الفهرس 
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Abstract
VAP and late VAP, and a high significant difference at the day of diagnosis between VAP (early and late) and VAT group (p <0.001).
But a non significant difference existed in CPIS, CRP and PCT at (D1) between early VAP, late VAP and VAT. This finding was expected as we included patient in the beginning of the study with no clinical or radiological evidence of pneumonia and normal serum levels of CRP and PCT. Although VAT patients in the present study showed the lowest values of CPIS, CRP and PCT versus both early and late VAP in the day of diagnosis with high statistical significance (p ˂ 0.001), VAT group had a high significant difference in values of the same parameters between (D1) and the day of diagnosis of VAT (p ˂ 0.001).
Regarding the isolated organisms in cases of VALRTI, pseudomonas aeruginosa was the most common isolated organism [5 patients with VAP 31.2%, 1 cases with early VAP (16.7%), 4 cases with late VAP (40%) and 3 cases with VAT (33.3%)]. Mixed microorganisms were presented in late VAP and VAT in (20% and 22.2% of cases respectively).
Regarding the diagnostic value of serum levels of procalcitonin and CRP and the CPIS scale, the optimal cut-off values of procalcitonin, CRP levels and simplified CPIS used to differentiate between the presence and the absence of ventilator associated lower respiratory tract infections were (≥ 2 ng/ml, ≥9.7 mg/L and ≥ 6) respectively and they were assessed by the area under the ROC curve. The use of simplified CPIS ≥6 points in combination with serum levels of procalcitonin ≥2ng/ml did not improve the sensitivity (72%) but resulted in (100%) in both specificity and positive predictive value.