Lung mechanical behavior during one-lung ventilation

Abstract

Objective: Switching from two-lung to one-lung ventilation would be expected to have large effects on lung mechanical properties, and these effects may depend on tidal volume and respiratory frequency. These changes in lung mechanics with one-lung ventilation may be similar to pulmonary edema. Deteriorating lung mechanics during pulmonary edema have been attributed to a loss of ventilated lung units. Therefore, changes in lung mechanics caused by one-lung ventilation were measured and compared with those previously seen during pulmonary edema. Design: Prospective study. Setting: Research laboratory. Interventions: After induction of anesthesia, beagle dogs' tracheas were intubated with an endotracheal tube with a bronchial blocker (Univent System Corp, Tokyo, Japan) to apply one-lung ventilation. The proper position of the bronchial blocker during one-lung ventilation was confirmed with a fiberoptic bronchoscope. Measurements and Main Results: Lung elastance (E L) and resistance (R L) were calculated from measurements of airway pressure, esophageal pressure, and airway flow in five anesthetized, paralyzed dogs during sinusoidal forcing at a constant mean airway pressure of 10 cmH 2O in a wide range of breathing frequencies (0.2 to 1.0 Hz in intervals of 0.2) and tidal volumes (50, 100, 200, and to 300 mL). Measurements 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 dependences were not increased, and no dependence on tidal volume was observed. Conclusions: The lack of tidal volume dependence in E L and lack of large-frequency dependence in R L during one-lung ventilation are inconsistent with changes induced by severe pulmonary edema. Although decreases in ventilatable lung volume may contribute to increases in lung elastance, other characteristics of mechanical behavior during one-lung ventilation differ from those of pulmonary edema; therefore, other additional mechanisms must be involved in determining lung mechanical properties during severe pulmonary edema.