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Ann Thorac Surg 2005;79:825-829
© 2005 The Society of Thoracic Surgeons
a Department of Cardiac Surgery, Catholic University
b Dialysis Unit, Catholic University
c Department of Cardiac Anesthesia, Catholic University
d San Giovanni Hospital, Rome, Italy
Accepted for publication August 9, 2004.
* Address reprint requests to Dr Gaudino, Divisione di Cardiochirurgia, Policlinico Universitario A. Gemelli, Largo A. Gemelli 8, 00168 Rome, Italy (E-mail: mgaudino{at}tiscali.it).
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Abstract |
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METHODS: We evaluated the preoperative and intraoperative features of the 69 out of 6,542 consecutive cardiac surgery patients who developed postoperative dialysis-requiring acute renal failure at our Institution during a 10-year period.
RESULTS: Age, valvular and aortic surgery, hypertension, extracardiac vasculopathy, timing of surgery, cardiopulmonary bypass time, and preoperative creatinine level greater than 2.0 mg/dL were identified as predictors by multivariate analysis. In a second analysis, patients were divided in two groups according to the preoperative creatinine level: group A (preoperative creatinine 2.0 mg/dL or less; 38 cases) and group B (preoperative creatinine 2.1 mg/dL or more; 31 cases). The two groups significantly differed in preoperative and intraoperative characteristics and in postoperative outcome: group A patients were younger, had a lower incidence of cardiac and vascular risk factors and comorbidities, were mainly operated on urgent or emergent basis for valvular or aortic pathologies, had longer cardiopulmonary bypass and cross-clamp time, and worse in-hospital outcome but higher midterm survival. Group B patients were older, had a higher prevalence of comorbidities, required more often in-hospital or after-discharge dialysis, had lower in-hospital mortality, but reduced midterm survival.
CONCLUSIONS: Postoperative dialysis-requiring acute renal failure can be the result of two different pathophysiological pathways: complicated perioperative course due to urgent-emergent surgery or main intraoperative technical complications in patients with preoperative normal renal function and uncomplicated perioperative course associated with reduced preoperative kidney function. The two patient groups significantly differ in baseline preoperative features, as well as in in-hospital and in midterm outcome.
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Introduction |
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TopAbstractIntroductionPatients and MethodsResultsCommentReferences |
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Patients and Methods |
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TopAbstractIntroductionPatients and MethodsResultsCommentReferences |
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Acute renal failure was defined as a postoperative increase of the creatinine concentration greater than or equal to 2 mg/dL with respect to the preoperative. Criteria for starting dialysis were mainly clinical and were established by the treating physician; oliguria (urine output < 200 mL/12 hours), iperkaliemia (K level > 6 Meq/L), blood urea nitrogen level greater than 50 mg/dL, sodium level less than 115 or greater than 160 Meq/L, and significant metabolic acidosis (pH < 7.1) or HCO3 concentration less than 18 Meq/L were usually considered sufficient to start the treatment.
Using these definitions we identified 69 patients who developed postoperative dialysis-requiring ARF (DRARF) in the study period (1.1%). Univariate and multivariate analysis to identify predictors of this complication were conducted on the overall population. In a second analysis, patients were divided in two groups according to the preoperative creatinine level: group A (preoperative creatinine 2.0 mg/dL or less; not impaired renal function, 38 cases) and group B (preoperative creatinine 2.1 mg/dL or more; impaired renal function, 31 cases).
Follow-up
Each patient was followed up regularly at our Institution 6 months after surgery and every year thereafter. At each time interval clinical examination was performed and the results of surface electrocardiography, stress Tl201 myocardial scintigraphy, 24-hour Holter monitoring, and transthoracic echocardiography were carefully reviewed. Invasive controls were proposed to the patients only in case of abnormal results of these first-line exams.
For the purpose of the present study all patients were recalled by phone and resubmitted to clinical examination and all exams reviewed at the time of the follow-up. In case of death all available clinical data were collected and reviewed by the authors to establish the cause of the fatality. Death was considered cardiac in origin when it was preceded by objective evidence of cardiac dysfunction and noncardiac when a clear systemic or accidental cause of death was evident. Follow-up was 100% complete (41 of 41 surviving patients) and mean follow-up time was 59 ± 11 months.
Statistical Analysis
All data were included in an electronic database and processed using SPSS 10.1 for Windows (SPSS, Chicago, IL). Values of variables are expressed as mean ± standard deviation for continuous variable or as percentage for discrete variable; Student's t or Mann-Whitney U test and 
2 correlation test were respectively performed. Yates correction and Fisher's exact were adopted when appropriate. Two-tailed statistical significance was set at the 0.05 level.
Baseline patient variables tested applying univariate and multivariable logistic regression analysis for association with the development of DRARF were: age, sex, body surface area, New York Heart Association-Canadian Cardiovascular Society functional class, hypertension, diabetes, preoperative serum creatinine (mg/dL), left ventricular ejection fraction, pulmonary disease, extracardiac vasculopathy, intraoperative evidence of ascending aorta arteriosclerosis, number of diseased coronary vessels, type of surgery performed (coronary, valve, aortic, combined procedure), timing of surgery (elective vs urgent-emergent), reoperation, cardiopulmonary bypass time, cross-clamp time, year of operation.
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Results |
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TopAbstractIntroductionPatients and MethodsResultsCommentReferences |
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Preoperative and intraoperative features of patients of the two groups are summarized in Table 4. Group A patients were younger, had a lower incidence of cardiac and vascular risk factors and comorbidities, were mainly operated on urgent or emergent basis for valvular or aortic pathologies, and had longer cardiopulmonary bypass and cross-clamp times. Group B patients were significantly older, had a higher prevalence of systemic pathologies, were mainly operated on elective basis, and coronary artery bypass grafting was their main indication for surgery.
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Causes of In-Hospital Death
The postoperative outcome of patients of groups A and B are summarized in Table 5. Complication rate was extremely high in Group A with all patients developing at least one major complication (p < 0.001 vs group B). At the time of hospital discharge 5 patients (all from group B, p < 0.001) were still in dialysis treatment. These patients were subsequently cared for in the dialysis outpatient ward. No group A patients where still in dialysis when discharged.
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After hospital discharge 10 patients (all from group B) had to start chronic dialysis treatment for progressive deterioration of renal function (p = 0.001 compared to group A patients; see Fig 1). No reoccurrence of renal failure nor mild impairment of kidney function occurred in group A survivors during the follow-up.
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Comment |
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TopAbstractIntroductionPatients and MethodsResultsCommentReferences |
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For this reason several authors have elucidated the risk factors and prognosis of postoperative DRARF [1–4]; in this setting our data confirm the importance of most of the classic risk factors for DRARF, even in the contemporary cardiac surgery population (see Table 1). However, it is surprising that in the past DRARF has always been considered as a single organ complication and not like the common expression of different processes affecting either the kidneys or the whole organism.
Our observations indicate that DRARF can be the result of two different pathophysiological pathways: complicated perioperative course due to urgent-emergent surgery or main intraoperative technical complications in patients with preoperative normal renal function (group A patients) and uncomplicated perioperative course in patients with reduced preoperative kidney function (group B patients). The two patient groups significantly differ in baseline preoperative features, as well as in in-hospital and midterm outcomes. In fact, in our series group A patients were younger and operated mainly for valvular or aortic indications in urgent-emergent situations; in contrast group B patients were mostly coronary artery bypass graft cases, significantly older, operated on elective basis, and with a very high prevalence of associated systemic and vascular pathologies. Group B patients represent a cohort in which DRARF developed postoperatively as an exacerbation of chronic renal failure, and have peculiar treatment and prognosis.
As a consequence, in-hospital mortality for group A patients was higher than that of group B patients and of patients who did not develop DRARF, whereas group B patients faced a surgical risk similar to that of non-DRARF cases. However, once group A patients survived the in-hospital phase their late mortality and dialysis free survival was significantly better than that of group B patients.
These observations reflect the intrinsic pathophysiological differences between the two subtypes of DRARF and provide an easy explanation of their different prognostic implications. On this basis it seems evident that the identification of the etiology of each single case of postoperative DRARF must be considered essential for postoperative risk stratification and prognosis prevision. This distinction can usually be quickly achieved through a critical evaluation of the preoperative and intraoperative features of the patient and should be part of the routine clinical decision practice.
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Appendix |
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Myocardial infarction: was diagnosed on the basis of echocardiographic evidence of regional hypokinesia or dyskinesia, MB fraction greater than 4% of the total hematic level of creatine kinase concentration, and appearance of new Q waves on the electrocardiogram.
Respiratory insufficiency: was defined as a PaO2 less than 60 mm Hg in current air.
Chronic obstructive respiratory disease: was defined by the long-term (
6 months) use of bronchodilators or steroids.
Intraoperative stroke: was defined as a new focal neurologic deficit or coma associated with computed tomography demonstration of recent ischemic cerebral lesion, which became evident at the moment of the awakening of the patient from the anesthesia and lasted greater than 24 hours.
Postoperative stroke: was defined as a new focal neurologic deficit or coma associated with computed tomography demonstration of recent ischemic cerebral lesion and lasting greater than 24 hours, which became evident after a normal awakening of the patient from the anesthesia and a normal postoperative neurologic status.
Major postoperative complications: death, stroke, shock, sepsis, myocardial infarction, reoperation.
Minor postoperative complications: renal insufficiency, mechanical ventilation for greater than 24 hours, respiratory insufficiency, inotropic support for greater than 24 hours, need for blood transfusions, revision for bleeding.
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= group A; 
= group B.