So it looks like with my current new timetable I can sort of squeeze one or two blog posts per week. Alright. Better than nothing.
So today finally I got to read one of the 15 lecture notes for the 15 hours of the 200 hours training for dialysis PIC.
Tried to print out the CD but couldn't, or else I could easily read it on my phone. Would have been done by now, seriously.
Anyway, in the mean time, I did read it already I think but at that point, the very beginning, it was difficult and the theory didn't quite make sense. Of course if you attend the lecture and there is someone explaining it, the experience would probably be a bit different.
This is an important lecture and I will share what I can here.
ADEQUACY OF HEMODIALYSIS
Dr Keng Tee Chau UMMC
These slides are prepared by
Dr. Keng Tee Chau
MBBS(MAL), MRCP(UK) Consultant Nephrologist & Senior Lecture Consultant Nephrologist & Senior Lecture Division of Nephrology Department of Medicine University Malaya Medical Centre
OUTLINE
•Marker for hemodialysis adequacy •Measurement of hemodialysis adequacy •Blood sampling method •Inadequate delivery of dialysis : What to do? •Inadequate delivery of dialysis : What to do?
HOW TO DEFINE HEMODIALYSIS ADEQUACY ?
•The ultimate goal of hemodialysis is removal of solutes or ‘uremic toxins’.
•Uremic toxins encompass a long list of solutes •Uremic toxins encompass a long list of solutes of different molecular weights.
CHARACTERISTICS OF AN IDEAL MARKER OF DIALYSIS ADEQUACY •Accumulated in renal failure •Eliminated by dialysis •Proven toxicity •Generation and elimination representative for •Generation and elimination representative for other solutes •Easily measured
Vanholder and Ringoir 1992
UREA AS A MARKER OF DIALYSER CLEARANCE •Traditionally urea has been used as ‘representative’ solute for measurement of dialysis adequacy •Urea, as a small solute, is effectively removed •Urea, as a small solute, is effectively removed during dialysis. •Dialyzer clearance of urea (Kt/V or URR) has been proven to be a measure of clinical outcome.
MEASUREMENT OF UREA CLEARANCE •Urea clearance (rather than its absolute value) is a sensitive marker of dialysis adequacy. •Urea clearance can be expressed in a few ways : :
1)Kt/V
2)URR
UREA REDUCTION RATIO (URR)
•URR = ( 1 –[postdialysis BUN / predialysis BUN] )
DILEMMA WITH URR
•Easy to calculate•Represent only a single snapshot in time of the patient’s adequacy of dialysis •Doesn’t include contraction •Doesn’t include contraction of body water volume and urea generation during dialysis •Inability to adjust the prescription accurately when the value is off target (by adjusting K or t)
Kt/V
•K = dilayser clearance (ml/min) •T = time on dialysis (min) •V = total body water (ml)
MEASUREMENT OF Kt/V
1)Formal Urea Kinetic Modeling (UKM) ** 2)Natural log formula Kt/V = -Ln(R -0.008 ×t)+(4 -3.5 ×R) ×UF/W 3)On line clearance 3)On line clearance
** KDOQI gold standard R = the ratio of postdialysis BUN to predialysis BUN, t= time on dialysis in hours W= body weight UF = ultrafiltration
FORMAL UREA KINETIC MODELING (UKM) •Computer software is needed to compute Kt/V using UKM •Data requires for calculation : 1.Pre/post dialysis BUN (Either 2 or 3 BUN 1.Pre/post dialysis BUN (Either 2 or 3 BUN samples method) 2.Patient’s data : weight, height 3.Treatment data : actual treatment time, effective dialyser clearance, pre/post dialysis weight, blood/dialysate flow rate.
EXPRESSION OF Kt/V
Single poolspKt/V
Double pooldpKt/V
EquilibratedeKt/V EquilibratedeKt/V
StandardstdKt/V
NormalizednKt/V
continuousEKR (t/V)
Dose expression for Kt/V
•Prescribed dose -calculated from doctor’s order for Qb, Qd, dialyzer and treatment time •Predicted dose -calculated from actual Qb, Qd, treatment time -calculated from actual Qb, Qd, treatment time recorded •Delivered dose -calculated from pre/post dialysis BUN and other variables -actual results based on how the patient really dialysed the blood samples are drawn
KDOQI GUIDELINES
•The preferred method of measurement of dialysis adequacy is Kt/V calculation using Formal Urea Kinetic Modelling (UKM), employing single pool model. employing single pool model. •Delivered dialysis dose should be measured at regular intervals no less than monthly.
KDOQI GUIDELINES
•For a patient on HD 3 times a week Kt/V -minimal : 1.2 per dialysis -target : 1.4 per dialysis -target : 1.4 per dialysis URR -minimal : 65% per dialysis -target : 70% per dialysis
BLOOD SAMPLING
•Both pre & post BUN should be taken during the same HD session (mid week)
PRE BUN SAMPLING -KDOQI GUIDELINES 2006
PRE BUN BLOOD SAMPLING FROM FISTULA Blood drawn as soon as cannulation done Before starting blood pump or bolus dose of heparin Ensure not mixed with heparin or saline
PRE BUN BLOOD SAMPLING FROM CATHETER Remove heparin block/saline (first * 5mlof blood). *Discardthe blood. Then use new syringe to draw * 5mlof blood sample sample
* New amendment in latest KDOQI 2006 guidelines
POST BUN BLOOD SAMPLING
•To avoid dilution of post BUN sample by recirculatingpost dialysis blood and to minimise effects of urea rebound , the blood should be taken by using SLOW FLOW/STOP PUMP sampling method PUMP sampling method
Non adherence will lead to over/underestimation of Kt/V or URR
UREA REBOUND
Fig I-2. Components of urea rebound. This illustration shows a total of 65% urea rebound of which over half is secondary to access recirculation (A→B). The contribution from cardiopulmonary recirculation is 15% (B→C), and the remaining 31% (C→D) is a consequence of flow and diffusion limitations
POST BUN BLOOD SAMPLINGKDOQI GUIDELINES
POST HD BLOOD SAMPLING RECOMMENDED BY KDOQI -SLOW FLOW/STOP PUMP METHOD
•Turn off dialysate pump •Reduce UF to 50ml/H or off •Widen pressure alarm limit •Widen pressure alarm limit •Reduce blood pump to 50-100ml/min for at least 15 s •Blood pump can be then either stopped or kept running at 50-100ml/min •Clamp venous needle tubing •Take blood from arterial port
POST BUN BLOOD SAMPLING RECOMMENDED BY KDOQI -STOP DIALYSATE FLOW METHOD
INADEQUATE Kt/V : What to do?
•CHECKLIST : 1.Vascular access 2.Dialyser 3.Blood flow rate 3.Blood flow rate 4.Dialysate flow rate 5.Treatment time 6.Blood sampling method
VASCULAR ACCESS
•Check for access recirculation (AR)
•Review needle placement -inadvertent needle placement -inadvertent needle placement -close promixity of both needle •Poor access flow -fistula stenosis (low prepump pressure < 200mmHg or high venous pressure)
RECIRCULATION
•A fully functional AVF should have blood flow > 600ml/min •If AVF blood flow is poor (due to either stenosis or poorly mature fistula) blood returning to patients from dialyser will be “sucked” back to arterial line from dialyser will be “sucked” back to arterial line and dialysed again. inadequate dialysis •Significant recirculation happens when blood pump (Qb) demands more blood supply than the AVF can deliver •Recirculation >10% will result in poor URR/Kt/V
DETECTION OF ACCESS RECIRCULATION
1)Urea based method (S BUN –A BUN )/ (S BUN -V BUN)x 100% SBUN = systemic BUN A= Arterial BUN ABUN= Arterial BUN VBUN= Venous BUN
2)Non urea based method, examples: Ultrasound dilution Thermal dilution
CAUSES FOR RECIRCULATION
1.Poor AVF flow (requires fistulogram for assessment) 2.Error in placement of cannulation needles : -reversed needle cannulation -reversed needle cannulation -distance of both arterial/venous needles too close
DIALYSER
•Low surface area -bigger size patient needs bigger dialyser •Excessive reuse of dialyser can significantly reduce its performance reduce its performance -Review dialyser reuse log to evaluate total cell volume (TCV) -TCV should not be allowed to drop more than 20%
BLOOD FLOW RATE
•Compare prescribed versus actual blood flow rate •If prescribed blood flow rate can not be achieved, look for the possible causes : achieved, look for the possible causes : Inadequate setting of blood flow rate Small needle size Fistula stenosis (requires fistulogram for assesment) Hemodynamic instability eg cardiac failure
DIALYSATE FLOW RATE
•Review dialysis log book to compare prescribed versus actual dialysate rate
TREATMENT TIME
•Actual treatment time may be shorter than prescribed time -late arrival of patient -early termination of dialysis -early termination of dialysis -interruption of dialysis due to intradialytic events eg hypotension, cramp -others
THANK YOU
That's basically what can be copied from the lecture notes in point form. There are some cool pics and diagrams that aren't included. Maybe in future if I have the time I will upload them.
The most important terms are the URR and KtV which sounded very foreign. After spending some time on the wards observing that 'which needs to be observed' according to the logbook, things begin to 'fall in place' just like final medical year.
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