Dialysis Machine: How It Works

The dialysis machine moves your blood through a filter (dialyzer) and returns it cleaned. It also pulls extra fluid (ultrafiltration) at a controlled rate. Staff program the settings; your job is to report how you feel.

Quick tour of the system

• Blood circuit: blood leaves your access through an arterial line, passes a pump and heparin line, flows through the dialyzer, then returns via a venous line.
• Dialyzer (“artificial kidney”): a bundle of tiny fibers. Waste and water cross the fiber walls into dialysate; blood cells and proteins stay in.
• Dialysate circuit: water + concentrates (acid and bicarbonate) mixed by the machine; temperature and conductivity are monitored for safety.
• Ultrafiltration (UF): the machine sets how much fluid to remove in total and per hour.
• Monitors & safety: venous/arterial pressure, air detector and clamp, blood-leak sensor, temperature, conductivity, and transmembrane pressure (TMP).

What you’ll see on the screen

• BFR (blood-flow rate): how fast blood moves through the circuit (mL/min).
• Venous / Arterial pressures: reflect needle position, needle size, and line/kink issues.
• UF goal & rate: total fluid to remove and how fast it’s coming off.
• TMP: pressure across the dialyzer; rising numbers can signal clotting or high resistance.
• Temp & conductivity: dialysate temperature and mix; the machine alarms if out of range.

Common alarms (what they mean)

• Venous pressure high/low: kinked line, needle issue, or patient position. Stay still and call staff.
• Arterial pressure high/low: needle angle, access position, or excessive suction. Call staff before moving.
• Air detector / venous clamp: safety triggered; machine stops blood pump and clamps line. Don’t panic—wait for staff.
• Blood-leak detector: possible dialyzer membrane issue; staff will test the effluent and likely change the circuit.
• Conductivity/temperature: dialysate mix or heat out of range; staff pause and correct.
• TMP high: dialyzer resistance climbing—may need rinse, slower BFR, or circuit change.

Water treatment (behind the scenes)

The center’s water system (reverse osmosis, carbon tanks, filters) prepares ultra-pure water for dialysate. Machines won’t run if tests fail—this is why start times can occasionally be delayed.

Safety basics

• Confirm your name/DOB, prescription, and access arm each run.
• Keep the access arm still and visible; avoid leaning on needles or lines.
• Tell staff fast: pain at the needle, swelling, numb fingers, dizziness, chest pressure, cramps, chills, or new cough.
• Hold steady pressure after needles come out; don’t peek. Report bleeding that won’t stop.

Comfort & practical tips

• Wear sleeves that roll up; bring layers—rooms can be cool.
• Gentle ankle/calf movements reduce cramps (ask what’s OK for your access).
• Plan a quiet post-treatment window for a snack, hydration (per plan), and rest.

When to call between treatments

• Call the clinic now: fever or chills, new redness/pus at access, swelling of the arm/hand, shortness of breath, chest pain, or loss of the fistula/graft thrill.
• ER/911: severe trouble breathing, chest pain that doesn’t ease, confusion, or you pass out.

Educational only. Your dialysis team will tailor machine settings and safety steps to you.