{"id":2227,"date":"2015-04-14T16:29:24","date_gmt":"2015-04-14T16:29:24","guid":{"rendered":"http:\/\/opentextbc.ca\/clinicalskills\/?post_type=chapter&p=2227"},"modified":"2021-05-20T20:47:28","modified_gmt":"2021-05-20T20:47:28","slug":"5-1-principles","status":"publish","type":"chapter","link":"https:\/\/opentextbc.ca\/clinicalskills\/chapter\/5-1-principles\/","title":{"raw":"5.2 Principles","rendered":"5.2 Principles"},"content":{"raw":"The air we breathe is made up of various gases, 21% of which is oxygen. Therefore, a patient who is receiving\u00a0no supplemental oxygen therapy is still receiving\u00a0oxygen from the air.\u00a0This amount of oxygen is adequate provided that the patient's airway is not compromised and there is sufficient\u00a0hemoglobin\u00a0in the blood. The\u00a0cardiovascular system must also be intact and able to circulate blood to all body tissues. If any of these systems fail, the patient will require\u00a0supplemental\u00a0oxygen to\u00a0increase the likelihood that adequate levels of oxygen will reach all vital body tissues necessary to sustain life.\r\n

Oxygen in the Blood<\/h2>\r\nHemoglobin (Hgb) holds oxygen in reserve until the metabolic demands of the body require more\u00a0oxygen.\u00a0The Hgb then moves\u00a0the oxygen to the plasma for transport to the tissues.\u00a0The body's demand for oxygen is affected by activity, metabolic status, temperature, and level of anxiety.\u00a0The ability of Hgb to move\u00a0the oxygen to the tissues depends on a number of factors, such as oxygen supply, ventilatory effectiveness, nutrition, cardiac output, hemoglobin level, smoking, drug use, and underlying disease.\u00a0Any one of these factors can\u00a0potentially\u00a0impede the supply and transport of oxygen to the tissues.\r\n

Measurement of Oxygen in the Blood<\/h2>\r\nThe vast majority of oxygen carried in the blood is attached to hemoglobin and\u00a0can be assessed by\u00a0monitoring the oxygen saturation through pulse oximetry (SpO2<\/sub>).The target range for oxygen saturation as measured by blood analysis (SaO2<\/sub>), such as arterial blood gas, is 92% to 98% for a normal adult. Arterial blood gas (ABG) <\/strong>is the\u00a0analysis of an arterial blood sample to evaluate the\u00a0adequacy of ventilation, oxygen delivery to the tissues, and acid-base balance status (Simpson, 2004). For patients with\u00a0COPD, the target SaO2<\/sub> range is 88% to 92% (Alberta Health Services, 2015; British Thoracic Society, 2008; Kane et al., 2013).\u00a0Only about 3% of the oxygen carried in the blood is dissolved in the plasma, which\u00a0can be assessed by looking at the partial pressure of oxygen in the blood through blood gas analysis (PaO2<\/sub>).\u00a0The normal PaO2<\/sub>\u00a0of a healthy adult is 80 to 100 mmHg. The SpO2\u00a0<\/sub>is\u00a0more clinically significant than the PaO2\u00a0<\/sub>in determining the oxygen content of the blood.\r\n\r\nOxygen is considered a medication and therefore requires continuous monitoring of the dose, concentration, and side effects to ensure its safe and effective use (Alberta Health Services, 2015). Oxygen therapy may be indicated for hypoxemia and hypoxia.\r\n

Understanding Hypoxemia and Hypoxia<\/h2>\r\nAlthough the terms hypoxemia<\/em> and hypoxia<\/em> are often used interchangeably, they do not mean the same thing. Hypoxemia<\/strong> is\u00a0a condition where arterial oxygen tension or partial pressure of oxygen (PaO2<\/sub>) is below normal (<80 mmHg). Hypoxemia is the inadequate supply of oxygen in the arterial blood.\u00a0Hypoxia<\/strong> is the reduction of oxygen supply at the tissue level, which is not measured directly by a laboratory value (Metrovic, 2014), but by pulse oximetry and SpO2<\/sub> (British Thoracic Society, 2008).\r\n\r\nGenerally, the presence of hypoxemia suggests that hypoxia exists. However, hypoxia may not be present in a patient with hypoxemia if the patient is able to compensate for a low PaO2<\/sub> by increasing oxygen supply. This is usually\u00a0achieved by increasing cardiac output (by raising the heart rate) or by decreasing tissue oxygen consumption.\u00a0Conversely, patients who do not show signs of hypoxemia may\u00a0be hypoxic if oxygen delivery to the tissues is diminished\u00a0or if the tissues are unable to adequately use the oxygen.\r\n\r\nHypoxemia is the most common cause of tissue hypoxia, and if the correct diagnosis is\u00a0made, it is readily treatable.\r\n

The Vancouver Coastal Health Authority (2015) lists\u00a0three causes of hypoxemia: deadspace and shunts, low inspired oxygen tension, and alveolar hypoventilation.<\/p>\r\n\r\n

Deadspace and Shunts<\/h3>\r\nVentilation and perfusion are not always equal\u00a0between the alveoli and pulmonary capillaries. There is sometimes too much perfusion and not enough ventilation in\u00a0some areas of the lungs, causing a shunt where the blood is unable to\u00a0pick up oxygen and unload carbon dioxide. In other areas of the lungs, there may be\u00a0too much ventilation and not enough perfusion, causing deadspace where oxygen is unable to\u00a0diffuse into the blood.\r\n

Low Inspired Oxygen Tension<\/h3>\r\nHypoxemia can be caused by breathing air at pressures less than atmospheric pressure, such as at high altitudes or\u00a0in an enclosed space with inadequate ventilation.\u00a0The enclosed space may be especially hazardous if there is a\u00a0low concentration of oxygen or if it contains toxic gases.\r\n

Alveolar Hypoventilation<\/h3>\r\nIf\u00a0a patient hypoventilates, the level of oxygen in the alveoli will fall, and the level of carbon dioxide will increase.\u00a0Hypoxemia occurs because\u00a0less oxygen is moved into the pulmonary blood flow.\r\n\r\nExamples of medical conditions that cause hypoxemia include:\r\n
    \r\n \t
  • Asthma<\/li>\r\n \t
  • COPD<\/li>\r\n \t
  • Heart failure<\/li>\r\n \t
  • Pleural effusions<\/li>\r\n \t
  • Pneumonia<\/li>\r\n \t
  • Pneumothorax<\/li>\r\n \t
  • Pulmonary edema<\/li>\r\n \t
  • Pulmonary emboli<\/li>\r\n<\/ul>\r\nWith hypoxia, there is inadequate transport of oxygen to the cells or tissues, either because of obstruction, secretions, or tumours in the lungs; hypoventilation due to disease, injury to the respiratory system, or medications; or poor blood flow due to a compromised circulatory system (British Thoracic Society, 2008). Hypoxia related to anemia or circulatory system compromise, such as decreased cardiac output, will respond poorly to oxygen therapy, and other appropriate interventions should be considered.\r\n\r\nHypoxia is a medical emergency (Alberta Health Services, 2015). Oxygen therapy will:\r\n
      \r\n \t
    • Decrease the work of breathing in patients with respiratory or cardiovascular conditions, which may prevent respiratory and muscle fatigue (Jardins & Burton, 2011).<\/li>\r\n \t
    • Decrease cardiopulmonary workload\u00a0by\u00a0reducing high cardiopulmonary demand (Perry et al., 2014). For example, patients with left ventricular failure benefit from additional oxygen to the tissues because the heart cannot provide enough oxygen to the tissues due to decreased cardiac output.<\/li>\r\n \t
    • Support post-operative recovery, and\u00a0may be ordered for a specific time frame at a specific rate while the patient recovers from the surgical procedure.<\/li>\r\n<\/ul>\r\n
      \r\n

      Critical Thinking Exercises<\/p>\r\n\r\n<\/header>\r\n

      \r\n
        \r\n \t
      1. How do you know if your patient is hypoxic or hypoxemic? Please explain.<\/li>\r\n \t
      2. Why would the post-surgical patient require supplemental oxygen?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>","rendered":"

        The air we breathe is made up of various gases, 21% of which is oxygen. Therefore, a patient who is receiving\u00a0no supplemental oxygen therapy is still receiving\u00a0oxygen from the air.\u00a0This amount of oxygen is adequate provided that the patient’s airway is not compromised and there is sufficient\u00a0hemoglobin\u00a0in the blood. The\u00a0cardiovascular system must also be intact and able to circulate blood to all body tissues. If any of these systems fail, the patient will require\u00a0supplemental\u00a0oxygen to\u00a0increase the likelihood that adequate levels of oxygen will reach all vital body tissues necessary to sustain life.<\/p>\n

        Oxygen in the Blood<\/h2>\n

        Hemoglobin (Hgb) holds oxygen in reserve until the metabolic demands of the body require more\u00a0oxygen.\u00a0The Hgb then moves\u00a0the oxygen to the plasma for transport to the tissues.\u00a0The body’s demand for oxygen is affected by activity, metabolic status, temperature, and level of anxiety.\u00a0The ability of Hgb to move\u00a0the oxygen to the tissues depends on a number of factors, such as oxygen supply, ventilatory effectiveness, nutrition, cardiac output, hemoglobin level, smoking, drug use, and underlying disease.\u00a0Any one of these factors can\u00a0potentially\u00a0impede the supply and transport of oxygen to the tissues.<\/p>\n

        Measurement of Oxygen in the Blood<\/h2>\n

        The vast majority of oxygen carried in the blood is attached to hemoglobin and\u00a0can be assessed by\u00a0monitoring the oxygen saturation through pulse oximetry (SpO2<\/sub>).The target range for oxygen saturation as measured by blood analysis (SaO2<\/sub>), such as arterial blood gas, is 92% to 98% for a normal adult. Arterial blood gas (ABG) <\/strong>is the\u00a0analysis of an arterial blood sample to evaluate the\u00a0adequacy of ventilation, oxygen delivery to the tissues, and acid-base balance status (Simpson, 2004). For patients with\u00a0COPD, the target SaO2<\/sub> range is 88% to 92% (Alberta Health Services, 2015; British Thoracic Society, 2008; Kane et al., 2013).\u00a0Only about 3% of the oxygen carried in the blood is dissolved in the plasma, which\u00a0can be assessed by looking at the partial pressure of oxygen in the blood through blood gas analysis (PaO2<\/sub>).\u00a0The normal PaO2<\/sub>\u00a0of a healthy adult is 80 to 100 mmHg. The SpO2\u00a0<\/sub>is\u00a0more clinically significant than the PaO2\u00a0<\/sub>in determining the oxygen content of the blood.<\/p>\n

        Oxygen is considered a medication and therefore requires continuous monitoring of the dose, concentration, and side effects to ensure its safe and effective use (Alberta Health Services, 2015). Oxygen therapy may be indicated for hypoxemia and hypoxia.<\/p>\n

        Understanding Hypoxemia and Hypoxia<\/h2>\n

        Although the terms hypoxemia<\/em> and hypoxia<\/em> are often used interchangeably, they do not mean the same thing. Hypoxemia<\/strong> is\u00a0a condition where arterial oxygen tension or partial pressure of oxygen (PaO2<\/sub>) is below normal (<80 mmHg). Hypoxemia is the inadequate supply of oxygen in the arterial blood.\u00a0Hypoxia<\/strong> is the reduction of oxygen supply at the tissue level, which is not measured directly by a laboratory value (Metrovic, 2014), but by pulse oximetry and SpO2<\/sub> (British Thoracic Society, 2008).<\/p>\n

        Generally, the presence of hypoxemia suggests that hypoxia exists. However, hypoxia may not be present in a patient with hypoxemia if the patient is able to compensate for a low PaO2<\/sub> by increasing oxygen supply. This is usually\u00a0achieved by increasing cardiac output (by raising the heart rate) or by decreasing tissue oxygen consumption.\u00a0Conversely, patients who do not show signs of hypoxemia may\u00a0be hypoxic if oxygen delivery to the tissues is diminished\u00a0or if the tissues are unable to adequately use the oxygen.<\/p>\n

        Hypoxemia is the most common cause of tissue hypoxia, and if the correct diagnosis is\u00a0made, it is readily treatable.<\/p>\n

        The Vancouver Coastal Health Authority (2015) lists\u00a0three causes of hypoxemia: deadspace and shunts, low inspired oxygen tension, and alveolar hypoventilation.<\/p>\n

        Deadspace and Shunts<\/h3>\n

        Ventilation and perfusion are not always equal\u00a0between the alveoli and pulmonary capillaries. There is sometimes too much perfusion and not enough ventilation in\u00a0some areas of the lungs, causing a shunt where the blood is unable to\u00a0pick up oxygen and unload carbon dioxide. In other areas of the lungs, there may be\u00a0too much ventilation and not enough perfusion, causing deadspace where oxygen is unable to\u00a0diffuse into the blood.<\/p>\n

        Low Inspired Oxygen Tension<\/h3>\n

        Hypoxemia can be caused by breathing air at pressures less than atmospheric pressure, such as at high altitudes or\u00a0in an enclosed space with inadequate ventilation.\u00a0The enclosed space may be especially hazardous if there is a\u00a0low concentration of oxygen or if it contains toxic gases.<\/p>\n

        Alveolar Hypoventilation<\/h3>\n

        If\u00a0a patient hypoventilates, the level of oxygen in the alveoli will fall, and the level of carbon dioxide will increase.\u00a0Hypoxemia occurs because\u00a0less oxygen is moved into the pulmonary blood flow.<\/p>\n

        Examples of medical conditions that cause hypoxemia include:<\/p>\n

          \n
        • Asthma<\/li>\n
        • COPD<\/li>\n
        • Heart failure<\/li>\n
        • Pleural effusions<\/li>\n
        • Pneumonia<\/li>\n
        • Pneumothorax<\/li>\n
        • Pulmonary edema<\/li>\n
        • Pulmonary emboli<\/li>\n<\/ul>\n

          With hypoxia, there is inadequate transport of oxygen to the cells or tissues, either because of obstruction, secretions, or tumours in the lungs; hypoventilation due to disease, injury to the respiratory system, or medications; or poor blood flow due to a compromised circulatory system (British Thoracic Society, 2008). Hypoxia related to anemia or circulatory system compromise, such as decreased cardiac output, will respond poorly to oxygen therapy, and other appropriate interventions should be considered.<\/p>\n

          Hypoxia is a medical emergency (Alberta Health Services, 2015). Oxygen therapy will:<\/p>\n

            \n
          • Decrease the work of breathing in patients with respiratory or cardiovascular conditions, which may prevent respiratory and muscle fatigue (Jardins & Burton, 2011).<\/li>\n
          • Decrease cardiopulmonary workload\u00a0by\u00a0reducing high cardiopulmonary demand (Perry et al., 2014). For example, patients with left ventricular failure benefit from additional oxygen to the tissues because the heart cannot provide enough oxygen to the tissues due to decreased cardiac output.<\/li>\n
          • Support post-operative recovery, and\u00a0may be ordered for a specific time frame at a specific rate while the patient recovers from the surgical procedure.<\/li>\n<\/ul>\n
            \n
            \n

            Critical Thinking Exercises<\/p>\n<\/header>\n

            \n
              \n
            1. How do you know if your patient is hypoxic or hypoxemic? Please explain.<\/li>\n
            2. Why would the post-surgical patient require supplemental oxygen?<\/li>\n<\/ol>\n<\/div>\n<\/div>\n","protected":false},"author":5,"menu_order":2,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-2227","chapter","type-chapter","status-publish","hentry"],"part":2226,"_links":{"self":[{"href":"https:\/\/opentextbc.ca\/clinicalskills\/wp-json\/pressbooks\/v2\/chapters\/2227","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/opentextbc.ca\/clinicalskills\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/opentextbc.ca\/clinicalskills\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/opentextbc.ca\/clinicalskills\/wp-json\/wp\/v2\/users\/5"}],"version-history":[{"count":28,"href":"https:\/\/opentextbc.ca\/clinicalskills\/wp-json\/pressbooks\/v2\/chapters\/2227\/revisions"}],"predecessor-version":[{"id":10136,"href":"https:\/\/opentextbc.ca\/clinicalskills\/wp-json\/pressbooks\/v2\/chapters\/2227\/revisions\/10136"}],"part":[{"href":"https:\/\/opentextbc.ca\/clinicalskills\/wp-json\/pressbooks\/v2\/parts\/2226"}],"metadata":[{"href":"https:\/\/opentextbc.ca\/clinicalskills\/wp-json\/pressbooks\/v2\/chapters\/2227\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/opentextbc.ca\/clinicalskills\/wp-json\/wp\/v2\/media?parent=2227"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/opentextbc.ca\/clinicalskills\/wp-json\/pressbooks\/v2\/chapter-type?post=2227"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/opentextbc.ca\/clinicalskills\/wp-json\/wp\/v2\/contributor?post=2227"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/opentextbc.ca\/clinicalskills\/wp-json\/wp\/v2\/license?post=2227"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}