Chapter 035. Hypoxia and Cyanosis (Part 5)

PERIPHERAL CYANOSIS Probably the most common cause of peripheral cyanosis is the normal vasoconstriction resulting from exposure to cold air or water. When cardiac output is reduced, cutaneous vasoconstriction occurs as a compensatory mechanism so that blood is diverted from the skin to more vital areas such as the central nervous system and heart, and cyanosis of the extremities may result even though the arterial blood is normally saturated.Arterial obstruction to an extremity, as with an embolus, or arteriolar constriction, as in cold-induced vasospasm (Raynauds phenomenon, Chap. 243), generally results in pallor and coldness, and there may be associated...
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Chapter 035. Hypoxia and Cyanosis (Part 5) Chapter 035. Hypoxia and Cyanosis (Part 5) PERIPHERAL CYANOSIS Probably the most common cause of peripheral cyanosis is the normalvasoconstriction resulting from exposure to cold air or water. When cardiac outputis reduced, cutaneous vasoconstriction occurs as a compensatory mechanism sothat blood is diverted from the skin to more vital areas such as the central nervoussystem and heart, and cyanosis of the extremities may result even though thearterial blood is normally saturated. Arterial obstruction to an extremity, as with an embolus, or arteriolarconstriction, as in cold-induced vasospasm (Raynauds phenomenon, Chap. 243),generally results in pallor and coldness, and there may be associated cyanosis.Venous obstruction, as in thrombophlebitis, dilates the subpapillary venousplexuses and thereby intensifies cyanosis. Approach to the Patient: CyanosisCertain features are important in arriving at the cause of cyanosis: 1. It is important to ascertain the time of onset of cyanosis. Cyanosispresent since birth or infancy is usually due to congenital heart disease. 2. Central and peripheral cyanosis must be differentiated. Evidenceof disorders of the respiratory or cardiovascular systems are helpful.Massage or gentle warming of a cyanotic extremity will increase peripheralblood flow and abolish peripheral, but not central, cyanosis. 3. The presence or absence of clubbing of the digits (see below)should be ascertained. The combination of cyanosis and clubbing isfrequent in patients with congenital heart disease and right-to-left shunting,and is seen occasionally in patients with pulmonary disease such as lungabscess or pulmonary arteriovenous fistulae. In contrast, peripheralcyanosis or acutely developing central cyanosis is not associated withclubbed digits. 4. PaO2 and SaO2 should be determined, and in patients with cyanosisin whom the mechanism is obscure, spectroscopic examination of the bloodperformed to look for abnormal types of hemoglobin (critical in thedifferential diagnosis of cyanosis).CLUBBING The selective bullous enlargement of the distal segments of the fingers andtoes due to proliferation of connective tissue, particularly on the dorsal surface, istermed clubbing; there is also increased sponginess of the soft tissue at the base ofthe nail. Clubbing may be hereditary, idiopathic, or acquired and associated with avariety of disorders, including cyanotic congenital heart disease (see above),infective endocarditis, and a variety of pulmonary conditions (among themprimary and metastatic lung cancer, bronchiectasis, lung abscess, cystic fibrosis,and mesothelioma), as well as with some gastrointestinal diseases (includinginflammatory bowel disease and hepatic cirrhosis). In some instances it isoccupational, e.g., in jackhammer operators. Clubbing in patients with primary and metastatic lung cancer,mesothelioma, bronchiectasis, and hepatic cirrhosis may be associated withhypertrophic osteoarthropathy. In this condition, the subperiosteal formation ofnew bone in the distal diaphyses of the long bones of the extremities causes painand symmetric arthritis-like changes in the shoulders, knees, ankles, wrists, andelbows. The diagnosis of hypertrophic osteoarthropathy may be confirmed bybone radiographs. Although the mechanism of clubbing is unclear, it appears to besecondary to a humoral substance that causes dilation of the vessels of thefingertip. FURTHER READINGS Fawcett RS et al: Nail abnormalities: Clues to systemic disease. Am FamPhysician 69:1417, 2004 [PMID: 15053406] Giordano FJ: Oxygen, oxidative stress, hypoxia, and heart failure. J ClinInvest 115:500, 2005 [PMID: 15765131] Griffey RT et al: Cyanosis. J Emerg Med 18:369, 2000 [PMID: 10729678] Hackett PH, Roach RC: Current concepts: High altitude illness. N Engl JMed 345:107, 2001 [PMID: 11450659] Levy MM: Pathophysiology of oxygen delivery in respiratory failure. Chest128(Suppl 2):547S, 2005 Michiels C: Physiological and pathological responses to hypoxia. Am JPathol 164:1875, 2004 [PMID: 15161623] Tsai BMet al: Hypoxic pulmonary vasoconstriction in cardiothoracicsurgery: Basic mechanisms to potential therapies. Ann Thorac Surg 78:360, 2004[PMID: 15223473]