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.