ACID-BASE METABOLISM AFTER BLADDER SUBSTITUTION WITH THE ILEAL URETHRAL KOCK RESERVOIR

Objectives To assess acid-base metabolism after bladder substitution w ith the ileal Kock reservoir, using capillary blood-gas analysis, meas urement of the renal excretion of ammonium and titratable acid and the evaluation of renal function by plasma clearance of Cr-51-labelled et hylenediamine tetra-acetic acid (Cr-51-EDTA). Patients, subjects and m ethods The investigation comprised both a cross-sectional study, with initial measurements after surgery, and a longitudinal study, with pre -operative measurements, both groups of patients being followed for 2 years after inclusion. The cross-sectional study included 26 patients (median age 66 years,range 44-75), with a median post-operative follow -up of 1.2 years (range 0.3-3.7), and 16 control subjects (median age 62 years, range 34-80), and the longitudinal study comprised seven pat ients (median age 57 years, range 42-68). Results The median values fo r capillary blood pH, carbon dioxide pressure, standard bicarbonate an d standard base excess were significantly lower in patients with a bla dder substitute than in the control subjects. An acid-base chart showe d that the values for 44% of patients and none of the controls were wi thin the area representing mild metabolic acidosis, This difference co uld not be attributed to differences in renal function because the Cr- 51-EDTA clearance was normal and similar in the two groups of patients and among patients and controls. Nevertheless, the median values for each of the variables measured by blood-gas analysis were within the r eference interval of the normal population. Net acid excretion was sim ilar in patients with a bladder substitute and control subjects, but u rinary pH was significantly higher in the patients, Accordingly, the r enal excretion of ammonium was significantly higher and the excretion of titratable acid significantly lower in patients after ileal bladder substitution. Conclusions The results are consistent with the hypothe sis that bladder substitution with the ileal Koch reservoir results in an acid load to the body, caused mainly by ammonium reabsorption in t he reservoir. The acid load is compensated by an increased renal excre tion of ammonium but causes a mild metabolic acidosis in about half th e patients.