Environmental 6:
Snake Bite Portal
Introduction
According
to the Centers for Disease Control and Prevention (CDC), an estimated
7000 to 8000 people per year are bitten by snakes in the United States,
and 5 of those die.1 Types of venomous snakes
include rattlesnakes
(found across the country), copperheads (found in the eastern states
and as far west as Texas), cottonmouths/water moccasins (found in
wetland areas, rivers, and lakes in the southeast), and coral snakes
(found in wooded, sandy, or marshy areas of the south). The most
prevalent family of venomous snakes is Crotalidae, which
includes
rattlesnakes, water moccasins, and copperheads. These are commonly
referred to as pit vipers. The venom from pit viper bites causes local
and systemic effects whereas the venom from coral snake bites is a
powerful neurotoxin that paralyzes the breathing muscles.
Initial
Evaluation
Upon
the patient’s arrival, contact your local or regional Poison Control
center, which has valuable resources for dealing with snakes, including
snake identification, snake bite care, the Antivenin Index (lists
location and number of vials of available antivenin), and lists of
physicians trained to manage patients. Regional and local zoos may also
be able to provide helpful information. The National Help Line for
Poison Control is 1-800-222-1222.
When contacting Poison Control, provide as much information as you can pertaining to snake species, timing of the bite, current physical findings, and laboratory values (if available).
Do not delay administration of antivenin if available at your facility. If needed, Poison Control will assist with dosing and administration. If antivenin is not available, Poison Control will assist with appropriate locations to obtain antivenin.
Signs and
Symptoms
All snake bites can be
painful at the bite site, but bites from pit vipers tend to increase in
pain with localized swelling and hemorrhagic changes. Pit vipers often
leave a pattern with 2 puncture wounds with smaller tracks below, while
coral snakes frequently leave chewing-like marks that may be difficult
to distinguish from an abrasion. Coral snake bites may not be painful,
and systemic findings, such as drowsiness or muscle twitching, may be
present before the patient realizes he or she was bitten.
Table 1. Snake bite-associated signs/symptoms vary depending on type of snake, but potentially include1:
| A
pair of
puncture marks at the wound or fang marks/scratches |
Labored breathing (in extreme cases, breathing may stop altogether) |
| Redness and swelling around the bite | Disturbed vision |
| Severe pain at the site | Increased salivation and sweating |
| Nausea and vomiting | Numbness/tingling around face and/or limbs |
Diagnosis
History
When
taking the patient’s history, include time of bite, description of
snake, field therapy (if any), underlying medical conditions, allergies
to either horse or sheep products, and history of previous venomous
snake bites and therapy. Assume
all snake bites are venomous until
clear identification of the snake species or a period of patient
observation dictates otherwise.
Species
Identification
Positive
identification of the correct species of snake as well as the patient’s
clinical manifestations is essential to diagnosis. Typically, the
patient has been in an area consistent with snake habitat such as tall
thick grass, cliffs, or swampy or rocky areas. Knowledge of snake
species characteristically found in the area as well as preferred
habitat is helpful. Many snakes remain in the area of the attack and
may be identified by a bystander. If the species is unknown, attempt to
obtain a description of the snake’s color and pattern, which helps in
identification.
Severity of
Envenomation
Timing of the
bite with the onset of symptoms aids in determining the degree of
envenomation. This is especially important for pit viper bites. If the
bite occurred within a relatively short time frame from the onset of
symptoms, it likely indicates that a significant level of venom has
been injected into the patient.
Table 2. Level of envenomation depends on2:
| Size* and species of snake | Age, size, health of patient |
| Amount of venom injected per bite (can't be determined by history) | Time between bite and treatment |
| Number of bites | Patient's response to venom |
| Location and depth of bite (envenomation from bites to head and trunk usually more severe than from bites to extremities) | |
| *Note that size does not matter when it comes to coral snake bites, for which antivenin is administered due to the risk of neurotoxicity, whether or not symptoms are present. | |
Progression of
Envenomation
Progression
of envenomation is evidenced by worsening of the patient’s signs and
symptoms of local injury, coagulation abnormalities, and systemic
effects. Use the following table to estimate grade of severity.
Communicate actual findings with Poison Control for help with
determining treatment.
Table 3. Severity of envenomation3
| Type of Signs or Symptoms |
Severity of Envenomation | ||
| Minimal | Moderate | Severe | |
| Local | Swelling, erythema, or eccymosis confined to site of the bite; bite progressively more painful | Progression of swelling, erythema, or ecchymosis beyond 12 inches from the site of the bite | Rapid swelling, erythema, or ecchymosis involving the entire body part; risk of compartment syndrome |
| Systemic | No systemic signs or symptoms | Non-life threatening signs and symptoms (nausea/vomting, mild hypotension, perioral parethesias, myokymia) | Markedly severe signs and symptoms
(hypotension [SBP<80 mm Hg], altered sensorium, tachycardia, tachyepnea, renal failure, and respiratory distress) |
| Coagulation | No coagulation abnormalities or other lab abnormalities | Mild abnormal coagulation profile without significant bleeding | Abnormal coagulation profile with bleeding (decreased INV, aPTT, fibrinogen; PLT count <20 000/mm3) |
| Snakebite Severity Score (SSS) |
0-3 | 4-7 | 8-20 |
| aPTT=activated
partial thromboplastin time; CroFab=Crotalidae polyvalent antivenin; INR=international normalized ratio; PLT=platelet; SBP=systolic blood pressure |
|||
Table 4. The Snakebite Severity Score (SSS)3
SSS assesses severity of envenomation.
SSS has correlated well with physician assessment.4
| Snakebite Severity Scorea | ||
| Symptoms | Points |
|
| Pulmonary system |
No symptoms/signs | 0 |
| Dyspnea, minimal chest tightness or discomfort, or RR 20-25 breaths/mn | 1 |
|
| Moderate respiratory distress(tachypnea, RR 26-40 breaths/minute, accessory muscle use) | 2 |
|
| Cyanosis, air hunger, extreme tachypnea, or respiratory insufficiency/failure | 3 |
|
| Cardiovascular system |
No symptoms/signs | 0 |
| Tachycardia (HR 100-125 bpm), palpitations, generalized weakness, benign dysrhythmia, or hypotension | 1 |
|
| Tachycardia (HR 126-175 bpm) or hypotension, with SBP > 100 mm Hg | 2 |
|
| Extreme tachycardia (HR>175 bpm), hypotension with SBP < 100 mm Hg, malignant dysrhythmia, or cardiac arrest | 3 |
|
| Local wound |
No symptoms/signs | 0 |
| Pain, swelling, or ecchymosis within 5-7.5 cm or bite site | 1 |
|
| Pain, swelling, or ecchymosis involving less than half of extremity 7.5-50 cm from the bite site) | 2 |
|
| Pain, swelling, or ecchymosis involving half to all of extremity (50-100 cm from bite site) | 3 |
|
| Pain, swelling, or ecchymosis extending beyond affected extremity (>100 cm from bite site) | ||
| Gastrointestinal system |
No symptoms/signs | 0 |
| Pain, tenesmus | 1 |
|
| Vomiting or diarrhea | 2 |
|
| Repeated vomiting, diarrhea, hematemesis, or hematochezia | 3 |
|
| Hematologic symptoms |
No symptoms/signs | 0 |
| Coagulation parameters slightly abnormal: PT<20 sec, PTT<50 sec, PLT 100K-150K/mL, or fibrinogen 100-150 µg/mL | 1 |
|
| Coagulation parameters abnormal: PT<20-25 sec, PTT <50-75 sec, PLT 50K-100K/mL, or fibrinogen 50-100 µg/mL | 2 |
|
|
Coagulation parameters abnormal: PT<50-100 sec,
PTT<75-100 sec, PLT 20K-50K/mL, or fibrinogen <50 µg/mL |
3 |
|
|
Coagulation
parameters markedly abnormal, with serious bleeding or threat of
spontaneous bleeding; unmeasurable PT or PTT: PLT<20K/mL; or undetectable fibrinogen; or other severe laboratory abnormalities |
4 |
|
| Central nervous system |
No symptoms/signs | 0 |
|
Minimal apprehension, headache, weakness, dizziness, chills, or paresthesia
|
1 |
|
| Moderate apprehension, headache, weakness, dizziness, chills, paresthesia, confusion, or fasciculation at bite site | 2 |
|
| Severe confusion, lethargy, seizures, coma, psychosis, or generalized fasciculation | 3 |
|
| RR=respiratory rate; HR=heart rate; PLTs=platelets; PT=prothrombin time; PTT=partial thromboplastin time; SBP=systolic blood pressure | ||
Treatment
Many
snake bite patients do not require antivenin and can be treated
symptomatically, requiring only pain control. After a pit viper bite,
if the patient has pain only from the initial puncture wound and the
pain subsides with time, the patient was likely not envenomated.
Monitor progression of symptoms and lab values.
The exception to this is a coral snake bite, for which antivenin is administered whether or not the symptoms are present due to the risk of neurotoxicity.
For patients who are hemodynamically unstable, follow the ABCs and treat shock, if present. Full monitoring should be in place with frequent evaluation of the bite site. Helpful laboratory studies include CBC, PT/PTT/INR, fibrinogen split products, type and cross for the appropriate amount of blood (2 units for adults, PEDS: 20 mL/kg for pediatrics) if the patient is in shock, chemistries including BUN and creatinine, and urinalysis for myoglobinuria.
Antivenin. Along with supportive care, antivenin is the mainstay of treatment. As the antivenin dose reflects venom size rather than patient size, the U.S. Food and Drug Administration (FDA) recommends the same doses (initial and subsequent) for adult and (PEDS) pediatric patients. Do not decrease dose in children (eg, based on weight or size).
For pit viper envenomation, equine-derived antivenin has been mostly replaced by ovine-derived Crotalidae polyvalent immune FAb antivenin (CroFab™), harvested from pit viper venom–immunized sheep. It is much less antigenic than its precursors derived from horse serum. There is still a risk of anaphylaxis with this antivenin but it is much lower than with previous antivenin. It can also cause delayed hypersensitivity reactions (serum sickness).
Cost. Note that CroFab carries a significant financial burden for both hospital and patient, with a 1-vial dose having an approximate (wholesale) cost of $1000.3 A completed course of treatment as recommended by the package insert6 can cost in excess of $18,000.3 For that reason, it is important to carefully implement and monitor the patient’s treatment to ensure proper administration and utilization of resources. Let Poison Control be your guide.
Patients are suitable for CroFab treatment if they meet the criteria for Minimal, Moderate, or Severe Envenomation. Administer CroFab within 6 hours of envenomation to prevent clinical deterioration and signs of systemic coagulation abnormalities. Rapid preparation and delivery of medication are essential.
If appropriate, treat patients with moderate-to-severe envenomations at a referral facility (with either plastic surgery or orthopedic capability for handling compartment syndrome) and intensive care facility (if the patient progress to systemic coagulopathy and end-organ dysfunction).
Pit viper species can affect dose. Compared with other pit vipers, copperhead bites are connected with significantly less toxicity than rattlesnake and cotton mouth envenomations. These seldom require antivenin, except in at-risk populations, (eg, children, the elderly),3 and patients with other medical conditions (eg, diabetes, coronary artery disease). Victims of copperhead bites may often be managed with pain control. This is different with many rattlesnake species, especially the Western Diamond Back. Remember that the basis for administration of antivenin is becoming species-specific.
Algorithm Notes
a
Initial response or control: Initial control is cessation of
progression of local effects, systemic effects, and coagulopathy from
envenomation. Monitor patients for 1-4 hours following CroFab dosing to
assess initial response/control.
Clinical response: pretreatment envenomation signs/symptoms
arrested or
improved after treatment.
Partial response: Envenomation signs/symptoms worsened after
treatment,
but at slower-than-expected rate.
Non-response: Patient’s condition not positively affected by
treatment.
b
Administer scheduled maintenance dosing to patients with documented
rattlesnake envenomations to prevent envenomation recurrence.
Preparation/Administration:
- Preparation: Prepare initial 4-6 vial dose in 2-vial increments administered with 100 mL of 0.9% NaCl USP. Adjust fluids for patients weighing <10 kg if needed. If no acute allergic reaction signs are evident within first 10 minutes of infusion, make subsequent doses and deliver to the patient’s bedside to be started immediately upon completion of first 2-vial dose. Dilute doses of 4-6 vials into 250 mL of 0.9% NaCl USP, unless fluid restriction is required.
- Administration: Begin infusion of first 2-vial dose at 25 mL/h for first 10 minutes to monitor for signs of acute reaction. If none are noted, increase rate to a maximum of 250 mL/h until completion. Infuse the first 4 vials over >1 hour. If serious acute reactions occur, administer antihistamines, epinephrine, and albuterol. Give subsequent doses over 30 minutes. For patients weighing < 10 kg, adjust fluids (ie, rate of administration and total amount of diluent prepared) if needed.
- Recommended pretreatment: Routine pretreatment prior to antivenin therapy is not recommended by several groups. If pretreatment is considered, H1 receptor antagonists have been suggested. PEDS: The recommended dose of diphenhydramine is 0.5-1 mg/kg/dose (6.25 mg) IV for patients < 6-years-old, 12.5-25 mg for 6- to 12-years-old, and 25-50 mg for ≥ 12-years-old.
Subsequent administration of CroFab doses:
Following patient’s initial response, additional doses of CroFab have been recommended as 2 vials q 6h x 3 doses (18 h) to limit chance of envenomation recurrence. Consider scheduled maintenance doses for patients with rattlesnake envenomation secondary to the incidence of recurrence of envenomation effects.
Contraindications/precautions: CroFab contains ethyl mercury in the form of thimerosal. CroFab use is contraindicated in patients with known hypersensitivity to papaya or papain or prior hypersensitivity to CroFab or any other sheep-derived products. Pregnancy category C.
Coral Snakes
Following
the initial hours of a coral snake bite, the patient may be relatively
symptom-free. But because coral snake venom is a neurotoxin, the
initial symptoms may be only drowsiness or anxiety (a sense of
impending doom). Place patients on monitors and obtain appropriate
access with a large-bore IV.
Perform frequent
neurological evaluation and continue close monitoring for at least 24
hours after the bite. Patients may deteriorate quickly and require
airway support. Be wary of the very anxious patient and the possibility
of inadequate ventilation. It is for this reason that antivenin is
administered to these patients, regardless of symptoms if they present
within the first 12 hours after the bite. Again, contact
Poison
Control for assistance in determining where to access antivenin as well
as the appropriate destination and treatment.
Micrurus
fulvius antiveninb is currently the only FDA-approved antivenin for
coral snake bites. This is produced specifically to treat the coral
snake species in the United States, and is commonly referred to as the
North American Coral Snake Antivenin. Unfortunately, it is yet to be
available in a purified form and is derived from horse serum increasing
the risk for anaphylaxsis. The dose for initial treatment is 3 to 6
vials over 2 hours; repeat if symptoms persist. PEDS: The dose is the
same in pediatrics, with the amount of diluent decreased to accommodate
the child’s size.
Reference
- NIOSH Workplace Safety and Health Topics. Venomous Snakes. Available at: http://www.cdc.gov/niosh/topics/snakes/. Accessed August 16, 2010.
- Snakebites. Available at http://www.merck.com/mmpe/sec21/ch325/ch325i.html#sec21-ch325-ch325g-1152. Accessed August 18, 2010.
- Weant KA, Johnson PN, Bowers RC, Armitstead JA. Evidence-based, multidisciplinary approach to the development of a crotalidae polyvalent antivenin (CroFab) protocol at a university hospital. Ann Pharmacother. 2010;44:447-455.
- Dart RC, Hurlbut KM, Garcia R, Boren J. Validation of a severity score for the assessment of crotalid snakebite. Ann Emerg Med. 1996;27:321-326.
- National Center for Emergency Medicine Informatics. Crotalid Snakebite Severity Score. Available at http://ncemi.org/shared/etools_c/etools_c.pl?cmd=run&resource_fn=edecision_crotalid_snakebite_severity_score.xml. Accessed August 18, 2010.
- Package Insert. CroFab (Crotalidae polyvalent immune fab [ovine]). Brentwood, TN. Protherics, 2002.
- U.S. Food and Drug Administration. Expiration Date Lot 4030026-North American Coral Snake Antivenin (Micrurus fulvius) (Equine). Available at http://www.fda.gov/BiologicsBloodVaccines/SafetyAvailability/ucm155092.htm. Accessed February 16, 2012.