Inspiratory pressure-volume curves at different positive end-expiratory pressure levels in patients with ALI/ARDS.
BACKGROUND
In lung protective strategy, positive end-expiratory pressure (PEEP) slightly higher than the Pflex (the airway pressure corresponding to the lower inflection point (LIP) on the inspiratory pressure-volume (P-V) curve measured with ZEEP) is generally recommended. However, this method to determine optimal PEEP lacks a theoretical background and there is no clinical report that investigated how the P-V relationship would be with such PEEP. Therefore, we measured inspiratory P-V curves at different PEEP levels to increase our knowledge about the inspiratory P-V curve with PEEP.


METHODS
In eight consecutive patients with ALI/ARDS, inspiratory P-V curves were repeatedly measured at different PEEP levels by low flow inflation technique and LIP was assessed in all inspiratory P-V curves. Afterwards, the minimum PEEP level at which LIP was not identifiable (PEEP(LIP)(-)) was determined and the relationship between Pflex and PEEP(LIP)(-) was investigated.


RESULTS
Pflex and PEEP(LIP)(-) could be determined in all patients. Pflex was 9.4+/-2.0 cmH2O (range: 7 to 12 cmH2O) and PEEP(LIP)(-) was 7.9+/-1.6 cmH2O (range: 5 to 10 cmH2O) (mean+/-SD, P=0.0877). PEEP(LIP)(-) was lower than the Pflex in five patients, and significantly lower than the Pflex + 2 cmH2O (P=0.0024).


CONCLUSIONS
From the analysis of inspiratory P-V curves at different PEEP levels, PEEP 2 cmH2O higher than the Pflex may not be necessary to prevent cyclic collapse and reopening of alveoli, at least in some ALI/ARDS patients. Further studies are needed to confirm this preliminary result.
Nagano
O
O
Department of Anesthesiology and Resuscitology, Okayama University Hospital, Okayama City, Japan. nagano@cc.okayama-u.ac.jp
Tokioka
H
H
Ohta
Y
Y
Goto
K
K
Katayama
H
H
Hirakawa
M
M
D000293:Adolescent; D000328:Adult; D000368:Aged; D000403:Airway Resistance; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration; D012123:Pulmonary Ventilation; D012128:Respiratory Distress Syndrome / Q000503:physiopathology* / Q000628:therapy; D015656:Respiratory Mechanics; D013990:Tidal Volume