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VENOMOUS SNAKEBITE:
WHAT'S HOT AND WHAT'S NOT!
Robert Norris, MD, FACEP
Wilderness Medical Society
Associate
Professor,
Surgery Snowmass, Colorado
Chief, Division of Emergency Medicine
July 25, 2004
Stanford University
"Their supreme arrogance, developed over millions of years as masters of their environment, commands respect out of all
proportion to their size."
- Chris Mattison, author of Snakes of the World
I. OBJECTIVES: Following this presentation, participants will be able to:
- Identify the venomous snakes indigenous to the U.S..
- Discuss appropriate first aid measures for venomous snakebite.
- Outline the appropriate hospital management of venomous snakebites.
II. INTRODUCTION:
- Approximately 3000 snake species in the world (approximately 375 are venomous); approximately 120 species
in the U.S. (20 venomous)
- U.S. venomous snakes can be divided into two groups:
- Pitvipers (98% of bites): rattlesnakes, water moccasins and copperheads
- Elapids: coral snakes (related to cobras, mambas, etc.)
- All 48 contiguous states (except Maine) have at least one species of venomous snake; none in Hawaii or
Alaska
- Approximately 8,000 venomous snakebites reported in the U.S. each year with 10-20 deaths
- An individual has a 1:10 million chance of dying of a snakebite in the U.S.
III. IDENTIFICATION OF U.S. SNAKES:
Nonvenomous Pitvipers
Coral
Snakes
Head:
round or triangular
triangular
round
Pupils: round
elliptical
round
Facial Pits: absent
present
absent
Fangs:
none (regular teeth)
anterior, elongated,
anterior, short,
retractable
fixed
Subcaudal Scales: double row
single row
double row
Rattles:
absent
usually present in rattlesnakes absent
Color:
variable
variable, little help in ID
red/yellow/black
IV. ANATOMY:
A. Pitvipers:
1. Venom
Apparatus: Venom Gland; Compressor Glandulae Muscle; Primary Duct; Accessory
Gland; Secondary Duct; Fang Sheath; Fangs
2. Facial Pit Organs (Foveal Organs): highly sensitive, paired receptors of infrared radiation that
can detect temp. changes of < 0.2 degrees C; used to detect warm blooded prey/predators and
aim strike and may have a role in determining volume of venom injected
3. Rattles: interlocking keratin rings at tip of tail in rattlesnakes; a new rattle is added with each
shed of the skin (every 50-400 days); some are lost due to trauma
4. The
Strike: aimed primarily by facial pits; rarely strike farther than 1/2 their body length; speed
= approximately 8 feet/second
- rattlesnakes generally inject 25-75% of their venom volume when they bite humans
- can bite without injecting any venom ("dry bite")
- overall: 20% no envenomation, 30% mild, 50% moderate to severe
