Intratidal compliance-volume curve as an alternative basis to adjust positive end-expiratory pressure: a study in isolated perfused rabbit lungs.
OBJECTIVE
Repeated collapse and reopening of alveoli have been shown to aggravate lung injury, which could be prevented by positive end-expiratory pressure (PEEP). Yet, how to adjust optimum PEEP is a matter of debate. We suggest a new strategy to adjust PEEP, which is based on the analysis of the intratidal compliance-volume curve. This approach was compared with a strategy based on the static pressure-volume curve. Furthermore, two other ventilator settings were investigated. One served as a negative control likely to provoke atelectasis, and the other was expected to induce overdistension.


METHODS
Prospective, randomized block design.


METHODS
Laboratory.


METHODS
Isolated, perfused, and ventilated rabbit lungs.


METHODS
Tidal volumes of 8 mL/kg of body weight were used throughout. After stabilization, the lungs were randomized to one of four protocols (lasting 120 mins; n = 6 per group). Group 1 was ventilated at zero end-expiratory pressure. In group 2, PEEP was set above the lower inflection point of the static pressure-volume curve. In group 3, adjustment of PEEP was based on the intratidal compliance-volume curve, as determined by the slice method. In group 4, increasing PEEP levels ensured a plateau airway pressure of 20-25 cm H2O likely to provoke overdistension.


RESULTS
The ventilation/perfusion (VA/Q) distribution was analyzed by the multiple inert gas elimination technique. Alveolar derecruitment was indicated by shunt and low VA/Q areas as observed in group 1. In groups 2 and 3, VA/Q data initially indicated full recruitment. In contrast to group 3, shunt increased in group 2 near completion of the experiments. Group 4 showed complete recruitment, but the VA/Q distribution included high VA/Q areas.


CONCLUSIONS
The intratidal compliance-volume curve represents a rational basis for adjusting PEEP in the isolated lung model. Because this strategy does not require invasive measures and facilitates continuous assessment of ventilator settings, it may be of clinical interest.
Department of Anesthesiology and Critical Care Medicine, University of Freiburg, Germany.
Gerd
G
Hermle
Georg
G
Mols
Annette
A
Zügel
Albert
A
Benzing
Michael
M
Lichtwarck-Aschoff
Klaus
K
Geiger
Josef
J
Guttmann
D000818:Animals; D066298:In Vitro Techniques; D008170:Lung Compliance; D008297:Male; D010477:Perfusion; D011175:Positive-Pressure Respiration / Q000379:methods*; D011817:Rabbits; D013990:Tidal Volume