Endomicroscopic analysis of time- and pressure-dependent area of subpleural alveoli in mechanically ventilated rats

- We observed alveoli during recruitment maneuvers and different pressure phases.
- We used a transthoracal endoscopic imaging technique.
- Alveolar size changed only slightly during pressure phases.
- Compliance increased after recruitment maneuvers.
- Volume insufflated by recruitment maneuver is distributed to deeper lung regions.

We investigated the effects of recruitment maneuvers on subpleural alveolar area in healthy rats. 36 mechanically ventilated rats were allocated to either ZEEP-group or PEEP - 5 cmH2O - group. The subpleural alveoli were observed using a transthoracal endoscopic imaging technique. Two consecutive low-flow maneuvers up to 30 cmH2O peak pressure each were performed, interrupted by 5 s plateau phases at four different pressure levels. Alveolar area change at maneuver peak pressures and during the plateau phases was calculated and respiratory system compliance before and after the maneuvers was analyzed. In both groups alveolar area at the second peak of the maneuver did not differ significantly compared to the first peak. During the plateau phases there was a slight increase in alveolar area. After the maneuvers, compliance increased by 30% in ZEEP group and 20% in PEEP group. We conclude that the volume insufflated by the low-flow recruitment maneuver is distributed to deeper but not to subpleural lung regions.