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Oral case 123

Created: 3/2/2005

A 70-year old 50 kg female who smoked two packs per day for forty years, is to undergo left upper lobe lung resection for probable cancer. She has had no angina since having a myocardial infarction one year ago. The electrocardiogram now shows first degree AV block, right bundle branch block, and LAH block. Hypertension is controlled by furosemide and clonidine. Cimetidine and antacids are required for hiatal hernia. Blood pressure is 130/85 mmHg, pulse is 80 bpm, respirations are 16, temperature is 37 degrees centigrade, hematocrit is 35%, and potassium is 3.0 mEq/l.

 Preoperative Evaluation

I. Pulmonary status

1. How do you evaluate pulmonary status?

2. Room air blood gas shows pH 7.39, PO2 of 70 mmHg, and PCO2 of 41 mmHg. Is this satisfactory in order to proceed?

3. Are pulmonary function tests needed? Explain.

4. Which ones are you most interested in? Explain.

5. What are the minimal criteria for lobectomy?

6. What are the minimal criteria for pneumonectomy?

II. Cardiac status

1. Would you insert a temporary pacemaker prior to anesthesia?

2. What technique would you use?

3. Discuss risks and benefits of a pacing SG catheter vs transvenous leads.

4. What is the management of complete heart block in the absence of a pacer?

5. Discuss the abbreviations used to describe pacemakers.

III. Hypokalemia

I. Is it dangerous if there are no dysrhythmias present?

2. Are risks increased by anesthesia and surgery? Explain.

3. Are risks increased by acute vs chronic potassium changes?

4. Would you delay the operation to replace potassium?

5. How would you determine the potassium requirement?

6. What is a safe rate of potassium replacement by infusion?

 Intraoperative Course

I. Monitoring

1. What are the best electrocardiograph lead or leads to detect ischemia? Note that the V leads are precluded by incision.

2. Is the SG catheter a useful alternative to lateral V leads to diagnose ischemia?

3. What changes are indicative of ischemia?

4. What is the mechanism?

5. Is a chest radiograph required after the SG is inserted?

6. What if the catheter tip was seen in the left pulmonary artery?

7. What is your interpretation of pulmonary artery pressures in the collapsed lung?

II. Airway

1. The surgeon desires the intraoperative collapse of the left lung. Would you choose a right-or a left-sided double-lumen endotracheal tube?

2. What are advantages and disadvantages of each?

3. If a pneumonectomy is necessary, how would you manage a left-sided tube?

4. Does hiatal hernia indicate reflux and aspiration precautions?

5. Which does it indicate?

6. Is a rapid-sequence induction/intubation feasible with a double-lumen endotracheal tube?

7. What are alternatives to a rapid sequence induction?

III. Anesthesia

1. Would you choose a volatile anesthetic or an opioid for maintenance? Explain.

2. Would you choose both?

3. Is nitrous oxide contraindicated during one-lung ventilation? Explain.

4. How do you maintain unconsciousness if nitrous oxide is not used?

5. Is 100% oxygen harmful?

6. What are alternatives to nitrous oxide in reducing FIO2?

IV. Hypoxemia

1. The saturation is 85% immediately after collapse of the left lung. Is this dangerous?

2. How will you proceed?

3. What are methods to improve the paO2 without re-expanding the left lung?

4. Would you ask the surgeon to clamp the left pulmonary artery?

V. Hypotension

1. The surgeon injects 20 ml of 0.5% bupivacaine into four intercostal spaces before closing the chest. The blood pressure goes from 100/70 to 60/40, and the heart rate decreases from 70 to 44 bpm. What is your immediate treatment?

2. What is the differential diagnosis?

3. How would you distinguish epidural block from myocardial toxicity?

4. What further treatment would you give?

 Postoperative Care

I. Extubation

1. Would you exchange a standard endotracheal tube for the double-lumen one? Explain.

2. Would you extubate this patient anesthetized or awake?

3. What are your criteria for extubation after lobectomy?

4. The patient bites down hard and occludes the endotracheal tube. What do you do?

 Pain treatment

1. Are epidural opioids satisfactory?

2. Would you choose a lumbar or a thoracic epidural?

3. What is the site of analgesic action for epidural opioids?

There are opioid receptors in the substantia gelatinosa of the spinal cord. This area processes pain signals, and has mu, delta, and kappa receptors.

4. What are side effects of neuraxial opioids?

Nausea and emesis, pruritis, urinary retention, respiratory and cardiac depression.

4. Discuss the different opioid receptor sites.

There are two mu receptor sites, mu-1 which provides analgesia, and mu-2, which cause respiratory depression, bradycardia, dependence, euphoria, and ileus. Delta receptors regulate mu activity. Kappa receptors lead to analgesia, sedation, dysphoria, and psychomimetic effects. There is no respiratory depression action here, and there is an antidiuretic action which promotes diuresis. The sigma receptor causes tachycardia, tachypnea, dysphoria, hypertonia, and mydriasis.

5. What do you know about endogenous opioids?

They are derived from one of three precursors, proenkephalin, prodynorphin, and pro-opiomelanocortin, which is also the precursor for adrenocorticotropic and melanocyte-stimulating hormones.

6. For spinal anesthesia, how do you know which opioid to select?

Lipid solubility determines selection of a particular opioid. A rapid onset and a shorter duration of action is seen with lipophilic opioids, and hydrophilic opioids have a slower onset. There is no metabolism of spinal opioids; systemic absorption determines duration of action of lipophilic ones, and absorption in neural tissues determines that of hydrophilic ones, which remain in the cord longer, and migrate slowly to rostral regions. Additionally, lipophilic opioids like fentanyl and sufentanil may have vascular absorption and significant intravenous concentrations.

4. What is the management of ventilatory depression?

5. Does naloxone antagonize epidural analgesia also?

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