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lunes, 12 de agosto de 2013

Effective Prehospital Care for a Scorpion Sting. Are antivenins always necessary?

Scorpion Centruroides exilicauda

Bryan Bledsoe, DO, FACEP, FAAEM, EMT-P | From the April 2013 Issue | Wednesday, March 27, 2013
FROM www.jems.com 
There’s much more to Las Vegas than the casinos, bars and the bright lights of the Strip. Many wonderful parks and unique points of interest are nearby and offer respite from the constant grind of the city. One such park is the Valley of Fire State Park located just north of Las Vegas. This is a beautiful and striking collection of rocks and escarpments and is often used for movie and television shoots.
During the early summer, a 24-year-old Canadian tourist was visiting the park and climbing the various trails that wind through the wondrous rock formations. Evidently, the patient reached up onto a rock and felt a severe burning sensation on the dorsal surface of her right hand. She immediately withdrew her hand and saw a scorpion fall to a rock below. The burning sensation soon became intense pain and itching, and she developed shortness of breath followed by generalized hives. Her boyfriend was at her side and quickly scooped up the scorpion into a paper cup and helped his girlfriend down to the base of the trail. By that time, she was more short of breath and slightly diaphoretic. He placed her into their car and drove quickly to a nearby convenience store. There, the clerk summoned local EMS.
Prehospital Care
First responders arrived approximately eight to 10 minutes following the initial call. They began their primary assessment, administered supplemental oxygen and awaited arrival of paramedics. They questioned the patient about whether she had an EpiPen or similar epinephrine auto injector. She didn’t.
Soon, paramedics arrived and took over assessment. Their primary assessment revealed the patient to be anxious, short of breath and diaphoretic, with hives. The initial vital signs were a blood pressure of 100/68, a pulse of 100, respirations of 24, and SpO2 of 95% on a non-rebreather mask. The paramedics promptly placed an IV line and administered 0.3 mg of epinephrine 1:1000 intramuscularly. The patient had an episode of transient tachycardia; however, her breathing improved and most of the hives disappeared. Although her breathing was better, the pain from the scorpion sting was increasing fairly quickly. In addition, she had developed some unusual twitches and jerkiness. As paramedics inspected the patient’s right hand, they noted it to be swollen and extremely tender. There was an area at the center of the swelling that appeared to be the location of the sting.
The paramedics administered a one-liter fluid bolus of normal saline followed by 5 mg of morphine sulfate via IV. The patient was somewhat nauseated and received 4 mg of ondansetron (Zofran) via IV. This resulted in improvement of her pain and normalization of her vital signs. She was subsequently transported to University Medical Center (UMC) for additional care.
Hospital Course
At UMC, the emergency medicine staff promptly evaluated the patient. Although she improved initially following the prehospital care provided, her pain and shortness of breath were starting to recur. An additional 5 mg dose of morphine was provided and standard laboratory tests were obtained. Examination of the right hand revealed swelling and a small area of ecchymosis. The pulses remained strong and the patient was fully alert. In addition, the patient again became nauseated and subsequently vomited. Following this, 1.25 mg of droperidol (Inapsine) was administered via IV. Her nausea and vomiting resolved.
On physical exam, the patient was in considerably more distress than what paramedics had reported on scene. She was carefully reassessed to try to determine whether her signs and symptoms were due to an allergic reaction to the scorpion sting or due to scorpion envenomation. The venom from scorpions in the U.S. is neurotoxic yet rarely fatal. Although rare, envenomation from certain scorpion species (e.g., bark scorpion) can cause uncontrolled muscle jerking, eye twitching (called opsoclonus) and increased salivation in addition to the localized pain, swelling and itching. Based on the examination, the patient didn’t have signs of envenomation.
Although an antivenin is available for scorpion stings, it wasn’t deemed necessary in this case. The patient received additional fluids as well as 25 mg of diphenhydramine (Benadryl) and 125 mg of methylprednisolone (Solu-Medrol) via IV. She was observed in the emergency department for approximately four hours and discharged home with medications for pain as well as antihistamines and corticosteroids.
Scorpions, which are eight-legged venomous invertebrates that are related to spiders and ticks, are common in the southwestern U.S., and the second-most common cause of poisonous stings worldwide. In the U.S., only four deaths in 11 years have occurred as a result of scorpion stings. Interestingly, in Mexico, approximately 1,000 deaths from scorpion stings occur per year.1
Scorpions primarily live in the desert and have adapted to the heat and lack of water. There are approximately 70 species of scorpions in the U.S. Of these, only the bark scorpion (Centruroides exilicauda) can cause clinically significant signs and symptoms. In actuality, significant scorpion envenomation is rare in the U.S. When it does occur, infants, children and the elderly are at increased risk.
The signs and symptoms of envenomation usually occur within 15 minutes following the sting. The severity of the symptoms depends on the amount of venom injected. For most people, the signs and symptoms of a scorpion sting are localized and include pain, swelling and itching.
In rare instances, significant envenomation from a bark scorpion sting can cause systemic signs and symptoms. These include the various neurologic symptoms detailed earlier. An antivenin (Anascorp) is available for significant stings. It’s derived from horse serum and is effective. However, it’s expensive and has associated allergic/anaphylactic risks because it’s derived from animal sources. It’s reserved only for severe, life-threatening envenomation where the benefits clearly outweigh the risks. It shouldn’t be used routinely unless neurotoxic signs and symptoms are noted. Most hospitals in the southwestern U.S. stock or have access to this antivenin.2,3
The use of antivenins in EMS is controversial. There are antivenins available for the bites and stings of numerous dangerous animals. These include snakes, spiders and scorpions. In some situations, such in the Australian state of Queensland, it makes sense for EMS providers to carry and administer antivenin. There are jellyfish species, primarily the box jellyfish (Chironex fleckeri), in the waters off Queensland and other parts of Australia that are extremely toxic, and stings can be rapidly fatal. In such cases, antivenin administration can be lifesaving. However, in most of the U.S., patients are able to access a hospital fairly rapidly and can receive antivenin there as needed.
Certainly, some rural EMS systems have prolonged out-of-hospital times and respond in areas where poisonous animals are found. In these systems, there may be a role for antivenin based on transport times and the types of indigenous poisonous species found in the region. Most of these cases would certainly be due to snakes, with insect bites and stings being less common.
It’s important to remember that the administration of antivenin isn’t always simple and without risk. Allergic reactions and other systemic reactions are common. In addition, many of these antivenin products are expensive and require special preparation to administer.
Interestingly, Miami-Dade (Fla.) Fire Rescue (MDFR) operates the world-recognized Venom Response Program.4 It consists of highly specialized paramedic/firefighters who are trained in the response, management and treatment of envenomations.
The program is necessary because Miami-Dade County is home to numerous venomous and poisonous animals, and is also the point of entry for a wide variety of venomous animals imported into the U.S. As in Miami, all EMS providers should be familiar with the identification and treatment of common animal bites and envenomations that can occur in their response area.
The case detailed here is relatively straightforward. We describe the case of a tourist who sustained a scorpion sting in a local state park. Her symptoms were more significant than typically seen with simple scorpion stings. The scorpion that was caught by her boyfriend was later determined to be a bark scorpion. However, following adequate prehospital treatment and detailed evaluation in the emergency department, the patient improved. It was determined that scorpion antivenin wasn’t indicated because of the lack of systemic signs and symptoms. The patient ultimately did well and completed her vacation in Las Vegas.
1. Chippaux JP, Goyffon M. Epidemiology of scorpionism: A global apprasial. Acta Trop. 2010;107:71–79.
2. Quan D. North American Poisonous Bites and Stings. Crit Care Clin. 2012;28:633–659.
3. Boyer LV, Theodorou AA, Berg RA, et al. Antivenom for critically ill children with neurotoxicity from scorpion stings. N Engl J Med. 2009;360:2090–2098.
4. Miami-Dade Venom Response Program. (Jan 19, 2012). In Miami-Dade County. Retrieved Feb. 17, 2013, from www.miamidade.gov/fire/about-special-venom.asp.
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