The risk of mortality in patients subjected to CABG surgery depends on the patients’ age, comorbidities, physiological functional reserve, degree of left ventricular dysfunction, the surgeons’ experience, and the hospital procedure volume [8,9,10]. The operative all-cause mortality rate in our hospital was 11.2%. Our mortality rate is significantly higher compared to that reported from other developing and developed countries. Data obtained from 1,145,285 patients referred for CABG in the United States of America (USA), from 1989 to 2004, showed a decline in mortality rate from 5.5 to 3.06%, irrespective of the presence of comorbidities [11]. A review of 17,335 CABG surgeries performed in Spain between 2013 and 2015 demonstrated a crude mortality rate of 5% [12]. Similarly, Swart et al. analysed outcomes post CABG in a South African cardio-thoracic private practice and reported a mortality rate of 3% [13].
Numerous clinical factors may have contributed to a higher mortality rate in our hospital. The patients in our cohort were older than those demonstrated in other studies, with a mean age of 60 years, while the mean age in the group of patients who demised was 63 years. Also, there may be a modest relationship between the surgical experience and the mortality rate. This hypothesis is argued by Peterson et al., who found that the surgeons’ experience was a predictor of mortality, independent of hospital volume, and the highest mortality rates were observed when patients were treated at low-volume hospitals by low-experience surgical teams, defined as performing 10 to 85 CABG surgeries per annum [14, 15]. In our hospital, the number of CABG surgeries was generally under 100 procedures per annum, except for the year 2017, where 107 CABG surgeries were performed. It is worth noting that although fewer CABG surgeries were performed in our hospital, most of our cardiothoracic surgeons are reasonably experienced as they also perform CABG surgeries in private hospitals.
Common postoperative complications associated with CABG reported in the literature are death, myocardial infarction, cardiac arrhythmia, stroke, wound infection, renal dysfunction, and bleeding requiring transfusion or repeat relook surgery [16]. In our study, 11.4% of patients required ventilation for more than 48 h, and the stroke rate was 1.2%. A similar rate of complications was reported in a study involving 36,588 patients after isolated CABG surgery, where 9% of patients required prolonged ventilation (> 24 h), and 1.2% experienced a stroke [17].
In our study, 1.3% of patients had deep sternal wound infections. This is a relatively high rate when compared to other studies. In larger cohorts, only 0.1% of patients had deep sternal wound infections [17]. Most data suggest that sepsis development following CABG portends a higher risk of mortality and a longer hospital stay [18,19,20]. In our cohort, patients with sternal wound infections were hospitalised for approximately 3 weeks.
In contrast, those without sternal wound infections had a median duration of hospitalisation of approximately 2 weeks. Variables associated with an increased risk of developing sepsis after CABG are a raised body mass index (BMI), poor preoperative glycaemic control, smoking, peripheral vascular disease, prolonged duration of cardiac bypass, and repeat or relook surgery [20]. In our study, the CPB time differed significantly between survivors and non-survivors (137 vs. 162 min) and independently predicted mortality (p = 0.000). Santos et al. studied 1628 patients post CABG surgery and found a median CPB time of 94 min. Similar to our findings, a longer CPB time predicted mortality [21].
Risk prediction models have been developed as tools for patient risk stratification. Widely-used risk models in patients planned for cardiac surgery include the Society of Thoracic Surgeons (STS) and the EuroSCORE II [22,23,24]. Although not externally validated in our population, the STS score and the EuroSCORE II are utilised in our hospital for risk assessment before CABG. The EuroSCORE II, revised in 2011, uses cardiac-specific and procedure-based variables to predict the patient’s risk of mortality following cardiac surgery. Studies reporting actual and predicted mortality risk categorize the EuroSCORE II into low (score between 0.17 and 0.80), intermediate (score between 0.81 and 2.02), high (score between 2.03 and 4.11), and very high (scores between 4.14 and 47.60) categories [25]. In this study, the EuroSCORE II independently predicted mortality and was significantly higher in the group of patients that demised.
Limitations
Our study had several limitations. The study’s retrospective nature limited our access to pertinent clinical data, as some records from the earlier years were incomplete. Only complications that occurred during the same admission as the CABG surgery were reviewed, and complications requiring readmission at a later stage were not analysed. Another limitation was a paucity of clinical information in the records of patients transferred from other hospitals within the referral network. In these instances, the clinical data was gathered from the referral letters and angiography reports.
We noted a variation in the mortality rate during the study period but could not account for this variation due to the study’s retrospective nature. Furthermore, we identified a high rate of sternal wound infections but could not describe the organisms causing the infections in all patients with sepsis, nor define the treatment plan utilised. Despite these limitations, this retrospective review of perioperative complications in patients subjected to CABG surgery in a state-sector, tertiary academic hospital, adds more insights into locally relevant predictors of mortality and reports on the crude mortality rate over 17 years.
