Blood collection and administration of fluids and drugs (rabbit):

Administration of Fluids and Drugs (Overview):

Gastro-Intestinal Tract:

• Oral or per os (po)- - through the mouth
• Gavage - - into the stomach via a feeding needle

Parenteral Administration; General Considerations:

• Intravenous (iv) directly into the vascular system through a vein
• Intraperitoneal (ip) - - into the abdominal cavity
• Subcutaneous (sc) - - under the skin
• Intramuscular (im) - - into a muscle

Blood Collection:

• Site Preparation:
• Marginal ear vein
• Central ear artery
• Cardiocentesis

Administration of Fluids and Drugs (Overview):

When drugs, vaccines, injectable anesthetics or other agents are to be administered, one of several different routes may be selected. The route is governed by the nature of the agent being administered, the animal, and the purpose of the administration, among other factors. Rabbits may exhibit sudden violent efforts to escape during restraint. In the process, intravenous needles, gavage tubes, etc. can be dislodged causing spills or otherwise endangering themselves or personnel. Therefore, complete restraint should be accomplished before attempting such procedures and rabbits should never be left unattended in restraint devices. Practice in using these devices can be arranged through the ACU.

Gastro-Intestinal Tract:

Oral: Substances may be administered orally by addition to the food or the drinking water. The amount of drug consumed by an animal will vary between each individual. If the drug imparts an unpleasant taste, affecting palatability, the drug will be consumed in decreased amounts. Environmental conditions such as the ambient temperature will also affect both water and food consumption. The general rule of thumb is that 5 grams of food and 10 mls of water will be consumed daily per 100 grams of body weight.

Gavage: If it is necessary to administer exact amounts of a substance a gastric feeding tube should be used. Feldman² describes the use of a 13 gauge 6 inch feeding needle that has been bent to approximate the pharyngeal curvature. Otherwise a mouth speculum used in concert with a rubber tube (4 mm diameter) can be used to administer compounds. Flexible or plastic tubes may be bitten or chewed and some care must be taken to prevent this. A tongue depressor with a centrally placed hole, when placed on end behind the diastema will serve as a satisfactory speculum. Care must be taken that the tube or needle does not enter the trachea or puncture the esophagus or stomach. In most cases, introduction of the tube toward the rear of the mouth will induce swallowing and the tube will readily enter the esophagus. A violent reaction (coughing, gasping) usually follows accidental introduction of the tube into the larynx or trachea. For multiple administrations it would be advisable to fashion a mouth speculum out of Plexiglas. ¹² Rabbits should be placed in a restraining device before attempting this procedure to avoid unnecessary struggling and injury. Alternatively, commercially available balling guns are available (future picture) to administer pills or compounds that have been placed inside gelatin capsules. A three milliliter syringe with the barrel cut to remove the end of the syringe can be used as an alternative to a commercial product (future picture). Care should be taken to smooth the edges of the cut syringe case to avoid damaging the oral mucosa. For the chronic administration of compounds placement of a pharyngostomy tube may be advisable.⁹

Parenteral Administration: General Considerations

• Intravenous (iv) - - directly into the vascular system through a vein
• Intra-arterial (ia) - - directly into the vascular system through an artery
• Intraperitoneal (ip) - - into the abdominal cavity
• Subcutaneous (sc) - - under the skin
• Intramuscular (im) - - into a muscle
• Intradermal (id) - - between layers of skin

General Considerations: Parenteral routes of administration involve injections into various compartments of the body. Sites used for collection of blood from veins may also be used for intravenous administration. Intraperitoneal administration is one of the most frequently-used parenteral routes in rodents. Other locations are the musculature and subcutis. Materials given intramuscularly must be in small volumes generally not more than 0.5 ml/site. Absorption by this route is more rapid than from subcutaneous administration. Regardless of the route used, it is essential that the subject be securely restrained to prevent unnecessary struggling by the animal and to avoid injury to personnel by dislodged needles.

The investigator should know the physiological and chemical properties of the substance that he/she plans to inject. Considerable tissue damage and discomfort can be caused by irritating vehicles, drugs or solutions when injected into animals. The rabbit does not have a foot pad and injection into the bottom of the foot is not acceptable. More suitable sites for antigen injections are subcutaneously over the scapula or lumbar area or deep in large muscle masses.

Demonstration/instruction sessions can be arranged with the ACU.

Substances may be administered orally by addition to the food or the drinking water, by use of a capsule or pill, by instillation into the mouth using a mechanical device, such as syringe or forceps, or by hand. Capsules or coated pills are rarely used in rabbits or rodents. When used in larger animals, capsules or pills are given by a "pilling gun" or "balling gun," or are placed in the mouth near the back of the tongue and the animal is induced to swallow by stroking the throat.

Stomach tubes or gastric feeding needles are inserted through the mouth into the stomach or lower esophagus (future picture). Care must be taken that the tube or needle does not enter the trachea or puncture the esophagus or stomach. In most cases, introduction of the tube toward the rear of the mouth will induce swallowing and the tube will readily enter the esophagus. A violent reaction (coughing, gasping) usually follows accidental introduction of the tube into the larynx or trachea. Flexible or plastic tubes may be bitten or chewed and some care must be taken to prevent this. With rabbits and some larger animals, a wooden or plastic dowel with a hole in the center is held crossways behind the incisors and the mouth is held shut by an assistant. This prevents chewing and permits entrance of the stomach tube through the hole in the dowel and on into the stomach. Rabbits should be placed in a restraining device before attempting this procedure to avoid unnecessary struggling and injury. A small curved metal tube with a ball on the end (feeding needle) is often used with rodents. Entry normally may be obtained without anesthesia using hand restraint. The ball at the end of the tube prevents trauma to the esophagus and oral cavity. With the stomach tube fitted to a syringe or aspirator, materials may be administered or withdrawn as required.

Rectal administration is infrequently used; however, certain agents are administered in this manner. Flexible tubing or inflexible blunt probes or tubes may be used, but in both cases complete restraint and gentle procedures are required. The catheter or probe must be lubricated with surgical jelly or petroleum jelly and entry should be accomplished slowly to permit the anus to dilate. Forcible entry should not be attempted and, if blockage is encountered, its cause must be carefully determined before proceeding.

Intravenous:

Equipment: 20 to 25 g needle of suitable length with syringe. (A short bevel needle not more than 1 inch long and a syringe of 5 ml capacity or less is recommended.) Butterfly infusion sets also work well. A rabbit holder of metal, or plastic is required (future picture).

Place the rabbit in a holder. (Do not attempt this procedure using manual restraint.) The marginal ear vein is used almost exclusively. The hair over the vein is clipped or shaved and the skin cleansed with alcohol or alcohol-iodine before making the injection. The vein can be distended by flicking the margin with the fingers a few times. Pinching off the vein near the base of the ear will also help to distend the vein. Xylene may be used as a vasodilator by gently rubbing a small amount of it over the outer surface of the ear. Xylene is a powerful skin irritant and extra care is necessary to clean the ear thoroughly with soap and water after its use. Nitroglycerin ointment or d-limonene⁷ are less irritating and also promote vasodilation. Xylene use can be avoided by using a light dose of Innovar-Vet, xylazine or Acepromazine which will dilate the vessels. Administration of 1 mg of Acepromazine to an adult rabbit facilitates restraint, reduces distress and dilates the marginal ear vein.

Prior to insertion of the butterfly it should be precharged with saline to avoid the unnecessary injection of air into the vascular system. The hub should be removed from the butterfly to allow the flow of blood into the hub of the needle to confirm correct placement of the butterfly needle. After blood flow is detected the syringe containing the material to be injected should be attached.

The total volume administered to an adult rabbit should not exceed 5.0 ml.

Intraperitoneal:

Equipment: 19 or 20 g, 1 or 1-1/2 inch needle with suitable syringe; a flat board or trough with cleats on the four corners for securing restraint cords; four lengths of soft 1/4-inch rope or 1/2-inch wide cotton or nylon tape to tie the legs.

The rabbit is stretched out on its back with his legs tied to the corner cleats. (An assistant may be very helpful, and chemical restraint with ketamine is recommended to reduce struggling.) The abdomen is clipped and the skin disinfected. The board is inclined slightly in a head down position. Injections are made in the lateral aspect of the lower abdominal quadrants. Caution must be taken to avoid puncturing a distended urinary bladder, the bowel, or the liver. Volume: 50-100 ml in an adult rabbit

Subcutaneous:

Equipment: 20 to 23 g, 1-inch needle.

The area most frequently used is between the scapulae. Clean the skin with alcohol, clip or part the hair, and fold the skin over the needle rather than thrusting the needle into the skin. Volume: 30-50 ml in and adult rabbit

Intramuscular:

Equipment: 22 or 23 g, 1-inch needle.

The most frequently-used sites are the back muscles lateral to the vertebrae and caudal to the ribs or the lateral thigh muscles (more desirable). If repeated injections are to be made, rotate sites. The hair should be clipped and the skin disinfected. Adequate restraint is important. Volume: 0.5 ml in an adult rabbit

Blood Collection:

The amount of blood needed and other factors will govern the method and sites of collection. Descriptions of the various techniques for venipuncture in different species is available in the Animal Care Unit (400 ML; 335-7985) in text and videotape format. Proper insertion of the needle into a vein or other part of the vascular system is normally the most difficult part of the procedure. Certain guidelines can be given, but only practice provides proficiency. Veins may be expected to roll, collapse, or shift, making entrance difficult. A precise, careful introduction of the needle is best and several attempts may be required. Starting at distal sites will allow repeat attempts more proximally. The needle is inserted parallel to the vein and the tip directed into the lumen along the longitudinal axis. When withdrawing blood from a vein, aspiration should be slow so the vessel does not collapse.

Site Preparation:

The area of blood withdrawal should be cleaned with alcohol. Some procedures will require sedation or anesthesia; others may be carried out without anesthesia provided suitable restraint is used.

In order to better visualize veins, one of several methods of dilation may be used. The marginal ear vein can be distended by flicking the margin with the fingers a few times. Pinching off the vein near the base of the ear will also help to distend the vein. When using the rabbit ear, a low-wattage light bulb can be used to supply heat. This also aids by providing additional light. Xylene may be used as a vasodilator by gently rubbing a small amount of it over the outer surface of the ear. Xylene is a powerful skin irritant and extra care is necessary to clean the ear thoroughly with soap and water after its use. Nitroglycerin ointment or d-limonene⁷ are less irritating and also promote vasodilation. Xylene use can be avoided by using a light dose of Innovar-Vet, xylazine or Acepromazine which will dilate the vessels. Administration of 1 mg of Acepromazine to an adult rabbit facilitates restraint, reduces distress and acts as a vasodilator.

Marginal ear vein

The marginal ear vein of the rabbit is useful for collection of small volumes of blood and may be used for intravenous injection. Sedation with acetylpromazine (1 mg) will allow handling of the animal and causes vasodilation. Blood collection is fairly simple at this site. The area is shaved and cleaned with alcohol. The vein is occluded, the needle carefully inserted, and blood slowly withdrawn. Use of a butterfly set may avoid damage to the vessel if the animal moves. Gauze held with pressure over the venipuncture site for a few minutes will prevent hematomas from forming.

Central ear artery

The central ear artery can be used for collecting larger volumes of blood from the rabbit. Phlebotomy from the central ear artery requires the use of a plain 20 ga. one inch needle attached to a silicone-coated tube. Alternatively, cutting the hub off a 20 gauge needle and collecting the flowing blood into a tube will decrease the time till coagulation of the needle. (future picture) Ten ml of blood/kg body weight can be collected in this manner but the rabbit must be carefully restrained and hematomas must be prevented by direct pressure. Prior sedation of the rabbit will minimize distress and movement while promoting vasodilation (picture; picture). Within 1 minute of administration of acetylpromazine (1 mg) the central ear artery should dilate. The central ear artery has a bounding pulse and generally runs cranial to (ahead of) the central vein (picture). Swab the artery with alcohol and catheterize with 20 or 21 gauge needle pointed towards the base of the ear (picture, picture), . Advance the needle approximately 5 mm into lumen of artery. When using the needle with hub removed the technician can release the needle which will remain in the vessel during phlebotomy (picture) . When blood collection is completed, withdraw the needled from the ear artery and apply firm pressure to the puncture site for at least on minute (picture). The rabbit may be returned to it's home cage once hemostasis is complete. A method for obtaining multiple blood samples has been described.¹¹

Cardiocentesis

Cardiac puncture is an acceptable method blood collection from rabbits when used as a terminal procedure to exsanguinate the anesthetized rabbit. This method is not suitable as a repetitive blood sampling procedure since it carries considerable risk to the animal. The rabbit should be at a surgical plane of anesthesia before performing cardiocentesis. The point of maximum intensity of heartbeat should be determine while palpating the laterally recumbent rabbit. An 18 gauge 1.5 inch bleeding needle attached to a vacuum tube should be directed into the heart at the point of maximum intensity. Blood will flow into the needle when the heart chamber is entered. A XX ml vacuum tube should car