Pediatric emergency medicine trisk 0506 0506
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diminished diffusion of O2 across the blood–gas barrier (see Chapter 86 Cardiac
Emergencies ). Several pulmonary vascular abnormalities can also lead to
cyanosis. These include primary pulmonary hypertension of the newborn or
pulmonary hypertension from other causes. When pulmonary pressures are high,
blood is shunted away from the lungs and the child becomes hypoxemic.
Pulmonary embolism and pulmonary hemorrhage, although rare in children, also
impair lung perfusion and must be considered.
Low perfusion states may lead to local or peripheral cyanosis, particularly of
the hands, feet, and lips. Moderate cold exposure, for example, can result in local
blueness. Patients in septic or cardiogenic shock may have perfusion-related
cyanosis as a result of pump failure. Poor perfusion can also result from
hyperviscous states such as polycythemia or leukemia. Acrocyanosis, or blueness
of the hands and feet with preserved pinkness centrally, is seen commonly in
newborns and is related to variable perfusion in the extremities. It is seen in wellappearing babies and resolves within the first few days of life.
Neurologic conditions can also lead to Hb deoxygenation and cyanosis.
Patients who hypoventilate because of central nervous system (CNS) depression,
whether from primary CNS lesions or drugs/toxins that depress the respiratory
center, are often centrally cyanotic at presentation to the ED. Episodic blue spells
in infants and young children who are otherwise well may be caused by breath
holding, especially when associated with a sudden insult such as fear, pain,
frustration, or anger (see Chapter 126 Behavioral and Psychiatric Emergencies ).
Cyanosis may be noted as part of the picture in an infant with a brief resolved
unexplained event (BRUE). Seizures are often associated with cyanosis from
inadequate respiration during the convulsion. A variety of neuromuscular diseases
that affect chest wall or diaphragmatic function may ultimately lead to
hypoventilation.
With respect to the Hb molecule itself, methemoglobinemia is an unusual but
important reason for presentation to the pediatric ED. Methemoglobinemia can be
either congenital or acquired. Congenital methemoglobinemia is caused by either
Hb variants designated M hemoglobins or deficiency of NADH-dependent
methemoglobin reductase. The more common acquired form occurs when red
blood cells are exposed to oxidant chemicals or drugs. Methemoglobinemia has
also been associated with diarrheal illnesses in children. Young infants are
particularly susceptible to the development of methemoglobinemia as a result of
immature enzyme systems required to reduce Hb. Even at low levels, skin
discoloration is prominent, often with intense or “slate gray” cyanosis from the
