Which assessment findings would indicate cyanosis in individuals with dark skin?

D Cyanotic Lesions (Table 7.13)

A hyperoxia test is used to evaluate the etiology of cyanosis in neonates. A baseline arterial blood gas (ABG) with saturation at Fio2 = 0.21 is obtained. Then the infant is placed in an oxygen hood at Fio2 = 1 for a minimum of10 minutes, and the ABG is repeated. In cardiac disease, there will not be a significant change in Pao2 following the oxygen challenge test. A Pao2 of >200 after exposure to Fio2 of 1.0 is considered normal, and >150 indicates pulmonary rather than cardiac disease.Note: Pulse oximetry is not useful for following changes in oxygenation once saturation has reached 100% (approximately a Pao2 of >90 mmHg).12–17 SeeTable EC 7.A for interpretation of oxygen challenge test (hyperoxia test).

Table EC 7.A. Interpretation of Oxygen Challenge Test (Hyperoxia Test)

FiO2, Fraction of inspired oxygen;PBF, pulmonary blood flow;PFO, patent foramen ovale.

From Lees MH. Cyanosis of the newborn infant: recognition and clinical evaluation.J Pediatr. 1970;77:484; Kitterman JA. Cyanosis in the newborn infant.Pediatr Rev. 1982;4:13; and Jones RW, Baumer JH, Joseph MC, et al. Arterial oxygen tension and response to oxygen breathing in differential diagnosis of heart disease in infancy.Arch Dis Child. 1976;51:667–673.

D Cyanosis and Oximetry

Cyanosis affects co-oximetry (i.e., blood gas analysis in the laboratory) differently than it affects pulse oximetry (i.e., equipment used at the bedside; see Chapter 20). Because co-oximetry can distinguish deoxyhemoglobin from other abnormal hemoglobin, it indicates hypoxemia only in patients with central cyanosis (i.e., it samples arterial blood and therefore indicates normal oxygen levels in peripheral cyanosis). Pulse oximetry, in contrast, detects the color of the pulsatile waveform in the digit. Although it also indicates hypoxemia in patients with central cyanosis, pulse oximetry may falsely indicate arterial hypoxemia in patients with peripheral cyanosis or with abnormal hemoglobin (see Chapter 20). Both co-oximetry and pulse oximetry indicate normal oxygen levels in pseudocyanosis.

Signs

There is significant interobserver variability in detecting cyanosis on physical examination. Room lighting and temperature may affect examination of the skin and mucous membranes. A patient's natural skin tone, thickness, and pigmentation also may alter findings.

Central cyanosis is often secondary to the shunting of venous unsaturated hemoglobin into the arterial circulation or the presence of abnormal hemoglobin. Central cyanosis is best seen on perioral skin, oral mucosa, or conjunctivae.

Peripheral cyanosis is secondary to vasoconstriction and slow flow of normally oxygenated hemoglobin in arterial blood, allowing for greater oxygen extraction by the tissues. Peripheral cyanosis affects capillary beds and typically is seen in the extremities and nail beds. Differential cyanosis may occur in the upper or lower (or the right or left) half of the body, with the remainder of the body appearing well oxygenated. This form of cyanosis is usually seen in patients with cyanotic heart disease with multiple anomalies.

Vital signs should be obtained from all patients. Temperature is typically normal. Blood pressure and heart rate vary, depending on the cause and acuity of cyanosis. Upper airway obstruction and other signs of respiratory insufficiency should be sought. Intermittent apnea in infants suggests central nervous system immaturity or a central lesion. Infants with cyanosis, increased respiratory depth, periodic apnea episodes, or diaphoresis with feeding may have congenital heart disease. Tachypnea (>60 breaths/min) in a newborn is nonspecific but may indicate a pulmonary disorder, congenital heart disease, infection, metabolic disorder, or gastrointestinal or central nervous system pathology.

The general appearance and mental status are evaluated. The head, eyes, ears, nose, and throat examination may reveal central cyanosis. Fundoscopic examination may detect dilated tortuous veins and papilledema in patients with cyanotic congenital heart disease.3 Jugular venous distention may be seen on the neck examination in patients with pulmonary edema.

The chest examination may reveal crackles, wheezing, or inadequate ventilation. Heart sounds should be assessed for tachycardia, abnormal rhythm, or gallops and the presence and quality of murmurs, especially in the newborn. Central pulse strength should be noted. The abdomen should be examined for the presence of hepatosplenomegaly, pulsatile mass, or abdominal bruit.

Extremity examination includes evaluation of the nail beds for peripheral cyanosis, strength and symmetry of distal pulses, and capillary refill. Evidence of chronic vascular disease, such as hair loss and temperature difference, should be noted. Clubbing of the nails may occur because of increased soft tissue and expansion of the capillary beds (Fig. 11.2). Clubbing may be idiopathic or hereditary but is usually the result of chronic hypoxemic states, such as cyanotic heart disease, infective endocarditis, pulmonary disease (eg, chronic obstructive pulmonary disease, cystic fibrosis) and some gastrointestinal disorders (eg, cirrhosis, Crohn's disease, regional enteritis). Thrombotic events should also be considered in patients with skin and nail bed hemorrhages or end-organ damage (eg, eye, kidney).

BACKGROUND

Cyanosis is a bluish discoloration of the skin, mucous membranes, tongue, lips, or nail beds and is due to an increased concentration of reduced hemoglobin (Hb) in the circulation.1 Clinically evident cyanosis typically occurs at an oxygen saturation of 85% or less.2 Mild cyanosis may be difficult to detect. Cyanosis is usually easier to detect with natural lighting and is typically more difficult to detect in patients with dark skin pigmentation or with anemia. Long-term complications include clubbing, polycythemia, cerebrovascular accident, brain abscess, platelet abnormalities, lower-than-expected IQ, scoliosis, and hyperuricemia.1

Central cyanosis is associated with arterial desaturation and involves the skin, mucous membranes, lips, tongue, and nail beds. Peripheral cyanosis occurs when there is increased oxygen uptake in peripheral tissues; it is not associated with arterial desaturation. Peripheral cyanosis often involves only the extremities.1 Differential cyanosis, in which the upper extremities are pink and the lower extremities are cyanotic, is associated with conditions such as coarctation of the aorta and interrupted aortic arch when there is right-to-left shunting through a patent ductus arteriosus.3 In newborns, acrocyanosis, or blueness of exposed extremities, is common and is typically insignificant. Similarly, isolated circumoral cyanosis due to prominent venous plexuses in the skin is insignificant, as long as cardiac output is normal.1

Differential Diagnosis

Thehyperoxia test is one method of distinguishing cyanotic CHD from pulmonary disease. Neonates with cyanotic CHD usually are unable to significantly raise their arterial blood partial pressure of oxygen (Pao2) during administration of 100% oxygen. This test is usually performed using a hood rather than nasal cannula or face mask, to best guarantee delivery of almost 100% oxygen to the patient. False-positive tests can occur if this is not done correctly. If the Pao2 rises above 150 mm Hg during 100% oxygen administration, an intracardiac right-to-left shunt can usually be excluded. This is not 100% confirmative, however, because some patients with cyanotic CHD may be able to increase their Pao2 to >150 mm Hg because of favorable intracardiac streaming patterns. In patients with pulmonary disease, Pao2 generally increases significantly with 100% oxygen as ventilation-perfusion inequalities are overcome. In infants with cyanosis from a central nervous system disorder, the Pao2 usually normalizes completely during artificial ventilation. Hypoxia in many heart lesions is profound and constant, whereas in respiratory disorders and in PPHN, Pao2 often varies with time or changes in ventilator management. Hyperventilation may improve the hypoxia in neonates with PPHN and only occasionally in those with cyanotic CHD.

Although a significant heart murmur usually suggests a cardiac basis for the cyanosis, several of the more severe cardiac defects (e.g., transposition of the great vessels) may not initially be associated with a murmur. The chest radiograph may be helpful in the differentiation of pulmonary and cardiac disease; in the latter, it indicates whether pulmonary blood flow is increased, normal, or decreased (Fig. 456.1).

Two-dimensional echocardiography with Doppler is the definitive noninvasive test to determine the presence of CHD. Cardiac catheterization is less often used for diagnostic purposes and is usually performed to examine structures that are sometime less well visualized by echocardiography, such as distal branch pulmonary arteries or aortopulmonary collateral arteries in patients with tetralogy of Fallot with pulmonary atresia (seeChapter 457.2), or coronary arteries and right ventricular sinusoids in patients with pulmonary atresia and intact ventricular septum (seeChapter 457.3). If echocardiography is not immediately available to confirm a diagnosis of cyanotic CHD, the clinician caring for a newborn with possible cyanotic CHD should not hesitate to start a prostaglandin infusion (for a possible ductal-dependent lesion). Because of the risk of hypoventilation associated with prostaglandins, a practitioner skilled in neonatal endotracheal intubation must be available.

1 What is the difference between central cyanosis and acrocyanosis?

Cyanosis is a common clinical finding in newborn infants. Central cyanosis is caused by reduced arterial oxygen saturation. Central cyanosis can be associated with life-threatening illnesses such as cardiac, metabolic, neurologic, infectious, and parenchymal and nonparenchymal pulmonary disorders. Normal infants have central cyanosis until up to 5 to 10 minutes after birth as the oxygen saturation rises to 85% to 95% by 10 minutes of age. Persistent cyanosis is always abnormal and should be evaluated and treated promptly. By contrast, acrocyanosis is seen in healthy newborns and it refers to the peripheral cyanosis around the mouth and the extremities including hands and feet. It is caused by benign vasomotor changes that cause peripheral vasoconstriction and increased tissue oxygen extraction. As opposed to in central cyanosis, in acrocyanosis the mucous membranes of the neonate remain pink. This may persist for 24 to 48 hours, and it is usually not pathologic.

117 At what Pao2 does cyanosis develop?

Cyanosis develops when the concentration of desaturated (i.e., reduced) hemoglobin is at least 3 gm/dL centrally or 4 to 6 g/dL peripherally. However, multiple factors affect the likelihood that a given Pao2 will result in clinically apparent cyanosis: anemia (less likely), polycythemia (more likely), reduced systemic perfusion or cardiac output (more likely), and hypothermia (more likely). Cyanosis is generally a sign of significant hypoxia. In a patient with adequate perfusion and a normal hemoglobin, central cyanosis is commonly noted when the Pao2 is about 50 mm Hg.

Cyanosis

Cyanosis is a bluish or purplish tinge to the skin due to very low oxygen saturation (SaO2) and thus excess reduced (deoxygenated) haemoglobin. Approximately 5 g/dL of reduced haemoglobin has to be present in the capillaries to generate the dark blue colour of cyanosis. For this reason, patients who are anaemic may be hypoxaemic without showing any cyanosis.

Peripheral cyanosis is a dusky or bluish tinge to the fingers and toes. When unaccompanied by hypoxaemia, it is caused by peripheral vasoconstriction as in the cold, especially in Raynaud disease.

Central cyanosis (where the colour is also seen in the lips or the mouth) is more serious and is usually an indication of hypoxaemia because of cardiac failure or respiratory disease, or both in cor pulmonale. Many factors, from natural skin pigment to room lighting, can affect detection of cyanosis and, if hypoxaemia is suspected, measurement of the oxygen level is necessary (arterial blood gas determination, pulse oximetry). Central cyanosis is an indication of gross hypoxia; such patients needing conscious sedation must be dealt with in hospital.

8 What is cyanosis?

Cyanosis is bluish discoloration of the skin, mucosa or both due to reduced oxygenation of the blood. Clinically, it becomes evident when the oxygenation of hemoglobin falls below 85%. Two forms of cyanosis are recognized:

Central cyanosis: Both the skin and the mucosa are bluish. Typically, it occurs when the oxygenation of blood is impeded (e.g., adult respiratory distress syndrome), there is shunting of unoxygenated venous blood into the arterial circulation (e.g., cyanotic congenital heart diseases), or hemoglobin cannot take up oxygen (e.g., methemoglobinemia).

Peripheral cyanosis: Also known as acrocyanosis, it is characterized by bluish discoloration of the skin of the fingers and toes or the nose. It is best observed under cold weather conditions. Peripheral cyanosis also occurs in chronic passive congestion. It is related to increased oxygen desaturation that occurs in stagnant blood. Hypovolemic shock is accompanied by cyanosis because of the shunting of blood from the skin into the internal organs.

Cyanosis

Cyanosis refers to a blue color of the skin and mucous membranes due to excessive concentrations of reduced hemoglobin in capillary blood. The oxygen content of capillary blood is assumed to be midway between that of arterial and that of venous blood. Areas with a high blood flow and a small arteriovenous oxygen difference (e.g., the tongue and mucous membranes) will not become cyanotic as readily as those with a low blood flow and a large arteriovenous oxygen difference (e.g., the skin of cold hands and feet). A distinction is therefore made between peripheral cyanosis (acrocyanosis), which is confined to the skin of the extremities, and central cyanosis, which includes the tongue and mucous membranes. Circumoral cyanosis is not an expression of central cyanosis and is rarely pathologic. The absolute concentration of reduced hemoglobin in the capillaries that is necessary to produce cyanosis is between 4 and 6 g/100 mL of blood. This level is usually present when the concentration of reduced hemoglobin in arterial blood exceeds 3 g/100 mL. Clinical cyanosis will occur at different levels of arterial oxygen saturation, depending on the amount of total hemoglobin (Fig. 1.13).

Physiologically, five mechanisms can cause arterial hemoglobin desaturation in the patient who breathes room air at normal altitude: (1) alveolar hypoventilation, (2) diffusion impairment, (3) right-to-left shunting, (4) mismatch of ventilation and perfusion, and (5) inadequate oxygen transport by hemoglobin. Clinically, diffusion impairment is of little importance as a single cause. Imbalance of ventilation and perfusion is by far the most common mechanism and is correctable by administration of 100% oxygen. The physician should therefore look for a change in cyanosis while the patient breathes oxygen.

Observer agreement regarding cyanosis was found to range from poor when assessing acrocyanosis to very good in the evaluation of young children with bronchiolitis. To minimize the variability of this finding, cyanosis is best observed under daylight and with the patient resting in a comfortably warm room. The distribution of cyanosis and the state of peripheral perfusion should be noted. Patients with decreased cardiac output and poor peripheral perfusion can be cyanotic despite normal arterial hemoglobin saturation. Some patients may become cyanotic only during exercise, a common response when restrictive lung disease reduces the pulmonary capillary bed and the transit time of erythrocytes becomes too short for full saturation to occur during episodes of increased cardiac output. Congenital heart disease in infants may lead to differential cyanosis, which affects only the lower part of the body (e.g., in patients with preductal coarctation of the aorta). Less commonly, only the upper part of the body is cyanotic (e.g., in patients with transposition of the great arteries in association with patent ductus arteriosus, and pulmonary to aortic shunting).

The clinical impression of cyanosis is usually confirmed by an arterial blood gas analysis or, more commonly, by pulse oximetry. Pulse oximetry, however, will not take into account the presence of abnormal hemoglobin. For example, in methemoglobinemia the oxygen-carrying capacity of blood is reduced and patients may appear lavender blue, but pulse oximetry may overestimate oxygen saturation in arterial blood (SaO2). The blood of newborn infants, conversely, can be well saturated and not cyanotic at lower arterial oxygen tensions because of the different oxygen-binding curve of fetal hemoglobin. In the patient with hypoxemia who does not present with cyanosis (e.g., the anemic patient), the physician has to pay particular attention to other clinical signs and symptoms of hypoxia. These include tachypnea and tachycardia, exertional dyspnea, hypertension, headache, and behavioral changes. With more severe hypoxia, there may be visual disturbance, somnolence, hypotension, and ultimately coma. In addition, the patient may have an elevated level of carbon dioxide. Depending on how rapidly and to what extent the level of carbon dioxide has risen, the clinical signs of hypercarbia will largely reflect vascular dilatation. These signs include flushed, hot hands and feet; bounding pulses; confusion or drowsiness; muscular twitching; engorged retinal veins; and, in the most severe cases, papilledema and coma.