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Oral case 113

Created: 5/11/2004

A 65-year old 80 kg man with a previously diagnosed abdominal aortic aneurysm is admitted for resection. He has had acute back pain, oliguria, and shortness of breath for three days. The aneurysm has been present for three years with no change in size. Prior history includes left nephrectomy ten years ago. Blood pressure is 180/100 mmHg, pulse is 96, respirations are 32, oral temperature is 37.5 degrees centigrade, blood urea nitrogen is 50 mg/dl, creatinine is 4 mg/dl, potassium is 6.0 mEq/L, and hemoglobin is 11.

 Preoperative Evaluation

I. Assessment of renal function

1. What might be the cause of his renal insufficiency?

2. How would you evaluate this?

3. What is the significance of renal insufficiency to anesthetic care?

4. What is the significance of the potassium level?

5. Is urgent correction indicated?

II. Blood pressure

1. Should the patient's blood pressure be lowered preoperatively? Explain.

2. You choose to treat it. What drug or drugs would you use? Explain.

III. Respiratory function

1. Why is the patient tachypneic?

2. How would you determine the cause?

3. What tests would you order? Explain.

4. How would you treat him if the etiology appears to be pulmonary edema? Explain.

 Intraoperative Course

I. Selection of monitoring

1. How will you assess the adequacy of renal perfusion during surgery? Explain.

2. Is a pulmonary artery catheter necessary? Explain.

3. After placement of a pulmonary artery catheter, pulmonary artery pressure is 55/32 mmHg, and the pulmonary artery occlusion pressure is 28 mmHg. What is your interpretation?

4. Would you want additional information? Explain.

5. What is your treatment?

II. Choice of anesthetic agents

1. Is ketamine appropriate for induction? Explain.

2. What is your choice for induction? Explain.

3. What is your choice for maintenance? Give reasons.

4. How do you control hypertension at the time of clamping?

5. Does heart failure or renal insufficiency affect your selection of agents? Explain.

III. Management of muscle relaxation

1. Is atracurium an appropriate muscle relaxant in this patient? Explain.

No. Atracurium is intermediate-acting, and is not significantly metabolized by the kidneys or the liver, as it is spontaneously broken down by Hoffmann elimination and ester hydrolysis. Rapid intubation is necessary in this patient, who will easily desaturate after induction.

2. You decide this is not appropriate. What is your choice? Explain.

3. Will you monitor neuromuscular function?

4. What is the difference between depolarizing and nondepolarizing neuromuscular blockers?

Depolarizing blockers mimick acetylcholine's action, and depolarize the postsynaptic membrane. Acetylcholine has no effect because the receptor is occupied and depolarized. In contrast, nondepolarizing agents competitively block the postsynaptic membrane, resulting in no depolarization.

5. Which muscle relaxants are dependent on the liver for degradation?

Vecuronium, pancuronium, pipecuronium, and rocuronium. Extrahepatic biliary obstruction may affect excretion of vecuronium and rocuronium.

6. Which muscle relaxants are dependent on renal excretion?

Tubocurarine, metocurine, doxacurium, pancuronium, and pipecuronium.

4. Will you monitor reversal?

IV. Fluid management in the presence of oliguria

1. There is no urine output prior to aortic cross clamping. What are possible causes?

2. What fluid would you use?

3. What are your goals in fluid management?

4. Are diuretics indicated? Explain.

V. Management of dysthythmias

1. The electrocardiogram shows runs of premature ventricular contractions. What is the significance of this?

2. What is your treatment? Explain.

3. Ventricular tachycardia follows. What is the significance of this?

4. What is your treatment? Explain.

5. Asystole follows. What is your management of cardiopulmonary resuscitation?

6. You have a successful resuscitation. Will you institute any special precautions now? Explain.

 Postoperative Care

I. Ventilatory management

1. In the operating room at the end of the case, blood gas shows pH=7.4, paCO2 = 40 mmHg, paO2= 60 mmHg on 100% FIO2. Should he be extubated? Explain.

2. What are your criteria for postoperative ventilatory support?

3. What ventilator settings would you want?

Intermittent mandatory ventilation will deliver all of the preset breaths, and will also receive a tidal volume for initiated breaths. The tidal volume should be set at 10-12 ml/kg, and it is best to begin with an FIO2 of 100%.

3. Is positive end-expiratory pressure indicated? Explain.

4. Is continuous positive airway pressure indicated? Explain.

5. What are the hazards of each?

6. What are indications for intermittent mandatory ventilation?

7. What are criteria for extubation?

II. Evaluation of delayed recovery

1. The patient is unresponsive two hours postoperatively. Is this due to effects of residual anesthesia? Explain.

2. Which drugs could cause this? Explain mechanisms.

3. What other causes could be causing this?

4. How will you establish the cause?

5. Discuss your management.

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