The instillation of dialysis fluid into the peritoneal cavity is accompanied by an increase in intra-abdominal pressure (IAP). The two principal determinants of its magnitude are dialysate volume and the position of the patient during the dwell. The supine position is associated with the lowest IAP for a given dialysate volume; sitting is associated with the highest. Furthermore, actions such as coughing, bending, or straining at stool transiently increase IAP. The increased IAP can lead to a variety of mechanical complications in peritoneal dialysis (PD) patients.

I. HERNIA FORMATION

A. Incidence and etiologic factors. The incidence and prevalence of hernias are difficult to assess. Hernias can be asymptomatic and may be missed on cursory examination. It has been suggested that as many as 10%-20% of patients may develop a hernia at some time on peritoneal dialysis.

Potential risk factors are listed in Table 28.1 and include large dialysate volumes and activities that involve isometric straining or the Valsalva maneuver. Furthermore, deconditioning of the musculature of the abdominal wall increases wall tension and predisposes to hernia formation.

B. Types of hernia. Many different types of hernia have been described in the peritoneal dialysis patient. These are listed in Table 28.2.

Indirect inguinal hernias are the result of bowel and/or dialysate tracking through the processus vaginalis, which in some individuals has remained patent rather than undergoing normal obliteration. It is much more common in males. In boys, it is very likely that if one processus vaginalis is patent (causing inguinal hernia), then the other side is patent also, and repair (see below) should be done bilaterally.

C. Diagnosis. As mentioned above, hernias can be clinically occult. To better detect them, it is often useful to have the patient stand and “bear down” as this increases IAP and makes a hernia more obvious. Pericatheter hernias need to be differentiated from masses caused by a hematoma, seroma, or abscess. Ultrasonography can distinguish the solid-appearing hernia from the fluid collections characterizing these other conditions. The scrotal fullness of an indirect inguinal hernia has in its differential diagnosis hydrocele (fluid/dialysate entering the scrotum through a patent processus vaginalis) and intrinsic scrotal or testicular pathology.

Delineation of a hernia can be aided by dye-assisted computed tomography (CT). First, 100 mL of Omnipaque 300 is added to a 2-L bag of dialysate and then instilled into the peritoneal cavity. It is important that the patient then be as active and ambulatory as possible for the next 2 hours to facilitate the entry of dye into the hernia sacs. CT scanning is then performed. In the case of inguinal hernias, it is important that the genitalia be scanned. The CT scan can indicate whether scrotal edema is the result of fluid tracking along a patent processus vaginalis or along the anterior abdominal wall (see below). This procedure can also help delineate anterior abdominal wall hernia from isolated leaks. In other types of hernia, such as umbilical hernia, CT scanning is not necessary because the diagnosis is usually obvious.

Magnetic resonance imaging may be useful in the diagnosis of abdominal wall and genital leaks, and it may be helpful in patients with allergy to conventional radiologic dye. The dialysate itself looks bright white on the MRI images.

D. Treatment. Small hernias, especially umbilical hernias, pose the greatest risk of incarceration or strangulation of bowel. These should be repaired surgically. The patient should be warned that if a hernia stops being reducible, and especially if it becomes tender, medical consultation should be sought immediately. Any patient presenting with peritonitis should be examined for the presence of small strangulated hernias, as these can lead to transmural leakage of bacteria and peritonitis. Large hernias can also be repaired surgically, as can cystocele and enterocele. Uterine prolapse (not really a hernia) can sometimes be managed with a pessary, but ultimately hysterectomy may be necessary.

After surgical repair of a hernia, IAP must be kept as low as possible to facilitate healing. If the patient has significant residual renal function (e.g., 10 mL/min or more), it may be possible to stop dialysis altogether for a week and then recommence with small volumes (e.g., 1 L). The patient must be watched for the development of uremic symptoms or hyperkalemia. If automated peritoneal dialysis (APD) is available, the patient can dialyze supine and hence with lower IAP. If there is little or no renal function, low-volume peritoneal dialysis should be started postoperatively. An alternative is to hemodialyse the patient until wound healing is more complete (2-3 weeks).

Options for the patient with recurrent hernias include a reduction in strenuous physical activity, more frequent dialysis exchanges with lower volumes, or transfer to hemodialysis.

If the patient is too ill or refuses surgery, mechanical support of the hernia can be effected with a corset or truss. The patient should be warned about symptoms of incarceration and strangulation.

II. ABDOMINAL WALL AND PERICATHETER LEAK.

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