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Oral case 119

Created: 5/11/2004

A 68-year old 80 kg man is scheduled for a left parietal craniotomy for tumor resection. He has had headaches, nausea, right hemiparesis, and the CT scan shows a midline shift to the right. He has a history of angina, and takes propranolol 160 mg/day. Blood pressure is 145/95 mmHg, pulse is 58 bpm, respirations are 16, temperature is 37 degrees centigrade, and hemoglobin is 13.

 Preoperative Evaluation

I. Assessment of neurological status

1. What neurologic assessment will you perform? Explain your rationale.

2. What are the risks of increased intracranial pressure?

3. What are the determinants of cerebral perfusion?

4. What are general goals of the preoperative evaluation?

Goals of the preoperative evaluation are to collect information, and to generate an anesthetic plan, thereby reducing morbidity and mortality. The procedure is delineated, and a review of history, physical exam, lab and other studies is done. Drug allergies and current use of medications or illicit drugs are described and documented. Prior anesthetics and any difficulties are charted as well. From this, the anesthesiologists determines the need for further tests, consultations, medical management of any preexisting conditions, and the patient's readiness for the case after informed consent is given. Informed consent includes a description of events from preoperative, intraoperative, and postoperative aspects, and includes risks and benefits of procedures done. A trusting doctor-patient relationship should be established.

5. When are specialty consultations appropriate?

They are indicated when a diagnosis needs to be made or quantified, or when additional specialty management intervention is needed to correct problems within the known diagnosis. Examples would be a consultation with a cardiologist to assess a patient with untreated chest pain, or a patient with poorly controlled hypertension.

4. What is your specific preoperative management?

5. What preoperative fluids or sedative recommendations do you have?

6. Describe the American Society of Anesthesiologists' classification of physical status.

It was originally created for statistics and recordkeeping, and is a measure of outcome and a simple way of communication between anesthesiologists, with the higher classes correlating less with actual anesthetic risk. Class I indicates a healthy patient with no medical problems. Class II patients have mild disease, and Class III patients have severe but not incapacitating disease. Class IV patients have systemic disease that is a constant threat to life. Class V patients are moribund, not expected to live 24 hours with or without surgery. Class VI patients are organ donors, and an "E" is added to describe an emergency case.

II. Assessment of cardiac disease

1. Discuss the usefulness of information gained from the history vs the electrocardiogram.

2. What is the significance of propranolol to anesthesia?

3. Do you want further studies?

 Intraoperative Course

I. Selection of monitors

1. Compare invasive vs noninvasive monitors.

2. When would you place the monitors?

3. Discuss interpretation of PETCO2.

4. How does this help with anesthetic management?

5. Give reasons for discrepancy between paCO2 and PETCO2?

6. What other monitors would you use? Explain.

7. How will you decide if myocardial ischemia is occurring intraoperatively?

II. Selection and management of anesthetic techniques

1. Do you prefer sufentanil for induction? Explain.

2. What are your goals for induction?

3. What are your drug choices for induction? Discuss your sequence, including reasons.

4. You are unable to intubate initially, and the blood pressure increases to 180 systolic. What is the significance of this?

5. What is your management?

6. Marked bradycardia after intubation occurs. What are possible causes?

7. Discuss your management.

8. Should nitrous oxide be used? Explain your reasons.

9. What are advantages and disadvantages of inhaled vs intravenous agents.

10. What are the effects on intracranial pressure?

11. Would isoflurane be preferable to halothane?

12. Are cardiac and cerebral requirements similar? Explain.

13. What are your goals for blood pressure management?

14. What are your goals for heart rate management?

15. Are muscle relaxants required? Explain.

III. Management of intraoperative cardiac ischemia

1. ST segment depression is noted in the lateral precordial leads. What is the significance of this?

2. What are advantages and disadvantages of nitroglycerin?

3. What are advantages and disadvantages of nitroprusside?

4. What are advantages and disadvantages of calcium channel blockers?

5. How do calcium channel blockers interact with general anesthesia?

They may exaggerate the myocardial-depressant effects of volatile anesthetics, prolong nondepolarizing muscle relaxants, and are additive when used with beta-blockers. They should not be withheld preoperatively.

5. In the case of calcium channel blocker overdose, how does one reverse the effects?

Giving calcium antagonizes effects by increasing calcium ion flux across unblocked channels. Catecholamines increase the number of calcium channels that can be activated, and atropine can reverse bradyarrhythmias. Glucagon and amrinone can relieve hypotension and myocardial depression, with glucagon stimulating adenyl cyclase through nonadrenergic mechanisms.

6. What are the effects of amrinone or milrinone?

These are phosphodiesterase inhibitors, which equally increase cardiac output as well as do dopamine and dobutamine. They increase inotropy and lusitropy (diastolic relaxation), and vasodilate, hence the term "inodilators". Venous and arterial dilation occur, so right and left ventricular filling pressures decrease, as well as pulmonary and systemic vascular resistance, and pulmonary and mean arterial pressures. Coronary dilation also occurs, and myocardial oxygen demand decreases in patients with congestive heart failure. Heart rate usually does not increase, and arrhythmias are less common. Milrinone has a much shorter half-life, so it is easier to titrate.

5. What are advantages and disadvantages of deeper anesthesia?

IV. Management of intraoperative hypoxemia

1. The paO2 is 80 mmHg despite an FIO2 of 100%. What are causes?

2. What is your management?

3. What are the pros and cons of positive end-expiratory pressure?

 Postoperative Care

I. Shivering during recovery

1. Is this due to surgery or anesthesia?

2. Does it matter?

3. What are the consequences?

4. Will you sedate the patient? Explain.

5. Compare the use of narcotic vs barbiturate.

II. Postoperative hypertension

1. The blood pressure is 200/80 on arrival to the recovery room. What are your concerns?

2. How will you lower the blood pressure?

3. What drug choices do you have?

4. Labetalol 20 mg intravenous is only transiently effective. What are your next steps?

5. What is the mechanism of action of labetalol?

Labetalol is an alpha-1 and a noncardioselective betablocker. It has negative inotropic and chronotropic effects, decreases renin release, and inhibits lipolysis. Beta-2 blockade can lead to bronchoconstriction, peripheral vasoconstriction, and inhibition of glycogenolysis. It has no partial beta-agonist activity, and no membrane-stabilizing effect. It is used to treat angina, hypertension, glaucoma, and pheochromocytoma.

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