Cyanosis

Cyanosis is a blue coloration of the skin and mucous membranes due to the presence of greater than, or equal to, 2.5 g/dL of deoxygenated hemoglobin in blood vessels near the skin surface.

A cyanotic baby. Note purple nailbeds.

Cyanosis in the newborn is defined as an arterial saturation less than 90% and a PO2 less than 60 MMHg. A careful history should be obtained from the parents with particular attention to any problems with feeding, breathing, or diaphoresis (sweating). The most common causes include :

•         Intrinsic pulmonary disease,

•        Congenital heart disease, 

•        Central nervous system depression with hypoventilation, 

•        Blood:

                                    o    Methemoglobinemia,
                                    o    Polycythemia.

•        Others:               

                                    o    High altitude

                                    o    Hypothermia.

The character of the infant’s respirations should be noted. Tachypnea is usually associated with the presence of pulmonary edema and increased pulmonary flow. Auscultation of the lung fields and precordium may reveal rales or murmurs, and abdominal examination may reveal hepatomegaly. Peripheral perfusion, pulses, and coloration should be assessed. Pulse oximetry and an arterial blood gas determinations should be performed immediately if cyanosis is present or suspected.

These measurements should be performed initially on room air to serve as a baseline. Subsequent measurements should be obtained on 100% oxygen and may help to differentiate between cardiogenic and non-cardiogenic causes of neonatal cyanosis. Infants with neurogenic or primary pulmonary causes of cyanosis will demonstrate substantial increases in arterial blood saturation on 100% oxygen while infants with congenital heart disease show minimal elevation. In general, patients with a PO2 greater than 250 mmHg on 100% oxygen will have a non-cardiac problem; conversely, those with PO2 less than 100 mmHg will likely have congenital heart disease.

There are three general sources of arterial desaturation in neonates with structural heart disease:

1. Lesions with decreased pulmonary blood flow (tetralogy of Fallot, severe pulmonary stenosis/atresia, and tricuspid atresia);
2. Admixture lesions, in which desaturated systemic venous blood mixes with intracardiac blood, and then enters the aorta (transposition of great vessels, partial anomalous pulmonary venous drainage); and
3. Lesions with increased pulmonary blood flow and pulmonary edema, in which diffusion barriers and intrapulmonary shunting prevent proper oxygenation (truncus arteriosus).