Factors associated with mortality in patients undergoing coronary artery bypass grafting

ABSTRACT Objective: to investigate the factors associated with mortality in patients undergoing coronary artery bypass grafting in a cardiovascular referral hospital in Santa Catarina. Method: quantitative, exploratory, descriptive and retrospective study. The medical records of 1447 patients, from 2005 to 2013, were analyzed for statistically related variables, these being: profile, hospitalization diagnosis, risk factors for coronary artery disease, complications recorded during the hospitalization, length of hospitalization and cause of death. Results: the mortality rate was 5.3% during the study period. Death was more common in females and those of black skin color, with a mean age of 65 years. Acute myocardial infarction was the most common hospitalization diagnosis. The majority of the complications recorded during hospitalization were characterized by changes in the cardiovascular system, with longer hospitalization periods being directly related to death from septic shock. Conclusion: the data provide subsidies for nursing work with preventive measures and early detection of complications associated with coronary artery bypass grafting. This reinforces the importance of using the data as quality indicators, aiming to guarantee care guided by reliable information to guide managers in planning patient care and high complexity health services.


(SUS) repres
nting 77% of all surgeries performed in both public hospitals and philanthropic or private hospitals (1) .

The decision for surgery is based on an individual analysis, taking into account factors such as the degree of angina, ventricular function, ischemic burden a d coronary anatomy.Individuals with multivessel coronary disease and ventricular dysfunction, left main coronary artery obstruction or large areas of ischemia usually receive an indication for CABG (2) .

Over the years CABG has received two essential contributions for the improvement of surgical outcomes throughout the world, both of which were introduced by Br zilian surgeons, namely: the technique of myocardial revascularization with cardiopulmonary bypass (CPB) and the use of double internal mammary artery grafts (3) .

Thus, over the course of 40 years, CABG has undergone considerable development favoring this surgical practice.However, over the last 20 years there has been a significant change in the profile of patients undergoing CABG, which is usually performed with older individuals with more severe heart damage, most often with comorbidities associated with Cardiovascular Disease (CVD), representing greater risk for reoperations, complications and mortality (4) .

The mortality rate is usually applied by health services as a quality indicator, however, this indicator is often used in a generalized way, without knowing the exact profile of the population studied.In an attempt to identify mortality risks related to CABG, seeking to understand the factors that influence the outcome of this surgical practice is essential for dealing with CVD.Although extensive literature shows data on the mortality rates of patients undergoing CABG (5)(6) , few studies portray the factors associated with mortality in this type of surgery.

In the health area, nursing is the only profession that includes, in its formation, theory combined with practice in relation to health management or administrati n (7) .In this sense, the use of reliable indicators is essential for the effective and efficient management of care, since this allows the identification of avoidable risks, subsidizes corrective action planning and directs prevention strategies for events and complications related to CVD.

The potential of the professional nurse to contribute to the changing reality of chronic diseases should be noted, particularly regarding CVD, by identifying risk actors and preventing potential events that complicate the state of health of the individual affected by CVD, with the aim of ensuring the quality of the care provided (8) .

Given the previously mentioned considerations, the


Method

The study had a quantitative, exploratory, artery disease (CAD), complications recorded during hospita ization, length of hospitalization and the main cause of death.Thus, the variables of the groups: profile, main diagnosis, risk factors, complications recorded during hospitalization and length of hospitalization were crossed with the main cause of death group.Data were analyzed using descriptive (means, medians, standard deviation, minimum and maximum amplitude) and inferential statistics, using the Fisher-Freeman-Halton Exact Test to compare the percentage between group

Studen
's t-test to compare continuous variables; and analysis of variance followed by Tukey's comparisons to compare the mean of more than two groups.In addition, the odds ratio was also calculated.

For the statistical tests, a significance level of 0.05 was assumed, equivalent to a 95% confidence interval.For this analysis the SAS version 9 software w s used, with help from a statistician.


Results In the period from 2005 to 2013, 1447 patients underwent CABG in the institution chosen for this study.

A total of 455 patients (31.4%) were female and 992 (68.6%) male.Regarding skin color, 1104 (76.45) patients were declared white and 26 (1.7%) black, with no information for 317 (21.9%).Of all the patients, 797 (55%) underwent CABG with CPB and 650 (45%) underwent surgery without CPB.Regarding the type of surgery, it was found that the majority of the patients, 1302 (89.9%), underwent CABG without any other associated surgery.Only 145 (10.1%) patients underwent CABG associated with another cardiac surgery.The results show a certain balance between the number of people that underwent CPB or not (Table 1).Rev. Latino-Am.Enfermagem 2016;24:e2748.

With regard to mortality, of the total number of patients who underwent surgery during the study period (1447), 1371 (94.7%) survived and 76 (5.3%) died.Thus, the analysis of the relationship between the number of dea hs and variables in this study was carried out.

When the annual mortality rates were considered, there was some increase over the years, especially when comparing the year 2005, in which the mort lity rate was 1.1%, and the year of 2012, in which this was shown in Table 2. To verify whether the percentages of causes of death were the same for the diagnostic groups, Fisher's exact test was carried out and the descriptive level of 0.691 obtained, which showed no sign ficant differences between the diagnostic groups

he complica
ions of the cardiovascular system showed a tendency with all the causes of death.

Among them, arrhythmia (75%) and AMI (50%)

showed a certain tendency with regard to death due The length of hospitalization is presented in Figure 1, which ranged from 1 to 98 days, with means of 27.9 and 70.2 days depending on the cause of death.Regarding the length of hospitalization and cause of death, higher means of hospitalization can be seen to be related to death from septic shock, mean of 70.2 days, median 72 days, standard deviation 20.8 days, minimum of 39 days and maximum of 92 days.


Discussion

The results demonstrate that the mortality rate of the study institution 5.3%) was slightly above the national mean of 4.8% (3) .With regard to the profile of patients that undergo CABG, in a study conducted in southern Brazil, the age varied from 32 to 86 years and the age group with the highest incidence was between 51 and 70 years, in which 688 individua s (68.5%) were male (9) .This information confirms the findings of the present study and the tendency for indication for CABG of an older, male population.

The high mortality rate was influenced by the final two years of the study, 2012 and 2013, in which mortality rates were 13.1 and 10.5%.This may be related to the hiring of new professionals in the institution with less experience, causing change in the medical teams and nursing practitioners, as well as the indication for CABG of more clinically severe and older subjects, highlighting the need for CVD preve tion strategies.

Despite the predominant population for CABG indication being male, mortality compared by gender, in this study, showed a higher rate of death for women.

A study of cardiac surgeries performed in the SUS nationwide, showed a lower mortality rate for males compared to females, 5.20% versus 8.25% (p<0.001) (1).

Therefore, it can be stated that being female is a clinicaldemographic characteristic associated with mortality in CABG (10) .
lder age appears as a risk factor for mortality in patients undergoing CABG.A study conducted in Brazil with, mostly male (56.3%), octogenarian patients that all underwent CABG with CPB, showed a mortality rate within the hospital of 14.8%, more than double the national mean.It cited cardiogenic shock (42.8%) as the main cause of death (11) , in agreement with t e findings of this study, which showed cardiogenic shock as the main cause of death, with an increased risk of death of 1.73 for every 10 more years of age.

Regarding race, studies in southern Brazil present a predominance of white patients with CABG indication, 68.9% (10) and 95.7% (12) in the states of Santa Catarina and Rio Grande do Su , respectively.However, it is pertinent to consider that these studies were conducted in southern Brazi , where the population is predominantly

Caucasian.In study conducted in northeastern Brazil, which sought to identify the sociodemographic characteristics of patients undergoing CABG, 53% of the patients were declared non-white (13) .In relation to the higher mortality ate in black patients undergoing CABG, there is evidence of a higher rate of deaths from circulatory system diseases in black men, as well as the association of death with the prevalence of hypertension in this race (14) .

The results of this study also indicate a higher chance of death for CABG associated with other surgeries, especially valve replacement surgery.A study conducted in southern Brazil that investigated preoperative risk factors for heart valve surgery found a signific nt increase in the rate of death, from 8.8% to 25%, in patients undergoing this procedure (15) .

The use of CPB in CABG demonstrated a significantly higher chance of mortality compared to its non-use.Conventional CABG in CPB is associated with a significant risk of related morbidity and mortality in older patients (16) .Other studies show the use and duration of CPB in CABG as a factor related to mortality within the hospital (10) .

Another study confirmed the results presented

ere with re
ard to hypertension as the main risk factor for CHD related to death in patients undergoing CABG.

In this same study, half of the patients were affected by ACS, in which UA appeared more often in relation to AMI, differing from the findings discussed that identified AMI as the main hospitalization diagnosis (17) .

Dyslipidemia, smoking, physical inactivity, obesity, diabetes mellitus (DM) and unhealthy diets are cited as potential aggravating factors for impairment of health and installation of complications in CAD (1)