Renal Replacement Therapy Flashcards
Describe the KDIGO criteria to classify the severity of acute kidney injury
Stage 1
Creatinine
- 1.5 - 1.9 x baseline <7days
- >26.5 umol/L increase < 48 hours
Urine output
- < 0.5 ml/kg/hr for 6 - 12 hours
Stage 2
Creatinine 2 - 3 x baseline
Urine output < 0.5 ml/kg/hr > 12 hrs
Stage 3
Creatinine > 3 x baseline or > 353.6 umol/l
or
RRT
Urine output < 0.3 for > 24 hours
Anuria > 12 hours
NB
The worse of the two categories that determines the stage of the AKI. (Creatinine lags)
Why do patients die from AKI and not with AKI. surely dialysis solves everything?
- Functional effects
Volume overload
Acidaemia
Electrolyte disorders - Inflammatory response to AKI –> MODS
- Immune dysfunction (uraemic toxins)
- Drug dosing in AKI
- may lead to treatment failure and adverse effects
What is dialysis
The alteration of concentration of a SOLUTE in the blood by exposing the blood to another solution (dialysate) across a semipermeable membrane.
Relies on the principles of diffusion and ultrafiltration
What is the difference between dialysis and haemo-ultrafiltration
Dialysis
- Remove specific solute (e.g. Urea)
- Dialysate flows in countercurrent direction to the blood. Solution moves down conc. gradient.
Haemo-ultrafiltration
- Remove fluids!
- Downstream adjustable pressure valve increases the hydrostatic pressure in the blood forcing plasma and small solutes across the semipermeable membrane.
Haemodiafiltration
- Fluid or solute or both
Summarise ArterioVenous haemofiltration
Patients own heart pumps the blood across the filter.
Need systolic pressure to move the blood through the system. Not possible in all patients.
Not efficient system - urea clearance low
So countercurrent dialysate flow was introduced.
Why is AVH and AVHDF no longer commonly used
Arterial cannulation associated with 15 - 20 % morbidity
Need for adequate BP (not all pts have)
Improved technology these days
- Double lumen catheters
- Peristaltic blood pumps
What are the indications for emergency dialysis
ABSOLUTE
A - Acidosis (pH < 7.2)
E - Electrolytes (K > 6.5 and rising)
I - Ingestion (toxic ingestion)
O - Oedema - Resistent pulmonary oedema
U - Uraemic Complications
1. Encephalopathy
2. Pericarditis
3. Bleeding
RELATIVE (resource limited… not common at GSH)
Oligoanuria
Hypermagnaesaemia (loss deep tendon reflexes)
Urea > 35 or Creat > 600
Anticipating worsening electrolytes
Volume creation (Feeding/Drugs)
What is haemoperfusion
Dialysis of toxin. Instead of the normal filter there is activated charcoal filter instead of a dialysis membrane. Heparinization is required
What are the possible complications of Haemoperfusion
- Heparinization required
- Hypoglycaemia (Glucose adsorbed by charcoal)
- thrombocytopaenia (plt destruction)
What are the advantages and disadvantages of Continuous Renal Replacement Therapy (CRRT)
The patient is Dialysed 24 hours of the day
Advantages
1. Smooth metabolic changes and control
2. Smooth haemodynamic control
Disadvantages
1. Prolonged exposure to extracorporeal circuit
- e.g. clotting / bleeding/platelet damage
- Hypothermia (old machines without thermoregulatory device –>
- May mask pyrexia with modern devices with warmers
What are the advantages and disadvantages of intermittent RRT? (IRRT)
Advantages
1. Logistics: to theatre/CT/break from anticoagulation
Disadvantages
1. Volume removed over short period of time –> high incidence of hypotension.
–> hypotensive episodes might delay renal recovery.
2. Solute removal is episodic
–> inferior uraemic and Acid Base control
–> Rapid shifts increase brain water and ICP (rapid shifts in electrolytes and pH)
What is SLEDD. and Why SLEDD
Slow/sustained low efficiency daily dialysis
- A form of Prolonged Intermittent RRT (PIRRT)
- 6 - 18 hours per day
- Longer than traditional IRRT (classically 3 -4 hours)
- Slower than traditional IRRT. Rationale is slower, gentler treatment will be better tolerated in the critically ill
- Comparable clinical outcomes: IRRT, PIRRT (SLEDD), CRRT
Which patients would benefit from CRRT vs SLEDD
- Cerebral oedema
- Risk of cerebral oedema (Liver Failure)
- Haemodynamically unstable
Fluid is removed more gently over long period of time
In which patients is Intermittent RRT preferable
Hamodynamically Stable patients
In patients where there is a concern for bleeding risk and you dont want to anticoagulate the patient (e.g. TBI)
Intermittent RRT preferable as the extracorporeal exposure is reduced and haparin infusion avoided
When should a patient who is haemodynamically unstable receive intermittent haemodialysis?
HD unstable after toxin ingestion or hyperkalaemic –> intermittent RRT will fix problem faster than CRRT.
When should RRT be started
Uncertain
(unless emergency indication)
Early
- but they might have got better –> waste + exposure to complications on RRT
Late
- some will get better
- but the longer you wait the less likely the patient is to recover renal function.
What are the problems with early RRT
- Kidneys might recover leading to unnecessary exposure to complications of RRT
- Fluid/solute shifts. Hypotension, disequilibrium syndrome - Anticoagulation complications
- Allergic complications
- Vascular access complications
What is the pathophysiology of dialysis disequilibrium syndrome
The symptoms of DDS are caused by cerebral edema, but the mechanism for development of cerebral edema is unclear.
The prevailing theory is that rapid clearance of urea and other osmoles by hemodialysis results in a rapid fall in the plasma osmolality, which leads to movement of water into the neurons
What are the problems with Late RRT
- Recovery of renal function is less likely
- Expose the rest of the organs to hostile environment
- Worsening renal and non-renal injury
–> Uraemic complications (encephalopathy/gastritis/plts/bleeding)
–> death before RRT
What literature speaks to timing of RRT
ELAIN - Compared very early with moderately delayed AKI
AKIKI - Compared delayed with very delayed AKI
IDEAL-ICU - Terminated early for futiliy
What did ELAIN trial find
Early RRT
- Lower 90 day mortality
- Greater renal recovery.
- shorter hospital stayW
Favoured Early
But more CLABSI
what did the AKIKI study find
No difference in 60 day survival
No difference ventilator free days
No difference
SO when to do it
AKIKI favoured conservative approach
ELAIN favoured Early RRT
Overall – delayed approach more appropriate but how long to wait undefined
Whats the optimal dose of RRT
- Measure urea kinetics in IHD and total effluent volume in CRRT
- Bigger not necessarily better
- Disequilibrium
- Removal Antibiotics and other meds
- Removal amino acids and essential minerals - Ceiling dose is likely, above which there is no benefit.
- Not yet defined
- Dynamic process to dose RRT over a patient’s course - “precision RRT”
when is anticoagulation required in CRRT, PIRRT and IHD
IHD
- Not needed for most treatments
–> Short duration and high blood flow rate so less likely to clot
CRRT and PIRRT (SLEDD)
- Longer duration, slower rate
- More likely to need anticoagulation
What is the furosemide stress test
Dynamic functional assessment of future renal function
- trying to predict whether on not patient will need to be dialysed
- Tests renal reserve in AKIN 1 or 2
–> 1mg/kg in furosemide naive patients
–> 1.5 mg/kg in furosemide exposed patients
If < 200 ml urine 2h post Furosemide Stress test then predicts progression to AKIN III
- Sensitivity 87%
- Specificity 73.9%
Send to facility with RRT if failed.
If pass don’t transfer yet
