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, inspiratory:expiratory ratio 1:2, respiratory rate to maintain end-tidal CO between 5.3-6.6 kPa (40-50 mmHg). The following settings were implemented sequentially: zero PEEP (ZEEP); PEEP 10 cmHO (PEEP); LRM (50 cmHO for 20 seconds) followed by 10 cmHO of PEEP (LRM + PEEP). Static compliance (C), 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; ΔEELV during LRM + PEEP was 14.28 ± 5.59 mL kg (p < 0.0001). The RLV was greater during the LRM + PEEP phase (12.30 ± 5.85 mL kg) than during PEEP (4.47 ± 3.97 mL kg; p < 0.0001). The C was unchanged from ZEEP to PEEP (0.75 ± 0.21 and 0.85 ± 0.22 mL cmHO kg, respectively, p = 0.36) but increased using LRM + PEEP (1.11 ± 0.25 mL cmHO kg, p = 0.0004). Driving pressure was lower during LRM + PEEP than during PEEP and ZEEP (16 ± 2, 19 ± 2 and 21 ± 4 cmHO, respectively, p < 0.0001).

Conclusions And Clinical Relevance: Unlike PEEP alone, PEEP preceded by LRM increased RLV and C and reduced driving pressure in horses under anaesthesia.