Haemodialysis

01Purpose and principlesWhat the treatment does and how it fits into care.

During haemodialysis, a pump draws blood through an extracorporeal circuit and thousands of semipermeable dialyser fibres. Solutes such as urea and potassium diffuse into dialysate, bicarbonate is delivered in the opposite direction and ultrafiltration removes prescribed fluid. Clearance depends on treatment duration, effective blood and dialysate flow, membrane characteristics, access performance and the gradient across the membrane; missed time cannot be fully recovered by simply increasing one setting.

Conventional in-centre treatment is often delivered three times weekly, whereas home programmes may be more frequent, longer or nocturnal. Frequency should never be inferred as universal because residual kidney function, haemodynamic tolerance, lifestyle, body size and local service models differ. Dialysis replaces only part of kidney function: endocrine, metabolic, dietary, vascular and medicine management continues between sessions.

Safe delivery rests on a trained team, reliable access, water-quality systems, machine alarms and repeated clinical assessment. The common immediate problems are hypotension, cramp, headache, nausea and access difficulty; rarer events include haemolysis, air embolism, dialyser reaction and severe disequilibrium. When a patient becomes unwell, stop assuming the machine is the cause and assess the whole ABCDE differential while securing the extracorporeal circuit.

Key points

Haemodialysis circulates blood through a dialyser: diffusion clears small solutes down concentration gradients, while transmembrane pressure produces ultrafiltration of water.
A functioning arteriovenous fistula is generally preferred for long-term access when appropriate; grafts and tunnelled central venous catheters have distinct advantages, maturation needs and infection risks.
The prescription is individual: treatment time, frequency, blood and dialysate flows, dialyser, dialysate composition, temperature, anticoagulation and ultrafiltration target are renal-specialist decisions.
Pre-dialysis weight minus target weight helps set fluid removal, but the target is a clinical estimate that must be revisited after illness, nutrition change or persistent hypertension and hypotension.
Intradialytic hypotension demands immediate assessment: stop or reduce ultrafiltration, position safely, check the circuit and evaluate bleeding, sepsis, arrhythmia, myocardial ischaemia and excessive target-weight reduction.
Fever or rigors during treatment is access infection or bloodstream infection until assessed; obtain cultures promptly and follow the local renal sepsis pathway without waiting for the session to end.
Never take blood pressure, insert a cannula or compress unnecessarily over a fistula arm; inspect and palpate the access before every use and confirm its continuous thrill.
Adequacy measures such as urea reduction ratio or Kt/V support quality review but cannot substitute for symptoms, nutrition, volume control, potassium and treatment attendance.
Sudden chest pain, dyspnoea, neurological change, collapse, visible circuit blood loss or loss of access bruit is an emergency requiring treatment cessation and senior renal or resuscitation support.

02Indications, selection and cautionsWho may benefit, who needs urgent treatment and important alternatives.

Expected treatment sequence

Identity and prescription checks, access assessment, baseline observations and weight precede connection, followed by continuous machine surveillance and post-treatment haemostasis and review.

Volume excess

Interdialytic weight gain, hypertension, oedema, raised JVP, crackles and breathlessness suggest that sodium and water balance exceeds current removal or residual urine.

Excessive removal

Cramps, yawning, nausea, dizziness and falling pressure during ultrafiltration can precede syncope and myocardial or cerebral hypoperfusion.

Access dysfunction

Difficult cannulation, low pump flow, high venous pressure, recirculation, prolonged needle-site bleeding or a changed thrill suggests stenosis or thrombosis.

Catheter infection

Exit-site inflammation, tunnel tenderness, fever or dialysis-associated rigors raises concern for local or catheter-related bloodstream infection.

Under-dialysis

Persistent nausea, pruritus, restless legs, cognitive slowing, poor appetite, hyperkalaemia or fluid overload may reflect inadequate delivered treatment, access recirculation or missed sessions.

Red flags requiring action

Unresponsiveness, absent breathing or pulselessness during dialysis requires the resuscitation algorithm, immediate circuit management by trained staff and early defibrillator use when indicated.
Visible blood loss from a disconnected needle or line can be rapidly fatal because the blood pump may continue; stop the pump, clamp the circuit and call for emergency help.
Acute chest pain, arrhythmia, focal neurology or severe dyspnoea requires urgent medical assessment rather than routine completion of dialysis.
Port-wine or unexpectedly dark circuit blood, chest or back pain and dyspnoea may indicate haemolysis; stop dialysis and do not return potentially haemolysed circuit blood.
Abrupt cough, hypoxaemia, chest pain or neurological change after circuit air is suspected requires immediate line clamping, emergency support and the unit air-embolism protocol.

03Assessment before treatmentTests and checks that guide safe selection.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Pre- and post-dialysis observationsFirst step
Why
Evaluate fluid removal, haemodynamic tolerance and departure safety during each treatment.
Interpretation and limitations
Compare weight and blood pressure with the current prescription and symptoms; a numerical target should be changed when clinical euvolaemia has shifted.
02
Access examination
Why
Detect infection, stenosis, aneurysmal change, steal and impending access failure before cannulation.
Interpretation and limitations
A continuous thrill and bruit are expected; a pulse-like access, localised high-pitched bruit, arm swelling or absent flow needs specialist access assessment.
03
Monthly or protocol blood profile
Why
Monitor potassium, bicarbonate, calcium, phosphate, albumin, haemoglobin and treatment-related complications.
Interpretation and limitations
Use trends and sampling timing; a pre-dialysis value reflects the interdialytic interval and should be interpreted with adherence, residual function and prescription.
04
Delivered dialysis adequacy
Why
Quantify urea clearance using the unit's validated urea reduction ratio or Kt/V method.
Interpretation and limitations
A low result prompts checks of treatment duration, access recirculation, flow and sampling technique; an acceptable number does not exclude poor volume or symptom control.
05
Blood cultures
Why
Identify bloodstream infection when fever, rigors or catheter inflammation occurs.
Interpretation and limitations
Take paired peripheral and dialysis-line cultures as locally specified before antibiotics when this does not cause unsafe delay, and document recent antimicrobial exposure.
06
ECG and urgent renal chemistry
Why
Assess arrhythmia, ischaemia and dangerous potassium disturbance in an acutely unwell patient.
Interpretation and limitations
Electrolytes may change rapidly around dialysis; relate the sample to session timing and treat ECG-toxic hyperkalaemia immediately.

04Treatment approachPreparation, options, escalation and aftercare.

01SESSIONRoutine haemodialysis treatmentFirst stepA patient arrives for a planned treatment and is clinically stable.

1Verify identity, prescription, allergies, interval events and medicines, then record weight, observations, symptoms and an access examination.
2EscalationAgree the ultrafiltration goal against current target weight and haemodynamic tolerance, escalating major weight or clinical discrepancies before connection.
3Cannulate or connect with aseptic technique, confirm circuit security and observe machine pressures, alarms, access sites and the patient throughout treatment.
4At completion, achieve haemostasis without occluding access flow, reassess weight and symptoms, and communicate prescription or follow-up changes.

02PRESSUREIntradialytic hypotensionBlood pressure falls with symptoms, reduced consciousness or poor perfusion during haemodialysis.

1Stop or reduce ultrafiltration, place the patient safely, call trained help and confirm that needles, lines and circuit remain connected without external blood loss.
2Assess ABCDE, rhythm, glucose, temperature and potential sepsis, bleeding, myocardial ischaemia or anaphylaxis rather than assuming simple volume removal.
3Give the locally specified small-volume saline intervention when clinically appropriate and reassess; avoid automatic large fluid loads in kidney failure.
4Review target weight, ultrafiltration rate, food intake, antihypertensive timing and dialysate settings with the renal prescriber before the next session.

03RIGORSFever during dialysisA patient develops fever, chills, rigors or unexplained hypotension during treatment.

1Assess for sepsis immediately, inspect catheter, fistula or graft and consider non-access sources including chest, urine, skin and dialysate contamination events.
2Obtain cultures through the unit pathway before antimicrobials if safe, while checking lactate and organ dysfunction as the clinical picture requires.
3Administer renal-adjusted empirical antibiotics according to local catheter or access infection guidance and involve nephrology and microbiology early.
4Decide whether the catheter can be retained, locked, exchanged or removed only with specialist source-control assessment and culture results.

04DELIVERYInadequate delivered dialysisAdequacy falls, symptoms persist or machine pressures suggest ineffective clearance.

1Confirm attendance, completed time, sampling method and prescription delivery before interpreting the adequacy calculation as biological failure.
2Examine access and investigate recirculation or stenosis when flows, pressures, bleeding time or physical findings are abnormal.
3Review body size, residual kidney function, diet, catabolism and the need for longer or more frequent treatment with the dialysis team.
4Track symptoms, potassium, phosphate, nutrition and fluid control after modification rather than judging success from urea clearance alone.

05Regimens, contraindications and interactionsTreatment details and the circumstances that modify them.

Prevent clotting of the extracorporeal circuit so prescribed blood flow and clearance can be delivered.

Circuit anticoagulation

Use the unit's unfractionated or low-molecular-weight heparin protocol, individualised to session length, access and bleeding risk.

Recent surgery, active bleeding, thrombocytopenia and suspected heparin-induced thrombocytopenia require a heparin-free or alternative specialist plan; accumulation differs between products.

Replace iron efficiently in dialysis-associated blood loss and support erythropoiesis-stimulating treatment where indicated.

Intravenous iron during haemodialysis

Give the renal-unit product-specific maintenance or repletion regimen after iron indices and infection context have been reviewed.

Observe for hypersensitivity and avoid automatic administration during active systemic infection; ferritin may rise with inflammation and should not be read as iron availability alone.

Reduce transfusion requirement and treat symptomatic renal anaemia after correctable iron deficiency and other causes are addressed.

Erythropoiesis-stimulating agent

Titrate the locally selected subcutaneous or intravenous preparation to haemoglobin trajectory under the renal anaemia protocol.

Rapid haemoglobin rise, uncontrolled hypertension, vascular-access thrombosis and excessive targets increase harm; dosing is not a single fixed dialysis prescription.

Reduce gastrointestinal phosphate absorption as part of CKD-mineral bone management in dialysis.

Phosphate binder

Take the individualised calcium-based or non-calcium binder dose with relevant meals, adjusted to dietary phosphate and serial results.

Pill burden, constipation, calcium balance and interactions undermine treatment; separate other medicines where the chosen product requires it and involve a renal dietitian.

06Complications, monitoring and follow-upAdverse effects, response and longer-term review.

Before and after each session, document weight, blood pressure, pulse, symptoms, access condition and whether the prescribed treatment was fully delivered.
Review home or interdialytic blood pressure when possible because readings in the dialysis unit alone incompletely represent cardiovascular load.
Trend potassium, bicarbonate, phosphate, calcium, haemoglobin, iron indices and albumin according to the renal-unit schedule and after meaningful prescription changes.
Measure delivered adequacy with a validated sampling technique, investigating low results rather than merely repeating them unchanged.
Inspect fistulae and grafts for skin thinning, aneurysm, stenosis, infection and distal perfusion; record catheter exit-site and tunnel findings.
Audit missed or shortened treatments compassionately, exploring transport, symptoms, work, health literacy and mental health before labelling non-adherence.
Reassess target weight after admission, amputation, nutritional change, pregnancy or persistent intra- or interdialytic pressure problems.

07Special situationsVariants, exceptions and circumstances that change the usual approach.

Dialysis dose includes time

Good pump flow cannot reliably compensate for repeatedly shortened sessions because fluid and compartmental solute removal remain constrained.

Target weight is dynamic

It is an evolving clinical estimate of euvolaemia, not an immutable number printed on the prescription.

The access is a lifeline

Every avoidable needle, pressure cuff and episode of prolonged compression can threaten future treatment delivery.

Alarms describe a problem

Silencing a pressure alarm without finding kinking, needle movement, clotting or access dysfunction removes a safety barrier.

Hypotension has a differential

Ultrafiltration is common, but sepsis, bleeding, arrhythmia, infarction and dialyser reaction can present in the same chair.

Residual urine still matters

Even modest native kidney clearance assists potassium, volume and middle-molecule control and should be protected from avoidable injury.

08Common pitfallsFrequent interpretation and management errors.

01
Do not prescribe or alter dialysate potassium, sodium, bicarbonate or ultrafiltration independently of the renal dialysis team.
02
Do not use the fistula arm for routine blood pressure measurement, venepuncture or peripheral cannulation.
03
Do not dismiss dialysis-associated rigors as a benign reaction before cultures and sepsis assessment.
04
Do not keep ultrafiltration running through symptomatic hypotension while only repeating an automated cuff reading.
05
Do not return circuit blood if haemolysis or major dialysate contamination is suspected; follow the unit emergency procedure.
06
Do not judge adequate care from urea reduction alone while ignoring fluid overload, malnutrition or severe treatment symptoms.
07
Do not remove a tunnelled catheter or attempt access salvage without coordinated renal, vascular and microbiology planning unless immediate life-saving action dictates otherwise.