Page 42 - Manual of Equine Field Surgery

38 PRESURGICAL PREPARATION AND ASSESSMENT

Oxygen supplementation can easily be done in ideal. The horse should be fitted with the correct

the field using a portable E oxygen tank, regula- size nylon halter and a sturdy lead rope should be

I tor, and flowmeter. A full E tank will hold approx- available. If an a.2-agonist-dissociative combina-
imately 650 L of oxygen. The oxygen can be
tion is used, the horse can easily be induced by one

administered via a nasal insufflation line at a flow person. After administration of the dissociative

rate of 5 to 10 Lim.in. Oxygen can also be supple- agent, the handler maintains control of the head.

mented using an E tank and a demand valve. The Generally, the horse will lean back and the handler

demand valve is attached to an endotracheal tube may have to hold the head down to keep the horse

and can be used in two ways. If the horse is breath- from going over backward. Alternatively, the

ing spontaneously, the demand valve is auto- handler can stand at the shoulder of the horse and

matically triggered during inspiration and the move the horse in a circle around him, One hand

inspired air is supplemented with oxygen. Alter- should be on the horse's shoulder and the other

natively, if the horse is not breathing well sponta- holding the lead rope close to the horse's head. As

neously, the demand valve can be manually the dissociative agent takes effect, the rear end of

triggered to start the oxygen flow. Once an ade- the horse will usually swing away from the

quate volume has been delivered, which is deter- handler. He or she should be on the side of the

mined by watching the chest excursion, the trigger patient that is to be up once the horse is anes-

is released and the horse passively exhales. The thetized if it is to be positioned in lateral recum- ,

demand valve must have a high maximum flow bency. As the horse goes down, the handler can

and have an adaptor to allow it to be attached to step toward the head and control its fall by

a11 equine endotracheal tube. Some demand holding onto the lead rope. If a guaifenesin

valves designed for human use do not have an mixture is used for induction, it is difficult to hold

adequate peak flow rate. The flow rate should be the horse and the drug container. A second person

iI1 excess of 150 LI min. At least one demand valve is needed to manage the drug bottle as the horse

has both the required flow rate and necessary is going down. If several assistants are available,

adaptors for equine use (Equine Demand Valve; an alternative method can be used. One person

JD Medical, Phoenix Ariz.). should be at the head holding the lead rope and a

second person should hold the tail. If the horse is

nervous, the person holding the tail should wait

INDUCTION AND RECOVERY FOR until the horse is almost ready to go down before

INJECTABLE FIELD ANESTHESIA grabbing it, recognizing that the horse may still

kick. Two additional assistants are at the horse's

Induction shoulders. As the horse begins to relax, the assis-

tants on the head and tail pull in opposite direc-

Before administering any anesthetic drugs, a tions and down. The assistants on the shoulders

quick physical examination should be performed. attempt to keep the horse from falling sideways.

Any obvious health problems or injuries should This should allow the horse to go down into a

be brought to the attention of the owner or agent sternal position, and it can then be rolled onto

and their effect on anesthesia discussed. The either side.

risk of anesthetic and surgical complications

should be discussed and made clear to the owner

as well. In a comprehensive survey of almost Recovery

42,000 equine anesthetic cases, the overall death Recovery after short injectable anesthesia is usu-

rate (excluding colic surgeries) was 2.4%.80 This ally relatively smooth. If the horse was nervous

.included horses that died or were euthanized. If and excited during induction, the recovery may be

only the horses undergoing injectable anesthesia less than optimal. Ideally during recovery, the

were evaluated, the death rate dropped to 0.3o/o. horse will move into a sternal position, wait a few

Although this may seem to be a big positive for minutes, and then stand uneventfully. Covering

injectable anesthesia, one must realize these were the horse's eyes with a towel often will help keep

generally healthy horses undergoing short proce- the horse from trying to get up before it is ready.

dures with anticipated high success rates. In addition, it is important to keep the surround-

A level area free of obstacles should be selected ings as quiet as possible during recovery. A sudden

for the procedure. AI1 open grass-covered area is loud noise may arouse the horse before it is able