e196 SECTION XV Pediatric Critical Care Board Review Questions intracellular concentrations of cGMP translates to vasodilation and the resultant physiologic effect of reduced blood pressure Sildenafil[.]
e196 S E C T I O N XV Pediatric Critical Care: Board Review Questions intracellular concentrations of cGMP translates to vasodilation and the resultant physiologic effect of reduced blood pressure Sildenafil augments the response to cGMP through selective inhibition of type phosphodiesterase, the enzyme that catalyzes degradation of cGMP Therefore sildenafil can react similarly with other drugs (e.g., nitroglycerin and hydralazine) that promote the generation of a nitric oxide species 3 The patient’s symptoms, physical exam, and laboratory values are most consistent with which of the following overdoses? A Acetaminophen B Ethanol C Ethylene glycol D Methanol E Salicylate Preferred response: C Chapter 125: Principles of Toxin Assessment and Screening Rationale This patient has symptoms and signs of a severe poisoning characterized by obtundation, tachypnea, elevated osmolar gap, elevated anion gap metabolic acidosis, and crystalluria In a massive overdose, acetaminophen can lead to acute fulminant hepatic failure, hepatic necrosis, and hepatorenal syndrome leading to all of these manifestations, except for an elevated osmolar gap and crystalluria Salicylates can also lead to these manifestations in a severe overdose, with the exception of an elevated osmolar gap and crystalluria Ethanol is a toxic alcohol which can lead to severe obtundation and elevated osmolar gap; however, it does not produce an anion gap metabolic acidosis or crystalluria Both methanol and ethylene glycol are osmotically active toxic alcohols and produce an elevated osmolar gap Both also lead to an elevated anion gap from the production of the toxic organic acids, formic acid from methanol, and glycolic, glyoxilic, and oxalic acids from ethylene glycol However, only ethylene glycol leads to crystalluria The oxalic acid metabolite forms a complex with calcium to precipitate as calcium oxalate monohydrate crystals in the renal tubules, leading to acute renal failure, the most prominent end organ effect of ethylene glycol The obtundation, tachypnea, elevated osmolar gap, elevated anion gap, and crystalluria are consistent with ethylene glycol poisoning Questions 1–3 refer to the following vignette: A 4-year-old toddler is transferred to the PICU with obtundation, increased respiratory rate, but otherwise normal vital signs, after an unwitnessed presumed accidental ingestion in the garage about hours ago Initial laboratory testing revealed the following serum concentrations: glucose, 62 mg/dL; Na1, 143 mEq/L; K1, mEq/L; Cl2, 110 mEq/L; HCO23 , mEq/L; BUN, 30 mg/dL; osmolality, 350 mOsm/L; urinalysis positive for monohydrate crystals The anion gap in this patient is A 240 mEq/L B 210 mEq/L C 110 mEq/L D 130 mEq/L E 1300 mEq/L Preferred response: D Rationale The anion gap is calculated by the formula Na1 K1 (Cl2 HCO23 ), where all components are expressed in milliequivalents per liter The “normal” anion gap ranges from to 16 mEq/L in older children and adults Increases in anion gap above normal are due to the presence of unmeasured anions that accompany acidosis The gap in this case is 30 mEq/L, a value that is well in excess of the normal gap (12–16 mEq/L) A significant increase can be produced by diabetic ketoacidosis, renal failure, or toxin-induced metabolic acidosis Drugs that cause an anion gap include metformin, methanol, monomethylhydrazines, paraldehyde, iron, isoniazid, cyanide, ethylene glycol, and salicylates The osmolar gap in this patient is A 250 mOsm/L B 210 mOsm/L C 110 mOsm/L D 150 mOsm/L E 1300 mOsm/L Preferred response: D Rationale The osmolar gap is the difference between the measured serum osmolality and the osmolarity calculated from the serum sodium, glucose, and BUN concentrations according to the equation: [2 Na (in mEq/L)] [Blood urea nitrogen (in mg/dL)/2.8] [Glucose (in mg/dL)/18] In this case, the measured osmolality is 350 mOsm/L, whereas the calculated osmolality is 300 mOsm/L; the difference is 150 mOsm/L Poisonings which can introduce osmotically active particles into the serum include the toxic alcohols, such as ethanol, isopropanol, methanol, and ethylene glycol A markedly elevated osmolar gap (.50 mOsm/L) is difficult to explain by anything other than a toxic alcohol 4 A severe ethylene glycol intoxication is suspected in an unknown toxic alcohol ingestion when there is: A An elevated serum osmolality measured by freezing point depression B A normal serum osmolality measured by vapor pressure method C A depressed anion gap D A normal anion gap Preferred response: A Rationale Ethylene glycol will contribute unmeasured, osmotically active molecules to the blood, which will elevate the serum osmolality above that value calculated with the conventional, osmotically active blood components (i.e., BUN, glucose, sodium) Thus the measured serum osmolality, when performed by the freezing point methodology, will reveal a gap However, the vapor pressure method allows some ethylene glycol metabolites to escape detection and will be falsely normal in a case of ethylene glycol poisoning Ethylene glycol is metabolized first in the liver by the enzyme alcohol dehydrogenase to glycoaldehyde This is then further transformed by degradation to glyoxylate, glycolate, and oxalate molecules, present as unmeasured anions and acids (e.g., glycolic and oxalic acids) in the blood Further metabolism of ethylene glycol metabolic products into glycine exhausts bicarbonate reserves and adds to the acid production Lactic acid is also generated in large amounts during ethylene glycol poisoning, resulting in profound acidemia These metabolic pathways account for both an elevated anion gap, as well as a dramatic metabolic acidosis CHAPTER 136 Board Review Questions e197 Methemoglobinemia is clinically characterized by which of the following? A Bright cherry-venous blood B Exposure to an oxidizing chemical C No change with the infusion of methylene blue D Reliable oxygen saturation readings by pulse oximetry Preferred response: B The herbs senecio, heliotrope, and comfrey are capable of producing which disease pathology? A Asthma, urticaria, angioedema B Coma, seizures, death C Diarrhea, anxiety, hypertension D Hepatic veno-occlusive disease Preferred response: D Rationale The first step in the creation of methemoglobin requires the presence of an oxidizing drug, food, or chemical Methemoglobin represents the formation of oxidized iron (ferric) within hemoglobin, such that the hemoglobin becomes nonfunctional in terms of oxygen carriage and unloading in the tissues Since the methemoglobin molecule absorbs more light at 660 and 940 nm than does either reduced hemoglobin or oxyhemoglobin, it imparts a dark brown color to the blood and conveys a grayish, cyanotic tone to the skin For the same reason, pulse oximetry is rendered inaccurate because it depends on the detection of light absorption of oxyhemoglobin and cannot correct for the presence of another light-absorbing but nonfunctional hemoglobin, giving variably falsely high or falsely low values With the IV infusion of the correct dose of the antidote, methylene blue, the intensivist can expect a resolution of the child’s respiratory complaints and the return to a normal skin color, often within minutes Rationale Hepatic veno-occlusive disease may be caused by the ingestion of senecio, heliotrope, and comfrey Echinacea is known to cause asthma, atopy, urticaria, and angioedema Diarrhea, anxiety, hypertension, and insomnia are characteristic of ginseng use Use of laetrile leads to cyanide toxicity, with manifestations of coma, seizures, and death Nutmeg use causes hallucinations, emesis, and headaches Life-threatening iron poisoning is characterized by: A Depressed anion gap B Elevated osmolar gap C Negative toxic screen D Metabolic alkalosis Preferred response: C Rationale Severe, life-threatening iron poisoning rapidly takes the patient to a stage characterized clinically by the presence of both hypovolemic shock and a metabolic acidosis The elaboration of excess, unmeasured acids in the blood elevates the anion gap However, these molecules are not osmotically active and so should not ordinarily affect the measured serum osmolarity Because the conventional “toxic screen” as performed in most hospitals does not include iron, it will be reported as negative The intensivist must order specifically a serum iron concentration Anticholinergic syndrome differs from sympathomimetic syndrome by the presence of which of the following? A Dilated pupils B Dry skin C Fever D Tachypnea Preferred response: B Rationale Anticholinergic syndrome may have features that are similar to those of the sympathomimetic toxidrome Examination of the skin usually provides clues to differentiate between the two because the patients will have dry skin in this scenario versus increased diaphoresis with sympathomimetic toxicity Hypertension and tachycardia are typically less severe than that seen with sympathomimetics Also, the dilated pupils of the anticholinergic syndrome are nonreactive because of associated cycloplegia 9 An adolescent exhibiting the agitated delirium produced by jimsonweed ingestion will have a clear sensorium after the administration of which of the following? A Diphenhydramine B Flumazenil C Naloxone D Physostigmine Preferred response: D Rationale Substances of abuse may cause delirium or hallucinations in the adolescent Jimsonweed (Datura stramonium) plant seeds, which contain atropine and other anticholinergic chemicals, can be intentionally chewed by adolescents for their euphoric (and delirium-producing) effects caused by a central anticholinergic syndrome Physostigmine can be of benefit in pediatric patients who have ingested jimsonweed seeds (D stramonium) or other pure anticholinergic agents; however, caution is dictated in unknown poisonings in which cardiac conduction toxicity is a consideration because physostigmine itself can cause severe cardiac toxicity, bradycardia, and asystole Chapter 126: Toxidromes and Their Treatment A 14-year-old boy presents to the emergency department (ED) in the early afternoon hours after an intentional ingestion of what he says was diphenhydramine He has dilated pupils, warm skin, dry mucous membranes, sinus tachycardia and is drowsy but arousable A complete blood cell count (CBC) and chemistry panel are within normal limits His urine toxicology screen is negative for opiates, benzodiazepines, cannabinoids, amphetamines, and cocaine He is observed for several hours and discharged into the care of his parents The evening of the following day he is seen again in the ED with right upper quadrant pain Repeat chemistry shows AST of 800 IU/L and ALT of 650 IU/L Total bilirubin is mg/dL International normalized ratio (INR) is 1.2 Which of the following toxins is most likely the cause of this abnormality? A Acetaminophen B Aspirin C Ibuprofen D Iron Preferred response: A e198 S E C T I O N XV Pediatric Critical Care: Board Review Questions Rationale Medications are frequently sold as combination products Diphenhydramine is commonly sold in combination with acetaminophen under different brand names This patient probably ingested such a product Unfortunately no acetaminophen level was performed on his first visit that would have identified it, and acetaminophen is asymptomatic until liver damage has occurred Aspirin and ibuprofen can also be found in combination products but not cause liver toxicity Iron may cause liver toxicity in the late phases following ingestion, but this is preceded by severe gastrointestinal manifestations and systemic toxicity It is important in the case of intentional ingestions to always measure an acetaminophen level to identify this silent toxin so that the appropriate antidote can be administered to prevent hepatotoxicity The constellation of miosis, coma, and respiratory depression is most consistent with exposure to which agent? A Atropine B Clonidine C Diphenhydramine D Lorazepam Preferred response: B Rationale Miosis, coma, and respiratory depression are hallmarks of opioid exposure, but other drugs such as central presynaptic a2-agonists can also cause those symptoms An example of this type of drug is clonidine Physostigmine is most appropriately indicated as an antidote for what agent? A Amitriptyline B Benzocaine C Methamphetamine D Scopolamine Preferred response: D Rationale Physostigmine is an antidote for antimuscarinic toxicity Scopolamine is such a drug Although amitriptyline has antimuscarinic properties, the use of physostigmine in tricyclic antidepressant overdose is contraindicated Which of the following signs is most suggestive of anticholinergic toxicity as opposed to the sympathomimetic toxidrome? A Dilated, nonreactive pupils B Hypertension C Hyperthermia D Tachycardia Preferred response: A Rationale The anticholinergic toxidrome, more appropriately referred to as an antimuscarinic toxidrome, is produced by a number of agents that possess antimuscarinic properties as their primary effect or as a side effect Muscarinic receptors are located in the central nervous system, the target organs of the parasympathetic nervous system, and the sweat glands (sympathetic nervous system) The syndrome may have features that are similar to those of the sympathomimetic toxidrome Examination of the skin usually provides clues to differentiate between the two because the patients will have dry skin in this scenario versus increased diaphoresis with sympathomimetic toxicity Hypertension and tachycardia are typically less severe than that seen with sympathomimetics Also, the dilated pupils of the anticholinergic syndrome are nonreactive because of associated cycloplegia Which of the following drug overdoses is most likely to respond to atropine? A Clonidine B Digoxin C Diltiazem D Propranolol Preferred response: B Rationale An overdose of digoxin presents with nausea, vomiting, lethargy or confusion, and cardiac dysrhythmias Although virtually every rhythm has been described in persons with digoxin toxicity, bidirectional ventricular tachycardia and atrial tachycardia with atrioventricular block are characteristic Sinus bradycardia or heart block may respond to atropine alone More serious arrhythmias are an indication for treatment with digoxin-specific Fab fragments (e.g., Digibind and DigiFab) An acute overdose of b-adrenergic antagonists results in bradycardia, hypotension, and conduction delay Toxicity is generally much lower than with calcium channel antagonists such as verapamil and diltiazem Propranolol, by virtue of its sodium channel–blocking activity, causes QRS widening, exaggerated negative inotropy, chronotropy, and conduction delay Treatment beyond monitoring is not necessary if the only manifestation is asymptomatic bradycardia Patients with bradycardia and hypotension may respond to atropine, although it is expected that such patients would have decreased vagal tone to start with b-agonists have variable effects in the presence of b-adrenergic blockade Glucagon acts via a nonadrenergic receptor to increase intracellular cyclic adenosine monophosphate and improve cardiac contractility Patients who not respond to these measures, such as patients with calcium channel blocker overdose, should be considered for extracorporeal life support Verapamil possesses vasodilatory effects and potent cardiac calcium channel–blocking activity and may cause bradycardia, heart block, and myocardial depression Diltiazem has effects similar to those of verapamil but is a less potent inhibitor of cardiac calcium channels Treatment depends on the agent involved and the severity of toxicity Except in extremely large ingestions, dihydropyridines produce hypotension and reflex tachycardia These patients may respond to volume expansion alone IV administration of calcium and vasopressors is indicated if the hypotension remains refractory to IV fluids Verapamil and diltiazem overdose is further complicated by pump failure These patients may benefit from inotropes such as dobutamine Glucagon, which acts at a receptor other than the b receptor, increases cyclic adenosine monophosphate and has been reported to reverse refractory hypotension in persons with calcium channel overdose Reversal of opioid toxicity has been associated with pulmonary edema, although this has also been described in the setting of opiate toxicity itself Anecdotally, naloxone has been reported to reverse clonidine overdose, although failure of naloxone to reverse clonidine has also been described Occasionally naloxone administration has been associated with significant hypertension, which is usually short-lived and does not require treatment If hypertension persists, treatment should consist of a short-acting antihypertensive agent such as nitroprusside so that the drug and its effects CHAPTER 136 Board Review Questions can be stopped quickly This treatment will prevent the development of hypotension as the hypertensive crisis resolves In which of the following toxin-induced hyperthermia states has dantrolene proven to be lifesaving? A Malignant hyperthermia B Neuroleptic malignant syndrome C Serotonin syndrome D Sympathomimetic toxicity Preferred response: A Rationale Malignant hyperthermia is a genetically determined condition that is triggered by exposure to depolarizing neuromuscular blocking agents (succinylcholine) or inhalational anesthetic agents It is a life-threatening condition that results from dysfunction of the ryanodine receptors, which elevates the intracellular calcium in somatic muscle cells, resulting in rigidity and muscle damage This syndrome requires prompt intervention with aggressive cooling and treatment with dantrolene, which allows muscle relaxation through the blockade of calcium release from the sarcoplasmic reticulum Which of the following toxins causes metabolic acidosis through the generation of a substance other than lactate? A Carbon monoxide B Cyanide C Ethylene glycol D Gyromitra mushroom species Preferred response: C Rationale Ethylene glycol is converted to a number of intermediate toxic products and ultimately to oxalate This conversion results in severe metabolic acidosis, renal failure, and hypocalcemia through binding of oxalate to calcium to form crystals Cyanide binds to heme iron in the cytochrome complex IV of the electron transport chain, cytochrome C oxidase, resulting in inhibition of oxidative phosphorylation Consequently, the patient is unable to use oxygen to produce adenosine triphosphate, and the result is energy failure Signs and symptoms are nonspecific and reflect tissue hypoxia; however, a symptomatic patient with a lactate of 10 mmol/L or more is highly suspect for cyanide toxicity Carbon monoxide causes tissue hypoxia through several mechanisms: It binds with high affinity to oxygen-binding sites of hemoglobin; it binds to myoglobin and disrupts the transfer of oxygen from erythrocytes to mitochondria; it binds to mitochondrial cytochrome oxidase; and it interferes with electron transport and adenosine triphosphate production Ingestion of mushrooms from the group of hydrazine-containing mushrooms, including the Gyromitra species, will produce toxicity identical to INH through its interference with pyridoxal5-phosphate and depletion of g-aminobutyric acid Reversal of which of the following toxins is most likely to produce life-threatening withdrawal? A Dapsone B Diazepam C Digoxin D Morphine Preferred response: B e199 Rationale When given for a benzodiazepine overdose, flumazenil may precipitate acute withdrawal in the patient who habitually uses benzodiazepines or may unmask seizures caused by a coingested substance Chapter 127: Airway Management Which of the following healthy children would be expected to have the highest tracheal absolute resistance to airflow? A A 3-day-old male B A 2-year-old male C An 8-year-old female D A 16-year-old female Preferred response: A Rationale The internal dimensions of the trachea in a newborn are approximately one-third those of an adult, and absolute resistance to airflow is higher in newborns than in older children and adults The most important factor determining resistance (R) is the radius (r) of an airway (Poiseuille’s law: R proportional to l/r4), therefore small changes in airway diameter in infants or young children as a consequence of edema or secretions have a far greater effect on resistance than similar changes in larger patients Which of the following physiologic effects does not result from the effect on endotracheal intubation: A Bronchoconstriction B Decrease in intracranial pressure (ICP) C Increase in systemic blood pressure D Tachycardia Preferred response: B Rationale Laryngoscopy is a potent physiologic stimulus It is a noxious stimulus, causing significant pain and severe anxiety, especially in children who cannot understand or accept the need for it Laryngoscopy causes an increase in systemic blood pressure and heart rate initiated by pressure on the back of the tongue or lifting the epiglottis Laryngoscopy and intubation are potent stimulators of laryngospasm and may cause bronchoconstriction, especially in patients with a history of reactive airway disease Increased airway resistance probably results from parasympathetic stimulation, with release of acetylcholine and stimulation of muscarinic receptors on airway smooth muscle, especially large central airways ICP rises immediately during laryngoscopy even in patients without intracranial pathology before changes in blood gas tensions occur Cerebral metabolic rate and blood flow increase Hypoxia, hypercarbia, and diminished jugular venous drainage, particularly in struggling patients, contribute further to increases in cerebral blood volume and increased intracranial pressure e200 S E C T I O N XV Pediatric Critical Care: Board Review Questions A 10-year-old male weighing 30 kg is admitted to the PICU following blunt force trauma after being struck by a car while riding his bicycle During trauma primary and secondary survey and emergency department imaging, the patient is found to have bilateral extensive pulmonary contusions, left femoral bone fracture, and grade splenic laceration Glasgow Coma Scale (GCS) is 15, and the patient’s vital signs on admission are initially stable Over the course of the next few hours, the patient becomes increasingly hypoxic, requiring escalating respiratory support Per parental report, the child ate a cheeseburger just prior to the accident, which occurred five hours ago Which of the following induction medications would be the best choice in this situation? A Etomidate B Fentanyl C Midazolam D Propofol Preferred response: A Rationale This patient meets criteria for a rapid sequence induction and intubation (RSI) for multiple reasons He had a full meal within hours of induction Trauma patients are usually considered to have full stomach as traumatic injury may slow gastric motility, even if the patient has not ingested any food recently Trauma patients may also be at risk for having blood collected in the stomach depending on the type of injury sustained Also, if there is blunt force trauma to the abdomen and it is tense and distended, RSI is recommended Once you have decided RSI is indicated, you must choose induction medications that have fast onset, ideally within 30–60 seconds and limited potential for hemodynamic instability Midazolam, fentanyl, and propofol not meet these criteria Etomidate has a rapid onset, with the added benefit of hemodynamic stability Which of the following adjuvant agent does not blunt the sympathetic response to intubation in the patient with increased intracranial pressure? A Dexmedetomidine B Fentanyl C Lidocaine D Ketamine Preferred response: D Rationale Patients with increased intracranial pressure are at risk for additional injury during intubation given the sympathetic surge associated with intubation and the risk for increasing CO2 and the associated increased blood flow to the brain during this time Adjuvant agents such as lidocaine, fentanyl, and dexmedetomidine may help blunt the sympathetic response to intubation and are therefore neuroprotective Chapter 128: Anesthesia Effects on Organ Systems A 4-year-old male with history of repaired tetralogy of Fallot and short gut secondary to necrotizing enterocolitis as a neonate is transferred to the PICU after exploratory laparotomy and extensive lysis of adhesions due to bowel obstruction He had bilateral thoracic paravertebral nerve block catheters placed preoperatively, and a continuous infusion of 0.2% ropivacaine was administered throughout the case After transfer of care, the patient appears to be uncomfortable, and his nerve blocks had been discontinued during transport The acute pain team is called, and they bolus the paravertebral catheters bilaterally Shortly thereafter the nurse calls you because the patient is tachycardic with ECG changes What is the next most appropriate step in this patient’s care? A The patient’s pain remains uncontrolled and opioid should be administered B Obtain a 12-lead ECG, echocardiogram, and page Cardiology, as this is most likely related to his cardiac defect C Stop the paravertebral infusions and prepare emergency medications for possible cardiovascular complications secondary to catheter migration and intravascular injection of local anesthetic D Administer a fluid bolus, as this is related to dehydration due to fluid losses during the open operative procedure Preferred response: C Rationale Continuous nerve block catheters may migrate into the intravascular space at any point and may or may not result in aspiration of blood prior to infusion or bolus of local anesthetic Intravascular injection of local anesthetic may result in tachycardia, bradycardia, or other arrhythmias and hemodynamic instability, and possible complete cardiovascular collapse Resuscitation equipment, continuous monitoring, including invasive monitoring, administration of lipid emulsion along with ongoing hemodynamic support is necessary until stability is achieved Continuous nerve block infusions should be discontinued immediately, and the managing service should be notified A 12-year-old, otherwise healthy, female is being admitted to the pediatric intensive care unit after a laryngospasm event in the operating room The patient received succinylcholine and was reintubated prior transfer to the PICU It has been one hour since admission, and the patient does not appear to be initiating respiratory effort on the ventilator You obtain a train of four monitor, and the patient does not have any twitches What you suspect is the underlying cause of these findings? A The patient suffered a severe anoxic event during the laryngospasm B The patient may suffer from prolonged paralysis due to unknown pseudocholinesterase deficiency C The patient has been inadequately ventilated since admission and is now hypercarbic resulting in a depressed mental status D The patient is hypoglycemic due to NPO guidelines preoperatively and a lactated Ringer’s infusion for maintenance intravenous fluid while intubated Preferred response: B ... but this is preceded by severe gastrointestinal manifestations and systemic toxicity It is important in the case of intentional ingestions to always measure an acetaminophen level to identify this... induction medications would be the best choice in this situation? A Etomidate B Fentanyl C Midazolam D Propofol Preferred response: A Rationale This patient meets criteria for a rapid sequence... appropriate step in this patient’s care? A The patient’s pain remains uncontrolled and opioid should be administered B Obtain a 12-lead ECG, echocardiogram, and page Cardiology, as this is most likely