Critical Care

2009 PREP SA on CD-ROM

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Question: 26

A 6-year-old boy who has severe vomiting and dehydration is admitted to the hospital. Initial laboratory studies demonstrate a serum sodium concentration of 126.0 mEq/L (126.0 mmol/L), potassium of 5.3 mEq/L (5.3 mmol/L), and pH of 7.26. After 24 hours of rehydration with 0.9% saline, his serum sodium concentration is 129.0 mEq/L (129.0 mmol/L) and potassium is 4.9 mEq/L (4.9 mmol/L). On physical re-examination, you note that his knees, elbows, dorsal fingers, and tongue are somewhat pigmented (Item Q26), and his skin is darker than that of other family members.

Of the following, the MOST useful diagnostic laboratory study at this time is measurement of serum

A. antidiuretic hormone (ADH) and alpha-melanocortin-stimulating hormone

B. cortisol and adrenocorticotropic hormone (ACTH)

C. cortisol and dehydroepiandrosterone

D. dehydroepiandrosterone and ACTH

E. insulin-like growth factor 1 and ADH


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Question: 26

Hyperpigmentation (arrows), as exhibitied by the boy in the vignette. (Courtesy of the Media Lab at Doernbecher)


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Critique: 26 Preferred Response: B

Acute or chronic vomiting and dehydration associated with hyponatremia and elevated potassium concentrations, as described for the boy in the vignette, suggest adrenocortical insufficiency. Primary adrenal insufficiency is associated with skin pigmentation (Item C26) because of ACTH overproduction. ACTH acts directly on the melanocortin receptors of skin to activate melanin production. Normally, ACTH controls the amount of cortisol produced by the adrenal cortex by stimulating adrenal steroidogenesis. Cortisol then feeds back both to the pituitary and hypothalamus to inhibit pituitary ACTH release. Measurement of low serum cortisol and markedly elevated serum ACTH concentrations at any time of the day usually confirms the diagnosis of primary adrenal insufficiency. The presence of skin pigmentation in the boy described in the vignette suggests that identifying an elevated ACTH value will be easy, but because there is diurnal variation in ACTH and cortisol, with highest concentrations during the early morning hours and lowest in the late afternoon and evening, children who have less severe adrenal insufficiency should have these hormones assessed in the early morning. In addition, an ACTH stimulation test might be necessary for diagnostic confirmation. In this test, synthetic ACTH1-24 is administered intravenously, and the adrenal cortisol response is measured before injection and at 1 hour postinjection. An adequate cortisol response at 1 hour rules out adrenal insufficiency. Although ADH concentrations might be elevated in primary adrenal insufficiency because of loss of intravascular fluid volume, measurement of this hormone does not help in the diagnosis of a child who has low serum sodium and somewhat elevated potassium values. Low serum sodium is associated with inappropriate ADH release, but the potassium would not be elevated. ACTH and melanocyte-stimulating hormone (a melanocortin) both are produced from enzymatic cleavage of a larger molecule, proopiomelanocortin. Although melanocyte-stimulating hormone might be overproduced to some extent in the presence of excess ACTH, elevated concentrations of this hormone are not necessary for skin pigmentation with ACTH excess. Dehydroepiandrosterone (DHEA) is a weak androgen precursor produced by the fetal adrenal initially; production increases again in mid-childhood with the onset of adrenarche. DHEA values rise slowly from age 4 to 6 years. Elevated values may be found with some adrenal tumors and some relatively rare types of congenital adrenal hyperplasia, but these disorders are associated with some degree of early puberty. DHEA-S, the sulfated product of DHEA, usually has stable serum values without diurnal variation. Therefore, normal DHEA or DHEA-S values in an adolescent or adult confirm the presence of a functioning adrenal gland. This test is less useful in a young child because onset of adrenarche is variable. Cortisol is low in primary or secondary adrenal insufficiency but tends toward low ranges in most people after the early morning hours. Insulin-like growth factor 1 is a marker for growth hormone sufficiency, and normal concentrations vary with age and sex. Because this child does not seem to have a growth problem, the result of this assay should be normal for age.

References:

Auchus RJ, Rainey WE. Adrenarche-physiology, biochemistry and human disease. Clin Endocrinol. 2004;60:288-296. Available at: http://www.blackwell-synergy.com/doi/full/10.1046/j.1365-2265.2003.01858.x

Coco G, Dal Pra XC, Presotto F, et al. Estimated risk for developing autoimmune Addison's disease in patients with adrenal cortex antibodies. J Clin Endocrinol Metab. 2006;91:1637-1645. Available at: http://jcem.endojournals.org/cgi/content/full/91/5/1637

Donohoue PA. Diagnosis of adrenal insufficiency in children. UpToDate Online 15.3. 2008. Available for


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subscription at: http://www.uptodateonline.com/utd/content/topic.do?topicKey=pediendo/20697

Perry R, Kecha O, Paquette J, Huot C, van Vliet G, Deal C. Primary adrenal insufficiency in children: twenty years experience at the Sainte-Justine Hospital, Montreal. J Clin Endocrinol Metab. 2005;90:3243-3250. Available at: http://jcem.endojournals.org/cgi/content/full/90/6/3243

Wilson TA, Speiser P. Adrenal insufficiency. eMedicine Specialties, Pediatrics: General Medicine, Endocrinology. 2007. Available at: http://www.emedicine.com/ped/TOPIC47.HTM


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Critique: 26

In Addison disease, excess adrenocorticotropic hormone acts on melanocortin, causing increased melanin production and hyperpigmentation of the mucous membranes and skin (arrows). (Courtesy of the Media Lab at Doernbecher)


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Question: 41

You are evaluating a 20-month-old boy who has a rectal temperature of 106°F (41.1°C) and a history of coughing. His mother reports that the child has had a decrease in activity and eating over the past 2 days. On physical examination, the boy appears moderately ill but is alert and easily interacts with you. He occasionally grunts, has a heart rate of 140 beats/min, and has a respiratory rate of 55 breaths/min. His neck is supple, he is circumcised, and he has no evidence of otitis media.

Of the following, the BEST initial test in the evaluation of this child is

A. chest radiography

B. C-reactive protein measurement

C. erythrocyte sedimentation rate

D. lumbar puncture

E. urinalysis


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Critique: 41 Preferred Response: A

Physical examination, a detailed history, and direct observation can help the clinician recognize up to 90% of children who have a serious illness. Carefully selected laboratory and diagnostic tests can enhance the detection of invasive bacterial infections in children who have fever. Infants younger than 3 months of age who present with a fever are at high risk of invasive bacterial infection due to their still-developing immune system. Specific high-risk factors, including a history of prematurity, evidence of an abnormally elevated or depressed white blood cell count, a focal source of infection such as otitis media or soft-tissue infection, or abnormal chest findings on radiography are associated with serious bacterial infection in almost 25% of cases. Infants younger than 3 months of age who do not have such high-risk factors still have a nearly 3% incidence of a serious bacterial infection. Infants between the ages of 3 months and 3 years remain at risk for serious bacterial infections, with reports of a 3% incidence of bacteremia associated with a temperature of 102.2°F (39.0°C) and 7% with a temperature of 104.0°F (40.0°C). A temperature higher than 105.8°F (41.0°C) frequently is associated with invasive bacterial infection. The child described in the vignette has both an elevated temperature and signs and symptoms suggestive of a primary respiratory infection that make chest radiography the best initial diagnostic test. A lumbar puncture can be deferred because of the patient's age and appropriate interaction with the examiner. The patient's age, sex, and circumcised status make a urinary tract infection unlikely; as a result, urinalysis also could be deferred pending results of chest radiography. Positive urinalysis can be suggestive of a urinary tract infection, but a urine culture remains the definitive test when a urinary tract infection is suspected. Elevated erythrocyte sedimentation rates and C-reactive protein measurements are indicative of the presence of acute inflammatory processes, but they are nonspecific findings. Their elevation in young children who have fever may be useful in guiding the clinician toward additional studies in selected children.

References:

Brook I. Unexplained fever in young children: how to manage severe bacterial infection. BMJ. 2003;327:1094-1097. Available at: http://www.bmj.com/cgi/content/full/327/7423/1094

McCarthy PL. Evaluation of the sick child in the office and clinic. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier; 2007:363-365


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Question: 57

You are treating a 14-year-old boy in the pediatric intensive care unit who suffered a traumatic brain injury in a motor vehicle crash earlier today and underwent surgery to drain a right-sided epidural hematoma. He is currently receiving mechanical ventilation and is sedated. The nurse calls you to the bedside because the intraventricular catheter is clotted and no intracranial pressure waveform is seen on the monitor. On physical examination, you note that his right pupil is dilated and unresponsive to light, which differs from findings on your examination immediately after surgery.

Of the following, the MOST appropriate immediate next step is

A. administration of fentanyl

B. administration of mannitol

C. cerebral angiography

D. replacement of the intraventricular catheter

E. ophthalmology consultation


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Increased intracranial pressure can cause herniation of the cerebral contents, which is a neurologic emergency. Transtentorial herniation results from downward or upward displacement of the brain through the tentorium at the level of the incisura. Temporal lobe (uncal) herniations are a subcategory of transtentorial herniations that are characterized by dilation of a unilateral pupil due to compression of the oculomotor nerve, as described for the boy in the vignette (Item C57). Uncal herniations usually occur with rapid expansion of the contents of the temporal lobe fossa, such as seen with epidural hematomas, focal injury, or infection. Findings for the boy in the vignette suggest rebleeding of the epidural hematoma, which requires prompt action to reduce the associated swelling and reverse the herniation. Osmotic agents such as mannitol or hypertonic saline should be administered while calling the neurosurgeon and planning for emergent radiologic evaluation. Pain or anxiety may produce bilateral, not unilateral, pupillary dilation. Therefore, treatment with fentanyl would not address this patient's neurologic emergency. Ischemic stroke can produce pupil dilation but is less likely than uncal herniation in this scenario. Cerebral angiography to evaluate blood vessel characteristics usually is performed after stroke is diagnosed by computed tomography scan or magnetic radiographic imaging. Replacement of the clotted intraventricular catheter is indicated for overall management, but acute measures to reverse the uncal herniation are of much higher priority. Ophthalmology consultation for anisocoria is not indicated at this time because the most likely cause of the patient's signs and symptoms is acute herniation.

References:

Avner JR. Altered states of consciousness. Pediatr Rev. 2006:27:331-338. Available at: http://pedsinreview.aappublications.org/cgi/content/full/27/9/331

Frankel LR. Neurological emergencies and stabilization. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier; 2007:405-410


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Critique: 57

Uncal herniation may result in ipsilateral pupillary dilation, diminished level of consciousness, and contralateral hemiparesis. (Courtesy of the Media Lab at Doernbecher)


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Question: 73

An 18-month-old boy fell into a swimming pool 12 hours ago. He had no heart rate when he was pulled from the pool, and cardiopulmonary resuscitation (CPR) was initiated at the scene. The CPR was continued for 30 minutes until spontaneous circulation was restored in the emergency department. He is now in the pediatric intensive care unit, receiving mechanical ventilation with maximal intensive care support. Over the past several hours, his blood pressure has increased, he has developed persistent bradycardia, and he exhibits no movement in response to stimulation. He has not received any neuromuscular blockers or sedation. In addition, his pupils are dilated bilaterally and do not respond to light. Bedside electroencephalography demonstrates generalized burst suppression with loss of reactivity to external stimuli.

In discussion with his parents, you inform them that these recent changes are MOST likely a result of

A. agitation

B. increasing intracranial pressure

C. myocardial failure

D. ongoing seizure activity

E. physiologic response to the ventilator


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Hypoxic-ischemic injury, which occurs after periods of impaired perfusion, such as with cardiopulmonary arrest, produces a broad spectrum of organ failure. Unfortunately, the brain is one of the organs most vulnerable to decreased oxygen and nutrient delivery, and hypoxic-ischemic central nervous system (CNS) injury is common following asphyxia. Irreversible CNS injury may occur after as little as 3 to 5 minutes of interrupted blood flow or oxygen delivery. Both ischemia and hypoxia trigger numerous pathophysiologic processes that result in cellular injury, cell death, and subsequent development of cerebral edema that compromises blood flow to adjacent areas of the brain. These areas are initially either potentially recoverable or uninjured but at risk due to impaired perfusion. The boy described in the vignette is exhibiting evidence of increased intracranial pressure due to significant global hypoxic-ischemic injury. His hypertension and bradycardia represent the Cushing reflex (the raising of systemic arterial pressure to increase cerebral perfusion with associated stimulation of the carotid bodies and subsequent bradycardia). Cushing triad (systemic arterial hypertension, bradycardia, and depressed or irregular respirations) is a late sign of increased intracranial pressure that often develops just prior to cerebral herniation. The lack of spontaneous movements and dilated, unresponsive pupils described for the boy are consistent with severe CNS injury and a poor outcome. Agitation or pain due to underlying injuries, ventilator asynchrony, or anxiety can produce hypertension, but this typically is associated with tachycardia and increased motor movements. Myocardial hypoxic-ischemic injury normally is manifested by decreased ventricular function and hypotension. Although patients who have hypoxic-ischemic injuries are at risk for the development of seizures, the electroencephalographic findings in this patient are consistent with a severe hypoxic-ischemic encephalopathy and portend a poor prognosis. Abnormal motor movements or vital signs in combination with neurologic examination results that are not consistent with a known cause should prompt the consideration of seizure and subsequent evaluation and treatment.

References:

Doherty DR, Hutchison JS. Hypoxic ischemic encephalopathy after cardiorespiratory arrest. In: Wheeler DS, Wong HR, Shanley T, eds. Pediatric Critical Care Medicine: Basic Science and Clinical Evidence. New York, NY: Springer-Verlag; 2007:935-946

Kallas HJ. Drowning and submersion injury. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier; 2007:438-449

Meyer RJ, Theodorou AA, Berg RA. Childhood drowning. Pediatr Rev. 2006;27:163-169. Available at: http://pedsinreview.aappublications.org/cgi/content/full/27/5/163

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Critical Care