Why are infants vulnerable during sleep?
In contrast to healthy older children and adults, healthy infants (children under the age of 12 months) are inherently vulnerable to sleep-related injury through a variety of mechanisms. This vulnerability evolves with age and fluctuates with other external factors, some of which are modifiable by the parent or caregiver.

This inherent vulnerability stems from the following:

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Compared with older children, an infant has:

• Smaller more easily compressed airways

• A large, heavy head relative to body size

• A protruding occiput (back of the head), such that the head tips forward even when lying on a flat surface

• More easily compressed chest wall

• Less respiratory stamina

• Reduced temperature control

• Reduced sleep arousal to rises in carbon dioxide

• If prone, a reduced ability to lift their face away from an obstruction (mattress/ pillow)

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What makes a sleep environment unsafe?
Whilst data on sleep product-associated injuries is problematic, an infant’s anatomical and physiologic vulnerabilities are (medically) well understood together with factors that might exacerbate these.
 

To understand the risk, you need to understand how infants work!

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How infants’ respiration and circulation work:
Respiration is initiated by the downward movement of the diaphragm. This generates negative pressure inside the chest. As air is drawn in, the ribs expand passively. Infants can suffocate if there is an obstruction (partial or complete) to diaphragmatic movement, air inflow or chest wall expansion.

Respiration is controlled by biofeedback loops that respond primarily to a rise in carbon dioxide levels. In some children who have chronic lung disease and elevated carbon dioxide levels (ex-premature infants) low oxygen levels may be the driver for respiration. Respiratory drive is reduced in sleeping infants and this can be further impacted if the infant is sick or exposed to sedative medication (prescription drugs, illicit drugs, alcohol) either directly or through the breast milk.
 

Circulation of blood requires squeezing and refilling of the heart and unimpeded flow to all organs but especially the brain (which controls vital body functions). Blood circulation can be impaired due to rises in intrathoracic or abdominal pressure or occlusion of arteries feeding organs (high pressure) or veins draining organs (low pressure). Occlusion of cerebral blood flow results in rapid unconsciousness and cessation of vital functions.

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Suffocation refers to deprivation of oxygen entering the body whereas asphyxia refers to deprivation of oxygen being delivered to the tissues. The causes of suffocation and asphyxia are largely the same, except that asphyxia can be caused by stopping blood flow independently of respiration.

Hazards that can be avoided in the sleep environment
Some of these hazards are already described in ISO/IEC Guide 50: 2014; Safety Aspects- guidelines for child safety on standards and other specifications (https://www.iso.org/standard/63937.html), with part 6.4 providing specific reference to hazards in the sleep environment. ISO references are highlighted in red in the relevant sections below.

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FIND OUT MORE ABOUT Suffocation and Asphyxia