Medical Pharmacology Question Bank
Chapter 15: Local Anesthetic Pharmacology — Module 5: Neuraxial Anesthesia
Clinical Vignette (11 questions)
1. A 31-year-old woman at 39 weeks' gestation receives a spinal anesthetic for elective cesarean delivery and is positioned supine on the operating table. Within three minutes her systolic blood pressure falls from 118 to 72 mmHg, she reports nausea, and the fetal heart rate tracing shows a prolonged deceleration to 90 beats per minute. What is the most appropriate immediate action?
ANSWER: B
Rationale:
In a term parturient placed supine, the gravid uterus compresses the inferior vena cava and aorta, and this aortocaval compression compounds the sympathectomy-induced vasodilation of the spinal to produce rapid maternal hypotension that preferentially reduces uteroplacental flow, manifesting as the fetal deceleration. The correct immediate response is to relieve the mechanical compression with left uterine displacement and to restore maternal pressure and uteroplacental perfusion with phenylephrine, the preferred vasopressor in this setting.
2. A 54-year-old man receives a spinal anesthetic for an inguinal hernia repair. Over several minutes he becomes anxious and dyspneic, reports tingling in both hands, and develops a heart rate of 44 beats per minute with a systolic pressure of 80 mmHg; the sensory level is testing at approximately T2. Which response best addresses the underlying problem?
ANSWER: D
Rationale:
The ascending sensory level near T2, hand tingling, dyspnea, bradycardia, and hypotension together indicate a high spinal: the block has reached the cardiac accelerator fibers (T1 to T4), removing sympathetic drive to the heart, while threatening the muscles of respiration. Management is simultaneous airway and breathing support, rapid fluids, and ephedrine (combined alpha and beta activity) for hypotension accompanied by bradycardia, with atropine for the vagally mediated slowing. Option B gives a beta-blocker to a bradycardic, hypotensive patient, worsening both. Option C uses a vasodilator that would deepen the hypotension. Option E relies on abrupt repositioning of an already-set block and dangerously leaves a deteriorating patient unmonitored.
3. A laboring patient with a dilute labor epidural infusion (low-concentration bupivacaine with fentanyl) has had excellent analgesia for hours. As the fetal head descends in late second stage, she develops new intense perineal pressure and pain, although her abdominal contraction pain remains well controlled. The catheter aspirates negative and was previously functioning well. What is the most appropriate next step?
ANSWER: A
Rationale:
This is a single-patient reasoning problem about sacral coverage. Late second-stage perineal pain with preserved abdominal analgesia is the classic picture of inadequately blocked sacral nerve roots, which are larger and harder to reach and are often incompletely covered by a dilute infusion in a recumbent patient. The remedy applies the concentration-density relationship and sacral anatomy: give a more concentrated bolus and/or reposition the patient upright to direct solution caudally toward the sacral roots. Option B discards a functioning catheter and abandons effective regional analgesia for an inferior systemic approach. Option C invokes a catastrophic complication that does not fit a comfortable patient with isolated perineal pain and a previously functioning catheter. Option E escalates to general anesthesia when a simple dosing and positioning adjustment is indicated.
4. A laboring patient with a well-functioning labor epidural develops a category III fetal heart rate tracing, and the obstetric team calls for an emergent cesarean delivery within minutes. You elect to extend the existing epidural to surgical anesthesia rather than perform a spinal or induce general anesthesia. Which agent injected through the catheter provides the fastest, most reliable dense surgical block?
ANSWER: C
Rationale:
When an existing epidural must be extended to surgical anesthesia under time pressure, 3% chloroprocaine gives the fastest, most reliable onset, on the order of 6 to 10 minutes. Although chloroprocaine has an unfavorable pKa, its very high concentration delivers a large mass of drug that crosses the nerve membranes by mass action, overcoming the ionization disadvantage to produce a dense block quickly.
5. A healthy 35-year-old is scheduled for an elective outpatient knee arthroscopy expected to last about 40 minutes, with planned same-day discharge. The patient prefers a spinal anesthetic. Which agent best matches this clinical goal?
ANSWER: E
Rationale:
The decision turns on matching agent duration and recovery profile to a short ambulatory case with same-day discharge. Preservative-free chloroprocaine offers rapid onset, a short predictable duration, full recovery suited to prompt discharge, and a very low rate of transient neurologic symptoms, making it the best fit.
6. A patient is three days into a continuous thoracic epidural infusion after major abdominal surgery. Over the preceding day he developed a fever to 38.7 degrees C, increasing back pain localized to the catheter insertion site, and a rising white blood cell count; he now reports new lower-extremity weakness. What is the most likely diagnosis and the correct management?
ANSWER: B
Rationale:
The subacute course over days with fever, insertion-site back pain, leukocytosis, and then neurologic deterioration is the characteristic presentation of an epidural abscess, most often due to Staphylococcus aureus. Because neurologic deficit is present, the correct management is urgent spine MRI, emergent neurosurgical decompression, and pathogen-directed antibiotics after cultures; antibiotics alone are insufficient once a deficit has developed. Option A dangerously dismisses a febrile, leukocytotic patient with a new deficit as simple over-blockade. Option C misassigns the picture to post-dural puncture headache, which is a postural headache, not a febrile progressive myelopathy. Option D trivializes a deep neuraxial infection with neurologic involvement as a superficial site issue.
7. A postoperative patient with a thoracic epidural catheter is receiving prophylactic low-molecular-weight heparin (LMWH). The surgical team asks you to remove the epidural catheter so the patient can be discharged. The last LMWH dose was given a few hours ago, and another dose is due soon. What is the correct approach to catheter removal?
ANSWER: A
Rationale:
The governing principle is that neuraxial anticoagulation intervals apply to catheter removal just as to placement, because withdrawing the catheter disturbs epidural vessels and carries comparable hematoma risk. With prophylactic LMWH, the catheter should be removed only after the recommended interval has elapsed since the last dose, and the next dose should be delayed for the recommended interval after removal. Option B is dangerously wrong because removal absolutely can precipitate an epidural hematoma. Option C is unnecessarily extreme; timed removal does not require abandoning all anticoagulation. Option E is hazardous because dosing LMWH immediately around removal maximizes, rather than minimizes, hematoma risk.
8. Two days after a labor epidural complicated by a recognized dural puncture, a patient has a severe headache that is mild when she lies flat and becomes disabling within minutes of sitting upright, with associated neck stiffness and photophobia. Bed rest, oral hydration, and caffeine over the past 24 hours have not provided meaningful relief, and she is unable to care for her newborn. What is the most appropriate definitive treatment?
ANSWER: D
Rationale:
The postural headache (mild supine, disabling upright) with neck stiffness and photophobia two days after a known dural puncture is a classic disabling post-dural puncture headache that has failed conservative care. The definitive treatment is an epidural blood patch: autologous blood injected into the epidural space at or near the puncture level clots and seals the dural leak, restoring cerebrospinal fluid pressure and typically relieving the headache promptly.
9. A patient with a thoracic epidural infusion for postoperative analgesia is noted to have mild new weakness in one leg. He is afebrile with no back pain. You stop the infusion and reassess 45 minutes later: the motor strength has substantially recovered and there is no further progression. What is the most appropriate interpretation and next step?
ANSWER: C
Rationale:
The motor-block workup hinges on the response to stopping the infusion. Weakness that substantially resolves and does not progress after the infusion is stopped, in an afebrile patient without back pain, is characteristic of pharmacologic over-blockade rather than a compressive lesion. The appropriate step is to resume analgesia at a lower concentration or rate (or a more dilute solution) and continue monitoring motor function; urgent imaging is reserved for weakness that persists or progresses despite stopping the infusion.
10. A 79-year-old with severe aortic stenosis requires open reduction of a hip fracture. The cardiology consult emphasizes that this preload-dependent, fixed-output physiology tolerates only gradual hemodynamic change. You plan a neuraxial technique. Which approach best protects this patient's hemodynamics?
ANSWER: B
Rationale:
In severe aortic stenosis the heart cannot compensate for an abrupt fall in afterload and preload, so the danger of neuraxial anesthesia is the speed and depth of the sympathectomy, not its use per se. A combined spinal-epidural with a low intrathecal dose, supplemented through the epidural catheter in titrated increments, builds the block gradually and avoids the rapid profound vasodilation and preload loss of a full single-shot spinal, matching the requirement for gradual hemodynamic change. Option A imposes exactly the abrupt sympathectomy this physiology tolerates worst. Option C deliberately drives a rapid high block, the most dangerous choice here. Option E produces a rapid dense block, again the opposite of the gradual approach required.
11. A 52-kg patient with compensated cirrhosis undergoes outpatient rotator cuff repair and is to be discharged home with a continuous peripheral nerve block (CPNB) infusion via a portable pump for postoperative analgesia. Considering her low body weight and hepatic impairment, how should the infusion be set up and the patient counseled?
ANSWER: E
Rationale:
Over a multi-day ambulatory infusion, local anesthetic can accumulate, and both low body weight (smaller volume of distribution) and hepatic impairment (reduced metabolism) raise plasma concentrations for any given rate, narrowing the safety margin. The appropriate plan is a reduced infusion rate, ropivacaine for its wider cardiac safety margin, and explicit education of the patient and caregiver about early LAST symptoms, fall precautions from motor block, and whom to contact. Option A wrongly denies systemic risk and omits essential safety counseling. Option B selects the agent with the narrower safety margin at a high rate, misframing a hazard as a benefit. Option D needlessly discards effective regional analgesia and overstates the risk as universal toxicity rather than a manageable, rate-dependent concern.