Postmortem Chemical Changes

Postmortem Chemical Changes

• The five postmortem chemical changes are: postmortem caloricity, postmortem stain, shift in pH, rigor mortis, and decomposition.

Postmortem Caloricity

• This is the postmortem increase in temperature, often seen in cases of sudden death.
• A postmortem chemical change is caused by the continuation of metabolism after death, generating heat.
• Metabolism refers to all chemical reactions within a cell.
• Anabolism is the building phase of metabolism.
• Catabolism is the breakdown phase, releasing heat and energy, which continues post-death if oxygen is available.
• Embalming considerations include understanding it speeds up the rigor cycle, decomposition and is usually seen in cases of sudden death.

Postmortem Stain

• It's a chemical extravascular change caused by hemolysis.
• Hemolysis, the breakdown of red blood cells, begins approximately 6-10 hours after death
• Hemolysis occurs faster in bodies of individuals who died from carbon monoxide poisoning or those refrigerated.
• Red blood cells contain hemoglobin molecules.
• Hemolysis releases hemoglobin, which decomposes into globin and heme.
• During hemolysis, heme passes through capillary walls/pores, staining tissues reddish.
• Postmortem reddish stain is permanently fixed.
• It is an extravascular discoloration.
• Postmortem stain typically occurs after 6 hours and depends on death circumstances and blood chemistry.
• It is generally not removable through arterial injection alone.
• It may result in gray discoloration when reacting with embalming chemicals.
• It is a sign of delay between death and embalming.
• The stain indicates an increased demand for preservation.
• It's a chemical change resulting from hemolysis, and pressing on the skin does not clear it

Additional info on Postmortem Stain

• It is not removed by blood drainage.
• Cooling/refrigeration, rapid blood cell hemolysis, and carbon monoxide (CO) deaths can speed it up
• It can be a false indication of fluid dyes and a cosmetic problem.
• Extravascular blood discoloration typically appears 10-24 hours after death, common in asphyxia or slow deaths, and is not removable by arterial injection.

Tardieu Spots

• They appear in the same dependent areas as livor mortis and postmortem stain.
• They are usually seen 18-24 hours after death.
• Tardieu spots are very common in asphyxia or slow deaths.

Formaldehyde Grey

• Discoloration of the body is caused by the reaction of formaldehyde from the embalming process with hemoglobin to form methyl hemoglobin.
• Formaldehyde grey can be either intravascular or extravascular.
• A major factor is poor drainage.

pH

• pH measures the degree of acidity or alkalinity.
• 7 is considered neutral.
• Acidity is below 7, with 0 as the maximum acidity.
• Alkalinity is above 7, with 14 as the maximum alkalinity.
• The normal pH of the body is 7.4.
• Approximately 3 hours post-death, the pH of blood and tissue fluid drops into the acid range.
• During rigor mortis it remains acidic.
• Increasingly, as the body decomposes, it becomes increasingly alkaline.
• The best pH for embalming is 7-7.38
• During decomposition, the pH of tissues becomes alkaline.
• Oxygen prevents lactic acid buildup in the living body.
• Lactic acid is no longer inhibited at the time of death and oxygen is gradually used up, accumulating in muscle tissue.
• Lactic acid buildup occurs during the first 3 hours after death and is directly related to the rigor mortis cycle.
• With rigor mortis, pH drops, recorded as low as approximately 6.0; 5.5

Proteins

• Conditions become right for protein breakdown as a result of acid buildup
• As proteins break down, nitrogen products like ammonia and amines gradually build up in the tissues.
• Alkaline ammonia neutralizes acids from carbohydrate breakdown in tissue.
• The body has more proteins than carbohydrates thus the pH gradually becomes alkaline.
• After death the pH of the tissues is alkaline

Rigor Mortis

• Ammonia neutralizes HCOH to urotropin.
• Shifts in pH may result in splotching of dye on the skin surface.
• Is the postmortem stiffening of body muscles by natural processes.
• Rigor mortis usually affects all muscles.
• Before death muscles are relaxed as death occurs; this is primary flaccidity.
• If the body is embalmed while muscles are flaccid, the proteins will react well with the preservative, and tissue fixation will occur.
• Rigor mortis naturally lasts from 36-72 hours leaving muscles relaxed called "secondary flaccidity".
• Greater demand for preservative and muscle protein is broken down in the second flaccidity phase
• If the body is embalmed while rigor is fully developed, the stiffness of the muscles will impede distribution.
• Rigor mortis occurs due to the body's inability to resynthesize adenosine triphosphate (ATP).
• The buildup of ATP causes the muscle proteins to lock together and form an insoluble protein.
• Rigor marks the end of muscle cell life and is generally observed 2-4 hours after death (3 on average).
• The minimum temperature at which rigor occurs is 32°F.
• The ideal temperature for rigor is 98-100°F.
• Rigor is halted above is the body temp is above 120°F or below 32°F.
• The first muscles to be affected are involuntary muscles of the eye.
• Rigor then continues to the jaw and face, next neck, upper extremities, trunk, and lower extremities.
• The directional occurrence of rigor from face to feet is known as Nysten's Law.
• Rigor can be forcibly broken but flexing, extending, rotating/massaging joints and muscles.
• Once broken, rigor does not redevelop.
• Cold stiffening, the solidification of body fats and tissues when the body is exposed to cold temperatures, can be mistaken for rigor.
• Cadaveric spasms are irregular muscle movements in limbs that can occur in rigor.
• Rigor is extravascular.

Embalming Considerations for Rigor

• Rigor mortis creates extravascular resistance
• Can make positioning and posing the body more difficult
• May contribute to tissue distention during the injection
• Increases the demand for preservatives
• Reduces absorption of preservative-firming which is difficult
• A pH change during rigor affects the chemical reaction of the embalming solution
• May contribute to uneven coloration if arterial dye is used
• It may create a false sign of preservation (fixation).
• Decomposition is usually minimal when rigor is present.

Decomposition

• Decomposition is the separation of compounds into simpler substances by the action of microbial and/or autolytic enzymes.
• The 3 major biochemicals in the body are proteins, carbohydrates, and lipids (fats).
• Proteins are essential.

Protein Facts

• Proteins are the most important biochemical.
• Proteins are the most important part of embalming because of successful cross linkages between proteins
• The chemical bond that links proteins is the peptide bond or linkage.
• Proteases are catalytic enzymes that cause the breakdown of protein chains during decomposition.
• The enzymes of decomposition have two sources: saprophytic bacteria and autolysis.
• Saprophytic bacteria obtain nourishment from the products of organic breakdown and decay.
• Saprophytic bacteria are normal residents of the digestive tract.
• Aerobic bacteria may enter through the respiratory tract and deplete tissues of oxygen, creating favorable conditions for anaerobic organisms which originate in the intestinal tract.
• Autolysis is cell self-decomposition.
• Lysosomes are organelles containing digestive enzymes.
• In autolysis, as cells' own digestive enzymes are released, they digest surrounding cellular material.
• Products of autolysis include amino acids, sugars, fatty acids, and glycerol, providing food/energy for microbes, thus accelerating microbial destructive action on remains.
• Hydrolysis is a reaction in which water is one of the reactants/compounds are often broken.
• Hydrolysis is the single most important factor in the initiation of decomposition.
• It is the first chemical reaction in the putrefactive process.
• Putrefaction is the decomposition of proteins by anaerobic bacteria.
• During hydrolysis, large protein molecules are broken down into smaller fragments called proteoses, peptones, and polypeptides.