Lung recruitment and positive end-expiratory pressure have different effects on CO2 elimination in healthy and sick lungs.
BACKGROUND
We studied the effects that the lung recruitment maneuver (RM) and positive end-expiratory pressure (PEEP) have on the elimination of CO(2) per breath (Vtco(2,br)).


METHODS
In 7 healthy and 7 lung-lavaged pigs at constant ventilation, PEEP was increased from 0 to 18 cm H(2)O and then decreased to 0 in steps of 6 cm H(2)O every 10 minutes. Cycling RMs with plateau pressure/PEEP of 40/20 (healthy) and 50/25 (lavaged) cm H(2)O were applied for 2 minutes between 18-PEEP steps. Volumetric capnography, respiratory mechanics, blood gas, and hemodynamic data were recorded.


RESULTS
In healthy lungs before the RM, Vtco(2,br) was inversely proportional to PEEP decreasing from 4.0 (3.6-4.4) mL (median and interquartile range) at 0-PEEP to 3.1 (2.8-3.4) mL at 18-PEEP (P < 0.05). After the RM, Vtco(2,br) increased from 3.3 (3-3.6) mL at 18-PEEP to 4.0 (3.5-4.5) mL at 0-PEEP (P < 0.05). In lavaged lungs before the RM, Vtco(2,br) increased initially from 2.0 (1.7-2.3) mL at 0-PEEP to 2.6 (2.2-3) mL at 12-PEEP (P < 0.05) but then decreased to 2.4 (2-2.8) mL when PEEP was increased further to 18 cm H(2)O (P < 0.05). After the RM, the highest Vtco(2,br) of 2.9 (2.1-3.7) mL was observed at 12-PEEP and then decreased to 2.5 (1.9-3.1) mL at 0-PEEP (P < 0.05). Vtco(2,br) was directly related to changes in lung perfusion, the area of gas exchange, and alveolar ventilation but inversely related to changes in dead space.


CONCLUSIONS
CO(2) elimination by the lungs was dependent on PEEP and recruitment and showed major differences between healthy and lavaged lungs.
Tusman
Gerardo
G
Department of Anesthesiology, Hospital Privado de Comunidad, Mar del Plata, Argentina. gtusman@hotmail.com
Bohm
Stephan H
SH
Suarez-Sipmann
Fernando
F
Scandurra
Adriana
A
Hedenstierna
Göran
G
D000818:Animals; D001784:Blood Gas Analysis / Q000379:methods; D018893:Bronchoalveolar Lavage / Q000379:methods; D002245:Carbon Dioxide / Q000032:analysis*; D045853:Exhalation / Q000502:physiology*; D008168:Lung / Q000502:physiology*; D008171:Lung Diseases / Q000503:physiopathology*; D008176:Lung Volume Measurements / Q000379:methods; D011175:Positive-Pressure Respiration / Q000379:methods*; D011659:Pulmonary Gas Exchange / Q000502:physiology; D011897:Random Allocation; D015656:Respiratory Mechanics / Q000502:physiology*; D013552:Swine
D002245:Carbon Dioxide