CONCEPTUALIZING PAIN

Kyle P. Edmonds, MDAssistant Clinical Professor

Doris A. Howell, MD, Palliative Care ServiceUC San Diego Health Sciences

Adapted from the Palliative Care International Curriculum Series Editor, Frank R. Ferris, MD

OBJECTIVES

• Pain may be nociceptive, neuropathic or both and the history tells you which.

• A standardized approach to the assessment of pain helps prevent miscommunication.

• For constant pain, schedule dose using data.

• For breakthrough pain, use PRN dose.

PAIN

“Pain is whatever the person says it is…”

- Margo McCaffery

MECHANISM OF PAIN- DESCARTES

BASIC STEPS: PAIN PROCESSING

• Transduction

• Transmission

• Perception

• Modulation

NOCICEPTOR

• Nerve cell

• Activation• Thermal • Chemical• Mechanical

• Transmits signal

PAIN TRANSDUCTION

• Response to noxious stimuli

• Carried by A-delta and C-fibers

TRANSMISSION: 3 STAGES

• Stimulus to cord

• Cord to brain stem

• Brain stem to higher cortex

• Sensation

• Somatosensory cortex

• Emotional response

• Frontal cortex

• Limbic system

TRANSMISSION

PERCEPTION

• Experience• Conscious

• Multidimensional

• Interaction of transmission / transduction

“TOTAL PAIN”

MODULATION

• Changing

• Inhibiting

• Spinal cord level

PAIN PROCESSING

• Transduction

• Transmission

• Modulation

• Perception

CLASSIFICATION OF PAIN

• Physiologic• Nociceptive

• Neuropathic

• Mixed

• Temporal• Acute

• Chronic

NOCICEPTIVE PAIN

• Somatic• Skin

• Soft tissue

• Bone

• Visceral

NEUROPATHIC PAIN

• Damaged or dysfunctional nerves

• Central

• Peripheral

MIXED PAIN

• Experiencing • nociceptive and

• neuropathic

CLASSIFICATION OF PAIN

• Physiologic• Nociceptive

• Neuropathic

• Mixed

• Temporal• Acute

• Chronic

TEMPORAL CLASSIFICATION: ACUTE

• Sudden or recent onset

• Identifiable cause

• Short duration

• Sympathetic response

TEMPORAL CLASSIFICATION: CHRONIC

• Persistent

• No obvious cause

• Functional impairment

• No sympathetic response

INTERVAL SUMMARY

Understanding the pathophysiologyleads to improved assessment and

targeted management that will improve outcomes

PAIN ASSESSMENT

1. Location2. Description (type)3. Change over time4. Severity (0 – 10)5. Effect of

treatments• Benefit (+)• Unwanted effects (-)

• Constant

• Breakthrough

• Intermittentacute

3. CHANGE OVER TIME

PAIN ASSESSMENT TOOLS

• Self Report

• NRS (adult)

• Behavioral Pain Scales

• Checklist of Non-Verbal Pain Indicators (CNPI) – non-critical care units

• Critical-Care Pain Observation Tool (CPOT) – ICUs

• Assumption that Pain is/will be Present (APP)

INTERVAL SUMMARY

Assessment of pain requires a thoughtful history and physical. This step helps you to tailor & target your treatment options.

FEEDBACK? QUESTIONS?

• New Opioid Naïve Pain Orders Set

• What’s working?

• Not working?

• More pages? Less?

• Easier? Harder?

• Next steps?

Pla

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0 Time

AbsorptionExcretion

First Order KineticsWhen biological effect

follows plasma concentration

MILD PAIN / MULTIMODAL PAIN

• Mild Pain: pain score 1-4• UCSD guidelines are to avoid use of opioids for

mild pain

• Multi-modal analgesic guidelines

• Scheduled vs PRN non-opioid agents

Pla

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0 Time

Principle: Scheduled Dosing Steady State

Pain control

Unwanted effects

MODERATE / SEVERE PAIN ORDERS

• Moderate (VAS=5-7) & Severe (VAS=7-10)

• Behavioral Scale/APP set to moderate dose

• Nurse reassessment around analgesic peak

• PO peak 1 hour

• IV peak 30 minutes

• Rescue dose available at reassessment

• Breakthrough

• Intermittentacute

PAIN CHANGE OVER TIME

Pla

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IV

PO / PR60min

Time to MaximumConcentration ( t Cmax )

10min

RESCUE OPTIONS

• Rescue is EITHER PO or IV

• No more than 3 (oral or IV) in 24 hrs.

• Used with EITHER moderate or severe pain after reassessment at the peak of the PRN drug administered.

PRINCIPLE:ACUTE PAIN PRN MED

• Treat rapidly & safely

• Short-acting dosed at point of maximum effect (Cmax)

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Cmax

Acute Pain Principle

PO / PR≈ 1 hr

Cmax

• Constant

• Breakthrough

PAIN CHANGE OVER TIME

PRINCIPLE:CONTINUOUS PAIN SCHEDULED

MED

• To achieve steady-state

• Schedule non-opioid

• Opioid use guided by data

• PRN usage or

• Short-acting meds scheduled on the T½

CONTINUOUS PAIN PRINCIPLE

Pla

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0

Dosing every half-life ( t ½ )Oral morphine = 4 hours

164 8 12Time ( hours )20 24

50%75%

87.5%93.75%

97%100%

Pla

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once

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Steady state after 5 half-lives≈ 20 hours

Pain control

Unwanted effects

Pla

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Co

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0

Time to Drip ( or Long-acting ) Steady State

164 8 12Time ( hours )20 24

50%75%

87.5%93.75%

97%100%

Pain Control

Change GTT12+ more hours!

Pla

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…20 Time

Steady State ~ 20 hours

Concentration needed to

control pain

Concentration where side-effects

start to occur

Pla

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once

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0 Time

STAGES OF RESPIRATORY DEPRESSION

Sedation

Bradypnea

Death

Awake & in Pain

PASERO OPIOID SEDATION SCALE (POSS)

• S = Asleep, easy to arouse

• 1 = Awake & Alert

• 2 = Slightly drowsy, easily aroused

• 3 = Frequently drowsy, arousable, drifts off to sleep during conversation

• 4 = Somnolent, minimal or no response to stimulation

SUMMARY

• Pain may be nociceptive, neuropathic or both and the history tells you which.

• A standardized approach to the assessment of pain helps prevent miscommunication.

• For constant pain, schedule dose using data.

• For breakthrough pain, use PRN dose.

PALLIATIVE CARE IS…

• A team that can help your patients and families manage the pain, symptoms, and stress of serious illness.

• Available at any age and at any stage in a serious illness and can be provided along with curative treatment.

• Expert communication for challenging situations.

• Partnering with you for better outcomes by helping your patients tolerate curative treatment.