Monitoring dead space during recruitment and PEEP titration in an experimental model

To test the usefulness of dead space for determining open-lung PEEP, the lowest PEEP that prevents lung collapse after a lung recruitment maneuver.

Prospective animal study.

Department of Clinical Physiology, University of Uppsala, Sweden.

Eight lung-lavaged pigs.

Animals were ventilated using constant flow mode with VT of 6ml/kg, respiratory rate of 30bpm, inspiratory-to-expiratory ratio of 1:2, and FiO(2) of 1. Baseline measurements were performed at 6cmH(2)O of PEEP. PEEP was increased in steps of 6cmH(2)O from 6 to 24cmH(2)O. Recruitment maneuver was achieved within 2min at pressure levels of 60/30cmH(2)O for Peak/PEEP. PEEP was decreased from 24 to 6cmH(2)O in steps of 2cmH(2)O and then to 0cmH(2)O. Each PEEP step was maintained for 10min.

Alveolar dead space (VD(alv)), the ratio of alveolar dead space to alveolar tidal volume (VD(alv)/VT(alv)), and the arterial to end-tidal PCO(2) difference (Pa-ET: CO(2)) showed a good correlation with PaO(2), normally aerated areas, and non-aerated CT areas in all animals (minimum-maximum r(2)=0.83-0.99; p<0.01). Lung collapse (non-aerated tissue>5%) started at 12[Symbol: see text]cmH(2)O PEEP; hence, open-lung PEEP was established at 14cmH(2)O. The receiver operating characteristics curve demonstrated a high specificity and sensitivity of VD(alv) (0.89 and 0.90), VD(alv)/VT(alv) (0.82 and 1.00), and Pa-ET: CO(2) (0.93 and 0.95) for detecting lung collapse.

Monitoring of dead space was useful for detecting lung collapse and for establishing open-lung PEEP after a recruitment maneuver.