icu

Prevention of Ventilator-Associated Pneumonia

　　 Marin H. Kollef, MD,[1] of Washington University School of Medicine, Manchester, Missouri, led off the symposium by focusing on pathogenesis and prevention of ventilator-associated pneumonia (VAP). He emphasized the importance of 2 factors in terms of pathogenesis: the microbial colonization of the upper airway and the aspiration of upper airway flora into the lower respiratory tract. He noted that in certain patients, aspiration of gastrointestinal (GI) material, or the influence of GI flora on upper airway colonization, were also important factors.
　　As general concepts, it should be apparent that the more virulent or antibiotic-resistant the organisms, the worse the lower respiratory infection will be. Similarly, the greater the frequency and quantity of aspiration, the greater the likelihood and severity of resulting pneumonia.
　　Dr. Kollef emphasized that risk factors for hospital-acquired pneumonia, or VAP, are thus fairly predictable. The prior use of antibiotics or the use of H-2 blockers predisposes to colonization of the GI and respiratory tracts with pathogenic and/or resistant organisms (bacteria and fungi). Factors that increase the risk of aspiration, such as failing to elevate the head of the bed, transport outside of the intensive care unit (ICU), or distention of the GI tract by enteral nutrition, are clearly factors that can facilitate development of hospital-acquired pneumonia. Furthermore, these factors are largely under the control of the ICU staff.
　　Dr. Kollef pointed out that VAP might be more appropriately designated, "endotracheal tube-associated pneumonia." Ventilation with an endotracheal tube is much more likely to produce VAP compared with mask ventilation. It has also been shown that protocols can hasten extubation (ie, they can reduce the time patients receive mechanical ventilation). Any factor that reduces time on mechanical ventilation will also reduce the incidence of nosocomial pneumonias. ICUs should be encouraged to have such protocols. Thus, the endotracheal tube really facilitates aspiration, and we need to reduce the time such devices are in place.
　　If endotracheal tubes are used, Dr. Kollef emphasized that tubes manufactured with suction ports can reduce the incidence of nosocomial pneumonias. Secretions pool above the cuff: we know that such material is aspirated into the lower respiratory tract despite the cuff. These cuffs with suction ports are used routinely in session moderator and speaker Dr. Paul Marik's unit at the University of Pittsburgh, Pennsylvania, according to Dr. Kollef. Shorr and O'Malley[2] have done a meta-analysis that shows that such cuffs can reduce the incidence of pneumonia in most studies, and can reduce the cost of care. Thus, Dr. Kollef endorsed the use of these tubes, although it was not clear if he was advocating their use in all patients in all ICUs.
Biofilm of the endotracheal tubes are also important in terms of the development of endotracheal tube-associated pneumonia. The biofilm can enhance the accumulation of bacteria, and the production of factors that interfere with antibiotic efficacy.[3] In the future, there may be agents available that can inhibit the development or the effects of these biofilms.
In animal models, Dr. Kollef indicated that endotracheal tubes coated with substances that interfere with microbial colonization can reduce colonization or bacterial adherence with organisms such as Pseudomonas. Overall, in these animals, reduction in all aerobic bacteria could be shown in biopsied lung tissue, and reduction in pneumonia-associated bacteremias as well. Thus, endotracheal tubes impregnated with antiseptic agents, or agents that interfere with biofilm production, could be useful devices for reducing the incidence of endotracheal tube-associated pneumonia. Nebulized aminoglycosides appear also to be effective for reducing biofilm development, but the effects of these drugs on microbial resistance will prevent this from being a useful technique for such a role. However, other inhibitors of biofilm could be developed that do not affect the resistance pattern for clinically useful antibiotics.
Oral decontamination via topical agents, as opposed to gut decontamination, might also be useful for preventing VAP. Mupirocin topical treatment of the nose for Staphylococcus aureus colonization is an example of a local approach that can reduce the incidence of clinically important infections.[4] The future may see the use of topical antiseptics such as mammalian peptides (eg, iseganaans), or vaccines (eg, against S aureus or Pseudomonas), that could reduce microbial colonization of mucosal surfaces.[5]
　　Dr. Marik asked Dr. Kollef whether frequent suctioning might be disadvantageous in terms of dislodging material from the endotracheal biofilm into the lower respiratory tract, producing a nidus for infection. Dr. Kollef indicated that in his unit, they try not to suction more than once per shift, and they do not routinely put saline down the endotracheal tube. However, he indicated that he did not have an easy solution for how to remove secretions and concurrently avoid inoculation biofilm and colonizing organisms into the lower respiratory tract.