Regional ventilation distribution and dead space in anaesthetized horses treated with and without continuous positive airway pressure: novel insights by electrical impedance tomography and volumetric capnography.

The research paper investigates the influence of continuous positive airway pressure (CPAP) on the distribution of ventilation and dead space in anesthetized horses, leveraging electrical impedance tomography and volumetric capnography.

Experimental Design

• The paper undertakes a randomized, experimental, crossover study involving eight healthy adult horses. Each horse was anesthetized twice with isoflurane in 50% oxygen and medetomidine under constant infused in dorsal recumbency.
• In addition, they were administered in random order either with CPAP that exerted a pressure of 8 cmH2O or without CPAP for 3-hour durations.
• The researchers performed electrical impedance tomography and volumetric capnography measurements every 30 minutes, calculating lung regions with low ventilation (referred to as dependent silent spaces or DSSs, and nondependent silent spaces or NSSs), centre of ventilation (CoV) and dead space variables, as well as venous admixture.
• The data were finally put under statistical analysis employing multivariate analysis of variance and Pearson correlation.

Key Findings

• The paper found that with the use of CPAP, the CoV shifted towards the dependent parts of the lungs. Additionally, it noted that DSSs significantly reduced in size, though no difference seen in NSSs due to the application of CPAP.
• Another important finding was that the venous admixture significantly correlated with DSS with the consideration of treatment time as a covariate.
• The paper, however, found no differences for any parameters relating to volumetric capnography (VCap).

Conclusions

• The paper hence concluded that administering CPAP of 8 cmH2O in dorsally recumbent anesthetized horses results in redistribution of ventilation towards the dependent lung regions. This consequently improves the match of ventilation and perfusion.
• Notably, this improvement was not associated with an increase in dead space, indicating that there was no distension of the airways or impairment of alveolar perfusion.