Challenges in Pain Assessment

Jeffrey A. Katz, MDAssociate Professor of Anesthesiology

Section of Pain MedicineFeinberg School of Medicine

Northwestern UniversityChicago, Illinois

AssessmentAssessmentPain as a 5th Vital Sign

• Better than VAS: • Verbal Numeric Rating Scale

– 0 = No Pain– 10 = Worst Pain Imaginable– What is your current (or average) pain?

• Also: None-Mild-Moderate-Severe• All have equal validity

VAS = visual analog scale.

Olsen S, et al. Anesthesiol Rev. 1992;19:11-15.

Re-AssessmentRe-Assessment• Obtain Verbal Numeric Rating Scale

– Remember, 0 is NOT always a goal!!!

• Also get Verbal RELIEF Score– 0 = No Relief– 10 = Complete Relief– What is your current (or average) relief?

Consequences of Consequences of Undertreatment of Pain Undertreatment of Pain

Treatment for Chronic Pain Has Not Improved

Louis Harris & Associates Inc. The 1999 National Pain Survey. 1999.Peter D. Hart Research Associates. America Speaks: Pain in America. 2003.Brookoff D. Hosp Pract. 2000;35:45-52, 59.

• Increasing prevalence and incidence of chronic pain

• 1999– 24% of American adults reported chronic pain

• 2002– 57% of adults reported chronic or recurrent pain

• As US population ages more patients will need pain treatment

Pain and Productivity

$0

$10

$20

$30

$40

$50

$60

$70

Cost of Lost ProductiveTime

Job productivity

• 13% reported a loss in productive time due to pain

• $61 billion/year in cost for lost productivity

77% due to reduced work performance

An

nua

l Co

st (

Bill

ion

s)

Stewart WF, et al. JAMA. 2003;290:2443-2454.

23% due to workplace absenteeism

Survey of lost productive time in working adults during a 2-week period (N = 28,902)

Pain and Quality of Life

• Interferes with daily life• Significant emotional impact• Impairs physical, social, and

psychological status• Impairs QoL of family members

and caregivers

QoL = Quality of Life.

Berry PH, et al. Pain: Current Understanding of Assessment, Management, and Treatments. Reston, Va: National Pharmaceutical Council and Joint Commission on Accreditation of Healthcare Organizations; December 2001. Roper Starch Worldwide Inc. Chronic Pain in America: Roadblocks to Relief. 1999.Bair MJ, et al. Arch Intern Med. 2003;163:2433-2445.Ferrell BR, et al. Oncol Nurs Forum. 1995;22:1211-1218.

Pain Management Improves Quality of Life

• Effective multidisciplinary management improves QoL– 84% report feeling happy and upbeat– 89% report feeling positive about life

• Inadequate pain control is unacceptable

Katz N. J Pain Symptom Manage. 2002;24(suppl 1):S38-S47.Roper Starch Worldwide Inc. Chronic Pain in America: Roadblocks to Relief. 1999.

Choosing Choosing PharmacotherapyPharmacotherapy

Nociceptive– Tissue damage– Transmitted

along pain pathways

– eg, Burn

Pain ClassificationNeurophysiologic Origin

Visceral– Visceral

stimulus– Diffuse, dull– Referred pain– eg, Colic

Neuropathic– CNS/PNS injury– Abnormal

sensory function– Spreads– No ongoing

damage– eg, PHN

CNS/PNS = central nervous syste/peripheral nervous system; PHN = postherpetic neuralgia.

Classification of Pain Practical

•Acute•Chronic•Cancer•AIDS

Acute PainAcute Pain• Serves a biologic function

• Resolves with treatment of cause

• Recent onset, short duration

• Goal: Treat symptoms until cause resolves

Chronic PainChronic Pain• Serves no biologic functionServes no biologic function• Persists despite treatment of known or Persists despite treatment of known or

presumed causepresumed cause• Goal: Maximize function independent Goal: Maximize function independent

of health care system constraintsof health care system constraints• As in treating diabetes or asthmaAs in treating diabetes or asthma

– Treat to manage, not cure

Analgesia and the Pain Pathway

NSAIDs = nonsteroidal anti-inflammatory drugs. Adapted from Gottschalk A, et al. Am Fam Physician. 2001;63:1979-1984.

Descending modulation

Dorsal horn

Ascendinginput

Spinothalamic tract

Dorsal root ganglion

Peripheral nerve

Peripheral nociceptors

Pain

Trauma

Local anestheticsOpioids Antiepileptic drugsAnti-inflammatory agents (cox-2 inhibitors, nonspecific NSAIDs)

Centrally acting analgesicsOpioids 2-Agonists TricyclicsAntiepileptic drugsAnti-inflammatory agents

Local anestheticsAnti-inflammatory agents

Local anesthetics Anti-inflammatory agents(cox-2 inhibitors, nonspecific NSAIDs)OpioidsAntiepileptic drugs

Available Pain Medications

Agent Mechanism of Action Typical Uses

Acetaminophen Weak inhibitor of COX-1 and COX-2; may inhibit “unidentified” COX enzyme (ie, COX-3)

Mild to moderate pain states

Nonspecific inhibitors

Inhibition of COX-1 and COX-2 isoenzymes

Mild to moderate pain states

COX-2 specific NSAIDs

Selective inhibition of COX-2 isoenzyme (GI mucosa sparing)

Mild to moderate pain states

Opioids Opioid receptor agonist action, inhibiting pain impulses

Moderate to severe pain states

Tramadol Opioid agonist plus norepinephrine/serotonin reuptake inhibitor

Moderate to moderately severe pain

Available Pain Medications, cont.

Agent Mechanism of Action Typical Uses

Antiepileptics Modulate sodium and calcium channels

Neuropathic pain

Tricyclic antidepressants

Block reuptake of norepinephrine and other amines

Neuropathic pain

Topical treatments

Analgesic/anesthetic action on sensory nerve fibers in skin

Neuropathic pain

Muscle relaxants Inhibition of polysynaptic events in the CNS

Musculoskeletal pain

NMDA receptor antagonists

Inhibition of NMDA-receptor induced neuronal excitation

Neuropathic pain

PKAPKA

PKCPKC

EP EP receptorreceptor

Tissue injuryTissue injury

PGEPGE22

COX-2 expressedCOX-2 expressed

TTx resistantTTx resistantsodium sodium channelchannel

P

COX-2 and Peripheral Mechanisms of Pain

PGE2 = prostaglandin E2; PKA = protein kinase A; PKCε = protein kinase C, TTx = tetrodotoxin.

Samad TA, et al. Nature. 2001;410:471-475.Woolf CJ, et al. Science. 2000;288:1765-1769.Byers MR, Bonica JJ. In: Bonica’s Management of Pain. 2001:27-72.

NociceptorNociceptorResting Resting

membranemembranepotentialpotential

Neuron Neuron firing thresholdfiring threshold

Prostaglandins and Pain

• PGs nociception in nerves and CNS

• PGs sensitize pain nerve endingsMore responsive to touch and pain

• PGs also mediate pain in CNS SP and glutamate release Sensitivity of 2nd order neurons Release inhibitory transmitters

PG = prostaglandis; SP = substance P.

NSAIDs and COX-2s NSAIDs and COX-2s

Are Not AnalgesicsAre Not Analgesics

They Are Anti-Hyperalgesics

NSAIDs and COX-2s Do not NSAIDs and COX-2s Do not Replace OpioidsReplace Opioids

They Greatly Enhance Opioid Analgesia

Central SensitizationCentral Sensitization• Sensitization: Amplification of

signals to CNS after intense pain• Usually the result of touch fibers

cross-circuiting to pain pathways– Touch Pain– Movement Pain– Slight pain Severe Pain

B Fibers: Myelinated Autonomics

C Fibers: Pain and Temperature

A Fibers: Myelinated Large

A-alpha: Motor

A-beta: Touch

A-gamma: Position

A-delta: Pain and

Temperature

Classification of Peripheral Nerve Fibers

Dorsal RootDorsal Root

Dorsal Dorsal RootRoot

GanglionGanglion

To BrainTo Brain

Central Sensitization Causing Allodynia

TO BRAIN

Dorsal HornPain Neuron + +

+

C

ININ

A-delta

+Mediated in part by NMDA receptor on the dorsal horn pain neuron

A-beta

_ _

0

ININ

IN = interneuron; NMDA = N-methyl-D-aspartate.

Woolf CJ, et al. Science. 2000;288:1765-1769.

Guyton’s textbook

A-beta touch fiber

To brain

Guyton’s Textbook of Physiology

Tricyclic AntidepressantsAmitriptylineImipramineNortriptylineDesipramineClomipramineDoxepinTrimipramineAmoxapineProtriptyline

Amitriptyline

• HCl

CH(CH2)2N(CH3)2

‘‘Inappropriate in Elderly’Inappropriate in Elderly’

Baldessarini. In: Goodman & Gilman’s The Pharmacological Basis of Therapeutics. 10th ed.

McGraw-Hill Professional; 2001.

Tricyclic Antidepressants: Pros and Cons

IOP = intraocular pressure; HR = heart rate.

Beers MH, et al. Arch Intern Med. 1997;157:1531-1536.Ray WA, et al. Clin Pharmacol Ther. 2004;75:234-241.

• Anti-Ach effects– Sedation– Constipation, urinary retention IOP, HR, etc

• At doses > 100 mg/day: risk sudden cardiac death– Conduction changes

Track record and inexpensive, but . . .

From body Dorsal horn

spinal cord

To brain

NENE

5-HT5-HT

Tricyclic Antidepressants and Serotonin-Norepinephrine Reuptake Inhibitors: Mechanisms

of Action

NE = Norepinephrine; 5-HT = Serotonin.

Baldessarini. In: Goodman & Gilman’s The Pharmacological Basis of Therapeutics. 10th ed. McGraw-Hill Professional; 2001.

From body Dorsal Horn

Spinal Cord

To Brain

NENE

5-HT5-HT– SSRIs only Act on SSRIs only Act on

serotonin pathwayserotonin pathway

– Ineffective in pain reliefIneffective in pain relief

Selective Serotonin Reuptake inhibitors

CaCa++++

GabapentinGabapentin

Gabapentin: Mechanism of Action

Benefits of Multimodal Analgesia

Kehlet H, et al. Anesth Analg. 1993;77:1048-1056.

• Reduced doses of individual analgesic

• Improved pain reliefdue to synergistic/additive effects

• May reduce severityof side effects ofeach drug

OpioidsOpioids

PotentiationPotentiation

NSAIDs, COX-2s,NSAIDs, COX-2s,acetaminophen,acetaminophen,

nerve blocksnerve blocks