Ch 30 Oxygen Therapy – Flashcards

Low levels of oxygen in the blood

Decreased tissue oxygenation

The oxygen content of atmospheric air is about 21%.

Oxygen therapy is prescribed when the oxygen needs of the patient cannot be met by atmospheric or "room air" alone. It is used for both acute and chronic breathing problems that cause decreased blood and tissue oxygen levels as indicated by decreased partial pressure of arterial oxygen (PaO2) levels or by decreased arterial oxygen saturation (SaO2).

The purpose of oxygen therapy is to use the lowest fraction of inspired oxygen (FiO2) to have an acceptable blood oxygen level without causing harmful side effects.

Increased partial pressure of arterial carbon dioxide [PaCO2] levels

Assess for oxygen-induced hypoventilation in the patient whose main respiratory drive is hypoxia (hypoxic drive), such as in the patient with chronic lung disease who also has carbon dioxide retention (hypercarbia). The arterial carbon dioxide (PaCO2) level for these patients gradually rises over time. Manifestations of hypoventilation are seen during the first 30 minutes of oxygen therapy. The patient's color improves (from ashen or gray to pink) because of an increase in the PaO2 level before the apnea or respiratory arrest occurs from slower and shallow respirations. Therefore carefully monitor the level of consciousness, respiratory pattern and rate, and pulse oximetry for those at risk for oxygen-induced hypoventilation, apnea, and respiratory arrest.

Loss of sensitivity to high levels of PaCO2

Oxygen toxicity is related to the concentration of oxygen delivered, duration of oxygen therapy, and degree of lung disease present. In general, an oxygen level greater than 50% given continuously for more than 24 to 48 hours may damage the lungs.

Although oxygen-induced hypoventilation is a serious concern, untreated or inadequately treated hypoxemia is a greater threat to life.

The causes and manifestations of lung injury from oxygen toxicity are the same as those for acute respiratory distress syndrome (ARDS). Initial symptoms include dyspnea, nonproductive cough, chest pain beneath the sternum, and GI upset. As exposure to high levels of oxygen continues, the symptoms become more severe with decreased vital capacity, decreased compliance, crackles, and hypoxemia. Prolonged exposure to high oxygen levels damages lung tissues. Atelectasis, pulmonary edema, hemorrhage, and hyaline membrane formation result. Surviving this critical condition depends on correcting the underlying disease process and decreasing the oxygen amount delivered.

Nitrogen in the air helps maintain patent airways and alveoli. Making up 79% of room air, nitrogen prevents alveolar collapse because it does not cross the alveolar-capillary membranes and remains in the airways and alveoli. When high oxygen levels are delivered, nitrogen is diluted, oxygen diffuses from the alveoli into the circulation, and the alveoli collapse. Collapsed alveoli cause atelectasis (called absorption atelectasis), which is detected by auscultation. Monitor the patient receiving high levels of oxygen closely for indications of absorption atelectasis (new onset of crackles and decreased breath sounds) every 1 to 2 hours when oxygen therapy is started and as often as needed thereafter.

When the prescribed oxygen flow rate is higher than 4 L/min, humidify the delivery system. For the patient to receive properly humidified oxygen, the humidifier or nebulizer must have a sufficient amount of sterile water and the flow rate must be adequate.

The humidifier or nebulizer may be a source of bacteria, especially if it is heated. Pseudomonas aeruginosa is often the organism involved. Oxygen delivery equipment such as cannulas and masks can also harbor organisms. Change equipment as per policy or protocol, which ranges from every 24 hours for humidification systems to every 7 days or whenever necessary for cannulas and masks.

Low-flow delivery systems include the nasal cannula, simple facemask, partial rebreather mask, and non-rebreather mask.

These systems are inexpensive, easy to use, and fairly comfortable. A disadvantage is that the actual amount of oxygen delivered varies and depends on the patient's breathing pattern. The oxygen is diluted with room air (21% oxygen), which lowers the amount of oxygen actually inspired.

The nasal cannula, or nasal prongs, is used at flow rates of 1 to 6 L/min. Oxygen concentrations of 24% (at 1 L/min) to 44% (at 6 L/min) can be achieved. Flow rates greater than 6 L/min do not increase oxygenation because the anatomic dead space (places where air flows but the structures are too thick for gas exchange) is full. In addition, high flow rates increase mucosal irritation.

The patient who retains carbon dioxide is rarely prescribed to receive oxygen at a rate higher than 2 to 3 L/min because of the risk for losing the drive to breathe, thereby increasing the risk for apnea or respiratory arrest.

Simple facemasks are used to deliver oxygen concentrations of 40% to 60% for short-term oxygen therapy or in an emergency. A minimum flow rate of 5 L/min is needed to prevent the rebreathing of exhaled air. Ensure the mask fits well to maintain inspired oxygen levels. Care for the skin under the mask and strap to prevent skin breakdown.

Partial rebreather masks provide oxygen concentrations of 60% to 75% with flow rates of 6 to 11 L/min. It is a mask with a reservoir bag but no flaps. With each breath, the patient rebreathes one third of the exhaled tidal volume, which is high in oxygen and provides a higher fraction of inspired oxygen (FiO2). Be sure that the bag remains slightly inflated at the end of inspiration; otherwise, the desired amount of oxygen is not delivered. If needed, call the respiratory therapist for assistance.

Non-rebreather masks provide the highest oxygen level of the low-flow systems and can deliver an Fio2 greater than 90%, depending on the patient's breathing pattern. This mask is often used with patients whose respiratory status is unstable and who may require intubation. The non-rebreather mask has a one-way valve between the mask and the reservoir and two flaps over the exhalation ports (Fig. 30-6). The valve allows the patient to draw all needed oxygen from the reservoir bag, and the flaps prevent room air from entering through the exhalation ports (room air would dilute the oxygen concentration). During exhalation, air leaves through these exhalation ports while the one-way valve prevents exhaled air from re-entering the reservoir bag. The flow rate is kept high (10 to 15 L/min) to keep the bag inflated during inhalation. Assess for this safety feature at least hourly. Ensure that the valve and flaps on a non-rebreather mask are intact and functional during each breath. If the oxygen source should fail or be depleted when both flaps are in place, the patient would not be able to inhale room air.

High-flow systems include the Venturi mask, aerosol mask, face tent, tracheostomy collar, and T-piece. These devices deliver an accurate oxygen level when properly fitted.

Venturi masks (commonly called Venti masks) deliver the most accurate oxygen concentration without intubation. It works by pulling in a proportional amount of room air for each liter flow of oxygen. An adaptor is located between the bottom of the mask and the oxygen source (Fig. 30-7). Adaptors with holes of different sizes allow specific amounts of air to mix with the oxygen. More precise delivery of oxygen results. Each adaptor uses a different flow rate. Humidification is not needed with the Venturi mask.

Venturis masks are best for the patient with chronic lung disease because it delivers a more precise oxygen concentration.

Noninvasive positive-pressure ventilation (NPPV) is a technique using positive pressure to keep alveoli open and improve gas exchange without the need for airway intubation. NPPV is now being used to manage dyspnea, hypercarbia and acute exacerbations of chronic obstructive pulmonary disease (COPD), cardiogenic pulmonary edema, and acute asthma attacks.

Although NPPV prevents the complications associated with intubation, including ventilator-associated pneumonia (VAP), some risks and complications are associated with this type of therapy. Masks must fit tightly in order to form a proper seal. This can lead to skin breakdown over the bridge of the nose or other areas of the face. Leaks can cause uncomfortable pressure around the eyes, and gastric insufflation can lead to vomiting and the potential for aspiration. Thus NPPV should be used only on patients with an intact mental status and the ability to protect their airway, although a nasogastric (NG) tube may still be required for safety.

The three most common modes of delivery for NPPV are (1) CPAP, which delivers a set positive airway pressure throughout each cycle of inhalation and exhalation; (2) volume-limited or flow-limited, which delivers a set tidal volume with the patient's inspiratory effort; and (3) pressure-limited, which includes pressure support, pressure control, and bi-level positive airway pressure (BiPAP), which cycles different pressures at inspiration and at expiration.

For BiPAP, a cycling machine delivers a set inspiratory positive airway pressure each time the patient begins to inspire. As he or she begins to exhale, the machine delivers a lower set end-expiratory pressure. Together, these two pressures improve tidal volume, can reduce respiratory rate, and may relieve dyspnea.

For CPAP, the effect is to open collapsed alveoli. Patients who may benefit from this form of oxygen or air delivery include those with atelectasis after surgery or cardiac-induced pulmonary edema or those with COPD. It is not beneficial for patients with respiratory failure following extubation. NPPV is also being used in palliative care for alleviating dyspnea, including for those patients with "do-not-intubate" orders. However, this practice is controversial. The Society of Critical Care Medicine (SCCM) recommends that goals of therapy and expected outcomes be discussed with the patient and family before initiating therapy.

Transtracheal oxygen (TTO) is a long-term method of delivering oxygen directly into the lungs. A small, flexible catheter is passed into the trachea through a small incision with the patient under local anesthesia. TTO avoids the irritation that nasal prongs cause. Patients also report it to be more cosmetically acceptable. TTO flow rates are prescribed for rest and for activity. A flow rate also is prescribed for the nasal cannula, which is used when the TTO catheter is being cleaned. Most patients using this delivery method have a 55% reduction in required oxygen flow at rest and a 30% decrease with activity.

For Medicare to cover the cost of home oxygen therapy, the patient must have severe hypoxemia defined as a partial pressure of arterial oxygen (PaO2) level of less than 55 mm Hg or an arterial oxygen saturation (SpO2) of less than 88% on room air and at rest. The criteria vary when hypoxemia is caused by cardiac rather than pulmonary problems or when oxygen is needed only at night or with exercise.

The nurse or respiratory therapist teaches the patient about the equipment needed for home oxygen therapy, including the oxygen source, delivery devices, humidity sources, and safety aspects of using and maintaining the equipment.

Compressed gas in an oxygen tank (green) is the most often used oxygen source. Liquid oxygen for home use is oxygen gas that has been liquefied. A concentrated amount of oxygen is available in a lightweight and easy-to-carry container similar to a Thermos bottle. The oxygen concentrator or oxygen extractor is a machine that removes nitrogen, water vapor, and hydrocarbons from room air. Oxygen is concentrated from room air to more than 90%. The concentrator, although noisy and large, is the least expensive system and does not need to be filled.

The surgical incision into the trachea to create an airway.

The (tracheal) stoma, or opening, that results from the tracheotomy.

1. Reduced oxygenation related to weak chest muscles, obstruction, or other physical problems 2. Inadequate communication related to tracheostomy or intubation 3. Inadequate nutrition related to presence of endotracheal tube 4. Potential for infection related to invasive procedures 5. Damaged oral mucosa related to mechanical factors (endotracheal tube)

Indicators of obstruction include difficulty breathing; noisy respirations; difficulty inserting a suction catheter; thick, dry secretions; and unexplained peak pressures (if a mechanical ventilator is in use). Assess the patient at least hourly for tube patency. Prevent obstruction by helping the patient cough and deep breathe, providing inner cannula care, humidifying the oxygen source, and suctioning. If tube obstruction occurs as a result of cuff prolapse over the end of the tracheostomy tube, the physician or advanced practice nurse repositions or replaces the tube.

For patients receiving mechanical ventilation, a cuffed tube is used in acute care settings. A noncuffed tube is used when mechanical ventilation is not required.

To reduce the risk for tracheal damage, keep the cuff pressure between 14 and 20 mm Hg or 20 and 30 cm H2O (ideally, 25 cm H2O or less)

Suctioning is needed when secretions are audible or noisy, when crackles or wheezes are heard on auscultation, or when restlessness, increased pulse or respiratory rates, or mucus in the artificial airway is present. Other indications include patient requests for suctioning or an increase in the peak airway pressure on the ventilator.

Prevent hypoxia by hyperoxygenating the patient with 100% oxygen with a manual resuscitation bag attached to an oxygen source. If the patient can take deep breaths, instruct him or her to do so three or four times with the existing oxygen delivery system before suctioning. If possible, monitor the heart rate or use a pulse oximeter while suctioning to assess tolerance of the procedure. Assess for hypoxia (e.g., increased heart rate and blood pressure, oxygen desaturation, cyanosis, restlessness, anxiety, dysrhythmias). Oxygen saturation below 90% by pulse oximetry indicates hypoxemia. If hypoxia occurs, stop the suctioning procedure. Using the 100% oxygen delivery system, reoxygenate the patient until baseline parameters return.

The tracheostomy tube sometimes tethers the larynx in place, making it unable to move effectively. The result is difficulty in swallowing. Also, when the tracheostomy tube cuff is inflated, it can balloon backwards and interfere with the passage of food through the esophagus. The wall between the back of the trachea and the front of the esophagus is very thin, allowing this pushing problem. Instruct the patient to keep the head of the bed elevated for at least 30 minutes after eating.

First, the cuff is deflated as soon as the patient can manage secretions and does not need mechanical ventilation. This change allows him or her to breathe through the tube and through the upper airway. Next, the tube is changed to an uncuffed tube. If this is tolerated, the size of the tube is gradually decreased. When a small fenestrated tube is placed (No. 4 or 6, depending on the size of the airway), the tube is capped so that all air passes through the upper airway and the fenestra, with none passing through the tube. Assess the patient to ensure adequate airflow around the tube when it is capped. The tube may be removed after he or she tolerates more than 24 hours of capping. Place a dry dressing over the stoma (which gradually heals on its own).