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Oral case 29

Created: 4/10/2004

A 21-year old female with idiopathic scoliosis is scheduled for spinal stabilization with rod placement. She has asthma treated with albuterol inhaler, and is otherwise healthy. Physical exam shows only scoliosis. Blood pressure is 110/60 mm Hg, pulse is 80 bpm, respirations are 16, and hemoglobin is 14.3

 Preoperative evaluation

I. Lung function

1. What workup is required, and why?

2. What are the changes one expects to see with scoliosis?

3. What changes does one expect to see with asthma?

4. Why is it important to know which changes are present?

II. Cardiac status

1. Do you want a preoperative electrocardiogram on this patient? Why or why not?

2. The electrocardiogram shows prominent P waves and right axis deviation. What is the significance of this?

3. How could you non-invasively evaluate right ventricular function?

4. Would you do this for this case?

III. Consent

1. What will you tell the patient about the wake-up test?

2. What are the risks?

3. The patient has heard that a test, the somatosensory evoked potentials, obviates the need for the wake-up test. What is your response?

 Intraoperative course

I. Monitors

1. Is a Foley catheter needed? Why or why not?

2. What are the hazards of Foley catheter placement?

3. Do you want a central venous catheter or a pulmonary artery catheter in this patient? Explain.

4. Deliberate hypotension is planned. Does this alter your decision? Why or why not?

5. The pulmonary artery pressures are 38/20 mm Hg and the pulmonary capillary wedge pressure is 6 mm Hg. Explain these findings.

II. Induction of anesthesia

1. Would etomidate be a good induction agent for this patient? Explain.

2. Would ketamine be a good agent for induction? Explain.

3. What is your rationale for choosing an induction agent in a patient with asthma?

III. Maintenance of anesthesia

1. Would enflurane be a good choice for maintenance of anesthesia? Why or why not?

2. What is the effect of volatile agents versus nitrous oxide/narcotic anesthesia on asthma?

Volatile agents cause bronchodilation, and are arrhythmogenic, especially halothane. Considerations are whether bronchodilator therapy would be necessary, with a subsequent increased risk of dysrhythmias. Nitrous/narcotic anesthesia would not increase this risk, and as long as the histamine-releasing opioids morphine, meperidine, and codeine are avoided, there should be no added risk of bronchoconstriction or dysrhythmias.

3. What breathing pattern is seen with narcotics?

There is a decreased respiratory rate, with an irregular pattern, and no change in tidal volume.

3. What is the effect on pulmonary vascular resistance?

4. What technique would you use in this patient? Explain.

5. Is fentanyl a good choice for balanced anesthesia? Why or why not?

Fentanyl is a good choice, due to lack of histamine release, prevention of sympathetic response to the endotracheal tube, and it has a stable cardiac profile. Its possible adverse effects include a vagally mediated bradycardia.

6. Do all of the opioids have a favorable cardiac profile?

Meperidine causes cardiac depression at doses of 2-2.5 mg/kg. Other opioids can have this effect at much higher doses than are clinically used.

7. Why does fentanyl have a shorter onset but a longer elimination half-life than morphine?

It is rapidly absorbed, because it has high lipid solubility. Then, it undergoes the pulmonary first-pass effect, and then it is redistributed. Thus, the duration is not affected by elimination, but after redistribution, it is slowly released into the blood volume.

8. Should the dose of morphine be reduced in patients with renal failure?

The liver converts morphine to morphine-3-glucuronide and morphine-6-glucuronide, an active metabolite, and both are excreted by the kidney. Therefore, the dose should be decreased.

IV. Deliberate hypotension

1. The surgeon requests you maintain a mean arterial pressure at 50 mm Hg. Your response?

2. What are the risks of deliberate hypotension?

3. Would deep inhalational agents be preferable to using sodium nitroprusside? Explain.

4. What is the rationale for using trimethaphan/nitroprusside versus nitroprusside alone?

5. What is your choice for hypotensive agent? Explain.

6. Is there a role for esmolol? Explain.

 Postoperative care

I. Extubation

1. What are your criteria for extubation?

2. Is deep extubation preferred in this patient? Why or why not?

3. You decide to leave the patient intubated. The recovery room nurse reports that the patient is wheezing. What is your differential diagnosis?

4. What is your management?

5. Is the absence of wheezing indicative of adequate bronchodilation? Explain.

6. What other signs or tests are helpful? Explain.

II. Postoperative analgesia

1. What are your options for postoperative analgesia?

2. Would you use subarachnoid opiates? Why or why not?

3. What are the side effects and risks of subarachnoid opiates?

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