Crotalid snake envenomation

Snake Envenomation

Snakebite envenomation (SBE) in horses can have devastating outcomes. Tissue damage, cardiotoxicity, coagulopathy, and neurotoxicity can be concerns with SBE. Understanding the actions of venom components is important in developing a successful treatment plan. Antivenom is the mainstay of treatment. Long-term deleterious effects can occur including cardiac dysfunction and lameness.

Thromboelastographic evaluation in dogs with Asian pit viper (Gloydius) envenomation

The objective of this study was to investigate the thromboelastography (TEG) variables and platelet count after Asian pit viper (Gloydius) envenomation in dogs compared with healthy control dogs. Ten dogs with snake envenomation and twenty healthy dogs were included. There was a significant decrease in G (P=0.017), maximum amplitude (MA) (P=0.012), angle value (P=0.041), platelet count (P<0.001, as well as an increase in K value (P=0.034) and R value (P=0.007) in dogs with snake envenomation. The results of this study revealed that dogs with Asian pit viper (Gloydius) envenomation showed a hypocoagulable state compared with healthy dogs. Our findings may support the use of TEG for diagnosing and monitoring coagulopathy after Asian pit viper (Gloydius) envenomation in dogs.

Early-Onset Respiratory Muscle Paralysis in Crotalic Envenomation: A Case Study

Crotalic envenomation is responsible for approximately 8%-13% of ophidism cases in Brazil, yet it is associated with the highest mortality among snakes. We describe the case of a patient bitten by a rattlesnake who developed ventilatory muscle paralysis within hours after envenomation. While diaphragmatic paralysis is a rare late neurotoxic event following crotalic envenomation, in this case, paralysis occurred early but was rapidly reversed after antivenom administration. This report discusses potential contributing factors based on a comprehensive literature review.

Snakebite: When the Human Touch Becomes a Bad Touch

Many issues and complications in treating snakebite are a result of poor human social, economic and clinical intervention and management. As such, there is scope for significant improvements for reducing incidence and increasing patient outcomes. Snakes do not target humans as prey, but as our dwellings and farms expand ever farther and climate change increases snake activity periods, accidental encounters with snakes seeking water and prey increase drastically. Despite its long history, the snakebite crisis is neglected, ignored, underestimated and fundamentally misunderstood. Tens of thousands of lives are lost to snakebites each year and hundreds of thousands of people will survive with some form of permanent damage and reduced work capacity. These numbers are well recognized as being gross underestimations due to poor to non-existent record keeping in some of the most affected areas. These underestimations complicate achieving the proper recognition of snakebite’s socioeconomic impact and thus securing foreign aid to help alleviate this global crisis. Antivenoms are expensive and hospitals are few and far between, leaving people to seek help from traditional healers or use other forms of ineffective treatment. In some cases, cheaper, inappropriately manufactured antivenom from other regions is used despite no evidence for their efficacy, with often robust data demonstrating they are woefully ineffective in neutralizing many venoms for which they are marketed for. Inappropriate first-aid and treatments include cutting the wound, tourniquets, electrical shock, immersion in ice water, and use of ineffective herbal remedies by traditional healers. Even in the developed world, there are fundamental controversies including fasciotomy, pressure bandages, antivenom dosage, premedication such as adrenalin, and lack of antivenom for exotic snakebites in the pet trade. This review explores the myriad of human-origin factors that influence the trajectory of global snakebite causes and treatment failures and illustrate that snakebite is as much a sociological and economic problem as it is a medical one. Reducing the incidence and frequency of such controllable factors are therefore realistic targets to help alleviate the global snakebite burden as incremental improvements across several areas will have a strong cumulative effect.

Efficacy and Safety of Snake Antivenom Therapy: Experience of a Regional Hospital

Introduction

Snakebite is a commonly encountered envenomation emergency in the rural areas of Hong Kong. The majority of cases do not warrant antivenom therapy. We looked into those receiving antivenom to enhance the understanding of the results of antivenom therapy.

Methods

This was a retrospective review of the snakebite cases treated with antivenom in Tuen Mun Hospital from 1st January 2000 to 31st August 2005, focusing on both the therapeutic and side effects of the antivenom.

Results

Twelve patients were identified. All had local symptoms of swelling or numbness. Two of them subsequently developed skin necrosis requiring operative treatment. Thrombocytopenia was less amenable to correction than prolonged INR. No early or late allergic reactions were observed.

Conclusion

Because of the small number of cases, the apparent safety of the antivenoms in the current review warrants larger trials in future.

Antivenom for Neuromuscular Paralysis Resulting From Snake Envenoming

Antivenom therapy is currently the standard practice for treating neuromuscular dysfunction in snake envenoming. We reviewed the clinical and experimental evidence-base for the efficacy and effectiveness of antivenom in snakebite neurotoxicity. The main site of snake neurotoxins is the neuromuscular junction, and the majority are either: (1) pre-synaptic neurotoxins irreversibly damaging the presynaptic terminal; or (2) post-synaptic neurotoxins that bind to the nicotinic acetylcholine receptor. Pre-clinical tests of antivenom efficacy for neurotoxicity include rodent lethality tests, which are problematic, and in vitro pharmacological tests such as nerve-muscle preparation studies, that appear to provide more clinically meaningful information. We searched MEDLINE (from 1946) and EMBASE (from 1947) until March 2017 for clinical studies. The search yielded no randomised placebo-controlled trials of antivenom for neuromuscular dysfunction. There were several randomised and non-randomised comparative trials that compared two or more doses of the same or different antivenom, and numerous cohort studies and case reports. The majority of studies available had deficiencies including poor case definition, poor study design, small sample size or no objective measures of paralysis. A number of studies demonstrated the efficacy of antivenom in human envenoming by clearing circulating venom. Studies of snakes with primarily pre-synaptic neurotoxins, such as kraits (Bungarus spp.) and taipans (Oxyuranus spp.) suggest that antivenom does not reverse established neurotoxicity, but early administration may be associated with decreased severity or prevent neurotoxicity. Small studies of snakes with mainly post-synaptic neurotoxins, including some cobra species (Naja spp.), provide preliminary evidence that neurotoxicity may be reversed with antivenom, but placebo controlled studies with objective outcome measures are required to confirm this.

North American Snake Envenomation

Native US snakes that produce clinically significant envenomation can be divided into 2 groups, crotalids and elapids. The crotalids include rattlesnakes, cottonmouths, and copperheads. Crotalid envenomation can result in significant local tissue damage as well as thrombocytopenia and coagulopathy. Rarely are bites fatal. Native US elapids are all coral snakes that possess neurotoxic venom that can cause weakness, respiratory paralysis, and rarely death. Treatment of both types of envenomation revolves around general supportive care and antivenom administration when indicated. Previously advocated treatments, such as tourniquets, venom extraction, and bite site excision are not recommended.

Administration of CroFab Antivenom by a Helicopter Emergency Medical Service Team

The case presented here highlights an unconventional use of a helicopter emergency medical service (HEMS) to provide a specialized medication to a critically ill patient when definitive transport was delayed. A 39-year-old man presented to a rural hospital 1 hour after sustaining a copperhead envenomation. He developed severe symptoms and was intubated. Arrangements were made for transfer to a tertiary referral center by HEMS, but because of incoming weather conditions, the team would not be able to make the return flight safely. The decision was made for the HEMS team to fly antivenom to the patient, administer the medication, and then transport the patient by ground to the tertiary medical center. This plan was executed, and the patient was safely transported to the accepting facility. Antivenom is most effective when administered early because this will halt the progression of edema and may reverse the systemic effects of envenomation. In this case, HEMS transport of antivenom to the patient with severe toxicity prevented a delay to administration and likely improved the patient's outcome. Although the traditional role of HEMS is to provide rapid transport to critically ill patients, HEMS teams can also function to deliver specialized medications to remote settings.

Identification of antinociceptive fraction of snake venom from Crotalus durissus collilineatus crotamine-negative and its acute toxicity evaluation

The crude venom of the snake Crotalus durissus collilineatus (CDC) promotes neurological signs and symptoms in accidents involving humans and animals and the victims reports analgesia at the bite site, without tissue destruction. Studies shows that CDC has analgesic activity, among others. The crude venom is considered unsuitable for therapeutic purposes, with encouragement to the fractionation and purification of the same. Thus, the aim with CDC venom is: to perform fractionation by preparative HPLC; to test the antinociceptive activity of fractions and acute toxicity of active fractions. The CDC was fractionated on preparative HPLC-PDA (Oliveira et al., 2015) and the fractions were tested for their antinociceptive activity for writhing test by acetic acid (0.6%) in mice. For one of the fractions, which showed high analgesic effect both p.o. and i.p. routes, it evaluated the acute toxicity by the up and down method (OECD, 2001). In the fractionation by HPLC-PDA, CDC yielded 10 peaks (P1P10). SDS-PAGE showed that there was a good separation of components of the venom. All peaks were evaluated for their ability to reduce writhing, and the only one that apparently showed antinociceptive effect was Fr5 fraction (40 μg/kg). The Fr5 was able to reduce by 47% the number of contortions (i.p.) and 87% (p.o.), compared to control. The Fr5 fraction showed no morbidity and no mortality in the acute toxicity test (dose of 1000 μg/kg, p.o.); so it was not possible to estimate the LD50. According to the results, it can be stated that the venom and Fr5 of Crotalus durissus collilineatus snake of crotamine-negative type, may exhibit antinociceptive activity by suppressing nociception induced by acetic acid, suggesting it is related to effects on peripheral sites spinal and presents low acute toxicity values in experimental animals.

Severe Pit Viper Envenomation with Extended Clinical Signs and Treatment Complications in a Dog

This manuscript describes the extended clinical abnormalities that can occur in severe snake envenomation and the clinical signs associated with antivenom hypersensitivity in a 3 yr old dog. Treatment consisted of IV fluid therapy, analgesics, a vasopressor, cardiac antiarrhythmia drugs, and polyvalent pit viper antivenom. Following initial response to treatment, relapse of clinical signs occurred. Most interesting was the recrudescence of clinical signs on day 7 that may have been caused by the release of deposited venom during surgical debridement of necrotic skin. The resulting extensive clinical signs required multiple vials of antivenom (22 vials over a 7 day period). Both F(ab′)2 antivenom and antivenin (Crotalidae) polyvalent were used in this dog because of availability logistics. It is thought that this large amount of antivenom resulted in type I (anaphylaxis) and type III hypersensitivity (serum sickness) reactions. The dog made a complete clinical recovery. This description of extended, fluctuating clinical abnormalities that were associated with envenomation together with the development of hypersensitivity reactions that were presumably secondary to antivenom administration is information that can be useful for the management of patients afflicted with severe pit viper envenomation.

Presumptive intraperitoneal envenomation resulting in hemoperitoneum and acute abdominal pain in a dog

OBJECTIVE

To describe the clinical features, diagnostic findings, treatment, and outcome of a dog with acute abdominal pain and hemoperitoneum secondary to a presumptive intraperitoneal (IP) snakebite.

CASE SUMMARY

A 10-month-old castrated male mixed-breed dog was evaluated for suspected snake envenomation. The dog presented recumbent and tachycardic with signs of severe abdominal pain. Two cutaneous puncture wounds and hemoperitoneum were discovered during evaluation. Ultrasonographic examination revealed communication of the wounds with the peritoneal cavity. The dog was treated with supportive care, parenteral analgesia, packed red blood cell and fresh frozen plasma transfusions, crotalid antivenom, and placement of an IP catheter to provide local analgesia. The dog recovered fully and was discharged 5 days after initial presentation.

NEW OR UNIQUE INFORMATION PROVIDED

To our knowledge, this is the first report of IP envenomation accompanied by hemorrhage treated with continuous IP analgesia in the veterinary literature.

Prospective evaluation of the incidence of wound infection in rattlesnake envenomation in dogs

OBJECTIVE

To evaluate the incidence of wound infection following crotalidae envenomation in dogs and determine if the use of prophylactic antibiotics is warranted.

DESIGN

Prospective observational study.

SETTING

A 24-hour private practice specialty and emergency center in Murrieta, California.

ANIMALS

One hundred and two dogs with acute rattlesnake envenomation.

INTERVENTIONS

One hundred and forty-three consecutive cases of suspected acute rattlesnake envenomation were evaluated between March of 2012 and May of 2013. One hundred and two cases received no antimicrobials as part of management. Eight cases were placed on prophylactic antimicrobials by the primary care veterinarian prior to referral and were excluded. Two cases were excluded because they were initiated on antimicrobials during hospitalization for reasons unrelated to snakebite. Three cases involved cats and were excluded. Three patients died acutely near the time of presentation and were excluded. Twenty-one cases of suspected envenomation were excluded for lack of strong evidence of snakebite. Four cases were lost to follow-up and were excluded. Follow-up was conducted within 2 weeks either by phone or by direct inspection of the wound.

RESULTS

Of the 102 patients included in the study only 1 infection developed. This patient developed an abscess subsequent to suspected compartment syndrome.

CONCLUSION

The incidence of wound infection in rattlesnake envenomation is low, and the use of prophylactic antimicrobials is not recommended. The use of antimicrobials should be reserved for wounds with necrosis or abscess and the choice of antimicrobial should be based on a culture and sensitivity of the wound.

North American poisonous bites and stings

Critters and creatures can strike fear into anyone who thinks about dangerous animals. This article focuses on the management of the most common North American scorpion, arachnid, hymenoptera, and snake envenomations that cause clinically significant problems. Water creatures and less common animal envenomations are not covered in this article. Critical care management of envenomed patients can be challenging for unfamiliar clinicians. Although the animals are located in specific geographic areas, patients envenomed on passenger airliners and those who travel to endemic areas may present to health care facilities distant from the exposure.

North American snake envenomation in the dog and cat

Snake envenomation can be a cause of significant morbidity in dogs and cats in North America. Being familiar with the venomous snakes in your area and understanding the mechanisms of action of their venom will allow for successful treatment of envenomation cases. Treatment of snake envenomation revolves around supportive care in mild to moderate cases and venom neutralization with antivenom in severe cases. Dogs and cats envenomated by North American snakes have a good prognosis if treated appropriately.

Is there a role for fasciotomy in Crotalinae envenomations in North America?

CONTEXT

The local effects of Crotalinae envenomation can cause significant tissue destruction, pain, paresthesias, and deformity of the limb, which mimic findings of compartment syndrome, despite rare subfascial penetration of the fangs. Complicating this are the various techniques and ideas about what determines compartment syndrome combined with the fact that elevated intracompartmental pressures have been documented after Crotalinae envenomation, without clear evidence of compartment syndrome or tissue hypoperfusion.

OBJECTIVE

The purpose of this review is to evaluate the North American literature to provide an evidenced-based conclusion about the indications for fasciotomy in Crotalinae envenomations.

METHODS

The search was conducted with studies published only in the English language. The search included all human and animal publications, regardless of the format of study. The Cochrane Central Register, MEDLINE/ Pub Med, Scopus, and Biological Science databases were searched. Citations from all the articles were also cross-referenced if they were pertinent to the review. Major toxicology and emergency medicine and surgical textbooks were also referenced. Abstracts from the North American Congress of Clinical Toxicology, Poisonidex®, and personal articles were also scanned to complete the process, resulting in a total of 640 sources. Papers were excluded if they were duplicates, non-North American, involved excisional therapy, or did not discuss fasciotomy. This left 99 publications applicable to our study.

FINDINGS

No randomized controlled trials, 8 animal experiments, 1 human prospective observational study, 24 retrospective reviews, 32 review articles, 10 case reports, 15 textbooks references, 2 abstracts, and 7 editorials were included in the analysis. Controlled animal experiments show that crotaline Fab antivenin reduces intracompartmental pressure and increases tissue perfusion, while fasciotomy either has no beneficial effect or worsens myonecrosis. The case reports and opinions supporting fasciotomy come from the surgical literature and precede the modern crotaline Fab antivenin.

CONCLUSION

The current evidence does not support the use of fasciotomy or dermotomy following Crotalinae envenomation with elevated intracompartmental pressures. At present, early and adequate administration of crotaline Fab antivenin is the treatment of choice. Fasciotomy cannot be recommended until further well-designed investigations are completed.

Use of antivenom for snakebites reported to United States poison centers

In 2001, a new antivenin was introduced to the United States and became widely available in the snakebite season of 2002. We investigated what impact this may have had on snakebite treatment and medical outcome.

METHOD

The study used a retrospective review of all snakebites to humans reported to the National Poison Center Database System from 2000 to 2007.

RESULTS

During the 8 years, there were 37,760 snakebites, with a mean of 4720 bites per year. There was a 27% increase in bites reported to a Poison center for the 8-year period and an overall 13.5% increase in the use of antivenin. The 2 categories primarily responsible for the increased use of antivenin were copperhead and crotaline-unknown. Rattlesnake bites remained the category most frequently treated with antivenin with a mean 52.5% treatment rate and only moderate increase for the 8 years. There was no change in the percentage or number of patients with a major outcome (mean, 3.8%) or death (mean, 0.5%). There was a decrease in patients with a minor outcome and an increase in patients with a moderate outcome.

DISCUSSION

The new antivenin is reported to have a reduced potential for adverse reactions. This may have had a role in the decision of which snakebite victims received antivenin.

CONCLUSION

With the introduction of a new antivenin, there has been a dramatic increase in the number of snakebite patients treated with antivenin. This has been most noticeable in snake bite categories that were less frequently treated with antivenin in the past.

Improving Crotalidae polyvalent immune Fab reconstitution times

BACKGROUND

Crotalidae polyvalent immune Fab (CroFab) is used to treat rattlesnake envenomations in the United States. Time to infusion may be a critical factor in the treatment of these bites. Per manufacturer's instructions, 10 mL of sterile water for injection (SWI) and hand swirling are recommended for reconstitution. We wondered whether completely filling vials with 25 mL of SWI would result in shorter reconstitution times than using 10-mL volumes and how hand mixing compared to mechanical agitation of vials or leaving vials undisturbed.

METHODS

Six sets of 5 vials were filled with either 10 mL or 25 mL. Three mixing techniques were used as follows: undisturbed; agitation with a mechanical agitator; and continuous hand rolling and inverting of vials. Dissolution was determined by observation and time to complete dissolution for each vial. Nonparametric 2-tailed P values were calculated.

RESULTS

Filling vials completely with 25 mL resulted in quicker dissolution than using 10-mL volumes, regardless of mixing method (2-tailed P = .024). Mixing by hand was shorter than other methods (P < .001). Reconstitution with 25 mL and hand mixing resulted in the shortest dissolution times (median, 1.1 minutes; range, 0.9-1.3 minutes). This appeared clinically important because dissolution times using 10 mL and mechanical rocking of vials (median, 26.4 minutes) or leaving vials undisturbed (median, 33.6 minutes) was several-fold longer.

CONCLUSION

Hand mixing after filling vials completely with 25 mL results in shorter dissolution times than using 10 mL or other methods of mixing and is recommended, especially when preparing initial doses of CroFab.

Recombinant factor VIIa for treatment of gastrointestinal hemorrhage following rattlesnake envenomation

North American rattlesnakes possess venom with primarily cytotoxic and hemotoxic properties. When persons are envenomated by these snakes, thrombocytopenia and coagulopathy commonly occur, yet patients rarely develop severe bleeding. This report describes a 44-year-old Native American man bitten on the index finger by an unknown species of rattlesnake. The man developed massive gastrointestinal hemorrhage that was ultimately treated with recombinant factor VIIa. He presented to an emergency department with a depressed level of consciousness, a blood pressure of 60/20 mm Hg, and heart rate of 148 beats per minute. He was diaphoretic and vomiting bright red blood. Initial laboratory results revealed thrombocytopenia and coagulopathy. Despite aggressive fluid resuscitation and administration of blood and antivenom in the emergency department, the patient continued to have profuse upper gastrointestinal bleeding, with hemoglobin as low as 1.8 g/dL. He received fluids, antivenom, and multiple blood products, with cessation of bleeding after administration of recombinant factor VIIa. Esophagogastroduodenoscopy revealed a single Mallory-Weiss tear as the source of hemorrhage. The patient stabilized after 6 hours of aggressive resuscitation but over the next several days developed several complications, including acute renal failure and gram-negative sepsis. The patient died on hospital day 5. In cases of life-threatening hemorrhage after rattlesnake envenomation in which traditional therapy with antivenom and aggressive supportive measures fail, recombinant factor VIIa should be considered as an additional therapeutic option to achieve hemostasis.

Crotalidae polyvalent immune Fab for the treatment of pediatric crotaline envenomation

Crotaline snakebites occur frequently in children, often resulting in significant morbidity. Crotalidae Polyvalent Immune Fab antivenom (FabAV) became available for clinical use in the US in 2000 and is currently the standard of care for the treatment of crotaline envenomation. The pediatric emergency care provider should be familiar with FabAV because its judicious use in affected children can greatly decrease morbidity caused by crotaline snakebites. This article will review the use of FabAV for the treatment of pediatric crotaline envenomation.

Case studies in pediatric toxicology

Intentional and unintentional poisonings are encountered commonly in the pediatric population. Providers should be familiar both with the general approach to the poisoned child and with specific interventions required for certain toxic exposures.

Envenomations

Numerous types of envenomations may be encountered by health care workers depending on where in North America they work. Clinicians should be familiar with the animals in their region that may lead to envenomation.A rational approach with use of poison center or medical toxicology consultation services ensures that cases are managed appropriately.

First report of a bite by the mottled rock rattlesnake (Crotalus lepidus lepidus)

Bites by the mottled rock rattlesnake (Crotalus lepidus lepidus) are rare. There appear to be no reports of bites by this subspecies in the literature. This is a case report of a bite by a captive specimen of this diminutive pit viper, and includes a review of what is known regarding its venom.

Fasciotomy worsens the amount of myonecrosis in a porcine model of crotaline envenomation

STUDY OBJECTIVE

We evaluate the efficacy of fasciotomy or crotaline snake antivenom in reducing myonecrosis.

METHODS

We used a randomized, blinded, controlled acute animal preparation. Twenty anesthetized swine were injected intramuscularly in the anterior tibiales muscle of both hind limbs with 6 mg/kg of Crotalus atrox venom (total of 12 mg/kg of venom per animal). Immediately after venom injection, the right hind limb underwent fasciotomy. Muscle biopsies were obtained from the fasciotomized hind limb at 0, 4, and 8 hours and from the other hind limb at the conclusion of the study (8 hours). In addition, animals received either 8 vials of reconstituted Crotalidae polyvalent immune Fab (ovine) (CroFab; FabAV) or an equal volume of normal saline solution intravenously 1 hour after venom injection. A pathologist blinded to the study determined the percentage of myonecrotic cells in each biopsy. Statistical analysis was performed using repeated measures analysis of variance for compartment pressure. Rank-order methods were used for comparison of myonecrosis between groups.

RESULTS

Biopsies from hind limbs undergoing fasciotomy revealed a progressive increase in the amount of myonecrosis over time (myonecrosis median at 0, 4, or 8 hours [or death]: 0%, 14%, or 14.5%, respectively; P<.001). Comparison of the amount of myonecrosis of biopsies at death or 8 hours revealed that limbs that underwent fasciotomy had significantly more myonecrosis than those that did not (myonecrosis median: 14.5% versus 2.5%, P=.048). No difference was detected in the amount of myonecrosis when FabAV was compared with normal saline solution on final biopsies from either fasciotomy or nonfasciotomy hind limb (myonecrosis median: 10.0% versus 10.0%, P=.64).

CONCLUSION

Fasciotomy significantly worsens the amount of myonecrosis in a porcine model of intramuscular crotaline venom injection. No change in the amount of myonecrosis was detected with the use of FabAV treatment at the dosages used in this animal model.

Surgical issues in the poisoned patient

Some toxicologic emergencies require immediate or urgent surgical intervention in addition to routine medical care. The EP must be familiar with the indications for operative care, even though many of these poisonings and exposures are relatively rare. The EP must also be knowledgeable regarding the various means of surgical decontamination that are available, including temporary cardiopulmonary bypass. Finally, a high level of vigilance must be maintained for patients who have delayed presentation and fulminant organ failure necessitating early involvement of the transplantation team.

Preclinical assessment of the ability of polyvalent (Crotalinae) and anticoral (Elapidae) antivenoms produced in Costa Rica to neutralize the venoms of North American snakes

Polyvalent (Crotalinae) and anticoral (Elapidae) antivenoms produced by Instituto Clodomiro Picado, Costa Rica, were assessed for their ability to neutralize various toxic activities of the venoms of North American snakes of the genera Crotalus, Agkistrodon and Micrurus, in assays involving preincubation of venom and antivenom. When the intraperitoneal route of injection was utilized, polyvalent (Crotalinae) antivenom was effective in the neutralization of the venoms of Crotalus atrox, Crotalus adamanteus, Crotalus viridis viridis, Crotalus horridus atricaudatus, Agkistrodon contortrix contortrix and Agkistrodon piscivorus piscivorus, whereas the venom of Crotalus scutulatus was not neutralized. When the intravenous route was used, results differed depending on the "challenge dose" of venom employed. Polyvalent antivenom neutralized all venoms when mice were challenged with 2 LD(50)s of venom. When 5 LD(50)s were used, antivenom neutralized the venoms of C. atrox, C. adamanteus, C. v. viridis and C. h. atricaudatus, being ineffective in the neutralization of C. scutulatus, A. c. contortrix and A. p. piscivorus. Polyvalent antivenom was effective in the neutralization of hemorrhagic and myotoxic activities of all venoms studied. It also neutralized coagulant activity of C. adamanteus venom, whereas most of the venoms were devoid of clotting activity on plasma in vitro. Moreover, it neutralized defibrinating activity of the only three venoms that induced this effect (i.e. C. adamanteus, A. c. contortrix and A. p. piscivorus). Anticoral (Elapidae) antivenom neutralized lethality induced by the venom of Micrurus fulvius, using either the intravenous or the intraperitoneal routes of injection. Moreover, it neutralized myotoxic effect of this venom as well. It is concluded that polyvalent antivenom neutralizes lethality and other activities of most of the crotaline venoms tested. However, since it is ineffective in neutralizing the lethal effect of C. scutulatus venom, it is suggested that a venom containing presynaptically-active neurotoxic phospholipases A(2) related to "mojave toxin" needs to be introduced in the immunizing mixture in order to increase the neutralizing scope of this product in North America. Anticoral antivenom is highly effective in the neutralization of the venom of M. fulvius.

Prospective study of morbidity associated with snakebite envenomation

BACKGROUND

The morbidity associated with snakebite envenomation has not been well documented.

METHOD

Using a standardized questionnaire all patients with snakebite reported to a regional poison center during the year 2001 were followed after hospital discharge by telephone until resolution of symptoms.

RESULTS

One hundred and twenty-eight snakebite cases were reported, of which 16 (12.5%) were lost to follow-up and 31 (24.2%) reported no progression of symptoms beyond puncture and were deemed "dry bites." Eighty-one (63.3%) patients were followed for the duration of symptoms. Age ranged from 1 to 86 years with a mean of 32 years. There were 64 males (79%). The snakes were identified as copperhead (n = 57), unidentified venomous (n = 17), timber rattlesnake (n = 6), and cottonmouth (n = 1). All patients were initially evaluated in a hospital emergency department of which 51 were admitted. Nine patients received antivenin. Of the 37 patients who had a job, 33 lost a mean of 14 days of work (SD +/- 18.1). Mean duration of edema was reported as 11.4 days (S.D +/- 12). Recurrent edema frequently occurred with limb activity. Pain was scored on a scale of 1 to 10, with a mean score of 4.8 (SD +/- 2.7). Mean duration of pain was reported as 7.8 days (SD +/- 6.4). Thirty patients required accommodation for ambulation including crutches (n = 11), limp (n = 11), and no shoes or loose shoes (n = 14). Of the 26 patients bitten on the hand or finger, duration of reduced function persisted for a mean of 14.3 days (SD +/- 10.4) and reduction of hand strength persisted for a mean of 22 days (SD +/- 25.5). Five patients had poorly healing wounds at the bite site which persisted from 14 to 77 days with a mean of 45 days (SD +/- 22.8)

CONCLUSION

In this study snakebite resulted in significant duration and extent of morbidity in a majority of patients.

Presentation and Treatment of Venomous Snakebites at a Northern Academic Medical Center

Poisonous snakebites are relatively rare in the United States. The incidence of venomous snakebites is comparatively high in the southern states compared with the northern states and reports of these accidents from northern states is particularly uncommon. We report the experience with treatment of venomous snakebites at the University of Michigan over a 25-year period from 1976 to 2001. Six cases were identified and are described in detail. All patients were male and all were bitten in the upper extremity by pit vipers. One patient suffered a moderate envenomation and was treated with antivenin. Four other cases of mild envenomation occurred and two of these cases required antivenin therapy. One case was considered to represent a “dry” bite and required only 24-hour observation. There were no severe envenomations and no mortalities. On short-term follow-up all patients recovered without sequelae. This report demonstrates that venomous snakebites can be treated effectively at low-volume centers.

Crotalidae polyvalent immune Fab antivenom limits the decrease in perfusion pressure of the anterior leg compartment in a porcine crotaline envenomation model

STUDY OBJECTIVE

Crotalidae Polyvalent Immune Fab (CroFab; FabAV) antivenom prevents a decrease in perfusion pressures in intramuscular crotaline envenomation compared with normal saline solution.

METHODS

We used a randomized, blinded, controlled acute animal preparation. Twenty anesthetized and instrumented swine were injected intramuscularly with 6 mg/kg Crotalus atrox venom into the anterior tibialis muscle of each hind limb (time 0). One hour after envenomation (time 1 hour), animals were randomized to receive 8 vials of reconstituted FabAV or an equal volume of normal saline solution (control) through a central venous line. The main outcome variable was the area under the perfusion-time curve (AUC) of the anterior compartment of the hind limb measured from time 1 hour to time 8 hours. Perfusion pressure was defined as mean arterial pressure-compartment pressure. Additionally, physiologic variables, including pulse rate, prothrombin time, fibrinogen level, platelet count, hemoglobin level, and hematocrit level, were monitored.

RESULTS

Venom injection resulted in a decrease in average perfusion pressures from 54.1 mm Hg (time 0) to 31.7 mm Hg (time 1 hour). Comparison of AUC between groups from time 1 hour (time of treatment) to the completion of the study at time 8 hours revealed a 57% greater AUC in animals that received FabAV (mean+/-SD: 211.1+/-67.9 versus 134.5+/-55.8 mm Hg/h; P =.036; 95% confidence interval for difference 5.9 to 147.3). Comparison of the time curves for the mean prothrombin time from time 1 hour to the completion of the study by means of repeated-measures analysis of variance revealed a significant increase in the control group (P =.02). No significant difference was detected in the time curves for the means of mean arterial pressure, compartment pressure, pulse rate, hemoglobin level, hematocrit level, fibrinogen level, or platelet count over the course of the study. FabAV was found to significantly increase survival time when compared with the effect of the normal saline solution control from time 1 hour to time 8 hours, as determined by means of Kaplan-Meier estimation and the log-rank test (P =.029).

CONCLUSION

FabAV limits the decrease in perfusion pressures in the anterior leg compartment after intramuscular crotaline venom injection in swine compared with saline solution. In addition, FabAV might prevent the development of coagulopathy and increase survival time in this model.

Clinical findings associated with prairie rattlesnake bites in dogs: 100 cases (1989-1998)

OBJECTIVE

To identify clinically relevant variables and treatments for dogs bitten by prairie rattlesnakes (Crotalus viridis viridis).

DESIGN

Retrospective study.

ANIMALS

100 client-owned dogs.

PROCEDURE

Records of dogs evaluated for rattlesnake envenomation from 1989 to 1998 were reviewed. Analysis was performed to test for significant associations among clinical variables or treatments and cell counts, costs, and duration of hospitalization.

RESULTS

Most prairie rattlesnake bites occurred between May and September. Dogs were 3 months to 12 years old (median, 3.7 years); most were bitten on the head in the late afternoon. There was no sex predilection. Median time to evaluation was 1 hour (range, 15 minutes to 13 hours). Swelling in the area of the bite was the primary physical abnormality. Principal initial laboratory findings were echinocytosis, thrombocytopenia, leukocytosis, and prolonged activated clotting time. Ninety-four dogs were hospitalized; 48 were discharged the following day. Antimicrobials and crystalloid fluids, glucocorticoids, antihistamines, and antivenin administered i.v. were the most commonly used treatments. One dog died, and small dogs were hospitalized longer than large dogs. Antivenin administration was not significantly associated with duration of hospitalization but was associated with higher platelet counts after treatment and higher total hospital costs.

CONCLUSIONS AND CLINICAL RELEVANCE

Prairie rattlesnake envenomation in dogs is associated with high morbidity rate but low mortality rate. The efficacy of administration of antivenin for dogs with bites from this snake species is questionable.

Initial postmarketing experience with crotalidae polyvalent immune Fab for treatment of rattlesnake envenomation

STUDY OBJECTIVE

We describe our postmarketing experience with patients receiving Crotalidae polyvalent immune Fab (CroFab; FabAV) antivenom for treatment of rattlesnake envenomation.

METHODS

The charts of 28 patients admitted between March 1 and September 9, 2001, with rattlesnake envenomation and treated with FabAV were reviewed for demographic information, time until antivenom treatment, laboratory findings, evidence of hypersensitivity reaction, length of hospital stay, and readmission to the hospital.

RESULTS

All patients had swelling, 20 patients had elevated prothrombin times (>14 seconds), 12 patients had low fibrinogen levels (<170 mg/dL), and 6 patients had thrombocytopenia (platelet count <120,000/mm(3)) on presentation. The total dose of FabAV ranged from 10 to 47 vials per patient. Hypofibrinogenemia was resistant to FabAV in some patients. On follow-up, recurrence of coagulopathy was detected in 3 patients, and recurrence of thrombocytopenia was detected in 1 patient. Two patients demonstrated delayed-onset severe thrombocytopenia. Recurrence or delayed-onset toxicity might have been underestimated because of incomplete follow-up in some patients. No acute hypersensitivity reactions occurred. Two patients reported mild symptoms of possible serum sickness on follow-up.

CONCLUSION

FabAV effectively controlled the effects of envenomation; however, initial control of coagulopathy was difficult to achieve in some cases, and recurrence or delayed-onset hematotoxicity was common. When initially managing hematotoxicity, a trend toward normalization of laboratory values might be a more reasonable end point for FabAV treatment than attainment of normal reference values in nonbleeding patients.

Airway obstruction following canebrake rattlesnake envenomation

We report an unusual case of canebrake rattlesnake (Crotalus horridus atricaudatus) envenomation whose major manifestation was orolingual edema and airway compromise. The likely source of swelling was mucosal absorption of venom following the first aid technique of cutting and sucking the bite site. Except for airway compromise, the patient had mild local bite site effects (swelling) and mild systemic findings (depressed fibrinogen and elevated creatinine phosphokinase). He was managed with fiberoptic nasotracheal intubation and Crotalid antivenin with good outcome.

Role of surgical intervention in the management of crotaline snake envenomation

Crotaline venoms produce various toxic effects. Although these are most commonly treated with specific antivenoms, surgical management of snakebite has also been practiced for many years. Surgical approaches to pit viper envenomation include incision or excision of the bite site, fasciotomy, and digit dermotomy. The evidence regarding each of these procedures is sparse; however, incision or excision of the bite site are difficult to advocate. Fasciotomy and digit dermotomy may be appropriate in carefully selected patients.

Epidemiology and hospital course of rattlesnake envenomations cared for at a tertiary referral center in Central Arizona

OBJECTIVE

To describe the demographics and primary inpatient treatment of victims of rattle-snake bites (RSBs) referred to a teritiary referral poison treatment center in central Arizona, and to compare the frequency of local tissue complications and hematologic toxicity during hospitalization in children with those for adults.

METHODS

This was a chart review of patients diagnosed as having RSB by a toxicology service between July 1994 and April 2000. Data collected included: age, sex, date, bite location, time to and length of hospitalization, time to and amount of antivenin, serial hematologic studies, and inpatient complications.

RESULTS

Of 241 patients admitted, 236 charts met inclusion criteria. The majority of RSB victims were male (81%). Children (< or =13 years) represented 22%. Most RSBs (78%) occurred between April and September. Mean time (+/-SEM) to presentation was 1.7 +/- 0.2 hours. Antivenin was administered to 77% of patients, with an average (+/-SEM) of 28.5 +/- 0.9 vials administered. Hematologic abnormalities included: coagulopathy (60%), hypofibrinogenemia (49%), and thrombocytopenia (33%). No statistically significant difference in the above parameters was detected between upper- and lower-extremity envenomations, or between children and adults. Immediate antivenin reactions occurred in 36% of patients. Hemorrhagic bullae formation occurred in 22%, occurring most frequently in upper extremities. Operative procedures were required in 3.4% of patients. Hospitalization averaged 2.5 +/- 0.1 days. There was no fatality.

CONCLUSIONS

In Arizona, RSB victims were typically adult males with upper-extremity bites. Hematologic abnormalities were common. Local tissue complications were more common with upper-extremity envenomations. No statistically significant difference was detected in frequency of hematologic disorders or local tissue complications when children were compared with adults.