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Oral case 63

Created: 8/10/2004

A 38-year old 5'5", 65 kg woman is to undergo mastectomy and axillary dissection for breast cancer. She has a hiatal hernia with occasional reflux, and mitral valve prolapse with a history of syncopal episodes that have markedly reduced in frequency since starting propranolol. Blood pressure is 110/80 mmHg, pulse is 70, respirations are 14, temperature is 37 degrees centigrade, hemoglobin is 13 gm/dL, and potassium is 2.5 mEq/L.

 Preoperative evaluation

I. Cardiac status

1. What are the anesthetic concerns in a patient with mitral valve prolapse?

2. What is the cause of syncope?

3. Do you want additional information about this patient? Explain.

4. It is important to assess her left-ventricular function?

5. How would you assess her left-ventricular function?

II. Hypokalemia

1. What is your differential diagnosis for hypokalemia?

The most common cause is diuretic therapy. Beta-blockers can also cause it .

1. What is the importance of hypokalemia in a patient undergoing general anesthesia?

2. What intraoperative events exaggerate hypokalemia?

3. Should surgery be delayed to correct her potassium?

4. How would you replace potassium in this patient?

III. Premedication

1. Would you administer propranolol on the morning of surgery?

2. What are the risks?

3. Would you give an anticholinergic? Why or why not?

Anticholinergic medication is elective therapy, and reasons for giving it include antisialogogue effects, sedation, amnesia, and antiemesis. While an anticholinergic like scopolamine may beneficially increase heart rate in this patient with mitral valve prolapse, it may also cause sedation, decreased airway responsiveness, and decreased secretions.

Other side effects of anticholinergics include decreased lower esophageal sphincter tone, central nervous system toxicity, mydriasis, cycloplegia, increased dead space, inability to sweat, and hyperthermia.

4. Why does scopolamine cause sedation and glycopyrrolate have no such action?

Scopolamine is a tertiary amine, and crosses the blood-brain barrier, causing sedation, whereas glycopyrrolate is a quaternary amine, and does not cross the blood brain barrier.

4. Would you give aspiration prophylaxis?

 Intraoperative course

I. Monitoring

1.Would you use a thermodilution-type pulmonary artery catheter for this case? Explain.

2. How would you detect mitral regurgitation?

3. Is it important to detect it for this case? Why or why not?

4. The surgeon requests deliberate hypotension to reduce blood loss from a large breast. Is there any particular concern relative to her mitral valve prolapse?

5. Will you alter your monitoring plans? Explain.

II. Anesthesia

1. How will you manage the airway during induction of anesthesia?

2. How will you minimize tachycardia in response to intubation?

3. What is your choice of muscle relaxant? Explain your rationale.

4. What is the priming principle?

5. What are the risks of priming?

III. Deliberate hypotension

1. Would you choose nitroprusside for deliberate hypotension in this patient? Why or why not?

2. What are alternative methods?

3. Is one volatile anesthetic preferable to the others for this purpose? Describe.

IV. Dysrhythmia

1. The heart rate slows from 70 to 50 bpm, and premature ventricular contractions occur at a rate of one per every 8-10 beats. Are you concerned?

2. What is your differential diagnosis?

3. The blood pressure returns to normal when the rhythm is normal. Why?

4. What is your treatment?

V. Blood volume

1. What is the estimated blood volume for this patient?

2. What is a safe loss of red blood cell volume in this patient?

3. Discuss the use of albumin vs hetastarch vs crystalloid to maintain blood volume.

4. Discuss the distribution of fluids between the intravascular fluid and the interstitial compartment.

There are hydrostatic and osmotic forces, which control fluid shifts. Arterial capillary hydrostatic pressure results in a net outward flow of fluid, and the venous capillary osmotic pressure causes reabsorption of fluid.

 Postoperative care

I. Analgesia

1. Are intrathecal or epidural opioids satisfactory? Why or why not?

2. What are the hemodynamic effects of intrathecal or epidural opioids?

3. Do you prefer morphine or fentanyl for epidural use in this patient? Explain.

4. Compare and contrast side effects of each.

5. How would you treat the side effects?

II. Oliguria

1. In the recovery room, urine output is 10 ml/hr for the first two hours. Is this satisfactory?

2. What are possible causes?

3. Do you anticipate a spontaneous increase in urine output as anesthetic recovery proceeds?

4. Is treatment indicated now?

5. How would you decide if treatment is indicated now?

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