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Keywords:

  • acid–base metabolism;
  • neobladder;
  • renal function;
  • sodium bicarbonate

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

Background:  The objective of this study was to determine whether renal function influences the acid–base metabolism in patients undergoing orthotopic bladder replacement using intestinal segment.

Methods:  Acid–base balance, serum electrolytes and renal function were studied in 30 patients with colon neobladder and 18 patients with ileal neobladder. Mean follow up was 51 months. Effects of renal function on acid–base metabolism in both types of bladder replacement were compared. Therapeutic efficacy of the sodium bicarbonate administration was also evaluated in cases with hyperchloremic acidosis.

Results:  No significant differences were observed in any of the variables examined between the colon and ileal neobladder groups, except for potassium concentration. Although metabolic acidosis was detected using the Siggard–Anderson acid–base nomogram in eight (26.7%) and seven (38.9%) patients in the colon and ileal neobladder groups, respectively, this difference was not significant. In both the colon and ileal neobladder groups, the serum creatinine concentrations in patients diagnosed with metabolic acidosis were significantly higher than in those diagnosed with a normal metabolic status. Furthermore, as a result of severe metabolic acidosis, three (10.0%) and three (16.7%) patients in the colon and ileal neobladder groups, respectively, were administered sodium bicarbonate and their metabolic status was fully normalized.

Conclusions:  Despite there being no statistical difference, patients with ileal neobladder may more easily develop metabolic acidosis compared with those with colon neobladder. In addition, a close association between the serum creatinine level and the degree of metabolic acidosis was observed in both groups. However, even if severe metabolic acidosis occurs, it is relatively easy to correct using sodium bicarbonate. These findings suggest that it might be safe to use a colon segment for orthotopic bladder reconstruction in patients with higher serum creatinine levels, despite no significant difference in acid–base metabolism and detection rates of metabolic acidosis between the colon and ileal neobladder groups.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

The use of intestinal segments for orthotopic bladder replacement after radical cystectomy has become common since the risk of surgical complication associated with this procedure has decreased with improved operative techniques; furthermore, it has been shown to improve postoperative quality of life.1 However, several investigators have reported the relatively frequent incidence of hyperchloremic metabolic acidosis, disturbances in electrolyte metabolism, osteomalacia and skeletal growth retardation after urinary reconstruction using intestinal segments.2–4 The kinds of problems associated with metabolic changes after urinary diversion are related to various factors, including the type and length of bowel segment used, the duration of exposure of bowel mucosa to urine, urinary pH and osmolarity, and general health, in particular renal and hepatic function.2,5,6 Mills and Studer reported that patients with pre-existing disease are less able to compensate for metabolic changes resulting from urinary diversion,2 and therefore a serum creatinine level greater than 150–200 µmol/L is thought to be indicative of a poor risk.7

Previous studies have shown that mild respiratory compensated hyperchloremic metabolic acidosis was noted after continent urinary diversion in patients with normal renal function.8,9 The main cause of the metabolic acidosis is absorption of ammonium through the intestinal mucosa, but secretion of bicarbonate plays a minimal role in the acid load. Moreover, in patients with poor renal function, renal excretion of ammonium decreases, resulting in the occurrence of systemic acidosis.10 Therefore, in states of chronic endogenous acid load, such as after incontinent urinary diversion, metabolic acidosis might be expected to become severe. However, to our knowledge, few studies have focused on the relationship between renal function and the metabolic problems in patients undergoing urinary diversion.5 Thus, we investigated the effect of renal function on metabolic changes in acid–base balance in patients with orthotopic neobladder according to the intestinal segment used for bladder reconstruction.

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

A total of 48 men who underwent radical cystectomy and orthotopic bladder replacement for invasive bladder cancer were included in the present study. The reconstruction of orthotopic neobladder was performed using the colon for 30 patients (sigmoid colon11 for 22 and ascending colon12 for 8) or the ileum13 for 18 patients. Currently, when the patient is physiologically able to tolerate a major operation and perform the normal activities of daily life, ileal or colon neobladder is selected as the procedure for urinary diversion at Hyogo Medical Center for Adults or Kobe University Hospital, respectively, with one exception: colon neobladder has been contraindicated in patients whose sigmoid colon is too short to connect to the urethra.

The mean patient age was 63.0 years (range 45–80 years) for both groups together, 65.8 years (range 45–80 years) for the ileal neobladder group and 61.2 (range 51–74 years) for the colon neobladder group. The mean follow-up period since the operation was 46.2 months (range 10–139 months) for both groups together, 53.0 months (range 21–139 months) for the ileal neobladder group and 41.7 months (range 10–124 months) for the colon neobladder group.

We measured serum electrolytes (sodium, potassium and chloride) as well as creatinine, blood urea nitrogen and blood gases (including pH, base excess, oxygen pressure, carbon dioxide pressure). Metabolic acidosis was determined using a Siggard–Anderson acid–base nomogram with 95% confidence intervals.3

All findings were presented as the mean ± SD. Differences between the groups were analyzed using the unpaired Student's t-test or χ2 tests. Probability values less than 0.05 were considered statistically significant.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

Table 1 shows the results of serum electrolyte and blood gas analysis. Despite the normal value, the mean concentration of serum potassium in patients with ileal neobladder was significantly higher than in patients with colon neobladder, whereas there were no significant differences between these two groups in the remaining variables analyzed in the present study. We then analyzed the presence of metabolic acidosis using a Siggard–Anderson acid–base nomogram. Metabolic acidosis was detected in 7 of the 18 patients (38.9%) with ileal neobladder and in 8 of the 30 patients (26.7%) with colon neobladder; however, the difference in the incidence of metabolic acidosis between these two groups was not significant.

Table 1.  Blood chemistry profile of patients with neobladder
 Ileal neobladder (n = 18)Colon neobladder (n = 30)P
Blood urea nitrogen (mg/dL) 20.5 ± 8.3 17.1 ± 5.9 0.140
Creatinine (mg/dL) 0.92 ± 0.27 0.87 ± 0.27 0.540
Sodium (mEq/L)141.2 ± 2.3142.3 ± 1.5 0.080
Potassium (mEq/L)  4.5 ± 0.3  4.1 ± 0.4<0.001
Chloride (mEq/L)107.8 ± 3.3109.4 ± 4.2 0.150
pH 7.37 ± 0.04 7.37 ± 0.04 1.000
PaO2 (mmHg) 88.6 ± 10.5 92.7 ± 10.4 0.200
PaCO2 (mmHg)37.30 ± 0.0438.10 ± 4.70 0.360
Base excess (µmol/L)−3.30 ± 3.60−2.43 ± 4.20 0.450

The values of serum electrolytes and blood gas analysis were compared between patients diagnosed as having metabolic acidosis and those with a normal metabolic status. As shown in Table 2, the mean level of serum creatinine in patients diagnosed as having metabolic acidosis was significantly higher than in patients diagnosed with normal metabolic status in both groups. We then examined whether the serum creatinine level correlated with pH, base excess and carbon dioxide pressure, which are regarded as the parameters reflecting the degree of metabolic acidosis, and demonstrated the close association between the serum creatinine level and all three parameters (Fig. 1).

Table 2.  Renal function in patients with neobladder according to metabolic status
 Ileal neobladder acidosisColon neobladder acidosisTotal acidosis
+P+P+P
  1. +, positive; –, negative; BUN, blood urea nitrate; Cr, creatinine.

BUN (mg/dL)19.0 ± 7.022.9 ± 10.1 0.34619.3 ± 8.416.4 ± 4.8 0.38020.9 ± 9.118.50 ± 5.6 0.260
Cr (mg/dL)1.07 ± 0.350.82 ± 0.15<0.0501.08 ± 0.310.80 ± 0.22<0.0101.08 ± 0.32 0.82 ± 0.20<0.050
imageimageimage

Figure 1. Correlation of creatinine and (a) pH (P < 0.0001), (b) PaCO2 (P = 0.0077) or (c) base excess (P < 0.0001) in patients with neobladder. Creatinine significantly correlated to pH, PaCO2 and base excess.

As a result of severe metabolic acidosis, three (10.0%) and three (16.7%) patients in the colon and ileal neobladder groups, respectively, required administration of sodium bicarbonate. In all six patients, however, their metabolic status was fully normalized with the use of sodium bicarbonate alone (Table 3).

Table 3.  Effect of sodium bicarbonate administration in patients with severe acidosis
Patient no.Age (years)Intestinal segment used for neobladderBefore administration of the sodium bicarbonateAfter administration of the sodium bicarbonate
pHPaCO2 (mmHg)Base excess (µmol/L)pHPaCO2 (mmHg)Base excess (µmol/L)
172Colon7.29429.4−10.77.37339.7−1.5
257Colon7.25525.6−14.07.46232.2−0.3
363Colon7.32833.8 −7.17.38037.3−2.2
471Ileum7.33927.4 −9.37.44236.0 0.2
571Ileum7.37529.0 −7.37.41539.5 1.4
668Ileum7.24029.2 −9.57.38940.0 0.5

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

Varying lengths and types of intestinal segments are used for urinary reconstruction after radical cystectomy. Following urinary diversion, the flux of ions across the intestinal mucosa by contact with urine can cause disorders to the acid–base and electrolyte balance. Among them, hyperchloremic metabolic acidosis is the most frequently observed complication after urinary diversion with up to 50% of cases affected. The frequency and severity of metabolic acidosis are mainly related to the type and length of intestinal segment used, as well as general health status. The current trend toward continent urinary diversion could subject an increasing number of patients to the risk of an imbalance in their metabolic status by constant contact of urine with the intestinal mucosa. In addition, patients undergoing urinary diversion following radical cystectomy suffer declining renal function because of aging and complications of their urinary reconstruction, suggesting that they could be at greater risk of developing disorders to the acid–base balance. However, to our knowledge, few studies have investigated the effect of renal function on the acid–base balance in patients with continent urinary diversion.5,8 Therefore, in the present study, we characterize the changes in the acid–base and electrolyte balance in patients who have undergone orthotopic neobladder replacement using the colon or ileum, focusing on the association with renal function.

In the present series, no significant differences were observed between the colon and ileal neobladder groups in the results of serum electrolyte and blood gas analysis, except for the potassium concentration, which was still in the normal range in both groups. The analysis using a Siggard–Anderson acid–base nomogram revealed that metabolic acidosis was detected in 38.9% of patients with ileal neobladder and in 26.7% of patients with colon neobladder. Although this difference was not significant, patients with ileal neobladder may more easily develop metabolic acidosis than those with colon neobladder. This finding is consistent with previously reported results assessed by both experimental and clinical means: that is, colonic segments absorb an equal or lesser amount of acid and secrete less alkali than ileal segments when electrolyte transport is examined as a function of the bowel surface area in a rat model.14 In addition, patients with colonic urinary diversions did not appear to create significant acid–base changes compared with those with ileal urinary diversion if their hepatic and renal functions were normal.8 We then analyzed the relation between renal function and acid–base metabolic status, and demonstrated that the serum creatinine level, which was distributed equally irrespective of the type of neobladder, correlated to the parameters reflecting the degree of metabolic acidosis (i.e. pH, base excess and carbon dioxide pressure) in patients with both types of neobladder. Considering these findings, it might be safe to use colonic segment for the creation of orthotopic neobladder in patients with relatively poor renal function in order to prevent metabolic acidosis.

Current treatment of hyperchloremic metabolic acidosis involves alkalizing agents and/or chloride transport blockers.2 Oral sodium bicarbonate is effective in restoring a normal acid–base balance, although intestinal gas formation could be a problem and the dose is not easily predictable. In the present series, 10.0 and 16.7% of patients in the colon and ileal neobladder groups, respectively, required administration of sodium bicarbonate because of severe symptomatic metabolic acidosis, and their metabolic status was fully normalized using oral sodium bicarbonate alone. However, in patients at high risk, sodium supplements could increase blood pressure or cause fluid retention and pulmonary edema; therefore, it is absolutely necessary to perform careful follow up for patients administrated sodium bicarbonate.

Conclusion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

Despite there being no significant difference, patients with ileal neobladder eight develop metabolic acidosis more easily than those with colon neobladder. In addition, a close association between renal function and degree of metabolic acidosis was observed in both neobladder groups. However, even with severe symptomatic metabolic acidosis, it was relatively easy to correct the imbalance of the acid–base metabolism by the oral administration of sodium bicarbonate. These findings suggest that it might be safe to use a colon segment for orthotopic bladder reconstruction in patients with higher serum creatinine levels, despite there being no significant difference in acid–base metabolism and detection rates of metabolic acidosis beween the colon and ileal neobladder groups.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References