Forensic Medicine: PMI Estimation (Henssge, Newton, Vitreous K+)

This set drills the quantitative and semi-quantitative methods used to estimate post-mortem interval (PMI) in forensic medicine. Newton's Law of Cooling underpins algor mortis-based estimation: rectal temperature falls from 37 degrees Celsius toward ambient at a rate governed by body mass, clothing, and environmental conditions, and the Henssge nomogram (1988, Forensic Science International) converts rectal temperature, ambient temperature, and body weight into a 95%% confidence interval for PMI, with body-weight correction factors (Cf) for clothing, substrate, and air movement. Vitreous humour potassium (K+) rises post mortem through ion-pump failure, and the Madea formula (PMI in hours = 5.26 x [K+] mmol/L minus 30.9) provides a chemical PMI estimate usable up to 120 hours, with a coefficient of variation of roughly plus or minus 15 hours. Gastric emptying (2 to 6 hours for a mixed meal) frames last-meal timing. Rigor mortis passes through onset, full rigidity, and resolution in 8 to 36 hours in temperate conditions; Indian tropical heat compresses this cycle significantly. Livor mortis becomes fixed (non-blanchable) between 8 and 12 hours, providing a body-position marker. Putrefaction begins at the right iliac fossa within 24 to 48 hours in Indian summer climates. Adipocere and mummification are long-PMI markers seen in weeks to months. Entomological PMI uses accumulated degree days (ADD) on blowfly life-cycle tables. BNSS 2023 Section 194 (replacing CrPC Section 174) governs inquest procedure and PM timing.

Aimed at UGC-NET Forensic Science Paper II candidates targeting Unit X (Forensic Medicine), AIIMS Delhi and NFSU MSc students, MBBS candidates preparing for legal medicine, and CFSL and state medico-legal officers.

Topics covered:

• Newton's Law of Cooling and algor mortis: rectal temperature fall rate and influencing factors
• Henssge nomogram 1988: body weight, rectal and ambient temperature, correction factor Cf
• Vitreous K+ Madea formula: PMI = 5.26 x [K+] minus 30.9, range and error margins
• Gastric emptying as a PMI clock: 2-6 hours and forensic caveats
• Rigor mortis timeline in Indian climate: compressed cycle in tropical heat
• Livor mortis fixation: 8-12 hours and body-position change detection
• Putrefaction onset at right iliac fossa: 24-48 hours
• Adipocere and mummification: long-interval PMI markers
• Entomological PMI: accumulated degree days (ADD) method
• BNSS 2023 Section 194 inquest procedure and PM timing

Allow 30 minutes.