supplies while minimizing waste and storage costs. Par levels, reorder points, and usage tracking support efficient inventory control. Rotation of stock prevents expiration of supplies.

Biomedical equipment must be inventoried, maintained, and replaced according to established protocols. Equipment records should include purchase date, maintenance history, and repair documentation. End-of-life planning ensures timely equipment replacement.

Facilities must maintain emergency supplies for responding to patient emergencies and equipment failures. Emergency supplies include crash cart medications, backup equipment, and emergency power systems.

Incoming supplies should be inspected for integrity, expiration dates, and proper storage conditions. Defective or expired supplies must be removed from use and reported to suppliers. Lot numbers should be documented for traceability in case of product recalls.

Dialysis machines have independent alarms that detect unsafe conditions: arterial and venous line pressures, air in the venous line, blood leaks, dialysate conductivity, dialysate temperature, and ultrafiltration errors. An alarm stops the blood pump or bypasses dialysate as designed; staff must find and correct the cause, never silence or override it.

The blood leak detector identifies blood in the dialysate compartment, indicating dialyzer membrane rupture. Blood leak alarms require immediate treatment termination and dialyzer replacement. Patients should not receive blood that has contacted dialysate.

Air detectors identify air bubbles in the venous blood line that could cause air embolism. Venous clamps automatically engage when air is detected to prevent air entry into the patient. Staff must resolve air detection alarms before resuming blood flow.

Conductivity monitors verify proper dialysate composition by measuring electrical conductivity. Abnormal conductivity indicates incorrect proportioning and triggers alarms. Dialysate with improper composition can cause electrolyte imbalances or hemolysis.

Facilities must maintain logs documenting equipment maintenance, repairs, and calibrations. Logs provide evidence of compliance and support troubleshooting when problems occur. Electronic documentation systems facilitate record-keeping and retrieval.

Water quality testing results, dialyzer processing records, and equipment monitoring data should be documented and retained according to regulatory requirements. Regular review of quality assurance records identifies trends and improvement opportunities.