What is the role of propranolol (beta blocker) in managing hyperthyroidism symptoms, such as tachycardia and tremors, in a pregnant patient in labor?

Propranolol for Hyperthyroid Patients in Labor

Propranolol is safe and effective for managing hyperthyroid symptoms (tachycardia, tremors, anxiety) in pregnant patients during labor, and should be used as adjunctive therapy while thioamide medications reduce thyroid hormone levels. 1

Mechanism and Rationale

• Propranolol controls the peripheral manifestations of hyperthyroidism including tachycardia, tremor, nervousness, and palpitations by blocking beta-adrenergic receptors, but does not affect the underlying thyrotoxic process itself 2, 3
• Beta-blockers are particularly valuable during labor because they provide rapid symptom control while thioamide therapy (propylthiouracil or methimazole) takes time to reduce thyroid hormone levels 1

Dosing and Administration

• The typical oral dose ranges from 40-320 mg/day, with an average of 160 mg/day, titrated to control heart rate and symptoms 4
• For acute situations, intravenous propranolol can provide symptom control in less than one hour if needed 4
• The goal is to use the lowest effective dose to maintain symptoms control 1

Safety Profile in Pregnancy and Labor

• Propranolol has been used successfully in pregnant hyperthyroid patients, including during labor, with no instances of thyroid storm when properly managed 5, 6
• Both metoprolol and propranolol are considered safe first-line beta-blockers during pregnancy based on their longer safety record 1, 7
• Neonates whose mothers receive beta-blockers at parturition should be monitored for 24-48 hours after delivery for hypoglycemia, bradycardia, and respiratory depression 7, 8

Critical Considerations for Labor

• Regional anesthesia is strongly preferred over general anesthesia in patients taking propranolol during labor 6
• If general anesthesia becomes necessary, continuous electrocardiogram and central venous pressure monitoring must be performed 6
• The impaired ability of the heart to respond to reflex adrenergic stimuli may augment risks during surgical procedures (such as emergency cesarean section) 8

Monitoring Requirements

• Monitor maternal heart rate to ensure adequate beta-blockade without excessive bradycardia 1
• Continuous fetal monitoring is essential as maternal arrhythmias or uncontrolled hyperthyroidism can cause fetal hypoperfusion 9
• Check thyroid function (FT4 or FTI) every 2-4 weeks during pregnancy to guide thioamide dosing 1

Risk of Thyroid Storm During Labor

• Labor is a recognized precipitating event for thyroid storm, which presents with fever, tachycardia out of proportion to fever, altered mental status, vomiting, diarrhea, and cardiac arrhythmia 1
• Thyroid storm carries high risk of maternal heart failure and requires immediate aggressive treatment with propylthiouracil or methimazole, iodine solution, dexamethasone, and propranolol 1
• Treatment should not be delayed for laboratory confirmation if clinical suspicion is high 1

Important Caveats

• Beta-adrenergic blockade may mask certain clinical signs of worsening hyperthyroidism, so abrupt withdrawal could precipitate thyroid storm 8
• Propranolol may prevent the appearance of premonitory signs of hypoglycemia (pulse rate and pressure changes), particularly important during the fasting state before potential cesarean section 8
• Do not use propranolol in patients with manifest Wolff-Parkinson-White syndrome, as severe bradycardia requiring pacemaker has been reported 8
• Avoid in patients with bronchospastic lung disease, as it may provoke bronchial asthmatic attacks 8

Postpartum Management

• Continue monitoring the newborn's physician must be informed of maternal Graves' disease due to risk of neonatal thyroid dysfunction 1
• Propranolol is excreted in human milk, so caution is advised during breastfeeding, though mothers taking propylthiouracil or methimazole can breastfeed safely 1, 8