ABP Local Anesthesia, Sedation and Medical Emergencies 5

Question 1

A 62-year-old patient taking propranolol 80 mg twice daily receives three cartridges of 2% lidocaine with 1:100,000 epinephrine for periodontal flap surgery. Within minutes, blood pressure rises from 138/84 to 210/115 mmHg and heart rate drops from 72 to 48 bpm. What best explains this response?

Accepted Answer

Epinephrine's alpha-1 vasoconstriction is unopposed because beta-2 vasodilation is blocked, and the resulting hypertension triggers a baroreceptor reflex bradycardia

Answer

Nonselective beta-blockers block both beta-1 and beta-2 receptors. Normally, beta-2 vasodilation in skeletal muscle offsets much of epinephrine's alpha-1 vasoconstriction. With beta-2 blocked, alpha-1 stimulation is unopposed, so peripheral resistance and blood pressure rise sharply. The baroreceptors respond with vagal slowing of the heart, and because beta-1 is also blocked, nothing counters the slowdown. Cardioselective agents such as metoprolol carry much less risk. For patients on nonselective beta-blockers, keep epinephrine to about 0.04 mg (roughly two cartridges of 1:100,000), aspirate, inject slowly, and recheck vital signs between cartridges.

Question 2

During a long periodontal procedure, a patient given several cartridges of local anesthetic seizes and then goes into pulseless ventricular tachycardia. CPR is started and 20% lipid emulsion is given. Under ASRA guidance for local anesthetic systemic toxicity (LAST), which change to standard ACLS is appropriate?

Accepted Answer

Reduce each epinephrine dose to 1 mcg/kg or less, and avoid vasopressin, calcium channel blockers, beta-blockers and other local anesthetics

Answer

ASRA's LAST guidance changes ACLS in specific ways. Epinephrine is given in small doses (1 mcg/kg or less) because standard 1 mg doses can make arrhythmias worse and reduce the effect of lipid rescue. Vasopressin is not recommended. Calcium channel blockers and beta-blockers are avoided, and lidocaine or procainamide should not be used for the arrhythmia, because they add more sodium-channel blockade. Amiodarone is the preferred antiarrhythmic. Benzodiazepines are the first choice for seizures. Propofol should be avoided when the cardiovascular system is unstable, and its small lipid content is no substitute for lipid emulsion therapy (1.5 mL/kg bolus followed by an infusion).

Question 3

A patient with documented G6PD deficiency receives a large total dose of 4% prilocaine during full-mouth scaling and root planing. Two hours later, they have cyanosis that does not improve with 100% oxygen, pulse oximetry stuck near 85%, and chocolate-brown arterial blood. Co-oximetry shows a methemoglobin level of 32%. What is the most appropriate treatment?

Accepted Answer

Avoid methylene blue; give high-dose IV ascorbic acid and arrange exchange transfusion or hyperbaric oxygen if symptoms are severe

Answer

Prilocaine's metabolite o-toluidine oxidizes ferrous hemoglobin to methemoglobin, which pulse oximetry reads at roughly 85% regardless of oxygen given. Methylene blue is the usual antidote, but it needs NADPH from the G6PD pathway to work. In G6PD deficiency it is ineffective and can cause hemolysis, which may make oxidative injury worse. The alternatives are high-dose IV ascorbic acid, a nonenzymatic reducing agent, with exchange transfusion or hyperbaric oxygen for severe or refractory cases.

Question 4

A patient with a seizure disorder controlled by long-term clonazepam is given IV midazolam for moderate sedation. They become unresponsive, breathing slows to 6 breaths per minute, and SpO2 falls to 86%. What is the most appropriate first step?

Accepted Answer

Support the airway (head-tilt/chin-lift or jaw thrust) and give positive-pressure ventilation with 100% oxygen, saving flumazenil for cautious use if ventilation fails

Answer

Airway support and ventilation always come first in sedation-related respiratory depression. This patient also has a specific reason to avoid giving flumazenil reflexively. In someone who depends on benzodiazepines, especially for seizure control, flumazenil can trigger acute withdrawal and seizures that are hard to treat. Basic airway maneuvers with bag-valve-mask ventilation will usually keep the patient oxygenated until the midazolam wears off. If flumazenil is ever used, it should be given in small increments, and the patient must be watched for resedation, because flumazenil (about 1 hour) wears off sooner than many benzodiazepines.

Question 5

A patient taking long-term nadolol has anaphylaxis (urticaria, wheezing, BP 70/40 mmHg) after receiving a penicillin-class antibiotic. Hypotension and bronchospasm continue despite two doses of IM epinephrine 0.5 mg and IV crystalloid. Which medication is specifically indicated next?

Accepted Answer

Glucagon 1–5 mg IV over 5 minutes, followed by an infusion

Answer

Beta-blockade can make anaphylaxis resistant to epinephrine, because epinephrine's beta-1 (heart) and beta-2 (bronchodilator) effects are blocked. Glucagon raises intracellular cAMP by a pathway that does not use beta receptors, so it has inotropic and chronotropic effects even under beta-blockade. The usual dose is 1–5 mg IV over 5 minutes, then 5–15 mcg/min. Watch for vomiting and protect the airway. Antihistamines and corticosteroids are add-on treatments only. Corticosteroids take hours to work and do not reverse acute shock or bronchospasm.

(ABP) American Board of Periodontology Practice Test

(ABP) American Board of Periodontology Practice Test

ABP Local Anesthesia, Sedation and Medical Emergencies 5