Anesthesiology Written Board Exam Sample Questions
Book 1 - 2006
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A-TYPE QUESTION

65.        A 28-year-old female, 34 weeks gestation, 115 pounds, is admitted with the diagnosis of severe preeclampsia.  Her blood pressure is 182/102, pulse 104, respiration 16.  She is given 6 grams magnesium sulfate intravenously, and an infusion of magnesium sulfate, 3 grams per hour is begun.  Twelve hours after admission she is somnolent and has shallow respirations at a rate of 4 per minute, deep tendon reflexes are absent and her blood pressure is 118/68.

The MOST appropriate treatment is:

A) Ephedrine 25 mg intravenously
B) Calcium gluconate 1 gm intravenously
C) Epinephrine 0.5 mg intravenously
D) Diazepam 1 mg intravenously
E) O2 with non-rebreathing mask 6 L/min

ANSWER

65.                   B          Calcium gluconate 1 gm intravenously

The differential diagnosis of altered mental status (somnolence) in a severe preeclamptic patient includes worsening preeclamsia versus magnesium toxicity.  Worsening preeclampsia present with hyperreflexia and clonus (not absent reflexes). The blood pressure remains elevated.

Magnesium sulfate remains the treatment of choice for seizure propylaxis in North America. The standard treatment is magnesium 4-6 gm bolus intravenously over 20 minutes followed by an intravenous infusion of 1-2 gm per hour. During maintenance therapy, patients are monitored clinically (e.g., patellar reflexes, respiratory rate, urine output). If oliguria or the suspicion of magnesium toxicity develops (loss of deep tendon reflexes, hypotension and somnolence between 5.8- 10 mEq/L), serum magnesium concentration should be measured, and the maintenance dose adjusted accordingly. The therapeutic level of magnesium is 5-7 mEq/L. Interpretation of the serum magnesium concentration is confounded by the fact that three sets of units can be used and it is important to know the units used in your laboratory to avoid clinical errors in dosing.

Her level was probably unacceptably high. The patient has been overdosed (6 gm bolus followed by 3 gm/hour).  In the event of suspected magnesium toxicity, magnesium sulfate must be discontinued immediately and the patient should be treated with intravenous calcium gluconate (1 g) or calcium chloride (300 mg). In the event of respiratory impairment patient may require endotracheal intubation and mechanical intubation until spontaneous respiration resumes.

Magnesium toxicity is more likely in patients with renal dysfunction since magnesium is eliminated entirely by the kidney.

1. Hughes SC, Levinson G, Rosen MA, (eds.).  Shnider and Levinson’s Anesthesia for Obstetrics.  4th edition Lippincott Williams & Wilkins.  Baltimore MD.  2002:304.

2. Gambling DR. Hypertensive disorders In Chestnut DH (ed) Obstetric 3rd edition. Elsevier Mosby, Philadelphia, PA. 2006:808-809.

K-TYPE QUESTION

126.      Precautions regarding eutectic mixture of local anesthetics (EMLA) cream include:

1. Contact on eye and oral mucous membranes should be avoided
2. Toxic plasma levels can occur if applied on broken or inflamed skin
3. Should be used with care in infants less than 3 months of age
4. Ototoxicity may occur if drug reaches middle ear through tympanic membrane

ANSWER

126.           E       All      (1,2,3,4)          

EMLA stands for Eutectic Mixture of Local Anesthetics and consists of a mixture of lidocaine (2.5%) and prilocaine (2.5%) in an oily cream. This combination of local anesthetics is considered a eutectic mixture of local anesthetics (EMLA), as the melting point of the combined drugs is lower than lidocaine or prilocaine alone, therefore, both local anesthetic exist as liquid oil rather than as crystals. EMLA applied onto intact skin under an occlusive dressing, provides dermal analgesia by release of lidocaine and prilocaine from the cream into epidermal and dermal layers of the skin. The onset, depth, and duration of dermal analgesia on intact skin provided by EMLA depend primarily on the duration of application.

EMLA used in oral mucous membranes should be avoided to prevent faster absorption of lidocaine and prilocaine. Similarly, EMLA in not recommended for broken or inflamed skin since local anesthetic toxicity can occur. However, EMLA may be applied to genital mucous membranes. While EMLA cream use in not contraindicated in children, care should be taken when used in infants less than 3 months of age since the risk of developing methemoglobinemia in increased in this age group. Finally, EMLA in not recommended for middle ear application since the possibility of migration beyond the tympanic membrane has been associated with ototoxicity.

1. Stoelting, RK. Pharmacology and Physiology in Anesthetic Practice. 3rd Edition. Lippincott-Raven. Philadelphia.1999:172-173.

2. Package Insert for EMLA Cream, AstraZeneca, Revision 02/2002

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