Introduction
Ventilator associated events (VAE) refers to new surveillance definition developed by Centre for Disease Control and prevention (CDC)/ National Healthcare Safety Network (NHSN) is in use since the year 2013, switching the focus of surveillance from VAP to VAE.1 VAEs are identified by using a combination of objective criteria: deterioration in respiratory status after a period of stability or improvement on the ventilator, evidence of infection or inflammation, and laboratory evidence of respiratory infection.2 The VAE surveillance definition algorithm includes a broad range of pulmonary complications, both infectious and noninfectious, that may occur in mechanically ventilated patients.3, 4 At least 2 days of stable or decreasing ventilator settings followed by at least 2 days of increased ventilator settings was used as definition of VAE.5 There are three definition tiers within the VAE algorithm:
Ventilator-Associated Condition (VAC);
Infection-related Ventilator-Associated Complication (IVAC); and
Possible VAP (PVAP)
Over recent years the causative microbes are usually multidrug resistant, therefore associated with significant morbidity and mortality. It has many important implications from patient care and prevention perspectives. Therefore, this study was undertaken to determine the incidence and outcome of VAE in patients on MV in adult medical ICU of BPKIHS using the new algorithms and to study the microbiological profile associated with VAE with special reference to their antimicrobial susceptibility status.
Materials and Methods
This prospective study was carried out in the Department of Microbiology, B.P. Koirala Institute of Health Science (BPKIHS), Dharan, Nepal in collaboration with the Department of Anaesthesiology & Critical care from January 2020 to December 2020. Ethical clearance for the study was obtained from the Institutional Review Committee of BPKIHS, Dharan. Ethical approval; Ref. No. Acd/422/077/078-IRC. Patients admitted in ICU on MV were evaluated daily using the VAE surveillance criteria. Three tiered approach of VAE, namely VAC, IVAC and PVAP was used for the final classification of cases. Clinical specimens relevant for the microbiological investigations mainly comprised of ET aspirates, were collected and submitted to the Department of Microbiology. Identification of bacterial isolates was established by colony morphology, Gram stained findings and results of various biochemical tests as per standard microbiological techniques.6 Antimicrobial susceptibility of the isolates to the commonly used antimicrobials in BPKIHS hospital was determined by Kirby Bauer disc diffusion method using Muellar Hinton Agar (MHA) as recommended by Clinical and Laboratory Standards Institute (CLSI-2019) guidelines.
Ventilator‑associated condition
It is defined as increase in the daily minimum positive end expiratory pressure (PEEP) of at least 3 cmH2O for at least 2 days or increase in daily minimum fraction of inspired oxygen (FiO2) of at least 20 points for at least 2 days.
Infection related ventilator associated condition
It is defined as any one out of the following four conditions: fever or hypothermia or leukocytosis or leukopenia, and new antimicrobial agent started and continued for ≥4 days.
Possible Ventilator associated pneumonia (PVAP)
It is defined as isolation of significant count of a pneumonia pathogen from respiratory specimens.
Data analysis
Of the 313 patients admitted to the ICU during the study period, 52 patients received MV for ≥2 days and met baseline criteria for VAEs Surveillance Algorithm. Collected data were entered into a database using MS Excel 2007. SPSS version 20 was used for statistical analysis. Chi-square test was applied for comparison of categorical variables. For cells with expected count less than 5, Fisher’s Exact Test was used. T-test was applied for comparison of mean values of two independent samples. P value less than 0.05 was statistically significant.
Results
Out of 52 patients, 28 (54%) were male and 24 (46%) patients were female. The mean age of patients with VAEs was 55.77 ± 16.08 years. Date of event (DOE) for the patients was from 3 to 6 days with mean duration being 4.35 ± 0.95. Out of 52 patients, 14(27%) developed VAC only, 13(25%) developed IVAC only and 25(48%) patients developed PVAP. Among the subtypes of VAE, 27% cases were VAC only (4.6/1000 ventilator days), 25% were IVAC only (4.2/1000 ventilator days), and 48% were PVAP (8.2/1000 ventilator days). Highest mortality rate seen in PVAP followed by VAC cases 44% and 35.7% respectively. However, percentage of improved cases seen in IVAC cases. Totally 25 (48%) patients were developed PVAP. Of total 9 (36%) patients had early onset PVAP and 16 (64%) had lateonset PVAP (P < 0.001). Table 1 shows incidence of VAC, IVAC, PVAP and overall VAE incidence rate, mortality and improved cases in each tier of VAE.
Table 1
Overall ventilator associated events incidence and mortality (n= number)
Endotracheal aspirate culture yielded the growth of bacteria in all cases of PVAP. All the organisms isolated were Gramnegative bacilli (GNB), Acinetobacter baumanii complex 14(53.84%), Pseudomonas aeruginosa 7(26.92%), Klebsiella pneumoniae4(15.38%), and Escherichia coli 1(3.84%). One of the patients had polymicrobial growth of Acinetobacter baumanii complex and Pseudomonas aeruginosa. Of the total isolates of PVAP, Multidrug resistance was observed in 25(96%) which comprised of Acinetobacter baumanii complex 14(53.84%), Pseudomonas aeruginosa 7(26.92%), Klebsiella pneumoniae 4(15.38%). Figure 1 shows percentage of microorganisms responsible for causing PVAP.
Patients who developed VAE had 8 to 18 days of ICU stay. Length of ICU stay was more than 16 days seen in Acinetobacter baumanii complex and Pseudomonas aeruginosa pathogens. Death was reported in 19 (36.5%) of the VAE patients, 27(51.9%) survived and 6(11.5%) patients left against medical advice.
Discussion
In this study, the overall VAE incidence and rate occurred as 16.6% and 17.1/1000 ventilator days, respectively. Our VAE rate was found to be lower than that of other studies conducted in India by Vaisakh et al.,7 Thomas et al.8 and Sharma et al.9 reporting VAE rates of 29.2%, 29.6% and 19.5% respectively. A study in India has reported the rates of the subtypes of VAE, 27% cases were VAC only (6.7/1000 ventilator days), 48.6% were IVAC (11.5/1000 ventilator days), and 24% were PVAP (5.7/1000 ventilator days) whereas a it was reported as 6.4/1000 ventilator days, which is quite low as compared to that of our study.10 Vaisakh et al.7 reported 58.3% VACs, 25% IVACs, and 8.3% PVAP. Our study encountered more cases of PVAP as compared to their study. All the Isolated organisms in this study were Gramnegative bacilli (GNB), Acinetobacter baumanii complex 14(53.84%), Pseudomonas aeruginosa 7(26.92%), Klebsiella pneumoniae 4(15.38%), and Escherichia coli 1(3.84%). Similar observation was made by John et al. that gram negative organisms were the most common pathogens associated with PVAP. Among these, the most predominant was Acinetobacter species (48.21%), followed by Klebsiella (19.64%) and Pseudomonas species (17.86%). Chastre and Fagon,11 who compiled data from 24 published studies found that 58% of the isolates were gram negative bacteria, Pseudomonas being the commonest followed by Acinetobacter species and Proteus species.
In our study total MV days in VAE cases was 3036 days, with a mean of 9.7 days. Patients who developed VAE had 8 to 18 days of ICU stay. Length of ICU stay was more than 16 days seen in Acinetobacter baumanii complex and Pseudomonas aeruginosa pathogens. Death occurred was observed in 19 (36.5%) of the VAE patients, 27(51.9%) survived and 6(11.5%) patients left against medical advice. Highest mortality rate seen in PVAP followed by VAC cases 44% and 35.7% respectively. This implies that events associated with infection are definitely associated with higher mortality as compared to noninfectious conditions leading to VAE. According to a study conducted by Sharma el al.9 total MV days in VAE cases was 685 days, with a mean of 18.5 days. The mortality for VAConly cases was significantly low (100% survived), but for IVAC, the mortality was high (83% expired) and PVAP was 77%. Another study conducted in Japan shown mortality rate who developed VAEs was 42.9%.10
Conclusion
VAE surveillance does focus on a broader category of patients on mechanical ventilation who suffer from many other complications apart from pneumonia. Better patient care and outcome may be achieved by identifying the noninfectious complications of ventilated patients through VAE surveillance and guiding the hospital in planning VAE prevention programs accordingly. VAE mostly being a health care associated event and prevalence of multidrug resistance in as observed in this study warrant stringent infection control practices and rationale use of antimicrobials as effective measures for control.
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