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INTRODUCTION

Bluish discoloration of the skin and/or mucous membranes is usually due to elevated quantity of reduced hemoglobin [>40 g/L (>4 g/dL)] in the capillary blood vessels. Findings are most apparent in the lips, nail beds, ears, and malar eminences.

CENTRAL CYANOSIS

Results from arterial desaturation or presence of an abnormal hemoglobin. Usually evident when arterial saturation is ≤85%, or ≤75% in dark-skinned individuals. Etiologies include:

  1. Impaired pulmonary function: Poorly ventilated alveoli or impaired oxygen diffusion; most frequent in pneumonia, pulmonary edema, and chronic obstructive pulmonary disease (COPD); in COPD with cyanosis, polycythemia is often present.

  2. Anatomic vascular shunting: Shunting of desaturated venous blood into the arterial circulation may result from congenital heart disease or pulmonary AV fistula.

  3. Decreased inspired O2: Cyanosis may develop in ascents to altitudes >4000 m (>13,000 ft).

  4. Abnormal hemoglobins: Methemoglobinemia, sulfhemoglobinemia, and mutant hemoglobins with low oxygen affinity (see Chap. 104, HPIM-18).

PERIPHERAL CYANOSIS

Occurs with normal arterial O2 saturation with increased extraction of O2 from capillary blood caused by decreased localized blood flow. Contributors include vasoconstriction due to cold exposure, decreased cardiac output (e.g., in shock, Chap. 12), heart failure (Chap. 133), and peripheral vascular disease (Chap. 135) with arterial obstruction or vasospasm (Table 40-1). Local (e.g., thrombophlebitis) or central (e.g., constrictive pericarditis) venous hypertension intensifies cyanosis.

TABLE 40-1CAUSES OF CYANOSIS

APPROACH TO THE PATIENT Cyanosis

  • Inquire about duration (cyanosis since birth suggests congenital heart disease) and exposures (drugs or chemicals that result in abnormal hemoglobins).

  • Differentiate central from peripheral cyanosis by examining nailbeds, lips, and mucous membranes. Peripheral cyanosis is most intense in nailbeds and may resolve with gentle warming of extremities.

  • Check for clubbing, i.e., selective enlargement of the distal segments of fingers and toes, due to proliferation of connective tissue. Clubbing may be hereditary, idiopathic, or acquired in association with lung cancer, infective endocarditis, bronchiectasis, or hepatic cirrhosis. Combination of clubbing and cyanosis is frequent in congenital heart disease and occasionally in pulmonary disease (lung abscess, pulmonary AV shunts, but not with uncomplicated obstructive lung disease).

  • Examine chest for evidence of pulmonary disease, pulmonary edema, or murmurs associated with congenital heart disease.

  • If cyanosis is localized to an extremity, evaluate for peripheral vascular obstruction.

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