Snake bitesHussein UnwalaDr. Ingrid Vicas

February 4, 2010

Identifying Venomous Snakes

Signs of Envenomation

Treatment of Presumed Snakebites

Objectives

Identifying the Pit Viper

Prairie rattlesnake - coiled and rattling

Longest fangs 3-4 cm

Significant local tissue destruction

Hey Doc! Is This Snake Poisonous?Identifying Coral Snakes

“Red on Yellow Kills a Fellow”

Sonoran Coral Snake

Hey Doc! Is This Snake Poisonous?

Milk Snake - nonvenomous

“Red on Black, Venom Lack”

Characteristics of a Venomous Snakebite◦ # strikes◦ Depth of envenomation◦ Size of snake◦ Potency/amount of venom injected◦ Size/health of victim◦ Location of bite

Is the patient Envenomated?

“mosaic of antigens” Proteolytic enzymes, procoagulants/anticoagulants,

cardiotoxins, hemotoxins, neurotoxins

Venom is both circulating and tissue-fixed◦ Thus, anti-venom can halt progression, but won’t

reverse clinical findings

So how does this venom work?

Local Reactions

What Clinical Signs are Present?

Extent of Envenomation

Clinical Observations Antivenom Recommendationa

Other Treatment Disposition

None ("dry bite") Fang marks may be seen, but no local or systemic symptoms after 8-12 hours

None Local wound careTetanus prophylaxis

Discharge after 8-12 hours of observation

Minimal Minor local swelling and discomfort only, with no systemic symptoms or hematologic abnormalities

None Local wound careTetanus prophylaxis

Admit to monitored unit for 24-hour observation

Moderate Progression of swelling beyond area of bite, with  local tissue destruction, hematologic   abnormalities, or systemic symptoms

Yes IV fluidsCardiac monitoringAnalgesicsFollow laboratory valuesTetanus prophylaxis

Admit to ICU

Severe Marked progressive swelling and pain, with blisters,  bruising, and necrosis; systemic symptoms such  as vomiting, fasciculations, weakness, tachycardia,  hypotension, and severe coagulopathy

Yes IV fluidsCardiac monitoringAnalgesicsFollow laboratory valuesOxygenVasopressors PRNTetanus prophylaxis

Admit to ICU

Systemic Signs◦ Venom travels via lymph/superficial veins to enter

circulation Mild: weakness, malaise, nausea, restlessness More Severe: confusion, abdominal pain/V/D,

tachycardia, hypotension, blurred vision, salivation, metallic taste in mouth

Rare: DIC, MODS In some envenomations, neurotoxins predominate Anaphylaxis

What Clinical Signs are Present?

What Lab Findings might you expect? Platelets 10-50,000

Fibrinogen approaches Zero

PT, PTT immeasurably high◦ The majority of patients have no clinical bleeding!

Observing asymptomatic patients◦ 8-12 hours, if skin broken, and unable to ID snake

Pressure immobilization?◦ Do not occlude venous+arterial flow!◦ Broad, firm, constrictive wrap at 50-70mmHg◦ NOT recommended for NA pit viper

envenomations

Venom Removal?◦ No benefit of negative pressure venom extraction

Okay, now what?

Delineate extent of edema, measure diameter of extremity

Look for any signs of clinical bleeding Labs initially, then q 4-6 h Tetanus Analgesia/Anxiolysis

Okay, now what?

First line therapy for moderate-severe envenomations

CroFab : ovine-derived Fab fragment Fewer hypersensitivity reactions vs equine derived Infused IV in 4-6 vials reconstituted in NS

Initiated at slow rate; if no signs of anaphylactoid rx, then rate is increased to complete the infusion over 1 hour

If progressive limb swelling, thrombocytopenia, coagulopathy, dose repeated prn

Once symptoms controlled, maintenance doses of 2 vials q 6h x 3 doses

What About Antivenom?

C u rre n t T rea tm e n t G u id e lin es

Y e s2 v ia ls q 6 h x 3 do ses

M ILD 1 0-12

Y e sco n tin u e w ith 2 v ia ls q6 h x3

M O D 14 -18

Y e s2 v ia ls q 6h x3

S E V E R E 1 8 -24

N ore p ea t 4 -6 v ia ls

N oT h en rep ea t 4 -6 v ia ls

co n tro lle d?

N oT h en rep ea t 4 -6 v ia ls

co n tro lle d?

E ven o m a tion con firm ed& d ec is ion to a d m in iste r an tive n om

In itia l con tro l w ith in 1 h r a fte r 4 -6 via ls?

Initial routine use of tissue excision, fasciotomy, or “exploration and debridement” not recommended

Surgical debridement usually done 3-6 days post envenomation

Surgery?

Low rates (0-3%) of wound infections

No rationale for routine use of corticosteroids or anthistamines

Careful followup of patients who received CroFabrecurrence phenomenonserum sickness, delayed type hypersensitivity

Fetal loss may be as high as 43% for bites during pregnancy

Avoid any activity where risk of bleeding increased!!

Other Management Points

Efforts should be made to identify snake Once snake identified, antivenom should be

obtained◦ Local zoos, poison centers, snake collector

Give antivenom if signs of envenomation (ie fang marks!)

Compression immobillization of entire extremity

What about exotic snakes?

Cases??