Effect of end-inspiratory pause on airway and physiological dead space in anesthetized horses.

The research investigates the effect a 30% end-inspiratory pause (EIP), a temporary halt during the inspiratory phase of mechanical ventilation, on the dead space in anesthetized horses’ airways and its impact on carbon dioxide (CO) expulsion and ratios of oxygen in arterial blood to inspired oxygen.

Methodology

• A prospective research study was conducted on a group of eight healthy research horses that were undergoing laparotomy, a surgical procedure involving an incision into the abdominal cavity.
• The horses were anesthetized and mechanically ventilated, defined as six breaths per minute, with an initial EIP of 0%, among other set parameters.
• The volume of carbon dioxide eliminated per breath (Vcobr) and the volume of air expired were recorded after induction, after adding a 30% EIP, and upon EIP removal.
• A stabilisation period of 15 minutes was given between phases to ensure that accurate results were obtained.
• Data results were comparatively analyzed using a mixed-effect linear model, with a significance level set at p < 0.05.

Findings

• The research results showed that a 30% EIP decreased the alveolar tidal volume, which refers to the volume of gas that flows into the alveoli in the lungs during each breath.
• Changes in EIP simultaneously increased the airway dead space, which represents the volume of a breath that does not take part in gas exchange (because it fills the airways but does not reach the alveoli).
• However, the physiological dead space – the sum of the alveolar and airway dead spaces – remained unchanged.
• The EIP also boosted the ratio of partial pressure arterial oxygen to fractional inspired oxygen (PaO:FiO), which is an indication of the effectiveness of oxygen transfer from the lungs to the bloodstream.
• The Vcobr, a measure of the efficacy of carbon dioxide removal from the body per breath, also increased without significant reduction in partial pressure of carbon dioxide.

Conclusions

• The use of a 30% EIP during the mechanical ventilation of anesthetized horses enhanced oxygenation and reduced both alveolar tidal volume and airway dead space without significant effects on carbon dioxide concentration in the blood.
• These results warrant further studies to examine the impact of different EIP percentages on both healthy horses and those with respiratory diseases while they are under anesthesia.