Effects of different levels of pressure support variability in experimental lung injury.
BACKGROUND
Noisy pressure support ventilation has been reported to improve respiratory function compared to conventional assisted mechanical ventilation. We aimed at determining the optimal level of pressure support variability during noisy pressure support ventilation.


METHODS
Twelve pigs were anesthetized and mechanically ventilated. Acute lung injury was induced by surfactant depletion. At four levels of pressure support variability (coefficients of variation of pressure support equal to 7.5, 15, 30, and 45%, 30 min each, crossover design, special Latin squares sequence), we measured respiratory variables, gas exchange, hemodynamics, inspiratory effort, and comfort of breathing. The mean level of tidal volume was constant among variability levels.


RESULTS
Compared to conventional pressure support ventilation, different levels of variability in pressure support improved the elastance of the respiratory system, peak airway pressure, oxygenation, and intrapulmonary shunt. Oxygenation and venous admixture benefited more from intermediate (30%) levels of variability, whereas elastance and peak airway pressure improved linearly with increasing variability. Heart rate as well as mean arterial and pulmonary arterial pressures decreased slightly at intermediate to high (30-45%) levels of variability in pressure support. Inspiratory effort and comfort of breathing were not importantly influenced by increased variability in pressure support.


CONCLUSIONS
In a surfactant depletion model of acute lung injury, variability of pressure support improves lung function. The variability level of 30% seems to represent a reasonable compromise to improve lung functional variables during noisy pressure support ventilation.
Spieth
Peter M
PM
Department of Anesthesiology and Intensive Care Therapy, University Hospital Carl Gustav Carus, Technical University of Dresden, Dresden, Germany.
Carvalho
Alysson R
AR
Güldner
Andreas
A
Pelosi
Paolo
P
Kirichuk
Oleg
O
Koch
Thea
T
de Abreu
Marcelo Gama
MG
D000399:Air Pressure; D000818:Animals; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000502:physiology; D018592:Cross-Over Studies; D004548:Elasticity; D005260:Female; D006339:Heart Rate / Q000502:physiology; D008171:Lung Diseases / Q000139:chemically induced / Q000628:therapy*; D010366:Peak Expiratory Flow Rate / Q000502:physiology; D011175:Positive-Pressure Respiration; D011651:Pulmonary Artery / Q000502:physiology; D011663:Pulmonary Surfactants; D012121:Respiration, Artificial / Q000379:methods* / Q000706:statistics & numerical data; D012129:Respiratory Function Tests; D015656:Respiratory Mechanics / Q000502:physiology; D013552:Swine; D007507:Therapeutic Irrigation; D013990:Tidal Volume / Q000502:physiology
D011663:Pulmonary Surfactants