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Chapter 035. Hypoxia and Cyanosis (Part 4)

Differential Diagnosis CENTRAL CYANOSIS (Table 35-1) Decreased SaO2 results from a marked reduction in the Pa O2. This reduction may be brought about by a decline in the FIO2 without sufficient compensatory alveolar hyperventilation to maintain alveolar PO2. Cyanosis usually becomes manifest in an ascent to an altitude of 4000 m (13,000 ft). Table 35-1 Causes of Cyanosis Central Cyanosis Decreased arterial oxygen saturation Decreased atmospheric pressure—high altitude Impaired pulmonary function Alveolar hypoventilation Uneven relationships between pulmonary ventilation and perfusion (perfusion of hypoventilated alveoli) Impaired oxygen diffusion Anatomic shunts Certain types of congenital heart disease Pulmonary arteriovenous fistulas Multiple small intrapulmonary shunts . | Chapter 035. Hypoxia and Cyanosis Part 4 Differential Diagnosis CENTRAL CYANOSIS Table 35-1 Decreased SaO2 results from a marked reduction in the PaO2. This reduction may be brought about by a decline in the FIO2 without sufficient compensatory alveolar hyperventilation to maintain alveolar PO2. Cyanosis usually becomes manifest in an ascent to an altitude of 4000 m 13 000 ft . Table 35-1 Causes of Cyanosis Central Cyanosis Decreased arterial oxygen saturation Decreased atmospheric pressure high altitude Impaired pulmonary function Alveolar hypoventilation Uneven relationships between pulmonary ventilation and perfusion perfusion of hypoventilated alveoli Impaired oxygen diffusion Anatomic shunts Certain types of congenital heart disease Pulmonary arteriovenous fistulas Multiple small intrapulmonary shunts Hemoglobin with low affinity for oxygen Hemoglobin abnormalities Methemoglobinemia hereditary acquired Sulfhemoglobinema acquired Carboxyhemoglobinemia not true cyanosis Peripheral Cyanosis Reduced cardiac output Cold exposure Redistribution of blood flow from extremities Arterial obstruction Venous obstruction Seriously impaired pulmonary function through perfusion of unventilated or poorly ventilated areas of the lung or alveolar hypoventilation is a common cause of central cyanosis Chap. 246 . This condition may occur acutely as in extensive pneumonia or pulmonary edema or chronically with chronic pulmonary diseases e.g. emphysema . In the latter situation secondary polycythemia is generally present and clubbing of the fingers see below may occur. Another cause of reduced SaO2 is shunting of systemic venous blood into the .