NARD Diving MedicineDiving MD

Snake Bites

An estimated 7,000 poisonous snake bites occur in the United States each year, and of these Texas leads the nation in occurrence. Texas doctors treat approximately 1,500 bites a year with the Diamondback Rattlesnake accounting for 2/3 of these, followed by the Copperhead, and then the Cottonmouth. All of the poisonous snakes, save one (the Coral snake belonging to the Elapidae family), belong to the family Crotalidae (pit vipers). This family as a whole have a highly developed venom apparatus consisting of large hollow, movable fangs located at the front of the upper jaw. When striking, these fangs swing forward from a folded position, stabbing and envenomateing in a rapid thrust. One must be very careful when trying to distinguish the various species. The diamond back is not only the most prevalent poisonous snake, but can be found in almost every color of the rainbow. The best indicators for species identification are the most prominent characteristics.

When attempting to identify a snake, the presence of a rattle should be the first thing looked for. All rattlesnakes, regardless of age, will have some semblance of a rattle. If it had been forcibly removed, the tail will appear stubby. The jaw of these genera will open to almost 180o so that a perpendicular ankle to the striking surface can be achieved. After opening the mouth, two fangs will be noted protruding from the maxilla, folded back, and encased in a soft tissue sheath. Both fangs will be easily mobil, and about 1 cm in length. The soft tissue sheath may be pulled back and the fang examined for a small hole at its distal end giving it a resemblance to a hypodermic needle.

A modified salivary gland acts as the venom apparatus, and can hold up to 1.5 ml of venom. With an average bite, about 11% of the venom is injected, but on very rare occasions up to 50% has been extruded. Clinical findings also show that in 15-30% of snakebite victims, no envenomation took place.

Listed below are the general characteristics of the members of the Crotalidae family found in the United States. Remember that if it has a rattle it is poisonous, if not you have to look a little closer.

DIAMONDBACK RATTLESNAKE (Crotalus atrox) This snake is best noted for its distinct alternating black and white rings on its tail, just above the rattle. A light stripe behind the eye reaches the lip in the front corner of the mouth. The diamond shaped pattern is not clear cut and distinct. The snake may appear speckled. The diamondback is responsible for most of the poisonous snake bites. It is a large aggressive pit viper that can exceed 6 feet in length.

CANEBRAKE RATTLESNAKE (Crotalus horridus atricaudatus) Looks similar to the diamondback but is characterized by a reddish-brown stripe running down its spine. This stripe divides the black dorsal spots in half. The record size for this snake is 6 feet 2 inches at 26 pounds.

PYGMY RATTLESNAKE (Sistrurus miliarius streckeri) A small viper that is rarely over 2 feet in length and distinguished by a reddish dorsal stripe along the spine, from head to tail. The general color of the snake is gray to grayish-brown with small dark spots running the entire length of the body. Its rattle is very tiny and usually not audible to human ears. Its favorite habitat is marshes and swampland. It is an irritable, aggressive snake that is quick to strike whatever disturbs it.

SOUTHERN COPPERHEAD (Agkistrodon contortrix) The most common copperhead encountered on the upper Gulf coast is the southern copperhead. This snake is lighter in color to other varieties of copperhead and has narrow hourglass markings across its back. Its body color is light brown or tan with a pinkish tinge. The head of the snake is the color of a brand new penny just after shedding its skin. The average adult length is between 20 to 36 inches.

COTTONMOUTH - WATER MOCCASIN (Agkistrodon piscivorus leucostoma) A large heavy, semi-aquatic snake being one of the deadliest in North America. The head of the cottonmouth is a large, flat and triangular in shape. There are great variations in the coloring of this snake. It is usually dark brown with 10 to 15 irregularly edged crossbands. Some specimens have well defined crossbands while others show no regular patterns. Other color variations are from black to olive green. The underside of the snake is lighter on the top. Juvenile forms are vividly marked with dark brown bands edged in white with a gray background or body. The inside of its mouth is snow white, thus its name is derived.

Because of the heterogeneous composition of the venoms it is difficult to classify as hematoxic, neurotoxic, or hemorrhagic however they can exert primary toxic and lethal effects upon hemopoietic, cardiovascular, respiratory or nervous systems. The exact components of this family's venom is unknown, but some components have been isolated and studied in detail. The lethal fractions appear to be closely related to its non-enzymatic components. The spreading factor is hyaluronidase, which can hydrolyze the hyaluronic acid gel of the tissue matrix allowing other enzymatic fractions to penetrate further into the tissue space. Trypsin like enzymes called proteinase cause tissue damage by breaking down the protein chains. The venom also produces an anticoagulant effect due to the proteolytic disintegration of fibrinogen

The usual clinical findings are, continuous oozing and bleeding from the injection site, profound anemia, profuse tissue damage with necrosis, and shock. The shock seen is not only from the derangement of the clotting mechanisms but also due to morphological changes in the erythrocytes, thrombocytes and the blood vessels. Pit viper venom causes profound changes in the hemopoietic system resulting in burring phenomenon. Burring phenomenon is the altering of the appearance of the erythrocyte from its normal bicave disk to that of a mulberry. This morphological change can be induced by trace amounts of venom and is considered a useful sign in quantitating the amount of envenomation. The extent of coagulatory derangement involves the entire spectrum of clotting factors and depends upon the amount of venom injected.

Primary toxic effect on the heart and CNS is limited. Cardiac and neural dysfunctions observed in patients are thought to be the result of hemorrhagic diathesis. The victim's prime problem is hypovolemic shock brought on by changes in RBC morphology, loss of capillary structural integrity and loss of intravascular fluids into the extra vascular space.

After envenomation the victim will feel local intense pain, followed by swelling, which progresses over time. Excessive swelling of tissue in a closed compartment may compromise circulation, producing compartment syndrome. Assess pulses, and watch for cyanosis frequently. In severe poisoning the pain may be minimal or completely absent. Ecchymosis and erythema develops, and with the fang marks, make the diagnosis of snakebite. In time the victim will have paresthesia and hypersthesia with some local anesthesia at the bite area.

Systemic manifestations are variable with clinical signs of fright difficult to distinguish from actual systemic poisoning. Findings of hemoptysis, hemoglobinuria and failure for the blood to clot in a test tube or at the wound site with burring phenomena indicate significant envenomation. In extreme cases toxic delirium associated with convulsions, coma and death may occur.

Secondary complications of tissue necrosis is common after the initial crisis. This necrosis can be so extensive that amputation of the extremity or extensive debridement may be necessary.

A grading system for the severity of pit viper bites has been established for the purpose of treatment. This classification divides the systemic manifestations into 4 grades. Note that no grading system is perfect and with time, clinical manifestations change requiring grading changes.

GRADE I: Minimal Envenomation. No general symptoms or systemic involvement. Fang or tooth marks are apparent. Moderate to severe pain is present. Edema and erythema from 1 to 5 inches in diameter is present during the initial 12 hours.

GRADE II: Moderate Envenomation. Systemic involvement possible with s/sx of severe local pain, nausea, vomiting, giddiness, low-grade fever, palpable lymph nodes. Edema and erythema 6 to 12 inches is present during first 12 hours.

GRADE III: Severe Envenomation. Systemic involvement is frequently present with s/sx severe pain, tachycardia, thready pulse, hypothermia, ecchymosis and generalized petechia. Rapid onset of shock. Edema and erythema is >12 inches.

GRADE IV: Extremely Severe Envenomation. Systemic involvement apparent with blood tinged secretions, renal shutdown, coma and death. Multiple bites are frequently present. Edema is widespread and may include the trunk ipsilateral to the involved extremity.

Treatment of any victim of snakebite can be quite a task, even when the snake was harmless, due to the fact that many people panic. Remember to use a systematic approach following these guidelines for initial treatment of any snakebite:

Calm the victim down. Keep in mind that their mental attitude can either help or hinder treatment efforts. Panicky persons tend to move around and hyperventilate, which can increase blood flow through the affected area and slow definitive therapy by having to treat the self induced dyspnea.

Identify the snake. Whenever possible bring in the snake, even if it is in pieces. It is better to know what type of victim you have than trying to guess.

Look for fang marks. Identifying fang marks can distinguish snakebite from other pain producing stings or bites.

Immobilize the involved part. Immobilization is best done with simple splints instead of frac-pac splints or air splints, because they allow access to the bite area without splint removal.

Apply a lymphatic tourniquet above the bite site. The easiest lymphatic tourniquet is a blood pressure cuff. To apply, feel the pulse distal to the bite and pump up the cuff until it is no longer felt, then release the pressure until the pulse returns. If the bite is in an area too large to allow use of a blood pressure cuff, then use an ace wrap, applied as a pressure bandage. Keep in mind the edema is rapid, and large, so distal pulses must be assessed frequently. Any applied tourniquet must be adjusted when pulses weaken or disappear.

Clean the wound with copious amounts of irrigating fluid.

Intermittent hypothermia for short periods of time (15 to 30) minutes should be produced by packing the injured site in ice. The involved area should not be submerged in ice water. Care must be taken to avoid frostbite.

Large bore IV LR to blood pressure
Grade the bite using the snakebite grading system.

Sometimes incisions that includes the fang marks is made and suction is applied. If this is to be done the incision must not exceed ½ inch in length, or more than a 1/4 inch deep. Suction should be done by suction cups, and continued for at least 30 minutes. Never do oral suction on a snakebite! This procedure must be done within the initial 15 minutes of envenomation or it is of no value.

The mainstay of treatment is the intravenous administration of antivenin. Antivenin is recommended for bites from the Crotalus, Sistrurus, and Agkistrodon genera (rattlesnakes, cottonmouths, and copperheads). It must be noted that the antivenin is prepared by hyperimmunizing horses and a possible hypersensitivity reaction to the horse serum may occur. There is a new Antivenin replacing the old that has no hypersensitivity reaction recorded at this time. Note also that a hypersensitivity skin test is not reliable in the presence of shock.

The recommended dose varies with the grade of manifestation as follows:

Grade I (mild): 1 vial

Grade II (moderate): 2 to 4 vials

Grade III (severe): 5 to 10 vials

Grade IV (extremely severe): 10 to 20 vials.

There is a new Antivenin  is an All or None Medicine Consult Your Local Poison Control on All Antivenin!

The patient should not be given anything by mouth for the first 24 to 48 hours due to the possibility of nausea and vomiting. An analgesic should be given to assure patient comfort.

CORAL SNAKE (Micrurus fulvius tenere) The coral snake is North America's representative of the Elapidae family, which has such infamous members as the cobra and mamba. The coral snake is a worthy member of this family having a venom much more poisonous than any of the pit vipers. This family is characterized by rigid, short, grooved fangs located near the front of the mouth.

The coral snake is a small deadly snake with a characteristic ring pattern of red, yellow, black, red, yellow, black, in regular order, encircling its entire body. There are several non-venomous snakes that greatly resemble the coral snake, but only the coral snake has a ring of red touching a ring of yellow. This brought about the old pioneer saying of "red on yellow kill the fellow" or "red on black venom lack".

The fangs of this snake are different in that they are short, immovable, and in multiple pairs located at the very end of the upper jaw. The coral snake is less than 2.5 feet long and a body diameter of about a half inch.

Even though this colorful snake is nonaggressive, and shy, it is one of the deadliest of snakes. For envenomation to occur the snake must use a chewing motion, and due to its small size it has limited jaw excursion. This means two things, first the victim knows when he is bitten, and second most bites occur in the webbing of the hand, between the thumb and index finger.

The venom of the coral snake is considerably more poisonous than that of pit vipers and is primarily a neurotoxin, however hemolysis, hemorrhage, tissue necrosis, burring phenomena and reactive vasomotor reaction is also seen. The neurotoxicity of the venom has a curare-like blockage of the neuromuscular transmitter resulting in paralysis and respiratory arrest.

Immediately following the bite one or more tiny punctures will be observed. Pain is usually very mild and swelling of the area is minimal. The wound resembles a superficial scratch. Systemic manifestations of poisoning is often delayed and complaints of apprehension, giddiness, nausea, vomiting, excessive salivation, and a sense of euphoria is quite common, appearing 1 to 7 hours post bite. The signs of neurotoxicity is manifested as paralysis of the cranial nerves followed by phrenic nerve paralysis. Hematologic toxicity induced by the coral snake is similar, though less extensive, to the pit viper. The main cause of death is respiratory arrest although the sensorium is clear as long as respirations are maintained

Immediate treatment is the same as for any other snakebite:

Calm the victim down.

Identify the snake.

Look for fang marks.

Immobilize the involved part.

Apply a lymphatic tourniquet above the bite site.

Clean the wound with copious amounts of irrigating fluid.

Intermittent hypothermia for short periods.

The administration of Coral Snake Antivenin (Wyeth Labs) should be given as soon as possible due to the neurotoxicity of the venom. The exact amount is governed by the severity of envenomation and the clinical manifestations. If mild to moderate use 2 to 8 vials and when sever use 8 to 12 vials; repeat the dose every 4 to 6 hours until the victim recovers. Crotalidae Antivenin (used with rattlesnakes) or Polyvalent Cobra Antivenin are not effective against the coral snake and should never be given. As with the Crotalidae Antivenin the coral snake variety comes from horses so the same precautions apply.

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