Influence of tidal volume and positive end-expiratory pressure on inspiratory gas distribution and gas exchange during mechanical ventilation in horses positioned in lateral recumbency.

The research article investigates the effect of different ventilation techniques on the distribution and gas exchange of air in an anaesthetised horse lying on its side. The study reveals that using Positive End-Expiratory Pressure (PEEP) during Intermittent Positive-Pressure Ventilation (IPPV) can significantly improve the distribution of inspired gas and oxygen levels.

Research Methodology

• The experiment was conducted on six healthy adult horses.
• The horses were put under anesthesia using a combination of thiopental sodium, guiafenesin and chloral hydrate.
• For functional separation of the lungs, a tube-in-tube intubation technique was used by the scientists.
• The researchers used an anesthetic circle system and a ventilator for IPPV of the horses’ lungs.
• They collected data at different points during spontaneous respiration and IPPV, increasing tidal volumes with and without PEEP of 10 and 20 cm of H2O.

Research Results

• The researchers observed that the uneven distribution of inspired gas between lungs during spontaneous respiration did not change by IPPV and larger tidal volumes.
• The use of PEEP lead to a significant and reversible shift of inspired gas to the dependent lung and increased functional residual capacity of the nondependent lung, contributing to an increase in PaO2.
• When used together, PEEP and large tidal volume during IPPV resulted in a further increase in the distribution of inhaled gas to the dependent lung, an increase of PaO2 and alveolar dead space in both lungs.

Conclusions

• The use of PEEP during IPPV alters the distribution of inhaled gas.
• The increase in PaO2 is owed to improved ventilation-perfusion, especially in the dependent lung.
• The previously collapsed lung units might have reopened and re-engaged in gas exchange due to the redistribution of the inhaled gas.
• However, the most significant effects of IPPV and PEEP were connected to high airway pressures which are likely to negate the beneficial effects of the increase of PaO2 on total oxygen availability due to probable negative effects on cardiac output.