how to improve peritoneal dialysis adequacy
TRANSCRIPT
ADEQUACY DILEMMAFrank Gotch introduced the concept of adequacy of dialysis when he proposed the ‘Urea Clearance’ concept as a measure of dialysis efficacy.Over 30 years the concept of adequacy of dialysis has been quite controversialAnd different concepts about (WHAT Adequacy IS?) is it a clinical state or an absolute Targeted Number ? How can Kt/V which is widely accepted can cope
with the well known truth of reversed epidemiology in Obese Dialysis patients!? How can the Kt/V can give us true picture while it doesn’t look at the
phosphorus level , the infections , Hyperkalemia or the cardiovascular status!!? We are Still waiting for answers
ADEQUACY FROM THE CLINICAL BROAD VIEW
Control of: –Acid-base status
–BP and volume status –Cardiovascular Risk
–Diet/nutrition –Mineral/Bone disorders –Small/middle molecules
OR The patient general well Being!!
ADEQUACY IN HISTORYNCDS (National Cooperative Dialysis Study) in 1981 which focused on HD suggested that there is a Minimal Dose of dialysis that must be delivered to improve the outcome , so the era of adequacy started.
Data from NCDS analyzed By Gotch and colleagues and the Kt/V came to life depending on the urea clearance in 1985.Teehan and colleagues studied Kt/V in PD for 5 years and yielded weekly target of 1.89 to have better survival in 1994.Blake and colleagues found no consistent predicitive power of Kt/V in PD patients.As studies gave conflicted data and all were small in size and
retrospective , it was clear that we need a larger prospective study
CANUSAIn the same time CANUSA Trial was conducted and has these criteria needed This was a prospective cohort study of 680 consecutive patients commencing CAPD in 14 centers in Canada and the United States. Between 1990 and 1992, Follow-up was terminated December 31, 1993. published in 1996.It was noted better 2 year survival in weekly Kt/V 2.1 and the relative risk of death increase when Kt/V decrease from this target.NKF-DOQI recommended in 1997 these targets CAPD Kt/V 2.0 , CCPD Kt/V 2.1 , NIPD Kt/V 2.2.
In 2001 after several reanalysis of CANUSA Data , Found that the contribution of the residual kidney Function to the total Kt/V was more predictive of survival the peritoneal Component
and they are not simply equal! That pushed the recommendations to clinicians to take special measures to attempt preserving the residual renal function in PD patients.Again suspicion about NKF recommendations raised as ADEMEX Trial in 2002 which was conducted in Mexico as No survival benefit could be seen if Kt/V was above 1.6 approx. !!
So no benefit for extra cost! A trial in Hong Kong also confirmed the same results of ADEMEX as Randomised CAPD patients in 3 groups according to targeted Kt/V , 1.5 – 1.7 , 1.7 – 2 and > 2.0 , no statistical
advantage in survival was detected !
Even in HD world in 2002, came the Famous HEMO study with its results showing that Patients undergoing hemodialysis have no major benefit from a higher dialysis dose or from the use of a high-flux membrane.
That pushed the K/DOQI to revise its recommendations as new studies results and no big benefits gained from the creatinine use more than the urea, so in 2006 Stated that
“The Minimal deliverd dose of total small solute clearance should be a total ( peritoneal and renal ) Kt/V urea of at
least 1.7 per week “And further they recommend to be measured after first
month of PD and monitored every 4 months in routine .
C J STEFANIDIS 2001
OPTIMAL AND ADEQUATE DOSE OF PD
Adequate dose: the amount of PD below which there is an increase in morbidity and mortality
Optimal dose: the amount of PD yielding clinical results which cannot further improve
KT/V K = Molecule clearance t = time V= Molecule Volume of DistributionIt is a unitless expression.In Urea usually the Volume of distribution is Total Body Water TBW which can be assessed by many methods.
In PD usually we use the Urea Kt = Peritoneal Clearance + Residual Renal Clearance in liters.
V = TBWPeritoneal urea clearance = D urea/P urea x Liters of dialysate (effluent )Residual Renal Clearance = U urea/P urea x Liters of Urine
And to calculate the weekly dose we Multiply by 7 (days number)So Kt/V x 7 = weekly target dose .
VOLUME OF DISTRIBUTIONThis is variable according to the molecule used. Usually we use urea and it’s Volume of Distribution equals the TBW.TBW is estimated by Watson formula .
Male = 2.447 - (0.09156 x age) + (0.1074 x height) + (0.3362 x weight)Female = -2.097 + (0.1069 x height) + (0.2466 x weight)Also there are other formulas like Hume-Weyers , Chertow's Bioelectrical Impedance , Mellits-Cheek (kids).
Some authors use simple formula to calculate = 0.59 x IBW = TBW
RESIDUAL RENAL FUNCTIONIt is well proved that it shares a bigger effect in the total Kt/V efficiency more than the peritoneal component.All Doctors must try to preserve it as possible.
Residual renal urine volume and residual renal Kt/V (rKt/V) should be measured every 3 – 6 months in patients with a peritoneal Kt/V (pKt/V) of less than 1.7 weekly, especially if RRF is rapidly declining. In all other PD patients, rKt/V and urinary volume should be measured together with pKt/V when clinically indicated (Canadian Guidelines)
It may help clinical understanding use a mean of 24-hour urine urea and creatinine clearance to express RRF as a glomerular filtration rate (GFR) in milliliters per minute.BP should be controlled to less than 130/80 mmHg provided that this is not associated with signs and symptoms of postural hypotension or volume depletion.
Angiotensin converting-enzyme inhibitors (ACEIs) or angiotensin receptor blockers (ARBs) should be strongly considered, unless contraindicated, in all PD patients with significant (>100 mL daily) urine output.
Strong consideration should be given to the use of high-dose oral furosemide (up to 250 mg daily) and oral metolazone (up to 5 mg daily) in all PD patients with significant (>100 mL daily) urine output, provided that this is not associated with signs and symptoms of postural hypotension or volume depletion. CANADIAN SOCIETY OF NEPHROLOGY GUIDELINES/RECOMMENDATIONS
The effect of PD modality on RRF is controversial. Some studies showed that automated PD (APD) is associated with more rapid loss of RRF; others did not . Randomized controlled trials of biocompatible PD solutions (with normal pH, low levels of glucose degradation products, and bicarbonate/lactate buffer) have not consistently showed better maintenance of residual renal clearance over at least 1 year of follow-up
It is recommended that total Kt/V be measured using 24-hour dialysate and urine collections soon after the patient has been stabilized on PD—that is, after 4 – 6 weeks. This is typically the time when the initial peritoneal equilibration test (PET) will also be done. If the weekly pKt/V is less than 1.7, and if achievement of the target total Kt/V depends on residual renal clearance, it is important that rKt/V be re-measured every 3 – 6 months because it will tend to decline with time. If the rKt/V is no longer sufficient to maintain the total Kt/V at target, the peritoneal prescription needs to be increased, with the total Kt/V being re-measured until the target is achieved. If the weekly pKt/V is greater than 1.7, it is not likely to change substantially while the peritoneal prescription remains the same. It is therefore not essential to re-measure pKt/V routinely unless there is an unexplained or unexpected change in the patient’s clinical or laboratory status.
CANADIAN SOCIETY OF NEPHROLOGY GUIDELINES/RECOMMENDATIONS
Small solutes clearance: For continuous ambulatory PD (CAPD), the usual starting prescription need not exceed 4×2-L exchanges daily.
If patients are experiencing uremic symptoms or are clinically not doing well, and if there is no identifiable cause other than insufficient dialysis, the prescription (that is, the pKt/V) should be increased, especially if the total Kt/V (that is, the pKt/V and rKt/V combined) is less than 1.7.For CAPD, lower volumes or fewer exchanges than 4×2 L daily can be used for smaller individuals or for those with significant RRF, especially if the total Kt/V is greater than 1.7
For APD, the recommended starting prescription should be designed to achieve a target total Kt/V of 1.7 or more, and should take into account membrane transport characteristics, with the number of nighttime exchanges typically ranging from 3 to 5 A measurement of total Kt/V should be carried out 4 – 6 weeks after initiation of PD . The measurement of total Kt/V should be repeated if there is an unexplained or unexpected change in the patient’s clinical status or a problem with ultrafiltration (UF)Strategies that are effective when attempting to raise clearance in CAPD are increases in dwell volume and addition of extra exchanges ; however, the small risk of mechanical complications should be considered when dwell volumes are increased, and the substantial risk of noncompliance should be considered when a fifth manual exchange is added
The most effective strategy when attempting to raise clearance in APD is to ensure that the patient has a day dwell. The next most effective strategies are the introduction of an additional day dwell (that is, 1 daytime exchange) and larger nighttime dwell volumes . Other options to consider are increasing the cycler time and the frequency of cycles.In a patient who is underweight or overweight, the calculation of Kt/V should use the patient’s ideal body weight to estimate V.
CASE 1 How to calculate Kt/V in CAPD patient?
Male CAPD patient 70 kg, with 4 exchanges , 2 L each , total volume drained per day is 9.5 L which is Vdialysate( UF 1.5 L/D) , we will take sample from effluent of each exchange and either measure the urea in each then calculate the average or take a sample from each and mix them , then analyze them to have the mean of dialysate urea which was 72 mg /dl = Durea.Blood urea = Purea = 80mg/dlSo Kt = Durea/Purea x Vdialysate = 72/80 x 9.5 = 8.6
V=TBW= 70 x 0.58 = 40.6 L
So daily Kt/V = 8.6 /40.6 = 0.21Weekly peritoneal Kt/V = 0.21 x 7 ( No. of days in week) =1.47For RRF Kt/V is calculated alsoHis urine output 1 L per day (Vurine) , Uurea = 180mg/dl , Purea=80mg/dl as mentioned before so Kt =180/80 X 1 = 2.25Daily Renal Kt/V = 2.25 /40.6 = 0.055Weekly Renal Kt/V = 0.055 X 7 = 0.38Total weekly Kt/V = Renal Kt/V + Peritoneal Kt/V = 1.47 + 0.38 = 1.85
Which is within accepted target of adequacy .
CASE 2How to calculate Kt/V in APD patient?
Same Male patient transferred to CCPD Modality , 70 Kg , we calculate the night and day separately then we add to them the renal Kt/V
with 4 night exchanges ( total with UF 9 L) , D urea = 58mg/dl , Purea= 80mg/dlNight Kt=58/80 X 9= 6.5
wet day with one dwell ( total with UF 3 L) , Durea = 75mg/dl Day Kt = 75/80 x 3 = 2.8So Peritnoeal daily Kt/V = (Night + day)/V= (2.8 + 6.5)/40.6 = 9.3/40.6=0.23Peritoneal weekly Kt/V = 7 x 0.23 = 1.61
Residual kidney Weekly Kt/v from previous calculation = 0.38So total weekly Kt/V = 1.61 + 0.38 = 1.99
Which is within accepted target of adequacy .
QUESTION
A 55 years woman has been on peritoneal dialysis for 3 years. She has had declining residual renal function. She used to have a Kt/V urea of > 2.2, but now her Kt/V urea is 1.81. The woman states that she feels great, and no different from how she felt a year ago when her Kt/V urea was 2.12. Her dialysis nurse is insistent that she increase the size and number of dwells, despite the reluctance of the patient.
The best evidence to back up the patient’s claims would be which statement:
–A. More than one RCT has shown no worse outcome with Kt/Vurea 1.7-2.0 versus >=2.0.
– B. More than one observational trial has shown no worse outcome with Kt/Vurea 1.7-2.0 versus >= 2.0.
–C. More than one RCT has shown African Americans have equivalent outcomes with Kt/Vurea 1.7-2.0 versus > 2.0
–D. More than one observational trial has shown that Kt/Vurea is not the optimal measurement of PD adequacy.
CORRECT ANSWER IS A
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