Positive end-expiratory pressure above lower inflection point minimizes influx of activated neutrophils into lung.
OBJECTIVE
To compare the effects of low vs. high tidal volume (Vt) with three positive end-expiratory pressure (PEEP) strategies on activated neutrophil influx into the lung.


METHODS
Prospective, randomized controlled animal study.


METHODS
Animal laboratory in a university hospital.


METHODS
Newborn piglets.


METHODS
Surfactant-depleted piglets were randomized in littermate pairs; to PEEP of either 0 (zero end-expiratory pressure [ZEEP]; n = 6), 8 cm H2O (PEEP 8; n = 5), or 1 cm H2O above the lower inflection point (LIP) (PEEP>LIP; n = 6). Within each pair piglets were randomized to a low VT (5-7 mL/kg) or high VT strategy (17-19 mL/kg). After 4 hrs of mechanical ventilation, 18-fluorodeoxyglucose (18FDG) was injected and positron emission tomography scanning was performed.


RESULTS
VT and PEEP changes on influx constants of 18FDG were assessed by analysis of variance. A within-litter comparison of Vt was nonsignificant (p = .50). A between-litter comparison, ordered in linear trend rank, from ZEEP, to PEEP 8, to PEEP>LIP, showed a strong effect of PEEP on influx constant (p = .019).


CONCLUSIONS
PEEP set above the LIP on the inspiratory limb of the pressure-volume curve affords a stronger lung protection than VT strategy.
Monkman
Shelley L
SL
Department of Pediatrics, McMaster University, Hamilton, Ontario, Canada.
Andersen
Chad C
CC
Nahmias
Claude
C
Ghaffer
Hasan
H
Bourgeois
Jacqueline M
JM
Roberts
Robin S
RS
Schmidt
Barbara
B
Kirpalani
Haresh M
HM
D000818:Animals; D000831:Animals, Newborn; D001707:Biopsy, Needle; D002465:Cell Movement; D004195:Disease Models, Animal; D005260:Female; D007150:Immunohistochemistry; D008170:Lung Compliance; D008297:Male; D009504:Neutrophils / Q000502:physiology*; D011175:Positive-Pressure Respiration / Q000379:methods*; D049268:Positron-Emission Tomography; D011336:Probability; D012123:Pulmonary Ventilation; D011897:Random Allocation; D012128:Respiratory Distress Syndrome / Q000000981:diagnostic imaging / Q000473:pathology* / Q000628:therapy*; D012680:Sensitivity and Specificity; D013990:Tidal Volume