Obstetric Anesthesia and Analgesia Flashcards

A parturient at 32 weeks gestation with known antiphospholipid syndrome on therapeutic low-molecular-weight heparin (LMWH) presents in active labour. Her last LMWH dose was 18 hours ago. Anti-Xa level returns at 0.18 IU/mL. What is the most appropriate neuraxial analgesia decision?

Answer: Withhold neuraxial analgesia; therapeutic LMWH requires 24 hours from last dose regardless of anti-Xa level

For therapeutic-dose LMWH, ESRA and ASRA guidelines recommend a minimum 24-hour interval before neuraxial blockade, not the 12-hour interval applicable to prophylactic dosing. Anti-Xa monitoring is not routinely recommended to guide timing and a level of 0.18 IU/mL in this context does not permit safe neuraxial access before the 24-hour window has elapsed. Antiphospholipid syndrome further increases thrombohemorrhagic risk, reinforcing strict adherence to the guideline interval.

During combined spinal-epidural (CSE) analgesia for labour, a parturient develops sudden severe hypotension (BP 68/40 mmHg) and fetal bradycardia 90 seconds after intrathecal injection of fentanyl 25 mcg + bupivacaine 2.5 mg. Uterine hyperstimulation is observed on CTG. What is the most likely mechanism and first-line treatment?

Answer: Intrathecal opioid-induced uterotonic effect causing tachysystole and uteroplacental insufficiency; treat with sublingual or IV nitroglycerin

Intrathecal fentanyl can paradoxically cause uterine hyperstimulation (tachysystole) via a spinal opioid-mediated mechanism, reducing uteroplacental blood flow and causing fetal bradycardia. This is a recognised complication of CSE with intrathecal opioids. The combination of hypotension plus CTG-confirmed hyperstimulation distinguishes this from pure aortocaval compression. Nitroglycerin (50–100 mcg IV or 400 mcg sublingual) is the preferred uterolytic in this setting. Vasopressors alone (ephedrine/phenylephrine) address maternal BP but do not resolve the uterine hyperstimulation.

A 28-year-old primigravida at 39 weeks requires emergency Category 1 Caesarean section for cord prolapse under general anaesthesia. RSI is performed; laryngoscopy reveals a Cormack–Lehane grade 3 view. Two intubation attempts fail. SpO2 is now 91% with bag-mask ventilation providing adequate chest rise. What is the correct next step according to the Difficult Airway Society (DAS) 2015 obstetric airway guidelines?

Answer: Maintain oxygenation, call for senior help, and plan whether to wake up or proceed with an supraglottic airway device, balancing maternal and fetal risk

DAS 2015 obstetric guidelines specify that after two failed intubation attempts, the anaesthetist should stop further intubation attempts and oxygenate the patient. Crucially, this is a 'cannot intubate, CAN oxygenate' scenario (SpO2 improving/stable with BMV). The decision to wake vs. proceed must be individualised, weighing fetal jeopardy (cord prolapse is immediately life-threatening to the fetus) against maternal airway risk. A supraglottic airway (e.g. ProSeal/Supreme LMA) may facilitate surgery. A third intubation attempt at this stage risks converting to a 'cannot oxygenate' crisis. FONA is reserved for the 'cannot intubate, cannot oxygenate' scenario.

A parturient with pre-eclampsia at 36 weeks receives a magnesium sulfate infusion (4 g loading dose, maintenance 1 g/hr). She requires urgent Caesarean section under spinal anaesthesia. Post-delivery, she develops hypotonia, respiratory rate of 6 breaths/min, and loss of patellar reflexes. Serum magnesium level is 4.8 mmol/L. What is the most appropriate immediate treatment?

Answer: Administer calcium gluconate 10 mL of 10% solution IV over 10 minutes and stop magnesium infusion

Magnesium toxicity at levels >3.5 mmol/L causes respiratory depression and loss of deep tendon reflexes. The specific antidote is intravenous calcium gluconate (10 mL of 10% solution = 2.25 mmol Ca²⁺ given over 10 minutes), which competitively antagonises magnesium at the neuromuscular junction. The infusion must be stopped simultaneously. Calcium chloride is more irritant and better reserved for cardiac arrest scenarios. Neostigmine reverses acetylcholinesterase inhibition, not magnesium toxicity. Furosemide has a role in chronic management but is too slow for acute toxicity with respiratory compromise.

In a parturient with a known intracardiac right-to-left shunt (Eisenmenger syndrome), which statement regarding neuraxial anaesthesia for Caesarean section is MOST accurate?

Answer: Epidural anaesthesia with slow titration is preferred over single-shot spinal because it allows gradual sympathectomy, minimising the fall in systemic vascular resistance

In Eisenmenger syndrome (fixed pulmonary hypertension with right-to-left shunt), falls in systemic vascular resistance (SVR) increase right-to-left shunting, worsening hypoxaemia and potentially causing cardiovascular collapse. Single-shot spinal produces rapid, unpredictable sympathectomy with precipitous SVR reduction and is therefore relatively contraindicated. Slow, incremental epidural titration allows haemodynamic monitoring and titration to effect, minimising SVR drops. While GA avoids neuraxial sympathectomy, it carries significant risks in this population (induction hypotension, positive pressure ventilation raising PVR). CSE with low-dose spinal does not eliminate hypotension risk. Neither option 'eliminates' hypotension — the goal is controlled, gradual management.

Remifentanil patient-controlled intravenous analgesia (PCIA) is being used for labour analgesia in a parturient who declined epidural. She has a demand dose of 40 mcg with a 2-minute lockout. After 90 minutes she becomes excessively sedated between contractions (RASS −3) with SpO2 nadir of 88% during sedation episodes. Fetal CTG remains reassuring. What is the MOST appropriate immediate action?

Answer: Stop the remifentanil PCIA, administer supplemental oxygen, ensure continuous one-to-one midwifery monitoring with pulse oximetry, and reassess when alert

Remifentanil PCIA requires continuous one-to-one midwifery care and pulse oximetry precisely because of its risk of maternal sedation and respiratory depression between contractions (the drug's peak effect coincides with the inter-contraction rest period). An SpO2 nadir of 88% with RASS −3 represents dangerous oversedation. The immediate priority is stopping the infusion and ensuring oxygenation. Naloxone should be used cautiously (small titrated doses if at all) as it abruptly reverses analgesia and can cause acute pain and cardiovascular stimulation; it is not the 'immediate first action'. Simply reducing the dose without stopping is inadequate given the current dangerous sedation level. Switching to epidural is a reasonable subsequent plan once the patient is safe, but not an 'immediate' action.