Cyanosis and the Clinical Assessment of HypoxemiaCyanosis is a bluish or purplish tinge to the skin and mucous membranes. See the images below. Show
 Before the era of rapid blood gas analysis, clinicians often assessed hypoxemia on clinical grounds alone, primarily by looking for cyanosis in the perioral area and fingers. [1, 2] Clinical assessment of hypoxemia is now known to be notoriously unreliable. A host of factors, from natural skin pigment to room lighting, can affect detection of cyanosis. As with many other physical examination findings, significant interobserver variation occurs in detecting cyanosis. [3] Physicians may diagnose cyanosis as an indicator of hypoxemia when the patient has normal oxygen saturation; alternatively, physicians may miss cyanosis when it should be present (the patient has very low oxygen saturation with normal hemoglobin). [4] Approximately 5 g/dL of unoxygenated hemoglobin in the capillaries generates the dark blue color appreciated clinically as cyanosis. For this reason, patients who are anemic may be hypoxemic without showing any cyanosis. Ancillary signs and symptoms of hypoxemia (eg, tachycardia, tachypnea, mental status changes) are nonspecific and of no value in reliably detecting hypoxemia. For example, patients may be dyspneic at rest for reasons other than hypoxemia (ie, they have normal PaO2 and SaO2). Conversely, many patients who are chronically hypoxemic (low PaO2 and/or low SaO2) are perfectly lucid and without any obvious physical signs of their low oxygen state (at least while at rest). Generation of CyanosisThe requirement of 5 g/dL of reduced (ie, deoxygenated) hemoglobin in the capillaries translates into a reduced hemoglobin content of 3.4 g/dL in arterial blood. [5] For this reason, patients with normal hemoglobin manifest cyanosis at higher SaO2 values than patients with anemia. Refer to the image below and consider the following examples:
See the image below. If hypoxemia is suspected for any reason, some measurement of the oxygen level is necessary (eg, arterial blood gas determination, pulse oximetry). No reliable alternative is available to measurement of PaO2 or SaO2 when diagnosing hypoxemia or assessing the need for supplemental oxygen therapy. [6] At the same time, one should not rely on the absence of cyanosis as reassurance that hypoxemia is not present. Most often, cyanosis is detected in the lips and fingers. See the images below. A case report of Eisenmenger syndrome (interrupted aortic arch with ventricular septal defect) in a 31-year-old pregnant woman discusses the rare condition of differential cyanosis. [7] In this situation, cyanosis is evident in both the fingers and the toes, but SaO2 level (measured by pulse oximetry) is much lower in the toes. Other Causes of CyanosisMethemoglobinNormal hemoglobin unbound to oxygen is called reduced hemoglobin and is symbolized HbFe+2. Methemoglobin (metHb), the oxidized form of hemoglobin, is HbFe+3. Normally, as much as 2% of hemoglobin is in the form of metHb. Because metHb is unable to bind with oxygen, arterial oxygen saturation is reduced by the same amount that metHb is increased. MetHb imparts an intense bluish tinge to the skin; therefore, the cyanosis that comes with methemoglobinemia is not related to reduced hemoglobin but to oxidized hemoglobin. [8, 9] Methemoglobinemia usually occurs as a drug reaction, especially to nitrite or nitrate-containing compounds (eg, nitroglycerin) and to some topical anesthetics. Dahshan and Donovan report a case of severe methemoglobinemia from topical benzocaine in a toddler. [10] Dapsone, a drug used in HIV and non-HIV conditions, can also cause methemoglobinemia. Although excess metHb reduces the measured SaO2, PaO2 is not affected; this is because metHb does not affect transfer of oxygen from the atmosphere to the lungs. A low PaO2 in a patient with excess metHb suggests a concomitant pulmonary problem. MetHb can be measured in a co-oximeter, a companion to the blood gas machine available in most hospital blood gas laboratories. The co-oximeter also measures carboxyhemoglobin, hemoglobin content, and SaO2. Note that standard pulse oximeters, which measure SaO2 using 2 wavelengths of light, do not measure metHb (or carboxyhemoglobin). However, a new generation of pulse oximeters that uses 8 wavelengths of light does have the ability to measure carboxyhemoglobin and metHb (Barker 2006).of light does have the ability to measure COHb and metHb. [11] SulfhemoglobinSulfhemoglobinemia is a rare condition caused by sulfur binding with hemoglobin so that oxygen cannot be bound. Unlike metHb, the iron moiety remains in the reduced state (HbFe+2). Sulfhemoglobin is similar to metHb in causing low SaO2 but not affecting PaO2 and in imparting an intense bluish color to the skin. Peripheral cyanosisPeripheral cyanosis is a dusky or bluish tinge to the fingers and toes and may occur with or without central cyanosis (ie, with or without hypoxemia). When unaccompanied by hypoxemia, as determined by blood gas analysis, peripheral cyanosis is caused by peripheral vasoconstriction. PseudocyanosisPseudocyanosis is a bluish tinge to the skin and/or mucous membranes that is not associated with either hypoxemia or peripheral vasoconstriction. Most causes are related to metals (eg, silver nitrate, silver iodide, silver, lead) or drugs (eg, phenothiazines, amiodarone, chloroquine hydrochloride). One report describes blue-gray discoloration in a man who for years ingested colloidal silver for a urinary tract infection [12] ; his oxygen levels were normal. One report describes a girl with intensely blue skin from food coloring. [13] Consider pseudocyanosis when the patient has no cardiopulmonary symptoms and the skin does not blanch under pressure. To be sure of the diagnosis, obtain a pulse oximetry or arterial blood gas measurement.
Author Specialty Editor Board Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference Disclosure: Received salary from Medscape for employment. for: Medscape. Chief Editor Zab Mosenifar, MD, FACP, FCCP Geri and Richard Brawerman Chair in Pulmonary and Critical Care Medicine, Professor and Executive Vice Chairman, Department of Medicine, Medical Director, Women's Guild Lung Institute, Cedars Sinai Medical Center, University of California, Los Angeles, David Geffen School of Medicine Zab Mosenifar, MD, FACP, FCCP is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, American Federation for Medical Research, American Thoracic Society Disclosure: Nothing to disclose. Additional Contributors Michael Peterson, MD Chief of Medicine, Vice-Chair of Medicine, University of California, San Francisco, School of Medicine; Endowed Professor of Medicine, University of California, San Francisco-Fresno, School of Medicine Michael Peterson, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, American Thoracic Society Disclosure: Nothing to disclose. When checking a patient for signs of cyanosis the tech should note the coloration of the?Skin Color
Purple or bluish skin: This can be is a sign of cyanosis. This typically indicates low blood oxygen. If this is accompanied by dyspnea (shortness of breath) or bradypnea (slow respiration), it can be a sign of hypoxia (lack of oxygen). 1.
When a patient needs to void during an examination in the imaging department?Patient Care Final. Which of the following statements is true with respect to taking a medical history for a radiographic examination?Which of the following statements is true with respect to taking a medical history for a radiographic examination? It is always taken by the radiologist. It includes pertinent information about the patient and indicates the reason for the examination.
Which of the following blood pressure readings would fall within the range of the new normal?The new blood pressure scale is as follows: Normal blood pressure: less than 120 mmHg systolic; less than 80 mmHg diastolic. Elevated blood pressure: 120 to 129 mmHg systolic; less than 80 mmHg diastolic.
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When checking a patient for signs of cyanosis the radiographer should note the coloration of the?
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