Ketamine is being considered as an adjunct during caesarean delivery. Why is its dose restricted to approximately 1 mg/kg in the parturient?

• A Doses above this range cross the placenta and cause fetal bradycardia through vagal stimulation
• B Doses above this range produce maternal tachycardia that compromises placental perfusion
• C Doses above this range abolish the laryngeal reflexes needed before extubation
• D Doses above this range increase uterine tone and can depress the neonate ✓

Explanation

At doses below about 1 mg/kg, ketamine provides analgesia without increasing resting uterine tone, and it is valued in obstetrics for supporting cardiovascular stability. Above roughly 1.5 to 2 mg/kg it increases uterine tone, which may hinder fetal extraction, and neonatal depression becomes more likely. Maternal tachycardia occurs even at small doses and is not the reason for the ceiling. Loss of airway reflexes is a general dose-related effect, not specific to parturients.

Reference: Morgan and Mikhail's Clinical Anesthesiology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.