<unk>  is the condition that there is inadequate oxygen delivery to peripheral tissue. Oxygen in the blood is carried in two physiologic states. Approximately 2% is dissolved in plasma and the other 98% is bound to hemoglobin. In central<unk>  there is increased level of deoxyhemoglobin around 3-5 g/dl.  In peripheral<unk>  there is  increased oxygen extraction by the peripheral tissues. Several factors can affect the appearance of<unk>  including skin pigmentation,Hemoglobin (Hb) levels, oxygen affinity to the hemoglobin (Hb).<unk>  was first described by deSenac who was the physician for King Louis XV in 1749. He described it as the mixture of arterial and venous blood due to an abnormal connection between the two sides of the heart.  In 1761, Morgagini showed association of<unk>  with pulmonary stenosis due to stasis of blood.<unk>  was described by Sandifort, a European, in 1777 as a "blue boy"  with tetralogy of Fallot. In 1892, Vaquez described the first case of polycythemia, as a cause of<unk> . In 1919, Christen Lundsgaard quantified the amount of blood required to be deoxygenated to give the bluish discoloration of<unk> . Blalock and Taussid performed the first anastomosis of subclavian to pulmonary artery on November 9, 1944 to lessen the<unk>  in tetralogy of Fallot. United States' Olympian and gold medalist Shaun White was born with tetralogy of Fallot and had<unk>  because of that.<unk>   may be classified into two groups including  central<unk>  and peripheral<unk> . Right to left shunt in congenital heart disease causes central<unk> . Secondary erythrocytosis (increased red blood cell mass due to hypoxia) and polycythemia (neoplastic proliferation of red blood cell) are different conditions and need different evaluation. Two mechanisms involved in the development of<unk>  including systemic arterial oxygen desaturation and increased oxygen absorption by tissues.<unk>  is evident when arterial oxygen saturation falls below 85% or the concentration of deoxygenated hemoglobin (Hb) exceeds 5 gm/dl. Common causes  in the development of<unk>  include congenital heart diseases with right to left shunt, presence of abnormal hemoglobin, carbon monoxide poisoning, respiratory disorders associated with impaired gas exchange, impaired gas diffusion via the alveoli, embolism, pulmonary arteriovenous malformations, cold exposure, and raynaud's phenomenon. Different causes of<unk>  may include pulmonary, cardiovascular, hematological, neurological, and vascular diseases. Prenatal echocardiography and genetic testing are useful methods for early detection of cyanotic congenital heart disease. Postnatal pulse oximetry is recommended for diagnosis of cyanotic congenital heart disease. Central<unk>   in the first hours or days of life in the neonate may happen and implies life-threatening conditions such as congenital cardiac abnormalities , airway obstruction , central nervous system problem, hemoglobinopathy. Peripheral<unk>  may happen in neonate called acrocyanosis. Prognosis is generally good if the underlying causes of<unk>  are determined and treated. Peripheral<unk>  improves with oxygen therapy. Conversely, central<unk>  does not respond to oxygen therapy because of the underlying  intrapulmonary or intracardiac shunt which is responsible for mixing the nonoxygenated  venous blood  and oxygenated arterial blood. All causes of central<unk>  may cause peripheral<unk> .<unk>  is a symptom of a disease process, then  physical examination may include tachypnea, tachycardia, abnormal heart sounds or murmurs, wheezing, crackles, fever, clubbing, edema. In every neonate presented with<unk>  and shock, congenital heart disease dependent on patency ductus arteriosus should be considered. The physiologic constriction of ductus arteriosus after birth in a neonate whose pulmonary blood flow or aortic blood flow is dependent on PDA leads to shock and collapse in the neonate. Infusion of prostaglan E1  is life-saving and keeps patency ductus arteriosus. Treatment of underlying causes of<unk>  such as tamponade or cardiogenic shock  due to low cardiac output state or peripheral vasoconstriction is considered. Cardiac defects causing central<unk>  include Transposition of the great arteries, Tetralogy of fallot, Tricuspid atresia, Truncus arteriosus,Total anomalous pulmonary venous connection, Ebstein anomaly, critical Pulmonary stenosis or atresia, functional single ventricle. The palliative surgical shunt maybe done in such lesions to increase pulmonary blood flow even in the presence of<unk> . Complete repair procedure leads to relief of<unk>  and shunt and also causes long-term complications. Effective measures for primary prevention in neonatal<unk>  include prenatal echocardiography and genetic testing for detecting congenital heart defects and prenatal corticosteroid therapy for prevention of neonatal respiratory distress syndrome and development of lung maturation. Secondary prevention in cyanotic congenital heart disease includes obtaining EKG Exercise stress test, Holter monitoring, Transthoracic echocardiography, Cardiac MRI, Cardiac CT Scan, Pulse oximetry every 12-60 months based on the stage of disease.
Cyanosis
Polycythemia
Acrocyanosis
Myxedema
Dry skin
Retinopathy
Dry eyes
Color blindness