French researchers have investigated which risk factors affect mortality by horses under anesthesia. The number of deaths with anesthetized horses remains high.
"It is especially important that horse owners are aware of the risk of a horse under anesthesia. For example, anesthesia often goes wrong with horses undergoing colic surgery. Weight is also a clear risk factor. Horses who are overweight die more often during anesthesia. This probably has to do with a reduced oxygen level in their blood and lungs. In addition, age is also a factor, older horses are more at risk. The longer the operation, the higher the risk. "
Source: The Horse