Influence of a recruiting maneuver on the effects of PEEP on lung function in healthy horses under general anaesthesia

The aim of this study was to evaluate the influence of a recruiting maneuver (RM) on the effects of PEEP on lung function in healthy horses under general anaesthesia. Fifteen horses were sedated with acepromazine (0.02 mg kg-1 IV) and detomidine (0.005 mg kg-1 IV), general anaesthesia was intravenously induced with midazolam (0.1 mg kg-1) and ketamine (2.2 mg kg-1) and maintained with isoflurane in 100% oxygen. After intubation all horses lungs were mechanically ventilated in a volume controlled mode: Vt (12 ml kg-1) and I:E (1:2) were unchanged during the study while RR was titrated to maintain the PE’CO2 between 40 and 45 mmHg. Three different ventilatory strategies were applied in all horses during the same anaesthetic episode: zero PEEP (ZEEP), 10 cmH2O of PEEP (PEEP) and a RM followed by the application of 10 cmH2O of PEEP (RMPEEP). The RM was performed applying 50 cmH2O for 20 seconds to the respiratory system. Thirty minutes after each ventilatory strategy was initiated, HR and MAP were recorded, an arterial blood sample was collected [PaO2, P(A-a)O2], static compliance of the respiratory system (CRSstat) and the PEEP recruited lung volume (RLV) (Grasso S et al 2005) were calculated. Data were compared with the ANOVA test (P<0.05). The PaO2 and Crsstat were higher while P(A-a)O2 lower at RMPEEP (60.7 ± 6.8 kPa, 473.5 ± 89.1 ml cmH2O-1 and 23.8 ± 7.5 kPa) compared to ZEEP (40.8 ± 16.9 kPa, 339.7 ± 81.9 ml cmH2O-1 and 44.5 ± 16.8 kPa) and PEEP (41.2 ± 17.8 mmHg, 360.9 ± 54.9 ml cmH2O-1 and 44.4 ± 17.6 mmHg). The RLV was larger at RMPEEP (5.5 ± 2.4 L) than at PEEP (2.6 ± 1.6 L). A RM significantly improved the effects of 10 cmH2O of PEEP on lung function in horses under general anaesthesia.