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

This study investigates the changes in lung ventilation distribution in standing, sedated horses when subjected to increasing intra-abdominal pressure due to carbon dioxide insufflation. The primary finding was that this condition (capnoperitoneum) caused a significant decrease in the total impedance change (a proxy for tidal volume), but did not significantly impact many other measures including heart and respiratory rate.

Research Methodology

• The study involved six healthy adult horses which were sedated using acepromazine, detomidine, and butorphanol. Detomidine infusion was used to maintain sedation.
• The horses were restrained in a stocks system and an electrical impedance tomography (EIT) belt was wrapped around the thorax at the fifth-sixth intercostal space. EIT is an imaging technique that provides real time, dynamic images of the lung ventilation.
• Different parameters were monitored and recorded as the intra-abdominal pressure (IAP) increased due to intentional insufflation of carbon dioxide (capnoperitoneum). These parameters included EIT images, arterial blood samples, oxygen pressure (PaO), carbon-dioxide pressure (PaCO), pH, and lactate concentration.
• The IAP increased from 0 (the baseline) to 5, 8, and 12 mmHg; and later decreased back to 0. At each IAP, after a two-minute stabilization period, five consecutive breaths were recorded to capture changes in lung ventilation.

Statistical Analysis and Results

• ANOVA for repeated measures with Geisser-Greenhouse correction and Tukey’s multiple comparison test was used for parametric data.
• Linear regression analysis was performed to test the relationship between PaO and the center of ventilation in the ventral-dorsal and right-left directions, and tidal volume.
• Significance was assumed when the p-value was less than or equal to 0.05.
• The results showed no significant changes in the distribution of lung ventilation, PaO, PaCO, lactate concentration, pH, heart rate, and respiratory rate with the increase in targeted IAP.
• However, there was a significant decrease in the overall change in impedance (proxy for tidal volume) compared to baseline at 5 mmHg IAP as the IAP was increased.

Conclusion

• The study concludes that capnoperitoneum, or the intentional insufflation of the abdominal cavity with carbon dioxide, causes a significant decrease in tidal volume in standing, sedated horses as IAP increases. However, it does not significantly impact many other measures such as heart rate, respiratory rate, and pH among others.