LUNG OVERINFLATION WITHOUT POSITIVE END-EXPIRATORY PRESSURE PROMOTES BACTEREMIA AFTER EXPERIMENTAL KLEBSIELLA-PNEUMONIAE INOCULATION

Objective: To determine the effect of peak inspiratory pressure (PIP) and positive end-expiratory pressure (PEEP) on the development of bact eremia with Klebsiella pneumoniae after mechanical ventilation of intr atracheally inoculated rats. Design: Prospective, randomized, animal s tudy. Setting: Experimental intensive care unit of a University. Subje cts: Eighty male Sprague Dawley rats. Interventions: Intratracheal ino culation with 100 mu l of saline containing 3.5-5.0 x 10(5) colony for ming units (CFUs) K. pneumoniae/ml. Pressure-controlled ventilation (f requency 30 bpm; I/E ratio = 1:2, FIO2 = 1.0) for 180 min at the follo wing settings (PIP/PEEP in cmH(2)O): 13/3 (n = 16) 13/0(n = 16); 30/10 (n = 16) and 30/0 (n = 16), starting 22 h after inoculation. Arte ria l blood samples were obtained and cultured before and 180 min after me chanical ventilation and immediately before sacrifice in two groups of non-ventilated control animals (n = 8 per group). After sacrifice, th e lungs were homogenized to determine the number of CFUs K. pneumoniae . Measurements and results: The number of CFUs recovered from the lung s was comparable in all experimental groups. After 180 min, 11 animals had positive blood cultures for K. pneumoniae in group 30/ 0, whereas only 2, 0 and animals were positive in 13/3, 13/0 and 30/10, respecti vely (p < 0.05 group 30/0 versus all other groups), Conclusions: These data show that 3 h of mechanical ventilation with a PTP of 30 cmH(2)O without PEEP in rats promotes bacteremia with K. pneumoniae. The use of 10 cmH(2)O PEEP at such PIP reduces ventilation-induced K. pneumoni ae bacteremia.