Chronic Renal Failure Flashcards
List the complications of chronic renal failure
Consider the functions of the kidney:
Anaemia Renal osteodystrophy Myopathy and neuropathy Immunopathy Hypertension Endocrine dysfunction Metabolic acidosis
What are the important consequences of haemodialysis to the anaesthetist?
Fluid depletion
Anticoagulation
Electrolyte levels
- Anaesthetists should be careful of a potassium measurement taken just after the end of dialysis. Ideally, wait a few hours for electrolytes to stabilize.
What is the importance of anticoagulation used for haemodialysis in the perioperative period
- Anticoagulation (usually with heparin) is required during dialysis. This is reversed with protamine at the end of the dialysis session, but may still be important postoperatively when the first dialysis session may precipitate postoperative bleeding.
When should electrolytes be sampled by the anaesthetist subsequent to haemodialysis
Wait 4 hours for electrolytes to stabilize
What are the important consequences of chronic ambulatory peritoneal dialysis for the anaesthetist
Electrolyte levels Protein loss Risk of infection Other complications - Anaesthetists need to make sure that the fluid is drained from the peritoneal cavity before inducing anaesthesia because there is a small risk of gastric regurgitation and of aorto-caval compression.
What is standard practice with regards to planning elective surgery for patients on haemodialysis
Plan the surgery for the day after the dialysis
Does dialysis restore Urea and Creatinine to normal
No: SCr between: 3 - 400 umol/L
Why can platelet count be reduced after haemodialysis
Consumption on the filter
Why are patients who have been on long term RRT likely to become hypophosphataemic
Phosphate is filtered and not replaced - to some extent this is balanced by tthe fact that CRF tends to present with hyperphosphataemia and hypocalcaemia
What are the consequences of RRT related hypopophosphataemia and how should this be addressed prior to anaesthesia
Severe low PO4 leads to cardiovascular instability and should by treated with a phosphate infusion prior to anaesthesia
Elimination of what kind of drugs will be reduced in CRF resulting in accumulation with potential for toxic effects. Give examples of some of this drugs used in anaesthesia
Water soluble drugs
- Muscle relaxants
- Morphine-6-glucoronide (more potent than the parent compound)
Metabolites of fat soluble drugs (If they are active metabolites - then there may be a prolonged effect of the drug in CRF, even though the drug itself does not accumulate). E.g. morphine-6-glucoronide
List the anaesthetic drugs that are unsafe in CRF
Volatile: Enflurane (Metabolism –> toxic level of Fl- ions)
Opioids: Pethidine (Norpethidine accumulation)
Analgaesic: NSAIDS (Renal VC -> worsen RF)
Muscle relaxant: Pancuronium (Prolonged action due to reduced metabolism and excretion by the kidney)
List the anaesthetic drugs that should be used with caution in CRF
Volatile: Sevoflurane (Fl- ions)
Opioid: Fentanyl/Morphine (delayed elim. of active metabolites)
MR:
- SUX - possible transient hyperkalaemia
- Vecuronium and Rocuronium - prolonged elimination
Which muscle relaxants are suitable in anaesthesia in patients with CRF and why.
Atracurium and Cisatracurium
- Hofmann elimination BUT cause histamine release with potential for hypotension and worsen renal function
Rocuronium
- t1/2 only slightly prolonged in CRF
- no histamin release
Why is TIVA problematic in CRF
Vd’s are unpredictable and extravasation can occur without warning due to increasing infusion pressure
How is the approach to vascular access altered in patients with CRF?
The patient’s lifespan may be dependent on the availability of arteries and veins for the formation of arterio-venous fistula.
- Avoid a-line if possible
- Avoid Subclavian CV cannulation if possible (avoid subclavian stenosis - limits the viability of future fistulae)
How should existing A-V fistulae be treated in the perioperative setting
Protect - wrap in cotton wool (visual cue)
Avoid NIBP measurement in fistulated arm
Avoid vascular access in fistulated arm
How should post-operative analgaesia be adjusted in patients with CRF
Concerns with regard to morphines active metabolite M - 6 - G are not practical.
–> M - 6 - G accumulation most commonly occurs in the ICU setting with morphine infusions
Standard prescription of morphine via PCA with standard monitoring is safe
Why is epidural blockade contraversial in CRF
All patients with CRF have subclinical coagulopathy (attributable to impaired platelet function) - increase risk of epidural hematoma/abscess
If scheduled for haemodialysis - epidural is contraindicated due to the need for anticoagulation during dialysis
