Print version ISSN 0100-6991
Rev. Col. Bras. Cir. vol.39 no.1 Rio de Janeiro 2012
Perioperative mortality in diabetic patients undergoing coronary artery bypass graft surgery
Michel Pompeu Barros de Oliveira SáI; Evelyn Figueira SoaresII; Cecília Andrade SantosII; Omar Jacobina FigueiredoII; Renato Oliveira Albuquerque LimaII; Rodrigo Renda EscobarIII; Fábio Gonçalves de RuedaIII; Ricardo de Carvalho LimaIV
IResident, General Surgery, Barao
de Lucena Hospital HBL, E-mail: firstname.lastname@example.org
IIMedical School Graduate, Faculty of Medical Sciences, University of Pernambuco - FCM / UPE-PE-BR
IIICardiovascular Surgeon, Emergency Hospital of Pernambuco - PROCAPE-PE-BR
IVHead, Division of Cardiovascular Surgery, Emergency Hospital of Pernambuco - PROCAPE-PE-BR
OBJECTIVE: Investigate risk factors for
in-hospital death in diabetic patients undergoing isolated CABG.
METHODS: Retrospective study of 305 consecutive diabetic patients undergoing CABG in the Division of Cardiovascular Surgery of our institution from April 2004 to April 2010. Univariate analysis for categorical variables was performed with the chi-square test or Fisher's exact as appropriate. Potential risk factors with P <0.05 in univariate analysis were included in multivariate analysis, which was performed by backward logistic regression. P values <0.05 were considered statistically significant.
RESULTS: The study population had a mean age of 61.44 years (± 9.81) and 65.6% (n=200) were male. The in-hospital mortality rate was 11.8% (n=36). The following independent risk factors for death were identified: on-pump CABG (OR 6.15, 95% CI 1 0.57 to 24, 03, P=0.009) and low cardiac output in the postoperative period (OR 34.17, 95% CI 10.46 to 111.62, P <0.001). The use of internnal thoracic artery (ITA) was an independent protective factor for death (OR 0.27, 95% CI 0.08 to 0.093, P=0.038).
CONCLUSIONS: This study identified the following independent risk factors for death after CABG: on-pump CABG and low cardiac output syndrome. The use of ITA was an independent protective factor.
Key words: Risk factors. Diabetes mellitus. Surgery. Coronary artery bypass. Myocardial revascularization.
The prevalence of diabetes mellitus (DM) throughout the swestern world has been increasing at an alarming rate in recent years1. Coronary artery disease (CAD) is often an associated condition2. Diabetic patients have a worse prognosis when compared to non-diabetics in relation to coronary heart disease and display different evolutions when treated by percutaneous intervention with catheter or by surgery3. Studies show that the presence of DM is an independent risk factor for postoperative mortality of coronary artery bypass grafting (CABG), with an odds ratio of 1.73 for death from cardiovascular causes4 and 2.94 for overall mortality5.
Medical evidence leads to a greater tendency of indicating CABG in diabetics with multivessel disease2. In such patients CABG should always be considered in view of the benefits in the medium and long term when compared to medical and interventional treatments. However, when indicating surgery in the presence of DM, one should consider the potential increased surgical risk and special care in pre-operative and postoperative handling2.
The search for factors that increase surgical risk, especially modifiable, is essential in order to decrease operative mortality.
The aim of this study was to investigate risk factors for in-hospital deaths of diabetic patients undergoing CABG at our local institution.
After approval by the ethics committee, we reviewed the records of 305 consecutive diabetic patients undergoing CABG at our institution from April 2004 to April 2010.
Definition of Diabetes and Variables
The presence of diabetes was defined as reported by patient and/or use of oral hypoglycemic medication and/or insulin.
The dependent variable was the in-hospital outcome (survival or death). The independent variables were divided into three categories:
1. CHARACTERISTICS OF PATIENTS
a. Age >70 years
b. Gender (male or female)
c. Obesity (body mass index e" 30Kg/m2)
d. Hypertension (reported by patient and/or use of anti-hypertensive medication)
e. Smoking (reported by patient; active or inactive for less than 10 years)
f. Chronic obstructive pulmonary disease - COPD (dyspnea or chronic cough AND prolonged use of bronchodilators or corticosteroids AND/OR compatible radiological changes - hypertransparency by hyperinflation and/or rectification of ribs and/or diaphragmatic rectification)
g. Renal disease (creatinine e" 2.3 mg/dL or pre-operative dialysis)
h. Previous cardiac surgery
i. New York Heart Association (NYHA) functional class
j. Ejection fraction < 50%
2. CHARACTERISTICS OF THE PROCEDURE
a. Emergency surgery (during acute myocardial
infarction, ischemia not responding to therapy with intravenous nitrates, cardiogenic
b. Use of internal thoracic artery (ITA)
c. Number of bypasses
d. Use of cardiopulmonary bypass CPB (on-pump or off-pump)
3. COMPLICATIONS IN THE POSTOPERATIVE PERIOD
a. Hyperglicemia (first blood glucose after closure
of skin >200mg/dL)
b. Low cardiac output syndrome (signs of poor peripheral and/or central perfusion decreased level of consciousness, cold extremities and/or oliguria/anuria and need for inotropic support with dopamine 4ìg/kg/min for a minimum of at least 12 hours or intraaortic balloon)
c. Reoperation (new sternotomy for bleeding, tamponade, or other reasons during the intra-hospital period)
d. Respiratory complications (pulmonary infection, acute respiratory distress syndrome, atelectasis, need for intubation for more than 48 hours)
e. Renal complications (creatinine e" 2,3 mg/dL or postoperative dialysis)
f. Multiple transfusions (more than 3 units of any blood products in the postoperative period before diagnostic definition of mediastinitis)
g. Sternal wound infection
The data were stored in SPSS program (Statistical Package for Social Sciences) version 15, from which calculations were performed with statistical analysis and interpretation. The data storage was done in double-entry to validation and conduction of data consistency analysis, in order to ensure minimal error in recording information in the software.
Univariate analysis for categorical variables was performed with the chi-square test or Fishers exact test, as appropriate. Potential risk factors with P<0.05 in univariate analysis were included in multivariate analysis, which was performed by backward logistic regression. P values <0.05 were considered statistically significant.
Description of Population and Mortality
The study population had a mean age of 61.44 years (± 9.81), 65.6% (n = 200) were male and 34.4% (n = 105) were female. The mortality rate was 11.8% (n = 36). The study population was identified among 849 coronary artery bypass surgeries, showing a prevalence of 35.9% (n = 305) of diabetes among patients undergoing this type of surgical procedure in our local institution.
Variables that were associated with increased risk of in-hospital deaths were:
1. CHARACTERISTICS OF PATIENTS (Table 1): age> 70 years (OR 2.67, 95% CI 1.30 to 5.46, p = 0.007), NYHA functional class IV (OR 3.24, 95% CI 1.15 to 9.12, p = 0.026), ejection fraction <50% (OR 2.08, 95% CI 1.01 to 4.30, p = 0.048);
2. CHARACTERISTICS OF THE PROCEDURE (Table 2): CPB (OR 2.62, 95% CI 1.21 to 5.64, p = 0.014);
3. POSTOPERATIVE COMPLICATIONS (Table 3): low cardiac output syndrome (OR 34.21, 95% CI 14.3 to 81.3, p <0.001), renal complications (OR 12.5, 95% CI 4.05 to 38.6, p <0.001), respiratory complications (OR 4.54, 95% CI 1.93 to 10.6, p = 0.001) and multiple transfusions (OR 2.93, 95% CI 1.39 to 6.13, p = 0.004).
The use of ITA was a protective factor for in-hospital death (OR 0.26, 95% CI 0.12 to 0.54, p <0.001), see table 2.
Multivariate Logistic Regression Analysis
We identified the following independent risk factors for in-hospital deaths: CPB (OR 6.15, 95% CI 1.57 to 24.03, p = 0.009) and low cardiac output in the postoperative period (OR 34.17, 95% CI 10.46 to 111.62, p <0.001). The use of ITA was an independent protective factor for in-hospital death (OR 0.27, 95% CI 0.08 to 0.093, p = 0.038).
Table 4 shows the data from multiple logistic regression analysis.
This study showed 35.9% prevalence of DM in patients undergoing CABG at our institution during the reference period. This rate was 33.4% higher than the one reported in the study of Lauruschkat et al..6 involving 7310 patients who consecutively underwent CABG, which observed a prevalence of 29.6% of DM diagnosed preoperatively.
The observed in-hospital post-CABG mortality rate of 11.8% is considered high. We should take into account that this study deals with a population under additional surgical risk, with a greater tendency to complications that can lead to death in the postoperative period, since all the individuals are diabetics2. Another aspect is the fact that we are studying a population operated at a public institution. Moraes et al.7 conducted a study involving 752 patients undergoing CABG in a private institution, showing a 1.7% mortality. Moreover, Oliver et al.8 recently published a work involving public hospitals and showed in-hospital mortality ranging from 7.0% to 14.3%. Another recent work9 involving 600 patients undergoing CABG in public hospitals showed a mortality rate during hospital stay of 12.2%. Sá et al.10 showed a mortality rate during hospital stay of 13% involving 500 patients undergoing CABG in a public institution. Apparently there is some influence of the institutional factor (public versus private), with in-hospital mortality of public institutions being higher than in private ones. This may be related to the probable difference between the population assisted by private institutions (population that has better access to basic and complex health services) and the population assisted by public institutions (population that has restricted access to basic health services and even more restricted access to high-tech services).
Lima et al.11 identified an important strategy to decrease surgical morbidity and mortality: off-pump CABG. In this study, which addressed specifically the diabetic population, it was observed that the use of CPB was an independent risk factor for in-hospital deaths. Taking into account that diabetes is a systemic disease with an important inflammatory component 2, it is assumed that there is a significant disarray after CPB. Off-pump CABG eliminates the non-pulsing flow and hypothermic myocardial ischemia, decreases release of inflammatory cytokines (tumor necrosis factor alpha, interleukins) and free radicals that are associated with cardiopulmonary bypass12. It has been noted that CPB is associated with higher levels of activated complement factors and markers of endothelial injury12. These effects are expressed in the clinical arena with a decrease of complications that increase mortality, such as renal failure, stroke, infections, atrial fibrillation, need for blood transfusions and low cardiac output13.
The latter complication, low cardiac output, occurs in 9.1% of CABGs14. Our study found a 14.8% occurrence of this complication in the postoperative period (n = 45), which means an increase of 62.6% in the incidence of low cardiac output compared with that described in the literature. This probably occurred because we studied a population with diabetes, a condition associated with an increase of 1.6 times the risk of low cardiac output postoperatively14. Rao et al, in a study involving 4558 consecutive CABGs, observed that operative mortality was higher in patients who developed low cardiac output in comparison to those who did not (16.9% versus 0.9%, p <0.001)14. Oliveira et al.8 and Pivatto et al.15 also identified low cardiac output as a risk factor for increased operative mortality. Our study also found that low cardiac output was an independent risk factor for in-hospital deaths. The low cardiac output syndrome is a clinical outcome that may result from inadequate myocardial protection or perioperative ischemia. Patients at high risk for low cardiac output should be the focus of trials of new techniques of myocardial protection to resuscitate the ischemic myocardium.
Despite the later impairment caused by diabetes, surgical treatment of diabetic patients (especially those with multivessel disease) is associated with significant improvement in event-free survival when compared to those undergoing medical treatment and percutaneous angioplasty, as reported in the BARI study16 and ratified by the BARI 2D study17. The better survival in the BARI study (mortality of 5.8% in the surgical group compared with 20.6% in the percutaneous group, with average follow up 5.4 years) was related to the implantation of at least one ITA, emphasizing the importance of such graft in improving late prognosis. It is known that implantation of ITA in the left anterior descending artery coronary constitutes an independent factor of improved survival in the long term. In some situations, surgeons are afraid to use the ITA in diabetics, especially if they are elderly and/or obese and/or present a poor quality sternum, because of the risk of a catastrophic infectious event secondary to postoperative sternal ischemia by the artery harvest of its original bed: the mediastinitis18,19. In other situations ITA is not used due to the discovery, during the operation, that its flow is inadequate. However, our study showed that the use of ITA in the making of a coronary bypass was an independent protective factor for death, showing that the benefit of using this type of graft in diabetics may already be initiated during hospitalization.
Being a retrospective analysis of medical records is this study's major limitation, leaving it at the mercy of all the biases associated with this type of study and also the quality of records' filling.
This study identified the following independent risk factors for in-hospital deaths after CABG in diabetics: CPB and low cardiac output syndrome. The use of ITA was an independent protective factor for death.
1. Schaan BD, Harzheim E, Gus I. Perfil do risco cardíaco no diabetes mellitus e na glicemia de jejum alterada. Rev Saúde Pública. 2004;38(4):529-36. [ Links ]
2. Kalil RAK. Cirurgia de revascularização miocárdica no diabetes mellitus. Arq Bras Endocrinol Metab. 2007;51(2):345-51. [ Links ]
3. Mansur AP, Dikran A, Amino JG, Souza AC, Simão AF, Brito AX, et al. Diretrizes de doença coronariana crônica angina estável. Arq Bras Cardiol. 2004;83(supl. 2):2-43. [ Links ]
4. Liao L, Kong DF, Shaw LK, Sketch MH Jr, Milano CA, Lee KL, et al. A new anatomic score for prognosis after cardiac catheterization in patients with previous bypass surgery. J Am Coll Cardiol. 2005;46(9):1684-92. [ Links ]
5. Thourani VH, Weintraub WS, Stein B, Gebhart SS, Craver JM, Jones EL, et al. Influence of diabetes mellitus on early and late outcome after coronary artery bypass grafting. Ann Thorac Surg. 1999;67(4):1045-52. [ Links ]
6. Lauruschkat AH, Arnrich B, Albert AA, Walter JA, Amann B, Rosendahl UP, et al. Prevalence and risks of undiagnosed diabetes mellitus in patients undergoing coronary artery bypass grafting. Circulation. 2005;112(16):2397-402. [ Links ]
7. Moraes F, Duarte C, Cardoso E, Tenório E, Pereira V, Lampreia D, et al. Avaliação do EuroSCORE como preditor de mortalidade em cirurgia de revascularização miocárdica no Instituto do Coração de Pernambuco. Rev Bras Cir Cardiovasc. 2006;21(1): 29-34. [ Links ]
8. Oliveira TML, Oliveira GMM, Klein CH, Silva NAS, Godoy PH. Letalidade e complicações da cirurgia de revascularização miocárdica no Rio de Janeiro, de 1999 a 2003. Arq Bras Cardiol. 2010;95(3):303-12. [ Links ]
9. Carvalho MRM, Silva NAS, Klein CH, Oliveira GMM. Aplicação do EuroSCORE na cirurgia de revascularização miocárdica em hospitais públicos do Rio de Janeiro. Rev Bras Cir Cardiovasc. 2010;25(2):209-17. [ Links ]
10. Sá MPBO, Soares EF, Santos CA, Figueiredo OJ, Lima ROA, Escobar RR, et al. EuroSCORE e mortalidade em cirurgia de revascularização miocárdica no Pronto Socorro Cardiológico de Pernambuco. Rev Bras Cir Cardiovasc. 2010;25(4):474-82. [ Links ]
11. Lima R, Diniz R, Césio A, Vasconcelos F, Gesteira M, Menezes A, et al. Revascularização miocárdica em pacientes octogenários: estudo retrospectivo e comparativo entre pacientes operados com e sem circulação extracorpórea. Rev Bras Cir Cardiovasc. 2005;20(1):8-13. [ Links ]
12. Ascione R, Nason G, Al-Ruzzeh S, Ko C, Ciulli F, Angelini GD. Coronary revascularization with or without cardiopulmonary bypass in patients with preoperative nondialysis-dependent renal insufficiency. Ann Thorac Surg. 2001;72(6):2020-5. [ Links ]
13. Sá MPBO, Lima LP, Rueda FG, Escobar RR, Cavalcanti PEF, Thé ECS, et al. Estudo comparativo entre cirurgia de revascularização miocárdica com e sem circulação extracorpórea em mulheres. Rev Bras Cir Cardiovasc. 2010;25(2):238-44. [ Links ]
14. Rao V, Ivanov J, Weisel RD, Ikonomidis JS, Christakis GT, David TE. Predictors of low cardiac output syndrome after coronary artery bypass. J Thorac Cardiovasc Surg. 1996;112(1):38-51. [ Links ]
15. Pivatto Júnior F, Kalil RA, Costa AR, Pereira EM, Santos EZ, Valle FH, et al. Morbimortality in octogenarian patients submitted to coronary artery bypass graft surgery. Arq Bras Cardiol. 2010;95(1):41-6. [ Links ]
16. Influence of diabetes on 5-year mortality and morbidity in a randomized trial comparing CABG and PTCA in patients with multivessel disease. Circulation. 1997;96(6):1761-9. [ Links ]
17. BARI 2D Study Group, Frye RL, August P, Brooks MM, Hardison RM, Kelsey SF, et al. A randomized trial of therapies for type 2 diabetes and coronary artery disease. N Engl J Med. 2009;360(24):2503-15. [ Links ]
18. Sá MP, Silva DO, Lima EN, Lima RC, Silva FP, Rueda FG, et al. Postoperative mediastinitis in cardiovascular surgery postoperation. Analysis of 1038 consecutive surgeries. Rev Bras Cir Cardiovasc. 2010;25(1):19-24. [ Links ]
19. Sá MP, Soares EF, Santos CA, Figueiredo OJ, Lima RO, Escobar RR, et al. Risk factors for mediastinitis after coronary artery bypass grafting surgery. Rev Bras Cir Cardiovasc. 2011;26(1):27-35. [ Links ]
Received on 18/03/2011 Work performed at the Division of Cardiovascular
Surgery, Emergency Hospital of Pernambuco - PROCAPE. Faculty of Medical Sciences
/ University of Pernambuco - FCM / UPE.
Accepted for publication 30/05/2011
Conflict of interest: none
Source of funding: none
Received on 18/03/2011
Work performed at the Division of Cardiovascular Surgery, Emergency Hospital of Pernambuco - PROCAPE. Faculty of Medical Sciences / University of Pernambuco - FCM / UPE.