Sudden infant death syndrome (SIDS or Cot death)

Sudden infant death syndrome (SIDS or Cot death)

This condition is defined as the sudden and unexpected death of a baby, usually between 1 month and 1 year of age, who was clinically healthy before the death or may have suffered from a mild or trivial disease or ailment, like fever or upper respiratory tract infection. A complete post-mortem examination, including histology and other relevant laboratory examinations, fails to identify an obvious cause of death.

Because the death is unexpected and without obvious cause, it must be dealt with according to the Inquests Act 58 of 1959. It is only after a post-mortem examination has been performed, and other causes, like violence, have beenexcluded, that the death can be regarded as natural. After other obvious morphological and even biochemical and microbiological causes of death have been excluded, the death can be attributed to this syndrome (sudden infant death syndrome or SIDS). This will therefore exclude conditions like pneumonia or congenital heart abnormalities.

Incidence

It is the most common cause of death in developed countries in babies 28 days to 1 year old. It involves approximately 2,3 babies per 1 000 live births in the USA. In the United Kingdom the incidence is 3 per 1 000 live births.

Predisposing factors

·              Age. It occurs between the ages of 1 month and 2 years, with most deaths between 2 months and 7 months. There is a peak at 3 months. True SIDS does not occur in the neonatal period and is rare before the age of 1 month. There are exceptions, namely premature and low birth-weight babies.

·              Sex. Females babies are more prone, with a ratio of 1,3:1.

·              Twins. Twins are twice as prone due to the higher incidence of prematurity and low birth weight.

·              Seasonal distribution. Most cot deaths occur in the colder and wetter months. Although attempts have been made to correlate the incidence of SIDS with temperature changes and respiratory infection, the results are contradictory. However, it has been proven that respiratory infections are indeed a precipitating factor for SIDS.

·              Social status. There is a higher incidence in the lower socio-economic group.

·              Other factors. Maternal factors:

o     smoking and drug abuse

o     anaemia

o     urinary tract infections/venereal disease during pregnancy

o     multiple pregnancies (twins)

o     previous complications of pregnancy (prematurity, still-born babies and miscarriage)

o     a young mother, especially younger than 20 years

o     poor antenatal clinic attendance

o     limited education (no secondary school education

o     short intervals between pregnancies (less than 6 months)

o     sub-optimal weight increase during pregnancy

Child-related factors:

o     prematurity

o     low birth weight

o     poor general condition at birth

o     female babies (see above)

o     twins (see above)

o     lengthy stay in hospital

o     poor postnatal clinic attendance

o     poor weight increase

o     babies who are not breastfed

Appearance

History and background

Most babies are healthy or may suffer from a mild upper respiratory tract infection or gastro-intestinal condition. They are usually laid down in the cot in an apparently healthy condition, just to be found dead the next morning. The deaths may sometimes also occur after the morning feed.

Scene of death

In most cases the scene of death is not investigated, as the parents will rush the child to the hospital for resuscitation. If the body of the baby is examined in the cot, there are usually no external signs of any significance. There may be a pink foam exuding from the nose and mouth, and the face and fingernails may be blue or cyanotic while the face may also be pale. Petechial or punctate (spotty) haemorrhages are usually not visible in the eyes or face.

It has been alleged that there is a higher incidence of SIDS in babies lying in the prone (on their stomach) position. If the baby was indeed lying in the prone position, the area of pallor surrounding the mouth and nose must not be misinterpreted as the result of smothering. This is due to the normal distribution of hypostasis, with a pale area surrounding the mouth due to pressure of the face on the underlying pillow. The dried out and delicate lips of the baby can also look like an abrasion. This is a normal post-mortem finding.

Post-mortem examination

The post-mortem signs are non-specific, but some are relatively common.

·              Intra-thoracic petechial haemorrhages (punctate haemorrhages in the chest cavity) are present in 50% of cases on the lung surface (pleura), the external aspect of the heart (epicardium) and also on the thymus (a gland in the upper chest cavity).

·              Respiratory infection as indicated by inflammation of the mucosal surfaces of the trachea and larynx is present in 50% of cases.

·              The lungs show pulmonary congestion and oedema. The surface of the lungs shows dark and light coloured areas consistent with patchy collapse of the lung tissue. There can also be an increased number of inflammatory cells, especially surrounding the airways.

·              Enlargement of lymphoid structures like the thymus and lymph nodes may be present. Histological examination, however, shows only non-specific signs of stimulation.

Theories

More than 2 000 articles have been published regarding possible causes of sudden infant death syndrome. The following is a list of the most common theories which have been postulated:

·              Hyperthermia/hypothermia or temperature abnormalities. This theory is based on the fact that SIDS occurs more frequently during winter months because the risk of hypothermia due to the lower environmental temperature, as well as the risk of hyperthermia is higher. The latter is due to the fact that the child is often covered with too many blankets. Hyperthermia will be further aggravated if the child has low-grade infection associated with fever.

·              Poisoning  -   carbon monoxide/carbon dioxide (CO/CO₂). This theory, which is at present widely accepted, is based on the fact that babies lying on their stomachs (prone) have a higher risk. The baby exhales carbon dioxide, which is heavier than air, and this accumulates around its head in the cot. Carbon dioxide is an anaesthetic agent and can cause apnoea (inability to breathe).

·              Death due to ``overlying'' is no longer an accepted cause of SIDS. The baby who died in the Bible story, where Solomon had to decide over the plight of the surviving living baby, was most probably a victim of SIDS.

·              Allergies, for instance for cow's milk and also dust mites.

·              Infections  -   low-grade and otherwise slight infections of especially the airways.

·              Metabolic disturbances such as metabolic enzyme defects, hypoglycae-mia (low blood-glucose level) and hypothyroidism (inactive thyroid).

·              Vitamins and electrolyte deficiency, such as vitamin C, D and E, thiamine, magnesium and calcium deficiencies.

·              Conduction system remodelling defects of the heart. The heart undergoes a process of remodelling. During the intra-uterine period the right ventricle is the most important heart chamber responsible for the forward propulsion of blood. However, after birth the left ventricle becomes more important, and the right ventricle only has to pump the blood through a relatively low pressure system in the lungs. Due to this the walls of the right ventricle will become thinner. This ``absorption'' of heart muscle is associated with changes in the anatomy of the conduction system, which increase the irritability of the heart system and the risk of arrhythmia (irregular heart rate) and even death.

·              Abnormalities of the brain, including a narrow foramen magnum (the opening at the base of the skull) causing pressure on the brain stem.

·              Obstruction of the upper airways, especially during sleep.

·              Immune deficiencies which lower the resistance of the baby.

During the period 1970 to 1980 the hypothesis was developed that all babies experience normal episodes of apnoea during sleep. This re-establishing of breathing after a period of apnoea is also known as auto-resuscitation. Some babies have a poor respiratory drive (the mechanism allowing you to breathe automatically), which may increase these episodes of apnoea. It has been alleged that progressive hypoxia and the inability to respond timeously and sufficiently to hypercapnia (increased carbon-dioxide levels in the blood) and hypoxia cause death. Carbon dioxide is the normal stimulus or drive for respiration. The sleeping baby will go into a downward spiral of hypoxia  -   apnoea  -   which will ultimately result in bradycardia and cardiac arrest. There are, however, also contradictions in this theory, as with each of the other theories mentioned above.

At present it is accepted that SIDS has many causes and that it is only the final situation leading to death in a child compromised by a number of factors which all have to come together in a baby to result in death. These factors are:

·              sleep (it depresses the brain stem, which inter alia controls respiration)

·              viral infections (especially of the respiratory tract): viraemia causes decreased oxygenation and narrowing of the airways due to swelling of the mucosa as well as mucus secretion

·              other factors such as prematurity and low birth weight

·              lying in the prone position: these babies are more vulnerable to the accumulation of carbon dioxide surrounding the head; carbon dioxide is a heavy gas and will accumulate in the space surrounding the face; carbon dioxide has an anaesthetic effect and depresses the respiration even more.

It has been proven that non-specific community health-care improvements (ie ante- and postnatal clinics) lead to a decrease in the incidence of SIDS. It has been also been proven that informing mothers about the position in which babies should sleep (on the face or side) helped in lowering the incidence.

How can you prevent SIDS in your own family? One solution is to use a sleep apnoea monitor or alarm, which is placed under the mattress in the cot. The moment that the baby stops breathing, an alarm is triggered, and both baby and mother are awakened. These monitors may be rented from most pharmacies.

The main reason for performing a post-mortem examination in a case of SIDS is to exclude murder and child abuse. Thereafter any morphological, biochemical and microbiological cause of death has to be excluded. If a significant abnormality cannot be demonstrated with a complete post mortem, the death is attributed to SIDS. It is therefore a diagnosis made by exclusion.