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| Forensic Autopsy Demonstration |
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Focus: Students will participate in an interactive human cadaver demo using video conferencing. The demo will discuss the basic procedure of a forensic autopsy, during which the principles of objectivity, scientific method and evidence gathering will be outlined. Major Concepts: The forensic autopsy is of paramount importance when investigating a suspicious death. Objectivity and meticulousness in evidence gathering are essential to the process. A solid understanding of human physiology as well as the processes that occur postmortem is also invaluable in this type of investigation. Objectives: After completing this activity students will be able to • Know the guidelines for proper evidence gathering • Recount the basic procedure for the forensic autopsy • Know the postmortem processes which assist in determining time and cause of death Prerequisite Knowledge: Students should be familiar with the following organ systems: Cardiovascular, Respiratory, Digestive, Musculoskeletal, and Urinary. They should also have a basic understanding of scientific method. This lesson might be best used as a follow up to a general cadaver demonstration. Time Required: 50 minutes (40 minute demonstration + ten minute post test) Materials and Preparation: • Video conferencing equipment. • Cadaver dissected to demonstrate an autopsy • Long forceps for identifying structures. • Post-test answer form (1 copy per student) Procedure: 1. Before unveiling the cadaver discuss with the students the importance of the cadaver in medical education. Discuss the body donor program and the basics of the embalming process. This is an appropriate time to inform the students that the face will remain covered and that the blood has been drained from the cadaver. Discuss the importance of discretion and respect in regards to the cadaver as it represents an individual who has given the ultimate gift, the gift of themselves, so that others might learn. 2. Methods of investigation: Discuss the purpose of a forensic investigation. The investigation uses a systematic, objective approach to determine the time, cause and manner of death (be sure to emphasize these 3 points for the posttest). In forensics there is a differentiation between cause of death, the mechanism of death and the manner of death. Cause of death refers to the event or object that initiates the process of dying. Mechanism of death is the process that causes death. Manner of death is categorized as one of the following; natural, homicide, suicide, accident, pending or undetermined. So for example a stab wound would be a cause of death and exsanguination would be the mechanism of death. There are several questions to be answered by a forensic investigation: Who is the deceased? When did they die? What were the circumstances of their death? What was the cause of death? External inspection: Since this is a forensic autopsy, discuss evaluation of the body at the scene, where one records the location and environment in which the body is found, as well as the degree of livor mortis, rigor mortis and algor mortis. The state of body decomposition, and any visible wounds are also recorded. Livor mortis , also known as hypostasis, is the process by which blood settles to the dependent portions of the body. It occurs within 2-4 hours and becomes "fixed" within 8-12 hours. It is readily apparent as a deep purple discoloration of the skin. Rigor mortis is the onset of muscle rigidity after death. This phenomenon is caused by the continued use of glucose for muscle metabolism after death resulting in the accumulation of lactic acid. At an acidic pH and in the absence of available ATP actin becomes permanently engaged with myosin. Heat accelerates and cold decelerates this process. Onset is usually about 6 hours post mortem with disappearance between 12-36 hours. Rigor mortis disappears as a result of muscle decay. Algor mortis is the term to describe the cooling of the body after death. The rate of cooling varies on the ambient temperature and the clothing that the person is wearing. There are many equations to calculate time of death based on body temperature but they are not considered an accurate enough to be used as an independent means of estimating time of death. A body can cool between .5 and 3.0 degrees F per hour. Complete cooling generally occurs between 18-24 hours after death. Complete cooling is the point at which the body is the same temperature as the environment. 3. Estimating Time of Death: The first step in determining time of death is to estimate a timeframe in which the death could have occurred. This is done by assessing factors such as last time the person was seen alive or missed days at work. Depending on that original time frame the characteristics of the body are used to estimate time of death. If time of death is thought to be less than 24 hours body temperature, rigor mortis and algor mortis may be used to estimate time of death. It is important to note that no single method for determining time of death exists and that all of the factors listed above are used in conjunction to estimating time of death ( be sure to make a point of this for the posttest). If the interval of death is on the order of days to weeks rigor mortis (up to 36 hours) and the state of body decomposition (putrefaction) are used to estimate time of death. You do not need to mention all four stages of putrefaction in detail, they have been included for your information. If you would like to include them gauge the maturity of your audience before proceeding. Putrefaction occurs in four stages: • Stage 1: blue green discoloration of the abdomen; 24 hours (partial discoloration, 36 hours (complete discoloration). • Stage 2: marbling, hemolyzed blood within the superficial veins of the abdomen mixes with hydrogen sulfide and turns a black color. The black veind upon the green abdomen give it a marbled appearance. • Stage 3: bloating, occurs in areas of loose skin like the scrotum and eyelids.around 36-48 hours and all-over bloating occurs between 60-72 hours. • Stage 4: epidermolysis, this occurs within 4-7 days and includes the loosening of hair and nails as well as the loss of skin in a glove and sock formation from the hands and feet. If the body is discovered outside, forensic entomology may be used to assist in estimating time of death as the invasion of the body by insects occurs in a predictable manner. If the death is thought to occur months to years prior to the investigation many factors such as the degree of mummification, the degree of saponification (body fat turning to soap as a result of bacterial invasion) of body fat and the degree of skeletonization of the body can be used to estimate time of death. 4. The internal examination: Discuss the procedure for an autopsy. Begin by describing the y-shaped incision made over the chest and abdominal cavity. The incision is made above the clavicles on either side and extends to the pubic bone. Care is taken not to cut into any of the organs in the abdominal cavity. Next, the chest-plate is removed using a bone saw. This exposes the organs of the thoracic cavity. Care is taken not to disturb the pericardium and pleura if possible to allow for measurement of any pleural or pericardial fluid. The aorta is examined and blood samples are drawn directly from the aorta at this time. If the aorta is devoid of blood this suggests exsanguination (be sure to emphasize for the posttest). The pulmonary arteries are sectioned looking for pulmonary emboli. The rest of the lung is then sectioned looking for emboli or other abnormalities. The heart is removed and sectioned (bread loafing) to look for heart attacks. The coronary arteries are serially sectioned every 2 mm looking for occlusion or evidence of vasospasm. A representative section of the SA node is taken for microscopic examination. In the forensic autopsy the neck is especially important. Careful dissection of the neck is needed to look for signs of asphyxia (petechial hemorrhages of larynx and trachea), signs of strangulation (broken hyoid or thyroid cartilage) or evidence of a foreign body obstructing the airway. [NOTE: in the standard forensic autopsy the entire pharynx including the toung is removed]. The brain is carefully removed by the pathologist who looks for signs of hemorrhage, cerebral edema, and midline shift. The organs of the abdominal cavity are removed in a block and each organ is examined individually. Run through the appearance of each organ at this time explaining any apparent abnormalities. Please include the points below when discussing each organ Stomach-- the amount of food in the stomach is measured as it may help to estimate time of death. The stomach contents are also examined for foreign objects. Liver-- tissue sections of the liver may show metabolic abnormalities or the results of poisoning. Small and large intestine-- these are thoroughly examined for evidence of perforation which could have resulted in peritonitis or exsanguination Abdominal aorta-- the aorta is examined for perforations or lesions that could have resulted in exsanguination. The genitals and sexual organs are removed and examined for semen, foreign bodies, foreign hair or other environmental debris. [NOTE: gauge your audience and your own comfort level when discussing this portion of the autopsy. If you do not feel that it is appropriate to discuss you may omit this section. Also, you may want to discuss this with the teacher prior to the presentation]. Posttest: 1. List 3 postmortem characteristics that help to estimate time of death. 2. (T/F) Time of death can be estimated using body temperature alone. 3. If there is very little blood in the aorta at the time of autopsy this could mean a. The person was strangled b. The person bled to death c. The person had sickle cell disease d. The person drowned 4. Rigor mortis describes which of the following: a. The pooling of blood in the body after death b. The cooling of the body after death c. the stiffening of the muscles after death 5. The forensic autopsy is used to determine what 3 things about a death? Educational Standards: The demonstration meets the following standards. National Science Education (NSE) content standards for grades 9-12: • Systems order and organization • personal and community health • form and function • matter, energy and organization of living systems • evidence, models and explanation Show Me Standards: (Science, and Health/Physical Education) • characteristics and interactions of living organisms • properties and principles of matter and energy • structures of, functions of, and relationships among human body systems • principles of movement and physical fitness • methods used to assess health, reduce risk factors, and avoid high risk behaviors (such as violence, tobacco, alcohol and other drug use) • diseases and methods for prevention, treatment and control ---------------------------------------------------------------------------------------------------------- Adapted From: Handbook of Forensic Pathology. Editor: Froede, Richard C. College of American Patholgists; 1990. Lecture Notes on Forensic Medicine; 2nd edition. Gee, D. J. Blackwell scientific publications, Oxford;1989. |
