Variable ventilation enhances ventilation without exacerbating injury in preterm lambs with respiratory distress syndrome.
BACKGROUND
As compared with constant respiratory rate (RR) and tidal volume (V(T)) during controlled conventional mechanical ventilation (CV), variable ventilation (VV) using the same breath-to-breath minute volume but variable V(T) and RRs enhances ventilation efficiency in preterm lambs. We hypothesized that if V(T) was adjusted to target permissive hypercarbia, VV would result in more efficient gas exchange without increasing inflammatory and injurious responses in the lung.


METHODS
Preterm lambs at 129 d gestation were anesthetized, tracheotomized, and randomized to either CV (n = 8) or VV (n = 8) using the same initial average V(T) and RR. Lung mechanics and gas exchange were measured intermittently, and average V(T) was adjusted to target partial pressure of arterial carbon dioxide (PaCO2) of 40-50 mm Hg for 3 h. Lung injury and inflammation were assessed from bronchoalveolar lavage fluid, lung tissue, and peripheral blood.


RESULTS
VV achieved permissive hypercarbia using a lower average V(T), peak inspiratory pressure, and elastance (increased compliance) as compared with CV. Oxygenation and markers of lung tissue inflammation or injury were not different apart from a lower wet:dry tissue ratio in the VV lungs.


CONCLUSIONS
VV improves ventilation efficiency and in vivo lung compliance in the ovine preterm lung without increasing lung inflammation or lung injury.
Centre for Neonatal Research and Education, School of Women's and Infants' Health, University of Western Australia, Perth, Australia.
Clare A
CA
Berry
Béla
B
Suki
Graeme R
GR
Polglase
J Jane
JJ
Pillow
D000818:Animals; D001992:Bronchoalveolar Lavage Fluid / Q000276:immunology; D004195:Disease Models, Animal; D005865:Gestational Age; D018836:Inflammation Mediators / Q000378:metabolism; D008168:Lung / Q000276:immunology / Q000473:pathology / Q000503:physiopathology*; D008170:Lung Compliance; D011014:Pneumonia / Q000209:etiology / Q000276:immunology / Q000473:pathology / Q000503:physiopathology / Q000517:prevention & control*; D011659:Pulmonary Gas Exchange; D012123:Pulmonary Ventilation; D012121:Respiration, Artificial / Q000009:adverse effects / Q000379:methods*; D012127:Respiratory Distress Syndrome, Newborn / Q000276:immunology / Q000473:pathology / Q000503:physiopathology / Q000628:therapy*; D056152:Respiratory Rate; D012756:Sheep; D013990:Tidal Volume; D013997:Time Factors; D055397:Ventilator-Induced Lung Injury / Q000209:etiology / Q000276:immunology / Q000473:pathology / Q000503:physiopathology / Q000517:prevention & control*
D018836:Inflammation Mediators