Sudden Infant Death Syndrome (SIDS)
Summary
Sudden Infant Death Syndrome (SIDS) is the sudden death of an infant under one year of age which remains unexplained after a thorough case investigation, including performance of a complete autopsy, examination of the death scene, and review of the clinical history. It is a sub-category of Sudden Unexpected Death in Infancy (SUDI). It remains the leading cause of post-neonatal death in developed countries. [1,2]
Key Facts
- The "Triple Risk" Model: SIDS is not a single disease but an intersection of three factors:
- Vulnerable Infant (underlying biological defect, e.g., arousal pathway).
- Critical Developmental Period (2-4 months, when cardiorespiratory control is immature).
- Exogenous Stressor (overheating, prone position, smoke).
- Success Story: The "Back to Sleep" campaign (early 1990s) reduced SIDS rates by >70% in the UK/USA.
- Protective Factors: Breastfeeding (reduces risk by ~50%), Pacifier/Dummy use (at sleep onset), and Room Sharing (for first 6 months).
Clinical Pearls
Sofa Sleeping: Co-sleeping on a sofa or armchair is the single most dangerous sleeping environment (Risk Ratio >50). The risk of entrapment/wedging is profound. Parents must strictly avoid this.
Feet to Foot: The baby's feet should touch the foot of the cot. This prevents the baby wriggling down under the blankets and getting their head covered (suffocation/overheating).
The "CONI" Scheme (Care of Next Infant): Parents who have lost a child to SIDS are terrified for their next baby. The CONI program (run by the Lullaby Trust/NHS) provides symptom diaries, apnea monitors, and extra health visitor support for the subsequent sibling. This drastically reduces parental anxiety.
Demographics
- Peak Incidence: 2-4 months of age. Rare less than 1 month or >1 year.
- Gender: Males > Females (60:40).
- Seasonality: Higher in winter (over-wrapping/heating).
Major Risk Factors
- Sleeping Position: Prone (Front) or Side. (Side is unstable and leads to rolling prone).
- Maternal Smoking: During pregnancy (damages fetal brainstem) and Post-natal (ETS). Dose-dependent risk.
- Bed Sharing: Particularly if parent is smoker, drunk, drugged, or extremely tired.
- Prematurity / Low Birth Weight.
- Social Deprivation.
The Serotonin Hypothesis
- The prevailing theory is a deficit in the serotonergic (5-HT) network in the medulla oblongata (brainstem).
- This network is responsible for Arousal and Gasping in response to hypoxia/hypercarbia.
- In a vulnerable infant, when challenged (e.g., rebreathing CO2 while face down), the brainstem fails to trigger the "wake up and gasp" reflex, leading to quiet asphyxia and death.
The Event
- External: Often normal. Sometimes frothy secretions at nose/mouth (pulmonary oedema).
- Internal:
- Intrathoracic Petechiae: Found on thymus, pleura, pericardium (80% of cases). Hallmark of SIDS (suggests gasping against closed glottis).
- Empty Bladder/Rectum.
- Absence of other fatal pathology (e.g., meningitis, congenital heart disease).
A sudden infant death triggers a multi-agency response (Police, Paediatrics, Social Services).
Immediate Investigation
- Skeletal Survey: X-rays to rule out fractures (NAI).
- Metabolic Screen: Blood/Urine/CSF/Skin biopsy (to rule out MCAD deficiency, etc).
- Microbiology: Blood/CSF/Tissue cultures (Sepsis?).
- Toxicology: Rule out accidental poisoning or overlaying by intoxicated parent.
- Scene Visit: Police/Coroner officer visits home to document sleep environment (temperature, bedding).
Genetic Autopsy
- If cause remains unknown, screening for cardiac channelopathies (Long QT - SCN5A, KCNQ1) usually undertaken. ~10% of "SIDS" are actually arrhythmias.
Management Algorithm (Prevention)
SAFE SLEEPING GUIDELINES
(ABC Rules)
↓
A - ALONE & ALWAYS
- Own cot/moses basket (NOT in parents' bed)
- In parents' room (for 6 months)
- Every sleep (Day and Night)
↓
B - BACK
- Always place baby on BACK
- NOT side or front
- Once they can roll, they find their own position
↓
C - CRIB (Environment)
- Feet to Foot (prevents sliding down)
- Flat, firm mattress (No pillows/duvets/bumpers)
- Temperature 16-20°C (Don't overheat)
- SMOKE FREE ZONE
Support for Families
- Immediate: Compassionate bereavement care. Do not criminalize the parents.
- Lactation: Suppression of lactation for the mother.
- Follow-up: Review meeting with Paediatrician to discuss PM results (usually 6-8 weeks later).
- CONI: Enrolment for future pregnancies.
- Psychological: PTSD, Complex Grief, Guilt ("If only I checked him").
- Family: Marriage breakdown is common.
- Legal: Safeguarding proceedings if NAI suspected.
- SIDS is fatal.
- Recurrence risk in subsequent siblings is slightly higher than general population but still very low (less than 1%), UNLESS there is an underlying genetic/metabolic cause (in which case risk is 25-50%).
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| Safer Sleep | Lullaby Trust | Back to sleep, avoid co-sleeping, room temp 16-20C. |
| SUDI Investigation | RCPCH / Baroness Kennedy | Standardised protocol for multi-agency investigation. |
| SIDS | AAP (American) | Endorses pacifier use and room sharing. |
Landmark Evidence
1. The "Back to Sleep" Studies
- The Avon Longitudinal Study of Parents and Children (ALSPAC) provided crucial epidemiological data confirming prone sleeping as the major modifiable risk factor.
What is SIDS?
It is when a seemingly healthy baby dies unexpectedly in their sleep, and even after a full examination, we cannot find a medical cause. It is sometimes called "Cot Death".
Did I do something wrong?
This is the most common question. SIDS is a tragedy, not a crime. While there are risk factors, sometimes it happens even when parents do everything "right".
Why on the back?
Babies asleep on their front sleep much deeper and find it harder to wake up if they get too hot or can't breathe well. Sleeping on the back protects their airway and allows them to wake up if something is wrong.
Can I sleep with my baby?
It is lovely to cuddle, but falling asleep with your baby in your bed increases the risk, especially if you smoke, have drunk alcohol, or are extremely tired. The safest place for a baby is in a cot next to your bed. Never sleep with a baby on a sofa.
Primary Sources
- Moon RY. SIDS and Other Sleep-Related Infant Deaths: Evidence Base for 2016 Recommendations. Pediatrics. 2016.
- Fleming PJ, et al. Sudden unexpected death in infancy. The CESDI SUDI Studies. London: The Stationery Office. 2000.
- Kinney HC, et al. The serotonin brainstem deficiency syndrome: hypothesis, evidence, and potential clinical implications. Neuropathol Appl Neurobiol. 2009.
Common Exam Questions
- Prevention: "Three protective factors?"
- Answer: Breastfeeding, Dummy, Room Sharing.
- Risk: "Most dangerous co-sleeping site?"
- Answer: Sofa/Armchair.
- Pathology: "Classic PM finding?"
- Answer: Intrathoracic Petechiae (Thymus/Pleura).
- Protocol: "CONI Scheme?"
- Answer: Support for the next infant (Care of Next Infant).
Viva Points
- Differential of SUDI: SIDS (Unexplained) vs Explained causes (Sepsis, NAI, Metabolic, Cardiac).
- Meadow's Law: Roy Meadow (discredited) famously said "One SIDS is a tragedy, two is suspicious, three is murder". This is FALSE and statistically flawed (because genetic causes run in families). Do not quote this law as fact.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.