You are the O&G intern called to the labour floor to assist at the LSCS of Harry Ingham, who is a term infant being delivered by LSCS for foetal distress.
On delivery Harry is crying and breathing well, but is cyanosed. His colour does not change with the delivery of oxygen via mask.
The paediatric registrar is concerned that Harry has a heart problem.
Normal Foetal Circulation:
Blood from the placenta enters and returns to the foetus through the vessels in the umbilical cord. Blood then goes to the liver and splits into 2 main branches. The blood then reaches the inferior vena cava, a major vein to the heart. Blood enters the right atrium. Most of the blood flows to the left side through the foramen ovale. Blood then passes into the left ventricle and then to the aorta. From the aorta, blood is sent to the head and upper extremities. After circulating there, the blood returns to the right atrium of the heart through the superior vena cava. About one third of the blood entering the right atrium does not flow through the foramen ovale, but, instead, stays in the right side of the heart, eventually flowing into the pulmonary artery.
Because the placenta does the work of exchanging oxygen and carbon dioxide through the mother's circulation, the foetal lungs are not used for breathing. Instead of blood flowing to the lungs to pick up oxygen and then flowing to the rest of the body, the foetal circulation shunts most of the blood away from the lungs. In the foetus, blood is shunted from the pulmonary artery to the aorta through a connecting blood vessel called the ductus arteriosus.
Changes at Birth:
With the first breaths of air the baby takes at birth, the foetal circulation changes. A larger amount of blood is sent to the lungs to pick up oxygen.
Causes of Cyanosis at Birth:
Tetralogy of Fallot:
Of the four components that comprise Fallot's tetralogy (VSD, pulmonary stenosis, right ventricular hypertrophy, overriding aorta) the important ones are pulmonary stenosis and the VSD.
In Tetralogy, the VSD is always large and severity refers to the degree of pulmonary outflow obstruction. Mild Tetralogy (i.e. with mild RVOTO) may actually have a pure left to right shunt and will function like a simple large VSD (so called "pink Tetralogy"). As the RVOTO gets more severe, the shunt across the VSD becomes less left to right and will then reverse to allow a right to left shunt which will result in systemic desaturation. Progressive RVOTO will result in progressive desaturation/cyanosis. Children with this condition are generally repaired within the first 6-12 months of life.
Transposition of the Great Arteries:
In this condition the aorta and pulmonary arteries arise from the incorrect ventricles. Systemic venous blood is directed through the right side of the heart back into the aorta and pulmonary venous blood through the left side of the heart back into the pulmonary circulation. Survival is dependent on transfer of blood across from each circuit into the other via a foramen ovale, ductus arteriosus or a septal defect. Affected infants generally survive for several days or even weeks because of shunting through the foramen ovale and/or ductus arteriosus, but few live longer than a month without help, unless they have a coexisting septal defect, e.g. a VSD.
Tricuspid Atresia:
In this malformation the tricuspid valve is blocked completely and there is no communication between the right atrium and ventricle. Systemic venous blood passes via the foramen ovale or an ASD into the left side of the heart, and at ventricular or arterial level a left-to-right shunt exists (via a VSD or PDA). This allows blood to perfuse the pulmonary circulation, usually in reduced amounts.
Transposition of the great arteries is a congenital heart defect. Due to abnormal development of the foetal heart during the first 8 weeks of pregnancy, the large vessels that take blood away from the heart to the lungs, or to the body, are improperly connected.
In transposition of the great arteries, the aorta is connected to the right ventricle, and the pulmonary artery is connected to the left ventricle. Oxygen-poor blood returns to the right atrium from the body, passes through the right atrium and ventricle, and then goes into the misconnected aorta back to the body. Oxygen-rich blood returns to the left atrium from the lungs, passes through the left atrium and ventricle, and then goes into the pulmonary artery and back to the lungs.
Two separate circuits are formed - one that circulates oxygen-poor blood from the lungs back to the lungs, and another that recirculates oxygen-rich blood from the body back to the body.
Other heart defects are often associated with TGA, and they actually may be necessary in order for an infant with transposition of the great arteries to live. An opening in the atrial or ventricular septum will allow blood from one side to mix with blood from another.
Tetralogy of Fallot:
Tetralogy of Fallot is a complex condition of several congenital defects that occur due to abnormal development of the foetal heart during the first 8 weeks of pregnancy. These problems include:
Blood Flow in Tetralogy of Fallot:
"Tet Spells": Increased intrathoracic pressure from crying or stress worsens the R-L shunt and causes a cyanotic episode characterized by marked pallor or cyanosis with dyspnoea and distress. Loss of consciousness may occur.
Tricuspid Atresia:
Tricuspid valve completely blocked - only way for blood to get to lungs is via a Patent Foramen Ovale AND a VSD. Systemic venous blood passes via the foramen ovale or an ASD into the left side of the heart, and at ventricular or arterial level a left-to-right shunt exists (via a VSD or PDA).
Pulmonary Atresia:
Complete occlusion of pulmonary valve. Need patent PDA to survive. Will require emergency surgery and medical management.