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The International Association for the Study of Pain defines pain as an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage. Pain is subjective: the client's self-report is the most reliable indicator, and the nurse accepts and acts on it. The absence of grimacing or normal vital signs does not mean the absence of pain.
Physiology: tissue injury activates nociceptors → transduction → transmission along A-delta (sharp, fast) and C (dull, slow) fibers to the spinal cord and brain → perception → modulation by descending pathways and endogenous opioids. The gate control theory explains why rubbing, massage, TENS, and distraction can reduce pain: stimulation of large sensory fibers "closes the gate" to pain signals in the spinal cord.
| Type | Features | Example |
|---|---|---|
| Acute | Sudden, related to injury, expected to resolve with healing; often raises heart rate and BP | Postoperative pain, fracture |
| Chronic | Persists beyond normal healing — longer than about 3 months; vital signs usually normal; linked to depression, sleep loss, disability | Low back pain, arthritis, cancer pain |
| Nociceptive — somatic | Well localized, aching or sharp | Bone, skin, muscle |
| Nociceptive — visceral | Poorly localized, cramping, referred | Bowel, bladder, myocardial ischemia |
| Neuropathic | Burning, shooting, tingling, electric | Diabetic neuropathy, postherpetic neuralgia |
| Nociplastic | Altered pain processing without clear tissue damage | Fibromyalgia |
Duration is the main feature that separates acute from chronic pain.
Assess pain on admission, regularly, with each new report, before and after every intervention (commonly 15–30 minutes after IV and 30–60 minutes after oral analgesics), and at rest and with movement.
Characteristics (PQRST / OLDCARTS): onset, location, duration, character (burning, stabbing), aggravating and relieving factors, radiation, timing, severity, and effect on function, sleep, and mood. Ask about the client's goal (a tolerable level that allows activity) and cultural beliefs.
| Tool | Population |
|---|---|
| Numeric Rating Scale (NRS 0–10) | Alert adults and older children — the standard |
| Visual Analog Scale | 10-cm line from "no pain" to "worst pain" |
| Wong-Baker FACES | Children about 3 years and older; adults with language barriers |
| FLACC (Face, Legs, Activity, Cry, Consolability) | Infants and young children, nonverbal clients |
| Neonatal tools (NIPS, CRIES, N-PASS) | Newborns — facial expression, cry, breathing, limb movement, state of arousal, vital signs |
| PAINAD | Older adults with advanced dementia |
| CPOT, Behavioral Pain Scale | Critically ill, intubated, or sedated clients |
Behavioral signs (grimacing, guarding, restlessness, moaning) are used when self-report is not possible; family input helps. Physiologic changes (tachycardia, hypertension, diaphoresis) occur with acute pain but adapt quickly and are unreliable alone.
| Level | Description | Action |
|---|---|---|
| S | Sleeping, easy to arouse | Acceptable |
| 1 | Awake and alert | Acceptable |
| 2 | Slightly drowsy, easily aroused | Acceptable |
| 3 | Frequently drowsy, drifts off during conversation | Unacceptable — hold or reduce opioid, monitor closely, notify |
| 4 | Somnolent, minimal or no response | Stop opioid, naloxone, call for help |
Sedation precedes respiratory depression — check sedation, respiratory rate and depth, and SpO₂ (or capnography).
Principles: multimodal analgesia (combining drugs and methods that work differently) lowers opioid doses and side effects; prevent pain rather than chase it — give scheduled (around-the-clock) doses for continuous pain with breakthrough doses for flares; use the oral route when possible; avoid IM injections (painful, unreliable absorption).
WHO analgesic ladder (for cancer pain): step 1 non-opioid ± adjuvant (mild pain); step 2 weak opioid or low-dose strong opioid ± non-opioid ± adjuvant (moderate pain); step 3 strong opioid ± non-opioid ± adjuvant (severe pain). Non-opioids and adjuvants can be used at every step. Current WHO cancer pain guidance treats the ladder as a flexible guide — clients with severe pain start directly at the level that matches their pain.
| Drug class | Key safety points |
|---|---|
| Acetaminophen | Maximum 4 g/day in adults (lower, often 2–3 g/day, with liver disease, heavy alcohol use, or low weight); count acetaminophen in combination products; antidote acetylcysteine |
| NSAIDs (ibuprofen, naproxen, ketorolac, celecoxib) | GI bleeding and ulcers, kidney injury, fluid retention, cardiovascular events; avoid in kidney disease, active bleeding, and some heart conditions; avoid from 20 weeks of pregnancy (fetal kidney dysfunction and oligohydramnios; FDA 2020) and in the third trimester (premature closure of the ductus arteriosus) unless specifically prescribed; ketorolac limited to 5 days |
| Opioids (morphine, hydromorphone, oxycodone, fentanyl) | Respiratory depression, sedation, constipation (most common and persistent — start a stimulant laxative regimen), nausea, pruritus, urinary retention, orthostatic hypotension; hold and notify for excessive sedation or a respiratory rate below about 10–12/min or shallow breathing, per policy; fentanyl patches only for opioid-tolerant clients — heat increases absorption |
| Naloxone | Opioid antagonist for respiratory depression; for clients receiving opioids for pain, give it diluted and titrated to restore breathing rather than full reversal (full reversal causes severe pain and withdrawal) — e.g., 0.4 mg diluted to 10 mL, given 0.04 mg (1 mL) every 1–2 minutes until breathing improves; it is shorter-acting than most opioids — watch for recurrent sedation |
| Codeine, tramadol | Unpredictable metabolism; contraindicated in children under 12 and after tonsillectomy/adenoidectomy in those under 18; not recommended during breastfeeding (ultra-rapid metabolizer risk to the infant); tramadol lowers seizure threshold and can cause serotonin syndrome |
| Meperidine | Avoid — toxic metabolite causes seizures |
| Adjuvants — gabapentin, pregabalin, duloxetine, amitriptyline, corticosteroids, local anesthetics | Neuropathic and bone pain; gabapentinoids add sedation and respiratory depression with opioids; tricyclics are anticholinergic (avoid in older adults) |
| Patient-controlled analgesia (PCA) | Only the client presses the button — PCA by proxy (family or staff) can cause overdose; lockout interval prevents overdose; continuous monitoring (capnography preferred with supplemental oxygen) for high-risk clients |
Switching opioids or routes: use an equianalgesic table only as a guide — reduce the calculated dose of the new opioid by about 25–50% for incomplete cross-tolerance and reassess sedation closely. Oral doses are much larger than IV doses (oral morphine is roughly 3 times the IV dose). Hydromorphone is several times more potent than morphine — confusing the two is a known fatal error. Fentanyl patch conversions follow the product's own table.
Tolerance, dependence, and addiction differ: tolerance (needing a higher dose for the same effect) and physical dependence (withdrawal if stopped abruptly) are expected physiologic changes with regular opioid use; opioid use disorder (addiction) is a behavioral disease of compulsive use despite harm. Fear of addiction should not lead to undertreatment of pain.
| Problem | Clues and response |
|---|---|
| Opioid-induced respiratory depression | Increasing sedation (POSS 3–4), slow shallow breathing, snoring, falling SpO₂ or rising EtCO₂ — stimulate, stop opioid, oxygen, naloxone titrated, call for help |
| Undertreated pain | Sleep loss, immobility, delayed recovery, chronic pain development |
| Severe constipation or ileus | No stool for days, distension |
| NSAID GI bleeding | Black stools, epigastric pain, anemia |
| Acetaminophen toxicity | Nausea, right upper quadrant pain, raised liver enzymes |
| Serotonin syndrome (tramadol with antidepressants) | Agitation, fever, clonus |
| New, sudden, or different pain | May signal a complication (compartment syndrome, myocardial infarction, anastomotic leak) — assess, do not simply medicate |
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