Introduction
Delivering anesthetics or other medications via a dart is an extremely useful tool for any veterinarian who works with non-domestic species. In the literature, darting is referred to as a remote delivery system (RDS). Remote delivery systems are most commonly used when human safety is at risk due to the size or temperament of the patient (e.g., large carnivores, or primates), and is also commonly used with non-domestic species that are difficult to approach (e.g., deer and antelope species).
RDS allows safe and effective medication or immobilization of animals. They provide a technique for anesthetizing free ranging and captive wild animals. Darting also allows treatments with medications such as antibiotics and anthelmintics. Modified darts can also be used for remote tissue collection which is often then used for DNA or genetic analysis.
Although RDS provides an extremely useful tool, it can be complicated, expensive and is not without risk to the staff or patient. It is critical that the veterinarian fully understand the application of a remote delivery system and that he/she and their staff are trained in all aspects of its use.
Equipment
In general, an RDS includes the dart and projector (instrument that the dart is fired through). The projector may be a blowpipe, a dart pistol or a dart rifle. Each of these delivery systems has a unique type of dart designed to work with that projector, and each system has different advantages and disadvantages depending on the circumstances (i.e., species, proximity, volume, etc.).
There are four commonly used types of darts. These include a lightweight plastic blow dart, a heavier plastic dart for use with CO2 powered pistols/rifles, aluminum self-assembly powder charged dart, and a fully assembled plastic/aluminum powder charged dart.
The lightweight blow dart is best used for smaller animals, in a sheltered or confined space, and at limited distances. It has the advantage of being relatively inexpensive and relatively non-traumatic to the animal. It is quiet and, once the technique is mastered, is very versatile with a variety of species. Because it is lightweight it is less durable than the other plastic darts and becomes less accurate as the distance increases, especially in fast-moving species.
The plastic darts used with a CO2 powered pistol or rifle are the most commonly used in zoological medicine. The darts and needles come in a wide variety of sizes and can be used with many species. The heavier plastic used with these darts makes them durable and re-usable. While they can be associated with some degree of tissue trauma, they are less traumatic than powder charge darts. These darts are very versatile and can be used in different captive and free ranging species.
CO2 powered pistols and rifles generally come in two sizes. The 11 millimeter barrel is used with 1 and 3 cc darts, while the larger darts (5 cc, 10 cc and 20 cc) require the use of a 13 millimeter barrel. These systems include both barrels, and an adapter is used on the pistol for the larger barrel. The rifle barrel can also be switched out, but is more complicated and requires some tools and training.
Powder charged darts have become less common over the last ten years. While they are effective, they are most commonly used in free ranging situations and with larger animals. They can cause significant trauma including life-threatening damage if placed in the wrong location. The aluminum dart has the advantage of being re-usable and, because it requires assembly, offers a combination of interchangeably sized needles and chambers. The other type of powder charged dart is made of hard plastic surrounding an aluminum core. This dart is very accurate at long distances, but can only be used one time.
The projector selected should be compatible with the dart used. For example, blow darts should only be used with a blow pipe and not interchanged with a CO2 pistol. The flight of the darts will be severely and negatively affected when merging incompatible systems and will greatly reduce the safety and efficacy of the application.
Whichever RDS is selected, it is critical to routinely practice with the equipment. This includes loading the drugs and developing target accuracy. Any veterinary staff that will be using the RDS must be familiar with basic gun safety and develop proficiency with darts of different sizes and different distances. This is especially true for veterinary staff that may be called in for dangerous animal escapes. All accredited zoological facilities maintain written guidelines on human and animal safety, train their staff on the use of anesthetic drugs, and require routine animal escape drills.
Dart Replacement
In general, drugs are most effective when placed in large muscle bellies. Typically in large mammals, the primary area of focus is the caudal dorsal muscles in the hind legs. In some animals the shoulder/neck region can also be used. Cervid species (e.g., deer) carry a layer of fat along their dorsum, so it is best to place the dart more ventrally for a good intramuscular injection. Intravenous and intra-osseous injections can occur and are often associated with very rapid inductions when anesthetic agents are being used. Severe trauma can be caused by inadvertent dart placement in the orbit, chest or abdomen. When using CO2 pistols or rifles with normal pressure settings, even chest of abdominal shots will not cause significant trauma.
Safety Hints
Preparation is critical. Keep dart equipment and supplies organized, well-stocked and ready to go at a moment's notice. This should include darts and needles in different sizes, syringes and properly labeled drugs.
Always bring back-up supplies and drugs. Missed darts are a common occurrence, so be ready to reload and try again.
Always check the barrel of the blow pipe, pistol or rifle. Many times a dart may have been left from a previous procedure.
Ensure that everyone using the equipment is fully trained and able to respond in the event of accidents, complications or adverse reactions. These can include excessive trauma to the patient (leg fracture, IV injection), and partial injection with incomplete immobilization.
Always have a safety protocol in place for accidental human exposure to anesthetic drugs. This is especially important if potent narcotics are being used.
Trouble Shooting
The most common problem with the use of RDS is operator error. Learn how to load a dart quickly, and routinely practice with a target.
Check that the dart plungers are moving and the pressure in the chamber is consistent and leak-free before loading the dart.
Check the needle prior to placing the silicone sleeve over the tip. Inadequately cleaned needles can clog if the previous medication or drug was viscous.
When aiming the dart, always attempt to place it at 90o to the patient's skin. Angled shots often bounce or do not provide good IM injections.
Keep in mind that many non-domestic animals will become very active and stressed when placed in a confined space or otherwise moved in preparation for darting. Attempt to keep the animal's daily routine intact and avoid allowing it to see the darting equipment, especially if it has had previous experience with it.
Partial injections are not uncommon. It is helpful to bring binoculars to facilitate viewing the depth of the plunger from a distance and determine the amount injected.
When possible, ensure there are no possible obstructions between the projector and the patient. Branches and tall grass can cause significant deviation to a dart's trajectory.
Helpful Product Websites
Pneu-Dart System - www.pneudart.com
Telinject Dart System - www.telinject.com
DanInject System - www.daninjectdartguns.com
Cap-Chur System - www.palmercap-chur.com
References
1. Bush M. 1992. Remote drug delivery systems. J Zoo Wildl Med. 23:159-180.
2. Jessup D. 1993. Remote treatment and monitoring of wildlife. In: Fowler M, ed. Zoo and Wild Animal Medicine, Current Therapy, 3rd ed. WB Saunders Co, Philadelphia. Pp 499-504.
3. Kreeger T. Analyses of immobilizing dart characteristics. 2002. Wildl Soc Bull. 30:968-970.
4. Kreeger T, Arnemo J, Raath J. 2002. Handbook of Wildlife Chemical Immobilization, int'l edition. Wildlife Pharmaceuticals, Fort Collins, CO.
5. Nielsen L. Chemical Immobilization of Wild and Exotic Animals. 1999. Iowa State University Press, Ames IA.
6. Isaza, R. Remote drug delivery. In: 2007. West G, Heard D, and Caulkett N (eds.). Zoo Animal & Wildlife Immobilization and Anesthesia. Blackwell Publishing, Ames, IA. Pp 61-74.