Incidence of postoperative pneumonia
Postoperative pneumonia occurred in 28% (104/373) of patients after cardiac surgeries, most occurred (95%) within 7 days post-surgery. This incidence is higher than the reported incidence in other countries ranging from 2–10%3–8.This variation could be related to several factors such as ethnic, cultural, and economic differences of the population studied, management practices and processes of care of hospitals, epidemiological surveillance adopted per institution, and level of compliance to infection control measures16.
Risk factors associated with pneumonia
Patients undergoing cardiac surgery have a higher risk of developing nosocomial infections. Risk factors for developing coronary artery disease, as well as various cardiac conditions, are also considered risk factors in the development of hospital infection. These include advanced age, diabetes mellitus, and smoking.
In our study, however, preoperative patient characteristics such as age, sex, BMI, DM, severe left ventricular systolic dysfunction, renal dysfunction, lung diseases, and smoking were not associated with the development of pneumonia. Likewise, other surgical factors such as ischemic time, bypass time, total surgical time, and urgency of surgery were not associated with pneumonia development.
In contrast, our results showed that more than two days of preoperative hospital stay and longer time on mechanical ventilation were both associated with an increased risk of developing pneumonia.
Prior to their cardiac surgery, these patients may be admitted to the intensive units for a variable period of time due to several reasons. They may present with cardiac symptoms necessitating hospital admission prior to surgery. Moreover, some patients have had acute coronary events which would take an additional 5–7 days to washout the antiplatelet agents given prior to CABG. These patients may have longer hospital stay before their scheduled operation, thus may be subjected to longer exposure to the hospital environment and possibly to pathogens.
Several studies have shown that prolonged intubation and mechanical ventilation increases the risk of postoperative pneumonia, length of hospital stay, and in-hospital complications12. Thus, one of the prominent focus of cardiac surgical quality improvement has been early weaning and extubation. Our study found a 0.8% increase in acquiring pneumonia for every hour delay of extubation from mechanical ventilation, hence, re-emphasizing the importance of timely postoperative extubations.
Impact of pneumonia on clinical outcomes
The overall in-hospital mortality observed was 4.55%, which is 17 out of the 373 patients included in the study. Ten out of the 17 patients who died had postoperative pneumonia. This translates to an attributable mortality rate of 58.8% among patients undergoing cardiac surgery who developed pneumonia. This is higher compared to a study done in eight European countries which showed a mortality rate of 35%4. On analysis, the development of postoperative pneumonia in our study was associated with a nearly 4-fold increase in in-hospital mortality.
In addition to mortality, pneumonia conferred a significant burden on patient morbidity. It is associated with a 4-fold increase in prolonged hospitalization, 6-fold increase in prolonged ICU stay, and a 9-fold increase in postoperative re-intubation.
Our study did not analyze the economic impact of pneumonia in the cardiac surgery population. However, due to the findings of prolonged hospitalization and ICU stay among patients who had pneumonia, it may be surmised that pneumonia may also incur an increased burden on resource utilization. A study by Ailawadi et al. 10 among cardiac surgery patients showed that the occurrence of major hospital acquired infection incurred an additional $38,000 to hospital cost on an individual level.
Timing of pneumonia and relationship to mortality
The median time to the onset of postoperative pneumonia was 3 days, ranging from 1 to 13 days. Ninety-five percent of patients who had pneumonia acquired it within 7 days post cardiac surgery. This is expected as majority of pneumonia would manifest early after surgery due to the occurrence of postoperative pain and need for narcotics, both resulting to inadequate respiratory mechanics.
Our study showed that at around 13th post-operative day, the probability of acquiring pneumonia is at 31% (Fig. 1). Given the chance of developing pneumonia even after first week post-surgery, this emphasizes the need for continuation and maintenance of intensive postoperative pulmonary care. This may include early ambulation and progressive cardiac rehabilitation. A study done by Stolbrink et al. among medical inpatients showed that early ambulation significantly decreased the incidence of hospital-acquired pneumonia (p < 0.0001)17. Furthermore, a study by Ferreira18 showed that an inspiratory muscle rehabilitation program significantly improved the respiratory mechanics of patients among post cardiac surgery patients. Herdy et al.19 also demonstrated decreased incidence of postoperative pneumonia among CABG patients who had early postoperative cardiopulmonary rehabilitation compared to those who had standard care (p = 0.004).
The median time to mortality is 8 days post cardiac surgery (range of 1 to 35 days). The probability of survival decreases in the presence of pneumonia, with Kaplan Meier curves beginning to diverge after around 3 days (Fig. 2). Further, among patients who had pneumonia, the estimated 30-day survival is 81.70%. This is in contrast to a 96.51% 30-day estimated survival to those who did not acquire pneumonia. Thus, clinicians should be aggressive in the management upon onset of nosocomial pneumonia. A study done by Luna et al20 showed that early initiation of antibiotic therapy improves survival of patients with ventilator associated pneumonia compared to those who had delayed initiation, with reported mortality rates of 29.2% versus 58.3%, respectively.
Our study has several limitations. Since the average length of stay of routine cardiac surgeries such as CABG is 5–7 days, the true incidence of pneumonia may be underestimated given the retrospective nature of this study. Late onset pneumonias which may have occurred after hospital discharge and during re-admissions could have been missed. Also, the results and conclusions of this study is based on a single center result, which cannot be extrapolated to other institutions. The differences in hospital preventive measures that are implemented and the level of compliance of health care professionals to infection control policies may be varied among hospitals.
Implications for Practice
Given the significantly increased in-hospital mortality and morbidity among those who acquired pneumonia, this study highlights the importance of infection control and preventive measures in the perioperative cardiac setting. Such emphases require behavioral and probably cultural changes which may be accomplished through repeated hospital education, audit, and feedback.
We recommend the creation and implementation of a clinical pathway for patients undergoing cardiac surgeries with a goal of improving clinical outcomes and hospital cost. The pathway should aim to provide coordinated care amongst health professionals, with particular emphasis on infection control and preventive measures.
Implications for Research
Future studies are needed to identify the different pathogenic organisms responsible for nosocomial pneumonia, as well as to determine the role of antibiotic prophylaxis in the prevention of infection in the cardiac surgical setting. Likewise, it would also be pertinent to determine the financial impact of postoperative pneumonia with the goal of improving hospital processes of care.