Cyanosis

The circulating quantity of reduced hemoglobin is elevated [_50 g/L (_5

g/dL)] resulting in bluish discoloration of the skin and/or mucous membranes.

Central Cyanosis

Results from arterial desaturation. Usually evident when arterial saturation is

_85%. Cyanosis may not be detected until saturation is 75% in dark-skinned

individuals.

• 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.

• Anatomic vascular shunting: Shunting of desaturated venous blood into the

arterial circulation may result from congenital heart disease or pulmonary AV

fistula.

• Decreased inspired O2: Cyanosis may develop in ascents to altitudes_2400

m (_8000 ft).

• Abnormal hemoglobins: Methemoglobinemia,sulfhemoglobinemia, and

mutant hemoglobins with low oxygen affinity (see HPIM-16,Chap. 91).

Peripheral Cyanosis

Occurs with normal arterial O2 saturation with increased extraction of O2 from

capillary blood caused by decreased localized blood flow. Vasoconstriction due

to cold exposure,decreased cardiac output (in shock, Chap. 14),heart failure

(Chap 126),and peripheral vascular disease (Chap. 128) with arterial obstruction

or vasospasm (Table 46-1). Local (e.g.,thrombophlebitis) or central (e.g., constrictive

pericarditis) venous hypertension intensifies cyanosis.

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

Approach to the Patient

• 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 most intense in nailbeds and may

resolve with gentle warming of extremities.

• Check for clubbing of fingers and toes; clubbing is the selective enlargement

of the distal segments of fingers and toes. Clubbing may be hereditary,idiopathic,

or acquired and is associated with a variety of disorders. Combination

of clubbing and cyanosis is frequent in congenital heart disease and occasionally

with 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.

• Obtain arterial blood gas to measure systemic O2 saturation. Repeat while

pt inhales 100% O2; if saturation fails to increase to _95%,intravascular

shunting of blood bypassing the lungs is likely (e.g.,right-to-left intracardiac

shunts).

• Evaluate abnormal hemoglobins by hemoglobin electrophoresis,spectroscopy,

and measurement of methemoglobin level.