Monitoring changes in distribution of pulmonary ventilation by functional electrical impedance tomography in anaesthetized ponies.

This research examines changes in the distribution of lung ventilation in anaesthetized ponies using electrical impedance tomography. The study found that uneven ventilation occurs within 30 minutes in ponies laying on their right sides under general anesthesia and remains largely unchanged over the next hour.

Introduction

• The research aimed to assess the variations in the distribution of pulmonary ventilation in anesthetized ponies using a non-invasive imaging technique called Electrical Impedance Tomography (EIT).
• Eight adult pony geldings were involved in this prospective experimental study. All ponies were put under general anesthesia using isoflurane in oxygen and volume-controlled ventilation was maintained.

Methods

• Measurements of the regional distribution of ventilation and the dimensions of the chest in two directions were taken at 30, 60, and 90 minutes post-intubation.
• The resulting images were divided into four regions of interest (ROIs) to determine the ratio of the ventilation distribution between dependent (lower) and non-dependent (upper) lobes of the lung, and changes in distribution within the lungs in the latero-lateral direction.
• The centre of ventilation (COV) and the ratio of the chest’s lateral and dorso-ventral dimensions were also calculated.

Statistical Analysis

• The influence of time on the dependent to non-dependent ratio, COV, and ROIs was analyzed using the ANOVA test followed by post hoc Bonferroni tests. Pearson correlation coefficient and the coefficient of determination were calculated to evaluate the relationship between the W/H ratio and D/ND ratio, and COV.
• Values were considered statistically significant at p < 0.05.

Results

• The results showed that the median dependent to non-dependent ratio and the COV, assessed at three different time points (T30-90), confirmed the expected uneven distribution of ventilation in the anesthetized ponies positioned on their right side.
• There was a moderate negative correlation between the chest width to height ratio and the dependent to non-dependent ratio, indicating that as the chest becomes flatter, the distribution of ventilation becomes more uneven. In contrast, there was no significant correlation between the COV and the W/H ratio.

Conclusion

• The study concluded that uneven ventilation in mechanically ventilated, right laterally recumbent anesthetized ponies occurs within 30 minutes and changes minimally over the following 60 minutes. This data suggests that the body position of the anesthetized pony has significant effects on the ventilation distribution in its lungs.