Optimization of lung ventilation and perfusion in anesthetized horses using a ventilation mode with flow-limited expiration.

The research was about improving the oxygen level in the blood of anesthetized horses by using a ventilation method called Flow-Limited Expiration (FLEX). The study found that FLEX helps in balancing ventilation-perfusion ratio, which probably functions by extending the expired aeration and reducing airway closure.

Study Methodology

In the study, the researchers used five healthy adult horses. The horses went through a process of volume-controlled ventilation for 60 minutes (VCV1), then 60 minutes of FLEX, and 30 minutes of VCV(VCV2). The main things observed were the ratio of arterial partial pressure of oxygen to Fio2 (PF) and the functional indices derived from electrical impedance tomography (EIT) at the end of each phase.

• The EIT data was utilized to make regional maps that showed relative lung ventilation and perfusion, and their ratios (V/Q ratios).
• The ventilation indices measured from the EIT included the fraction of expired volume in 1 second (FEV1; %) and the duration it took for the EIT signal to drop to 50% of the peak signal at the end-inspiration (TClose50; seconds).

Data collected was analyzed using 2-way ANOVA for repeated measures and a P-value of less than .05 was considered significant.

Study Findings

The PF ratio increased significantly when using FLEX as compared to both VCV1 and VCV2 (P < .01). However, there were no differences spotted in the relative distribution of ventilation or perfusion between the ventilation strategies.

• Upon superimposing ventilation and perfusion to construct V/Q ratio maps, it was found that FLEX worked to equalize the values toward 1.0.
• The FEV1 (fraction of expired volume in 1 second) was found to be shorter (P < .01) and the TClose50 (time it took for the EIT signal to drop to 50% of the peak signal at the end-inspiration) was found to be longer (P < .001) in all regions during FLEX compared to both VCV1 and VCV2.

Conclusion

The study concluded that FLEX ventilation in anesthetized horses enhances the regional ventilation-perfusion (V/Q) matching. They suggest it does this by prolonging the expiratory aeration period and reducing airway closure. This helps improve the arterial oxygenation which is crucial for anesthetized horses.