PURPOSE: We have demonstrated that there is considerable variability in mechanics and airway pressures during mechanical ventilation for ARDS. Others have demonstrated that PEEP can prevent pneumonia complicating acute lung injury. This probably reflects preservation of airway patency by PEEP. Multifocal atelectasis is the most likely mechanism of the mechanical variability which we have reported, and if PEEP does maintain airway patency it should reduce this variability. This study was conducted in order to test this possibility.
METHODS: 20 patients on mechanical ventilation for ALI/ARDS were studied. Clinical data were extracted from charts. Mechanics and airway pressures were recorded every 20 minutes for 2 hours on 0, 5 and 10 cmH2O of PEEP. Mean values and variability (range of values) were recorded and calculated for every parameter at each level of PEEP. The significance of changes in values was assessed using Student's T test for paired values.
RESULTS: The patients were 10 male and 10 female, aged 78 ± 10. The mean alveolar opening pressure (Pflex) was 18±4 cmH2O. Compliance increased slightly with decreased variability at both PEEP levels . Resistance decreased with 5 cm. PEEP but rose with 10 cm. Plateau pressure, which reflects alveolar pressure, was unchanged on 5 cm. PEEP but rose with 10 cm. The variability of both resistance and plateau pressure fell by 80% on increasing PEEP from 0 to either 5 or 10 cm. Peak airway pressure (which reflects airway resistance) and its variability were reduced at both PEEP values. The reported changes in variability were all significant at the level of p≤;0.005.
CONCLUSION: 5 cm. of PEEP reduced the variability of mechanics in patients ventilated for ALI/ARDS. The concurrent reduction in resistance and peak pressure suggest that the mechanism was increased airway patency, preventing atelactasis. 10 cm. PEEP provided no improvement over the results obtained with 5cm., but did increase plateau pressure.
CLINICAL IMPLICATIONS: At least 5 cm. PEEP should be used in all cases of mechanically ventilated ALI/ARDS unless there is a contraindication.
DISCLOSURE: William Marino, No Financial Disclosure Information; No Product/Research Disclosure Information