Hydrocyanic acid: HCN (pruss,cyanogen or scheele’s acid)

Introduction

• HCN is  a vegetable  acid found  in  fruits  and leaves  of almonds,  apricots,  cherry  pear, plum etc  in  the  form  of  amygdalin
• Enzyme emulsion convert it to cyanide in presence of bacteria of small intestine.
• Young linseed plants yields free HCN.
• Cyanide  inhibits  cellular  respiration by inhibiting  cytochrome  oxidase, hence  oxygen cannot  be utilized  by  cells.  
• Death  is  due to  histotoxic  (cytotoxic)  anoxia.
• HCN is  less  effective  if  kept  too  long  or if  patient  has  achlorhydria

Fatal dose of HCN can be shown as follows:

1. HCN gas: 100-200 ppm in air
2. HCN liquid: 50-60 mg.
3. KCN,NaCN: 150-300 mg

However recovery has been recorded with far larger doses of upto 2.4g of  potassum cyanide.

Postmortem appearance:

Externally

• Characteristic smell  of bitter  almond at  nose and mouth
• Cherry  red or pinkish  red or  bright  red postmortem  lividity.
• Fine  froth  at  mouth.
• Bright, glistening  and  prominent  eyes  with  dilated  pupil.

 Internally

• Characteristic smell  of bitter  almonds  in  stomach  and serous  cavities.
• Mucous  membranes  of  stomach,  intestine  and other  viscera  are  congested  and red
• veins  appear  pink as  all  contain  oxygenated  blood.
• oxygenation of tissues  by  cyanide  leads to  formation  of cyanmethaemoglobin.
• Ingested potassium  cyanide  shows  corrosion  of  the  mouth  and reddening  of  gastric  mucus  membrane erosions  and. haemorrhages  in walls of  stomach  and altered  blood  in  its  humen.

Treatment:

1. Nitrites (amylnitrite or sodium nitrite) are given to convert hemoglobin to methemoglobin)
2. This then  forms  cyanmethemoglobin  by  combining  with  cyanide.
3. amyl nitrite by inhalation, are all effective in reversing the lethal effects of cyanide poisoning.
4. 0.3 mL ampule crushed and contents poured onto a gauze and placed in front of patient’s mouth or endotracheal tube.
5. DMAP and hydroxylamine hydrochloride are effective when given by the intramuscular route.
6. Sodium  thiosulphate  is  given  to  convert  cyanomethemoglobin  into  sodium  thiocyanate,  which  is  excreted  in  urine.
7. PAPP(para-amino-propio-phenone),dicobalt EDTA (chelatecyanide) and hydroxycobalamine (B₁₂).

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