Ventilation and cardiovascular studies during mechanical control of ventilation in horses.

The research article revolves around a study that revealed that during halothane anaesthesia, the majority of horses were found to be under-breathing leading to a high level of arterial carbon dioxide. The application of mechanical control ventilation, however, was able to normalize these levels. In addition, within these horses, significant variances between arterial and alveolar oxygen levels were found.

Introduction

• The study was conducted on twelve horses that were undergoing halothane anaesthesia. Through this research, the scientists aimed to explore the levels of certain gasses in the bloodstream of these horses during their anaesthetic state.

Observations

• During anaesthesia, it was observed that the horses were underventilating. This means they weren’t breathing deeply or frequently enough to expel carbon dioxide from their bodies properly. As a result, this led to high arterial carbon dioxide tensions.
• There were also large variances between alveolar (related to the alveoli of the lungs) and arterial (related to the arteries) levels of oxygen. This is known as the alveolar to arterial oxygen tension gradient.

Mechanical Control Ventilation

• The research then explored the application of mechanically controlled ventilation. This type of ventilation utilizes an external machine that assists with or completely controls the act of breathing. During the study, this was achieved using an intermittent positive pressure of 20-30 cm H2O.
• Usage of mechanically controlled ventilation was found to reduce arterial carbon dioxide levels to normal. This indicates that it aided in enhancing the overall ventilatory efficiency of the horses during anaesthesia.
• The alveolar to arterial oxygen gradients didn’t increase – indicating no worsening of the oxygen distribution status. In fact, some even decreased, which implies an improvement in oxygen distribution between these two areas.

Analysis of the Oxygen Gradient

• The observed alveolar to arterial Po2 (partial pressure of oxygen) gradients were primarily due to a true shunt (a situation where blood bypasses the lungs and doesn’t undergo oxygenation) of around 30%. This suggests that a considerable proportion of the blood wasn’t being oxygenated as it passed through the lungs.
• However, these gradients were not due to ventilation-perfusion inequality, which is an abnormal distribution of ventilated air and blood flow within the lungs.