Overview
Abdominal pain is one of the most common paediatric emergency and primary care presentations. It spans benign self-limiting conditions to life-threatening surgical emergencies. Effective management requires age-appropriate pain assessment, understanding of underlying aetiology, and judicious analgesia - including adherence to the WHO two-step analgesic ladder adapted for children. Adequate analgesia does not mask surgical pathology and must not be withheld pending diagnosis.
Epidemiology and Aetiology
Abdominal pain accounts for approximately 5-10% of paediatric ED presentations. Aetiology varies substantially by age.
| Age Group | Common Causes | Surgical / Red Flag Causes |
|---|---|---|
| Neonate (0-28 days) | Colic, constipation, overfeeding | NEC, malrotation ± volvulus, Hirschsprung disease, incarcerated hernia |
| Infant (1-12 months) | Colic, constipation, gastroenteritis | Intussusception, malrotation, incarcerated hernia |
| Toddler (1-3 years) | Constipation, gastroenteritis, intussusception | Appendicitis (atypical), Meckel diverticulum |
| School-age (4-12 years) | Constipation, functional abdominal pain, mesenteric adenitis, appendicitis | Appendicitis, Meckel diverticulum, ovarian torsion |
| Adolescent (12-18 years) | Functional abdominal pain, dysmenorrhoea, IBD, appendicitis | Ectopic pregnancy, ovarian/testicular torsion, IBD complications |
Functional abdominal pain disorders (FAPDs) - Rome IV criteria - include functional dyspepsia, irritable bowel syndrome (IBS), abdominal migraine, and functional abdominal pain NOS. These are diagnoses of inclusion, not exclusion, requiring positive clinical features rather than only normal investigations.
Pathophysiology
Acute Abdominal Pain
- Visceral pain: Distension, ischaemia, or inflammation of hollow/solid organs; transmitted via C-fibres; diffuse, cramping, poorly localised, typically midline.
- Somatic (parietal) pain: Irritation of parietal peritoneum; transmitted via A-delta fibres; well-localised, sharp, worsened by movement.
- Referred pain: Diaphragmatic irritation → shoulder tip; ureteric colic → groin/testicle.
Functional / Chronic Abdominal Pain
- Central sensitisation and gut-brain axis dysregulation with altered visceral afferent signalling and heightened central processing of normal gut stimuli.
- Psychological co-morbidities (anxiety, depression) are common and bidirectional - they amplify pain perception and result from chronic pain.
- Contributing factors: genetic predisposition, prior GI infection, adverse childhood experiences.
Clinical Features
Age-Specific Variations
| Age | Key Features | Pitfalls |
|---|---|---|
| Neonate | Abdominal distension, bilious vomiting, blood PR, failure to pass meconium | Limited behavioural expression; physiological instability may be the only sign |
| Infant | Intermittent crying, drawing up legs, vomiting, pallor | "Red currant jelly" stool is a late sign in intussusception; USS preferred early |
| Toddler | Points periumbilically; anorexia, vomiting; may appear well | Cannot accurately localise pain; serious pathology can be occult |
| School-age | Can describe character and location; pain migration to RIF (appendicitis) | Recurrent functional pain begins here; avoid over-investigation |
| Adolescent | Adult-like presentation; gynaecological history essential in females | Ectopic pregnancy and ovarian torsion must not be missed |
Pain Assessment - Developmental Framework
| Age | Validated Tool | Type |
|---|---|---|
| <3 years | FLACC scale, CHEOPS, NIPS, PIPP (neonates) | Behavioural / observer-rated |
| 3-7 years | Faces Pain Scale - Revised (FPS-R) | Self-report; identifies presence and intensity |
| ≥5 years | Visual Analogue Scale (VAS), NRS-10 | Numeric; reliable from ~age 5 |
| All ages | COMFORT scale (ICU/postoperative), Modified Observational Pain Scale | Multidimensional including physiological parameters |
Key developmental milestones (evidence-based): - Age ~2 years: can identify presence and location of pain - Age ~4 years: can grade intensity - Age ~5 years: can participate in formal pain ratings (VAS/faces) - Age ~8 years: can describe quality of the pain experience
Multiple factors influence pain assessment: developmental stage, intelligence, temperament, previous pain experience, expectation, coping strategies, cultural background, and parental anxiety.
Investigations
Investigations are guided by clinical assessment, not performed reflexively.
| Investigation | Indication |
|---|---|
| FBC, CRP, ESR | Suspected infection/inflammation (appendicitis, IBD) |
| UEC, LFTs, lipase | Metabolic causes, pancreatitis, hepatic pathology |
| Urinalysis ± MCS | UTI, urolithiasis |
| Urine βhCG | All post-menarchal females |
| Stool MCS, faecal calprotectin | IBD, infectious diarrhoea |
| Abdominal X-ray | Suspected obstruction or significant constipation (limited routine role) |
| Ultrasound abdomen/pelvis | First-line imaging: appendicitis, intussusception, ovarian/testicular pathology |
| CT abdomen/pelvis | Diagnostic uncertainty after USS; minimise radiation (ALARA) |
| Endoscopy (upper/lower) | IBD, H. pylori, coeliac disease |
| Coeliac serology (IgA anti-tTG, total IgA) | FAPDs, anaemia, faltering growth |
Diagnostic Criteria
Appendicitis
Clinical scoring tools (e.g., Paediatric Appendicitis Score, Alvarado score) aid triage. USS is preferred initial imaging; CT reserved for equivocal cases to minimise radiation exposure.
Intussusception
Triad: colicky abdominal pain, vomiting, and bloody stool (late sign). USS (target/doughnut sign) is diagnostic. Pneumatic or hydrostatic reduction under fluoroscopy or USS guidance is first-line treatment; surgical reduction for failures or complications.
Functional Abdominal Pain Disorders - Rome IV Criteria
| FAPD | Diagnostic Criteria |
|---|---|
| Functional dyspepsia | Bothersome postprandial fullness, early satiation, or epigastric pain/burning; no structural explanation; symptoms ≥2 months (adolescents) / ≥1 month (children) |
| IBS | Abdominal pain ≥4 days/month associated with defaecation and/or change in stool form or frequency |
| Abdominal migraine | Paroxysmal periumbilical/midline pain ≥1 hour with associated nausea/vomiting/pallor; symptom-free intervals; ≥2 episodes in 6 months |
| Functional abdominal pain NOS | Does not meet criteria for other FAPDs; ≥4 episodes/month over ≥2 months |
Management
WHO Two-Step Analgesic Ladder - Adapted for Children
The classic three-step WHO ladder has been reformulated as a two-step model by the WHO Guideline Review Committee, primarily because "weak" opioids at Step 2 (codeine, tramadol) failed to meet safety/efficacy standards in children. The current two-step approach applies the following principles:
- By the ladder (two-step)
- By the clock (regular dosing intervals; avoid PRN-only orders)
- By the appropriate route (oral or least invasive route preferred)
- By the child (individualised to the patient)
| Step | Pain Severity | Pharmacological Approach |
|---|---|---|
| Step 1 | Mild | Paracetamol ± NSAID (e.g., ibuprofen) ± adjuvant |
| Step 2 | Moderate-to-severe | Potent opioid (morphine paradigm) ± non-opioid ± adjuvant |
Adjuvant analgesics include anticonvulsants, antidepressants, corticosteroids, psychostimulants, and neuroleptics - used when their primary indication is not pain management but they are efficacious for specific pain syndromes.
Pharmacological Analgesia - Key Agents
| Analgesic | Route | Dose / Notes |
|---|---|---|
| Paracetamol | PO/IV/PR | Age- and weight-adjusted dosing; safe from neonates onward; regular dosing preferred |
| Ibuprofen | PO | 5-10 mg/kg per dose every 6-8 hours; avoid in renal impairment, dehydration, GI bleeding risk; use >3 months of age |
| Morphine | IV/PO/SC | Gold-standard opioid; titrate to effect; respiratory monitoring mandatory; loading dose IV (neonates/infants: 10-50 µg/kg bolus; children: 50-100 µg/kg); infusion rates age-adjusted |
| Intranasal fentanyl (INF) | IN | ~1.5 µg/kg per dose via mucosal atomisation device; onset 5-10 minutes; needle-free; useful in ED and pre-IV access settings |
| Codeine | - | Contraindicated in children - variable CYP2D6 metabolism, risk of ultra-rapid metabolism causing fatal respiratory depression; FDA black-box warning; removed from paediatric formulary |
| Tramadol | - | Insufficient safety/efficacy data in paediatric palliative/persistent pain settings - not recommended by current WHO guidelines in this context, though widely available globally |
Note on fentanyl in neonates/infants: Hepatic clearance of fentanyl may be drastically reduced during intra-abdominal surgery or with raised intra-abdominal pressure; dosing must account for significantly prolonged effect in this setting. Chest wall rigidity has been reported even with analgesic doses (3-5 µg/kg); treat with naloxone or neuromuscular blockade.
Intranasal Fentanyl - Practical Points
- Weight-based dosing: approximately 1.5 µg/kg IN (some guidelines use 1-2 µg/kg)
- Administered via mucosal atomisation device (MAD) to maximise bioavailability
- Onset 5-10 minutes; duration 30-60 minutes
- Suitable for acute severe pain in ED, pre-procedural analgesia, and when IV access unavailable
- Monitor: oxygen saturation, respiratory rate, level of sedation
- Reversal: naloxone (weight-based IV/IM/IN)
Procedural Sedation - Ketamine
Ketamine is a dissociative NMDA-receptor antagonist with proven efficacy and safety for procedural sedation and analgesia in children.
| Parameter | Detail |
|---|---|
| Mechanism | Centrally acting NMDA-receptor antagonist; potent analgesic and dissociative agent |
| IV dose (analgesic/sub-anaesthetic) | 0.5-1 mg/kg IV |
| IV dose (procedural sedation) | 1-2 mg/kg IV |
| IM dose | 3-5 mg/kg IM (slower onset ~4 minutes; useful without IV access) |
| PR dose | 3-8 mg/kg (limited use) |
| Onset (IV) | ~45 seconds |
| Caution: 2 mg/kg IV approaches anaesthetic dosing and may cause apnoea | Airway equipment and skilled practitioner mandatory |
| Cardiovascular effects | Promotes cardiovascular stability; particularly advantageous in hypovolaemic patients |
| Respiratory effects | Maintains respiratory drive; bronchodilator - a key advantage |
| Adverse effects | ↑ Salivation/secretions - co-administer anticholinergic (e.g., atropine 10-20 µg/kg IV); emergence reactions - consider low-dose midazolam (e.g., 25-50 µg/kg IV) |
| Contraindications (relative) | Raised intracranial pressure, active psychosis, thyrotoxicosis, age <3 months (use with caution) |
| Setting requirements | Pre-procedural fasting, IV access, monitoring (SpO₂, HR, RR), resuscitation equipment, skilled airway practitioner |
Ketamine also has emerging utility in paediatric neuropathic pain (NMDA-receptor antagonism) and end-of-life pain management (PCA/infusion), though further evidence is needed.
Management of Functional / Chronic Abdominal Pain
A biopsychosocial model is the framework; functional outcome (school attendance, social participation) is the primary treatment target, not pain elimination.
| Domain | Intervention |
|---|---|
| Education | Validate symptoms; explain gut-brain axis; make a positive diagnosis of FAPD |
| Dietary | Fibre, hydration; low-FODMAP diet for IBS (dietitian-supervised); identify food triggers |
| Psychological | Cognitive behavioural therapy (CBT) - strongest evidence; gut-directed hypnotherapy; relaxation/mindfulness |
| Physical | Regular aerobic activity improves pain frequency and severity |
| Pharmacological - first-line | Peppermint oil (IBS-type); antispasmodics (e.g., hyoscine) short-term |
| Pharmacological - second-line | Low-dose amitriptyline (TCA) for central sensitisation in adolescents (specialist guidance); melatonin for abdominal migraine prevention |
| Adjuvant / neuropathic pain | Gabapentinoids, duloxetine or venlafaxine (SNRIs - minimal paediatric evidence, emerging); specialist paediatric pain service involvement required |
| School/social functioning | Multidisciplinary team (paediatric pain, psychology, school liaison); early referral - do not await complete investigation before psychological referral |
WHO principles apply equally to chronic pain: avoid PRN-only opioids for chronic functional pain; regular dosing prevents pain recurrence. Opioids have limited role in functional abdominal pain and should only be considered under specialist guidance.
Red Flags Requiring Urgent Assessment
- Bilious vomiting at any age
- Involuntary weight loss or faltering growth
- GI blood loss (haematemesis, melaena, haematochezia)
- Fever with localised peritonism
- Rash, arthritis, uveitis (IBD, IgA vasculitis/HSP)
- Family history of IBD, coeliac disease, peptic ulcer disease
- Perianal disease
- Pain consistently waking child from sleep
- Hepatosplenomegaly or palpable abdominal mass
Complications
| Complication | Context |
|---|---|
| Perforation with peritonitis | Delayed diagnosis of appendicitis; higher risk in young children with atypical presentations |
| Septic shock | Perforated viscus, infectious aetiology |
| Opioid-related respiratory depression | Inadequate monitoring; naloxone (weight-based IV/IM/IN) is reversal agent; all infants <6 months on opioids require HDU monitoring |
| Procedural sedation adverse events | Laryngospasm, apnoea, aspiration - require pre-procedural fasting, skilled team, full monitoring |
| Chronic pain disability | School absenteeism, social isolation, anxiety/depression, health-seeking behaviour |
| Missed surgical cause in apparent FAPD | Reassessment mandatory if red flags emerge or presentation changes |
Prognosis and Follow-up
Acute Abdominal Pain
- Surgical causes (appendicitis, intussusception) have excellent outcomes with timely intervention.
- Diagnostic delay - particularly in neonates and toddlers with atypical presentations - carries significantly higher morbidity and mortality.
Functional Abdominal Pain
- Approximately 30-50% of children with FAPD continue to have symptoms into adulthood.
- Predictors of persistence: co-existent anxiety/depression, parental reinforcement of sick-role behaviour, pain catastrophising.
- With multidisciplinary treatment, the majority achieve significant functional improvement even without complete pain resolution.
Follow-up Framework
| Timeframe | Action |
|---|---|
| Acute presentation | Safety-net advice; clear return precautions; GP/general paediatric follow-up within 1-2 weeks if not admitted |
| Recurrent / functional pain | Structured multidisciplinary review; reassess for organic cause at each visit if red flags develop |
| Chronic pain | Regular paediatric pain service review; functional outcome measures; psychological co-management |
Referral and Admission Criteria
Admit to Hospital
- Peritonism, perforation, or surgical emergency
- Bilious vomiting or suspected obstruction/volvulus
- Haemodynamic instability
- Unable to maintain oral hydration
- Intussusception requiring radiological or surgical reduction
- Neonates with any concerning abdominal signs (same-day surgical consult)
- Age <3 months with unexplained abdominal pain
Specialist Referral
| Specialty | Indication |
|---|---|
| Paediatric Surgery | Appendicitis, hernia, Meckel diverticulum, malrotation |
| Paediatric Gastroenterology | IBD, coeliac disease, H. pylori, FAPD not responding to primary management |
| Paediatric Pain Service | Chronic/recurrent pain with functional impairment; complex analgesic requirements; neuropathic pain |
| Paediatric Psychology / Psychiatry | Co-existent anxiety, depression, school refusal, family dysfunction amplifying pain |
| Dietitian | IBS (low-FODMAP), IBD, coeliac disease |
| Gynaecology | Post-menarchal females with suspected pelvic pathology, dysmenorrhoea, suspected ectopic pregnancy |
Early multidisciplinary referral is essential. Delaying psychological input until investigations are complete implicitly communicates to families that the pain is not real, worsens outcomes, and is not consistent with current RACP/evidence-based guidance.