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Practical fluid therapy (Proceedings)

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Nov 01, 2010

The goals of fluid therapy in camelids are similar to those in other species. The mechanics and details are somewhat different. Of the possible routes, oral and intravenous are the major routes used to correct problems of hydration. Subcutaneous, intraperitoneal, and intraosseus administration all have specialty applications, but are not useful or necessary in most situations.

ORAL FLUIDS

Oral fluids are best administered by tube. I prefer to pass the tube through the mouth, as camelids have very narrow nasal passages. Small bore feeding tubes can be used nasally in crias and left in place. Passing an orogastric tube on an adult camelid can induce struggling and a stress response, so it is important to assess whether the patient can tolerate the procedure, have a plan to perform the procedure quickly and competently, and have a plan to abort the procedure if necessary. Alpacas may be manually restrained, whereas llamas may be better restrained in a llama chute. Sedation may help. My preference is to use intramuscular butorphanol, which has less deleterious effects on airway protective responses or cardiac output than many other sedatives. For a speculum, we use a block of wood with the edges rounded and a hole drilled through the center that the tube can fit through. The block is introduced from the side into the interdental space, then seated onto the molars. The tube is passed through the hole, over the base of the tongue and into the esophagus. Negative pressure when sucking back on the tube, palpating the tube adjacent to the cervical trachea, or hearing fluid bubbles over the abdomen when blowing on the tube confirm correct placement.

The camelid may respond by struggling, regurgitating, or going into respiratory distress. Any of these may lead to reassessment of the adequacy or restraint or the safety of the procedure.

Once the tube is in place, we usually think it is safe to administer up to about 3.5% of total body weight in fluids at one time (3.5 L to a 100 kg llama). Administering more may be safe in some situations, but also increases the chances of gastric regurgitation. That amount may be given every few hours, unless gastric distention develops, but we usually try to limit ourselves to 3 tubings a day.

The easiest thing to give by tube is water. In dehydrated camelids that have a tendency towards hypernatremia and hyperchloremia, that may be acceptable, but it is likely that a salt solution with an osmolality similar to plasma will have fewer shock effects on gastric microbes, and may be absorbed better. We generally avoid calf electrolyte powders because of the sugar, and make our own isotonic salt solutions.

INTRAVENOUS FLUIDS

Much has been made of the difficulty of catheterization in recent years. In my opinion, there are six identifiable and preventable problems that may inhibit catheterizations:
     1) Inadequate restraint. We use a restraint chute for most adult camelids, and chemical restraint with butorphanol if needed.
     2) Inadequate identification of the cervical landmarks. The jugular vein runs between the trachea and the transverse processes of the cervical vertebrae. If the vein itself cannot be visualized by holding it off and then letting off the pressure, the point midway between these landmarks approximately one-third of the distance from the ramus on the mandible toward the shoulders is a good place to try.
     3) Too much local anesthetic. Camelid skin is very thick. A large bleb of local will tend to compress in and hence block venous flow, rather than blebbing out the skin. I try to use no more than 0.5 cc.
     4) Not puncturing the skin full thickness prior to catheterization. The vein is very superficial. If you try to introduce a catheter through uncut skin, often the initial momentum of passing it through the resistant tissue propels the catheter through the jugular vein before you realize it. I pick up the skin below my bleb, pull it away from the vein, and make a full-thickness stab incision with a #15 blade. If I feel resistance or see the skin depress as I try to introduce the catheter, I repeat the stab incision.
     5) Going too deep. This is rarely a problem, unless #2 or #4 were also problems. If you are in the right place and do not miss the jugular on the first stab, then it should be the first vascular structure you encounter. Going too deep may lead to inadvertent carotid puncture. This is best recognized by the rapid back-flow of blood. I immediately hold off the site where I believe the carotid was punctured, withdraw my catheter and apply firm pressure for 5 minutes. If you respond quickly, you can simply try again. If a large hematoma develops, it may be better to choose another site where the anatomy is less affected. On the next attempt, blood coming back from a hematoma may resemble blood from a successful catheterization, except that the catheter will not feed.
     6) Getting frustrated. Suffice it to say here that most camelids can be catheterized, and that practice, the right technique and equipment, good restraint facilities, and possible sedation make the procedure more successful. If you are not having success, a deep breath, a short break, and a reassessment of landmarks is usually warranted.