7.8 RRT Flashcards
Define AKI
AKI can be defined as an abrupt (1 to 7 days)
+
sustained (more than 24 hours) decrease in kidney function.
How can you classify AKI
RIFLE
AKIN
KDIGO
Discuss the RIFLE Criteria
Creatinine increase / % eGFR increase
Risk - 1.5 / 25%
Injury 2 / 50%
Failure 3 / 75%
Loss - Persistent ARF = complete loss of function >24 hours
End stage renal disease
What are the ECG features of high potassium?
Rate and rhythm
* Bradycardia
* Asystole
* Ventricular tachycardia and fibrillation
* Sine wave appearance
Waves
* Absent P waves
* Wide QRS
* Peaked T waves
Intervals and segments
* Slurring of ST segments
How would you treat this condition?
immediate measures to prevent cardiac arrest (especially if potassium > 6.5 mmol/L)
- Calcium: 5–10 mmol intravenously;
repeated if necessary. ECG changes
are reversed within 1 to 3 min. - Insulin to push the potassium into intracellular compartment.
- Nebulised salbutamol increases cellular uptake of potassium.
- Sodium bicarbonate: 50 mls of 8.4% intravenously in the presence
of acidosis (exchanges potassium for hydrogen ions across cell
membranes). - Diuretics if renal function is adequate.
- Calcium resonium:
polystyrene sulphonate resins orally or rectally. It might
take 6 hours to achieve full effect.
Delayed measures depending on the cause of hyperkalaemia
* Aimed at correcting the disease and preventing further increase in plasma
potassium
When would you institute renal replacement therapy (RRt)?
The indications of RRT can be
- Acute kidney injury with:
° K > 6.5 mmol/L
° Metabolic acidosis (pH < 7.1)
° Deteriorating renal parameters (urea > 30 mmol/L)
° Signs of fluid overload with oliguria/anuria
- Acute kidney injury with:
- Drug poisoning
° Water-soluble and non-protein-bound drugs (e.g. salicylates)
What types of RRT are being used?
Depending on the mechanism of solute removal and the duration of
treatment, RRT can be classified as:
- Intermittent haemodialysis (IHD)
- Continuous renal replacement therapy (CRRT)
° Continuous venovenous haemofiltration (CVVH)
° Continuous venovenous haemodialysis (CVVHD)
° Continuous venovenous haemodiafiltration (CVVHDF)
° Continuous arteriovenous haemofiltration (CAVHF)
- Continuous renal replacement therapy (CRRT)
- Peritoneal dialysis
- Sustained low-efficiency dialysis
Haemofiltration (filtration)
This method involves the use of a
semipermeable membrane for ultrafiltration
in an extracorporeal system.
Blood is pumped through,
and the hydrostatic pressure that is
created on the blood-side of the filter drives plasma water
across the membrane.
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Molecules that are small enough to
pass through the membrane (< 50,000 Daltons)
are dragged across the membrane
with the water by the process of convection.
The filtered fluid (ultrafiltrate)
is discarded, and a
replacement fluid is added in an adjustable fashion
according to the desired fluid balance.
Haemodialysis (diffusion)
Blood is pumped through an extracorporeal system
that has a dialyser,
where blood is separated from a crystalloid solution
(dialysate) by a semipermeable membrane.
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Solutes move across the membrane along their
concentration gradient from one compartment to the other,
obeying Fick’s laws of diffusion.
In order to maintain concentration gradients and therefore
enhance the efficiency of the system,
the dialysate flows counter-current to the flow of blood.
Fick’s laws of diffusion
It states that the rate of diffusion across a membrane is
directly proportional to the concentration gradient of the substance
on the two sides of the membrane
inversely related to the thickness of the membrane.
Haemodiafiltration
It is a combination of filtration and dialysis.
It has the benefits of both techniques
but to a lesser extent than when the individual techniques are used on their own.
Peritoneal dialysis
Same principle as haemodialysis,
but peritoneum acts as the membrane.
2 L of sterile dialysate is placed in the peritoneal cavity via a catheter.
The electrolyte movement is by osmosis,
and the fluid is drained out at frequent intervals.
Sustained Low-Efficiency Dialysis (sLeD)
It is a hybrid therapy that aims to combine the
logistic and cost advantages of IHD
with the cardiovascular stability of CRRT.
Treatments are intermittent but usually daily and
with longer-session durations than conventional IHD.
Solute and fluid removal are slower than IHD but faster than CRRT.
How would you determine the type of RRt to use?
This depends on:
- The size of particles to be removed from plasma
° Urea, creatinine, K+ < 500 Daltons Dialysis and Filtration
° Large drugs 500–5000 D Filtration
° Cytokines, complement 5000–50000 D Filtration
° Water 18 D Filtration
- The size of particles to be removed from plasma
- Patient’s cardiovascular status
° Continuous RRT is better than IHD.
- Patient’s cardiovascular status
- Clinician experience
- Availability of resources
° CRRT is labour intensive and expensive.
- Availability of resources
What are the complications of RRT?
- Anticoagulation related
* Bleeding
* Heparin-induced thrombocytopenia - Catheter related
* Sepsis
* Thrombosis
* Arterio-venous fistulae
* Arrhythmia
* Pneumothorax - Procedure related
* Hypothermia
* Anaemia
* Hypovolaemia
* Hypotension
* Electrolyte abnormalities (hypophosphataemia, hypokalaemia) - Drug related
* Altered pharmacokinetics
