Outcome of Ventilator-Associated Pneumonia in Children Post Cardiac Surgery: A Prospective Observational Study

Introduction

Ventilator-associated pneumonia (VAP) refers to hospital-acquired infection (HAI) of lung parenchyma occurring 48 hours or more after initiation of mechanical ventilation (MV).¹ In the pediatric intensive care unit (ICU) VAP is the second most common HAI accounting for approximately 20% of all HAI.², ³, ⁴ VAP is commonly caused by hospital acquired pathogens like Acinetobacter species, Pseudomonas aeruginosa, Klebsiella species, E. coli, and methicillin-resistant Staphylococcus aureus (MRSA).⁵, ⁶, ⁷, ⁸

Risk factors for VAP in children include prolonged MV, reintubation, aspiration, use of H₂ antagonist, blood stream infection, age younger than 12 months, congenital immunodeficiency, burns, airway malformations, and genetic syndromes.⁴, ⁹, ¹⁰, ¹¹ Cardiac surgeries especially with cardiopulmonary bypass (CPB) trigger inflammatory responses leading to impaired lung function, resulting in high risk for VAP.¹²

Information about VAP in children after congenital heart surgery is scarce and further studies are need of the hour. Children are highly vulnerable to VAP post-cardiac surgery and occurrence of multidrug resistance (MDR) pathogens is very frequent as reported by Tang et al.² We conducted this study with the objective to determine incidence, risk factors, and mortality due to VAP in post cardiac surgical children and to study the causative microorganisms and their antibiotic resistance profile.

Material and Methods

Results

Out of 1,953 patients admitted to the ICU, 371 patients fulfilled the inclusion criteria, while 1,582 patients were excluded as per the exclusion criteria as shown in the flow diagram (Fig. 1).

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Fig. 1

Flow diagram showing study population and exclusion criteria.

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Preoperative and Intraoperative Variables

As delineated in Table 1, the median age of patients with VAP was 0.17 years (2 months) and without VAP was 0.75 years (9 months). Fifty-four (14.6%) patients who developed VAP were younger than 1 year (p ≤0.001). Median body weight of patients with VAP was 4.12 kg and patients without VAP was 7.20 kg. Fifty-eight (15.6%) male and nine (2.4%) female children developed VAP. Patients with longer duration of preoperative hospital stay had higher incidence of VAP (odds ratio [OR]: 2.25; 95% CI:1.11–4.52; p = 0.007). The mean CPB time in patients with VAP and without VAP was found to be 121.53 ± 57.71and 99.19 ± 44.60 minutes, respectively (p = 0.0005). The median duration of ACC time in patients with VAP was 75 minutes and without VAP was 67 minutes (p = 0.0049). The CPB time, ACC time, and total duration of surgery were found to be statistically significant and associated with higher risk of VAP. More number of patients from RACHS category 2 and 3 developed VAP in comparison to others (RACHS category 1, 4, and 5).

Discussion

VAP has been a topic of profound interest in adults and pediatric population due to the high morbidity and mortality associated with it. But there is scanty literature in the prospective studies in particular pertaining to VAP in children undergoing congenital heart surgeries. Cardiac surgeries and CPB induce a cascade of changes that result in hemodynamic alteration, capillary leak syndrome due to cytokine surge and decreased pulmonary compliance and increased airway resistance. Consequently, the altered respiratory mechanics lead to prolonged invasive MV, tracheostomies, hemodynamic instability requiring longer duration and higher doses of inotropes and renal impairment, making these children highly vulnerable to VAP. In this study we focused exclusively on VAP in post cardiac surgical children in a high volume tertiary care teaching institute.

In this prospective observational study, the incidence of VAP was 18% and VAP incidence density was 36.3 per 1,000 MV days. This was higher in the study conducted by Tang et al where VAP incidence was 13% and VAP incidence density was 21.6 per 1,000 MV days.² But the authors Ghassan et al and Roeleveld et al reported the incidence of VAP in post cardiac surgical children as 7 and 8.8%, respectively which was much lower as compared with our study.¹³, ¹⁴ The median age of patients with VAP was 0.17 years (2 months). 80.6% of the patients who developed VAP were children younger than 1 year. Pediatric population after cardiac surgery is at high risk of VAP due to younger age, malnutrition, and lower body weight. Use of invasive devices, invasive MV, invasive monitoring after cardiac surgery further increases the risk of VAP. CPB time, ACC time, and total duration of surgery were directly proportional to incidence of VAP as the extracorporeal circulation induces severe inflammatory changes in almost all organ systems causing myocardial and pulmonary dysfunction. This was in concordance to that reported by Sahu et ¹⁴, ¹⁵ Tang et al have previously documented that complex CHD was associated with VAP after surgery.² In our study, RACHS-1 scoring was used to define complexity of surgical procedure. 10.2% of VAP patients belonged to RACHS 3 category (p = 0.003) in our study. Complex surgical procedures take longer time to recover in postoperative period, along with requirement of longer MV, invasive devices, high inotropic support, and multiple transfusions.

Prolonged MV (p ≤0.001) was found to be an independent and modifiable risk factor for VAP in this study. Similar finding was reported in study by Tang et al (OR: 15.19; 95% CI: 2.15–107.2) and Awasthi et al (OR: 3.76; 95% CI:1.41–10.02; p = 0.008).², ⁷

Various risk factors of VAP (such as prolonged MV, delayed sternum closure, tracheostomy, reintubation, use of uncuffed endotracheal tube, peritoneal dialysis) have been identified as published in many studies.⁵, ⁹, ¹⁵ In our study we found that prolonged preoperative hospital stay, delayed sternum closure, tracheostomy, reintubation, use of uncuffed endotracheal tube and peritoneal dialysis were significantly associated with VAP in postoperative period.

Diagnosis of VAP was established according to CDC guidelines. However, microbiological confirmation from LRT secretions was a mandatory criteria in our study as infiltrates on CXR in cardiac patients can occur due to multiple other causes (infectious, fluid overload, atelectasis, and pleural effusion).

On the basis of LRT aspirate culture findings, we concluded that Acinetobacter baumannii (43%) and Klebsiella pneumoniae (23%) were the most frequently isolated pathogens causing VAP. The other organisms implicated in causing VAP were less frequent and are described in Table 4. In total, 5% of the children in our cohort had super-added fungal VAP caused by Aspergillus and some patients had polymicrobial infection too. However, in previous studies, most common etiological agents reported were P. aeruginosa, S. aureus, H. influenza, and M. catarrhalis.¹⁶

Emergence of MDR to common broad-spectrum antibiotics like cephalosporins, aminoglycosides, and carbapenems was found to be major hurdle in pediatric post cardiac surgery patients. Similar findings were reported in studies by Sahu et al and Ensminger et al.¹⁵, ¹⁶ VAP after cardiac surgery causes significant increase in MV duration, ICU stay, and hospital stay which add to the morbidity in the pediatric population and this study confirms these findings. Similar findings were reported in the studies by Tang et al, Ghassan et al, Roeleveld et al, and Sahu et al.², ¹³, ¹⁴, ¹⁵

In this study we found that patients who developed VAP had a mortality of 32.8% and Acinetobacter baumannii was the most common pathogen causing death. High mortality of 38.4% was observed by Tang et al in his study.² Majority of patients who died were less than 1 year old. No neurological complication was noted after recovery from VAP. We thus emphasize that timely identification of risk factors, early diagnosis of VAP, appropriate treatment of VAP, and prevention of complications are needed to help these children convalescing better, earlier and reducing mortality rate.

The study had certain limitations. Though this study was conducted in a tertiary care high volume teaching institute, but because of the COVID pandemic we could not garner more number of patients as routine surgeries were interrupted often during the study period, and the total study population was less in number than expected and also because it was a single center study, thus the results cannot be generalized. None of our patients had corona virus infection pre or postoperatively.

Conclusion

VAP is the most common hospital acquired infection amongst pediatric cardiac surgical patients in our ICU with a mortality rate of 32.8%.The incidence of VAP in our study was 18% and VAP incidence density was 36.3 per 1,000 MV days which carried with it a high morbidity in terms of longer invasive ventilation, ICU, and hospital stay. Postoperatively high index of suspicion of clinical infection, combination of laboratory tests, radiological findings, and microbial cultures are helpful to diagnose and treat VAP-induced sepsis at an early stage. Implementation of VAP prevention bundle, strict implementation of infection control surveillance policies, and antimicrobial stewardship help in reducing the incidence of VAP and its high fatality.