Snake bite

Introduction
In Sri Lanka most dangerous venomous snakes are Sri Lankan Krait, Saw scaled viper, Russel's Viper, Humped nose pit viper, Cobra, Green pit viper

Poisonous snakes inject venom using modified salivary glands. During envenomation (the bite that injects venom or poison), the venom passes from the venom gland through a duct into the snake's fangs, and finally into its prey. Not all bites lead to envenomation. Snakes can regulate whether to release venom and how much to release.  Snake venom is a combination of numerous substances with varying effects. (Emedicinehealthcom, 2015)
These proteins can be divided into 4 categories:

1. Cytotoxins cause local tissue damage.
2. Hemotoxins cause intrnal bleeding.
3. Neurotoxins affect the nervous system.
4. Cardiotoxins act directly on the heart.

Presentation
Signs & symptoms

·         Local effects: These are the effects on the local skin and tissue surrounding the bite area. Bites by vipers and some cobras (Naja and other genera) are painful and tender. They can be severely swollen and can bleed and blister. Some cobra venoms can also kill the tissue around the site of the bite.

·         Bleeding: Bites by vipers and some Australian elapids can cause changes in the victim's hematologic system causing bleeding. this bleeding can be localized or diffuse. Internal organs can be involved. A victim may bleed from the bite site or bleed spontaneously from the mouth or old wounds. Unchecked bleeding can cause shock or even death.

·         Nervous system effects: The effect on the nervous system can be experienced locally close to the bite area or affect the nervous system directly. Venom from elapids and sea snakes can affect the nervous system directly. Cobra (Naja and other genera) and mamba (Dendroaspis) venom can act particularly quickly by stopping the breathing muscles, resulting in death without treatment. Initially, victims may have vision problems, speaking and breathing trouble, and numbness close to or distant to the bite site.

·         Muscle death: Venom from Russell's vipers (Daboia russellii), sea snakes, and some Australian elapids can directly cause muscle death in multiple areas of the body. There can be local effect of muscle death (necrosis), or distant muscle involvement (rhabdomyolysis). The debris from dead muscle cells can clog the kidneys, which try to filter out the proteins. This can lead to kidney failure.

·         Eyes: Spitting cobras and ringhals (cobralike snakes from Africa) can actually eject their venom quite accurately into the eyes of their victims, resulting in direct eye pain and damage. (Emedicinehealthcom, 2015)

Investigations

• Bloods:
  • Full blood count
  • Clotting studies
  • Fibrinogen and fibrinogen degradation products
  • Blood crossmatching
  • Routine blood biochemistry
  • Urinalysis 
  • Blood gases (where there are systemic symptoms or signs)
• Other investigations:
  • Standard chest X-ray if indicated
  • Wound X-ray for retained teeth/fangs
  • The enzyme-linked immunosorbent assay (ELISA)-based rapid Snake Venom Detection Kit (SVDK) is available in Australia It can be used for clinically significant snakebites with a swab of the bite site or even urine to identify which antivenom is appropriate.

First Aid for Snake Bites

·         Keep the victim calm and still. Movement can cause the venom to move more quickly through the body. Consider making a splint to restrict the movement of the affected area.

·         Remove constricting clothing or jewelry. The area of the bite will likely swell, so it is important to remove these items quickly.

·         Carry or transport the victim by vehicle. This person should not be allowed to walk.

·         If the snake is dead, take it with you for identification. Do not waste time hunting it down, though.

There are also several outdated first aid techniques that are now believed to be unhelpful or even harmful.

 Do not do any of the following:

·         Do not use a tourniquet.

·         Do not cut into the snake bite.

·         Do not use a cold compress on the bite.

·         Do not give the victim any medications unless directed by a doctor.

·         Do not raise the area of the bite above the victim’s heart.

·         Do not attempt to suck the venom out by mouth.

·         Do not use a pump suction device. While these devices were formerly recommended for pumping out snake venom, it is now believed that they are more likely to do harm than good.

Management

Observation of all patients for local swelling (at least 2 hours). Patients who are asymptomatic with no evidence of swelling after 2 hours may be discharged; all others must be admitted for observation.

Wound care:

Clean the bite site and splint the limb.

Give anti-tetanus prophylaxis as required.

General care:

Monitor pulse, blood pressure and respiration (every 15 minutes).

Apply cardiac monitor to look for arrhythmias.

Ensure adequate hydration.

Achieve intravenous access.

Drug therapy.
Give anti venom serum (AVS) 

Supportive and symptomatic therapy should be provided as necessary:

Hypotension: treat with colloid infusion.

Angioneurotic edema: use antihistamines, prednisolone, adrenaline, depending on severity.

Nausea and vomiting: use antiemetics.

Pain: give simple analgesia. (Emedicinehealthcom, 2015)

References

Emedicinehealthcom. 2015. EMedicineHealth. [Online]. [29 April 2015]. Available from: http://www.emedicinehealth.com/snakebite/page3_em.htm

Emedicinehealthcom. 2015. EMedicineHealth. [Online]. [6 May 2015]. Available from: http://www.emedicinehealth.com/snakebite/article_em.htm

Emedicinehealthcom. 2015. EMedicineHealth. [Online]. [6 May 2015]. Available from: http://www.emedicinehealth.com/snakebite/page7_em.htm