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Effect of pressure support on end-expiratory lung volume and lung diffusion for carbon monoxide
Nathalina Pinto Da Costa1, Fabiano Di Marco, Aissam Lyazidi
1Réanimation Médicale, AP-HP, Centre Hospitalier Albert Chenevier-Henri Mondor, INSERM Unité 955, Université Paris EST, Créteil, France. nathalia.pintodacosta@rdb.aphp.fr
Objectives:
The level of pressure-support ventilation can affect mean airway pressure and potentially lung volume, but its increase is usually associated with a reduced respiratory rate, and the net effects on the gas exchange process and its components, including end-expiratory lung volume, have not been carefully studied. We measured pulmonary conductance for gas exchange based on lung diffusion for carbon monoxide in patients receiving pressure-support ventilation.
Design:
Prospective, randomized, crossover study.
Setting:
Medical intensive care unit of a university hospital.
Patients:
Sixteen patients mechanically ventilated in pressure-support ventilation mode and free from chronic obstructive pulmonary disease.
Interventions:
Two pressure-support ventilation levels (5 cm H2O difference) at the same level of positive end-expiratory pressure.
Measurements And Main Results:
End-expiratory lung volume, lung diffusion for carbon monoxide, and SpO2/Fio2 were evaluated. Increasing pressure-support ventilation by 5 cm H2O significantly increased the mean tidal volume from 6.8 to 8.5 mL/kg of predicted body weight and decreased the mean respiratory rate by 6.6 breaths per minute. Although SpO2/Fio2 did not change significantly, there was a slight but significant decrease in lung diffusion for carbon monoxide (average decay rate of 4.5%) at high pressure-support ventilation. The pressure-support ventilation level did not significantly affect end-expiratory lung volume (1737±629 mL at 9.6±2.5 cm H2O pressure-support ventilation level vs. 1749±657 mL at 14.9±2.1 cm H2O pressure-support ventilation level).
Conclusions:
A 5-cm H2O increase in pressure-support ventilation neither affected end-expiratory lung volume nor increased the pulmonary volume participating in gas exchange. A target tidal volume closer to 6 mL/kg of predicted body weight than to 8 mL/kg during pressure-support ventilation was associated with better gas exchange.
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