Page 1753 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

1222 PART 11: Special Problems in Critical Care

the long half-life of some of these drugs, toxic combinations may not be reactions. In Crotalidae bites, local effects develop within minutes and
apparent for days to weeks. consist of stinging, burning, swelling, erythema, ecchymosis, and hem-
When taken as a single overdose, the most toxic SSRIs are cita- orrhagic blebs. Extremities swell over the next several hours, occasion-
lopram and escitalopram. They are both (although citalopram more ally resulting in compartment syndrome. Facial bites with severe local
commonly) associated with seizures. Patients with acute ingestion swelling may obstruct airways. Systemic effects of Crotalidae venom
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of these medications can develop QT prolongation and clinically sig- include fever, nausea, vomiting, delirium, seizures, muscle cramps, jaun-
nificant arrhythmias—a finding that can be delayed up to 24 hours after dice, disseminated intravascular coagulation, acute renal failure, and
ingestion. Most fatalities associated with SSRI overdose are in the setting shock. Death is rare but may occur hours to days after envenomation.
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of ingestion of multiple other medications or massive solitary overdose. Elapidae snake bites may produce minimal initial local symptoms
Multiple diagnostic criteria based on clinically apparent neuromus- or signs of bite. In contrast to Crotalidae envenomation, the effects of
cular abnormalities and autonomic alterations have been developed for Elapidae envenomation are primarily neurologic—most commonly
serotonin syndrome. Common signs and symptoms include agitation, cranial nerve palsies but also progressing to dysarthria, dysphagia, and
confusion, tachycardia, nausea, diarrhea, vomiting, fever, hyperreflexia, respiratory muscle fatigue—and may be delayed up to 12 hours. One
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myoclonus, tremor, and diaphoresis. 368,369 The diagnosis requires exposure exception of this differentiation by family is the Mohave rattlesnake,
to a medication known to be serotonergic. The differential diagnosis for which causes symptoms more similar to those seen with coral snakes.
a patient presenting with serotonin syndrome is broad and includes neu- Treatment of rattlesnake bite consists of splinting and immobilizing
roleptic malignant syndrome, malignant hyperthermia, anticholinergic the bitten extremity below heart level to slow the spread of venom.
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toxicity, infection, thyroid storm, and environmental hyperthermia. Tourniquets or field incision and drainage are not recommended.
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Trazodone, which also acts as an α-adrenergic blocker, may cause hypoten- Surgical consultation should be obtained for management of serious
sion. Other findings include hyponatremia and SIADH. 371,372 Death is rare. wounds, and debridement of necrotic wounds may be necessary. If
The diagnosis of serotonin syndrome should be considered in any compartment syndrome is suspected, tissue pressure should be mea-
patient with compatible clinical features, particularly if there is a history sured. Surgery should be reserved only for severe and refractory cases
of depression. Blood levels in serotonin syndrome are not helpful because and may not improve outcome. Tetanus prophylaxis should be
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the syndrome is a result of increased concentrations at nerve endings. provided. Initial laboratory investigation in the setting of pit viper
Treatment of serotonin syndrome starts with identifying and treating envenomation should include a DIC panel, blood typing, and evaluation
life-threatening problems, immediate discontinuation of the offending of renal and hepatic panels.
agents, and avoidance of other serotonergic medications (such as fentanyl Rapid volume infusion is indicated in the initial management of
for pain/sedation or ondansetron for nausea). Activated charcoal should be hypotensive patients. Several liters of isotonic fluid may be required.
considered for patients presenting with acute ingestion. Dialysis and hemo- If unresponsive to initial crystalloid resuscitation, some sources
perfusion are not effective. Prognosis is generally good in mild cases, with advocate use of colloid infusion, with vasopressors acting as a last
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resolution within 24 to 36 hours with supportive therapy alone. In moder- resort. Patients with significant Crotalidae envenomations with progres-
ate cases, benzodiazepines are good first-line therapies for symptomatic sive local or systemic effects should be considered for specific treat-
control. Severe cases with refractory hyperthermia and agitation may ment with sheep- or equine-derived Crotalidae antivenin (CroFab or
require sedation, paralysis, and mechanical ventilation. Anecdotal reports Antivenin Crotalidae Polyvalent [ACP]). ACP is more frequently associ-
suggest that the serotonin antagonist cyproheptadine (8 mg by mouth or ated with anaphylactic reactions than is CroFab and although skin testing
via NG tube as an initial dose) may be beneficial. 373,374 Chlorpromazine had been advocated in the past, it has largely been abandoned because
and olanzapine have also been used to treat serotonin syndrome, although of poor predictive value. Antivenin is dosed by vial based on degree of
others recommend against their use as neuroleptic malignant syndrome envenomation. Exact dosing varies based on which antivenin is being
may complicate serotonin syndrome treatment or diagnosis. Bromo- used. Most patients respond to the initial antivenin infusion, but some
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criptine should be avoided, as it may worsen serotonin syndrome. patients require additional infusions every few hours. Patients should be
■ ENVENOMATIONS monitored closely for immediate hypersensitivity reactions and delayed
hypersensitivity reactions (ie, serum sickness) which can occur 5 to
Snake Bite: The majority of poisonous snake bites in the United States 14 days later. If a hypersensitivity reaction occurs, the need for con-
involve the Crotalidae (pit viper) family of snakes (eg, rattlesnakes, cop- tinued antivenin infusion should be reconsidered. If more antivenin is
perheads, and cottonmouths) in the southwest, west, and southeast. Pit necessary, it should be given with histamine blockade, intravenous
vipers are named for a small pit between their eyes and nostrils, and steroids, and possibly epinephrine if necessary.
large venom glands result in triangular shaped heads. The other family Of note, commercially available equine antivenin is also available for
of poisonous snakes in the United States is the Elapidae (specifically, eastern coral snake (Micrurus fulvius) and Texas coral snake (Micrurus
the coral snakes). A common rhyme helps distinguish venomous coral fulvius tenere) envenomation. In cases of confirmed coral snake bites,
snakes from other harmless snakes: “Red on yellow kill a fellow. Red on this antivenin should be started even in the absence of symptoms, as
black, friend of Jack”—describing their stripe pattern. they may be delayed and are possibly life threatening.
Most bites are accidental, involving native, noncaptive snakes. Spider Bite: In North America, only the widow spiders (Latrodectus
Accidental bites are more common in the summer months, in the after- species) and the recluse spiders (Loxosceles species) are medically impor-
noon or evening, and during recreational activities. Young men are the tant. The female black widow spider (Latrodectus mactans) has a shiny
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most frequent victims. black body approximately 1 cm in diameter with a red hourglass mark
Most snakes strike when they are disturbed. Telltale fang marks on the abdomen. This spider, which favors woodpiles, dimly lit sheds,
appear as paired puncture wounds or lacerations a few millimeters greenhouses, basements, and outdoor toilets, is most often encountered
deep. Atypical wounds consisting of single or multiple puncture sites during the summer months. It bites aggressively to introduce potent
or scratches are also seen, so the bite pattern cannot reliably categorize venom into its victim. Envenomation results in local pain and erythema
the bite as venomous or nonvenomous. Twenty-five percent of bites do followed by muscle cramps and fasciculations near the bite site. Painful
not result in envenomation (ie, “dry bites”), and half of all bites result cramps may generalize to the abdomen, back, and chest, mimicking
in minimal or no envenomation. 376,377 Dry bites are generally benign, myocardial infarction or an acute surgical abdomen. Cramps may
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although there is potential for infection due to bacteria in the snake’s last for several days. Hypertension, tachycardia, tremor, fever, agitation,
mouth or on the victim’s skin. diaphoresis, and nausea are also common. Rarely, black widow spider
When envenomation occurs, a variety of toxic proteins and enzymes bite results in hypertensive crisis or cardiopulmonary arrest. Treatment
are introduced into the victim that can cause serious local and systemic of black widow spider bite consists of general supportive measures

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