Cardiopulmonary effects of positive end-expiratory pressure in anesthetized horses.

The research paper examines the impact of various levels of positive end-expiratory pressure (PEEP) on the cardiopulmonary functions of anesthetized horses during spontaneous breathing.

Methodology

• The researchers worked with anesthetized horses that were spontaneously breathing. They employed a 4 by 4 Latin-square design for the experimental framework, which allowed for comprehensive data analysis given the limited sample size.
• They studied the cardiopulmonary effects at four levels of PEEP: 0, 5, 10, and 15 cm of H2O. These specific levels were chosen to gauge the range of physiological responses at varying pressures.

Findings

• The study revealed that several major cardiopulmonary parameters like cardiac output, alveolar-arterial oxygen tension difference, alveolar ventilation, the dead space/tidal volume ratio, and carbon dioxide elimination were not significantly impacted by the various levels of PEEP.
• However, as the PEEP increased, it was noted that alveolar and arterial oxygen tensions, respiratory exchange ratio, and pH decreased. This suggests that higher positive pressures at the end of the expiratory phase could negatively affect oxygen transport and acid-base balance in horses.
• The study additionally indicated an increase in arterial carbon dioxide tension and oxygen consumption with higher PEEP levels. This could imply augmented metabolic activity and potential respiratory distress due to an increase in pressure.

Conclusions

• The research concluded that PEEP is not recommended for anesthetized horses that are lying on their sides (laterally recumbent) and breathing spontaneously in air. The main reason is that PEEP, in these circumstances, may lead to alveolar hypoventilation, which means an inadequate ventilation of the alveoli, and does not enhance pulmonary gas exchange.
• This study contributes to the enhanced understanding of the physiological effects of PEEP on anesthetized horses, which can inform better veterinary anesthesia practices, particularly in surgery or other clinical procedures.