Chapter 74 Sudden Infant Death Syndrome
PATHOPHYSIOLOGY
Sudden infant death syndrome (SIDS) is defined as “the sudden death of an infant under 1 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” (Willinger, James, & Catz, 1991, p. 681). The autopsy report can include the following findings. External examination reveals a body that appears well developed and nourished. There is a small amount of mucous, or watery or bloody secretions present at the nares. Cyanosis of the lips and nail beds is almost always present. The internal examination findings indicate a subacute inflammation of the upper respiratory tract and petechiae on the pleura, the pericardium, and the thymus (this is found in 80% of cases). There is pulmonary edema and congestion. The autopsy reveals symptoms of chronic hypoxemia including brainstem changes; persistence of brown fat, especially around the adrenals; and hepatic erythropoiesis. Some of these autopsy findings are demonstrated in about 80% of SIDS cases, and their absence does not exclude the diagnosis. Risk factors associated with the incidence of SIDS are listed in Box 74-1.
Box 74-1 Risk Factors
Infant Risk Factors
The pathophysiology of SIDS remains unclear, but current research is focused in the following six areas:
1. Abnormalities of the central nervous system (CNS): There are two areas of focus within this category. The first is delayed myelination or gliosis (or scarring) in the respiratory control areas of the brainstem. The second is altered neuronal pathways within the brainstem, which prevent an infant from responding to life-threatening hypercapnea, hypoxemia, hyperthermia, or cardiovascular episodes during sleep.
2. Primary cardiac arrhythmias, particularly those causing bradycardia secondary to a decrease in vagal nerve tone and occurring simultaneously with central apnea and prolonged QT interval.
3. Carbon dioxide rebreathing and airway obstruction associated with the prone sleeping position and soft bedding: This position can cause an increased frequency of oxygen desaturation in the blood, exposing the infant to periods of hypoxemia and hypercapnea as well as pharyngeal collapse that causes a functional obstruction of the infant’s airway.
4. Impaired temperature regulation and its effects on the respiratory pattern, chemoreceptor sensitivity, and cardiac control
5. Infant sleep state: Infants sleeping in the prone position may have more time in quiet sleep and less time in active sleep. In quiet sleep, an infant experiences fewer awakenings and an increased arousal threshold.
INCIDENCE
1. Sudden infant death syndrome is the most common cause of death before 1 year of age.
2. Since the introduction of the “Back to Sleep” campaign in 1992, which resulted in a steady decrease in the prone sleeping rate, the SIDS rate has decreased from 1.2 deaths per 1000 live births to 0.56 death per 1000 live births in 2001. This represents a 53% decrease.
3. Age range of peak incidence is 2 to 3 months; it is uncommon before 2 weeks of age or after 6 months of age.
