Introduction

Ventilator-associated pneumonia (VAP) is a clinical form of hospital-associated pneumonia, which may develop within 48 h in patients on mechanical ventilation (MV) who had no pre-existing pneumonia at the time of intubation [1–3]. Mechanical ventilation has found increasing application following the advances in medical technology, which, however, are associated with a number of complications. Among these is VAP, a complication linked with prolonged mechanical ventilation. VAP may be seen in 8–28 % of patients connected to mechanical ventilation and is associated with 24–50 % mortality [2]. The risk is higher during the first days of mechanical ventilation; the relative risks are estimated to be 3 %/day during the first 5 days, 2 %/day during the first 5–10 days, and 1 %/day thereafter. VAP is a major factor contributing to mortality in patients hospitalized at intensive care units. It represents the one-third of all nosocomial infections. VAP is also associated with longer duration of stay at intensive care units or hospitalization [4]. The incidence of VAP ranges from 6 to 52 % in intubated patients depending on the patient’s risk factors. The cumulative frequency is approximately 1–3 % per day of intubation [5].

Associated with an increased risk of mortality and morbidity, pneumonias have been reported to be linked with the length of hospital stay, the incidence being increased in patients hospitalized for longer than 7–9 days. It is vital for intensive care units to reduce the prevalence of VAP by determining the factors contributing to occurrence of VAP and by taking relevant measures [6]. The prevalence of acquired pneumonia and other infections of the lower respiratory tract in intensive care units is 28 % in Turkey [7]. Prevalence of VAP is 5.29 % in Latin America, Turkey, India and Morocco [8].

In a multinational nosocomial infections study, VAP was reported to occur in 10–15 cases on average for every 1,000 days of ventilation, although there was a variation dependent on the group under study. This rate was reported to be markedly increased in surgical intensive care patients, compared to medical intensive care patients. There was no correlation between the patients’ sex and incidence, but an increased prevalence was noted with increasing age [9]. According to Rosenthal et al. [8], 1,038 (5.29 %) out of 19,594 patients developed VAP (rate of VAP was 24.6 per 1,000 mechanical ventilation days).

Materials and methods

Objective

This is a descriptive, analytical, randomized study to compare ventilator-associated pneumonia among patients connected to HME filters and HHs for mechanical ventilation.

Design

This study was carried out at the intensive care unit of a privately owned hospital between September 2007 and July 2008 with 35 patients using HME filters and HHs who met the inclusion criteria. The patients were monitored for 1 week and were studied to determine if there were any differences regarding VAP between the treatment groups.

Instruments

The data were collected using a daily checklist and a questionnaire. The questionnaire included items questioning age, sex, smoking habit, chronic conditions, diagnosis at presentation and date of hospitalization. Daily checklists were developed to monitor patients throughout the intubation period (for 7 days). The patients were evaluated against the questions in the checklist twice during the 24-h period. The daily checklist included items questioning antibiotic use in patients, the presence of fever, leucocytosis, duration of mechanical ventilation, head height, presence and character of secretion, frequency of aspiration, endotracheal aspirate culture growth, HME filter changeover, frequency of ventilator circuit changeover, Glasgow coma score, nasogastric feeding probe, cuff pressure value, and whether or not there was infiltrate on chest radiography.

Data collection

In this intensive care unit, HME filters and HHs are used in routine practice. Patients were assigned to HME filters or HHs, by a random number list generated using Excel software. HME filters were used in 18 patients, and HHs in 17 patients.

Oral hygiene was performed six times a day for each patient. In both patient groups, identical measures for the prevention of nosocomial pneumonia were established: routine change of ventilator circuits, a closed tracheal suction system, a semi-recumbent body position, continuous enteric nutrition, periodic verification of the residual gastric volume, oral washing with clorhexidine, and no selective digestive decontamination. Filters of the ventilator were replaced on a daily basis for patients using HME filters. Similarly, the distilled water was replaced by an investigator every 24 h for patients using HHs. Endotracheal aspirate cultures were collected from patients over the first 24 h and were studied with chest radiography. Patients’ assessments were assigned based on the filtration observed with chest radiography.

Oral washing with clorhexidine during the study was performed six times a day. Patients were repositioned every 2 h in bed a day.

Ethical considerations

Approval of the ethics committee of the research centre was obtained. Patients’ relatives also provided consent for the inclusion of the patients, since the latter were unconscious and under sedation. No procedures other than those described to the patients’ relatives were undertaken.

Inclusion criteria

Patients who were on the first day of intubation, had no pre-intubation pneumonia, referred to the clinic from other institutions without any infections, not on antibiotics treatment for pulmonary infection, and whose pulmonary radiography did not involve evidence of infiltration were eligible inclusion in the study. A total of 35 patients who met these criteria were included in the study.

Data analysis

The statistical analyses were carried out using SPSS, with a statistical significance level of p < 0.05. Data are presented using mean and percentage values. Mann–Whitney’s U test, Student’s t test, Fischer’s exact and Chi-square tests were used for comparisons.

Results

Mean ages of patients using HHs and HME filters were 44.5 ± 2.1 and 47.9 ± 2.2 years, respectively. Of the patients, 80 % were males, and 34.3 % of them were smokers (Table 1). There were no significant differences between the groups with regard to the duration of ventilation or duration of hospitalization although both the mean duration of mechanical ventilation and the mean duration of hospitalization were higher in the HME group compared to the heated humidifier group (Table 2).

Table 1 Subjects’ socio-demographic and clinical characteristics (N = 35)
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Table 2 Comparison of HME filters and HHs groups by number or duration of mechanical ventilation and duration of hospitalization
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Presence of fever was noted significantly more frequently in patients using HHs than those using HME filters. Although the two groups did not differ significantly regarding endotracheal aspirate culture growth within the first 24 h, the measurements were higher than expected in the HHs group and lower than expected in the HME filter group (Table 3).

Table 3 Comparison of HME filters and HHs groups by presence of fever within the first 24 h and by endotracheal aspirate culture results
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Presence of infiltration in chest radiography was not statistically different between the groups, although occurrence of infiltration based on pulmonary radiography was earlier in the HHs group compared to the HME filter group (Table 4).

Table 4 Comparison of HME filters and HHs groups with regard to pulmonary infiltration
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Discussion

In their study titled “VAP using a heated humidifier or a heat and moisture exchanger” on 120 randomly chosen patients, Lorente et al. [10] reported mean ages of their subjects as 42.3 in their HME group and as 43.1 in their HHs group. In their study comparing HME filters and HHs, Kirton et al. [11] reported the mean ages as 49.9 of the subjects in their HME filter group as 52.1 of the subjects in their HHs group. Lorente and Kirton have reported lower mean ages for subjects in their HME filter groups.

The groups did not differ significantly regarding the duration of mechanical ventilation or the duration of hospitalization. However, both the mean duration of mechanical ventilation and mean duration of hospitalization were higher in the HME filter group compared to the HHs group (Table 2). Lorente et al. [10] reported no marked difference between their groups with regard to days of ventilation. Comparing HME filters and humidified filters, Kirton et al. [11] described no significant difference between the two groups in terms of growth and mechanical ventilation duration. In their study on the efficacy of HME filters in preventing VAP, Kola et al. [12] identified significant differences between the groups in terms of the duration of mechanical ventilation and hospitalization. The findings of the present study differed from the findings of Kola, but are consistent with those reported by Lorente and Kirton.

The two groups were compared for occurrence of fever over the first 24 h. Incidence of pyrexia over the first 24 h among patients using HHs were significantly higher than those using HME (Table 3). In a study on VAP, Tascı [4], described that presence of fever <38 °C accompanied by leucocytosis should suggest presence of VAP. In the present study, fever was noted for patients with VAP in both groups with, but it had an earlier onset in the HHs group development of infiltration as identified by chest radiography was earlier in the HHs group. There were no statistically significant differences between the groups in terms of endotracheal aspirate culture growth within the first 24 h, although the growth results were higher than the expected levels in the HHs group and below the expected levels in the HME group. In their study comparing HME filters and HHs, Kirton et al. [11] determined no differences between the groups regarding culture growth. In the present study, growth was above the expected levels in the HHs group, although the difference between the two groups was not statistically significant.

The two groups did not differ significantly with regard to occurrence of pulmonary infiltration, although lung infiltration occurred more frequently than expected in the HME filter group and less frequently in the HHs groups (Table 4).

In their study on VAP with HME filter or HHs use, Lorente et al. [10] reported a higher rate of VAP in the HHs group compared to the group using HME filters. Kirton et al. [11] on the other hand, identified a lower rate of VAP in the HME filters group. In their study comparing HME filters and heated systems with regard to VAP development, Memish et al. did not identify any differences between the two groups. The present study is consistent with the study by Memish [13].

There were no significant differences between the groups regarding the onset of pulmonary infiltration, although lung infiltrations occurred earlier in the HHs group compared to the HME filters group (Table 4). In their study comparing three HME filters during the period of mechanical ventilation, Sottiatux et al. [14] recommended use of HHs. The Turkish Thoracic Association’s Consensus Report on Diagnosing and Treating Hospital-Associated Pneumonia in Adults recommends use of HME filters, if not contraindicated, instead of HHs [3].

As the main indictor of ventilator-associated pneumonia, first day of infiltration as demonstrated by chest radiography was studied in both groups. Infiltration occurred on day 6.33 in the HME filter group and on day 5.8 in the heated humidifier group. Thus, VAP in both groups were considered as late-onset VAPs.

Conclusion

In conclusion, incidence of pyrexia within the first 24 h among patients using HHs were significantly higher than those using HME. However, there were no significant differences between the two groups in terms within 24 h endotracheal aspirate culture growth or presence of infiltration as determined by pulmonary radiography. And, based on mean days to infiltration, infiltration had a later onset in the patients using HME filters. Therefore, use of HME filters is recommended in intensive care units.