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Oral case 39

Created: 5/10/2004

A 26-year old female injured her right knee while ice-skating and presents for arthroscopy as an outpatient. She has a long history of asthma, taking theophylline 300 mg bid, and occasionally uses metaproterenol inhaler. Four days prior to surgery, during this consult for outpatient surgery; she is recovering from an upper respiratory infection. She has diffuse wheezes on exam. Further history reveals an intubation, which took thirty minutes during a prior case. She was told that the intubation was very difficult. Blood pressure is 120/70 mm Hg, pulse is 88 bpm, respirations are 16, and temperature is 36.8 degrees centigrade.

 Preoperative evaluation

I. Appropriateness as an outpatient

1. The surgeon asks if the patient will need to be admitted. Your response?

2. Do you need additional information, or further tests? Explain.

II. Evaluation of respiratory status

1. What further evaluation of her respiratory system is indicated? Explain.

2. Would you postpone this case? Why or why not?

3. Would you suggest further medical therapy?

4. What and why?

III. Risk

1. She asks you if she is at increased risk. What is your response?

 Intraoperative course

I. Choice of anesthesia

1. What technique would you use for this case? Explain.

2. How does her airway affect your decision?

Airway management becomes important because of anatomic abnormalities, which may make ventilation insufficient to provide oxygenation to tissues. Securing the airway to maintain ventilation is of prime importance.

3. How does her asthma affect your decision?

4. She insists on being awake for the case. What is your response?

II. Regional anesthesia

1. What are her options?

2. Compare and contrast spinal versus epidural versus leg block

3. What local anesthetic agent would you use for a subarachnoid block? Explain your choice.

4. Is epinephrine necessary? Explain.

5. What level of block is needed for this procedure?

6. How does her outpatient status influence your decision?

III. Discomfort under spinal

1. She has a meniscectomy and tendon repair with a tourniquet time of ninety minutes at 260 mm Hg. She complains of leg discomfort. The surgeon still needs another forty-five minutes. What do you do?

IV. Bronchospasm under general anesthesia

1. You give general anesthesia with halothane and nitrous/oxygen by mask. Fifteen minutes later, she develops marked wheezing and heart rate increases to 122 bpm. What is your evaluation and management?

2. Her end-tidal CO2 has fallen from 35 to 22 mm Hg. Why?

3. What is the mechanism by which halothane causes arrhythmias?

Prolonged conduction through the His-Purkinje system may favor reentry, and alpha-1 adrenergic stimulation may occur. Halothane also causes a cholinergic, vagally induced bradycardia in children.

4. Discuss the metabolism of volatile anesthetics, with a clinical basis.

Oxidative metabolism by the liver's cytochrome P-450 system occurs, and the kidneys, lungs, and gastrointestinal tracts have a lessor role. Isoflurane and desflurane undergo virtually no metabolism, and more than 20% of halothane is metabolized by the liver. When hypoxia occurs, reductive metabolism may occur in the liver, contributing to hepatic necrosis. Halothane hepatitis is most likely due to an autoimmune hypersensitivity reaction. Fluoride production is associated with methoxyflurane metabolism, causing renal dysfunction, which is why it is no longer available.

 Postoperative care

I. Persistent nausea and vomiting

1. What are possible causes of nausea and vomiting in the recovery room?

2. What is your management?

II. Discharge

1. How will you decide if she is suitable to be discharged from the recovery room to home?

2. Would you allow her to go home?

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