[Physiologic response to external positive end-expiratory pressure in mechanically ventilated chronic obstructive pulmonary disease patients].
OBJECTIVE
To evaluate the effects of external positive end-expiratory pressure (PEEPe) on respiratory system mechanics in passively ventilated chronic obstructive pulmonary disease (COPD) patients.


METHODS
Fifteen patients with acute exacerbation of COPD were randomly enrolled into the study. The patients were admitted into respiratory intensive care unit (RICU) from Jan, 2005 to Jun, 2006 for controlled mechanical ventilation. PEEPe was applied stepwise from zero to 120% of intrinsic PEEP (PEEPi) in all the 15 patients. At each PEEPe level, airway resistance, compliance (Crs), plateau pressure (Pplat), and total PEEP (PEEPtot) were measured. According to the changes of Pplat after PEEPe application, the patients were divided into 2 sub-groups, abnormal response group (n=11) and a perplexing response group (n=4).


RESULTS
In all of the 15 patients, airway resistance at PEEPe equal to 80% and 100% of PEEPi (18.5+/-2.0) cm H2O.L(-1).s(-1) (1 cm H2O=0.098 kPa), (18.0+/-2.2) cm H2O.L(-1).s(-1) were significantly lower than that at zero PEEPe [(23.0+/-2.9) cm H2O.L(-1).s(-1), t=5.36, 6.27 respectively, all P<0.01]. At PEEPe levels equal to 120% of PEEPi, airway resistance (17.3+/-2.1) cm H2O.L(-1).s(-1) and PEEPtot (12.7+/-2.2) cm H2O were significantly different compared with those at zero PEEPe (23.0+/-2.9) cm H2O. L(-1).s(-1), (10.0+/-1.1) cm H2O (t=6.79, -3.90 respectively, all P<0.01). There were no significant differences in baseline PEEPi levels (10.0+/-1.0) cm H2O, (10.0+/-1.4) cm H2O, resistance (22.8+/- 1.9) cm H2O.L(-1).s(-1), (23.1+/-4.1) cm H2O.L(-1).s(-1), Crs (39+/-6) ml/cm H2O, (42+/-9) ml/cm H2O and Pplat (20+/-4) cm H2O, (21+/-3) cm H2O between the normal response and the perplexing response groups (t=0.03, 0.10, 0.60, 0.15 respectively, all P>0.05). However, the corresponding values of Pplat changes at different PEEPe levels in the normal response group [DeltaPplat40 (-0.020+/-0.970) cm H2O, DeltaPplat80 (1.6+/-1.0) cm H2O, DeltaPplat100 (4.0+/-2.9) cm H2O, DeltaPplat120 (6.4+/-3.3) cm H2O] were found to be significantly different compared with those in the perplexing response group [DeltaPplat40 (-7.500+/-0.920) cm H2O, DeltaPplat80 (-4.4+/-1.4) cm H2O, DeltaPplat100 (-3.8+/-1.9) cm H2O, DeltaPplat120 (-1.6+/-1.2) cm H2O] (t=-9.64, -5.90, -3.80, -3.92 respectively, all P<0.01).


CONCLUSIONS
At least in some passively ventilated COPD patients, the applied PEEPe may offer benefit by decreasing the Pplat.
Liu
Yang
Y
Department of Respiratory Medicine, Affiliated Hospital, Police Army Medical College, Tianjin 300162, China.
Wei
Lu-qing
LQ
Lü
Fu-yun
FY
Wang
Huo
H
Cao
Wen-li
WL
Su
Bin
B
D000368:Aged; D000403:Airway Resistance; D005260:Female; D006801:Humans; D008170:Lung Compliance; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration / Q000379:methods*; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology / Q000628:therapy*; D011659:Pulmonary Gas Exchange / Q000502:physiology; D012123:Pulmonary Ventilation; D015656:Respiratory Mechanics / Q000502:physiology*; D016896:Treatment Outcome