Pain Management in PICU

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	$0.5-1\text{ mug/kg}$ q1-2h	Transmucosal: $10\text{ mug/kg}$	$70-100$ 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	$5-25\text{ mug/kg/day}$ 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 $\to$ Nonopioid (e.g., Acetaminophen, NSAIDs, Celecoxib).
  • Step 2: Moderate to severe pain (or failure of Step 1) $\to$ Weak opioid combined with a nonopioid.
  • Step 3: Very severe pain (or failure of Step 2) $\to$ 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.