Ventilation distribution assessed with electrical impedance tomography and the influence of tidal volume, recruitment and positive end-expiratory pressure in isoflurane-anesthetized dogs

Objective To examine the intrapulmonary gas distribution of low and high tidal volumes (V-T) and to investigate whether this is altered by an alveolar recruitment maneuver (ARM) and 5 cmH(2)O positive end-expiratory pressure (PEEP) during anesthesia. Study design Prospective randomized clinical study. Animals Fourteen client-owned bitches weighing 26 +/- 7 kg undergoing elective ovariohysterectomy. Methods Isoflurane-anesthetized dogs in dorsal recumbency were ventilated with 0 cmH(2)O PEEP and pressure-controlled ventilation by adjusting the peak inspiratory pressure (PIP) to achieve a low (7 mL kg(-1); n = 7) or a high (12 mL kg(-1); n = 7) V-T. Ninety minutes after induction (T90), an ARM (PIP 20 cmH(2)O for 10 seconds, twice with a 10 second interval) was performed followed by the application of 5 cmH(2)O PEEP for 35 minutes (RM35). The vertical (ventral = 0%; dorsal = 100%) and horizontal (right = 0%; left = 100%) center of ventilation (CoV), four regions of interest (ROI) (ventral, central-ventral, central-dorsal, dorsal) identified in electrical impedance tomography images, and cardiopulmonary data were analyzed using two-way repeated measures ANOVA. Results The low V-T was centered in more ventral (nondependent) areas compared with high V-T at T90 (CoV: 38.8 +/- 2.5% versus 44.6 +/- 7.2%; p = 0.0325). The ARM and PEEP shifted the CoV towards dorsal (dependent) areas only during high V-T (50.5 +/- 7.9% versus 41.1 +/- 2.8% during low V-T, p = 0.0108), which was more distributed to the central-dorsal ROI compared with low V-T (p = 0.0046). The horizontal CoV was centrally distributed and cardiovascular variables remained unchanged throughout regardless of the V-T, ARM, and PEEP. Conclusions and clinical relevance Both low and high V-T were poorly distributed to dorsal dependent regions, where ventilation was improved following the current ARM and PEEP only during high V-T. Studies on the role of high V-T on pulmonary complications are required.