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Study Guide

1. Many different procedures can be performed on animals in the laboratory, from treatments of disease in sick animals through anesthesia and surgery; from diagnostic testing to the production of monoclonal antibodies needed to make test.  Animals can be  genetically engineered in the laboratory to produce cells  for transplantation into people and to create better animal models that are more susceptible to diseases.  

2. Routes of Drug Administration:

   Sick animals can be treated with  drugs to make them better.  Healthy animals can be injected with anesthetics to prepare them for surgery or to administer a new substance for testing.  It is important that the laboratory animal technician knows how and why to give substances.  
   
   The route of administration will vary with the species of animal, the characteristics of the drug and the speed at which it needs to be absorbed.  

   Topical substances are placed on the surface of the animal, such as flea spray or ointment in the eye.  These are considered superficial methods to administer drugs, and the medication generally remains where it is placed (i.e. on the fur or in the eye).

   Systemic drugs are distributed throughout the animal's body (system).  These are either enteral or parenteral medications.  Enteral drugs enter the animal through its gastrointestinal tract, either per os (by mouth) or per rectum (by the rectum, such as an enema).  When experimental liquids are administered per os, the animal is often gavaged--a tube or needle is passed down the esophagus into the stomach--this ensures that the animal receives the entire dose.

   Parenteral drugs are systemic drugs given outside (par-) of the digestive system:  they are injected into the animal.  The most common routes are: 

   • Intracardiac (IC)-  injected directly into the heart  

   • Intravenous (IV)-  injected into a vein

   • Intraosseous (IO)-  injected into the bone marrow

   • Intraperitoneal  (IP)-  injected into the peritoneal cavity

   • Intramuscular (IM)-  injected into a muscle mass

   • Subcutaneous  (SC or SQ)-  injected under the skin

   • Intradermal (ID)-  injected between the layers of the skin

Parenteral administration of drugs results in more rapid absorption than the enteral route.  The intracardiac route is the quickest, and is used for administering emergency drugs or to collect the maximum amount of blood by exsanguination.  Intravenous and intraosseous injections are the next most rapid, followed (in order of speed) by intraperitoneal, intramuscular and subcutaneous routes.  Substances injected intradermally are generally not distributed throughout the body, but remain at the injection site.

Large volumes of drug should be injected intravenously (or more rarely by the intraosseous route).  A moderate volume of drug can be injected subcutaneously in animals with loose skin, such as rodents, rabbits, dogs and cats.  Smaller volumes can be administered intramuscularly--the substance injected pulls muscle fibers apart, and the more fibers separated, the more the injection hurts.  The smallest volume should be injected intradermally.  

Irritating or caustic substances must be injected intravenously--this immediately dilutes the drug with blood and minimizes the animal's reaction to the drug.  If a caustic substance is accidentally injected  perivascularly  (around the blood vessel), the skin and tissue underneath may be damaged, causing slough.   Any substance injected by IM, SC or ID must be nonirritating.

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3. Anesthesia and Analgesia:

   People who work with laboratory animals have a legal and ethical obligation to avoid unnecessary pain and distress in their animals.  If this is unavoidable, it must be justified by the investigator on the Animal Care and Use Plan.

   An anesthetic is a chemical that causes total loss of sensation and unconsciousness (anesthesia) by depressing the nervous system.  Some anesthetics are local and only affect a limited area, such as lidocaine gel used on the rabbit's pinna prior to blood collection.  General anesthetics cause unconsciousness and are given by injection or as a gas.  

   Analgesics are chemicals that alleviate pain (produce analgesia).  They may act by a variety of mechanisms, but usually increase the threshold of pain in the pain perception areas of the brain.

   Tranquilizers are chemicals that produce calmness by interacting with the central nervous system, reducing anxiety and decreasing struggling.  They do not cause loss of consciousness.  

   It is important when using any drug on an animal to understand that drugs are processed and deactivated by the liver and eliminated from the body via the kidneys.  You must ensure that the liver and kidneys are functioning properly by performing a preanesthetic evaluation and laboratory testing.

   An animal must be monitored and supervised while it is anesthetized.  The depth of anesthesia can be assessed by evaluating the animal's reflexes:

   • Palpebral reflex-  touch the eyelid to elicit an eyelid twitch

   • Corneal reflex-  touch the cornea to elicit a blink

   • Pedal reflex-  squeeze the toes to cause animal to withdraw its foot

   As an animal is anesthetized, it passes through a number of stages and planes that can be anticipated and identified:

Stage I-    Narcosis (sleeping), sedation and analgesia
Stage II-   Delirium and excitement (should be rapid, but supervise animal!!)
Stage III-  Surgical stage
                Plane 1-  Nonreactive to painful stimuli, but reflexes are still present
                 Plane 2-  Palpebral reflex loss, respirations are deeper;  surgical plane
                 Plane 3-  Respiratory muscles somewhat paralyzed & respirations erratic
                 Plane 4-  All reflexes absent, respirations very slow-  near overdose
Stage IV- Paralysis of respiratory center in brain- overdose causes death

It is important to be alert for signs of pain and distress in animals at all times, whether the animals are on experiment or not.  It is always your responsibility to ensure that the animal's welfare is foremost.

Abnormal posture and anorexia are two indications that an animal is uncomfortable.  Guarding is sometimes seen, when the animal moves away from or attempts to bite the handling.  Some animals self-mutilate, licking, biting or scratching a painful area.  Listen for the animal vocalizing when it moves in its cage or when you palpate a painful area.  Some animals are restless when they are in pain or frightened, pacing in their cage, getting up and down and shifting their weight from foot to foot. 

When any sign of pain or distress is noted, it should be recorded on the animal's chart and reported to your supervisor.

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4. Surgery and Aseptic Technique:

   According the the Animal Welfare Act amendment of 1985, survival surgery (when we expect the animal to live) must be performed using aseptic techniques.  This includes wearing sterile gloves, masks and gowns, using sterile instruments and working in a sterile area.

   The surgery suite should be in a separate site located outside of the normal traffic pattern and should have areas for surgical preparation, surgery and intensive care.  The surgical room should have positive pressure ventilation to keep contaminants out of the room.

   It is essential to pay attention to every step when preparing for surgery--any error can lead to infection and invalidation of a research project.  Surgical equipment and supplies must be purchased and autoclaved. 

   The animal must be prepared for surgery.  The animal should have a complete physical examination and laboratory testing to ensure that they are healthy enough for surgery.

   Many animals need to be NPO  (nothing per os) prior to surgery--this means that food and water must be withheld.  Withholding food and water prevents vomiting of stomach contents and its aspiration into the lungs, causing injury and possible pneumonia.  The length of time varies with the species of animal.   It is not necessary to NPO rabbits, rats and other rodents, because they are unable to vomit (although abdominal surgery is much easier without a full stomach and intestines!).  Dogs and cats vomit easily, and they are held off food and water for twelve hours prior to surgery. 

   When the time for surgery approaches, anesthesia should be induced.  Hair over the surgery site must be clipped and a surgical scrub is performed.  The animal must be properly positioned on the surgery table and monitoring equipment should be attached.

   The surgeon and surgical assistants will perform surgical scrubs and dress in sterile caps, masks, gowns and gloves.

   Proper perisurgical care (during surgery) requires proper preparation.  Aseptic surgery is used to prevent wound contamination and subsequent infection--for this reason, a sterile surgical field must be maintained.  Homeostasis must be ensured by monitoring the physiologic condition of the animal, including the vital signs, mucous membrane color and capillary refill time.  The animal should be protected from hypothermia by using an insulated or heated pad.

   Proper postoperative care requires careful and competent observation and monitoring.  Anesthetic recovery is a critical time;  crises can occur quickly.  Acute postoperative care is the time from the end of surgery until the animal is returned to standard husbandry and eating and drinking have resumed.  This allows for stabilization of the animal.  Long-term postoperative care is also essential. This includes observation of the surgical site, suture removal, dressing changes and antibiotics.  The animal should be monitored to determine if analgesics are needed.

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   Diagnostic Testing:

   Diagnostic laboratory testing is needed to monitor the health of the animals, to diagnose disease in sick animals and as a pre-experimental evaluation to provide a baseline with which to compare results. 
   
   Diagnostic images are made by exposing animals to radiation.  Radiographs are made when x-rays pass through an animal onto radiation-sensitive film.  The denser materials, such as bone, block the x-rays and show white on the film; less dense substances, like air in the lungs, are black.  Fractures, obstructions and other abnormalities can be seen.  Images can also be created using magnetic resonance imaging, computerized tomography and other methods. 

   Anatomical pathology includes necropsy (looking for obvious lesions) and histology (microscopic examination of structures and cells looking for abnormalities).

    Clinical laboratory pathology consists of a variety of tests; generally, the veterinarian will select the most appropriate tests based on the signs exhibited by an animal.  These tests include:

   • Microbiology-  culturing micro-organisms, such as bacteria and fungi, on media and testing them for their sensitivity to antibiotics or monitoring the ecological status of an SPF or axenic animal

   • Complete blood count (CBC)-  a panel of tests performed on blood to evaluate the quantity and morphology of red blood cells and white blood cells

   • Clinical chemistries-  panel of tests for chemicals dissolved in blood that evaluate the function of the liver, kidneys, pancreas, etc.

   • Immunoserology-  detection of an immune response (antibodies or antigens), especially the ELISA (enzyme-linked immunosorbant assay) test, which is used to diagnose feline leukemia virus and canine heartworm

   • Parasitology-  identification of ectoparasites and endoparasites though skin scapings and fecal examinations

   • Urinalysis-  evaluation of the physical, chemical and microscopic characteristics of urine, assessing renal function and a whole lot more!

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