CEN: Bites, Exposures and Wound Care

In depth

The one-page summary above is what the PDF prints. These sections go further.

Pit viper envenomation in depth

Merck: edema and erythema at and around the bite usually appear within 30 to 60 minutes, ecchymosis within 3 to 6 hours and bullae within about 8 hours; nausea, vomiting, diaphoresis, spontaneous bleeding, hypotension and shock are the systemic picture, and thrombocytopenia is usually the first sign of coagulopathy. About a quarter of pit viper bites are dry, and a dry bite is called only when no sign appears within 8 hours. Baseline labs for any but a trivial bite: CBC with platelets, PT, PTT, fibrinogen, fibrin degradation products, urinalysis, electrolytes, BUN and creatinine; type and crossmatch, ECG and CK for moderate or severe envenomation. Measure limb circumference on arrival and mark the leading edge every 15 to 30 minutes.

The 2011 unified treatment algorithm (Lavonas) gives 4 to 6 vials of Fab antivenom for signs of envenomation and 8 to 12 vials for shock or serious active bleeding; Merck gives 4 to 12 vials and states that the dose is not reduced for children and that antivenom should not be withheld because the species is a copperhead or cottonmouth. The CroFab label reconstitutes each vial and dilutes the dose to 250 mL saline, runs it at 25 to 50 mL/h for the first 10 minutes to catch reactions, then 250 mL/h. Coagulation tests and platelets are rechecked within about an hour of dosing. Initial control is arrest of local progression, a clear improving trend in hematologic effects and resolution of systemic effects; without it, the initial dose is repeated, and failure after two doses calls for a physician expert. The label adds 2-vial doses every 6 hours for up to 18 hours once control is reached; the algorithm panel called these controversial and left them to a poison center or expert.

The algorithm lists what not to do: incision and suction, ice or ice water, arterial tourniquets, pressure immobilization or constricting bands, prophylactic antibiotics, prophylactic fasciotomy, routine blood products before antivenom, NSAIDs and electric shock. Merck allows fasciotomy only when compartment pressure stays at 30 mm Hg or more for over an hour despite antivenom, elevation and mannitol, with severe vascular compromise; massive edema alone is not an indication. A tourniquet already in place is left until the patient is in the hospital unless it is causing limb-threatening ischemia.

Apparent non-envenomation (fang marks only) is observed in a health care facility for at least 8 hours, with repeat platelets, PT, fibrinogen and hemoglobin before discharge; children and leg bites may need longer. Minor envenomation that is not progressing is observed 12 to 24 hours. After control, inpatients are watched 18 to 24 hours with exams every 6 to 8 hours and labs 6 to 12 hours after control and before discharge.

Reactions: immediate hypersensitivity occurs in 5 to 6% of Fab recipients (Lavonas). For hives with wheeze or hypotension the infusion is stopped and epinephrine, antihistamines and fluids are given; whether to resume is a risk-benefit decision with an expert, and Merck notes it can often be resumed more dilute and slower. Allergy to papaya or papain is a contraindication on the CroFab label unless benefit outweighs risk and anaphylaxis care is ready. Serum sickness (fever, rash, hives, joint pain) appears about 1 to 3 weeks later in up to 16% of Fab patients (Merck) and is treated with antihistamines and a steroid taper.

Recurrent coagulopathy after Fab antivenom can last 1 to 2 weeks or more (CroFab label); in the phase III trial recurrent thrombocytopenia occurred in 9 of 16 patients given no maintenance doses and 2 of 14 given them (Lavonas). Teach the patient to come back at once for bruising, bleeding gums after brushing, blood in urine or stool, or heavy periods, and to report a delayed rash or itching; antiplatelet and anticoagulant drugs are reviewed with the provider. Follow-up labs at 2 to 3 days and 5 to 7 days after discharge are recommended for patients who had coagulopathy (Lavonas). Keep the limb elevated at home. Field care for EMTs is on Assessment by Chief Complaint.

Coral snake in depth

Eastern and Texas coral snakes are elapids; their venom blocks neuromuscular transmission. Pain and swelling may be minimal or absent, which falsely suggests a dry bite. Weakness of the bitten limb can appear within hours, systemic signs may be delayed about 12 hours (Merck) and up to 13 hours (Simmons 2026), and once established they are hard to reverse and can last 3 to 6 days. Merck advises at least 12 hours of monitoring with oxygen saturation and serial peak flow or vital capacity; the Florida Poison Information Center practice is hourly neurologic exams for at least 24 hours, which generally means an ICU bed.

The North American Coral Snake Antivenin label says not to give it prophylactically to asymptomatic patients; the adult dose is 3 to 5 vials by response, the first 1 to 2 mL given over 3 to 5 minutes while watching for reaction, with epinephrine and antihistamines at hand, and delayed reactions or serum sickness are watched for up to 14 days. In 301 Florida cases (1998 to 2021) of patients asymptomatic on arrival, empiric antivenom was associated with more ICU admission (75.2% vs 56.8%) and a reaction rate of about 20%, without a difference in intubation or outcomes. Empiric antivenom for every coral snake bite is the older teaching; the current label and the cohort support watch-and-treat, with the airway ready.

Rabies risk by animal

ACIP 2008: rodents are not reservoirs of rabies; small rodents (squirrels, chipmunks, rats, mice, hamsters, guinea pigs, gerbils) and lagomorphs (rabbits, hares) are rarely infected and have not been known to transmit rabies to humans. Woodchucks are the exception: in raccoon-rabies areas they made up 93% of 371 rodent rabies cases reported to CDC from 1990 to 1996. For every rodent exposure the state or local health department is consulted before PEP is started; CDC asks clinicians to call the health department for the risk assessment in any possible exposure. Raccoons, skunks and foxes are the terrestrial carnivores most often rabid, so their bites are possible exposures and PEP starts unless the animal can be tested promptly. Any possible bat exposure needs a full evaluation, and most bats submitted for testing (about 94%) are not rabid. The 10-day observation applies to a healthy domestic dog, cat or ferret only. Care for a squirrel bite is washing and irrigation, tetanus review and infection teaching. PEP doses: CEN Musculoskeletal and Wound.

B virus after a macaque exposure

B virus is an alphaherpesvirus carried by more than 70% of adult rhesus, pig-tailed and cynomolgus macaques (CDC). Human infection is rare, 50 documented cases and 21 deaths since 1932, but most patients with central nervous system involvement die even with antivirals; ascending paralysis with respiratory failure is the usual cause. Symptoms usually start within a month and can start in 3 to 7 days: fever, myalgia, headache, then blisters at the site, lymphangitis, and neurologic signs.

First aid is the most time-sensitive step: skin is washed thoroughly for 15 minutes with povidone-iodine, chlorhexidine or detergent soap, and eyes or mucosa are flushed for 15 minutes with sterile saline or water. Wounds cleansed within 5 minutes and irrigated a full 15 minutes are less likely to become infected; a brief rinse at the sink is repeated properly on arrival. A culture positive after cleansing is itself an indication for treatment. CDC recommends prophylaxis for a deep puncture bite, a laceration of the head, neck or torso, inadequately cleansed broken skin or mucosa, any exposure to a high-risk (ill, immunocompromised or shedding) macaque, and needlesticks with nervous tissue or lesion material; it is considered for adequately cleaned broken skin, and not recommended when the skin stays intact. Regimen: valacyclovir 1 g by mouth every 8 hours for 14 days, or acyclovir 800 mg five times daily for 14 days. Every exposed patient is monitored, treated or not, and occupational health is involved.

Community needlestick in depth

CDC 2025 nPEP: start as soon as possible, ideally within 24 hours and no later than 72 hours, for 28 days, when an exposure carries substantial risk and the source has HIV without sustained viral suppression; when the source status is unknown the decision is case by case, and nPEP is not recommended when the exposure carries no substantial risk. Baseline HIV antigen/antibody test, creatinine, liver enzymes, hepatitis B tests and pregnancy test; follow-up HIV testing at 4 to 6 weeks and 12 weeks if PEP is given. The guideline does not address discarded needles. The PEP consultation line, as reported in a 2011 AFP letter, does not recommend PEP for discarded community needles: no transmission has been reported, risk is considerably lower than the roughly 1 in 300 after a needlestick from a known HIV-positive source in health care, and drying at room temperature reduces HIV in blood by 90 to 99%. ACIP 2018: after exposure to a source of unknown HBsAg status, a person with written documentation of a complete hepatitis B series needs no further treatment; a person in the middle of the series completes it; an unvaccinated person starts the series, preferably within 24 hours. Sexual-assault PEP is on Forensic Care and Abuse.

Foreign bodies and fishhooks in depth

Foreign bodies are missed at the first visit in about 38% of cases, often when no imaging was done (Rupert 2020). Radiography has limited ability to show glass fragments under 2 mm, although all glass is radiopaque; 57% of retained glass would have been missed without radiography, and a patient saying nothing is in the wound had a negative predictive value of only 89% (Halaas 2007). In one series films found glass in 6.9% of wounds clinicians had judged glass-free. Wood and other plant material absorb tissue fluid and are often invisible on films; ultrasound detects radiolucent material better than radiography or CT, and spares a child radiation, but depends on the operator. MRI is avoided when metal is possible. Removal is abandoned if not achieved in 15 to 30 minutes, and objects in the face, deep hand or foot spaces, joints, or near nerves and vessels go to a surgeon. Inert glass or metal that is hard to reach can be left in place.

Fishhooks (Halaas 2007, Rupert 2020): the back-out technique suits barbless hooks; the string-yank and needle-cover techniques are other described options; for a barbed hook whose point lies just under the skin, advance-and-cut has the highest reported success: after local or digital anesthesia the point is pushed through, the barb (or the eye) cut off, and the rest withdrawn. Wounds are cleaned with saline or tap water, which carry the same infection risk; antiseptic solutions are cytotoxic. Antibiotics have no proven benefit for simple wounds in healthy patients; consider them for high-risk wounds, and delayed presentation over 18 hours is a listed risk factor for infection. A plantar puncture through footwear is the classic Pseudomonas setting (AAFP suggests a fluoroquinolone). Punctures are not clean minor wounds: with 3 or more prior doses, a booster is given if the last was 5 or more years ago (full grid on CEN Musculoskeletal and Wound).

Diabetic foot infection in depth

IWGDF/IDSA 2023 grades diabetes-related foot infection as mild (two or more local signs, erythema over 0.5 cm but under 2 cm, skin and subcutaneous only), moderate (erythema 2 cm or more from the wound edge or deeper tissue, no systemic signs) or severe (two or more of: temperature over 38 °C or under 36 °C, heart rate over 90, respiratory rate over 20 or PaCO2 under 32 mm Hg, white count over 12,000 or under 4,000 or over 10% bands); osteomyelitis adds an (O). It suggests considering admission for every severe infection and for moderate infection with key comorbidities such as peripheral arterial disease. Plain films are routine for a new infection, to look for bone involvement, gas or a foreign body, repeated in 2 to 3 weeks or followed by MRI if osteomyelitis remains in doubt. Cultures come from tissue by curettage or biopsy, not superficial swabs. In temperate climates, Pseudomonas is not targeted empirically unless it grew from the site recently. Soft-tissue infection is treated 1 to 2 weeks. Neuropathy explains late presentation: the patient did not feel the wound.

Fingertips and replantation in depth

AAOS: a small fingertip wound that does not reach bone may heal by itself, usually in 2 to 4 weeks, though stiffness and sensitivity can last longer. Larger losses may need a graft or flap; exposed bone may be shortened so skin can close over it. In children under 6, the tip may continue to grow relatively normally even when bone was exposed. Nail bed injuries may need the nail removed and the bed repaired, and a painful blood collection under the nail can be drained through it. Part care: wrap in moist gauze, seal in a watertight bag, place on ice without direct contact, bring it along.

Bregman and Nicholson 2024: the classic indications are the thumb, multiple digits and a child (early publications said replantation should always be attempted in children, which the authors present as historical); a single finger cut distal to the flexor digitorum superficialis insertion was also an accepted case. A single finger proximal to that insertion was traditionally not replanted because it heals stiff at the middle joint, though newer patient-reported outcomes are more favorable; index finger replantation is now debated, and one study found no added benefit of replanting a little finger at any level over revision amputation. Sharp guillotine cuts do best; crush and avulsion do worse, and 3 or more comorbidities raise failure risk. Children regain good function and sensation and have fewer complications than adults. Bregman quotes digit ischemia limits of 6 to 12 h warm and 12 to 24 h cold (the Musculoskeletal and Wound page quotes 12 h and 24 h, the upper ends of these ranges, from another author; both are guides, not cutoffs) and notes success falls for major limbs after 2 to 4 h warm. The surgeon decides; the ED nurse cools the part correctly and records the time of injury.

Braden scale in depth

The Braden scale is a licensed instrument; this page describes its use and does not reproduce its items. It scores six domains (Merck names them sensory perception, moisture, activity, mobility, nutrition and friction/shear), each with a short ordinal rating; the total is up to 23, and a lower total means higher risk. Cutoffs of 16 and 18 are most used; a 2021 meta-analysis of 60 studies found moderate predictive validity (sensitivity 0.78, specificity 0.72, AUC 0.82) and favored 18. Merck notes that risk scales have not been shown to prevent more injuries than skilled clinical assessment, so a scale is used together with judgment. The nutrition domain rates usual intake, not laboratory values; Merck adds that albumin and prealbumin are not reliable alone. Age over 65, diabetes and peripheral arterial disease raise risk but are not scored. Read the low subscales as a care plan: moisture means prompt cleansing and a barrier, immobility means turning at least every 2 hours and a support surface, poor intake means a nutrition referral. ED boarders on hard surfaces and devices count. Staging and dressings: Pressure Injury Staging and Wound Care.

Exam pearls

• Pit viper progression after antivenom: repeat the loading dose, not maintenance and not fasciotomy.
• Coral snake with no symptoms: watch closely for a day; antivenom at the first neurotoxic sign.
• A copperhead bite with fang marks only still needs at least 8 hours and repeat labs.
• Normal labs at discharge do not end the bleeding risk after Fab antivenom.
• Squirrels and pet rodents do not need rabies shots by reflex; the health department decides.
• Macaque bite: a 15-minute antiseptic or soap wash comes before the antiviral.
• Discarded community needle: test and counsel; HIV PEP rarely.
• Wood hides on x-ray; glass shows. Film glass wounds before closing.
• Fever and tachycardia with a foot infection in diabetes is a severe infection: admit.
• Thumb, several fingers or a child: replant. One little finger: least likely.
• Braden scores intake, not albumin.