Introduction to Pain Management

Jeff Gadsden

Epidemiology of Pain Presentation

Pain is the most common presenting complaint to the emergency department (ED).
- In France, pain-related issues account for 67% of the presenting complaints.
Pain is initially assessed 90% of the time but reassessments occur less frequently (48% on discharge).
- For those assessed on discharge, 27% still had pain (8% severe).
Delay for pain management is related to ED volumes, lack of triage nurses (especially in small departments), and initial pain intensity.
Pain intensity follow-up is important to assess to determine analgesic effectiveness.
Patient satisfaction is related to earlier effective pain management.
Quality indicators for pain management include
- Time to first dose of analgesic in all painful conditions.
- Percentage of patients with documented pain assessment.
The mean expectation for time to analgesic administration for ED patients is 23 minutes, compared with actual mean time to analgesic administration of 78 minutes.

Concepts in Pain Management

Multimodal pain management is better than any one agent alone.
- Adding acetaminophen to ibuprofen, for example, is better than either agent alone.
- As well, both can be given to complement narcotic therapy.
Dosing intervals should be according to the earliest allowable time to avoid loss of pain control and optimize pharmacokinetics (see Chapter 10).
Once nausea is controlled, oral options for analgesics should be explored to facilitate early conversion.
For people presenting with acute on chronic pain, management should take into consideration their current daily opiate consumption.
“Muscle relaxants,” such as Robaxacet (acetaminophen/methocarbamol) and Flexeril (cyclobenzaprine), have little evidence to support their use.
Neuropathic pain is a challenging issue.
May need to consider the use of nontraditional analgesics, for example, pregabalin, amitriptyline, or gabapentin.
Consider regional nerve blocks.
- Intercostal nerve blocks have been shown to be beneficial in rib fractures.
- See Chapter 12.
Prior studies have suggested that protocol-driven analgesia can be more effective than provider initiated analgesia.
Protocolized analgesic administration facilitates a greater percentage of patients being treated in a timely fashion and should be part of every ED with appropriate supporting infrastructure.

Anatomy and Physiology of Pain

Acute Pain

Acute pain is defined as “pain of recent onset and probable limited duration. It usually has an identifiable temporal and causal relationship to injury or disease.”
Also, it can be thought of as “physiological pain” or “useful pain.”
In contrast, chronic pain typically lasts beyond time of healing and frequently has no identifiable cause.
Acute and chronic pain in fact may represent a continuum rather than two separate entities.

Peripheral Receptors and Afferent Fibers

Axons of primary afferent nerves end in skin, subcutaneous tissue, periosteum, joints, muscles, and viscera.
There are no specialized pain receptors: free nerve endings (nociceptors) are sensitive to noxious physical stimuli.
- These respond to chemical, mechanical, or thermal energy that threatens the integrity of the tissue.
There are two main types of nociceptive afferents:
- Aδ-fiber mechanothermal nociceptors:
  - Thinly myelinated (therefore, faster than unmyelinated C-fibers)
  - Responds to heat, cold, and pressure
  - Provides “first pain” information critical for protective withdrawal reflex
- C-fiber polymodal nociceptors:
  - Unmyelinated (slow)
  - Respond to a broad range of physical (heat, cold, pressure) and chemical stimuli
  - Provides “second pain” that is classically burning in nature
- Tissue damage (e.g., trauma, infection, inflammation, or ischemia) disrupts cell structure and promotes the release of an “inflammatory soup” of chemical mediators that activate and/or sensitize nearby C-fibers (e.g., protons, bradykinin, histamine, prostaglandins, serotonin, and substance P).
- Most tissues have both types of nociceptors; exceptions include liver, brain, and lung tissue which have no afferent pain fibers.

Visceral Referred Pain

Occasionally, axons from visceral afferent nerve converge onto the same second-order neuron as somatic afferents.
The brain is unable to distinguish between the two inputs and projects the sensation to the somatic structure.
- Examples: myocardial ischemia felt as aching pain in left shoulder; gallbladder distention felt as pain in right shoulder.

Pain Transmission