Medical Pharmacology Question Bank
Chapter 15: Local Anesthetic Pharmacology — Module 5: Neuraxial Anesthesia
Extended Clinical Cases (24 questions)
1. [CASE 1 — QUESTION 1] A 29-year-old woman at 39 weeks' gestation, healthy apart from mild gestational hypertension, is brought to the operating room for an elective repeat cesarean delivery. After standard monitors are placed, a single-shot spinal is performed with hyperbaric bupivacaine, intrathecal fentanyl, and intrathecal morphine, and she is laid supine with a wedge briefly removed for line placement. Within three minutes her systolic blood pressure falls from 124 to 70 mmHg, she becomes nauseated, and the fetal heart rate tracing shows a prolonged deceleration to the high 80s. What is the most appropriate immediate action?
ANSWER: C
Rationale:
A term parturient laid supine is subject to aortocaval compression by the gravid uterus, and when this is added to the vasodilation of spinal sympathectomy the result is rapid maternal hypotension that preferentially reduces uteroplacental perfusion, producing the fetal deceleration. The correct immediate response is to restore left uterine displacement to relieve the mechanical compression and to give phenylephrine, the preferred vasopressor for maintaining uteroplacental flow.
2. [CASE 1 — QUESTION 2] Continuing with the same patient. You restore left uterine displacement and treat the hypotension. After repeated phenylephrine boluses the blood pressure improves, but the maternal heart rate now drifts down to 48 beats per minute while a mild degree of hypotension persists. How should you adjust vasopressor therapy for this combination of hypotension with bradycardia?
ANSWER: A
Rationale:
Phenylephrine is a pure alpha agonist, and the rise in blood pressure it produces commonly provokes a reflex decrease in heart rate; when bradycardia accompanies persistent hypotension, the rational change is to ephedrine, whose combined alpha and beta effects support both pressure and rate, with atropine reserved for vagally mediated, symptomatic bradycardia. Option C gives a beta-blocker to a bradycardic, hypotensive patient, worsening both. Option D is a vasodilator that would deepen the hypotension. Option E wrongly treats a heart rate of 48 with persistent hypotension as never requiring intervention.
3. [CASE 1 — QUESTION 3] Continuing with the same patient. Before delivery, she becomes increasingly anxious and dyspneic, reports tingling in both hands, and her speech becomes faint; the sensory level is now testing near T2 and she remains bradycardic and hypotensive. What is the priority response to this evolving picture?
ANSWER: D
Rationale:
An ascending sensory level near T2 with dyspnea, bilateral hand tingling, faint speech, bradycardia, and hypotension signals an evolving high spinal that is approaching the cervical levels and threatening the muscles of respiration; the cardiac accelerator fibers (T1 to T4) are already blocked. The priority is simultaneous airway and breathing support (oxygen, and intubation if respiratory failure ensues), rapid fluids, and continued ephedrine with atropine, while preparing for a possible total spinal. Option B uses a vasodilator that would worsen hypotension. Option C relies on abruptly repositioning an established block and dangerously leaves a deteriorating patient unattended. Option E gives a beta-blocking antihypertensive to a bradycardic, hypotensive patient.
4. [CASE 1 — QUESTION 4] Continuing with the same patient. The high block is managed successfully, the infant is delivered, and mother and baby are stable. Recall that her spinal included intrathecal morphine for postoperative analgesia. What postoperative plan does this specific choice require, and why?
ANSWER: B
Rationale:
Morphine is poorly lipid-soluble, so after intrathecal administration it remains in cerebrospinal fluid and is carried rostrally over hours toward the brainstem respiratory centers; this gives the prolonged analgesia that makes it valuable after cesarean delivery but also creates a characteristic risk of delayed respiratory depression up to roughly 18 to 24 hours after injection. The required plan is therefore extended respiratory monitoring over that window on a unit equipped to observe for it. Option A wrongly treats morphine as a short, segmental agent. Option C confines monitoring to the early period and misses the delayed window. Option D denies a real and well-described risk.
5. [CASE 2 — QUESTION 1] A 27-year-old nulliparous woman in active labor requests epidural analgesia. She is receiving an oxytocin infusion for augmentation. After the epidural catheter is threaded, you prepare to give a test dose of lidocaine with epinephrine 1:200,000, and you note that her heart rate rises and falls cyclically with her contractions. Why does this circumstance complicate test-dose interpretation, and how should you proceed?
ANSWER: B
Rationale:
The epinephrine marker depends on detecting a discrete rise in heart rate, but contraction-related tachycardia, intensified by an oxytocin infusion, can be mistaken for or can obscure that response. The correct approach is to inject during a quiescent interval between contractions and to document the immediate pre-injection baseline so a true epinephrine response can be distinguished from contraction-related changes. Option E is unsafe and false, as intravascular catheter placement remains a real risk in labor.
6. [CASE 2 — QUESTION 2] Continuing with the same patient. The test dose is negative and a dilute bupivacaine-fentanyl infusion provides excellent analgesia for several hours. As she reaches late second stage and the fetal head descends, she develops intense new perineal pressure and pain, although her abdominal contraction pain remains well controlled. The catheter aspirates negative. What is the most appropriate next step?
ANSWER: D
Rationale:
Late second-stage perineal pain with preserved abdominal analgesia is the classic picture of inadequately blocked sacral nerve roots, which are large and difficult 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: a more concentrated bolus and upright repositioning direct solution caudally toward the sacral roots. Option A discards a functioning catheter for an inferior systemic approach. Option B 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.
7. [CASE 2 — QUESTION 3] Continuing with the same patient. Before sacral dosing takes full effect, the fetal heart rate tracing becomes category III and the obstetric team calls for emergent cesarean delivery within minutes. You elect to extend the existing, well-functioning 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: A
Rationale:
When an existing epidural must be extended to surgical anesthesia under severe time pressure, 3% chloroprocaine provides the fastest, most reliable onset, on the order of 6 to 10 minutes; despite its unfavorable pKa, its very high concentration delivers a large mass of drug that crosses the nerve membranes by mass action to produce a dense block quickly.
8. [CASE 2 — QUESTION 4] Continuing with the same patient. After the chloroprocaine top-up, testing reveals a patchy, asymmetric block with a clear unblocked segment over the planned incision, and the obstetric urgency does not allow prolonged further titration. The patient reports sharp sensation when the skin is tested. What is the most appropriate decision?
ANSWER: C
Rationale:
A patchy, asymmetric block with a clearly unblocked incisional segment, in a setting where time does not permit prolonged titration, is a failed block; the safe decision is to convert to general anesthesia, while anticipating and preparing for the elevated airway-management and aspiration risks of the pregnant patient.
9. [CASE 3 — QUESTION 1] A 68-year-old man is scheduled for open lower-extremity vascular surgery, and the team plans a thoracic epidural for postoperative analgesia. He is receiving prophylactic low-molecular-weight heparin (LMWH), with his most recent dose given a few hours ago. The surgeon asks you to place the epidural now. What is the correct approach to the timing of epidural needle placement?
ANSWER: E
Rationale:
Neuraxial anticoagulation guidelines specify a minimum interval between the last LMWH dose and neuraxial needle placement, because puncture within the drug's active window raises the risk of epidural hematoma. With a dose given only a few hours ago, the correct approach is to delay placement until the recommended interval has elapsed. Option B is dangerous because giving more LMWH immediately before puncture maximizes hematoma risk. Option D wrongly treats timing as irrelevant and substitutes monitoring for the required interval.
10. [CASE 3 — QUESTION 2] Continuing with the same patient. The epidural is placed uneventfully after the appropriate interval and provides good analgesia. On postoperative day two, you learn he has chronic kidney disease (CKD) with substantially reduced creatinine clearance, and prophylactic LMWH has been continued. The team wishes to remove the catheter. How does his renal function affect the timing of catheter removal?
ANSWER: B
Rationale:
Two principles combine here. First, anticoagulation timing intervals apply to catheter removal just as to placement, because withdrawing the catheter disrupts epidural vessels and carries comparable hematoma risk. Second, reduced renal clearance in CKD prolongs the effect of renally cleared LMWH, so its residual anticoagulant activity persists longer; the safe interval before removal must therefore be extended beyond the standard. Option A is dangerous because removal does carry hematoma risk. Option C wrongly exempts removal from interval and renal considerations. Option E denies the established influence of renal function on anticoagulant duration.
11. [CASE 3 — QUESTION 3] Continuing with the same patient. The catheter is removed after the extended interval. About six hours later, the nurse reports that he has new, worsening bilateral lower-extremity weakness and new back pain; he is afebrile. Over the next hour the weakness clearly progresses. What is the correct interpretation and immediate action?
ANSWER: A
Rationale:
A rapidly progressive bilateral motor deficit with new back pain, developing within hours after catheter removal in an anticoagulated patient, is the classic presentation of an epidural hematoma compressing the cord, a neurosurgical emergency. Because neurologic outcome depends on prompt decompression, the correct action is urgent spine MRI and emergent neurosurgical decompression without delay. Option B is dangerous because residual local anesthetic does not cause a progressive deficit hours after the infusion and catheter are gone. Option C misassigns an afebrile, hyperacute, anticoagulation-related event to abscess and substitutes antibiotics for the needed surgery. Option E falsely reassures and omits the emergent evaluation the situation demands.
12. [CASE 3 — QUESTION 4] Continuing with the same patient. A trainee asks how this presentation would have differed had the cause been an epidural abscess rather than a hematoma. Which statement best distinguishes the two?
ANSWER: D
Rationale:
The two catastrophic neuraxial complications differ in tempo and systemic features. Epidural hematoma usually develops rapidly, over hours, is frequently associated with impaired hemostasis or anticoagulation, and lacks signs of systemic infection. Epidural abscess usually evolves more slowly, over days, with fever, insertion-site pain, and leukocytosis, and is most often caused by Staphylococcus aureus. Both demand urgent imaging and decompression, but the clinical context helps anticipate which is present. Option A wrongly denies any distinguishing features. Option E falsely claims neither causes a deficit, when both can be devastating.
13. [CASE 4 — QUESTION 1] A healthy 34-year-old woman presents for an elective outpatient knee arthroscopy expected to last about 40 minutes, with planned same-day discharge. She prefers a spinal anesthetic and wishes to recover quickly. Which spinal agent best matches this clinical goal?
ANSWER: C
Rationale:
The choice turns on matching duration and recovery profile to a short ambulatory case with same-day discharge. Preservative-free chloroprocaine offers rapid onset, a short predictable duration, prompt recovery, and a very low rate of transient neurologic symptoms, making it the best fit.
14. [CASE 4 — QUESTION 2] Continuing with the same patient. As you prepare the spinal, a trainee asks which needle characteristics minimize the risk of post-dural puncture headache (PDPH) should the dura be breached, and how needle design relates to that risk. Which answer is correct?
ANSWER: E
Rationale:
Two needle features independently reduce PDPH risk: a smaller gauge produces a smaller dural hole that leaks less cerebrospinal fluid, and a pencil-point tip (Whitacre or Sprotte) spreads rather than cuts dural fibers, producing substantially less PDPH than a cutting Quincke needle at the same gauge. The most protective choice combines a small gauge with a pencil-point tip. Option A is wrong on both counts, since a larger gauge and a cutting tip both increase risk.
15. [CASE 4 — QUESTION 3] Continuing with the same patient. The arthroscopy proceeds well, but on the first postoperative day she calls reporting a headache that is barely noticeable when she lies flat and becomes severe within minutes of sitting or standing, accompanied by neck stiffness and mild ringing in the ears. Which feature most strongly identifies this as a post-dural puncture headache?
ANSWER: B
Rationale:
The defining feature of PDPH is its postural character: the headache is mild or absent supine and becomes severe upright, because loss of cerebrospinal fluid through the dural puncture lowers pressure and allows downward traction on pain-sensitive structures when the patient is vertical. The associated neck stiffness and tinnitus fit the low-pressure picture.
16. [CASE 4 — QUESTION 4] Continuing with the same patient. Over the next two days the headache becomes disabling, preventing her from caring for herself, and bed rest, oral hydration, and caffeine provide only transient relief. What is the most appropriate definitive treatment?
ANSWER: D
Rationale:
A disabling PDPH that has failed conservative management is treated definitively with 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.
17. [CASE 5 — QUESTION 1] An 80-year-old man with severe symptomatic aortic stenosis requires open reduction and internal fixation of a hip fracture. The cardiology consultant stresses that his fixed-output, preload-dependent physiology tolerates only gradual hemodynamic change. You plan a neuraxial technique. Which approach best protects his hemodynamics?
ANSWER: A
Rationale:
In severe aortic stenosis the heart cannot compensate for an abrupt fall in preload and afterload, so the hazard of neuraxial anesthesia is the speed and depth of the sympathectomy rather than 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 of a full single-shot spinal, matching the requirement for gradual hemodynamic change. Option B imposes exactly the abrupt sympathectomy this physiology tolerates worst. Option C deliberately drives a rapid high block, the most dangerous choice. Option D produces a rapid dense block, again the opposite of the gradual approach required.
18. [CASE 5 — QUESTION 2] Continuing with the same patient. Having chosen the combined spinal-epidural approach, you want the initial spinal component to stay low and controlled so that the sympathectomy remains limited. How can baricity and patient positioning be used to keep the initial block confined?
ANSWER: C
Rationale:
Block height can be limited by combining a small intrathecal dose with a hyperbaric solution and deliberate positioning: because a hyperbaric solution sinks to the dependent region, positioning the patient so that the lower segments are dependent keeps the dense drug low and limits cephalad spread, which in turn limits the height of the sympathectomy that this fragile physiology tolerates poorly. Option A misuses a hypobaric solution, which rises rather than stays low, and head-down position would drive it cephalad. Option B abandons control by using a full isobaric dose supine. Option E denies the established influence of baricity and position on block height.
19. [CASE 5 — QUESTION 3] Continuing with the same patient. Immediately after the intrathecal injection, you wish to confirm that the epidural catheter is not intrathecal before relying on it for supplementation. Why is an immediate test dose unreliable in this situation, and what should you do?
ANSWER: D
Rationale:
A test dose detects intrathecal catheter placement chiefly by producing a rapid motor block; but immediately after the combined spinal-epidural, the spinal component has already produced dense lower-extremity motor block, which masks any additional motor response and makes the test uninterpretable. The correct approach is to defer catheter testing until the spinal block has partially resolved.
20. [CASE 5 — QUESTION 4] Continuing with the same patient. Midway through the procedure his systolic pressure drifts down despite the gradual block, while he remains in sinus rhythm at a rate of 70 beats per minute. Given his severe aortic stenosis, what is the most appropriate hemodynamic priority and treatment?
ANSWER: B
Rationale:
In severe aortic stenosis the hypertrophied, pressure-overloaded ventricle is critically dependent on coronary perfusion pressure and on a controlled heart rate in sinus rhythm; hypotension is dangerous because it reduces coronary perfusion to the thickened myocardium and can precipitate ischemia and a downward spiral. The priority is to restore afterload and perfusion pressure promptly with an alpha agonist such as phenylephrine, maintain preload with judicious fluids, preserve sinus rhythm, and avoid tachycardia and vasodilators.
21. [CASE 6 — QUESTION 1] A 60-year-old man recovers from an open upper-abdominal operation with a thoracic epidural catheter placed at the dermatomal level of his incision. You are setting the postoperative infusion with the goal of analgesia covering the incisional dermatomes while preserving lower-extremity strength so he can mobilize early. Integrating how concentration governs block density with how volume governs segmental spread, which infusion strategy best meets both goals?
ANSWER: A
Rationale:
Meeting both goals requires using concentration and volume for their separate roles. A low concentration produces predominantly sensory analgesia while sparing motor fibers, preserving the leg strength needed for early mobilization, and an adequate volume and rate spread that dilute solution across the several incisional dermatomes; adding a low-dose opioid exploits epidural local-anesthetic-opioid synergy to deepen analgesia without increasing motor block. Option B confines the block to too few segments and, at high concentration, causes unwanted motor block. Option C maximizes density and spread but produces dense motor block, defeating the mobilization goal. Option D discards the local anesthetic contribution and the synergy that allows effective analgesia at low drug exposure.
22. [CASE 6 — QUESTION 2] Continuing with the same patient. On the first postoperative day the nurse reports new lower-extremity motor weakness. He is afebrile with no back pain. What is the correct first step, and how does the response to it guide the next decision?
ANSWER: E
Rationale:
The correct first maneuver for new motor weakness during an epidural infusion is to reduce or stop the infusion and reassess after a short interval. Weakness that resolves indicates pharmacologic over-blockade, managed by adjusting concentration or rate; weakness that persists or progresses despite stopping the infusion is a red flag for epidural hematoma and mandates urgent spine MRI and neurosurgical evaluation. This stepwise logic separates benign from dangerous causes.
23. [CASE 6 — QUESTION 3] Continuing with the same patient. He recovers well, and weeks later he returns for an elective shoulder operation and is to be discharged home with a continuous peripheral nerve block (CPNB) infusion for several days. He has since been found to have compensated cirrhosis and weighs only 54 kg. How should the ambulatory infusion be set with respect to agent and rate, given these factors?
ANSWER: C
Rationale:
Over a multi-day ambulatory infusion, local anesthetic can accumulate, and both hepatic impairment (reduced metabolism) and low body weight (smaller volume of distribution) raise plasma concentrations for any given rate, narrowing the safety margin. The appropriate response is to reduce the infusion rate and favor ropivacaine for its wider cardiac safety margin with equivalent analgesic efficacy. Option A wrongly denies accumulation and the relevance of patient factors. Option B selects the agent with the narrower safety margin at a high rate and misframes that as an advantage. Option E needlessly discards effective regional analgesia and overstates the risk as universal toxicity rather than a manageable, rate-dependent concern.
24. [CASE 6 — QUESTION 4] Continuing with the same patient. Before discharge with the portable infusion pump, you provide safety counseling to him and his spouse. Which counseling content is most important for safe outpatient use of a continuous peripheral nerve block?
ANSWER: B
Rationale:
Safe ambulatory CPNB depends on the patient and a caregiver understanding the small but real risk of local anesthetic systemic toxicity from absorbed drug and being able to recognize its early symptoms (perioral numbness, tinnitus, metallic taste), observing fall precautions and protecting the insensate limb, and knowing exactly whom to call and when to seek emergency care.