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Oral case 122

Created: 3/2/2005
 

Preoperative preparation for pheochromocytoma

1. How is pheochromocytoma diagnosed?

Diagnosis is initially based on physical presentation, with a history of hypertension, headache, sweating, and flushing. It is confirmed by detection of elevated levels of urinary vanilla-mandelic acid, normetanephrine, and metanephrine.

1. How would you prepare a patient with a pheochromocytoma who is to undergo surgical resection?

The patient is given an alpha-antagonist, and is hydrated. A beta-blocker is instituted if tachycardia ensues.

2. Describe the receptors involved in the sympathetic nervous system.

There are alpha-1, alpha-2, beta-1, and beta-2 adrenergic receptors. All are postsynaptic, but for alpha-2 receptors, which provide negative feedback inhibition for presynaptic norepinephrine release. Alpha-1 stimulation produces arteriolar constriction, piloerection, salivation, mydriasis, lacrimation, as well as contraction of the vas deferens, trigone, ureter, and the splenic and prostatic capsules. Beta-1 stimulation causes positive cardiac inotropy and chronotropy, and also increases renin secretion and lipolysis. Beta-2 stimulation causes bronchial dilation, skeletal muscle vasodilation, and glycogenolysis.

Dopaminergic receptors have distinct adrenergic effects. DA1 receptors dilate renal, coronary, and splanchnic vessels, and DA2 receptor stimulation leads to nausea, vomiting, and psychic reactions.

2. What is the mechanism of norepinephrine and epinephrine synthesis?

Tyrosine enters the presynaptic terminal and in the cytoplasm, is hydroxylated to dopa, then dopa decarboxylase forms dopamine. Tyrosine hydroxylase is the rate-limiting step. Dopamine is carried to storage vessels, where a beta-hydroxylase converts it to norepinephrine. The adrenal medulla forms epinephrine through the same steps, with most of the norepinephrine being converted to epinephrine by a n-methyltransferase.

3. How are norepinephrine and epinephrine metabolized?

Norepinephrine undergoes reuptake into the presynaptic terminal, and is inactivated at other non-neuronal tissues. Enzymatic metabolism is by monoamine oxidase, or MAO, and catecholamine )-methyl transferase, or COMT. Metabolites include metanephrine, normetanephrine, and 3-methoxy-4-hydroxy-mandelic acid, or VMA.

4. What is your intraoperative management?

Invasive arterial catheter monitoring, and infusion of alpha antagonist or nitroprusside for control of hypertension. Upon completion of surgical excision, the patient is observed for hypotension and hypoglycemia.

2. Suppose you do not see the patient until the evening before surgery. The Blood pressure is 220/120 mmHg. Would you cancel the case? Explain.

Postoperative bleeding

A 5-year old is status post tonsillectomy and adenoidectomy, and continues bleeding in the recovery room. The IV has infiltrated.

1. How would you induce anesthesia for surgical exploration?

2. How would you position the patient?

3. Discuss airway management.

4. Discuss prevention of aspiration.

5. Discuss choice of agents.

Pain management for pancreatic cancer

1. How would you manage pain in a 60-year old male with pancreatic cancer?

2. What agents would you use?

3. What landmarks would you use under fluoroscopy?

4. What do you tell the patient concerning risks?


ArticleDate:20050203
SiteSection: Article
 
   
    
                                            
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