Diagnostic nerve blocks
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Diagnostic nerve blocks. classic differential nerve blocks. differential neural blockade verifying a particular diagnosis delineating a treatment plan of management anatomic approach somatic and sympathetic nervous system fibers 의 actual anatomical separation 에 기초함

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Classic differential nerve blocks
classic differential nerve blocks

differential neural blockade

verifying a particular diagnosis

delineating a treatment plan of management

anatomic approach

somatic and sympathetic nervous system fibers의 actual anatomical separation에 기초함

injection of local anesthetic solution blocks one modality without affecting the others

pharmacologic approach

difference in the sensitivity of various type of nerve fibers to local anesthetics

different concentrations may selectively block different types of fibers

Classic differential nerve blocks2
classic differential nerve blocks

differential spinal block

Classic differential nerve blocks3
classic differential nerve blocks

psychogenic pain

prolonged or permanent relief -> truly psychogenic

temporary pain relief -> placebo reaction

sympathetic pain

clinical signs of complete sympathetic block and no detectable sensory changes

somatic pain

A-delta fibers and/or C fibers -> somatic

0.25% procaine에 sympathetic nervous system blockade의 sign이 보인 후 analgesia 또는 anesthesia와 동반하여 pain relief의 과정

이는 variability in Cm for B fibers 때문에 중요

(elevated Cm for B fibers -> 0.5% procaine에 의한 pain relief는 sensory block보다는 sympathetic block에 의한 것)

central pain

solution D relieve the pain -> somatic을 고려

(elevated Cm for A-delta and C fibers)

Classic differential nerve blocks4
classic differential nerve blocks

modified differential spinal block

only solution A and D are injected

less labor intensive, efficacious

solution A의 injection 후에 pain relief -> 위의 해석과 같다

solution D의 injection 후에 pain relief가 없으면 -> 위의 해석과 같음

complete pain relief after injection of solution D

-> somatic and/or sympathetic

regression of blockade가 중요

(motor block -> sensory block -> sympathetic block)

pain returns when the patient again appreciates pinprick as sharp (recovery from analgesia) -> somatic (A-delta fibers and/or C fibers)

pain relief persist for a prolonged period after recovery from analgesia

-> sympathetic (B fiibers)

Classic differential nerve blocks5
classic differential nerve blocks

differential epidural block

an effort to circumvent the possibility of producing post lumbar puncture cephalgia

better assessment of incident pain if a catheter is placed

solution A - placebo

solution B - 0.5% lidocaine (sympathetic block)

solution C - 1% lidocaine (sensory block)

solution D - 2% lidocaine (block all modalities)

<two shortcomings of the technique>

delay in the onset of blockade of each modality

local anesthetics fail to give discrete endpoints when administered in subarachnoid space -> more frequently when administered epidurally

differential spinal block과 마찬가지로 modified 될 수 있음

Classic differential nerve blocks6
classic differential nerve blocks

anatomic approach to differential block

utility of the technique -> painful conditions affecting any body region

three injections - placebo, sympathetic nerve block, somatic sensory and motor block

sympathetic block is carried out at a site where the sympathetic fibers are anatomically separate from sensory and motor fibers (blocked independently of one another)

Classic differential nerve blocks8
classic differential nerve blocks

<differential brachial plexus block>

upper extremity pain

two sequential injections are made into perivascular compartment

at the interscalene (for shoulder pain)

subclavian (for pain between the shoulder and the wrist)

axillary level (for pain in the lower forearm to the finger)

normal saline solution, 2% chloroprocaine

the same observation are made as for differential spinal block

Classic differential nerve blocks9
classic differential nerve blocks

limitations of differential blocks

<three potentially false premises>

1) pathology causing pain is located in an exact peripheral location and

impulses from this site travel via a unique and consistent neural route

2) injection of local anesthetic totally and selectively abolishes sensory

function of intended nerves

3) relief of pain following local anesthetic block is due solely to block of

the target neural pathway

Role of diagnostic blocks1
role of diagnostic blocks

anatomic location of pain source

direct injection of local anesthetics into tender superficial or deep tissues -> delineate the source of pain

ex) nerve entrapment syndromes including radiculopathies,

post-traumatic neuroma formation, myofascial trigger points,

and focal muscle spasm

confounding factors

-> possibility of placebo effects, systemic uptake of local anesthetics,

spread to adjacent nerves/structures

Role of diagnostic blocks2
role of diagnostic blocks

visceral versus somatic trunk pain

origin of pain in the chest, abdomen, or pelvis

somatic source confirmed by injections into costochonral tissue, truncal muscles, or intercostal nerves

pain is visceral structures

-> treatment may be directed towards exploration of abdominal or

pelvic organ, or towards denervation of visceral structures

(untreatable malignancy)

celiac plexus block, hypogastric plexus block, intercostal nerve block, local infiltration technique

-> diagnosis of painful states involving the viscera and the trunk

Role of diagnostic blocks3
role of diagnostic blocks

sympathetic versus somatic peripheral pain

sympathetic nerve activity가 chronic pain을 가진 환자에서 중요한 역할을 한다고 생각되면 sympathetic block이 diagnosis를 confirm하는데 도움을 줌

performed at anatomic sites separate from somatic nerve fibers

(cervicothoracic and lumbar sympathetic chain)

confirmation of pain relief and complete sympathetic block

-> presence of sympathetically maintained pain state

failure to obtained relief

-> sympathetically independent pain (SIP)

somatic nerve blocks may assist in the diagnosis of specific musculoskeletal or neuropathic pain syndrome

Role of diagnostic blocks4
role of diagnostic blocks

referred pain states

injection of the original pain site simultaneously relieves pain in the referral zone -> somatic-somatic pain states

segmental levels of nociceptive input

determining the spinal segments associated with somatic or visceral pain, coupled with knowledge of the segmental innervation of body tissues

-> indirectly aid in locating the bodily structures involved

Role of diagnostic blocks5
role of diagnostic blocks

central pain states

arises from the brain or spinal cord

occur after a central lesion or as result of abnormal central modulation of nociceptive and non-nociceptive input

ex) thalamic syndrome after cerebrovascular accident and traumatic

spinal cord injury

classic response - inadequate analgesia after multiple peripheral blocks

inadequate pain relief after epidural anesthesia, poor analgesia with systemic or intraspinal opioids

neuropathic pain associated with lesions of the peripheral nervous system -> altered central processing of nociception와 관련

often relieved with spinal or plexus anesthesia

partial response to opioid analgesics

central and peripheral neuropathic pain may be relieved by intravenous local anesthetic administration

Role of diagnostic blocks6
role of diagnostic blocks

<psychogenic pain>

failure to relieve pain with complete sensory and motor block of segmental levels -> presence of supraspinal mechanisms

temporary pain relief after placebo block -> common phenomenon (only for the diagnosis responder)

placebo injection후에 지속되는 dramatic analgesia 또는 excessive pain behavior 같은 unusual responses를 관찰하는 것이 initial history와 physical examination를 통해 형성된 clinical impression과 관련됨

Prerequisites for optimal diagnostic block
Prerequisites for optimal diagnostic block

complete evaluation of patient prior to undertaking any diagnostic nerve


신뢰도를 향상시키기 위해 조절해야 할 것

limit the use of pre-procedure sedatives and analgesics

limit the volume of local anesthetics to minimize

make liberal use of radiography

employ peripheral nerve stimulator

repeat positive blocks with local anesthetic of different duration

detailed observations and records

record patient's pain scores, vital signs, sensory and motor examination findings, signs of sympathetic nervous system function, and presence of pain behaviors

neurologic symptoms, degree of pain relief, pain scores, activity levels, analgesic intake following discharge 등을 환자가 기록하게 함

Prerequisites for optimal diagnostic block1
Prerequisites for optimal diagnostic block

pitfalls in evaluating results

pain relief due to an unintended action of a block

- false positive response

due to a placebo response, systemic effects, unreliable patient report

placebo response occurs in about 30% of patients and should always be considered after a positive diagnostic block

systemic effects of local anesthetics -> neuropathic pain states에 영향(particularly after use of large doses)

false-negative responses <- incomplete block, presence of alternative pain pathways, unappreciated referred pain syndrome, unreliable patient block effects, diagnostic testing performed at inappropriate times, deficiencies in technique

diagnostic block은 환자가 분명한 pain이 있을 때 시행해야 하며 pain relief의 정도는 maximum local anesthetic effect에 도달했을 때 조사되어야 함