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
Why is epidural blockade relatively contraindicated for renal transplant
Increased CVS instability associated with epidural blockade compromises the transplanted kidney
When can regional blocks be used in the context of CRF
Haemodialysis access procedures in the upper limb
- brachial plexus blockade (axillary/supraclavicular approach)
In patients receiving CAPD - insertion or removal of peritoneal dialysis catheter
- Rectus sheath block
- Transversus abdominis plane block (TAP)
How should planning of the first postoperative dialysis session proceed?
It is sometimes appropriate to delay the first postoperative dialysis session if bleeding would be a problem.
Patients rarely come to harm because a single dialysis session is delayed or omitted, so there is a place for discussion with the responsible nephrologist, particularly if bleeding would pose particular problems or the use of epidural analgesia is contemplated.
What are the three categories of the current functional status of a transplanted kidney
- Normal urine volumes and NO dialysis
- Avoid nephrotoxic drugs
- immuosupression - Urine passed but still requires dialysis
- Consider fluid balance
- Avoid nephrotoxic drugs
- immunosupression - Anuric and dialysis dependent
- Transplant has failed.
- Dialysis dependent patient.
- The patient may still require immunosuppression and may even present for a transplant nephrectomy.
In a patient with a renal transplant, what electrolyte abnormality might imply transplant dysfunction
Hyperkalaemia
if > 6.0 –> indication for pre-operative dialysis
How does creatinine provide a valuable reflection of renal function
Due to constant rate of production in skeletal muscle and free filtering at glomerulus.
Explain how GFR should be interpreted relative the the SCr level
As GFR decreases to 40 ml/min - SCr rise slowly to ± 200 umol/l.
At SCr > 200 –> small changes in GFR lead to large rises in serum creatinine
What are the symptoms of hypocalcaemia
MSK
Paraesthesia
Muscle cramps
Tetany
CARDIAC
Cardiac arrhythmias
Prolonged QT
RSP
Stridor
HAEM
Coagulopathy
How can fatal hyperphosphataemia be caused in CRF
Administration of PO4 containing bowel prep
How is GFR measured from creatinine clearance
24 hour urine specimen
What does the Cockcroft-Gault formula estimate and what variables are required
Creatinine clearance
- Age
- Weight
- Sex
What does the Modification of Diet in Renal Disease estimate (MDRD) and what variables are required
Estimated GFR
- Age
- Sex
- Race
Classify the severity of Chronic Kidney Disease
Normal: GFR > 90 ml/min/1.73m^2 an no proteinuria
CKD 1: GFR > 90 + Evidence of kidney damage
CKD 2: 60 < GFR < 90 + Evidence of kidney damage
(Mild)
CKD 3: 30 < GFR < 60
(Moderate)
CKD 4: 15 < GFR < 30
(Severe)
CKD 5: GFR < 15 (dialysis or kidney transplant needed)
What causes anaemia in CKD
Normocytic normochromic anaemia occurs as uraemia affects erythropoeisis
Rx: EPO
How does CKD affect PT and aPTT
It doesn’t
Recent haemodialysis –> may cause a residual heparin effect
What causes coagulopathy in CKD
Uraemia affects platelet function
Residual heparin affect after haemodialysis
What can be considered to improve platelet function
DDAVP –> Desmopressin Acetate Tablets may be considered to improve platelet function
Is transfusion to Hb > 8 g/dl in patients with CKD still standard practice?
No
Transfusion may have immunomodulatory effects
When is a kidney transplant patient considered steroid free?
If their last dose of steroid > 3/12 ago
Name 4 steroids and dose equivalents to prednisone 5mg
Hydrocortisone 20mg
Methylprednisolone 4mg
Triamcinolone 4mg
Describe Cushing’s Syndrome
APPEARANCE Moon Face Truncal Obesity Easy bruising and fragile skin Buffalo hump
MSK
Proximal myopathy
BONES
Osteoporosis
RENAL/ENDOCRINE
Diabetes Mellitus
Mineralocorticoid excess (High Na and low K)
CVS
Hypertension and LVH
GIT
GI reflux
RSP
Sleep Apnoea
What is a common immunosuppressive regimen in kidney transplant patients
Prednisolone
Tacrolimus (Inhibits IL-2 gene transcription –> blunting
T-cell activation and proliferation)
Mycophenolate (inhibiting purine biosynthesis and blocking lymphocyte proliferation.
What is the mechanism of action and adverse effects of tacrolimus
Tacrolimus - Inhibits IL2 gene transcription –> blunting of T-cell activation and proliferation
Adverse effects
- Nephrotoxicity
- HPT
- Hyperglycaemia
- Neurotoxicity
CP450
What is the mechanism of action and adverse effects of mycophenolate
Mycophenolate Mofetil (MMF) is an oral prodrug of mycophenolic acid that acts by inhibiting purine biosynthesis and blocking lymphocyte proliferation
Adverse Effects
- Diarrhoea
- Leukopaenia
- Anaemia
What is the mechanism of action and adverse effects of cyclosporin
Acts by inhibiting IL-2 gene transcription and blunting T-lymphocyte proliferation. Therefore can be used instead of tacrolimus.
Toxic plasma levels
- nephrotoxicity,
- hypertension,
- neurological problems,
- gingival hyperplasia and
- hirsutism.
Undergoes cytochrome P-450 metabolism.
What is the mechanism of action and adverse effects of azathioprine
Acts by inhibiting purine salvage and biosynthesis, thus blocking lymphocyte proliferation.
Adverse effects
- leukopaenia,
- macrocytic anaemia,
- cholestatic hepatitis and
- pancreatitis.
How does perioperative fasting affect immunosuppressive medications
Medications are taken with food and prolonged perioperative fasting may lead to dangerous fall in plasma levels
Liaise with renal/transplant physicians when prolonged nil by mouth expected
Why is tight haemodynamic control important in renal transplant patients
Denervated kidney –> impaired vascular autoregulation
What should be considered prior to administration of vasopressors in transplant patients
Possible exaggerated alpha adrenergic response
What is the anaesthetic relevance of the superficial position of a transplanted kidney
Positioning to avoid compression
