Anatomy, Regional, and Pain Flashcards
What are the signs of local anesthetic toxicity
Initial symptoms are lightheadedness and dizziness then perioral numbness and tinnitus
Progressive CNS excitatory effects include visual/auditory disturbances, shivering, and ultimately tonic-clinic seizures
CNS depression can ensue, resulting in respiratory depression
Where do spinally administered opiates exert their action?
The substantia gelatinosa of the spinal cord
What are the classifications of local anesthetics?
Esters (only 1 i in name):
Procaine
Chlorprocaine
Tetracaine
Amides (2 i's in name): Lidocaine Mepivacaine Prilocaine Bupivacaine Etidocaine Ropivacaine
Describe local anesthetic metabolism
Esters undergo plasma clearance by cholinesterases and have short half-lives
- PABA is a metabolic breakdown product of esters and can be responsible for allergic reactions
Amides undergo hepatic clearance and have longer half-lives
What is the major disadvantage of the interscalene block for hand/forearm surgery as opposed to other approaches to the brachial plexus?
Ulnar nerve is often spared
Blockade of the ipsilateral phrenic nerve also commonly occurs, which can cause respiratory distress in patients with lung disease
What are the symptoms of cauda equina syndrome? What is thought to be the cause?
Low back pain, bilateral lower extremity weakness, saddle anesthesia, and loss of bowel/bladder function
Thought to be caused by maldistribution of local anesthetic (pooling in dependent areas of the spine)
What are the structures (in order) traversed by a midline needle prior to reaching the epidural space? What about during a paramedian approach?
Midline approach: Skin Subcutaneous tissue Supraspinous ligament Interspinous ligament Ligamentum flavum
Paramedian approach: Skin Subcutaneous tissue Paraspinous muscles Ligamentum flavum
Describe the order of differential nerve block
Small, unmyelinated sympathetic fibers
Unmyelinated C fibers (pain and temperature)
Small, myelinated fibers (proprioception, touch, pressure)
Large, myelinated fibers (motor)
Which nerves are blocked in an ankle block?
Deep Peroneal Nerve:
- located on the dorsum surface of the foot just lateral to the extensor hallucis longus tendon
- sensory between the 1st/2nd toes
- motor to extend the toes
Superficial Peroneal Nerve:
- located just above the lateral malleolus
- sensory to the dorsum of the foot
Posterior Tibial Nerve:
- located posterior to the medial malleolus
- sensory for the sole of the foot
- motor to flex the toes
Sural Nerve:
- located between the lateral malleolus and the Achilles’ tendon
- sensory to the lateral foot
Saphenous Nerve:
- located anterior to the medial malleolus
- sensory to the medial foot
What are the symptoms of complex regional pain syndrome (CRPS)? What are the two types? What is the treatment?
Syndrome of continuous burning pain exacerbated by normal movement, cutaneous stimulation or stress, usually weeks after a trauma. May have cool, red, and clammy skin. Chronic cases may lead to atrophy and osteoporosis.
CRPS I (reflex sympathetic dystrophy) - caused by non-nerve specific trauma
CRPS II (causalgia) - similar to type I but after a nerve-related injury
1st line treatment - physical therapy
2nd line - amitriptyline, gabapentin, opioids
3rd line - sympathetic blocks
4th line - spinal cord stimulators
What is anesthesia dolorosa?
A complication of neurolytic blocks for the treatment of trigeminal neuralgia
- numbness and pain in an area that lacks sensation
For local anesthetics:
What determines potency?
What determines speed of onset?
What determines duration of action?
Potency - lipid solubility
Onset - pKA
Duration - protein binding
What is the progression of epidural abscess symptoms? How do they differ from an epidural hematoma?
- Localized back pain
- Nerve root / radicular pain
- Motor and sensory deficit
- Paraplegia
Epidural hematoma pts complain of severe back pain rather than radicular pain
What nerves are blocked by a retrobulbar block? How does it compare to a peribulbar block?
Cranial nerves III, IV, and VI (eye movement)
Ciliary nerves (anesthesia to conjunctiva, cornea, and uvea)
Ophthalmic branch of trigeminal nerve
Main advantage over a peribulbar block is the reduced onset time, but it does not cover the eyelid which a peribulbar block will
What is the innervation of the larynx?
Motor:
All muscles of the larynx are innervated by the recurrent laryngeal nerve, except for the cricothyroid muscle, which is innervated by the external branch of the superior laryngeal nerve
Sensory:
- The internal branch of the laryngeal nerve provides sensory above the cords
- The recurrent laryngeal nerve provides sensory below the cords
What dermatome covers the thumb? The 2nd and 3rd fingers? The 4th and 5th fingers?
Thumb - C6
2nd and 3rd fingers - C7
4th and 5th fingers - C8
How do TENS units work? What are the indications for its use?
Transcutaneous electrical nerve stimulation (TENS) is thought to produce analgesia by releasing endogenous endorphins that have an inhibitory effect at the spinal cord
Indications for use:
- chronic intractable pain
- acute post-surgical or post-traumatic pain
- arthritis pain
List the sites in order (greatest to least) of LA uptake after regional anesthesia
Intravascular Endotracheal Intercostal Caudal epidural Lumbar epidural Brachial plexus Sciatic/femoral Subcutaneous
When doing a popliteal block for an ankle/foot surgery, which other nerve must be blocked? Why?
Saphenous nerve
The popliteal block will block the tibial and peroneal nerves (both originating from the sciatic nerve). However, the Saphenous nerve is a branch of the femoral nerve and is not covered in a popliteal block.
What are the risk factors for post-dural puncture headache?
Young age (20 - 40 years)
Female
Pregnancy
Large needle
What effect does adding sodium bicarbonate to local anesthetics solutions cause? Which local anesthetics will precipitate when bicarbonate is added?
It hastens the onset of action, since raising the pH causes more of the local anesthetic to be in the non-ionized, lipid-soluble state
It also decreases pain with skin infiltration
Cannot be added to Ropivacaine or Bupivacaine due to precipitation
Describe the anatomy of the axillary block
With the humerus at the bottom of the screen:
Median nerve is located superficially and lateral to the artery
Ulnar nerve is medial to the artery
Radial nerve is inferior to the artery
Musculocutaneous nerve is far lateral to the artery
What is meralgia paresthetica?
Compression of the lateral femoral cutaneous nerve by the inguinal ligament producing pain, numbness, and parathesias over the anterolateral thigh
Which nerve is commonly missed during an axillary block? How can it be anesthetized?
Musculocutaneous nerve (lateral forearm) - can be anesthetized by injecting local anesthetic into the belly of the coracobrachialis muscle
Describe IV regional anesthesia (Bier block)
Can provide complete motor and sensory anesthesia for up to approximately 90 minutes
Performed by:
1) placing a small IV in operative extremity
2) placing a double tourniquet on extremity
3) exsanguinating extremity
4) injecting 40-50 mL of 0.5% lidocaine
Mechanism of block is diffusion of LA from veins into capillaries surrounding peripheral nerves and then into the vasa nervora
- LA will also diffuse extravascularly into the nerves supplying the skin
- tourniquet causes distal ischemia which also contributes to anesthesia and analgesia
What is considered a positive test dose during placement of an epidural?
An increase in HR by 10 beats indicates intravascular injection
Tinnitus, odd taste, perioral numbness are all signs of intrathecal injection
What blocks can be done to block the coughing reflex? Where are they performed?
Superior laryngeal nerve:
Blocked at the cornu of the hyoid
Recurrent laryngeal nerve:
Blocked via transtracheal block
What is Naltrexone? How should it be handled peri-operatively?
Naltrexone is an oral opioid antagonist for treatment of alcohol or opioid dependency
- blocks downstream events that contribute to euphoria and reinforcing effects
Will block the effects of opioids so must be stopped pre-operatively
- Does not need to be tapered
What is Gabapentin used for? How does it work? What are it’s side effects?
Used to treat neuropathic pain
Works via calcium channel modulation
Side effects of chronic use:
- Weight gain
- Cognitive effects
- Peripheral edema
- Sedation
Which local anesthetic has been implicated in causing transient neurologic symptoms (TNS)? What factor has the largest impact on the risk?
Lidocaine has an incidence 5 to 10 times greater than other LAs
Patient position confers the greatest impact on risk
- lithotomy > supine
What are the effects of epidurals on the GI system?
It is thought that epidurals can shorten duration of post-op ileus and ultimately decrease morbidity, hospital stay, and overall cost
Sympathectomy induced by epidural removes the tonic sympathetic inhibition resulting in increased gut motility
Decreased post-op pain results in less systemic opioids and also reducing amount of circulating catecholamines, promoting better gut contraction
During spinal anesthesia, what factors are most important in determining the level of blockade?
Total dose of LA
Baricity
Patient position
What is the difference in pain transmitted by A-delta fibers and C fibers?
A-delta fibers are responsible for the “first” pain experienced after a stimulus
- generally easily localized and sharp
C fibers are responsible for the delayed “second” pain
- dull and achey
What are the ASRA guidelines for anticoagulation and neuraxial anesthesia?
Antiplatelet agents:
ASA/NSAIDs - no restriction
Clopidgrel - 7 days
Prophylactic anticoagulation:
LMWH - 12 hours
Therapeutic anticoagulation:
LMWH - 24 hours
Coumadin - 5 days (or reversed with INR
What are the potential side effects of NSAIDs?
- renal vasoconstriction leading to renal failure
- elevated blood pressure
- edema
What is the most common nerve injury associated with the lithotomy position?
Common peroneal nerve
- presents with foot drop
What are the borders of the femoral triangle?
The femoral triangle is bordered by the inguinal ligament superiorly, the adductor longus muscle medially, and the sartorius muscle laterally.
What are the conversions from intrathecal to epidural to IV to oral dosing for Morphine?
1mg of IT Morphine = 10mg Epidural = 100mg IV = 300mg oral
List and describe some common sympathetic blocks
Stellate ganglion block
- Located between C6-C7
- Done for pain in upper extremities and thorax
- Complications include Horner syndrome, recurrent laryngeal nerve injury
Celiac plexux block
- Located beside the aorta and inferior vena cava at the level of L1
- Done for pain relating to abdominal cancers
- Complications include retroperitoneal hematoma
Lumbar sympathetic chain block
- Located anterior to L1-L5, anteromedial to the psoas major muscle
- Done for neuropathic pain in the lower extremities or visceral pain involving intestinal/urinary symptoms
- Complications include genitofemoral nerve injury
Describe myofascial pain syndromes
Characterized by localized pain in an area of repititive use or trauma with resultant trigger points that cause non-dermatomal pain radiation upon palpation
Autonomic dysfunction and spontaneous EMG activity can be seen in the affected region
What are the potential complications from a retrobulbar block and how would they present?
Puncture of posterior globe - ocular pain and restlessness following block without an increase in intraocular pressure
Retrobulbar hemorrhage - closing of upper eyelid, proptosis, and increased intraocular pressure
Central retinal artery occlusion - painless loss of vision
Penetration of optic nerve - loss of vision or color vision
What area does the lateral cutaneous femoral nerve cover? How is it blocked?
LCFN provides sensory innervation to the anterolateral thigh
Can be blocked by injecting ~10cc of LA at a spot 2.5cm medial and 2.5cm inferior to the ASIS
What are the ASA practice guidelines for cancer pain?
Mild pain
- non-opioids
Mild to moderate pain
- non-opioids
- opioids
Moderate to severe pain
- non-opioids
- higher dose/frequency of opioids
At any point, adjuvants (antidepressants and neuromodulators) may be added
What are the 5 criteria for the use of neurolytic blocks?
- presence of severe pain
- failure of less invasive techniques to relieve pain
- presence of well localized pain
- relief of pain with diagnostic local anesthetic block
- absence of adverse side effects after diagnostic block
What is fibromyalgia? How is it diagnosed?
Fibromyalgia is a complex pain syndrome associated with widespread pain, sleep disturbances, fatigue, and depression
Diagnosed when:
- pain cannot be attributed to other pain syndromes
- pain has been present > 3 months
- widespread pain index and symptom severity score criteria are met (WPI > 7 + SS > 5 OR WPI 3-6 + SS > 9)
Which regional block carries the highest risk of pneumothorax?
Supraclavicular block
What nerves are blocked by a transversus abdominal plexus (TAP) block?
Intercostal
Subcostal
Ilioinguinal
Iliohypogastric
How do spinal cord stimulators work to treat chronic pain?
Spinal cord stimulators most significantly affect the dorsal horn of the spinal cord
They provide electrical stimulation to larger A-alpha and A-beta nerve fibers, closing the “gate” and impeding conduction of pain sensation
For what type of patients should transdermal fentanyl be considered? In what patients is it contraindicated?
Should be considered in chronic pain patients (including cancer pain) who are taking more than 45 mg of morphine equivalents
Contraindicated for patients with acute pain or any pain states that have pain free intervals
Describe discogenic back pain vs spinal stenosis
Discogenic back pain is usually worse when sitting or flexing and relieved by extension (standing upright or laying supine)
Spinal stenosis pain is worsened by extension (standing or walking), and is made better by flexion (sitting or walking uphill)
