Differential artificial ventilation in anesthetized horses positioned in lateral recumbency.

This research involved a comparison of the effects of differential and conventional ventilation on gas exchange in laterally recumbent horses under Isoflurane anesthesia. The study utilized a specialized tracheal intubation technique and investigated the effects of differing tidal volume distribution patterns and levels of positive end-expiratory pressure (PEEP).

Methodology

• Seven horses under Isoflurane anesthesia and placed in lateral recumbency were selected for the study.
• A tracheal tube-in-tube intubation technique was employed to let each lung connect separately to an anesthetic circle system using a ventilator.
• Two different tidal volume distribution patterns were investigated: one where half of the tidal volume was distributed to each lung and another where two-thirds of the tidal volume was sent to the dependent lung.
• The researchers checked the effects of combining these patterns with positive end-expiratory pressure (PEEP) of 10 and 20 cm of H2O for the dependent lung.

Findings

• Differential ventilation sustained the amount of carbon dioxide in the blood (PaCO2), but significantly boosted the concentration of oxygen in the blood (PaO2) from 180 to 270 mm of Hg (+44%), and shunt perfusion was decreased from 22% to 19% (-15%). These changes occurred regardless of the tidal volume distribution pattern.
• The average airway pressure observed during differential ventilation was less than that measured during conventional ventilation.
• The combination of differential ventilation with the selective application of PEEP resulted in decreased PaCO2 and a further increase in PaO2. Shunt also decreased, showcasing similar changes across both distribution patterns.
• The effects of applying a PEEP of 20 cm of H2O were greater than when a PEEP of 10 cm of H2O was used.
• With combined differential ventilation and selective PEEP, PaO2 rose to 399 mm of Hg, and shunt went down to 15%, representing an increase of 112% and decrease of 33% respectively, compared with the results from conventional ventilation.
• The maximum increase observed in mean airway pressure was 23 cm of H2O, which was 11 cm of H2O more than the value recorded during conventional ventilation.

Implications

The study indicates that differential ventilation can potentially improve gas exchange in horses under anesthesia and laid on their side, through increasing oxygen levels and reducing shunt perfusion. These findings provide essential insights into the benefits of differential ventilation over conventional methods and may likely lead to better respiratory management practices in veterinary anesthesia. The use of PEEP also appeared beneficial, especially at higher levels, which warrants further investigations.