Hemodialysis vs. Peritoneal Dialysis

My attention was caught by the recent article in CJASN which compared the mortality of peritoneal dialysis (PD) and hemodialysis (HD) patients in the first 2 years of dialysis therapy. When comparing survival outcomes of PD and HD patients, the data we have so far is based on observational studies. A randomized controlled study has never been successfully completed because of difficulties in randomization. The only randomized study so far - the NECOSAD study (Netherlands) managed to randomize only 5% of the eligible subjects3.  

Most of the observational studies looking at survival had methodological limitations like suboptimal adjustment for modality switch over time (PD patients more likely to switch to HD), inability to account for time-varying confounding by laboratory values and inappropriate adjustment for the differential longitudinal censorship of transplantation across modalities (PD patients more likely to get a transplant). While analyzing such time-varying covariates which are simultaneously confounders as well as predictors of outcome and subsequent exposure, traditional methods like logistic or proportional hazards regression are biased and hence they pose unique analytical challenges. Hence a new statistical model – a Marginal Structural Model (MSM) which employs  inverse probability weights (IPWs) to determine the effects of these time varying covariates on the primary outcome (which was survival  in this study) was utilized  in this study. In order to adjust for the effect of each dialysis modality and censorship from transplantation, a combination of inverse probability of treatment weights (IPTWs) and inverse probability of censoring weights (IPCWs) was used. The IPTW (or IPCW) will have estimated probabilities of treatment (or censorship) using baseline covariates as the numerator and estimated probabilities of treatment (or censorship) using baseline and time-dependent covariates as the denominator. The MSM helped to derive meaningful survival data, adjusting for the above mentioned confounders

The study used information from two large databases viz. USRDS and Da Vita, providing a large cohort of almost 24000 incident dialysis patients. Separate analysis was conducted using a Kaplan–Meier survival curve, cox proportional hazards and the MSM model. A 48% greater survival for incident PD patients at 2 years was found using the MSM model. These findings were in contrast to findings in other studies in the past which showed either no difference in survival or marginal survival advantage especially in the first year for PD compared to HD5. Additionally, a comparison between the cox model and the MSM   demonstrated that the time-dependent confounders determined the difference in survival. Changes in modality during the first 2 years of dialysis affected the survival patterns over time and the reason for this trend is not completely understood at this point. This study supports greater use of PD in the treatment of ESRD patients especially in US where less than 8% of prevalent patients with ESRD are on PD.A comprehensive dialysis modality education program should be encouraged to expand the practice of PD.

See these two previous posts on the debate between PD and HD.

Posted by Bijin Thajudeen

Retroperitoneal leak in PD patient

Ultrafiltration failure is a frequent clinical problem in PD patients. The most common etiologies are: fast peritoneal membrane transport, loss of peritoneal surface membrane and high lymphatic absorption. Mechanical and anatomical etiologies are occasionally seen.

Rule of 4's is used to diagnose membrane ultrafiltration failure: less than 400ml UF using 4.25% bag after 4 hours.

Sudden onset of ultrafiltration failure may occur in the setting of peritoneal leakage. Though sometimes associated with localized subcutaneous edema, it is generally difficult to detect clinically. Retroperitoneal leakage is likely to arise from a tear or a gap in the peritoneum precipitated by an increase in intra-abdominal pressure associated with walking, coughing, straining, or using a high instilled volume (2.5 L or 3 L). Red flags may include history of hernia, pleuroperitoneal communication and large infusion volumes. The acute onset of ultrafiltration failure is another suggestive finding.

Best diagnostic modality is MRI (PD fluid can be used as constrast medium).



Management: involves interruption of PD. But few reports have achieved success by using fast cycles (1hour/exchanges x8) twice a week and leaving abdominal cavity empty between sessions for 4-8 weeks.

Home Dialysis University

The dates and locations for this year's Home Dialysis University for Fellows have been released. This is a series of courses on home HD and PD aimed at graduating fellows that is sponsored by the ISPD. You can check out the RFN review of the course here and our twitter feed from it here under #HomeDialysisU. The 4 locations are Charlotte, Dallas, Denver and Chicago and they are going to take place once a month from February to May.

The site for the fellows version is here. There is a similar course run for practicing renal physicians although this is starting in just 2 days in New Orleans. The website for the non-fellow's version is here. 

Conference Review: Home Dialysis University

It doesn't take much to get me to take a trip to San Diego so when the opportunity came up to attend this year's Home Dialysis University conference I booked my flight.  Having lived in San Diego for many years prior to moving to the Bay Area I took the opportunity to both check out this great conference and stay and visit with old friends.

The conference (formerly known as Peritoneal Dialysis University) now has significant content going over home hemodialysis therapies with much of this being delivered by Brent Miller who was one of the FHN daily investigators and part of the ongoing FREEDOM study.

The conference registration and up to $350 in hotel and travel are covered for fellows by a grant from the International Society of Peritoneal Dialysis.  The conference and accommodations were at the Westgate Hotel in the Gaslamp district.  Great location and high marks for tasty breakfast, lunch and frequent snacks (all at no additional cost!)

Conference size was small, under 20 people so lots of opportunity to interact with the faculty and other attendees. Also a short conference, one full day and two half days.

John Burkart from Wake Forest gives a great lecture on how PD and HD work in terms of small and other solute clearance and reviews the uses and limitations of Kt/V.  He also gives a very practical lecture on the financial considerations related to home dialysis.  Anjali Saxena (one of my attendings who is the PD director down at the Stanford affiliated Santa Clara Valley Medical Center) covers PD access issues, the challenges that face the long-term PD patient and the infrastructure requirements for starting your own home unit.  Joanne Bargman from Toronto does some great case based discussions surrounding commonly encountered PD issues.

One of the highlights is the hands-on demonstration session were home dialysis RNs actually do a walk through with a PD cycler and a NxStage machine. Very informative.

An area where many fellows unfortunately have limited exposure is the nuances of the dialysis prescription writing for the NxStage system.  Brent Miller gives a really nice talk going over the details of this.  Lots of nice compare and contrast examples to conventional HD to put things in a more familiar context.

At least as of this writing, they haven't announced when the 2013 fellows conferences are going to be held so stay tuned to their website for dates.  In past years they've had sessions in several locations on several different dates so hopefully you'll find something that will fit your schedule.

I again tried my best to keep up a solid twitter feed of interesting points for RFN which you can find here with all the tweets indexed under #HomeDialysisU.

Honey for the Achilles Heel

In the PD literature, peritonitis has been referred to as an Achilles’ heel because it could lead to catheter removal and PD treatment failure. Topical antibiotics have been used for prevention of an exit site infection (ESI) which may precede and lead to peritonitis.

For this purpose, most centers use mupirocin as their first choice. It has reduced the ESI significantly, but mupirocin-resistant S. aureus and P. aeruginosaESI have emerged. Then came gentamicin which is superior to mupirocin. However, gentamicin-resistant P. aeruginosa has already been reported… How can we break this cycle?

FOOD was the bright idea! Not any food but a very specific sweet treat – honey. Honey has been applied to wounds since ancient times, but only recently have we come to understand its antibacterial properties: acidity (pH 3-4), high osmolarity (3000 mOsm/kg), H₂O₂, methyl glyoxal, bee defensin-1, etc. In vitro, honey killed bacteria including MRSA, β-lactamase producing E. Coli, ciprofloxacin-resistant P. aeruginosa and VRE! Because of its multiple antibacterial mechanisms, there is a low likelihood that bacteria will gain resistance.

But does it work in vivo? It has been shown that honey heals wounds and maintains sterility. Then, an Australian and New Zealand group tested standardized antibacterial honey (Medihoney) for HD catheter-associated infections and its effectiveness was comparable to mupirocin.

Now the same group is conducting the HONEYPOT study to see its efficacy in reducing the risk of PD infection. This is one of the initiatives to improve the PD technique survival in the region which is lower than in other parts of the world.

The results of the HONEYPOT study are pending, but it would be exciting if honey is proven to be an effective alternative prophylaxis with less chance of bacterial resistance. Penicillin was discovered from fungi. Gentamicin is synthesized by bacteria. Maybe it’s time to ask for honey bees for help.

Posted by Tomoki Tsukahara

Bury it!

One of the issues that we come across repeatedly in the clinic is the timing of access insertion. We all want to avoid the use of catheters and so we refer patients early (when possible) for fistula formation. This is a bigger problem when your patient wants to start PD. You don’t want the patient to have the catheter placed too early because then they will be unnecessarily exposed to the risk of infection. At the same time, you don’t want to wait too long and get to the stage where the patient requires urgent HD (and often, once they start HD it is difficult to make the transition to PD). I saw a patient in the clinic a few weeks ago that fits this bill perfectly. He is an otherwise healthy man in his 60s who has a very active life and a full-time job. His creatinine had been stable for 2-3 years but climbed rapidly earlier this year and we thought he would need to start soon. However, his creatinine stabilized again and he is feeling well so we have him in a holding pattern with regard to the PD catheter insertion. Our surgeon suggested implanting a buried PD catheter, a technique that he has just started doing in our institution.

For this technique, the catheter is buried subcutaneously at the time of insertion. Then, when the patient is ready to start dialysis, the subcutaneous portion is externalized and the catheter can be used straight away. This can be done in the dialysis clinic and does not require a trip to the OR. Thus, a catheter can be inserted months (or even years) prior to use and the problem of timing is dealt with very elegantly. Recently, a paper was published which described the experience of the University of Denver where they have been using this technique as standard since 2000. In total, 134 catheters were implanted in that time. The period prior to externalization varied between 2 and 788 days with an average of 40 days. There was no relationship between catheter embedment time and the risk of catheter failure. 90% of catheters worked immediately and of the remaining 13 catheters, 12 were easily corrected laparascopically. Only 1 patient failed this technique and required transition to HD. This seems like a great technique and I look forward to seeing the results here over the next few months.

See also this earlier paper in KI about the experience with the use of buried catheters in Ottawa.

PD or HD post cardiac surgery?

A few months back I was covering the inpatient consult service when one of our patients on peritoneal dialysis came in for an elective combined aortic valve replacement and coronary artery bypass grafting. She had recently switched over from in-center HD to PD and still had a functional arteriovenous graft in place. The surgery went well and the patient came out of the operating room to the cardiac critical care unit.

 As I sat reviewing the chart my attending posed the following question "So is it reasonable to continue PD here in the unit or should we switch over to HD until she's extubated and clinically improving?"

Would the increased intra-abdominal pressure from PD lead to prolonged intubation time? Given the manipulation of the thoracic cavity was there a higher risk of dialysate leak through the diaphragm? Would we be able to provide adequate clearance and ultrafiltration with PD? Would the infection risk be higher for PD given the relative unfamiliarity of the nursing staff?

A recent article in Peritoneal Dialysis International comparing perioperative outcomes in patients on PD and HD post cardiac surgery sheds some light on the situation. In the study the Southern California Permanente Group at Los Angeles Medical Center looked back at 15 years of CABG and cardiac valve replacement surgeries in ESRD patients and compared a variety of outcomes between 36 patients on PD and 76 on HD.

There were no reported significant differences between the two groups at baseline including age, dialysis vintage, presence of diabetes, type of surgery and Charlson comorbidity index.  The only statistically significant difference in terms of outcomes was a slightly longer median length of stay in the cardiac surgical unit for HD patients (4 vs 2 days) though the median total hospital length of stay between the two groups was no different (PD 9.5 days, HD 10 days).

There was trend towards more infections in the HD group (19% vs 6%) but this did not reach statistical significance. Median intubation time was the same between groups.  Survival perioperatively (defined as during the hospital stay or within 30 days of operation) and at one and two years was similar between groups (PD 89%, 81%, 69%, HD 90%, 78%, 66%).

Conversion of PD patients to HD occurred in just 6% percent of patients. One for dialysate leak and another for uncontrolled azotemia.  CRRT was needed in 1 HD patient due to hemodynamic instability.

The study doesn't answer the question of whether converting a patient on PD to HD or CRRT might improve outcomes but it does provide reassurance that PD patients don't have an excessive risk of dialysate leak or inability to achieve adequate clearance and ultrafiltration.  It also shows that in general outcomes post cardiac surgery between PD and HD patients are similar.

In our patient we continued peritoneal dialysis using an automated cycler without difficulty.  Over the weekend the covering team changed to HD via the arteriovenous graft over concern that PD might lead to a dialysate leak.  Unfortunately the patient tolerated HD poorly with episodes of hypotension so we transitioned back to PD when we came back on.  The rest of her hospitalization was without incident.