Enteric and Bladder Drainage of the Exocrine Pancreas and Enteric Conversion

Ty B. Dunn

DEFINITION

Successful pancreas transplantation requires management of the gland’s exocrine secretions.
From the first pancreas transplant until present, the management of the exocrine pancreas has evolved through a variety of operative techniques (end stoma, duct ligation, open duct, duct injection, ureteral anastomosis, bladder and enteric drainage), each with their own complications and utility.
Enteric or bladder drainage of the duodenal cuff are the currently preferred methods.
Knowledge of other techniques is required for optimal care of the pancreas transplant recipient, as they may be used in rare cases to salvage a technical problem or have been used in a patient transplanted in an earlier era.
Exocrine leak is a major cause of surgical complications after pancreas transplantation.

PATIENT HISTORY AND PHYSICAL FINDINGS

As enteric drainage emulates normal physiology, it is associated with decreased complications compared to bladder drainage technique. Enteric drainage of the pancreas allograft has increased in popularity in the recent era, as compared to bladder drainage, as first described by Sollinger in 1984 and modified by Corry.¹^,²^,³ However, for recipients of solitary pancreas transplants (pancreas after kidney [PAK] or pancreas transplant alone [PTA]) or simultaneous kidney and pancreas (SPK) with perceived high risk of rejection or technical problem, some centers prefer bladder drainage due to lower early posttransplant intraabdominal infection rate, thrombosis, and enhanced ability for graft monitoring for rejection.⁴
The choice of technique used to accomplish drainage of exocrine secretions is impacted by several key issues including consideration of recipient comorbidities such as gastroparesis or neurogenic bladder, the type of pancreas transplant, and the estimated immunologic risk.⁵^,⁶
Some diabetics have gastroparesis or diabetic colopathy, which may manifest as delayed gastric emptying, vomiting, or alternating diarrhea and constipation. These conditions can increase the risk of early enteric leak, graft pancreatitis, and inconsistent absorption of immunosuppression. This subset of patients may be better suited for bladder drainage.
If bladder drainage is considered, it is important to ensure normal bladder function. Long-standing diabetics often have increased bladder capacity and incomplete bladder emptying, which increases the risk of stasis and infection as well as the possibility of reflux graft pancreatitis.
- Significant urologic dysfunction can usually be ascertained by a careful history. A history of recurrent infections, bladder outlet obstruction (prostatic hypertrophy or urethral stricture), pretransplant dehydration or acute kidney injury episodes, and neurogenic bladder are relative contraindications for bladder drainage. In some cases, obtaining urodynamic studies may be helpful.

IMAGING AND OTHER DIAGNOSTIC STUDIES

The exocrine pancreas is first affected by rejection yet isletitis can be seen on histology. Hyperglycemia occurs later in the or with severe cases of rejection. Elevations of serum amylase and lipase cause concern for potential rejection and can trigger a graft biopsy. Unfortunately, biopsies can cause significant complications, and elevations of serum amylase and lipase are not specific for allograft rejection.⁷^,⁸
Serial testing of posttransplant serum amylase and lipase levels will establish a posttransplant “normal” range. Deviations (>25% of baseline) from this range may indicate rejection or inflammation caused by relative obstruction (reflux) of exocrine secretions. A sustained increase in serum amylase or lipase not resolved by treatment of constipation (enteric drained), Foley catheter drainage (bladder drained), or when observed in the absence of native pancreatitis should prompt a pancreas graft biopsy.
Discordant rejection (of one organ and not the other) in SPK has been reported as high as 38%, so pancreas graft dysfunction cannot be reliably inferred from kidney graft function or biopsy.⁹ As the incidence of rejection in the nonuremic solitary pancreas transplant recipient is higher than in SPK and can be difficult to diagnose by elevations in serum amylase and lipase alone, the use of bladder drainage may afford an increased ability to detect rejection in this subset of recipients. Newer techniques that enable endoscopic biopsy of enteric-drained grafts have been recently reported.¹⁰^,¹¹^,¹²
Calculation of urinary amylase (units per hour) is done by urine collection (8 hours) to monitor pancreas exocrine function of a bladder-drained graft. Serial monitoring will define the usual range observed in an individual; with each pancreas allograft having a unique normal range.
- A sustained 25% decrease in urinary amylase excretion signifies exocrine pancreas dysfunction.
- Cystoscopy for duodenal mucosal biopsy has a low complication rate compared to percutaneous biopsy. It can be particularly useful when allograft parenchyma is not accessible due to overlying bowel.
As bladder drainage can be associated with metabolic and urologic complications refractory to medical management, enteric conversion may become indicated in up to 25% of bladder-drained grafts. These complications include
- Fluid and bicarbonate loss (recurrent dehydration and metabolic acidosis)
- Change in bladder pH, with recurrent infections
- Inflammation causing cystitis, urethritis, and hematuria
- Foreign body (exposed suture/staple) as a nidus for infection, hematuria
- Reflux pancreatitis due to the bladder/bladder outlet dysfunction
When indicated, enteric conversion is usually performed after the first year of transplant when the morbidity of complications outweighs the risk of missed rejection. The procedure involves disconnecting the duodenocystostomy, closure of the bladder, and anastomosing the graft duodenum to the small intestine.
Enteric conversion can also be performed to treat posttransplant acquired native pancreatic exocrine insufficiency, which can present as refractory diarrhea exacerbated by dietary fat intake and confirmed by fecal elastase or fat quantification.

SURGICAL MANAGEMENT

Preoperative Planning

The graft duodenum should be prepared during procurement by instillation of amphotericin B or Betadine solution (via the nasogastric tube) in order to decrease microbial burden and subsequent operative field contamination.
Preoperative urine culture should be negative.
Preoperative antibiotics are chosen to empirically target enteric bacteria and yeast, both during pancreas transplantation and enteric conversion operations.
Most surgical complications of pancreas transplant are related to donor-derived issues (anatomic, physiologic, and reperfusion related). As such, careful graft selection is paramount.

Positioning

Patient position is supine with both arms out.
Use a three-way Foley catheter in all cases; the use of the bladder drainage technique may be planned or unexpected. In rare cases of vascular insufficiency of the head of the pancreas after reperfusion, bladder drainage could be useful because management of a bladder leak is less morbid (decreased rates of intraabdominal infection, reoperation, and graft loss) compared to an enteric leak.

TECHNIQUES

PLACEMENT OF INCISION

Modern approach to pancreas transplant is through a midline incision:
- Low midline for systemic venous and enteric- or bladder-drained grafts
- Periumbilical for portal venous and enteric-drained grafts
The retroperitoneal approach is rarely done due to an increased risk of peripancreatic abscess and pancreatitis due to proteinaceous fluid loculation in the retroperitoneal space. If a retroperitoneal approach is chosen, the peritoneum should be opened at the conclusion of the procedure and/or the graft widely drained.

ENTERIC DRAINAGE

Exposure

Small bowel adhesions should be lysed and proximal/distal orientation of the bowel confirmed. Select a proximal segment of small bowel that reaches the pancreas without tension or kinking for anastomosis to the graft duodenum.
Control duodenal secretions to avoid unnecessary soilage of the operative field. This spillage may cause a peripancreatic abscess or mycotic aneurysm.

Anastomosis