After adjusting the covariates under propensity-score matched method in this large-scale population-based study, ESRD patients with preoperative dialysis therapy, either PD or HD, encountered significantly higher postoperative complication and mortality rates compared with controls when receiving non-cardiac surgery, and facing significantly high risks of acute myocardial infarction, pneumonia, bleeding and septicemia. Compared with dialysis patients with neither hypertension nor diabetes mellitus, dialysis patients with hypertension and diabetes mellitus were found to have the highest relative risks for postoperative complications among groups. Increasing numbers of medical conditions were linked with incremental increases in rates for overall postoperative complications, and medical utility when compared with dialysis patients without additional comorbidities.
Discrepancies were noted between the risks for systemic infection (pneumonia and septicemia) and deep wound infection among patients under dialysis management in our data and previous studies 
. This might be explained by recent improvements in restrictive fluid management for surgical patients under dialysis therapy. During the last decade, worldwide acceptance of restrictive fluid regimens applied to surgical patients receiving major operations such as thoracic surgery resulted in significant decreases in pulmonary morbidity 
. The restrictive fluid strategy for surgical patients further provided better outcomes than liberal fluid regimen in overall postoperative morbidity 
. Cardiopulmonary and tissue-healing complications were also significantly reduced under a limited fluid administration regimen for patients receiving elective colorectal surgeries 
. Most patients would receive dialysis treatment followed by restriction of perioperative fluid before elective surgery, and surgeons keep patients in a relatively dehydrated status to limit the potential risk of local/deep wound infection 
. However, further prospective study is needed for an evidence-based explanation.
When kidney dysfunction progresses to ESRD, patients must choose a type of renal dialysis, PD or HD, for replacement therapy depending on patients’ preference, economic status, geographic location and severity of comorbid illnesses 
. Although the patients maintained on HD seem to have a higher comorbid burden than those on PD, outcome benefits were still equivocal 
. The impact of different types of renal dialysis on surgical adverse outcomes in large scale has not been documented previously. After adjustment of patients’ demographics and comorbidities with propensity-score matched-pair controls, we demonstrated that surgical patients under HD had relatively higher risk of in-hospital mortality than the PD group when compared with non-dialysis controls. As for postoperative complications, patients with HD showed similar risks in overall complications when compared with patients with PD except for acute myocardial infarction.
Comorbidities may predispose uremic patients to higher mortality and morbidity 
. However, the impact of complex pre-existing comorbidities, as shown by numbers or types, on surgical outcomes in ESRD patients had not been well demonstrated. In our data, surgical dialysis patients with hypertension and diabetes mellitus exhibited the highest complication rates than patients with either hypertension or diabetes or neither. According to the 2005 annual data report by Taiwan’s renal registry, causes other than chronic glomerulonephritis, chronic interstitial nephritis, hypertension or diabetes mellitus constituted a high proportion, 24.6% of ESRD, in prevalent dialysis patients 
. The disparity in etiology other than common medical conditions might partially explain the relatively lower mortality of ESRD patients in Taiwan (118.2 per thousand dialysis patients) in comparison with that in the United States (236 per thousand dialysis patients) 
. Similar conditions also exist in the Western world with environmental pollutants and drug abuse 
. A possible explanation for this phenomenon might be attributed to etiologies other than hypertension and diabetes for this specific population. First, Orientals such as Taiwanese people were frequent users of traditional alternative medicine, and habitually received herbal remedies 
. Another reason might be chronic use of self-prescribed over-the-counter analgesics such as aspirin, acetaminophen or conventional non-steroidal anti-inflammatory drugs which were universal 
. Long-term exposure to these medications might result in chronic kidney disease and subsequent ESRD 
. Renal impairment due to heavy metal intoxication should also be taken into consideration because environmental pollutants are ingested with water, food or herbal drugs; this is a critical health issue in Taiwan and over the world 
. Lin et al. showed that low-level environmental lead exposure can accelerate progression of renal dysfunction in patients without diabetes mellitus or hypertension 
Patients with both hypertension and diabetes mellitus had higher risks over the non-hypertensive, non-diabetic group in postoperative pneumonia and septicemia, but these risks were not significantly different in patients with hypertension or diabetes alone. Patients with both hypertension and diabetes mellitus also had the significant risk in postoperative adverse outcomes. These results indicate the combination of hypertension and diabetes might have an additive influence surpassing each disease’s individual effect on postoperative outcomes, especially systemic infection (pneumonia and septicemia) and cerebrovascular events. In contrast, dialysis patients without hypertension or diabetes exhibited lower morbidity rate, and it can be explained by difference in etiological severity between diabetes/hypertension, herbal drugs, analgesics, heavy metal intoxication and etc. In our data, the combined effect of hypertension and diabetes increased the risk of deep wound infection without statistical significance and the independent association between diabetes and deep wound infection in dialysis surgical patients is still controversial.
Several limitations of this study must be addressed. First, the study is retrospective, and the database did not disclose detailed information regarding characteristics or severity of dialysis, such as specific etiology and definite duration of dialysis. The administrative database also lacked detailed profiles of dialysis management including dialysis time, type of dialysate, use of specific drugs and body weight changes. All of these factors might relate to surgical risks in patients under regular maintenance dialysis. In addition, detailed variables concerning the perioperative risks of surgery and anesthesia are not available in this database, such as preoperative laboratory data, blood pressure, oxygenation status, total blood loss, transfusions, and the use of prophylaxis antibiotics or inotropes. With such a large sample size in this study, we assumed that the influence of all of these covariates was evenly distributed between groups and bias would be diminished. Third, the study’s design and grouping of hemodialysis versus peritoneal dialysis, hypertension versus diabetes mellitus, and categorization by the numbers of comorbidities, are all procedure- or diagnosis-oriented. Thus the study can validate only the association of factors and outcomes, not causation. Finally, our retrospective study did not achieve randomized distribution between groups. In spite of meticulous adjustment of major covariates, this non-randomization might still influence risk estimations and need further investigation.
In this nationwide population-based study using Taiwan’s National Health Insurance Research Database with propensity-score matched method, we found significant increases in postoperative mortality and complication rates among surgical patients with preoperative regular dialysis underwent non-cardiac surgeries, either HD or PD. Increasing numbers of comorbidities, including hypertension or diabetes, may predispose these patients to higher rates of postoperative complications. Our findings suggested that meticulous preoperative assessment, optimal control for diabetes and hypertension, early recognition of morbidities and appropriate interventions might reduce adverse outcomes in dialysis patients receiving non-cardiac surgery.