Pattern of inspiratory gas delivery affects CO2 elimination in health and after acute lung injury.
OBJECTIVE
To avoid ventilator induced lung injury, tidal volume should be low in acute lung injury (ALI). Reducing dead space may be useful, for example by using a pattern of inspiration that prolongs the time available for gas distribution and diffusion within the respiratory zone, the mean distribution time (MDT). A study was conducted to investigate how MDT affects CO2 elimination in pigs at health and after ALI.


METHODS
Randomised crossover study in the animal laboratory of Lund University Biomedical Center.


METHODS
Healthy pigs and pigs with ALI, caused by surfactant perturbation and lung-damaging ventilation were ventilated with a computer-controlled ventilator. With this device each breath could be tailored with respect to insufflation time and pause time (TI and TP) as well as flow shape (square, increasing or decreasing flow).


RESULTS
The single-breath test for CO2 allowed analysis of the volume of expired CO2 and the volume of CO2 re-inspired from Y-piece and tubes. With a long MDT caused by long TI or TP, the expired volume of CO2 increased markedly in accordance with the MDT concept in both healthy and ALI pigs. High initial inspiratory flow caused by a short TI or decreasing flow increased the re-inspired volume of CO2. Arterial CO2 increased during a longer period of short MDT and decreased again when MDT was prolonged.


CONCLUSIONS
CO2 elimination can be enhanced by a pattern of ventilation that prolongs MDT. Positive effects of prolonged MDT caused by short TI and decreasing flow were attenuated by high initial inspiratory flow.
Aström
Elisabet
E
University Hospital, Department of Clinical Physiology, SE-221 85, Lund, Sweden. elisabet.astrom@med.lu.se
Uttman
Leif
L
Niklason
Lisbet
L
Aboab
Jerome
J
Brochard
Laurent
L
Jonson
Björn
B
D000818:Animals; D002245:Carbon Dioxide / Q000378:metabolism*; D018592:Cross-Over Studies; D001239:Inhalation; D011659:Pulmonary Gas Exchange; D011897:Random Allocation; D012044:Regression Analysis; D012126:Respiratory Dead Space; D012128:Respiratory Distress Syndrome / Q000378:metabolism*; D015656:Respiratory Mechanics; D013552:Swine; D013990:Tidal Volume
D002245:Carbon Dioxide