Biologically variable ventilation improves gas exchange and respiratory mechanics in a model of severe bronchospasm.
OBJECTIVE
Mechanical ventilation can be lifesaving for status asthmaticus, but how best to accomplish mechanical ventilation is unclear. Biologically variable ventilation (mechanical ventilation that emulates healthy variation) and conventional control mode ventilation (monotonously regular) were compared in an animal model of bronchospasm to determine which approach yields better gas exchange and respiratory mechanics.


METHODS
A randomized prospective trial of biologically variable ventilation vs. control mode ventilation in swine.


METHODS
University research laboratory.


METHODS
Eighteen farm-raised pigs.


METHODS
Methacholine was administered as a nebulized aerosol to initiate bronchospasm, defined as doubling of peak inspiratory pressure and respiratory system resistance, and then randomized (n = 9 each group) to either continue control mode ventilation or switch to biologically variable ventilation at the same minute ventilation. Over the next 4 hrs, hemodynamics, blood gases, respiratory mechanics, and carbon dioxide expirograms were recorded hourly. At end-experiment, tracheobronchial lavage was undertaken to determine interleukin-6 and -10 concentrations.


RESULTS
Measurements of physiologic variables and inflammatory cytokines showed that biologically variable ventilation significantly improved gas exchange, with greater arterial oxygen tensions (p = .006; group x time interaction), lower arterial carbon dioxide tensions (p = .0003; group effect), lower peak inspiratory pressures (p = .0001; group x time), greater static compliance (p = .0001; group x time), greater dynamic compliance (p = .0001; group x time), and lower total respiratory system resistance (p = .028; group x time), compared with conventional ventilation. The appearance of inflammatory cytokines in bronchoalveolar lavage fluid (interleukin-6 and -10) was not affected by mode of ventilation.


CONCLUSIONS
In this experimental model, biologically variable ventilation was superior to control mode ventilation in terms of gas exchange and respiratory mechanics during severe bronchospasm.
Mutch
W Alan C
WA
Department of Anesthesia, University of Manitoba. amutch@cc.umanitoba.ca
Buchman
Timothy G
TG
Girling
Linda G
LG
Walker
Elizabeth K-Y
EK
McManus
Bruce M
BM
Graham
M Ruth
MR
D000818:Animals; D001986:Bronchial Spasm / Q000628:therapy*; D016207:Cytokines / Q000378:metabolism; D016018:Least-Squares Analysis; D016210:Methacholine Chloride; D011659:Pulmonary Gas Exchange; D011897:Random Allocation; D012121:Respiration, Artificial / Q000379:methods*; D015656:Respiratory Mechanics; D013224:Status Asthmaticus / Q000628:therapy*; D013552:Swine
D016207:Cytokines; D016210:Methacholine Chloride