Use of a demand valve for postoperative administration of oxygen to horses.

The study examines the efficiency of a demand valve in administering oxygen to horses post-anesthesia. It finds that the use of the demand valve corrects potentially dangerous levels of low blood oxygen that occur in horses when laying on their sides after surgery.

Research Details

This study tested the effectiveness of a demand valve in administering oxygen to horses after they have undergone anaesthesia. This was done due to the following reasons:

• When horses are subjected to general anaesthesia, their cardiopulmonary functions often get disturbed, which can lead to a decrease in alveolar ventilation and impairment in oxygenation.
• If anaesthesia is maintained with 100% oxygen inhalation, satisfactory arterial oxygen tensions are normally maintained. However, when the animal breathes room air alone during recovery, hypoxaemia (low levels of oxygen in the blood) can occur.

Methodology

Twelve horses of various breeds, which had undergone various surgeries, were divided into two groups. Group A consisted of horses that were allowed to breathe spontaneously post-surgery whereas Group B consisted of horses that were ventilated using the demand valve at a rate of 6 breaths per minute. The researchers followed the following methodology:

• The horses were premedicated with acepromazine maleate and then anaesthetised with thiopentone sodium followed by suxamethonium chloride.
• Anaesthesia was then maintained with halothane and oxygen.
• Post-operation, horses were disconnected from the anaesthetic machine and placed in a recovery box with the demand valve which was connected to the piped oxygen supply.
• Arterial blood samples were collected at various points – before disconnection from the anaesthetic machine, immediately after reaching the recovery box, and after 2 and 5 minutes of oxygen administration through the demand valve. These samples were analysed for pH and carbon dioxide and oxygen tensions.

Research Findings

The administration of oxygen via the demand valve significantly increased the levels of oxygen in the blood for both spontaneously breathing and mechanically ventilated horses. Some key results include:

• Both groups revealed significantly lowered oxygen tensions when they reached the recovery box. However, oxygen tensions significantly increased after oxygen administration via the demand valve.
• Assisted ventilation proved more effective in raising the oxygen tension in the blood.
• The demand valve caused a significant rise in carbon dioxide tensions in the spontaneously triggering group. However, there was no significant variance in the carbon dioxide levels in the ventilated group.
• All of the horses exhibited respiratory acidosis (excessively acidic blood from abnormal gas exchange) at the end of the surgery, which improved once they were disconnected from the anaesthesia machine.

The exploration concluded that the use of the demand valve significantly improved oxygenation in horses post-surgery when they are at serious risk from low levels of oxygen. The article also highlighted its effectiveness for horses under about 400 kg and spontaneously breathing animals. It suggested that the valve is a cost-effective and highly efficient way to ventilate such horses. Moreover, it accelerated the elimination of anaesthetic gases, so the horses seemed to recover quicker.