Congenital High Airway Obstruction (CHAOS)


Congenital High Airway Obstruction (CHAOS) is a syndrome in which there is a blockage of the upper airway of the fetus during pregnancy. During development, portions of the amniotic fluid are produced and exhaled by the lungs. If there is a blockage of the airway at any level, fluid from the lungs can back up. Longstanding and severe cases of CHAOS can cause heart failure and can lead to fetal demise. Although most infants will make it to birth without problems, there is great concern that the infant will not be able to breathe at time of delivery. This will require special considerations and treatments, such as an EXIT (Ex Utero Intrapartum Treatment) procedure at birth.


  • Massively enlarged lungs
  • A flattened diaphragm
  • A dilated tracheobronchial tree
  • Fluid in the abdomen
  • Other signs of in utero heart failure (non-immune hydrops) due to complete or nearly complete obstruction of the fetal airway


The airway obstruction in Congenital High Airway Obstruction Syndrome / CHAOS may be due to:

  • The absence of or blockage of the larynx
  • The absence of or blockage of the trachea
  • A cyst which blocks the airway


Congenital High Airway Obstruction Syndrome / CHAOS is detected by ultrasound as a complete or nearly complete obstruction of the upper airway.

The lungs appear extremely large. The diaphragm may be inverted and the heart compressed.

The heart may appear elongated with its chambers compressed by the enlarged large lungs.

The tracheobronchial tubes may be dilated and the fetus may have abnormal breathing movements.

Although a fetus diagnosed with Congenital High Airway Obstruction Syndrome (associated with hydrops) is unlikely to survive without fetal intervention, in some cases the hydrops resolves and the fetus can survive.


The mother should have a detailed ultrasound to detect associated abnormalities. A fetal echocardiogram will detect structural heart disease. A prenatal karyotype (the study of the chromosomes of cells) will confirm chromosomal abnormalities.

The fetus should be followed closely for early signs of hydrops (in utero heart failure). The parents will want to consult with a medical geneticist and a pediatric surgeon to plan for delivery at a tertiary-care hospital that has expertise and experience in the EXIT (ex utero intrapartum treatment) procedure.

Fetal intervention for Congenital High Airway Obstruction Syndrome / CHAOS depends upon the gestational age at diagnosis and the presence or absence of hydrops. In rare cases, less than 30 weeks gestation, where it is known that the fetus is at significant risk for intrauterine death, open fetal surgery may be attempted. After 30 weeks gestation, an EXIT procedure may also be performed in order to obtain an airway at the time of delivery.