Effects of positive end-expiratory pressure alone or an open-lung approach on recruited lung volumes and respiratory mechanics of mechanically ventilated horses

Objective: To evaluate the effects of positive end-expiratory pressure (PEEP) alone and PEEP preceded by lung recruitment manoeuvre (LRM) on lung volumes and respiratory system mechanics in healthy horses undergoing general anaesthesia. Study design: Controlled, prospective clinical study. Animals: A group of 15 horses undergoing arthroscopy. Methods: Following anaesthetic induction, initial ventilatory settings were: tidal volume 15 mL kg–1, inspiratory:expiratory ratio 1:2, respiratory rate to maintain end-tidal CO2 between 5.3–6.6 kPa (40–50 mmHg). The following settings were implemented sequentially: zero PEEP (ZEEP); PEEP 10 cmH2O (PEEP); LRM (50 cmH2O for 20 seconds) followed by 10 cmH2O of PEEP (LRM + PEEP). Static compliance (Cst), driving pressure, delta end-expiratory (ΔEELV) and recruited lung volumes (RLV) were obtained 30 minutes after initiating each ventilatory strategy. Data were analyzed with paired t test or analysis of variance followed by Tukey's post hoc test. Data are shown as mean ± standard deviation; p < 0.05 was considered significant. Results: PEEP induced ΔEELV of 6.68 ± 3.36 mL kg–1; ΔEELV during LRM + PEEP was 14.28 ± 5.59 mL kg–1 (p < 0.0001). The RLV was greater during the LRM + PEEP phase (12.30 ± 5.85 mL kg–1) than during PEEP (4.47 ± 3.97 mL kg–1; p < 0.0001). The Cst was unchanged from ZEEP to PEEP (0.75 ± 0.21 and 0.85 ± 0.22 mL cmH2O−1 kg–1, respectively, p = 0.36) but increased using LRM + PEEP (1.11 ± 0.25 mL cmH2O−1 kg–1, p = 0.0004). Driving pressure was lower during LRM + PEEP than during PEEP and ZEEP (16 ± 2, 19 ± 2 and 21 ± 4 cmH2O, respectively, p < 0.0001). Conclusions and clinical relevance: Unlike PEEP alone, PEEP preceded by LRM increased RLV and Cst and reduced driving pressure in horses under anaesthesia. © 2019 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia