New approaches for the prevention of airway infection in ventilated patients. Lessons learned from laboratory animal studies at the National Institutes of Health

Despite early diagnosis and appropriate antibiotic therapy, ventilator-associated pneumonia (VAP) remains the leading cause of death from hospital-acquired infection in ventilator-dependent patients. Strategies to prevent bacterial colonization of the trachea and lungs are the key to decrease mortality, hospital length of stay, and cost. It is well established that the VAP can result from entry of infected oropharyngeal/gastric secretions into the lower airways. Aspiration may occur during 1) intubation, 2) mechanical ventilation through leakage around the tracheal tube cuff, 3) suctioning of the tracheal tube when bacteria can detach from the biofilm within the tube, or 4) areosolization of bacterial biofilm during mechanical ventilation through the tracheal tube or the ventilator circuit biofilm. From experimental studies in sheep, we drew 3 relevant conclusions: 1) The tracheal tube and neck should be oriented horizontal/below horizontal to prevent aspiration of colonized secretions and subsequent bacterial colonization of the lower respiratory tract. 2) Continuous aspiration of subglottic secretions (CASS) can lower bacterial colonization of the respiratory tract, but at the price of severe tracheal mucosal damage at the level of the suction port. 3) Coating the interior of the tracheal tube with bactericidal agents can prevent bacterial colonization of the tube surface and of the entire respiratory circuit, during 24 hours of mechanical ventilation.

Investigation of porphyrins and metalloporphyrins using two-step laser mass spectrometry

Laser desorption time-of-flight mass spectrometry with laser postionization at 193 nm has been used to study a series of selected porphyrins and metalloporphyrins. Molecular ions are predominantly formed under soft ionization conditions, with extensive fragmentation of the peripheral substituents being observed under hard ionization conditions. Cu-octaethylporphyrin is found to exhibit anomalous demetallation at this ionization wavelength. At high ionization laser fluences it is also possible to observe extensive fragmentation of the porphyrin macrocycle. Much of the observed fragmentation can be understood with reference to previous studies using electron impact (EI) ionization. The stability of the porphyrin nucleus allows the fragmentation of the side chains to be examined. As in earlier EI studies dehydration products are observed in the mass spectra of hematoporphyrin IX. These products are shown to be thermally induced during infrared laser desorption, rather than fragments arising from photoionisation. The flexibility of this two-step laser mass spectrometric approach has allowed the analysis of chlorophyll a directly from an organic matrix. The data obtained suggest that information concerning the interaction between adsorbate and substrate can be extracted.

Direct analysis of polycyclic aromatic hydrocarbons in cloud-water aerosol filtrates using laser desorption mass spectrometry

A novel technique for the rapid screening of polyaromatic hydrocarbons (PAHs) in atmospheric particulates is presented. Two-step laser desorption laser photoionisation time-of-flight mass spectrometry was used to assay for PAHs in cloud-water particulates collected near Peebles in southern Scotland. The particulates were examined in situ on their host filters removing the requirement for time-consuming sample extraction and separation. The mass spectra obtained from a single filter are shown. The principal components of these are assigned to PAH contaminants and phthalate contaminants. A distribution of PAHs was observed using 193 nm laser photoionisation. The mass spectrum obtained on using 248 nm laser photoionisation exhibits a different intensity distribution demonstrating an ionisation wavelength dependence. The utility of the technique for rapid screening of PAHs and other polyaromatic species is discussed.