Utility of deadspace and capnometry measurements in determination of surfactant efficacy in surfactant-depleted lungs.
OBJECTIVE
To investigate if bronchoalveolar lavage leads to increased alveolar and physiologic deadspace or a deadspace/ tidal volume ratio and if surfactant replacement restores the lung to its prelavage condition.


METHODS
Prospective, animal cohort study.


METHODS
An animal laboratory in a university medical center.


METHODS
Seven adult rabbits receiving artificial ventilation.


METHODS
Our single-breath CO2 analysis station contained the following equipment: pneumotachometer Ventrak 1550, a mainstream capnometer Capnogard 1265, a signal processor, and computer software. Repeated bronchoalveolar lavage was performed in seven adult rabbits to simulate acute respiratory distress syndrome. Surfactant therapy was administered after bronchoalveolar lavage induced a 20% reduction in baseline arterial PO2. The calculated parameters of alveolar and physiologic deadspace and the deadspace/tidal volume ratio were derived from the single-breath CO2 plot by Ventrak 1550 in combination with the Capnogard 1265. The arterial end-tidal Pco2 difference, the alveolar-arterial PO2 difference, and the arterial/alveolar PO2 ratio were obtained by capnography and arterial blood gas analysis. Measurements of these parameters were performed before bronchoalveolar lavage, during bronchoalveolar lavage, and after surfactant application.


RESULTS
The alveolar and physiologic deadspace and the deadspace/tidal volume ratio were significantly higher in lavaged animals. After application of natural surfactant, these parameters were significantly reduced but the baseline values could not be reached. Bronchoalveolar lavage led to a significant fall in the arterial/alveolar PO2 ratio, which increased after surfactant therapy. There was a negative correlation between the arterial/alveolar PO2 ratio and the deadspace/tidal volume ratio. The alveolar and physiologic deadspace and the deadspace/tidal volume ratio correlated with the arterial end-tidal Pco2 difference. The best correlation was obtained between the arterial end-tidal Pco2 difference and the alveolar deadspace/tidal volume ratio (r = 0.98).


CONCLUSIONS
Bronchoalveolar lavage elevates the alveolar and physiologic deadspace and the deadspace/tidal volume ratios and is combined with a fall in the arterial/alveolar PO2 ratio. Surfactant treatment improves the gas exchange but does not restore the lung to its prebronchoalveolar lavage condition, which indicates that the exogenous surfactant affects only partly the recruitment of the atelectatic areas.
Wenzel
U
U
Department of Neonatology, Charité-Hospital, Humboldt University, Berlin, Germany.
Rüdiger
M
M
Wagner
M H
MH
Wauer
R R
RR
D000818:Animals; D001992:Bronchoalveolar Lavage Fluid; D019296:Capnography / Q000379:methods*; D004195:Disease Models, Animal; D016903:Drug Monitoring / Q000379:methods*; D016014:Linear Models; D011446:Prospective Studies; D011659:Pulmonary Gas Exchange / Q000187:drug effects; D011663:Pulmonary Surfactants / Q000172:deficiency* / Q000627:therapeutic use*; D011817:Rabbits; D015203:Reproducibility of Results; D012126:Respiratory Dead Space; D012815:Signal Processing, Computer-Assisted; D013990:Tidal Volume
D011663:Pulmonary Surfactants