Evaluation of a modification of the Hudson demand valve in ventilated and spontaneously breathing horses.

The research evaluates a modification to the Hudson demand valve, a device used in general anaesthesia to increase arterial oxygen. The study observed the effects of this device and its modifications on arterial oxygen and carbon dioxide in horses during anaesthesia and recovery.

Study Context

• This research revolves around the Hudson demand valve, a device frequently used during general anaesthesia in horses. Hypoxaemia, or low blood oxygen, often develops during the anesthesia and recovery periods in horses. The Hudson valve increases arterial oxygen but also increases airway resistance during spontaneous ventilation. This study evaluates a modification to this valve, aiming to reduce such resistance.

Research Methodology

• The researchers tested the valve and its modification on four ponies that were anesthetised using a total intravenous technique. They evaluated the effects on arterial oxygen (PaO2) and carbon dioxide (PaCO2) tensions in the horses’ blood during both spontaneous ventilation and intermittent positive pressure ventilation.
• The device’s effects were also analyzed in 20 additional clinical cases during their recovery from halothane anaesthesia.

Findings

• In the anaesthetised ponies, the Hudson demand valve increased PaO2 significantly, both during spontaneous ventilation and intermittent positive pressure ventilation. With the valve modification, PaCO2 was increased during spontaneous ventilation though PaO2 remained essentially the same.
• In the 20 halothane anaesthesia cases, the device also increased PaO2 during both spontaneous and positive pressure ventilation, while the valve modification increased the PaO2 to a lesser extent.
• During spontaneous ventilation, both the unmodified valve and the modification slightly increased PaCO2.

Implications

• The results suggest that the Hudson demand valve significantly increases arterial oxygen during anaesthesia and recovery, but it can raise airway resistance during spontaneous ventilation. The proposed modification reduces this resistance but does not improve arterial oxygen to the same extent as the original unmodified valve.