Obstetric Anesthesia and Analgesia Flashcards

A parturient presents for an emergency Cesarean section due to fetal distress. After placement of a spinal anesthetic with hyperbaric bupivacaine and fentanyl, her blood pressure drops from 125/75 mmHg to 70/40 mmHg despite a 500 mL crystalloid co-load. The fetal heart rate is now 80 bpm. What is the most appropriate initial pharmacological intervention?

Answer: Phenylephrine 100 mcg IV

Phenylephrine is the first-line vasopressor for managing spinal-induced hypotension in obstetrics according to international consensus guidelines. It is a pure alpha-agonist that increases systemic vascular resistance (SVR) without significant beta-adrenergic effects. This helps maintain uteroplacental perfusion effectively. While historically favored, ephedrine crosses the placenta to a greater extent and can cause fetal tachycardia and acidosis. Adrenaline is reserved for severe, refractory hypotension or cardiac arrest. Glycopyrrolate would treat bradycardia but not the primary problem of vasodilation.

Which of the following physiological changes in pregnancy has the most significant clinical implication for the induction of general anesthesia?

Answer: Decreased functional residual capacity (FRC)

The combination of a decreased functional residual capacity (FRC) and an increased metabolic rate (oxygen consumption) in pregnant patients leads to a much more rapid desaturation and development of hypoxia during periods of apnea, such as after induction of general anesthesia. This makes thorough pre-oxygenation critically important. While increased plasma volume, GFR, and decreased cholinesterase activity are important considerations, the accelerated risk of hypoxia is the most immediate life-threatening concern during airway management.

A 32-year-old G1P0 parturient develops a severe headache 24 hours after an uneventful epidural for labor analgesia. The headache is postural, worsening when upright and relieved by lying flat. Which of the following is considered the most definitive treatment for her condition?

Answer: Epidural blood patch (EBP)

The patient's symptoms are classic for a post-dural puncture headache (PDPH). While conservative measures like hydration, simple analgesics, and caffeine are often tried first, the epidural blood patch (EBP) is considered the most effective and definitive treatment, especially for severe or persistent symptoms. It works by forming a clot over the dural hole, preventing further CSF leakage and restoring intracranial pressure. Success rates for an EBP are high, often providing immediate relief.

A 28-year-old patient with severe pre-eclampsia is receiving an intravenous infusion of magnesium sulfate for seizure prophylaxis. During her Cesarean section under general anesthesia, she receives a non-depolarizing neuromuscular blocking agent (NMB). What effect should be anticipated regarding the NMB?

Answer: Potentiation of both onset and duration of action

Magnesium sulfate potentiates the effects of non-depolarizing neuromuscular blocking agents. It acts at the pre-synaptic nerve terminal to inhibit the release of acetylcholine and also depresses the post-synaptic membrane excitability. This results in a faster onset and a prolonged duration of neuromuscular blockade. Therefore, the dose of the NMB should be reduced, and neuromuscular function must be monitored carefully.

Regarding the use of local anesthetics for labor epidural analgesia, which statement best describes a primary advantage of ropivacaine over bupivacaine?

Answer: It produces less motor block at equipotent analgesic concentrations.

Ropivacaine is an S-enantiomer that exhibits a greater degree of sensory-motor differentiation compared to the racemic mixture bupivacaine. This means that at concentrations providing similar levels of sensory analgesia, ropivacaine causes less profound motor blockade. This is advantageous for laboring patients, allowing for greater mobility. It also has a lower potential for cardiotoxicity. Onset and duration are generally comparable in clinical practice, and pruritus is primarily related to the use of opioids, not the local anesthetic itself.

A patient undergoes an emergency Cesarean section for placental abruption. Following delivery, there is significant ongoing hemorrhage due to uterine atony. Initial administration of oxytocin and ergometrine has been ineffective. Which of the following is the most appropriate next-line uterotonic agent to administer?

Answer: Intramuscular carboprost

Carboprost (a prostaglandin F2-alpha analogue) is a potent uterotonic agent used as a second or third-line treatment for postpartum hemorrhage (PPH) due to uterine atony when first-line agents like oxytocin and ergometrine are insufficient or contraindicated. It is typically administered intramuscularly. Vasopressin is not a primary uterotonic for PPH. Salbutamol and magnesium sulfate are tocolytics and would relax the uterus, worsening the atony.