In a state of hypercapnia, the accumulation of carbon dioxide in the blood causes the pH of the blood to drop, leading to a state of respiratory acidosis. Hypercapnia is caused by hypoventilation or when the alveoli are ventilated but not perfused. This level is measured by the PaCO2 level in an ABG test and is indicated when the PaCO2 level is greater than 45. Hypercapnia, also referred to as hypercarbia, is an elevated level of carbon dioxide in the blood. Late signs of hypoxia include bluish discoloration of the skin and mucous membranes called cyanosis. As hypoxia worsens, the patient’s level of consciousness and vital signs will worsen with an increased respiratory rate and heart rate and decreased pulse oximetry readings. Hypoxemia is a specific type of hypoxia that is defined as decreased partial pressure of oxygen in the blood (PaO2) indicated in an arterial blood gas (ABG) result.Įarly signs of hypoxia are anxiety, confusion, and restlessness. Hypoxia has many causes, ranging from respiratory and cardiac conditions to anemia. Hypoxia is defined as a reduced level of tissue oxygenation. The SaO2 level is also calculated in ABG results, which is the calculated arterial oxygen saturation level. The normal range of pH level for arterial blood is 7.35-7.45, and the normal range for the bicarbonate ( HCO3-) level is 22-26. The normal PaCO2 level of a healthy adult is 35-45 mmHg. It is typically used to determine if sufficient ventilation is occurring at the alveolar level. The PaCO2 level measures the pressure of carbon dioxide dissolved in the blood and how well carbon dioxide is able to move out of the body. The partial pressure of carbon dioxide in the arterial blood is the PaCO2level. The PaO2 reading is more accurate than a SpO2 reading because it is not affected by hemoglobin levels. The normal PaO2 level of a healthy adult is 80 to 100 mmHg. PaO2 measures the pressure of oxygen dissolved in the arterial blood and how well oxygen is able to move from the lungs into the blood. The partial pressure of oxygen in the arterial blood is referred to as PaO2. ABG results indicate oxygen, carbon dioxide, pH, and bicarbonate levels. An ABG is a blood sample that is typically drawn from the radial artery by a respiratory therapist. ABG results are often used for patients who have deteriorating or unstable respiratory status requiring emergency treatment. Figure 8.3 Portable Pulse OximeterĪ more specific measurement of oxygen and carbon dioxide in the blood is obtained using an arterial blood gas (ABG). Additionally, other substances can attach to hemoglobin such as carbon monoxide, causing a falsely elevated SpO2. Decreased perfusion of the extremities can also cause inaccurate SpO2 levels because less blood delivered to the tissues causes a false low SpO2. For example, if a patient is severely anemic, the patient has a decreased amount of hemoglobin in the blood available to carry the oxygen, which subsequently affects the SpO2 reading. Although SpO2 is an efficient, noninvasive method for assessing a patient’s oxygenation status, it is not always accurate. For patients with chronic oxygenation conditions such as COPD, the target range for SpO2 is often lower at 88% to 92%. The target range of SpO2 for an adult is 94-98%. This reading refers to the amount of hemoglobin that is saturated. See Figure 8.3 for an image of a pulse oximeter. Measuring Oxygen, Carbon Dioxide, and Acid Base Levelsīecause the majority of oxygen transported in the blood is attached to hemoglobin, a patient’s oxygenation status is easily assessed using pulse oximetry, referred to as SpO2. See Figure 8.2 for an illustration of carbon dioxide transport. Carbon dioxide is transported throughout the body by three major mechanisms: dissolved carbon dioxide, attachment to water as HCO3-, and attachment to the hemoglobin in red blood cells. When oxygenated blood reaches tissues within the body, oxygen is released from the hemoglobin, and carbon dioxide is picked up and transported to the lungs for release on exhalation. When all four hemoglobin structures contain an oxygen molecule, it is referred to as “saturated.” See Figure 8.1 for an image of hemoglobin protein within a red blood cell with four sites for carrying oxygen molecules. Each hemoglobin protein is capable of carrying four oxygen molecules. \)Īlthough the bloodstream carries small amounts of dissolved oxygen, the majority of oxygen molecules are transported throughout the body by attaching to hemoglobin within red blood cells.
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