Oxygen Therapy PDF

Oxygen Therapy RCP 110 Why oxygen? - Oxygen is essential for life via **aerobic metabolism.** - It is critical for normal muscular, nervous, and visceral function. - Brain cells begin to suffer irreversible damage after **6 minutes** without oxygen - Oxygen/O2 - Atomic number on...

Oxygen Therapy RCP 110 Why oxygen? - Oxygen is essential for life via **aerobic metabolism.** - It is critical for normal muscular, nervous, and visceral function. - Brain cells begin to suffer irreversible damage after **6 minutes** without oxygen - Oxygen/O2 - Atomic number on the periodic table of the elements = 8 - Atomic weight (mass) = 16 - Colorless, odorless - Non-explosive, but [supports combustion] - Terminology **Hypoxia:** an abnormal condition in which oxygen is **unavailable** to the body cells at the **tissue or organ** **level**, and is inadequate to meet their needs. - Generally **precedes** hypoxemia - Types of Hypoxia **[Hypoxemic Hypoxia]:** decrease in **diffusion of** **O2** across alveolar capillary membrane. - Diffusion (gas exchange) defects - R to L shunt in heart (anatomic defect) - Ventilation/Perfusion (V/Q) mismatch in lungs - Hypoventilation - Decreased FIO2's - High altitudes - Types of Hypoxia **[Anemic Hypoxia]:** decreased oxygen **carrying capacity** in blood (hemoglobin deficit). - Anemia - Carbon monoxide (CO) poisoning - Types of Hypoxia **[Stagnant Hypoxia]:** decreased **cardiac** **output** (Qt) resulting in decreased tissue perfusion. - Shock - Myocardial insufficiency **[Histotoxic Hypoxia]:** inability of tissue to **utilize** oxygen. - Cyanide poisoning - Cardiac Output - The delivery of oxygen to the tissues is a product of the **cardiac output (Qt)** which is the amount of blood the heart ejects or pumps in one minute - - - [Cardiac output] is a result of the heart rate and the ventricular stroke volume (SV) - [Stroke volume] is the amount of blood the heart ejects with every contraction - Caluculating Cardiac output Cardiac output equals the [stroke volume multiplied by the heart rate], usually about 4-8 liters a minute depending on the individual's size - - Hypoxemia - **Definition:** an abnormal deficiency of oxygen in the **[arterial blood]**. - This may be [quantified] by way of examining the **PaO2** in an ABG or measuring the patient's oxygen saturation level (**SPO2 or SaO2**) - Clinical Signs of Hypoxemia - Increased work of breathing - Tachypnea - Tachycardia - Increased blood pressure and cardiac output - Decreased PaO2 and SaO2 - Cyanosis - Clinical Signs of Hypoxemia (con't) - Pulmonary hypertension (vasoconstriction of pulmonary vasculature) - Vasoconstriction of vessels supplying skin, muscles, and abdominal viscera. - Vasodilation of vessels supplying heart and brain. - Evaluation of Hypoxemia - **Decreased PaO2** Arterial Blood Gas (ABG) measurement - [PaO2] = Partial pressure of arterial oxygen in mm Hg - **Invasive** (most accurate) assessment. - Arterial Blood Gases\ PaO2 The following values (in mm Hg or torr) are based on a healthy **adult** under 60 years old: - 80-100 / normal - 60-79 / mild hypoxemia - 40-59 / moderate hypoxemia - below 40 / severe hypoxemia - PaO2 The normal PaO2 decreases with age - Formulas to [estimate] the predicted normal PaO2: - - - Evaluation of Hypoxemia **Pulse Oximetry (SpO2):** Measures the oxygen saturation of hemoglobin **non-invasively**. Normal SpO2 95-97%= PaO2 greater than 90 mm Hg - - Pulse oximetry performed with a device known as a **pulse oximeter**, that measures not only SpO2 but heart rate - Pulse Oximetry - SpO2 of 90% = PaO2 of about 60-70 - SpO2 of 80% = PaO2 of about 40-50 - Oxygen dissociation curve drops off sharply between an SpO2 of 90 and 80% - **SaO2** may be assessed [via ABG] - - Pulse Oximetry - Pulse oximetry is used as an **approximate** indicator of the patient's oxygenation status - An arterial blood gas is a much more **accurate** method of assessing the oxygenation status since it is an **invasive** procedure - An **arterial blood gas (ABG)** is more expensive, takes longer, requires more equipment, and is an invasive procedure with associated hazards - Because of all the above, pulse oximetry is **widely utilized** to quickly assess a patient's oxygenation status inexpensively and without a needle puncture - Principle of Pulse Oximetry - Pulse oximetry uses the physical principle of **photospectrometry** - **Infra-red light** passes through body tissue from a transmitter to a receiver - The amount of light that is absorbed is **relative to** the amount of **oxyhemoglobin** (O2Hb) in the blood - - - Pulse Oximetry - The **heart rate** is assessed during pulse oximetry by measuring cyclic changes in blood volume during the cardiac cycle via infra-red light transmission through the tissue - Pulse Oximetry Equipment - Pulse oximeters are constructed in many sizes and shapes from large table-top models to small hand-held units - Pulse oximeter **monitors** have high and low SpO2 and heart rate alarms compared to simple units for assessment purposes only - Monitors are constructed for **continuous** use - Pulse Oximeters - **Two types of basic pulse oximeters used for "spot checks" or simple non-invasive oxygenation assessment** - Two examples of larger table-top pulse oximeter monitors used for continuous analysis - Pulse Oximeter Equipment - Most smaller oximeters are battery powered, while larger units are electrically powered with a battery "back-up" - Monitors often have a rechargeable internal battery - Sensors - - - Pulse Oximeter: Sensor Placement - Finger clip sensors are usually permanent - Disposable sensors may be used in some facilities for adults - Disposable sensors are used for all small children or neonates - **Sensor placement:** - - - Pulse Oximeter: Sensor Placement - Accuracy and Limitations of Pulse Oximetry Factors affecting **accuracy** of pulse oximetry include: - - - - - - Clinical Applications of Pulse Oximetry To monitor the adequacy of **arterial oxygenation,** - - To assess the adequacy of **oxygen therapy** - - Clinical Applications of Pulse Oximetry To **correlate** arterial blood gas measurement when results are questionable - To comply with mandated government **financial reimbursement** regulations for home oxygen therapy - - Correlation of SpO2 and PaO2 Is there a clinical correlation of the SpO2 and PaO2? **Yes** - We will cover this in great detail studying the **oxygen dissociation curve** in RCP 114 - Basically, providing the patient has a normal hemoglobin level, **an SpO2 of 95-97% = a PaO2 of about 90-100 mm Hg** - SpO2 / PaO2 - An SpO2 of 90%=a PaO2 of about 60 mm Hg; this is a **critical threshold** for the patient's oxygenation status. - Oxygen Dissociation Curve - Hemioximetry (CO-oximetry) Hemioximetry is indicated when accurate measures of any hemoglobin (Hb) parameters are needed and when you calibrate a pulse oximetry reading (SpO2) against the actual arterial saturation. It is important to remember that a CO-Oximeter is a separate measurement and sometimes separate machine from a blood gas analyzer. Some facilities have blood gas analyzers that give co-oximetry readings in one blood sample. Pulse oximetry (SpO2) accuracy can be affected by many factors such as artifacts and physiologic conditions. When in the presences of low readings, abnormal waveforms or CO exposure suspicion, a CO-oximetry test must be done to assess for SpO2 accuracy. - Carboxyhemoglobin (COHb) - Normal CO levels are \ - Refractory Hypoxemia Hypoxemia demonstrating a **negligible** **increase** in the PaO2 with the application of supplemental oxygen. - Less than a 10 mm increase in the PaO2 with an FIO2 increase of 20%. - Primary etiology: **shunt** R to L intra-cardiac [anatomical shunt] *[or]* consolidation (pneumonia), atelectasis, pulmonary edema: [intrapulmonary shunt] - Indications for Oxygen Therapy **Prerequisite:** Must be prescribed by a physician by **route (type of device) and LPM or FIO2;** standing orders are acceptable 1\. Treat hypoxemia 2\. Reduce the work of breathing (stimulation of peripheral chemoreceptors) 3\. Reduce myocardial work (compensatory response to hypoxemia) 4\. Reverse pulmonary hypertension - Hazards of Oxygen Therapy **[Retinopathy of Prematurity (ROP)]** (older term Retrolental Fibroplasia) - Development of **opaque fibrotic tissue** behind the lens of the eye in neonates resulting in **blindness**. - Caused by high FIO2's / PaO2's (retinal arterial constriction), usually more than 3 days in length - American Academy of Pediatrics recommends PaO2 \< 80 mm Hg - Hazards of Oxygen Therapy **[Oxygen Toxicity]** - Damage to Type II pneumocytes producing [surfactant] - Produces [atelectasis] and refractory hypoxemia - Etiology: FIO2's greater than 40% for extended periods of time. - Hazards of Oxygen Therapy **[Absorption Atelectasis]** - **Atelectasis** = collapse of lung tissue - N2 = 80% of alveolar gas / Maintains stability and **keeps alveoli expanded**. - FIO2's greater than 70% for extended periods of time "wash out" or eliminate N2, and results in **decreased alveolar size and atelectasis.** - Hazards of Oxygen Therapy **[Oxygen Induced Hypoventilation]** - Suppression of the **peripheral** **chemoreceptors** by supplemental oxygen. - Occurs primarily with chronic hypoxemia and **"hypoxic drive";** chronically elevated PaCO2 and decreased PaO2 - Oxygen should be used very carefully with patients breathing via this physiologic mechanism (COPD) - FIO2 - **FIO2** is the concentration of oxygen in inspired air or a gas mixture - Fractional concentration (F) of inspired (I) oxygen (O2) = **FIO2** - The FIO2 of any gas mixture will indicate the amount of oxygen expressed as a **decimal or fraction** - The FIO2 of room air is 21% **or**.21 - Medical Oxygen - Regulated by the [FDA (Food and Drug Administration)] - Must be [99% pure] - Can be stored as a compressed gas in cylinders or as liquid oxygen (LOX) that is converted into a gas by adding heat - Oxygen cylinders are color coded [green] in the United States; white is the international color for oxygen