Standing start

In some cases, keeping a horse on his feet for surgery is safer and more effective than general anaesthesia. Patrick Pollock FRCVS outlines what’s involved

- Patrick Pollock FRCVS

GENERAL anaesthesia is a wonderful technique, but it is not without risk.

The anaesthetic mortality rate is around one in 100 for otherwise healthy horses, for reasons including an abnormal reaction to the medication used to induce and maintain anaesthesia, an unforeseen event leading to severe depression of the heart or lungs, or a significant musculoskeletal injury such as a fracture or dislocation during recovery.

Once a horse is anaesthetised, many-body systems become compromised. The heavy abdominal organs compress the thoracic cavity and lungs, reducing the amount of oxygen getting into the blood, and the lungs gradually collapse. As the anaesthetic progresses, it is possible for the horse to become hypoxic (starved of oxygen).

At the same time, the great blood vessels – the aorta and vena cava – are compressed, reducing the amount of blood returning to the heart and making the heart work harder to pump the blood around the body. Alongside hypoxia, this can lead to poor blood flow to the muscles, causing further problems such as myopathy (muscle damage) and occasionally even abnormal heart rhythms (arrhythmias), which can have fatal complications.

Some surgical procedures can be performed only during general anaesthesia, so work goes on to reduce these risks. In recent years, however, an increasing number have been attempted with the horse standing and sedated, and with appropriate pain control.

After the first equine standing surgery procedures took place in the 1990s, reproductive, airway, ocular and even some colic surgery performed by this technique became commonplace.