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 cmH(2)O (PEEP); LRM (50 cmH(2)O for 20 seconds) followed by 10 cmH(2)O of PEEP (LRM + PEEP). Static compliance (C-st), driving pressure, delta end-expiratory (Delta EELV) 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 Delta EELV of 6.68 +/- 3.36 mL kg(-1); Delta EELV 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 C-st was unchanged from ZEEP to PEEP (0.75 +/- 0.21 and 0.85 +/- 0.22 mL cmH(2)O(-1) kg(-1), respectively, p = 0.36) but increased using LRM + PEEP (1.11 +/- 0.25 mL cmH(2)O(-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 cmH(2)O, respectively, p < 0.0001). Conclusions and clinical relevance Unlike PEEP alone, PEEP preceded by LRM increased RLV and C-st and reduced driving pressure in horses under anaesthesia.