Snakes Bites and Venom (Schlangenbisse etc)How Dangerous Is A Snakebite ?
A snakebite is usually not dangerous , unless it involves one of the more than two hundred species that produce a potent venom like the Sea Snake
. Every day , people are bitten by nonvenomous snakes and experience only the slight discomfort caused by the snake’s teeth puncturing or scratching the skin .Of course , such wounds may be painful if the snake has long teeth , such as those of a python or large ratsnake , but serious effects are rare . Bites by nonvenomous species can be treated by washing the wound and applying an antiseptic to the punctures or scratches . Bites by venomous snakes require medical treatment . If untreated , a venomous bite may result in serious tissue or organ damage and even death . Serious secondary bacterial infections , such as gas gangrene and tetanus , may also follow venomous snakebites , and loss of a limb , finger , or toe is not uncommon . A nonvenomous snakebite usually involves several puncture marks of equal depth ; that of a venomous snake is characterized by one or two larger and deeper punctures among more shallow marks . However , tooth marks are not a reliable method for identifying the potential danger of a snakebite .
If the snake is venomous , discomfort is usually felt within a few minutes . a burning sensation or pulsating pain is often accompanied by swelling or discoloration of the tissues surrounding the wound . Such localized
discomfort is particularly particularly characteristic of hemotoxic envenomation by pitvipers and true vipers , but moderate to severe local pain may also accompany neurotoxic bites of some elapids .
Medical
treatment should be obtained for all elapid bites , even when there is no pain . Serious elapid bites are not usually apparent , since immediate pain does not always occur . A characteristic early sign of a serious neurotoxic
elapid bite is drooping eyelids , followed by difficulty in swallowing , slurred speech , severe thirst , vertigo , and difficulty in breathing . Later , blood pressure often drops , and cardiac arrest may occur .
The most
extensive study , published nearly fifty years ago , estimated that 300,000 venomous snakebites occurred throughout the world each year , almost 40,000 of which resulted death . More recent coordinated data is unavailable . The
rate of death from snakebite is highest in developing nations with extensive natural snake habitat and scarce medical facilities , and lowest in developed nations with plentiful medical facilities .
The more natural the
habitat , the greater the chance of encountering a venomous snake . On the Indian subcontinent , about 7,000 to 15,000 people died annually of snakebite from 1940 to 1949 , a probable mortality rate of about four deaths per 100,000
people . The most frequent culprits were the various kraits (Bungarus) , cobras (Naja , Ophiophagus) , saw-scaled vipers (Echis) , and the Russel’s viper (Vipera russelii) . In Brazil 2,000 to 4,800 persons died annually of
snakebite between1929 and 1949 , mostly due to the bites of the tropical rattlesnake (Crotalus durissus) and various large species of lanceheads (Bothrops) . In the United States , by contrast , only 10 to 20 persons died of
snakebite each year from 1944 to 1950 , or fewer than 0.2 per 100,000 people . Over 90% of these fatal bites were attributed to the cottonmouth (Agkistrodon piscivrus) , western rattlesnake (Crotalus viridis) , and eastern and
western diamondback rattlesnakes (C . adamanteus , C .atrox) . In 1957 and 1966 , H . M . Parrish reported 6,000 to 7,000 annual envenomations by snakes in the United States , causing 14 to 15 deaths . In Canada fewer than fifteen
people died of snakebite during the period 1944-1948 , and in Europe the death rate from all venomous animal bites was less than 0.5 per 100,000 people .
Today , snakebite mortality worldwide is probably about 50% of what
it was when the preceding data were compiled . Modern medical treatment has improved survivorship , and treatment is more widely available . Between 1965 and 1971 , for instance , only 18 of 5,387 venomous snakebites in Malaysia
and 191 of 14,578 in Thailand were fatal .
How Do You Avoid Snakebites?
Do not handle venomous snakes . In Europe and North America , most
snakebites occur when the victim is either holding a snake or attempting to pick up or kill it .
Never play with venomous snakes . Remain at a safe distance-no nearer than two snake body lengths-from the snake .
Do
not pick up a “dead” snake ! It may only be injured , stunned , or playing dead . Even with a truly dead snake , reflex action can cause the jaws to open and close .A fatal envenomation from the decapitated head of a canebrake
rattlesnake (Crotalus horridus atricaudatus) has been reported .
Bites from unseen snakes in the wild may be prevented by common sense and proper dress . Boots and coarse long trousers should be worn in such areas . Most
bites that occur in the wild are on the extremities . Do not put your hands or feet in places that you have not visually examined first . At night , one’s path should always be lighted to make snakes visible , since many venomous
snakes are nocturnal .
If Bitten What Next?
A person bitten by a venomous snake should be taken to a hospital immediately . The traditional cut-and
suck first-aid methods for snakebite are now subject to serious doubt . Because they involve cutting and constriction of blood flow , they can do more harm than good . Self-treatment is likely to worsen an already serious condition
.
Before arriving at the hospital , (1) keep the patient as calm and still as possible ; (2) immobilize the bitten limb , using a splint if possible and positioning below the level of the heart ; (3) do not perform such
traditional measures as cooling with ice , applying a tourniquet , cutting and sucking , giving alcohol or aspirin , pouring turpentine onto the wound , and the like ; and (4) if the bite is that of a neurotoxic snake , wrap the
limb in a pressure bandage to localize the venom (a measure that has proven effective for bites of Australian elapids) . Whenever possible , the snake responsible for the bite should be brought to the medical facility for purposes
of identification . It is better to avoid a second bite , however , if the snake is difficult to capture . And neither capture nor first-aid measures should delay transport of the patient to a hospital .
At the hospital ,
encourage the medical staff to call a poison-control center for expert advice on snakebite treatment . Because snakebites are uncommon in the United States , few medical personnel have experience in treating them . Generally
speaking , the recommended course of action is to observe the patient to determine the extent of envenomation . Venomous snakes can strike and bite entirely in defense without injecting venom . Such “dry” bites account for 20 to
40% of all snakebites .
The patient is typically observed for at least eight hours , because the onset of some symptoms (particularly those of neurotoxic venom) may occur hours after the bite . Like all puncture wounds ,
bites must be thoroughly cleaned , and antitetanus serum and a broad-spectrum antibiotic are often recommended .
Antivenom is the only specific treatment for envenomation , and it should be given only to persons with
symptoms or signs of envenomation . Antivenom should be administered only in a medical facility and only by a health-care specialist . The patient must first be tested for hypersensivity to horse serum , since antivenom derives
from purified horse blood .In the United States , an anti-crotalid antivenom produced by Wyeth-Ayerst Laboratories is used for patients exhibiting hemotixic effects .
Antivenoms are developed for specific venomous snakes .
Thus a European antivenom would not neutralize the toxin of North American pitvipers , because it was developed for different vipers . The Wyeth-Ayerst anti-crotalid polyvalent antivenom also includes antibodies to the neurotoxic
rattlesnakes , and may be used for bites by the Mojave rattlesnake (Crotlaus scutulatus) . Symptomatic coralsnake (Micruroides , Micrurus) envenomation should be treated with North American coralsnake antivenom , also produced by
Wyeth-Ayerst Laboratories .
Treatments
Venoms And Clinical Manifestations
: Snake venoms are complex mixtures of enzymes, low-molecular-weight polypeptides, glycoproteins, and metal ions. The enzymes and polypeptides affect the human body in a multisystem fashion. Among the deleterious components are hemorrhagins that render the vasculature leaky and thus cause both local and systemic bleeding; various proteolytic enzymes that cause local tissue necrosis, affect the coagulation pathway at various steps, or impair organ function; myocardial depressant factors that reduce cardiac output; and neurotoxins that act either pre- or postsynaptically to inhibit peripheral nerve impulses. Most snake venoms can adversely affect multiple organs.
Treatment (Field Management)
: First-aid or "field" measures to be used in the management of venomous snakebite should focus on delivery of the victim to definitive medical care as quickly as possible; the victim should be as inactive as is feasible to limit systemic spread of the venom. Beyond this, any measure employed should at least do no further harm.
After viperid bites, local mechanical suction may be beneficial if applied to the puncture wounds within 3 to 5 min. A useful device is the Extractor (Sawyer Products, Safety Harbor, FL), which delivers one atmosphere of
negative pressure to the wound. Suction should be continued for at least 30 min. Mouth suction should be avoided as it inoculates the wound with oral flora and theoretically can also result in the absorption of venom by the rescuer
through lesions of the upper digestive tract. A proximal lymphatic-occlusive constriction band may limit the spread of venom if applied within 30 min. To avoid compounding of tissue necrosis, however, the band should not be allowed
to interrupt arterial flow. A bitten extremity should be splinted if possible and kept at approximately heart level. Incisions into the bite site should never be made, and no form of cooling or electric shock is advantageous.
For elapid or sea snake bites, the Australian pressure-immobilization technique, in which the entire bitten extremity is wrapped with an elastic or crepe bandage and then splinted, is highly beneficial. The bandage is applied
as tightly as it would be to treat a sprained ankle. This technique greatly restricts the absorption and circulation of venom from the bite site. However, an assessment of the potential utility of this method in viperid poisoning
requires further research, as it may compound local tissue damage following these bites.
Treatment (Hospital Management)
: Once in the hospital, the victim should be closely monitored (vital signs, cardiac rhythm, and oxygen saturation) while a history is quickly obtained and a brief but thorough physical examination is performed. The level of erythema/swelling in a bitten extremity should be marked and the circumferences measured in several locations every 15 min until swelling has stabilized. Large-bore intravenous access in unaffected extremities should be obtained in the event that hypotension develops. Early hypotension is due to pooling of blood in the pulmonary and splanchnic vascular beds; hours later, hemolysis and loss of intravascular volume into soft tissues may play important roles. Fluid resuscitation with normal saline or Ringer's lactate should be initiated for clinical shock. If the blood pressure response is inadequate after the administration of 20 to 40 mL/kg body weight, then a trial of 5% albumin (10 to 20 mL/kg) is in order. If volume resuscitation fails to improve tissue perfusion, vasopressors (e.g., dopamine) should be administered. Invasive hemodynamic monitoring (central venous and/or pulmonary arterial pressures) can be helpful in such cases. Central access must be obtained with extra caution if coagulopathy is evident.
Blood should be drawn for laboratory evaluation (including determination of blood type and cross-matching) as soon as possible, before the effects of circulating venom interfere with typing. Also important are a complete
blood count to evaluate the degree of hemorrhage or hemolysis, studies of renal and hepatic function, coagulation studies to identify signs of consumptive coagulopathy, and testing of urine for blood or myoglobin. In severe cases
or in the face of significant comorbidity, arterial blood gas studies, electrocardiography, and chest radiography may be necessary.
Attempts to locate a source of appropriate antivenin should begin early in all cases of
known venomous snakebite, regardless of symptoms. If signs or symptoms develop, they may progress rapidly, making any delay in the administration of antivenin dangerous for the victim. Antivenins rarely offer cross-protection
against snake species other than those used in their production unless the species are closely related. An example of good cross-protection is in the use of Australian tiger snake (Notechis scutatus) antivenin for sea snake bites
(see below). The package insert accompanying a particular antivenin should be consulted for information regarding the spectrum of coverage. In the United States, assistance in finding antivenin can be obtained 24 hours a day from
the University of Arizona Poison and Drug Information Center (520-626-6016).
Rapidly progressive and severe local findings (soft tissue swelling, ecchymosis, petechiae, etc.) or manifestations of systemic toxicity (signs
and symptoms or laboratory abnormalities), are indications for the administration of intravenous antivenin. The package insert outlines techniques for reconstitution of antivenin (when necessary), skin-testing procedures (for
potential allergy), and appropriate starting doses. Most antivenins are of equine origin and carry a risk of anaphylactic, anaphylactoid, and delayed-hypersensitivity reactions. Skin testing does not always reliably predict which
patients will have an allergic reaction to equine antivenin; a skin test can be either false negative or false positive. Before antivenin infusion, the patient should receive appropriate loading doses of intravenous antihistamines
(e.g., diphenhydramine, 1 mg/kg to a maximum of 100 mg; and cimetidine, 5 to 10 mg/kg to a maximum of 300 mg) in an effort to limit acute reactions. Expanding the patient's intravascular volume with crystalloids may also be
beneficial in this regard (unless contraindicated by the patient's cardiac status). Epinephrine should be immediately available, and the antivenin dose to be administered should be diluted (e.g., in 1000 mL of normal saline,
Ringer's lactate, or 5% dextrose in water for adults or in 20 mL/kg for children). This volume can be decreased if necessary for the treatment of patients with compromised cardiovascular reserve. The antivenin infusion should be
started slowly, with the physician at the bedside to intervene in the event of an acute reaction. The rate of infusion can be increased gradually in the absence of allergic phenomena until the total starting dose has been
administered (over a period of 1 to 4 h). Further antivenin may be necessary if clinical abnormalities worsen. Laboratory values should be rechecked hourly, particularly if abnormal, until stability is ensured.
The
management of a life-threatening envenomation in a victim with an apparent allergy to antivenin requires significant expertise. Consultation with a poison specialist, an intensive care specialist, or an allergist is recommended.
Often, antivenin can still be administered in these situations under closely controlled conditions and with intensive premedication (e.g., with epinephrine, antihistamines, and steroids).
Care of the bite wound should
include application of a dry sterile dressing and splinting of the extremity with padding between the digits. Because of the risk of central spread of venom, an extremity should be elevated only when antivenin is available. Tetanus
immunization should be updated as appropriate. The use of prophylactic antibiotics is controversial, as the incidence of secondary infection following venomous snakebite appears to be low. Many authorities, however, prescribe a
broad-spectrum antibiotic (such as ampicillin or a cephalosporin) for the first few days.
If swelling in the bitten extremity raises concern that subfascial muscle edema may be impeding tissue perfusion (muscle-compartment
syndrome), intracompartmental pressures should be checked watched for at least 6 to 8 h before discharge. An occasional viperid "dry" bite progresses to significant toxicity after a delay of several hours, and the onset
of systemic symptoms is commonly delayed for a number of hours after bites by several of the elapids (especially the coral snakes) and sea snakes. Patients bitten by these reptiles should be observed in the hospital for 24 h.
Morbidity And Mortality
: The overall mortality rates for venomous snakebite are low in areas of the world with rapid access to medical care and appropriate antivenin. In the United States, for example, the mortality rate is 1 percent for victims who receive antivenin. Eastern and western diamondback rattlesnakes (Crotalus adamanteus and Crotalus atrox, respectively) are responsible for most snakebite deaths in the United States. Snakes responsible for large numbers of deaths in other regions of the world include the cobras (Naja species) of Asia and Africa, the carpet and saw-scaled vipers of the Middle East and Africa (Echis species), Russell's viper (Vipera russelli) of the Middle East and Asia, the large African vipers (Bitis species), and the lancehead pit vipers of Central and South America (Bothrops species).
The incidence of morbidity in terms of permanent functional loss in a bitten extremity is difficult to estimate but is probably substantial. Such loss may be due to muscle, nerve, or vascular injury or to scar contracture.
In the United States, such loss due to snakebite tends to be much more common and severe after rattlesnake bites than after bites by copperheads or water moccasins.
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