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Ann Thorac Surg 2003;76:1443-1449
© 2003 The Society of Thoracic Surgeons

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Original article: cardiovascular

Peritoneal dialysis after surgery for congenital heart disease in infants and young children

^a Division of Paediatric Cardiology, Department of Paediatrics and Adolescent Medicine, Grantham Hospital, Hong Kong, People's Republic of China
^b Division of Cardiothoracic Surgery, Department of Surgery, The University of Hong Kong, Hong Kong, People's Republic of China

Accepted for publication April 25, 2003.

^* Address reprint requests to Dr Cheung, Division of Paediatric Cardiology, Department of Paediatrics and Adolescent Medicine, Grantham Hospital, The University of Hong Kong, 125 Wong Chuk Hang Rd, Hong Kong, China.
e-mail: xfcheung{at}hkucc.hku.hk

	Abstract

Top Abstract Introduction Material and methods Results Comment References

 
BACKGROUND: We determined the risk factors for peritoneal dialysis (PD) in young children undergoing open heart surgery and, in those patients requiring PD, factors associated with prolonged PD and mortality.

METHODS: The clinical records of 182 children, aged 3 years or younger, who had undergone open heart surgery during a 2-year period were reviewed. Demographic data, preoperative risk factors, intraoperative variables, and postoperative complications were compared between patients requiring PD and those who did not, and between survivors and nonsurvivors of PD.

RESULTS: Of the 182 patients, 31 (17%) required PD. Patients requiring PD were lighter and more likely to have required preoperative ventilation; had undergone more complex surgery requiring longer bypass and circulatory arrest; and had experienced a pulmonary hypertensive crisis (p < 0.01). Logistic regression identified circulatory arrest (relative risk, 9.4; p = 0.002), cardiopulmonary bypass duration (relative risk, 1.02; p = 0.028), and low cardiac output syndrome (relative risk, 12.9; p < 0.0001) as significant determinants. Peritoneal dialysis was effective in achieving negative fluid balance, although serum urea and creatinine levels remained static. Prolonged PD was associated with younger age, higher preoperative serum creatinine, higher postoperative oxygen requirement, postoperative pulmonary hypertensive crisis, and low cardiac output syndrome (p < 0.05). When compared with survivors (n = 22), nonsurvivors (n = 9) were more likely to have had syndrome disorders and required preoperative ventilation and higher postoperative ventilatory settings (p < 0.05).

CONCLUSIONS: Risk factors for PD in young children undergoing open heart surgery are circulatory arrest, cardiopulmonary bypass duration, and low cardiac output syndrome. The preoperative and postoperative cardiopulmonary status has a significant bearing on PD duration and patient survival.

	Introduction

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Acute renal failure is a well-documented complication after pediatric open heart surgery [1–5]. Risk factors of acute renal failure and the need for renal replacement therapy include young age, complex cardiac lesions, long cardiopulmonary bypass time, and a low cardiac output state after surgery [6–8]. Although the choice of renal replacement therapy remains controversial [9, 10], peritoneal dialysis (PD) has been demonstrated to be useful in light of the ease of application, effectiveness in fluid removal and avoidance of the need for anticoagulation, and establishment of additional vascular access [1–3, 8–10].

Given the significance of young age as a determinant of acute renal failure and PD after pediatric cardiac surgery [3, 6, 7], we determined the prevalence and significant determinants of acute renal failure requiring PD in 182 young children aged 3 years or younger undergoing open heart surgery for congenital heart disease. In contrast to previous studies [6, 7, 11], a multivariate analysis approach was adopted to adjust for potential confounding variables. In patients requiring PD, we further assessed the efficacy and complications of this renal replacement therapy, determined risk factors predisposing to prolonged PD, and identified factors associated with mortality.

	Material and methods

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Patients
The hospital records of 222 consecutive patients, aged 3 years or younger, who underwent heart surgery for congenital heart disease between September 1999 and August 2001 were reviewed. Six premature babies, who were born before 37 weeks' gestation and had ligation of patent ductus arteriosus, and 9 patients who died within 72 hours after open heart surgery were excluded. Exclusion of the latter 9 patients was considered justifiable as such short postoperative survival (mean of 16 hours; range, 0 to 72 hours) might have precluded detection of acute renal failure and the need for PD in a few had they survived. Of the remaining 207 patients, 25 underwent closed heart surgery whereas 182 underwent open heart surgery, the latter being the subjects of this study.

Data collection
For the 182 patients, the following data were collected: demographic information, associated syndrome (eg, Down and DiGeorge syndromes) or chromosomal abnormality, requirement of preoperative ventilation, preoperative renal impairment, preoperative pulmonary hypertension (half systemic systolic blood pressure), cardiac diagnosis, surgical procedures performed and complexity of surgery (classified into six risk categories according to a consensus panel of pediatric cardiologists and cardiac surgeons [12], with category 6 procedures having the highest risk), cardiopulmonary bypass and aortic cross-clamp duration, need for and duration of circulatory arrest, postoperative complications including low cardiac output syndrome and pulmonary hypertensive crisis, and mortality. Low cardiac output syndrome was defined as a mean arterial pressure of less than 60 mm Hg on three or more separate readings for infants, or less than 50 mm Hg for neonates, and requirement of two or more inotropic agents [1]. Pulmonary hypertensive crisis was defined as an episode in which the pulmonary arterial systolic pressure exceeded 75% of the systemic systolic arterial pressure, as measured by either a pulmonary arterial line or echocardiography, coupled with a fall in systemic arterial pressure and a drop in systemic oxygen saturation to less than 90% [13].

For patients requiring PD, the following data were additionally collected: timing of PD catheter insertion (intraoperative versus postoperative); time to initiation and duration of PD; indications of PD; serum urea and creatinine levels before operation, before the start of PD, during PD, and just before discharge; the absolute amount of fluid withdrawn per day; daily fluid balance; and PD-related complications. Ventilatory settings including peak inspiratory pressure, ventilatory rate, and oxygen requirement just before institution of PD were noted. Prolonged PD was defined by a PD duration exceeding the median duration of PD of 84 hours in the present study. This median duration of PD is similar to those reported in previous studies [2, 3, 6].

Peritoneal dialysis
Peritoneal dialysis is the first treatment of choice for postoperative acute renal failure at our institution. Acute renal failure was defined as creatinine level more than 75 µmol/L or oliguria (<1 mL · kg^-1 · h^-1) for more than 4 hours despite aggressive diuretic therapy and optimization of inotropic support, or a combination of both. Indications for PD included oliguria for more than 4 hours despite medication interventions and, in the absence of established oliguria, increased creatinine level in association with one of the following: clinical signs of fluid overload, hyperkalemia (>5.5 mmol/L), persistent metabolic acidosis, or low cardiac output syndrome. Metabolic acidosis was persistent when it failed to be corrected by at least two boluses of intravenous sodium bicarbonate infusion and adjustment of fluid status and inotropic support. No attempt was made to differentiate acute renal failure secondary to renal hypoperfusion from that caused by acute tubular necrosis. Indications for stopping PD included return of sufficient of urine output to maintain or achieve negative fluid balance and normalization of serum electrolytes and acid-base status. On the other hand, in the event of PD failure, venovenous hemofiltration will be instituted.

The Dacron-cuffed silicone rubber peritoneal catheter (Tenckhoff catheter set; Cook, Bloomington, IN) was inserted either intraoperatively, if the cardiac surgeon anticipated a high possibility of postoperative hemodynamic and renal compromise, or percutaneously through the paraumbilical approach by means of a subcutaneous tunnel in the cardiac intensive care unit. Although placement of the PD catheter might be prophylactic, the initiation of PD was in accordance with the preceding indications. The PD catheter was connected to a closed system for peritoneal drainage. The dialysate solutions used were standard commercial preparations (Dianeal PD-2; Baxter Healthcare, Guangzhou, China). Heparin (500 U/L of dialysate) was added, and potassium chloride was added as appropriate. Antibiotic was also added if there was evidence of clinical sepsis or peritonitis. Peritoneal dialysis was started with a dwell volume of 10 mL/kg, a dextrose concentration of 1.5%, a fill time of 10 minutes, a dwell time of 30 minutes, and a drainage time of 20 minutes. According to the targeted fluid balance, the dextrose concentration varied from 1.5% to 4.5% and the dwell time from 1 to 2 hours. Trained nurses changed the dialysate bags every 24 hours. Serum albumin was regularly monitored, and intravenous albumin infusions were given as necessary.

Statistical analysis
Data are expressed as mean ± standard deviation or median (range) as appropriate. Univariate analysis was performed to compare demographic data, preoperative risk factors, intraoperative variables, and postoperative complications of patients who required PD with those who did not, using unpaired Student's t test, Mann-Whitney U test, and Fisher's exact test as appropriate. Multivariate analysis by logistic regression was used to identify predictors of the need for PD. Variables that were entered into the regression model included age, sex, weight, need for preoperative ventilation, preoperative renal failure, complexity of surgery, cardiopulmonary bypass duration, need for circulatory arrest, postoperative low cardiac output syndrome, and pulmonary hypertensive crisis. The risk categories of surgical procedures were collapsed into four groups, with risk categories 4 to 6 [12] being considered as category 4. This was justifiable as only one of the patients had undergone a risk category 6 procedure, Norwood stage I operation, whereas none had a category 5 procedure. Univariate analysis was also performed to compare preoperative, intraoperative, and postoperative variables of survivors of PD with those of nonsurvivors, and patients requiring prolonged PD with those who did not. The daily fluid balance was compared with a hypothetical mean of 0 by unpaired Student's t test. Serial changes in serum urea and creatinine levels after institution of PD were compared using repeated analysis of variance. A p value of less than 0.05 was considered statistically significant. All statistical analyses were performed using SPSS version 10.0 (SPSS, Chicago, IL).

	Results

Top Abstract Introduction Material and methods Results Comment References

 
Patients
Of the 182 young children undergoing open heart surgery, 31 (17%) experienced acute renal failure and required PD. The surgical procedures performed and their risk categories are shown in Table 1. The median age of these 31 patients at surgery was 3.1 months (range, 0.03 to 35.6 months), and their median body weight was 4.2 kg (range, 2.45 to 11.0 kg).

Risk factors for peritoneal dialysis
When compared with patients who did not require PD, the 31 patients who required PD (Table 2) were significantly lighter in weight and more likely to have required preoperative ventilation, undergone more complex surgery requiring longer cardiopulmonary bypass and circulatory arrest, and experienced postoperative low cardiac output syndrome and postoperative pulmonary hypertensive crisis (all p < 0.01).

Efficacy and complications of peritoneal dialysis
The amount of fluid removed from day 1 through day 3 by PD was 84 ± 39, 63 ± 20, and 53 ± 22 mL · kg^-1 · d^-1, respectively. Effective fluid withdrawal was indicated by the significant negative daily fluid balance (Fig 1). The serum urea and creatinine levels just before the start of PD were 7.7 ± 5.5 mmol/L and 78.4 ± 30.1 µmol/L, respectively. There was, however, no significant reduction in these levels after institution of PD (Fig 2).

View larger version (9K): [in this window] [in a new window]   Fig 1. Significant negative fluid balance was achieved after the first and second days of peritoneal dialysis (*p < 0.01).

View larger version (11K): [in this window] [in a new window]   Fig 2. Serial changes in serum urea (A) and creatinine levels (B) in patients requiring peritoneal dialysis (PD). Although both of these measurements increased significantly just before institution of peritoneal dialysis, as compared with preoperative values, they remained static despite the renal replacement therapy (p = 0.37 for urea; p = 0.75 for creatinine).

Univariate analysis showed that nonsurvivors were more likely to have syndrome disorder, required preoperative ventilation, and had higher postoperative ventilatory settings (all p < 0.05; Table 4). Nonsurvivors also tended to have low cardiac output syndrome (p = 0.077). There were, however, no significant differences in time to initiation of PD, duration of oliguria before institution of PD, and preoperative and postoperative renal function between the two groups.

	Comment

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The prevalence of acute renal failure requiring renal replacement therapy in children after cardiopulmonary bypass surgery has been reported to range from 1.6% to 9% [1–7, 14]. The relatively high prevalence of 17% (31 of 182 patients) in this study can perhaps be explained by a number of reasons. First, we reviewed a cohort of young subjects aged 3 years or younger who are at greater risk of renal impairment after cardiopulmonary bypass [3, 6, 7]. The advantage of selecting this high-risk group is that it enables us to analyze important risk factors that would have otherwise been masked by the strong confounding influence of age. Second, discrepancies do exist among different studies with regard to indications of PD after pediatric open heart surgery. Prophylactic PD in infants anticipated to be at high risk of renal impairment after cardiopulmonary bypass has resulted in a dialysis rate of 33% [15]. In contrast, a 2.3% PD rate has been reported when a duration of anuria exceeding 24 hours is the indication [3]. In the present study, one third of our patients were started on PD within 4 hours of oliguria because of concurrent electrolyte disturbance, excessive fluid retention, or low cardiac output.

Several studies have attempted to identify risk factors of acute renal failure requiring renal replacement therapy in children undergoing surgery for congenital heart disease [6–8]. In agreement with previous studies [6, 7], univariate analyses revealed low body weight, more complex surgeries, long bypass time, and need for circulatory arrest, as well as postoperative cardiovascular complications, to be significant risk factors. Additionally, we identified the need for preoperative ventilation and postoperative pulmonary hypertensive crisis to be risk factors. Nevertheless, after adjusting for possible confounding influences among variables by logistic regression, three independent risk factors, namely circulatory arrest, duration of cardiopulmonary bypass, and postoperative low cardiac output syndrome, were identified.

The mortality rate of our patients undergoing PD was 29%. This is similar to the 27% as reported recently by Dittrich and colleagues [15], but lower than the 33% to 79% as described in earlier reports [1, 6, 9, 16]. Although Dittrich and associates [15] speculated that the lower mortality rate may be related to prophylactic and early start of PD with better control of fluid balance, it is possible that a proportion of their patients may in fact be less ill and hence have a more favorable outcome [3]. Indeed, we did not find any differences in the time of initiation of PD from surgery and duration of oliguria before PD between survivors and nonsurvivors. In the only study that compared clinical variables between survivors and nonsurvivors after PD [11], no preoperative, operative, or postoperative variables could be identified to be risk factors. On the other hand, we found that associated syndrome disorders (Down syndrome and DiGeorge syndrome in our cohort), requirement of preoperative ventilation, and higher postoperative ventilatory settings were significant risk factors. A low cardiac output state also tended to be significant. Thus, the important determinants of outcome of patients requiring PD appear to be the preoperative and postoperative cardiopulmonary status rather than the renal status or timing of initiation of PD per se.

We further determined factors associated with a longer duration of PD. The risk factors identified were younger age, higher preoperative serum creatinine level, and postoperative occurrence of low cardiac output syndrome, pulmonary hypertensive crisis, and a higher oxygen requirement. Thus, the postoperative cardiopulmonary status affects not only survival in children requiring PD but also the duration of PD.

Similar to previous studies [2, 3, 6, 9], we demonstrated the effectiveness of PD in achieving a negative fluid balance. The daily amount being withdrawn, similar to that reported previously [2], allowed for better nutritional intake, which helps to decrease the risk of mortality [17]. Furthermore, we and others [18] have shown that PD could be performed safely in neonates and young infants without causing acute hemodynamic compromise. It is true, however, that the serum levels of urea and creatinine remained relatively static during PD, as contrasted with the significant drop after institution of continuous arteriovenous or venovenous hemofiltration [9]. Furthermore, fluid removal might be more effective with hemofiltration [9]. Nonetheless, these potential advantages have to be balanced against the risks of anticoagulation, vascular thrombosis, and ischemia [9, 10]; the need for additional vascular access that might be difficult in small infants; and the expertise required. Most of the complications of PD, on the other hand, are usually minor and easily manageable.

A number of limitations deserve comments. First, multivariate analysis was used to determine risk factors for PD only. Ideally, this approach should have also been used to identify significant determinants of prolonged PD and mortality. Nonetheless, the relatively small number of patients requiring PD renders this impossible. Second, although exclusion of patients who died within 72 hours may prevent misclassification of patients who died early as not requiring PD or only required short duration of PD, there exists a possibility of selection bias. Of the 9 open heart patients who were excluded, 2 had low cardiac output syndrome after Norwood stage I procedure and required PD. Similar risk factors are thus operating in these patients. Third, although previous studies have shown improved hemodynamics after initiation of PD [1, 18], we have not assessed the effect of PD on cardiac function or its surrogate markers as any changes are probably results of the interplay between recovery of myocardial function with time, optimization of inotropic support, and potential effects of PD on cardiovascular function.

In conclusion, PD is effective in achieving a negative fluid balance in young children with acute renal failure after open heart surgery. Risk factors for PD after cardiopulmonary bypass surgery in young children, as determined by multivariate analysis, are circulatory arrest, duration of cardiopulmonary bypass, and postoperative low cardiac output syndrome. Among patients who required PD, the preoperative and postoperative cardiopulmonary status has a significant bearing on the total duration of PD and survival. Given the ease of institution, the effectiveness in achieving fluid balance, the absence of significant hemodynamic compromise, and the relatively minor complications, PD is considered as an optimal therapy for the management of acute renal failure in young children after surgical repair of congenital heart disease.

	References

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