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Oral case 132

Created: 4/3/2005

Pediatrics- regional anesthesia

A 10-year old 35 kg child sustained a forearm fracture two hours after eating dinner.

1. Will you proceed now with regional anesthesia? Explain.

2. You decide to place an axillary block. What local anesthetic drug would you use? Explain.

3. How are local anesthetics classified?

They are classified as either amide or esters. Both have an aromatic and an amine joined by an intermediate chain, which is either an amide or an ester. Common amides include lidocaine, etidocaine, bupivacaine, and mepivacaine. Esters include cocaine, procaine, tetracaine, and chloroprocaine.

4. How are ester and amide local anesthetics metabolized?

Esters are hydrolyzed by pseudocholinesterase in the plasma. Amides are metabolized in the liver by hydroxylation, N-dealkylation, and amide hydrolysis.

3. What is the mechanism of action of local anesthetics?

The unionized form crosses the nerve sheath, equilibrates between the acidic and basic forms in the axoplasm, then binds to a receptor site inside the sodium channel, blocking it.

3. What dose will you use?

4. What volume will you use?

5. Will you sedate the child prior to performing the block?

6. What are the risks?

Need for muscle relaxation following reversal of non-depolarizer

The surgeon has completed a laparotomy in an obese patient. After reversal of pancuronium with neostigmine, a lap sponge is found to be missing, and the surgeon requests relaxation for re-exploration.

1. How will you proceed?

2. What are common side effects of nondepolarizing muscle relaxants?

Histamine release is seen with atracuronium, doxacurium, d-tubocurarine, and mivacurium. Tachycardia can be seen with pancuronium.

Pre-operative chest pain

A 74-year old man scheduled for repair of an inguinal hernia arrives in the pre-operative area complaining of chest pain. He was premedicated with morphine 5 mg intramuscular, one hour prior.

1. Discuss a systematic approach to evaluation of chest pain.

Since perioperative myocardial infarction causes a mortality of 50%, it is important to diagnose ischemia to prevent infarction. The patient should describe its onset, whether it occurs on exertion, and its character, frequency, location, and any radiation of the pain. Associated symptoms of diaphoresis, radiation of pain, dyspnea, or nausea should be known.

Physical exam should include review of blood pressure, heart rate and rhythm. Signs of congestive heart failure should be assessed, like jugular venous distension, a third heart sound, and peripheral edema. The electrocardiogram should be reviewed, and compared with a prior one. If there is a history of cardiac disease, an old record, discussion with a cardiologist, or review of prior treadmill tests, echocardiograms, or cardiac catheterizations should be sought.

If there are acute electrocardiogram changes indicating acute myocardial infarction, consultation with a cardiologist for treatment should be done rapidly. If further evaluation is required, the case should be postponed until further identification of ischemic heart disease is made. Exercise electrocardiogram has reasonable sensitivity and specificity, and measures the patient's response to ischemia related to heart rate and blood pressure. Thallium radioisotope imaging can further enhance these results, and if the patient is unable to exercise, pharmacologic agents can elicit areas of thallium redistribution in areas of ischemia. Cardiac catheterization is the definitive test to obtain information on coronary blood flow, areas of myocardial risk, and ventricular function.

2. Under what conditions is it reasonable to obtain a cardiology consult?

A cardiology consult is appropriate for patients with ischemic heart disease that needs further evaluation, for patients with known ischemic heart disease that has a change in condition or is not adequately treated, for asymptomatic patients at risk for ischemia. This includes diabetics, hypertensive patients with left ventricular hypertrophy, and patients scheduled for vascular surgery, all of whom are at increased risk for ischemia.

3. What is your differential diagnosis of chest pain?

4. What is your treatment?

5. Should surgery be cancelled?

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