Definition and Physiology of Pain
- The International Association for the Study of Pain (IASP) defines pain as an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage.
- Pain is a highly personal experience influenced by biologic, psychologic, and social factors (biopsychosocial model).
- Pain categories include somatic (superficial or deep), visceral, and neuropathic pain.
- In infants and children, untreated pain extracts a significant physiologic, biochemical, and psychologic toll. Repetitive acute pain in neonates can cause uncoupling of $\mu$-opioid receptors and create long-term neural changes that affect future pain vulnerability and cognitive development.
Assessment of Pain in Children
Behavioral and Physiologic Indicators
- Behavioral and physiologic signs are essential for preverbal children, infants, and cognitively impaired children.
- Physiologic changes: Include tachycardia, tachypnea, increased blood pressure, increased muscle tone, oxygen desaturation, sweating, flushing, and pallor.
- Behavioral changes: Include facial grimacing (bulging brow, tightly closed eyelids, deeply furrowed nasolabial groove, taut/quivering tongue), finger clenching, thrashing of limbs, back arching, inconsolable crying, sleep disturbance, poor feeding, and pseudoparalysis.
Pain Assessment Scales
- Pain scales must be chosen based on the child's developmental age, cognitive ability, and clinical condition.
| Scale Name | Target Age/Population | Features & Utility | Limitations |
|---|---|---|---|
| Visual Analog Scale (VAS) | $6-8 \text{ yrs}$ and older | Horizontal $10 \text{ cm}$ line from "no pain" to "most pain imaginable". | Requires cognitive ability to understand proportionality; cannot be used in younger children. |
| Numerical Rating Scale (NRS) | $6-8 \text{ yrs}$ and older | Integers from $0$ to $10$. Considered the gold standard for children $>8 \text{ yrs}$. | Requires numerical processing skills. |
| Faces Scales (e.g., FACES-R, Wong-Baker) | $>3 \text{ yrs}$ | Line drawings or photos of faces indicating progressive distress. | Choice of "no pain" face (neutral vs. smiling) affects response; not universally applicable across cultures. |
| FLACC / Revised FLACC | Infants, preverbal, cognitively impaired | Assesses Face, Legs, Activity, Cry, and Consolability on a $0-2$ scale (Total $0-10$). | May overrate pain in toddlers and underrate persistent pain. |
| CRIES Scale | Neonates | Assesses Crying, Requires $O_2$, Increased vital signs, Expression, and Sleeplessness. | Score $>4$ requires immediate nonpharmacologic and pharmacologic interventions. |
Pharmacologic Management
Nonopioid Analgesics (Anti-inflammatory Medications)
- These are used as first-line agents for mild-to-moderate pain and as opioid-sparing adjuncts for severe pain.
- Aspirin is generally avoided due to the risk of Reye syndrome in viral infections.
| Medication | Dosage & Administration | Comments |
|---|---|---|
| Acetaminophen | $10-15 \text{ mg/kg}$ PO/IV q4h; Max daily: $75 \text{ mg/kg/24 hr}$. | No antiplatelet or adverse gastric effects. Overdose causes fulminant hepatic failure. |
| Ibuprofen | $8-10 \text{ mg/kg}$ PO q6h; Max daily: $2400 \text{ mg}$. | Transient antiplatelet effects; may cause gastritis. |
| Naproxen | $5-7 \text{ mg/kg}$ PO q8-12h; Max daily: $1000 \text{ mg}$. | Longer duration of action than ibuprofen. |
| Ketorolac | Loading $0.3 \text{ mg/kg}$, then $0.25-0.3 \text{ mg/kg}$ IV q6h. Max duration: $5 \text{ days}$. | Useful when oral dosing is not feasible. Reversible antiplatelet effects. |
| Celecoxib | $\ge 2 \text{ yrs}$ and $10-25 \text{ kg}$: $50 \text{ mg}$ PO bid. | COX-2 selective; minimal gastric/antiplatelet effects. Cross-reactive with sulfa allergies. |
Opioid Analgesics
- Indicated for moderate-to-severe acute pain, postoperative pain, trauma, and cancer pain.
- Opioids act on $\mu$-opioid receptors in the central and peripheral nervous systems.
- Patient-Controlled Analgesia (PCA) or Parent/Nurse-Controlled Analgesia (PNCA) allows a basal infusion with intermittent boluses, providing superior pain control with fewer side effects compared to intermittent IM/IV dosing.
- Contraindications: The FDA strictly contraindicates the use of codeine and tramadol in children $<12 \text{ yrs}$, and in adolescents $<18 \text{ yrs}$ post-tonsillectomy/adenoidectomy, due to risks of ultra-rapid metabolism causing severe respiratory depression.
| Medication | Parenteral Dose | Oral Dose | Comments |
|---|---|---|---|
| Morphine | $0.05-0.1 \text{ mg/kg}$ q2-4h | $0.3 \text{ mg/kg}$ q3-4h (immediate release) | May cause histamine release and hypotension. Active metabolites excreted renally. |
| Fentanyl | 0.5-1 mcg/kg q1-2h | Transmucosal: 10 mcg/kg | $70-100$ times more potent than morphine. Rapid onset, stable hemodynamics. |
| Hydromorphone | $0.01 \text{ mg/kg}$ q2-4h | $0.04-0.08 \text{ mg/kg}$ q3-4h | Five times more potent than morphine. No histamine release. |
| Methadone | $0.1 \text{ mg/kg}$ q8-24h | $0.1 \text{ mg/kg}$ q8-24h | Long half-life ($15-40 \text{ hrs}$). Useful for chronic pain. Requires monitoring for QTc prolongation. |
| Oxycodone | Not Available | $0.1-0.2 \text{ mg/kg}$ q3-4h | Strong opioid, preferable to hydrocodone. |
Local and Topical Anesthetics
- Local anesthetics block neuronal sodium channels. Systemic toxicity can cause seizures, arrhythmias, and cardiovascular collapse.
- Lidocaine infiltration maximum safe dose is $5 \text{ mg/kg}$ without epinephrine and $7 \text{ mg/kg}$ with epinephrine.
| Agent | Dose / Application | Notes |
|---|---|---|
| EMLA (Lidocaine $2.5%$ + Prilocaine $2.5%$) | Dose depends on age/weight (e.g., $1 \text{ g}$ for $<3 \text{ mo}$). | Requires $60 \text{ min}$ under occlusive dressing to achieve maximum effect. |
| LMX4 (Liposomal Lidocaine $5\%$) | $1-20 \text{ g}$ depending on age. | Requires $30-60 \text{ min}$ under occlusive dressing. |
| LET (Lidocaine, Epinephrine, Tetracaine) | Apply to open wounds in children $\ge 1 \text{ yr}$. | Requires $20 \text{ min}$ for maximum effect. |
Adjuvant and Unconventional Analgesics
- Used primarily for neuropathic pain, complex regional pain syndrome (CRPS), migraines, and severe muscle spasms.
- Tricyclic Antidepressants (TCAs) inhibit norepinephrine reuptake and are useful for neuropathic pain, functional abdominal pain, and sleep disorders.
| Medication | Starting Dose | Indications & Side Effects |
|---|---|---|
| Gabapentin | $10-15 \text{ mg/kg/day}$ divided bid/tid. | Adjunct for neuropathic pain. Side effects: somnolence, dizziness. |
| Pregabalin | $2.5 \text{ mg/kg/day}$ divided bid/tid. | Neuropathic pain, fibromyalgia. Side effects: ataxia, weight gain, drowsiness. |
| Amitriptyline / Nortriptyline | $0.1 \text{ mg/kg}$ PO qhs (for $25-50 \text{ kg}$). | Neuropathic pain, migraines. Side effects: sedation, dry mouth, prolonged QTc. |
| Clonidine | $5-25 \text{mcg/kg/day}$ divided q4-8h. | Anxiolytic, manages opioid withdrawal, neuropathic pain. Side effects: hypotension, bradycardia. |
| Ketamine | Loading $0.25-0.5 \text{ mg/kg}$ IV. | NMDA receptor antagonist. Excellent for opioid-tolerant patients. Side effects: hallucinations, excess secretions. |
Non-Pharmacologic Management
Modalities by Age
- Neonates: Non-nutritive sucking, breastfeeding, pacifier use, administration of $24\%$ sucrose (which is opioid-mediated and reversible with naloxone), swaddling, skin-to-skin (kangaroo care), and gentle tactile-kinesthetic stimulation.
- Infants and Toddlers: Distraction with bubbles, lighted wands, interactive sound or music, holding, and cuddling.
- Preschool and School-Age: Distraction (video games, stories, movies), controlled deep breathing (e.g., pretending to blow up a balloon), guided imagery, and medical play (puppets, art therapy).
- Adolescents: Hypnotherapy, biofeedback, progressive muscle relaxation, yoga, mindfulness meditation, and TENS (transcutaneous electrical nerve stimulation).
Cognitive-Behavioral Therapy (CBT)
- CBT modifies behavioral and environmental factors that exacerbate pain and disability.
- Parents are taught to encourage wellness behaviors rather than reinforcing illness behaviors (e.g., minimizing secondary gains from pain complaints).
- CBT has large positive effects on children with chronic headaches, functional abdominal pain, and fibromyalgia.
Management in Specific Clinical Scenarios
Procedural Sedation and Analgesia
- Requires combination of hypnosis, amnesia, and analgesia depending on the painfulness of the procedure.
- Midazolam ($0.1-0.15 \text{ mg/kg}$ IV or $0.5-1.0 \text{ mg/kg}$ PO) is the most common anxiolytic/amnestic but provides no analgesia.
- For painful procedures, combinations like fentanyl/midazolam or propofol/fentanyl are utilized under strict cardiorespiratory monitoring.
- Psychological Coaching: Use positive-focus language. Avoid negative focus like "This will feel like a bee sting" or "The medicine will burn." Instead, use "Tell me how it feels" or "Some children feel a warm feeling".
Burn Pain Management
- Burn pain is multifactorial and requires a multimodal approach addressing background, acute, procedural, neuropathic, and inflammatory pain.
- Background Pain: Best addressed with long-acting oral agents like methadone or sustained-release morphine given twice daily.
- Acute/Procedural Pain: Requires potent short-acting IV opioids (fentanyl, morphine) often combined with anxiolytics (midazolam) or dissociative anesthetics (ketamine $1-4 \text{ mg/kg}$ IV) prior to dressing changes.
- Neuropathic Pain: Scheduled oral gabapentin given four times daily mitigates the "pins and needles" sensation during healing.
- Post-traumatic stress disorder (PTSD), anxiety, and depression are common and require psychological support, selective serotonin reuptake inhibitors (SSRIs), or prazosin.
Cancer and Palliative Care
- Pain management is guided by the World Health Organization (WHO) Analgesic Ladder.
- Step 1: Mild to moderate pain $\rightarrow$ Nonopioid (e.g., Acetaminophen, NSAIDs, Celecoxib).
- Step 2: Moderate to severe pain (or failure of Step 1) $\rightarrow$ Weak opioid combined with a nonopioid.
- Step 3: Very severe pain (or failure of Step 2) $\rightarrow$ Strong opioid (Morphine, Fentanyl) with or without nonopioid adjuncts.
- Routes of administration should prioritize oral, transmucosal, or transdermal delivery to facilitate outpatient and home management.
- In cases of refractory pain, invasive options such as intrathecal opioid/clonidine pumps or continuous subcutaneous infusions may be considered.