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.