Recruitment, overdistension and barotrauma pressures in healthy rabbit lungs

Background and Goal of Study: One of the main concerns of recruitment maneuvers (RM) in pediatric patients is the risk of barotrauma, especially in neonates and small children. The safe range of recruitment pressures needed to fully recruit the lung especially not resulting in barotrauma has not been explored yet in healthy small lungs. Materials and Methods: Fourteen female New Zealand rabbits (weight 2.8 ± 0.1 kg) were studied. Rabbits were euthanized, a median sternotomy was preformed and both pleural spaces were exposed. Animals were randomly allocated in two groups and submitted to two experimental phases: Phase 1: PEEP incremental steps of 5 cmH2O from ZEEP to a PEEP of 20 cmH2O (group PEEP-20) or a PEEP of 50 cmH2O (group PEEP-50) maintaining a fixed driving pressure of 15 cmH2O. Phase 2: once maximal PEEPs were reached, driving pressure was further increased in steps of 5 cmH2O until gross macroscopic barotrauma occurred. During pressure increments three distinctive macroscopic visual conditions were defined: anatomic open lung, overdistension and barotrauma. PEEP, MIP, mean airway pressure (Paw) and driving pressure at which these conditions occurred were recorded and compared between the two groups. Safety range of pressures, defined as the difference between barotrauma MIP and overdistended MIP, was also determined. Results and Discussion: Both groups showed similar anatomic open lung MIP (PEEP-20: 21.7 ± 2.6 cmH2O; PEEP-50: 21.4 ± 2.4 cmH2O, p>0.05) and overdistended MIP (PEEP-20: 33.3±2.6 cmH2O; PEEP-50: 33.6 ± 2.4 cmH2O, p> 0.05). However, barotrauma MIP in PEEP-50 was higher (65.7 ± 3.4 cm- H2O) than in PEEP-20 group (56.7 ± 5.2 cmH2O) (p=0.003) and driving pressure when barotrauma occurred was also different between the two groups (PEEP-20: 37.5 ± 6.1 cmH2O; PEEP-50: 16.4 ± 2.4 cmH2O; p=0.000). Safety range of pressure was 23.3 ± 6.1 cmH2O and 32.1 ± 3.9 cmH2O in PEEP- 20 and PEEP-50 groups, respectively (p=0.009). In this study, barotrauma seems to be non-related to PEEP or Paw, since lungs at higher PEEP and Paw had higher barotrauma MIP (group PEEP-50). The relevant factors that determine direct barotrauma were MIP and driving pressure. Conclusion(s): There is a wide safety range of pressures with both pressure controlled RMs in healthy small lungs. However, an increased safety margin may be obtained when a higher PEEP is employed during RM, by maintaining a low and constant driving pressure during the all RM.