Scorpion Envenomation Treatment & Management

Primary assessment of airway, breathing, and circulation takes precedence.

Few studies have evaluated the utility of most first aid.

The utility of negative pressure extraction devices has not been evaluated for scorpion stings.

Perform endotracheal intubation and vascular access as needed.

Supportive care in all cases and antivenom in severe cases are used for the treatment of scorpion envenomation.

Grades of Centruroides envenomation are as follows:

• Grade I - Local pain and/or paresthesias at the site of envenomation

• Grade II - Pain and/or paresthesias remote from the site of the sting, in addition to local findings

• Grade III - Either cranial nerve/autonomic dysfunction or somatic skeletal neuromuscular dysfunction, as follows:

  • Cranial nerve dysfunction - Blurred vision, roving eye movements, hypersalivation, tongue fasciculations, dysphagia, dysphonia, problems with upper airway

  • Somatic skeletal neuromuscular dysfunction - Restlessness, severe involuntary shaking or jerking of the extremities that may be mistaken for a seizure

• Grade IV - Combined cranial nerve/autonomic dysfunction and somatic nerve dysfunction

Androctonus australis Hector Hospitalization Score is as follows (total ≥2 = Hospitalization) ^[31] :

• Priapism: +3

• Vomiting: +2

• SBP >160: +2

• Corticosteroid PTA: +2

• Temperature >38ºC: +1

• Heart rate >100 bpm: +1

Although grading and scoring systems have been developed, they are limited due to species specificity and low-degree symptoms that would lead to hospitalization or therapy.

Because the clinical manifestations and severity of the symptoms vary among patients, individualize management of scorpion stings. Furthermore, frequent patient monitoring allows earlier recognition of the life-threatening problems of scorpion envenomation. Treatment generally consists of moving the patient away from the scorpion and stabilizing the patient's airway and vital signs, followed by administration of antivenin and institution of symptomatic and local treatment.

Local treatment

Use ice bags to reduce pain and to slow the absorption of venom via vasoconstriction. This is most effective during the first 2 hours following the sting. Alternatively, hot water immersion has been described as a first aid treatment for scorpion bites in Australia and in Taiwan. ^{[32, 33]} A randomized controlled trial performed in Taiwan suggests that hot water immersion for Scolopendra bites is as effective as ice pack treatment in relieving pain.

Immobilize the affected part in a functional position below the level of the heart to delay venom absorption.

Calm the patient to lower the heart rate and blood pressure, thus limiting the spread of the venom.

For medical delay secondary to remoteness, consider applying a lymphatic-venous compression wrap 1 inch proximal to the sting site to reduce superficial venous and lymphatic flow of the venom but not to stop the arterial flow. Only remove this wrap when the provider is ready to administer systemic support. The drawback of this wrap is that it may intensify the local effects of the venom.

Apply a topical or local anesthetic agent to the wound to decrease paresthesia; this tends to be more effective than opiates and ice application. ^[34]

Administer local wound care.

Administer tetanus prophylaxis.

Administer systemic antibiotics if signs of secondary infection occur.

Administer muscle relaxants for severe muscle spasms (ie, benzodiazepines.)

Systemic treatment

Systemic treatment is instituted by directing supportive care toward the organ specifically affected by the venom.

Establish airway, breathing, and circulation (ie, ABCs) to provide adequate airway, ventilation, and perfusion.

Monitor vital signs (eg, pulse oximetry; heart rate, blood pressure, and respiratory rate monitor).

Use invasive monitoring for patients who are unstable and hemodynamic.

Administer oxygen.

Administer intravenous fluids to help prevent hypovolemia from vomiting, diarrhea, sweating, hypersalivation, and insensible water loss from a tropical environment.

Perform intubation and institute mechanical ventilation with end-tidal carbon dioxide monitoring for patients in respiratory distress.

For hyperdynamic cardiovascular changes, administration of a combination of beta-blockers with sympathetic alpha-blockers is most effective in reversing this venom-induced effect. Avoid using beta-blockers alone because this leads to an unopposed alpha-adrenergic effect. Also, nitrates can be used for hypertension and myocardial ischemia.

For hypodynamic cardiac changes, a titrated monitored fluid infusion with afterload reduction helps reduce mortality. A diuretic may be used for pulmonary edema in the absence of hypovolemia, but an afterload reducer, such as prazosin, nifedipine, nitroprusside, hydralazine, or angiotensin-converting enzyme inhibitors, is better. Inotropic medications, such as digitalis, have little effect, while dopamine aggravates the myocardial damage through catecholaminelike actions. Dobutamine may be a better choice for the inotropic effect. ^[35] Finally, a pressor such as norepinephrine can be used as a last resort to correct hypotension refractory to fluid therapy.

Administer atropine to counter venom-induced parasympathomimetic effects.

Other treatment

Insulin administration in scorpion envenomation animal experiments has helped the vital organs to use metabolic substrates more efficiently, thus preventing venom-induced multiorgan failure, especially cardiopulmonary failure. Unfortunately, no human studies have been conducted.

Administer barbiturates and/or a benzodiazepine continuous infusion for severe excessive motor activity. In some cases, be aware that meperidine and morphine may potentiate the venom. Also, the concurrent use of barbiturates and narcotics may add to the respiratory depression in patients who have been envenomated.

The use of steroids to decrease shock and edema is of unproven benefit.

A vaccine preparation was tried in experimental animals but was not pursued because of the need to prepare different antigens according to different geographical areas and to different species of scorpions living in the same area.

Antivenom

Antivenom is the treatment of choice after stabilization and supportive care. Because of the heterogeneity of venom composition between different scorpion species, one species' antivenom will have limited effect on another scorpion species' venom. Thus, correct scorpion species identification is a prerequisite for proper antivenom treatment.

For newer scorpion antivenom, the exact dosing has not been established as animal studies treatment amount does not translate into human studies treatment amount. In addition, the quantity to be used is determined by the patient’s clinical severity, symptom evolution, and treatment response. Unfortunately, predicting the patient’s response treatment is difficult, which makes exact antivenom dosing difficult. Furthermore, underdosing will result in limited or no effect, while overdosing increases the side effects and hypersensitivity reactions. Because the new antivenoms are highly purified immunoglobulin fragments, adverse reaction is less frequent and tends to be mild.

The antivenom significantly decreases the level of circulating unbound venom within a few hours. The persistence of symptoms after the administration of antivenom is due to the inability of the antivenom to neutralize scorpion toxins already bound to their target receptors. Thus, symptomatic and supportive treatment is needed with immunotherapy. ^[35]

General time guidelines for the disappearance of symptoms after antivenom administration are as follows:

• Centruroides antivenom: Severe neurologic symptoms reverse in 15-30 min. Mild-to-moderate neurologic symptoms reverse in 45-90 min.

• Non-Centruroides antivenom: In the first hour, local pain abates. In 6-12 hours, agitation, sweating, and hyperglycemia abate. In 6-24 hours, cardiorespiratory symptoms abate.

While an anaphylaxis reaction to the antivenom is possible, the patient is at lower risk for this than with other antivenoms for other envenomations if there is a scorpion venom—induced large release of catecholamines. Also, animal-derived antivenom increases the risk of hypersensitivity reaction compared to human monoclonal-derived antivenom. Finally, the larger the dose of antivenom, the greater the change for serum sickness.

In a prospective, randomized, double-blind study, Boyer et al compared scorpion-specific F(ab')₂ antivenom (Anascorp, Centruroides [scorpion] immune F(ab)₂ intravenous [equine], Instituto Bioclon) (n=8) with placebo (n=7) in children who developed neurotoxic symptoms following scorpion envenomation. ^[36] Neuromotor abnormalities were present in all patients at baseline, and respiratory distress was present in 20%. Beginning 2 hours after treatment, symptom resolution differed significantly in the antivenom group compared with the placebo group. Plasma venom concentrations were undetectable and cessation of the neurologic syndrome occurred within 4 hours in 100% of antivenom recipients compared with 1 placebo recipient (p=0.001).

Thus, the Boyer et al study suggests that scorpion-specific F(ab')₂ antivenom successfully treated the clinical syndrome, reducing the need for concomitant sedation and reducing circulating unbound venom levels for Centruroides envenomation. ^[36]

For Mesobuthus tamulu envenomations, horse-derived antivenom has been developed. Natu et al compared the newer antivenom treatment versus the traditional prazosin treatment in their open label study of 81 envenomated patients and found that antivenom decreased clinical recovery time to 4.14 hours +/- 1.6 hours compared to prazosin’s clinical recovery time of 19.28 hours +/- 5.03 hours. ^[37]

Natu et al also found that the antivenom plus prazosin combination group had a recovery time of 3.46 hours +/- 1.1 hours but felt it was comparable to the antivenom group recovery time and recommended that the combination therapy be reserved for patients presenting with pulmonary edema with hypertension.

Bawaskar et al compared antivenom plus prazosin versus prazosin in their open label trial of 70 patients with only grade 2 envenomations (beginning of systemic involvement) and found that 91.4% of the combination treatment group had resolution of their clinical symptoms within the 10-hour mark compared to 22.9% in the prazosin treatment group. ^[38] Both the Natu and the Bawaskar studies suggest the utility of the new Mesobuthus tamulus antivenom for systemic symptoms envenomations.

Kumar et al found that early (< 4 h) administration of antivenom with prazosin increases the percentage of children not developing myocardial dysfunction. ^{[39, 40]}

Further inpatient care

Inpatient care is dictated by the severity of the envenomation and consists of stabilizing the patient, neutralizing the venom, providing supportive therapies, and preventing complications. Patients with grade III or grade IV Centruroides stings and other severe Buthidae envenomations should be admitted to the intensive care unit (ICU) and/or treated with antivenom.

Treat all patients with severe systemic symptoms in an intensive care unit (ICU) setting because of the unpredictability of the symptomology, the risks associated with antivenin administration, and the need for airway or blood pressure support.

Young children do worse than adults. Young children may not recover as quickly as adults after scorpion envenomation and are more likely to require observation.

Transfer

Transfer is appropriate if antivenin administration or ICU treatments are not available at the institution where the patient initially presents.

Local poison control centers may assist in management of envenomations.

Contact the American Association of Poison Control Centers (800-222-1222) to be connected to a local poison control center.

The University of Arizona Poison and Drug Information Center (520-626-6016 from outside Arizona or 800-362-0101 from Arizona only) has special experience in Centruroides envenomation.

The Antivenom Index, published jointly by the American Association of Poison Control Centers and the American Zoo and Aquarium Association, lists the locations, amounts, and various types of antivenom stores.

Rest and immobilization of the sting site is recommended to prevent rapid absorption of the venom into the circulation.

Protective clothing, such as shoes or gloves, may prevent some scorpion envenomations. Check shoes, gloves, clothing, and backpacks for scorpions prior to use.

Keep yards free of debris, which can serve as a place for scorpions to hide.

Make sure windows and doors fit tightly to prevent scorpions from entering the house.

Avoid walking barefoot, especially at night when scorpions are active.

Use a Wood lamp at night because the cuticle of the Centruroides species is fluorescent under ultraviolet light.

Methods of biological control of scorpions include introducing chickens, ducks, and owls to the area.

Methods of chemical control of scorpions include using organophosphates, pyrethrins, and chlorinated hydrocarbons.

Government monitoring of the scorpion public health problem is warranted.

Patients displaying local nonascending reactions to the venom may be discharged after 6 hours of observation, with close follow-up. If the patient was treated with a pressure bandage, the symptoms may be delayed and inpatient observation is warranted. Patients with grade I or grade II Centruroides envenomations may be discharged. Discharge of patients with other Buthidae envenomations is more problematic because onset of systemic symptoms may be delayed up to 24 hours.

If an antivenin is administered, monitor the patient for serum sickness over next the few weeks.

Inform the patient about the possibility of persistent pain or paresthesia at the sting site.

Instruct patient regarding progression. Discuss symptoms of delayed serum sickness with patients treated with antivenom.