Dispelling PD Myths: Abdominal Surgery and Obesity

The National Kidney Foundation Spring Clinical Meetings in Boston in April 2022 included a session entitled Debunking Common Myths About Patient Eligibility for Home Dialysis. Dr. Rob Quinn from Canada talked about the myth that patients with prior abdominal surgery or who are obese should not be offered PD.

Prior Abdominal Surgery

Dr. Quinn reported that 30% of patients have had prior abdominal surgery. The assumption is that prior abdominal surgery leads to adhesions and a PD catheter won't work. He said that science doesn't back this up. A laparotomy increases the risk. However, those who have not had prior surgeries have adhesions too. Surgeons have told him that they can't predict whether they'll find adhesions or not.

When patients with adhesions were followed long-term, there was no increased risk of infectious complications, mechanical complications, or problems with catheter longevity according to data from the North American PD Catheter Registry.¹ Of the 1470 patients in the registry, 855 patients had non-buried PD catheters and 1-year follow-up. When 257 of them with prior abdominal surgeries were compared with 596 patients without abdominal surgeries, there were similar risks for temporary interruption of PD or terminating PD.

Neither the presence nor the number of abdominal surgeries predicted risk of catheter complications. The risk of interruption or termination of therapy was about 1 in 5 whether the patient had prior abdominal surgery or not. Temporary interruptions in PD were more common than terminations. There was no difference in ER visits, hospitalizations, and invasive procedures between those with and without prior abdominal surgeries, either.² Here are talking points he suggested for patients:

• About 1 in 5 people on PD will have either a temporary interruption in PD or termination of PD due to a significant catheter complication.

• Prior abdominal surgery is not associated with a significant increase in risk.

• Even if there is a small increased risk, this shouldn't change a physician's decision-making about whether to offer a patient PD.

Obesity

Obesity is common in the U.S., and the majority of dialysis patients seen today meet BMI criteria for obesity. There is a concern that PD gives obese patients dialysate loaded with sugar that could lead to weight gain, high blood lipids, elevated A1c levels, and increased insulin requirements.

Looking at weight gain, a study of about 140 incident PD patients who had a PET initially and 6 months later found that the average person gained .5 kg (about a pound) in their first year on PD. Most replaced lean mass with fat mass.³ Males, high transporters and those who used higher glucose dialysate did worse.

Questioning whether it would be better to put obese patients on HD instead of PD, a study compared both and found there was no difference in weight gain or replacement of lean mass with fat mass.⁴

So far as a concern about the higher risk of death for those on PD who have a higher BMI, there is a higher risk of death in both PD and HD patients who have a very high—or a very low—BMI.⁵ This is also true for those who don't have kidney failure.⁶ Many believe BMI contributes to technique failure. A study by Obi found that people with high BMI were more likely to transfer to HD, but when looking at why, almost 25% transferred to HD because they failed to meet adequacy targets. The author believes that the Kt/V formula overestimates V (total body water) in obese patients. V is calculated from a formula that uses a patient's age, height, and weight. The Kt/V equation for men is different from women because men are assumed to have more lean mass and women are believed to have more fat mass. However, fat mass does not contribute to total body water. So, a malnourished patient may appear to be meeting the adequacy target while an obese patient with the same clearance looks like s/he isn't getting enough dialysis. KDOQI guidelines for HD suggest using ideal weight or body surface area instead of V for HD adequacy,⁷ so ideal body weight should be used for PD adequacy as well.

• Infection

  Obese patients do have a higher risk of all kinds of infection. Obi found an increased risk of hospitalization for peritonitis with higher risk as BMI increased. The risk starts to rise when BMI is 25 and rises more at 35 or higher.⁵ That said, Dr. Quinn noted that he has skinny patients he worries about more with regard to peritonitis, because they have worse hygiene than his obese patients.

• Catheter Complications

  Studies have not shown an increased risk of catheter complications in obese PD patients. Preliminary data from the Registry found no increased risk of catheter complications with increased BMI.²

• BMI

  

  Dr. Quinn said that BMI is a really crude measure. If you look at BMI alone, Duane Johnson (“The Rock”) who has a BMI of 31 and all football players would be considered obese. Instead, he suggests looking at fat distribution, and whether someone has a big belly with fat rolls, or a firm belly. A presternal catheter could overcome this barrier but few patients have them.

Dr. Quinn suggested these talking points for patients about obesity:

• Expect a weight gain of .5 kg/year.

• Risk of death and infection are higher when your BMI is very low or very high, and what option you choose doesn't affect this.

• There does not appear to be an increased risk of catheter complications with BMI, but we don't know if that's true for people with bigger bellies.

• Fat mass and distribution are more important than BMI.

He suggested these talking points to providers about prior abdominal surgeries and obesity:

• Set expectations for catheter function - 1 in 5 will have a problem, but prior abdominal surgery doesn't affect this.

• Obesity is associated with poorer outcomes, but this isn't treatment-related.

• When using Kt/V, base V on desired weight to avoid adequacy estimation errors.

A patient attending the session asked what to say when a provider believes a patient is ineligible to do a treatment because of these myths. Dr. Quinn suggested that patients be their own advocates, talk with the provider about research they've read that shows different outcomes, and if they feel strongly enough, ask for a second opinion. His job, he noted, isn't to allow a patient to do a certain treatment, but to inform patients about the risks and benefits of all modalities, and educate them about their options. Then patients can make an informed choice. This is what we at Medical Education Institute support as well.