May House Staff Quiz Answers
Poisoning/Hazardous Substances
1. 2010 Question 32 – Answer C. The single most useful diagnostic and prognostic test
in the setting of a TCA overdose is electrocardiography. In a study from 1985,
toxicologists found that a QRS duration of greater than 100 msec predicted seizures in
34% and dysrhythmias in 14% of patients who had TCA overdoses. The QRS widening
is related to fast sodium channel blockade caused by direct TCA effects and exacerbated
by acidemia. These effects can be overcome by the administration of sodium bicarbonate
boluses. Sodium bicarbonate should be administered until the QRS duration is less than
100 msec. The exact mechanism for this effect is unknown.
Adenosine and synchronized cardioversion are treatments for supraventricular
tachycardia. Amiodarone is a drug of choice for ventricular arrhythmias. External pacing
is appropriate treatment for refractory, symptomatic bradycardia.
2. 2011 Ques. #161. Answer C. In most cases, gastric foreign bodies may be managed
conservatively, but esophageal impactions require urgent removal. Button batteries
present a unique problem because they contain toxic heavy metals as well as alkaline
compounds (eg, sodium and potassium hydroxide) that are caustic to esophageal mucosa.
Significant esophageal injury (including perforation) has been reported from button
batteries lodged in the esophagus for as few as 6 hours. Most complications are caused by
larger batteries (20 to 23 mm diameter), although significant esophageal injury has been
reported with batteries as small as 8 mm in diameter. Symptoms of dysphagia (including
feeding refusal, excessive drooling, difficulty swallowing) or emesis suggest esophageal
impaction. Regardless of the presence or absence of symptoms, a radiograph of the neck,
chest, and abdomen should be obtained in all patients who present with a history of
possible battery ingestion.
A coin lodged in the esophagus must be removed emergently if the patient is unable to
handle secretions. Otherwise, endoscopy may be carried out within 12 to 24 hours, by
which time up to 30% of coins (mostly those in the distal third of the esophagus) will
have passed into the stomach.
3. 2010 Ques. #64 Answer A. The progressive lethargy, ataxia, seizures, anion gap
metabolic acidosis of 30 mEq/L, and osmolar gap of 53 mmol/L described for the boy in
the vignette are highly suggestive of alcohol poisoning. This is a particular diagnostic
possibility because the boy may have had access in the garage to such potential toxic
alcohols as ethylene glycol (antifreeze) and methanol (windshield wiper fluid). The
hypocalcemia suggests ethylene glycol exposure because the metabolism of ethylene
glycol uses the patient's calcium stores to create calcium oxalate, which is excreted in the
urine as crystals. Other findings in ethylene glycol poisoning may include flank pain,
hematuria, and acute renal failure.
Rapid diagnosis is critical for a patient who has symptomatic ethylene glycol poisoning
because delay in treatment can lead to renal damage, cerebral herniation, multiple organ
system failure, and death. Many household products are toxic and frequently accessible
to young children. Gasoline and turpentine are volatile hydrocarbons that cause
pulmonary injury after aspiration. Motor oil also is a hydrocarbon, but because of its high
viscosity and low volatility, it poses little risk for aspiration or toxicity. Organophosphate
insecticides inhibit acetylcholinesterase and cause a cholinergic crisis manifested by
bradycardia, hypersalivation, bronchorrhea, diarrhea, and muscle weakness.
4. 2010 Ques. #192 Answer E. Nausea, headache, bleeding from the external auditory
canal, and hearing loss in the setting of blunt head trauma, as described for the boy in the
vignette, are consistent with a temporal bone fracture. Other findings may include facial
paralysis, cerebrospinal oto- or rhinorrhea, and vertigo. Because temporal bone fractures
result from significant force, many patients have multiple other intracranial and
orthopedic injuries.
Although temporal bone fractures can be associated with other skull fractures, an
occipital fracture usually is characterized by occipital scalp swelling, and an orbital floor
fracture is characterized by maxillary tenderness, periorbital swelling, and abnormal
extraocular movements. A subdural hematoma or diffuse axonal injury causes altered
mental status.
Know that temporal bone fractures are commonly manifested by bleeding from the
external auditory canal or hemotympanum, hearing loss, facial paralysis, and cerbrospinal
fluid otorrhea.
5. 2011 Ques.#25 Answer A. Acute respiratory failure remains a significant cause of
morbidity and mortality in hospitalized pediatric patients. The most severe forms of acute
respiratory failure are acute lung injury (ALI) and acute respiratory distress syndrome
(ARDS), which are defined by: acute onset, severe arterial hypoxemia (PaO2/FiO2 ratio
<200 mm Hg for ARDS and PaO2/FiO2 ratio <300 mm Hg for ALI), bilateral infiltrates
on chest radiography, and absence of left atrial hypertension. Various treatment
strategies have been studied for adult patients who have ARDS, and results have been
extrapolated to the pediatric population. The use of low tidal volumes (4 to 6 mL/kg) has
been the only approach demonstrated to decrease mortality in several adult studies. The
improvement in mortality is believed to be due to the avoidance of high tidal volume
strategies, which have been shown to produce secondary lung injury. In addition, goals of
respiratory support include a PaO2 of 60 to 80 mm Hg, SpO2 of 90% or greater, and pH
of 7.30 to 7.45. Therefore, decreasing the PEEP (with subsequent loss of lung volume
and increased oxygen requirement) or increasing the oxygen to ensure an SpO2 greater
than 95% are not indicated. Early use of corticosteroids in adult patients who have ARDS
has shown conflicting results and is not recommended routinely. Surfactant has been
shown to improve oxygenation, but it has not been demonstrated to have an effect on
long-term outcome.
6. 2011 Ques.#208 Answer B. Because most serious plant ingestions have cardiac effects,
electrocardiography should be considered in affected patients. This is especially true for
the patient described in the vignette, who has ingested foxglove, a source of potent
cardiac glycosides.
7. 2011 Ques.#44 Answer D. Antibiotic therapy for infected dog bites should have a
broad spectrum to cover the oral flora of the animal, including Pasteurella,
Staphylococcus aureus, streptococci, and oral anaerobes. Clindamycin and trimethoprimsulfamethoxazole is the recommended regimen to cover this spectrum in the penicillinallergic child. Amoxicillin-clavulanate is otherwise considered the drug of choice.
Methicillin-resistant S aureus infections have not been reported in animal bites to date.
Azithromycin and trimethoprim-sulfamethoxazole, cefdinir, and doxycycline do not
provide adequate coverage for anaerobes or Pasteurella.
Antibiotic prophylaxis at the time of an animal bite might be considered for hand bites or
deep wounds because they are at the highest risk of infection. Cat bites transmit similar
flora, and treatment recommendations are the same as for dog bite infections.
Rabies exposure may be another major concern after an animal bite. As in this vignette, if
the animal seems well and can be captured and observed for 10 days, rabies prophylaxis
is not necessary. With dog, cat, and ferret bites, if the animal is suspected of being rabid,
it should be sacrificed immediately and tested for rabies. If the animal escaped,
consultation with the local health department is advised for bites from dogs, cats, or
ferrets. Skunks, raccoons, foxes, and most other carnivores as well as bats should be
considered rabid unless laboratory tests prove the animal is negative. Rodents and
lagomorphs (rabbits, hares) are unlikely to carry or transmit rabies.
If rabies prophylaxis is indicated, recent Centers for Disease Control and Prevention
guidelines recommend a four-dose vaccine series (rather than the previously
recommended five doses) plus an initial dose of rabies immune globulin. In all instances,
the patient's tetanus immunization status should be reviewed. If it is not up to date,
tetanus immune globulin or tetanus vaccine should be administered.
8. 2011 Ques. #10. Answer E. The boy described in the vignette has meningitis, with low
serum sodium and potassium and normal glucose concentrations. The serum electrolyte
findings are typical for the syndrome of inappropriate antidiuretic hormone release
(SIADH) associated with central nervous system inflammation or injury. Another
possibility in the differential diagnosis is adrenal insufficiency. However, primary adrenal
insufficiency leads to hyponatremia and hyperkalemia. Isolated cortisol deficiency due to
adrenocorticotrophic hormone (ACTH) deficiency can present with hyponatremia and a
normal potassium concentration but generally is associated with hypoglycemia. Urinary
electrolyte assessment could clarify this picture because urine osmolality and sodium are
increased (urine osmolality > serum osmolality, and urine sodium >20 mEq/L [20
mmol/L]) in SIADH, whereas a dilute urine is excreted in adrenal insufficiency.
Fluid restriction is the most important first step in management of SIADH. If there is
reason to suspect cortisol deficiency (blood pressure instability or evidence of vascular
instability), administration of hydrocortisone hemisuccinate is appropriate, but if it is
possible to await laboratory results of cortisol and ACTH measurements, glucocorticoid
therapy can follow laboratory confirmation of the condition.
9. 2012 Ques. 246 Answer E. Over-the-counter cough and cold medications may contain
one or more components, usually with decongestant, antihistamine, expectorant, or cough
suppressant effects. Multiple studies have shown that these medications have little or no
efficacy in the treatment of upper respiratory tract infections in children compared with
placebo. Although experts further recommended that the products be eliminated for
children younger than 6 years of age, a pharmaceutical trade group subsequently
voluntarily changed labeling to warn about their use in children younger than 4 years.
The most common decongestant in cold and cough preparations is pseudoephedrine,
which may have sympathomimetic effects, such as tachycardia, arrhythmia, hypertension,
central nervous system stimulation, and rarely seizures. Antihistamines such as
diphenhydramine, brompheniramine, chlorpheniramine, and carbinoxamine can lead to
central nervous system agitation or depression, dysrhythmias, hypertension, seizures, and
in extreme cases, respiratory depression. Guaifenesin, the most commonly used
expectorant, is generally well tolerated but may cause mild gastrointestinal discomfort.
Dextromethorphan and codeine are the most widely used cough suppressants and appear
to have efficacy greater than placebo in adults, but such efficacy is not noted for children.
Dextromethorphan is derived from opiates and acts at the central nervous system level to
inhibit cough. Although it does not have the addictive or analgesic properties of other
opiates, it can cause euphoria, hallucinations, lethargy, coma, nausea, dizziness,
drowsiness, ataxia, nystagmus, and urinary retention. It does have abuse potential
because of the euphoric effects it may produce. In lower doses, codeine can lead to
somnolence, ataxia, gastrointestinal distress, and pruritus; in higher doses, it leads to
depressed mental status and respiratory depression. Since 1997, the American Academy
of Pediatrics has recommended against the use of codeine- and dextromethorphancontaining cough remedies in children. Because some cold and cough preparations may
contain analgesics, it is prudent to measure the serum concentration of acetaminophen for
this patient, but agitation, tachycardia, and hypertension are not characteristic of
acetaminophen overdose.
10. 2011 Ques.#144; Answer B. The acute onset of hand pallor following a supracondylar
fracture of the humerus as described for the boy in the vignette should alert the clinician
to a brachial artery injury, an uncommon but serious complication of this type of fracture.
Approximately 5% to 20% of children who have distal humeral fractures experience
vascular injury, especially with fractures that involve posterolateral displacement of the
distal fragment. In most cases, the artery is compressed by the fracture fragment, and
prompt reduction of the fracture restores distal perfusion. The brachial artery is
particularly vulnerable because it travels along the anterior humerus before dividing into
the radial and ulnar branches below the antecubital fossa.
Anterior interosseous nerve injury can occur with this fracture but causes weakness of the
index and middle fingers. Compartment syndrome occurs in approximately 1% of
supracondylar fractures, but pallor is a late finding. Cubitus varus is the most common
late complication of a supracondylar fracture and results in a cosmetic deformity in which
the forearm deviates toward the torso when the arm is extended with the palm facing
forward. Volkmann contracture is a late sequela of forearm muscle ischemia related to
upper extremity compartment syndrome and results in a flexion contracture of the
fingers, hand, and wrist.