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Oral case 127

Created: 3/2/2005

A 70-year old 70 kg man is scheduled for a right carotid endarterectomy because of recurrent transient ischemic attacks. He has had two myocardial infarctions, the most recent being four months ago. He is on propranolol 40 mg tid for hypertension, and occasional sublingual nitroglycerine. Blood pressure ranges from 130/90 to 180/105 mmHg. Pulse is 60 bpm, oral temperature is 37 degrees centigrade, and hematocrit is 50.

 Preoperative Evaluation

I. Evaluation of control of hypertension

1. Is this patient's blood pressure adequately controlled?

2. Would you lower the blood pressure preoperatively?

3. What are the hazards of acute blood pressure reduction?

4. What are the effects of blood pressure on cerebral blood flow to an ischemic brain?

II. Cardiac evaluation

1. What is the importance of the recent myocardial infarction to the anesthetic and surgical risks?

2. What is the significance of occasional angina?

3. Would you want further cardiac evaluation prior to surgery?

4. What are some common drugs used in patients with cardiac disease?

Digitalis, beta-blockers, diuretics, angiotensin-converting enzyme inhibitors, coronary vasodilators, and calcium channel blockers.

5. What three drugs are used for the treatment of angina?

Nitrates, beta-blockers, and calcium channel blockers.

4. What specifically would you want?

5. Would you postpone surgery? Explain.

III. Evaluation of carotid status

1. How will you evaluate the patient's neurologic status?

2. What is the importance of head position?

3. What is the importance of angiographic findings?

4. What is the importance of blood pressure changes with position?

 Intraoperative Course

I. Choice of monitors

1. Are there special indications for an arterial cannula in this patient? Explain.

2. Do you check adequacy of collateral circulation prior to radial artery cannulation? Explain why.

3. Which electrocardiogram lead or leads should be monitored? Explain.

4. What information does the electroencephalogram provide, and how does it affect anesthetic management?

II. Choice of anesthesia

1. Are there any advantages of cervical plexus block over general anesthesia? Explain.

2. Are there disadvantages?

3. How would you manage the patient if he became restless and confused during carotid cross clamping?

4. The patient requests general anesthesia. Which agents will you use for induction?

5. What will you use for maintenance?

6. Discuss the effects of the agents chosen on cerebral blood flow and metabolism.

7. What are the effects of these agents on the cardiovascular system, especially on myocardial oxygen supply and demand?

8. What is the relative importance of the central nervous system and the cardiac effects?

9. Should muscle relaxants be used? Explain.

10. Which relaxant would you use? Explain.

11. The hands are tucked at the sides. How would you monitor relaxation?

12. How would you monitor reversal?

III. Management of bradycardia

1. During surgery, the patient's heart rate decreases from 75 to 40 bpm and the blood pressure decreases from 170/100 to 90/60 mmHg. What is your differential diagnosis?

2. What is the likely mechanism?

3. What is your management?

IV. Brain protection

1. Would you attempt to protect the brain during carotid cross-clamping? Explain.

2. Are these methods effective?

 Postoperative Care

I. Management of postoperative hypertension and tachycardia

1. In the immediate postoperative period, the blood pressure is 220/120 mmHg and the pulse is 110 bpm. What are the dangers of this?

2. What is your treatment?

II. Failure to awaken postoperatively

1. What is your differential diagnosis?

Acute anticholinergic syndrome, residual paralysis, pseudocholinesterase deficiency, narcotic overdosing, or nonspecific effects of residual anesthetic gases.

2. What drugs potentiate nondepolarizing muscle relaxants?

Calcium-channel blockers, volatile anesthetics, local anesthetics, beta blockers, aminoglycosides, polymixins, linosamines, hexamethonium, trimethaphan, immunosuppressants, high-dose benzodiazepines, dantrolene, lithium, and magnesium. Inhalational agents decrease neuronal activity, local anesthetics decrease propagation of the action potential, antibiotics inhibit formation of acetylcholine, and certain ions inhibit the release of acetylcholine at the nerve terminal.

3. What drugs potentiate depolarizing muscle relaxants?

Drugs that inhibit plasma cholinesterase activity, like echothiophate eye drops and organophosphate pesticides, can prolong the action of succinylcholine.

2. Would you administer naloxone?

3. Would you administer physostigmine?

4. How would you decide whether or not to give one of these?

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