Embalming Science and Practice
This domain tests the reasoning behind embalming decisions: the chemistry of dilution, the choice of injection and drainage sites, special-case handling, and the safety rules that apply in the preparation room. Expect calculation items and "which site/fluid" items more than anatomy trivia.
Chemistry you must be able to compute
Arterial fluid strength is expressed as index - grams of formaldehyde per 100 mL (a 30-index fluid is about 30% formaldehyde). Index is not the same as the diluted solution strength. Formula:
Ounces of fluid = (desired % × gallons of solution × 128) ÷ fluid index
Co-injection fluid modifies solution (wetting agents, dyes, buffers); pre-injection is used to clear the vascular bed before formaldehyde reaches it, especially with edema or gas.
Vessel selection
- Injection: right common carotid is the default; femoral is preferred for autopsied, edematous, or obese cases; axillary or brachial for restricted access.
- Drainage: right internal jugular accompanying carotid injection; femoral vein with femoral injection. Drain intermittently, not continuously, and keep the solution moving - drainage before adequate injection collapses vessels.
- Cavity treatment is separate: aspirate thorax and abdomen, then inject undiluted cavity fluid (high index) - cavity fluid is never used arterially.
Body analysis before you inject
Cause and manner of death, time since death, refrigeration history, weight, edema, decomposition, jaundice, trauma, and autopsy status all change pressure, volume, and fluid choice. Autopsied cases need lower pressure and higher index because clots are absent and leakage is high.
Safety and regulation
Formaldehyde is an OSHA-regulated carcinogen: 0.75 ppm 8-hour TWA, 2 ppm short-term exposure limit, with monitoring and medical surveillance duties. Bloodborne pathogens rules require universal precautions, PPE, sharps handling, and disinfection; contaminated waste and instruments follow the facility's written exposure-control plan.
Worked example
You need 2 gallons of 2.0% solution from 30-index fluid. (2 × 2 × 128) ÷ 30 = 512 ÷ 30 ≈ 17 ounces of 30-index fluid, with water added to reach 2 gallons total. Reasoning: the formula converts desired strength and volume into ounces of concentrate; adding water to the final volume, not to the fluid, keeps the percentage correct. If the case is edematous, you would add co-injection and possibly a pre-injection, and drain early.
Traps that cost marks
Confusing index with diluted percentage; treating 2 ppm as the 8-hour limit; using cavity fluid in the arterial machine; over-injecting an edematous case and causing purge; and skipping cavity treatment because the arterial injection "looked good."