Ventilator-associated pneumonia (VAP) is defined as pneumonia occurring more than 48 hours after endotracheal intubation and the initiation of mechanical ventilation.(1) However, the diagnosis of VAP continues to be difficult. The classical clinical criteria; the appearance of infiltrates on chest radiographs, purulence of respiratory secretions, variations in body temperature or the number of circulating leukocytes, have a low specificity for the diagnosis of VAP. Microbiological confirmation takes 24-72 h and the frequent previous use of antibiotics may give false-negative information.(2)
The usual infection-related signs and symptoms can be missing in such patients because of the deep alterations of their immune status as well as the exposure to specific therapies and procedures. This results from the lack of specificity of the clinical diagnosis of infection, and the fear of not treating life-threatening infection in critically ill patients.(3)
Efforts have been made to develop new biomarkers that accurately predict sepsis occurrence in such patients. Among them, serum procalcitonin (PCT) is one of the most promising.(5) Procalcitonin, the precursor molecule of calcitonin, is a 116-amino acid and is produced by parafollicular cells of the thyroid and by the neuroendocrine cells of the lung and intestine. Serum levels of procalcitonin are very low in healthy individuals. Despite little being known about the biologic properties of procalcitonin and its origin, procalcitonin levels rise during bacterial infections but not during viral infections or inflammatory reactions of noninfectious origin.(6)
Procalcitonin level rises in response to a proinflammatory stimulus, especially of bacterial origin. In this case, it is produced mainly by the cells of the lung and the intestine. In blood serum, procalcitonin has a half-life of 25 to 30 hours. (7) Remarkably the high procalcitonin levels produced during infections are not followed by a parallel increase in calcitonin or calcium serum levels. (8)
Considering the variability of PCT levels, it is possible to theorize that increasing levels indicate presence of sepsis, whereas decreasing values suggest resolution.(7)
METHODS
This study was conducted on 92 patients. All patients consecutively admitted to the ICU in Alexandria University hospital suspected of VAP were included in this study. Written informed consent was obtained from all patients or one of his relatives to participate in this study, also approval from the ethical committee was tacked. Patients at least 20 years old were recruited. Full history, complete physical examinations beside necessary investigations were done to all suspected patients to fulfill inclusion and exclusion criteria. Exclusion criteria were a previous diagnosis of systemic infection or severe debilitating disease. Pneumonia was considered ventilator-associated when it occurred after 48 hours of mechanical ventilation. VAP was considered early-onset when it occurred during the first four days of mechanical ventilation and late-onset when it developed five or more days after the initiation of mechanical ventilation(8); APACHE II was calculated during the first 24 hours of admission to ICU.(9)
Diagnosis of pneumonia was suspected when a patient developed a new and persistent radiographic infiltrate plus two of the following: (1) body temperature more than 38°C; (2) white blood cells more than 11,000/mm3; (3) macroscopically purulent tracheal aspirate ;Purulent endotracheal aspirate was defined on inspection.(10)
Chest X-ray, arterial blood gases, complete blood count, creatinine, total bilirubin, albumin, PCT and CRP were obtained by the that time VAP was suspected (D1) and repeated on the third day of (D3) and on the seventh day treatment (D7). Quantitative endotracheal aspirate (QEA) was obtained on D1, D3 and then weekly. Sterile endotracheal aspirates were obtained with a suction catheter adapted to a mucus collector without saline instillation, and two samples of hemocultures were collected from different veins with a 15-minute interval before starting antimicrobial treatment.
Recorded data included age (years), sex, cause of ICU admission, arterial blood gases report, co-morbidities including chronic obstructive pulmonary disease, history of smoking, history of congestive heart failure, history of malignancy, duration of mechanical ventilation, duration of stay in ICU before VAP.
Adequacy of the empirical antimicrobial treatment was recorded on the basis of microbiological results. Adequate antibiotic therapy was defined as coverage of all the pathogens isolated (from QEA culture or from blood), by at least one antimicrobial administered by the onset of VAP, determined by the sensitivity pattern in the antibiogram.(11) Treatment was considered adequate when cultures were negative.
PCT was determined with the commercially available ELISA assay (Uscn Life Science Inc. Wuhan) with an analytical sensitivity of7 pg/ml and analyzed with BA-88A MINDRAY, Semi-automated chemistry analyzer. Blood was drawn from peripheral vein when a diagnosis of VAP was clinically suspected, before empirical antibiotic treatment was started. Samples of serum were prepared and frozen immediately after blood was drawn, then stored at -80°C. Assays were performed in batches at the end of the study period.(12)
Statistical Method:
The Data was collected and entered into the personal computer. Statistical analysis was done using Statistical Package for Social Sciences (SPSS/version 15) software.
The statistical test used as follow:
Arthematic mean, standard deviation, for categorized parameters, Chi square test was used or Fisher exact test. While for two groups t-test was used for parametric data, and Mann Whitney test was used. Spearman correlation coefficient was used to detect the correlation between different variables. The level of significance was 0.05.
RESULTS
This study was done (prospective study) on 92 patients admitted to our ICU in the period of 6 months; patients were selected among those who needed mechanical ventilation for 48 hours or more. VAP was clinically suspected in 54 (59%) patients. Among the 54 (VAP group) patients, 28 had unfavorable outcomes (12 deaths, 13 recurrences, and 3 documented extrapulmonary infections), with a mean time to unfavorable outcome of 16 ± 6 days. No patients had a concomitant extrapulmonary infection at the time of entry. Patients' characteristics at ICU admission and VAP Day (1) are shown in table 1. At the time of VAP onset, patients whose outcome would be unfavorable were more critically ill than those with a subsequent favorable outcome, with significantly higher mean WBC counts and sepsis-related organ failure assessment scores and lower PaO2/FIO2 ratios.
Microorganisms considered responsible for VAP group are listed in table II. The percentage of Pseudomonas aeruginosa infections was higher in patients with bad outcome.
Serum procalcitonin was significantly higher at day (1) in patients with VAP than those with non VAP, it decreased between Days (1) and (7) in VAP groups but were significantly higher in patients whose outcomes were unfavorable (64.8 pg/ml) than in those with subsequent favorable outcome (31.8 pg/ml) (Figure 2&3). There was positive correlation between procalcitonin level and WBCs count in first day (p=0.009), at third day (p<0.001) and at seventh day (p<0.001) (Figure 4).
The serum level of CRP was significantly higher in VAP group than non VAP at day (1) (98.7 and 6.4 mg/l in day) and there was a significant correlation between the CRP level and serum procalcitonin (r=0.86). The serum level of CRP remained higher in day 3(54.34 mg/l) and day 7 (48.9 mg/l) in VAP patients than non VAP (12.6 &14.4), however the level of CRP in patients with bad outcome was similar to those with good outcome.
Table I: Patients characteristic in VAP and non-VAP groups.
VAP group
n=54
Non VAP group
n= 38
P Value
Age (years)
Mean ±S.D.
48.7±13.68
46.5±14.99
0.63 #
Sex male/female
30/24
22/14
0.081 $
APACH II score
Range (median)
7.3-16.4 (13)
6.8-18(10)
0.044 *
WBC (c/mm3)
Range (median)
10.83 (3.34)
5.28 (1.09)
0.001*
PaO2/FiO2
Mean ±S.D
206.36 ± 22.03
254.44 ± 18.10
0.001#
History of DM
28 (51.9%)
21 (55.3%)
0.216 $
Exacerbated COPD
16 (29.6%)
10 (26.3%)
0.43 $
Cardiogenic Shock
3 (5.6%)
2 (5.3%)
0.53 ##
Days in ICU
(Range) median
(8-21) 14
(6-15) 9
0.28 *
Values are mean ± SD median or numbers, # t test, $ chi square test,
* Mann Whitney test ## Fisher Exact test
Statistically significant at p ≤ 0.05
Table II: Microorganisms considered responsible for VAP group
Microorganism
Patients with VAP
n=54
Patients with bad outcome
n=28
Pseudomonas aeruginosa
22 (40.7%)
16 (57.1%)
Escherichia coli
5 (9.3%)
2 (7.1%)
Enterobacter species
7 (12.9%)
--
Klebsiella species
5 (9.3%)
3 (10.7%)
Haemophilus species
8 (14.8%)
4 (14.3%)
Coagulase-negative
Staphylococci
4 (7.4%)
2 (7.1%)
Enterococcus species
3 (5.6%)
1 (3.6%)
Values are number (%)
Fig 1: Comparison between good and bad outcome cases according to WBCs count at different periods.
Fig 2: Procalcitonin level in VAP and NVAP group
procalcitonin Pg/ml
Fig 3: Serum procalcitonin at the time of ICU admission in patients with bad and good outcome.
Fig 4 a: Correlation between WBC with procalcitonin level at 1st day.
Fig 4 b: Correlation between WBC with procalcitonin level at 3rd day.
Fig 4 c: Correlation between WBC with procalcitonin level at 7th day.
Fig4: Correlation between WBC with procalcitonin level
DISCUSSION
The most frequently encountered intensive care unit (ICU) acquired infections are ventilator associated pneumonia (VAP) and bacteremia. It is generally associated with an increased risk of death, a greater length of stay and increased cost.(13) Moreover the usual infection-related signs and symptoms can be missing in such patients because of the deep alterations of their immune status as well as the exposure to specific therapies and procedures. As a result, the management of VAP infection is probably delayed in number of cases. On the other hand, the overuse of antibiotics is a common feature in ICU.(14) This results from the lack of specificity of the clinical diagnosis of infection, and the fear of not treating life-threatening infection in critically ill patients.
Recently, Duflo and colleagues reported that serum procalcitonin could be used as a complementary diagnostic marker of VAP and, moreover, that its serum levels were higher in nonsurvivors than survivors. However, until now, the usefulness of procalcitonin as a prognostic marker during an episode of microbiologically proven VAP has not been evaluated.(17) Therefore, we studied procalcitonin kinetics during the first week of VAP and tested the hypothesis that serum procalcitonin concentrations could serve as a novel marker of prognosis for patients with VAP.
The results of the present study showed that the serum level of procalcitonin was significantly higher at day (1) in patients with VAP than those with non VAP, it decreased between Days (1) and (7) in VAP groups but were significantly higher in patients whose outcomes would be unfavorable (64.8 pg/ml) than in those with subsequent favorable outcome (31.8 pg/ml). In addition,the percentage of pseudomonas aeruginosa infections higher in patients with bad outcome.
Studies revealed that the incidence of VAP in patients receiving mechanical ventilation varies widely [9-27%](15, 16) this variation may be due to the inaccuracy of the criteria used. The sensitivity and specificity of the classical clinical criteria are deficient. One study reported that the combination of new and persistent infiltrates on chest radiographs and two or three of: fever (>38°C), leukocytes (>12,000cells/mm3) or purulent tracheal secretion, had a sensitivity of 69% and a specificity of 75%. With regard to microbiological confirmation, the problems are the delay in obtaining culture results (48-72 h), and the potential interference of antibiotic use.(15)
In our results, PCT levels were significantly higher in non-survivors on D1 (p = 0.003) and D3 (p = <0.001). Furthermore, the decrease in PCT levels was significantly predictive of survival. Other studies on patients with VAP have reported higher PCT levels in non-survivors than in survivors.(19, 20)
In our results CRP level was higher in VAP than non-VAP, and the level of CRP remained elevated on the third and seventh day which strongly agreed with the results of Póvoa et al and Simon et al .(12,14)
Ugarte et al(19) have demonstrated in a large cohort study of critically ill patients, that infected nonsurvivors have higher concentrations of serum procalcitonin compared with infected survivors.(19) Interestingly, Shröder et al (20) have recently studied 24 patients with septic shock and have shown that in nonsurvivors, serum procalcitonin remained increased, whereas the course of survivors was characterized by decreased values, which were significantly lower at every time point compared with those patients who died. In our study, the serum procalcitonin concentrations were more increased in nonsurvivors with VAP. In addition, Bonten et al.(22) investigated the correlation between the circulating IL-6 and IL-8 concentrations and the prognosis in patients with VAP. They found that high serum concentrations of cytokines were associated with higher mortality rates
The results of Wanner et al(23) were in agreement with our result they found highest PCT concentration at diagnosis in patients with ARDS due to sepsis were 6.9 ng/dl ±2.5 ng/dl compared with patients without sepsis which was 1.1ng/dl±0.2ng/dl . Also they demonstrated that there was a correlation between serum PCT and severity of sepsis, organ failure (MODS), and mortality in injured patient.
Duflo et al. found a diagnostic cut-off point of3.9 ng/ml, with a sensitivity of 41% and a specificity of 100%; they also, found no differences in alveolar procalcitonin values among different groups. They concluded that Procalcitonin mainly forms part of the systemic response to infection and, consequently, alveolar values are lower than serum values.(17)
Gibot et al.(25) analysed the behaviour of procalcitonin in pneumonia (community- and ventilator-acquired) and concluded that there were no differences between the groups with and without pneumonia. However, a high percentage of patients with pneumonia had other infections, which increased the serum procalcitonin values.
In conclusion from this study; Serum PCT seems to be a good marker for early diagnosis of VAP before establishment of the microorganism results and the level of PCT may help in determination of the outcome, In addition PCT is a better marker of sepsis than CRP.
