Tuesday, March 6, 2007

The Art of Darting

Today was yet another busy day. After another gaur immobilization this morning, there was a physical exam that needed to be done on this puma. He is going to be shipped out to another institution, so he needed to have the works done. While anesthetized, he had his teeth checked (at right: they were beautiful, and didn't require much in the way of cleaning), his eyes examined, his heart and lungs ausculted, his abdomen palpated, blood drawn for routine banking and testing and his vaccinations brought up-to-date. After everything was done with him, we got started on vaccinationg some of the big cats, so this is a great opportunity to go into that unique aspect of zoo medicine!

As I have mentioned previously, darting is a common procedure used to medicate, vaccinate and anesthetize large and/or dangerous animals that are difficult to handle safely. There are three remote systems: pole syringe, blow dart, and darting rifle. Like it sounds, a pole syringe is a long pole with a syringe on the end that the veterinarian can stick through the openings on a cage and -- with pressure applied by pressing the whole apparatus up against an animal -- deliver the needed drugs. This method has the benefits of being the least traumatic and most accurate and reliable of the three methods. The disadvantage is that the vet needs to be relatively close to the animal, and an animal that is moving around a lot can be a difficult target for the somewhat awkward pole The rifles come in all shapes and sizes from air-charged pistols to bona fide rifles that use gunpowder to launch the dart. While this method is the most practical in field situations where the target is a long distance away, it also has the potential of causing the most damage when the dart hits the animal. I will talk about the blow darting method more in depth today.

Blow darting combines some of the benefits of both pole syringing and use of the rifle. It is typically used in a situation where an animal is confined to a smaller holding, "shifting" or "off exhibit" cage. The animal still has plenty of room to move around (and is, therefore, difficult to hit with a pole syringe), but is no where near the distance required for a rifle. It won't cause the degree of tissue damage that a rifle will, but it allows the vet to be more mobile and to hit a moving target. And there certainly is something of an art to it. You don't want to blow too hard, and cause unnessecary tissue trauma. However, if you don't have enough force behind your dart, it will simply bounce off of the animal's skin. The two targets that you typically aim for are the haunches or the shoulder. This can vary depending on the animal. For example, it is not recommended to dose a bear in the haunches, because they have significant fat stores back there that can hamper the delivery and efficacy of whatever drug you are using. This is especially important when you are giving immobilizing agents, and are concerned about the precise amount that is getting into vascularized tissue.

Like you would expect, there are numerous available darting systems available for the zoo veterinarian. Interestingly enough, the preferred method at the HDZ is a system that was designed by Dr. Simmons himself. These specially designed darts are made by the veterinary technician staff here at the zoo. I'll go over how they work, starting weith the needle. At right is a close-up picture of the needle. You can see a plastic sheath around it near the tip. On the top needle, it is covering the two openings through with the drug will be delivered. The needle tip itself is sealed, so the only way out is through those side openings. This design serves two purposes. First, it prevents the needle from getting clogged. The pointed end still helps the needle to enter the skin cleanly, but skin can't get stuck in it, preventing drug delivery. Secondly, it provides a way for the dart to get charged, which I will explain next.

At left is a lettered diagram I will use. Sorry that the letters are so small! "A" is the needle, here covered by its protective cap. "B" is the drug chamber. "C" is the plunger. "D" is the pressure chamber. Butane is put into this chamber after the drug is put in and the protective sheath is placed over the holes in the needle. Now you see why that is so important! As pressure is put into that chamber, the plunger naturallay wants to press up onto the drug chamber. As long as the sheath is over the needle holes, that drug can't go anywhere, so you can build up pressure in that chamber. When the dart hits the animal, the needle will enter while the plastic sheath (refer to the picture above) will be pushed back toward the hub of the needle by the skin. This will then allow the drug to be pushed through the needle holes due to the pressure from the butane. Drug delivered! "E" is the tail piece which provides a counter balance to the front of the dart and also has a special port that the techs make in order to charge the dart with the butane.

So, that is the basic way the darts here work! It's a pretty neat system, and I actually got to try it out today on some animals! Like I mentioned, several of the big cats need to be vaccinated. Since they don't need to be anesthetized for any reason in the near future, they are just being darted. I used the blow pipe six times, and didn't have any misses! We were vaccinateing jaguars such as the one pictures at left. Fortunately, the ones that I darted were of the spotted variety, so I had little bull's eyes to aim for. ;) It was a great experience!
Below is a video I shot of myself practicing on a box. While I'm certainly no Annie Oakley, these are two pretty good shots, if I say so myself!

So, that is about the extent of events I will write about today. Make sure to stop by tomorrow....we have a big event going on tomorrow, and the local media is invited to attend! meanwhile, I will end with this shark. The Kingdom of the Seas is an amazing aquarium, one of the big features of which is an impressive 70 ft long walk-through tunnel through a large tank with lots of sharks, large seas turtles and rays. Also featured in other exhibits are puffins, penguins, jellyfish, octapus, sea horses and a myriad of tropical and freshwater fish. Most impressive!

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