Positive end-expiratory pressure in anaesthetized spontaneously breathing horses.

This study suggests that applying indiscriminate end-expiratory pressure during equine anaesthesia may not have a significant effect on oxygenation but can cause an increase in carbon dioxide levels and in some cases reduce cardiac output.

Research Context

• This study observes horses which are breathing spontaneously under halothane anaesthesia.
• Halothane is a type of inhalation anaesthetic that is often used for general anaesthesia in veterinary procedures.
• The study investigates the effects of imposing a resistance to their breathing during expiration (the release of air from the lungs).
• This intervention is known as end-expiratory pressure.

Methodology and Observations

• The researchers introduced a water-trap into the expiratory limb of a circle absorber to create resistances of 10 and 20 cm H2O.
• They measured the arterial oxygen partial pressure (PaO2), finding no significant increase during halothane/air and halothane/oxygen anaesthesia
• They observed an increase in the partial pressure of carbon dioxide in arterial blood (PaCO2) and a significant increase in mixed venous PCO2, which measures carbon dioxide content in the venous blood.
• Among three animals subjected to 20 cm H2O resistance under halothane/air anaesthesia, the cardiac output was reduced.

Conclusions

• The researchers concluded that the application of end-expiratory pressure does not have a significant effect on increasing oxygen levels (PaO2) during anaesthesia.
• However, significant increases in carbon dioxide (PaCO2 and mixed venous PCO2) were observed.
• In some cases, this indiscriminate application of end-expiratory pressure also led to a reduction in the cardiac output (amount of blood the heart pumps through the circulatory system).
• Based on these findings, the study suggests that indiscriminate application of end-expiratory pressure may not have a usual place in routine equine anaesthesia.