Evaluation of lung ventilation distribution using electrical impedance tomography in standing sedated horses with capnoperitoneum

Objective To determine changes in distribution of lung ventilation with increasing intra-abdominal pressure (IAP) from carbon dioxide (CO2) insufflation in standing sedated horses. Study design Prospective experimental study. Animals A group of six healthy adult horses. Methods Each horse was sedated with acepromazine, detomidine and butorphanol and sedation maintained with a detomidine infusion. The horse was restrained in a stocks system and a 32 electrode electrical impedance tomography (EIT) belt was wrapped around the thorax at the fifth-sixth intercostal space. EIT images and arterial blood samples for PaO2 and PaCO2, pH and lactate concentration were obtained during capnoperitoneum at 0 (baseline A), 5, 8 and 12 mmHg as IAP increased and at 8, 5, 0 (baseline B) mmHg as IAP decreased. At each IAP, after a 2 minute stabilization period, EIT images were recorded for >= 2 minutes to obtain five consecutive breaths. Statistical analysis was performed using ANOVA for repeated measures with Geisser-Greenhouse correction and a Tukey's multiple comparison test for parametric data. The relationship between PaO2 and the center of ventilation in the ventral-dorsal (CoV-VD) and right-left (CoV-RL) directions or total impedance change as a surrogate for tidal volume (delta ZV(T)) were tested using linear regression analysis. Significance was assumed when p <= 0.05. Results There were no significant changes in CoV-VD, CoV-RL, PaO2, PaCO2, lactate concentration, pH, heart rate and respiratory rate with targeted IAP. There was a significant decrease in delta ZV(T) compared with baseline A at 5 mmHg IAP as IAP was increased. Conclusions and clinical relevance Capnoperitoneum causes a significant decrease in delta ZV(T) in standing sedated horses with increasing IAP.