Lung mechanics and gas exchange during pressure-control ventilation in dogs. Augmentation of CO2 elimination by an intratracheal catheter.
Increased awareness of pressure-related injury to the alveolar-capillary interface has renewed interest in modes of ventilation that limit alveolar distention such as pressure-controlled ventilation (PCV). We examined respiratory system mechanics and gas exchange during PCV in six dogs. Our data conformed to the predictions of our single-compartment mathematical model of respiratory dynamics during PCV (J Appl Physiol 1989; 67:1081-92). For a fixed pressure (Pset) and inspiratory time fraction (Tl/Ttot) (15 cm H2O and 0.3, respectively), minute ventilation (VE) reached a well-defined plateau as frequency (f) increased from 10 to 50 breaths/min and tidal volume (VT) fell progressively. Concomitantly, the physiologic dead-space fraction (VD/VT) increased from 0.50 +/- 0.04 to 0.85 +/- 0.04, and arterial PCO2 (PaCO2) rose from 39 +/- 4 to 76 +/- 12 mm Hg. At a fixed combination of frequency, applied pressure, and Tl/Ttot (40 breaths/min, 15 cm H2O, and 0.3), VE did not change when we introduced fresh gas continuously from an intratracheal catheter. However, PaCO2 and VD/VT fell progressively as catheter flow increased from zero to 14 L/min (60 +/- 12 to 40 +/- 12 mm Hg and 0.83 +/- 0.03 to 0.25 +/- 0.14 mm Hg, respectively). We conclude that during PCV at a fixed Pset and Tl/Ttot increasing frequency caused VT to fall and VE to reach a plateau. Declining VT was associated with a rise in PaCO2 because of a subsequent fall in alveolar ventilation. Insufflating fresh gas by an intratracheal catheter increased alveolar ventilation and improved CO2 elimination by washing out the anatomic dead space.(ABSTRACT TRUNCATED AT 250 WORDS)
Nahum
A
A
University of Minnesota, Section of Pulmonary and Critical Care Medicine, St. Paul-Ramsey Medical Center, Minnesota 55101-2595.
Burke
W C
WC
Ravenscraft
S A
SA
Marcy
T W
TW
Adams
A B
AB
Crooke
P S
PS
Marini
J J
JJ
D000818:Animals; D002245:Carbon Dioxide / Q000502:physiology; D002408:Catheters, Indwelling; D004285:Dogs; D005260:Female; D007327:Insufflation; D007442:Intubation, Intratracheal; D008297:Male; D008962:Models, Theoretical; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012121:Respiration, Artificial / Q000379:methods*; D012126:Respiratory Dead Space / Q000502:physiology; D015656:Respiratory Mechanics / Q000502:physiology*
D002245:Carbon Dioxide