Background. Pressure-controlled ventilation (PCV) has been suggested to reduce peak
airway pressure (Ppeak) and intrapulmonary shunt during one-lung ventilation (OLV) when
compared with volume-controlled ventilation (VCV). At the same tidal volume (VT), the
apparent difference in Ppeak is mainly related to the presence of a double-lumen tracheal
tube. We tested the hypothesis that the decrease in Ppeak observed in the breathing
circuit is not necessarily associated with a decrease in the bronchus of the dependent lung.
Methods. This observational study included 15 consecutive subjects who were ventilated
with VCV followed by PCV at constant VT. Airway pressure was measured simultaneously in
the breathing circuit and main bronchus of the dependent lung after 20 min of ventilation.
Results. PCV induced a significant decrease in Ppeak [mean (SD)] measured in the breathing
circuit [36 (4) to 26 (3) cm H20, P,0.0001] and in the bronchus [23 (4) to 22 (3) cm H2O,
P¼0.01]. However, the interaction (ventilatory mode × site of measurement) revealed that
the decrease in Ppeak was significantly higher in the circuit (P,0.0001). Although the mean
percentage decrease in Ppeak was significant at both sites, the decrease was significantly
lower in the bronchus [5 (6)% vs 29 (3)%, P,0.0001].
Conclusions. During PCV for OLV, the decrease in Ppeak is observed mainly in the respiratory
circuit and is probably not clinically relevant in the bronchus of the dependent lung. This
challenges the common clinical perception that PCV offers an advantage over VCV during
OLV by reducing bronchial Ppeak.

Tidal volumes have tremendously decreased over the last decades
from <15 ml kg
1 to w6 mlkg
1 actual body weight. Guidelines, widely agreed and used, exist for patients with acute lung injury or acute respiratory distress syndrome (ARDS). However, it is questionable if data created in patients with acute lung injury or ARDS from ventilation on intensive care units can be transferred to healthy patients undergoing surgery. Consensus criteria regarding this topic are still missing because only a few randomised controlled trials have been performed to date, focussing on the use of the best intra-operative tidal volume. The same problem has been observed regarding the application of positive end-expiratory pressure (PEEP) and intra-operative lung recruitment. This article provides an overviewof the current literature addressing the size of tidal volume, the use of PEEP and the application of the open-lung concept in patients without acute lung injury or ARDS. Pathophysiological aspects of mechanical ventilation are elucidated.