Sudden Infant Death Syndrome

Sudden infant death syndrome is the sudden death of an infant under 1 year of age that remains unexplained after a thorough investigation, including a complete autopsy, review of the circumstances of death and the clinical history. It is a diagnosis of exclusion.

Rates have fallen by more than half in countries that promoted back sleeping. It is the commonest cause of postneonatal infant death in high income countries. The peak age is 2 to 4 months, and more than 90% of deaths occur before 6 months. It is more common in boys, in winter and in the night and early morning.

The triple risk model proposes that death occurs when a vulnerable infant (for example with brainstem abnormalities of serotonergic arousal control) meets a critical developmental period and an exogenous stressor.

Risk factors include prone and side sleeping, bed sharing (especially on a sofa, with parental smoking, alcohol or sedative use), soft bedding, head covering, overheating, maternal smoking in pregnancy and after birth, prematurity, low birth weight, young maternal age, poverty, and recent minor illness. Protective factors include supine sleeping, breastfeeding, room sharing without bed sharing, and pacifier use.

Pathophysiology.

The mechanism is not known. Failure of arousal, cardiorespiratory control and autonomic responses to hypoxia, hypercapnia or rebreathing is proposed. Abnormalities of serotonin signalling in the medullary raphe are found in many.

A minority of cases involve undetected genetic arrhythmia disorders (long QT syndrome), fatty acid oxidation disorders or infection.

• A previously well infant, or one with a minor illness, found dead or in extremis after a sleep period, often in the early morning.
• Circumstances may include prone sleeping, sleeping on a sofa or adult bed, soft bedding, or overheating.
• Autopsy may show petechiae in the thymus, lungs and pericardium, and pulmonary congestion, which are non-specific.

Red flags.

• Features that suggest an alternative or non-accidental cause: bruising, fractures, retinal haemorrhage, inconsistent history, previous unexplained infant death in the family or previous child protection concern.
• Features of metabolic or cardiac disease: previous unexplained collapse, faltering growth, family history of sudden death or arrhythmia.
• Death during feeding, or in an infant over 1 year (not sudden infant death syndrome).

• Diagnosis follows a standardised investigation: review of the history, scene examination, full autopsy, and ancillary tests, and a multi-agency case review.
• Autopsy with histology, microbiology (blood, cerebrospinal fluid, swabs), virology, toxicology, metabolic screening (acylcarnitines on blood spot, urine organic acids), and skeletal survey and ophthalmic examination to exclude abuse.
• Genetic testing for cardiac channelopathies and cardiomyopathy (post-mortem DNA sample) and metabolic disease where indicated, with cardiac screening of first degree relatives if a cause is found.
• Review of the sleeping environment, with photographs and measurements.

Differential diagnosis. Suffocation (accidental asphyxia, overlay), infection (sepsis, myocarditis, meningitis), inherited metabolic disease, cardiac arrhythmia or cardiomyopathy, congenital heart disease, abusive head trauma, poisoning, and neglect.

Immediate response.

• Resuscitate unless death is clearly established. Attempt resuscitation in the usual way, and transport the infant to hospital.
• Inform the senior paediatrician and the coroner or equivalent authority, and the child death review service. Take a careful history, record the circumstances, and examine the infant and take samples as directed by the investigation (blood, urine, cerebrospinal fluid, skin biopsy or blood spot for metabolic tests) while preserving evidence.
• Support the parents with sensitive, honest communication. Allow them to hold and spend time with the infant, offer mementos, and avoid assigning blame.

Follow up.

• Offer a meeting with the paediatrician after autopsy results to discuss findings and answer questions.
• Bereavement support for parents, siblings and grandparents, and counselling when needed. Review the health of surviving siblings.
• Plan for subsequent pregnancies with extra support. Home apnoea monitors are not shown to prevent sudden infant death syndrome and are not advised.

Prevention advice for all families.

• Place babies on their back to sleep, in a cot in the parents' room for the first 6 months, on a firm, flat mattress without pillows, duvets or soft toys, with feet at the foot of the cot and no head covering.
• Avoid smoking in pregnancy and around the baby, avoid alcohol and drugs, never sleep with a baby on a sofa or armchair, and avoid bed sharing when a parent has consumed alcohol or sedatives, smokes, or when the baby is premature or small.
• Breastfeed if possible, avoid overheating, and offer a pacifier at sleep once breastfeeding is established.

Monitoring. Bereavement follow up, and genetic follow up of relatives where a cardiac or metabolic cause is found.

Referral and escalation. Refer to the child death review team, a clinical geneticist or cardiologist where indicated, and bereavement services.

Special groups. Preterm and low birth weight infants and those exposed to tobacco smoke need targeted counselling before discharge.