LUNG MECHANICAL-BEHAVIOR DURING ONE-LUNG VENTILATION

Objective: Switching from two-lung to one-lung ventilation would be ex pected to have large effects on lung mechanical properties, and these effects may depend on tidal volume and respiratory frequency. These ch anges in lung mechanics with one-lung ventilation may be similar to pu lmonary edema. Deteriorating lung mechanics during pulmonary edema hav e been attributed to a loss of ventilated lung units, Therefore, chang es in lung mechanics caused by one-lung ventilation were measured and compared with those previously seen during pulmonary edema. Design: Pr ospective study. Setting: Research laboratory. Interventions: After in duction of anesthesia, beagle dogs' tracheas were intubated with an en dotracheal tube with a bronchial blocker (Univent System Corp, Tokyo, Japan) to apply one-lung ventilation. The proper position of the bronc hial blocker during one-lung ventilation was confirmed with a fiberopt ic bronchoscope. Measurements and Main Results: Lung elastance (E-L) a nd resistance (R-L) were calculated from measurements of airway pressu re, esophageal pressure, and airway flow in five anesthetized, paralyz ed dogs during sinusoidal forcing at a constant mean airway pressure o f 10 cmH(2)O in a wide range of breathing frequencies (0.2 to 1.0 Hz i n intervals of 0.2) and tidal volumes (50, 100, 200, and to 300 mL). M easurements were made before and after the left mainstem bronchus was occluded with the bronchial blocker. During ventilation of both lungs, E-L and R-L depended relatively little on frequency, and both E-L and R-L were independent of tidal volume. During one-lung ventilation, E- L doubled and, at most frequencies, R-L increased; frequency dependenc es were not increased, and no dependence on tidal volume was observed. Conclusions: The lack of tidal volume dependence in E-L and lack of l arge-frequency dependence in R-L during one-lung ventilation are incon sistent with changes induced by severe pulmonary edema, Although decre ases in ventilatable lung volume may contribute to increases in lung e lastance, other characteristics of mechanical behavior during one-lung ventilation differ from those of pulmonary edema; therefore, other ad ditional mechanisms must be involved in determining lung mechanical pr operties during severe pulmonary edema. Copyright (C) 1997 by W.B. Sau nders Company.