EXPECTED CONTRIBUTION FROM CURRENT PROJECT Preventing infection and limiting the emergence of antibiotic-resistant strains are two important issues in critical care medicine. To find a natural antimicrobial peptide as an adjuvant therapy for antimicrobial agents in treatment of the antibiotic-resistant strains, or as a regimen to increase immunity and to prevent infection is one of the directions of researches. LF is one of the promising agents in many vitro and animal studies. The study is trying to examine if LF is an ideal natural SDD regimen for the prevention of nosocomial pneumonia or sepsis in patients with PMV. If the result is positive, LF can be used clinically to increase the survival of the critically ill patients, increase weaning rate from MV, reduce the prescription of antibiotics and finally medical cost.