NEW CASE
Snakebite in Central Park?

CASE PRESENTATION:
Ruben Olmedo
New York City Poison Center
New York, NY

CASE DISCUSSION:
Richard Dart*
Rocky Mountain Poison Center
Denver, CO

Int J Med Toxicol 1999; 2(1):1


These case conferences are supported by a grant from Orphan Medical, Inc.

CASE PRESENTATION (Ruben Olmedo)

A 60 year-old man presented to the hospital complaining of increasing left arm pain and swelling after being bitten on dorsal base of left thumb by a snake. The patient states that he was playing Frisbee in Central Park (New York) on a cool October morning. When he went to get the Frisbee after it landed in the tall grass, something bit him. His hand swelled within an hour and he came to the hospital. In the emergency department the patient denied previous snakebites or having been treated with snake antivenin. He also denied any significant past medical or surgical history, or having allergies to medications. On review of systems the patient did note a bitter taste in his mouth. His initial vital signs were: blood pressure, 150/90 mm Hg; pulse, 90 beats/minute; respirations, 16 breaths/minute; temperature, 98.6 °F. On physical examination, Two puncture wounds were noticed at the base of the left thumb, and were oozing a serosanguinous fluid (Figure 1).

Figure 1. Two puncture wounds were noticed at the base of the left thumb.

Click here for a higher resolution image (for slower Internet connections, this may take a few minutes).

There was marked swelling of the left hand and forearm with a bluish discoloration extending to the elbow. Two large bore intravenous lines were started in the other arm. Tetanus immunization and antibiotics were given. Laboratory values including platelets, coagulation profile, fibrinogen, fibrin split products, blood urea nitrogen and creatinine were all normal. Within two hours (three hours after the bite) the swelling had moved about half way up the patient’s humerus (Figure 2). During this time many different people interviewed the patient because there are no indigenous venomous snakes on Manhattan, but he remained certain about his history.

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Figure 2. Swelling had moved about half way up the patient’s humerus.

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In addition, the New York City Police Department, the Parks Department, and the Department of Animal Affairs began extensive investigations because it was just a few days before the New York City Marathon and there would be thousands of people in the park. By four hours after the bite, the swelling had reached the patient’s shoulder and his hand appeared cool and was held in partial flexion. Laboratory parameters and vital signs had not changed. Compartment pressures measured in the thenar and hypothenar compartments of the hand were 46 and 50 mm Hg, respectively.

QUESTIONS AND DISCUSSION (Richard Dart)

1. Do you need to routinely measure compartment pressures in patients with significant swelling?

No, we do not recommend routine measurement of compartment pressure in patients with swelling. We use the traditional signs of compartment syndrome, along with a high level of caution to guide the assessment of the snakebite with pain and swelling. Thus, if the patient develops pain consistent with compartment syndrome (especially if the pain seems difficult to treat), pallor, paresthesia, palpable tenseness of a compartment, paralysis, etc, we would recommend immediate determination of compartment pressure.

It may seem that all patients with snakebite, especially crotalid snake bite, would fulfill these criteria. However, there are relatively clear differences in the clinical presentation of compartment syndrome and the usual pain and swelling of snakebite. To my knowledge, the pain of any snakebite is nearly always limited to the bite site, to areas of extension such as proximal progression (leading edge), and to areas of lymphatic drainage. There is often only minimal increase in pain during a maneuver such as flexion. The pain is typically blunted or reduced by adequate antivenom administration.

Use of narcotic analgesics is also a important consideration. It is common to use small to moderate doses of an opioid analgesic (e.g. morphine 5 – 10 mg or meperidine 50 - 75 mg). These doses should produce a clinically notable response. If repeated doses are needed or the pain is increasing despite antivenom administration, then something is wrong. Like much of emergency medicine, the most important step in making a diagnosis is realizing that the original diagnosis must be questioned. The repeated need for parenteral analgesia despite antivenom therapy indicates that that you should consider compartment syndrome.

The location of swelling is also important. A bite on the finger may produce swelling and lead to a condition similar to compartment syndrome. Although not a true compartment, the strong limiting membrane of the skin may produce signs of vascular compromise in the distal finger. This is a very difficult situation to assess. It is primarily the palpable tenseness of the finger that indicates that elevated pressure may be present. The use of dermotomy for the snakebitten finger has been described and appears a reasonable option in patients with a compromised digit. This procedure involves incising just the skin along the lateral margins of the finger. This allows the finger to pop open like a plumping hot dog on the grill. When performed properly, it has little risk of damaging the finger and leaves an acceptable cosmetic result (1). Dr. Charles Watt was a general surgeon with an exceptionally balanced view of snakebite. While he used antivenom generously, he recognized that it is inconceivable that adequate blood flow could enter some of these very tight digits after the swelling had already developed. The dermotomy allowed blood (and antivenom) to enter the digit. He has now passed the torch to Edward Hall, MD, another surgeon with similar attitudes. If cases arise that could benefit from his experience, we can provide his phone number.

2. If you do elect to measure pressures and they are elevated, would you try antivenin, go straight to fasciotomy, or both.

We have a standard protocol for the management of potential compartment syndrome:

  1. Consider consultation with orthopedic surgery or whatever service will be responsible for performing the surgery, if needed.
  2. Measure the compartment pressure.
  3. If it is elevated, immediately administer another 10 vials of antivenom as well as mannitol, 1 g/kg.
  4. If the compartment pressure remains elevated, consider fasciotomy.

This approach is recommended by more than one poison center, but it is true that there are no data to support it. Anecdotal experience, including my own, has shown that the use of mannitol may quickly reduce a marginal compartment pressure (e.g. 40 – 50 mm Hg) to below 30 mm Hg, thereby avoiding fasciotomy in some cases.

This approach combines medical and surgical treatment in order to provide maximal therapy for a limb-threatening condition. Although the process culminates in fasciotomy, there is really no evidence that fasciotomy is effective. Unlike the situation in compartment syndrome following trauma, snakebite would be expected to have two pathophysiological processes developing simultaneously. First, the venom causes cellular injury and produces swelling. Second, as the swelling increases, the intracompartmental pressure has increased above the perfusion pressure of the compartment. Thus, simply correcting the second component does not necessarily improve the first. After all, the injury has already progressed to the point of causing sufficient swelling to cause markedly increased pressure. Antivenom works, but it cannot reverse cell death that has already occurred.

The experimental evidence available does not support the use of a surgical approach. First, one should recognize that there are no human studies available. Stewart et al. (1989; 2) provided the only controlled comparative animal study. His group reported that the best outcome after intracompartmental injection of venom was treatment with antivenom alone (2). Even the group that combined antivenom and fasciotomy had a poorer outcome.

Thus, we are simply throwing everything we have at a very difficult problem for which there may be no adequate treatment. Like a trauma patient, we can’t reverse cellular death that has already occurred, however, we can hopefully limit the consequences or progression by administration of antivenom and quality supportive care.

3. In this unknown and confusing story that may involve an exotic snake, would you empirically use Wyeth antivenin? Would your opinion change if you had access to Crotab?

This patient has a clinical syndrome that is characteristic of a viper bite: localized pain and swelling that is spreading proximally. Mild hypertension and the bluish discoloration are useful clues that this is consistent with a crotalid envenomation. The only native snake species that can cause this condition in the United States are the crotalid snakes. The wild card is that there are no indigenous venomous snakes to Central Park and it is well known that there are a substantial number of individuals who keep snakes as pets. Nevertheless, the most likely perpetrator is an indigenous species. Thus, we would recommend proceeding on that conclusion while simultaneously attempting to discover the full story.

Our recommendation would have been to administer Antivenin (Crotalidae) Polyvalent. The indication for treatment is evidence of progressive venom effect. As soon as this patient’s swelling progressed, we would have recommended immediate administration of 10 vials over a 1 hour infusion period. If the antivenom terminated extension of the swelling, I would be relatively confident that this was a crotalid envenomation. If it did not stop the swelling, the diagnosis must be reconsidered. I would not recommend the use of an exotic antivenom (even though conveniently available at the Bronx Zoo) unless there was clear evidence that an exotic snake was involved.

The availability of CroTAb would not affect the decision. The critical decision is: Does the patient have progressive injury? The answer in the case presented is yes: there is obvious and serious evidence of progression. This amount of swelling will mean prolonged convalescence and possible permanent dysfunction (3) as well as a prolonged hospitalization. If antivenom is used early, the patient typically can be discharged in 48 hours. Thus, the patient should receive antivenom. When CroTAb, an Fab based product analogous to Digibind for digoxin poisoning, becomes available, the decision will become more difficult. Because it is an Fab, CroTAb may penetrate tissues better than Wyeth antivenom. This is a logical but theoretical argument that only further research can answer.

CASE PRESENTATION - FURTHER INFORMATION (Ruben Olmedo)

Five hours after the bite, the patient was treated with 5 vials of Wyeth Antivenin (Crotalidae) Polyvalent. In addition, a fasciotomy of the forearm and the hand was performed under general anesthesia. (Figure 3)

Figure 3. Fasciotomy of the forearm and the hand was performed under general anesthesia.

Cick here for a higher resolution image (for slower Internet connections, his may take a few minutes).

The patient never became hypotensive, or developed respiratory distress. Post operatively, laboratory values remained normal. On hospital day 2 under extensive pressure, the patient admitted that he was a purveyor of rare meats and that the bite was the result of a Western Diamondback rattlesnake. A police raid of his home yielded numerous live snakes in his refrigerator, as well as meats from Bobcat and other rare species. On day 4 of hospitalization the patient had the fasciotomy scar partially closed, and complete closure was achieved on hospital day 11. The patient never developed myalgias, joint pain, fevers or other symptoms of serum sickness. He was discharged from the hospital on day 16, with excellent function and adequate cosmesis.

FURTHER DISCUSSION (Richard Dart)

This is a new one! While I have seen bites for myriad reasons, this is the first purveyor of exotic meats!

The lack of coagulopathy is an important teaching point. While the presence of a coagulopathy is a common manifestation, it is far from universally present. It seems more common with bites of the Eastern Diamondback and is often present with other crotalid, but is almost never present following the bite of a Copperhead. Thus, the lack of coagulopathy should not be used to exclude a crotalid snake bite.

A couple of points regarding the management of exotic snake bite. First, it is important to realize that there is no magic bullet. Some of the antivenoms for exotic snakes are very effective, some are not. In general, a patient should have progressive signs before an antivenom is administered. One exception is that some neurological effects do not reverse after antivenom. If one is sure an envenomation has occurred, it is reasonable to administer antivenom before symptoms and signs develop. Our native Eastern and Texas coral snakes are examples. In the case of exotic snakes, however, it is nearly always true that a substantial amount of time has elapsed before the antivenom is available. If the patient still doesn’t have significant signs of envenomation at the time the antivenom becomes available, the decision to administer antivenom should be reconsidered. Many vials of antivenom have been administered in a useless manner and the phenomenon seems more common with the exotic antivenoms.

Second, the way to find an exotic antivenom quickly is to be prepared. There is a resource named the Antivenin Index. The Index is a list of antivenoms stocked by members of the American Zoo and Aquarium Association. The Index also includes home phone numbers for a large number of physicians experienced in the management of venomous snakebite. While the Index is provided to each poison center in the United States, several centers have indicated that they are not comfortable using it. It may be necessary to contact more than one center to find the information you want. Determining this information beforehand will reduce the confusion and frustration that often accompanies cases involving exotic species.

It is not unusual for a zoo to pay $25,000 – $50,000 just to have these antivenoms available for use by their keepers if a bite were to occur. In certain cases, the zoo members are willing to share their antivenom. However, this willingness has deteriorated some in recent years owing to the annoying tendency of physicians to: 1) request the inappropriate antivenom or use their antivenom for patients who did not need it and 2) refuse to pay for the antivenom once it is used. The antivenom should not be requested unless the facility is willing to pay for it and then bill the patient. Obviously, the cost of just the antivenom could be several thousand dollars. Nevertheless, the system has been effective on several occasions and the medical world owes the zoos and aquariums a large debt of gratitude.

* Dr. Dart has received research support from Therapeutic Antibodies, Inc. 

References

  1. Watt CH. Treatment of poisonous snakebite with emphasis on digit dermotomy. South Med J 1985;78:694-699.
  2. Stewart RM, Page CP, Schwesinger WH, McCarter R, Martinez J, Aust JB. Antivenin and fasciotomy/debridement in the treatment of severe rattlesnake bite. Am J Surg 1989;158:543-547.
  3. Dart RC. Sequelae of pit viper envenomation, in Biology of Pit Vipers, Campbell JA, Brodie ED, Jr. eds. Selva Publishing, Tyler, Texas, 1992, pp 395-404.

 

 



Int J Med Toxicol 1999; 2(1):1

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