Read circuit pressures, fix access problems, prevent early filter clotting and handle common alarms.
At the bedside
- 1
Read the pressures
Access pressure (normally -50 to -150 mmHg), return pressure (+50 to +150), filter pressure, effluent pressure, TMP (rising > 200-250 mmHg suggests clotting), pressure drop across filter (rising = clotting).
- 2
Access alarms (very negative pressure)
Catheter kinked, patient position (femoral - straighten leg), catheter against vessel wall, thrombus. Reposition, flush with saline, reverse lines (increases recirculation), reduce blood flow; replace catheter if persistent.
- 3
High return pressure
Kink or clot in return limb/venous chamber, catheter problem. Check line, chamber, catheter.
- 4
Early filter clotting (< 24 h)
Check anticoagulation (citrate post-filter iCa, aPTT), catheter function, FF > 25%, frequent interruptions, high haematocrit. Increase blood flow, increase pre-dilution, reduce net UF, optimise catheter (right IJ, correct length).
- 5
Return blood before the filter clots fully
If TMP rising rapidly, return blood to the patient (saves ~150-200 mL blood) and replace the circuit.
- 6
Patient-side issues
Hypothermia (use warmer), hypotension at connection (prime with saline/albumin, start low blood flow), electrolyte drift (6-12 hourly labs), catheter infection.
CRRT alarms and actions
| Alarm/finding | Likely cause | Action |
|---|---|---|
| Access pressure very negative | Catheter kink/position/clot, hypovolaemia | Reposition, flush, reverse lines, reduce Qb, change catheter |
| Return pressure high | Kink or clot in return line/chamber/catheter | Check lines, change chamber/catheter |
| TMP rising, pressure drop rising | Filter clotting | Check anticoagulation, FF; return blood and replace set |
| Air detector | Loose connection, empty bag | Check connections, remove air per machine |
| Blood leak | Filter membrane rupture (or hydroxocobalamin colour) | Stop, do not return blood if true leak, replace filter |
References
- 1
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CRRT pressure alarm
Step 1 of ~4
Decision: Which pressure is abnormal?
Based on Kidney Disease: Improving Global Outcomes (KDIGO) AKI Work Group. Educational use; follow local protocol.
Pathophysiology
Filter clotting results from blood-membrane contact activation, haemoconcentration at the filter outlet (especially with high post-dilution UF), blood stasis during flow interruptions, and inadequate anticoagulation.
Evidence
- KDIGO and RICH data: citrate and adequate catheter function are the main determinants of filter life [KDIGO 2012; RICH 2020].
Controversies
- Routine filter change interval (often 72 h maximum per manufacturer).
🇮🇳 India notes
- Filters are the major cost item; filter lives under 24 h are common without citrate. Audit filter life monthly.
References
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Test yourself
Module quiz · score 70% to complete the module
Educational reference for trained clinicians. Check doses against your hospital protocol and the patient in front of you.