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Oral case 75

Created: 11/10/2004


Anesthesia for elective cesarean section in a patient with idiopathic hypertrophic subaortic stenosis. She weighs 80 kg.

1. Would a regional or a general be preferred? Explain your rationale.

2. What local anesthetic and technique would you use for a regional?

3. What is ion trapping, and what is its significance to obstetrics?

Ion trapping occurs in an acidic environment when ionized local anesthetic accumulates. It can be seen in the case of an acidic fetus, and leads to an increased concentration of local anesthetic in the fetal blood, and can jeopardize the fetal circulatory system's own response to asphyxia.

4. What is the maximum dose of 0.25% bupivacaine that the surgeon can use for infiltration of the surgical incision site?

The maximum dose is 80 kg X 2mg/kg, which is 160 mg total. At 2.5 mg per cc, the total injected safe dose is 160 divided by 2.5, or 64 cc.

5. Why is epinephrine added to local anesthetics?

To cause local vasoconstriction, decrease the vascular absorption of local anesthetic, reduce the risk of toxicity, and to prolong its effects.

6. When is the addition of epinephrine or phenylephrine contraindicated?

With myocardial dysfunction including unstable angina pectoris or cardiac arrhythmias, and when used to areas without collateral blood flow, as to a digit.

7. What are signs of local anesthetic toxicity?

Symptoms involve the central nervous system and then the cardiac system. It may begin with the patient complaining of lightheadedness, tinnitus, perioral numbness, and confusion. It progresses to muscle twitches, auditory or visual hallucinations, and then tonic-clonic seizures, unconsciousness, and respiratory arrest. Cardiac symptoms begin with hypertension and tachycardia, then decreased cardiac output and contractility, leading to hypotension. Later, bradycardia, ventricular dysrhythmias, and full circulatory arrest may ensue.

8. What regional blocks are associated with increased systemic absorption of local anesthetic? Begin with the greatest degree of systemic absorption.

Intercostal nerve block > caudal > epidural > brachial plexus > sciatica-femoral > subcutaneous.

9. What is ropivacaine?

It is a local anesthetic that can provide a differential blockade, with sensory loss and no motor loss, making it a useful drug for use in obstetrics. It is structurally similar to bupivacaine, being highly protein bound and having a lengthy duration of action, with less cardiotoxicity.

Management of reflex sympathetic dystrophy

A 67-year old woman has reflex sympathetic dystrophy after an arm fracture.

1. What physical findings do you expect?

2. What is your management?

3. How does your chosen treatment work?

Neurologic dysfunction following aortofemoral bypass

A patient in the recovery room two hours after an aortofemoral bypass performed with epidural and light general anesthetic is awake but has no movement or sensation in the lower extremities.

1. What is your differential diagnosis?

2. How do you evaluate the patient?

3. What is your treatment?

4. What do you tell the patient and the surgeon?

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