Pain Management in PICU

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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 $μ$ -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)	$6 - 8 yrs$ and older	Horizontal $10 cm$ line from "no pain" to "most pain imaginable".	Requires cognitive ability to understand proportionality; cannot be used in younger children.
Numerical Rating Scale (NRS)	$6 - 8 yrs$ and older	Integers from $0$ to $10$ . Considered the gold standard for children $> 8 yrs$ .	Requires numerical processing skills.
Faces Scales (e.g., FACES-R, Wong-Baker)	$> 3 yrs$	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	$10 - 15 mg/kg$ PO/IV q4h; Max daily: $75 mg/kg/24 hr$ .	No antiplatelet or adverse gastric effects. Overdose causes fulminant hepatic failure.
Ibuprofen	$8 - 10 mg/kg$ PO q6h; Max daily: $2400 mg$ .	Transient antiplatelet effects; may cause gastritis.
Naproxen	$5 - 7 mg/kg$ PO q8-12h; Max daily: $1000 mg$ .	Longer duration of action than ibuprofen.
Ketorolac	Loading $0.3 mg/kg$ , then $0.25 - 0.3 mg/kg$ IV q6h. Max duration: $5 days$ .	Useful when oral dosing is not feasible. Reversible antiplatelet effects.
Celecoxib	$\geq 2 yrs$ and $10 - 25 kg$ : $50 mg$ 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 $μ$ -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 $< 12 yrs$ , and in adolescents $< 18 yrs$ post-tonsillectomy/adenoidectomy, due to risks of ultra-rapid metabolism causing severe respiratory depression.

Medication	Parenteral Dose	Oral Dose	Comments
Morphine	$0.05 - 0.1 mg/kg$ q2-4h	$0.3 mg/kg$ q3-4h (immediate release)	May cause histamine release and hypotension. Active metabolites excreted renally.
Fentanyl	$0.5-1 \text{ \mu g/kg}$ q1-2h	Transmucosal: $10 \text{ \mu g/kg}$	$70 - 100$ times more potent than morphine. Rapid onset, stable hemodynamics.
Hydromorphone	$0.01 mg/kg$ q2-4h	$0.04 - 0.08 mg/kg$ q3-4h	Five times more potent than morphine. No histamine release.
Methadone	$0.1 mg/kg$ q8-24h	$0.1 mg/kg$ q8-24h	Long half-life ( $15 - 40 hrs$ ). Useful for chronic pain. Requires monitoring for QTc prolongation.
Oxycodone	Not Available	$0.1 - 0.2 mg/kg$ 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 $5 mg/kg$ without epinephrine and $7 mg/kg$ with epinephrine.

Agent	Dose / Application	Notes
EMLA (Lidocaine $2.5$ + Prilocaine $2.5$ )	Dose depends on age/weight (e.g., $1 g$ for $< 3 mo$ ).	Requires $60 min$ under occlusive dressing to achieve maximum effect.
LMX4 (Liposomal Lidocaine $5$ )	$1 - 20 g$ depending on age.	Requires $30 - 60 min$ under occlusive dressing.
LET (Lidocaine, Epinephrine, Tetracaine)	Apply to open wounds in children $\geq 1 yr$ .	Requires $20 min$ 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	$10 - 15 mg/kg/day$ divided bid/tid.	Adjunct for neuropathic pain. Side effects: somnolence, dizziness.
Pregabalin	$2.5 mg/kg/day$ divided bid/tid.	Neuropathic pain, fibromyalgia. Side effects: ataxia, weight gain, drowsiness.
Amitriptyline / Nortriptyline	$0.1 mg/kg$ PO qhs (for $25 - 50 kg$ ).	Neuropathic pain, migraines. Side effects: sedation, dry mouth, prolonged QTc.
Clonidine	$5-25 \text{ \mu g/kg/day}$ divided q4-8h.	Anxiolytic, manages opioid withdrawal, neuropathic pain. Side effects: hypotension, bradycardia.
Ketamine	Loading $0.25 - 0.5 mg/kg$ 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 ( $0.1 - 0.15 mg/kg$ IV or $0.5 - 1.0 mg/kg$ 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 $1 - 4 mg/kg$ 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.