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Print version ISSN 0102-7638
Rev Bras Cir Cardiovasc vol.20 no.4 São José do Rio Preto Oct./Dec. 2005
Fernando Antoniali; Cledicyon Eloy da Costa; Luciano dos Santos Tarelho; Maurício Marson Lopes; Ana Paula Nunes de Albuquerque; Gleice Agnes Almeida Reinert; Gustavo Calado de Aguiar Ribeiro
assess the impact of new preventive measures of surgical site infections after
coronary artery bypass graft (CABG) surgery.
METHOD: A retrospective study of 468 patients who underwent CABG surgery with cardiopulmonary bypass was performed. These patients were distributed into two groups: Group A (n=224) and Group B (n=244), respectively before and after a new protocol. The two groups were compared by statistical analysis to determine differences in risk factors, the incidence of sternotomy surgical site infections (superficial and deep), recurrent infections and hospital readmission.
RESULTS: There was a greater use of internal thoracic artery grafts (p=0.003) and a shorter time of mechanical ventilation (p=0.001) in Group B. Surgical site infections occurred in 44 patients of Group A (19.6%); 33 superficial (14.7%) and 11 deep (4.9%) while in Group B only 13 patients had this complication (5.3%); 10 superficial (4.1%) and 3 deep (1.2%) surgical site infections. Significant improvements were seen in the total number of surgical site infections (p<0.001), of superficial infections (p<0.001) and of deep infections (p=0.037). There were 36.3% and 7.7% of recurrent infections in Groups A and B, respectively (p=0.102). Hospital readmissions due to surgical site infections were 21 in Group A and 3 in Group B (p<0.001).
CONCLUSION: The new preventive measures and treatment for surgical site infections after CABG surgery in this series of patients significantly reduced the incidence of sternotomy surgical site infections and hospital readmissions related to this complication.
Descriptors: Infection. Surgical wound infection. Infection control. Cardiac surgical procedures. Myocardial revascularization.
Even when surgical treatment for heart diseases is successful, costs and distress will always be higher, not only for the patient but also for the medical team, if incision site infections are not prevented.
According to the proposed Centers for Disease Control and Prevention (CDC) classification , infection of surgical wounds of sternotomies should be considered as superficial if only the skin and subcutaneous tissue is involved; deep, when the infection reaches the sternum but does not involve it and as organ or space infections when sternal osteomyelitis or mediastinitis occur. This classification also establishes when the infection should be considered as a wound infection and enables a better comparison among scientific works .
The incidence of superficial surgical site infections (SSSI) in sternotomies should be similar to any clean surgical procedure, that is, approximately 2% . However, the infection rate reaches three times this value among heart disease patients, since these patients face a higher number of risk factors than the population in general. In respect to deep surgical site infections (DSSI), the incidence is from 0.5% to 5% [4,5]. But the incidence of mediastinitis, following median sternotomies, ranges from 0.4% to 2%, independent of the type of surgery and this is accompanied by a high mortality rate .
Some factors related to specific populations, associated diseases and social and economic levels elevate these incidences, as does, inappropriate care during the peri-operative period. Borer et al. , who identified this problem, suggested more strictly controlled prevention measures as the solution.
Thus, the aim of the current study was to assess the effects of a protocol of prophylactic conduct based on published recommendations [8,9] and specifically the control of postoperative infection, on surgical site infections and morbimortality rates.
A total of 474 records of patients successively submitted to on-pump myocardial revascularization (MR) without associated procedures and whose surgeries were performed by the same surgical team at the Hospital Irmãos Penteado in Campinas, São Paulo, within the period from January 1, 2001 to December 31, 2004, were assessed.
Six patients were excluded as the patients died during the postoperative period of deaths not related to infection. Thus, 468 patients' records were included in the study, divided into two groups according to whether prophylactic measures were used with the patients or not. Group A consisted of 224 patients' records and Group B consisted of 244 who had undergone surgery, before and after the adoption of measures to control infection, respectively.
The parameters considered for comparative analysis were: age, gender, length of preoperative hospitalization, time in intensive care unit (ICU), times of surgery, cardiopulmonary bypass (CPB) and orotracheal intubation (OTI), the number of internal thoracic artery grafts (mammary arteries) and the urgent/elective nature of the surgery. Associate risk factors included smoking, alcohol use, diabetes mellitus (DM), obesity (body mass index BMI > 30), chronic obstructive pulmonary disease (COPD), peripheral arterial disease (PAD), chronic renal insufficiency (CRI) and congestive heart failure (CHF).
Only the infection to the wound of the median incision used in the sternotomy was considered as a surgical site infection. Identification and classification of the infectious process were based on the criteria recommended by the CDCs . Analyses were made comparing the overall number of infections, SSSI, DSSI, recurrences, re-admittance to hospital and re-operations to each group's incision surgical site for infections.
The present work was approved by the Ethics Committee of the Hospital Irmãos Penteado.
Changes in preventive measures for surgical site infection control
Changes were introduced for preoperative care and for standard procedures during the intra-operative and postoperative periods. Also changes to postoperative monitoring during outpatient visits and in the indication of antibiotics and reoperations due to surgical site infections were established. The adopted changes are detailed in Table 1.
The groups were assessed according to the following statistical tests: Student t-test to compare continuous variables, chi-square or Fischer exact tests (when values were less than 5) to compare categorical variables. The level of significance was set at 5% (p-value<0.05). For all data that demonstrated statistical difference, the relative risk reduction (RRR), the absolute risk reduction (ARR), the number needed to treat (NNT) and the odds ratio (OR) were estimated.
Patient characteristics and surgical and in-hospital aspects
The groups were homogenous in terms of age, gender, the patients' habits and associated diseases (Table 2). There were no differences between the groups with regards to the preoperative hospital stay, duration of the surgery, ICU stay and the urgent nature of surgeries. There was a greater use of mammary artery grafts (p=0.003) and also shorter OTI times (p=0.002) with Group B (Table 3).
Surgical site infections
Within Group A, there were 44 (19.6%) infections of surgical sternotomy wounds reported; 33 (14.7%) SSSI and 11 (4.9%) DSSI. Within Group B, there were 13 (5.3%) infections related to sternotomy reported; 10 (4.1%) SSSI and three (1.2%) DSSI. The details of patients who suffered infections in both groups are shown in Table 4.
When comparing all the events of infection, Group B had a lower incidence in terms of overall numbers of SSSI and DSSI. The comparative analysis between the groups to identify associated risk factors showed that, within Group B, the infection rates related to smokers, diabetics and obese patients was lower than the rates in Group A, when these factors were examined separately. The reduction in the infection rates occurred independently of the functional class of CHF (Table 5).
Among the 44 patients who suffered infections in Group A, two of them developed organ and space infections, one had sternal osteomyelitis and the other, who eventually died due to septic shock, suffered from mediastinitis. Within this group 16 recurrent infections occurred with the necessity of 28 new surgical procedures and 21 rehospitalizations, all of which were related to infection of the sternotomy surgical wound. The average follow-up period for this group was 11.6 months.
Among the patients of Group B, no surgical site infections evolved to organ or space infections. In this group one recurrent infection occurred, nine surgical procedures were required and three patients were re-hospitalized, all of which were related to surgical wound infections. The average follow up was 10.8 months.
There was a significant difference in the number of recurrent infections between the groups (7.1% and 0.4%; p-value < 0.001), but not among patients with infections within each group (36.3% and 7.7%; p-value = 0.102). In respect to the need of new surgical interventions, there was also a significant difference between the groups (12.5% and 3.7%; p-value < 0.001), but not among infected patients (63.6% and 69.2%; p-value = 0.136). There was a difference in terms of overall number of rehospitalizations related to surgical wound infections; 21 (9.3%) in Group A (5 due to late diagnoses and 16 due to recurrences) and three (1.2%) in Group B (2 late diagnoses and one recurrence), giving a p-value < 0.001.
The values related to risk reduction, NNT and OR, which gave statistical differences, are shown in Table 6.
Many works address the issue of postoperative wound infections in heart surgery. Most Brazilian studies focus on the risk factors of DSSI and its evolution to mediastinitis [10-12]. Although the mortality rate due to mediastinitis following heart surgeries is extremely high, ranging from 14% and 47%, the incidence of such infection varies from 0.4% to 2% . The incidence of SSSI, however, is higher; from 1.6% to 6.4 % and there are few works that specifically focus on this issue probably due to its lower mortality rate . It is known that there are differences in the risk factors among DSSI and SSSI. , however, general preventive measures can be effective in all cases. In fact, risk classifications for wound infections after sternotomies are based on factors that have an effect not only on the incidence of DSSI but also SSSI. .
The high surgical site infection rates, which occurred in our service in 2002, led to the implementation of prophylactic measures based on published data with the purpose of reducing this incidence. The results in the reduction of infection rate motivated retrospective analysis of this group of patients. The study was, thus, focused on patients who had been submitted to on-pump MR without other associated procedures, corresponding to the largest number of procedures in our service and also the majority of other heart surgery services.
Chlorhexidine was chosen as the first-line antiseptic agent, not only to be used in the preoperative period but also in the intraoperative period, due to its better residual effect in relation to other iodine-based antiseptic agents and also because it can be inactivated by the blood. [8,15]. The use of nasal mupirocin reduces the number of infections caused by Staphylococcus aureus. Additionally, gastric catheters and tele-thermometer leads should not be inserted in these orifices in the intra-operative period; only the oral cavity should be used for these purposes. [8,16].
It has been recommended that surgical teams should only change gloves when there is contact with large contaminated areas or when perforations occur. However, frequently in surgeries, such perforations are not detected. There is evidence that the longer the surgery takes the greater the probability of perforations is, with this rate reaching as high as 60% [17,18]. Thus, changing gloves more frequently during intra-operative periods, as set forth in the protocol, aims to reduce contamination by hands.
In respect to obese patients, who have thick subcutaneous tissue; the formation of collections between adipose tissue and the sternum is a serious problem as it poses a higher risk for infection. For such patients, the use of a permanent suction drain over 24 hours in the region that is liable to form accumulation of collections is recommended, a measure that was included in our protocol. Because of this measure, reductions in infection and dehiscence rates occur . In our study, the RRR was 0.77 and the ARR was 40.8% among obese patients with the NNT equivalent to 2 and the OR 0.13.
Unquestionably, an extremely important change occurred in respect to patients suffering from DM. The tight glycemic control of such patients, in the pre- inter- and post-operative periods, independently reduced surgical site infection rates . The RRR was 0.75 and ARR was 30.5% among diabetic patients in our study. In this group of patients, NNT was 3 and OR was 0.16.
Even though, in our service, daily assessment of surgical wounds was already routinely performed, the new protocol established a stricter sampling of wound secretions for culturing and an earlier start to antibiotic therapy. The empirically selected antibiotic agent was cephadroxil as it has a better range compared to cephalexin, with a better action against strains of Staphylococcus and Streptococcus, as well as exhibiting a good penetration into bone tissue . Specific antibiotic therapy, on the other hand, is limited to subsequent stages, according to the results of cultures.
Among patients who had surgical wound infections and who required future surgical interventions, patients from Group B were submitted to earlier treatment according to the new protocol guidelines. Francel & Kouchoukos , when assessing treatment alternatives for complications after sternotomies, concluded that the earlier the surgical procedure is performed the better the results produced, particularly when it involves a surgical wound infection. They also reported the sequence of treatment adopted for their patients. In our study, the methodology used does not allow us to reach conclusions about early treatment, but other authors compared the traditional treatment with a more aggressive approach which proved to provide more benefits .
Thus, it was impossible to identify the extent to which more intensive monitoring of preventive measures adopted in Group B really contributed to the reduction of infection rates .
The significant reduction in the surgical site infection rates reported in the present study can be attributed to changes which were established on January 1, 2003, because of the similarity between the studied groups in respect to the characteristics of patients and the operative and in-hospital aspects. It must also be stressed that the percentages of infections achieved after the adoption of the new protocol are consistent with incidences reported in the literature [4,5,7,13]. Similar values of RRR (0.73) and RRA (14.3%) calculated in this study, were also demonstrated in similar works on control of surgical site infections [7,24]. The NNT rate was 7, when assessing the overall incidence of surgical site infections and the value of OR was 0.23.
The comparison among infection rates for both groups and the association with habits and underlying diseases showed a significant reduction for smokers, diabetics and obese patients. There was a reduction of surgical site infections in all CHF functional classes. The fact that the reduction in other groups did not give a significant difference is probably due to the low number of patients studied.
Although this was not an objective of this study, the significant reduction in the rates of rehospitalizations for surgical site infections (9.3% to 1.2%; p-value < 0.001) results in lower costs to treat these patients .
The present work did not allow a more detailed analysis of some important aspects and it was not possible to identify which measures had the strongest impact on the reduction of infection rates. However, it can be concluded that, for this group of patients, the changes in preventive measures and how the patients were treated resulted in significant reductions in the incidences for superficial and deep surgical site infections and in a lower number of rehospitalizations in connection with infections. This has a direct effect on the costs of treatment, on reduced stress of the surgical team and, particularly, a better quality of life for these patients.
The authors wish to thank Prof. Dra. Glória Maria Braga Potério for her invaluable collaboration during the development of this work.
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Dr. Fernando Antoniali
R. José Lins do Rego, 665 casa 34. Pq. Taquaral
Campinas, SP. CEP: 13087-080
Tel: (19) 3241-3659 / 97905667
Fax: (19) 3232-3856
in July, 2005
Article accepted in October, 2005
Work performed in Hospital Irmãos Penteado. Campinas, SP.