Respiratory: Oxygen Flashcards
Types of Respiratory Drugs:
Bronchodilators: Beta2-Receptor Agonists:
Basic Understanding:
Oxygen is a basic element essential for human life; oxygen
deprivation leads to rapid death. Therapy with oxygen is necessary for life in several diseases that interfere with normal
oxygenation of blood and tissues. Oxygen as a therapeutic gas
is delivered from steel containers and is 99% pure.
Types of Respiratory Drugs:
Bronchodilators: B2RAs:
Pharmacodynamics:
Oxygen is prescribed to treat hypoxia, or tissue deprivation
of oxygen. Hypoxia can be caused by an inadequate supply
of oxygen to the lungs, which can be due to poor ventilation
or inadequate partial pressure of inspired oxygen. Inadequate
pulmonary function can lead to hypoxia, as in a mismatch
between ventilation and perfusion. Tissue hypoxia may occur
with inadequate delivery of oxygen to the tissues, such as occurs
in low cardiac output. Tissue hypoxia may also occur if the oxygen concentration of the blood is low, as occurs in anemia.
The effects of hypoxia can be observed in all major organ
systems. The respiratory system increases the ventilatory rate
and depth as a result of stimulation of carotid and aortic
chemoreceptors. The heart increases cardiac output by increasing the heart rate. With severe hypoxia, bradycardia develops and ultimately leads to circulatory failure. The CNS is
the most sensitive to hypoxia, with initial impaired judgment
and psychomotor ability, leading to confusion; restlessness;
and ultimately stupor, coma, and death.
Types of Respiratory Drugs:
Bronchodilators: B2RAs:
Pharmacokinetics: Absorption and Distribution:
The oxygen content of inhaled air is normally 20.9%, equivalent to a partial pressure of 159 mm Hg. As oxygen is inhaled,
it enters the pulmonary airways and travels to the distal airways
and alveoli. In the distal airways, the partial pressure of oxygen
(PO2) is decreased by dilution with carbon dioxide and water
vapor and by uptake into the blood. The diffusion of oxygen
into the pulmonary capillary blood is driven by the gradient
between the PO2 in mixed venous blood and that in the alveolar
gas. The pressure gradient increases when 100% oxygen is
administered, causing increased oxygen diffusion into the pulmonary capillary blood. Oxygen is delivered via the circulation
to the tissue capillary beds, where it is diffused by its higher
partial pressure out of the blood and into the cells.
Oxygen in the blood is carried by the hemoglobin, with a
small amount in physical solution in the plasma. The amount
of oxygen carried by the hemoglobin depends on the partial
pressure of carbon dioxide (PaCO2) and is usually illustrated
with the oxyhemoglobin dissociation curve.
Types of Respiratory Drugs:
Bronchodilators: B2RAs:
Pharmacotherapeutics: Precautions and Contraindications:
The only contraindication to oxygen use is concurrent smoking while the oxygen is running. Oxygen is a flammable gas
that will ignite if a flame is too near. This has implications for
chronic smokers, who should turn off their oxygen to smoke.
Oxygen should be prescribed to patients with chronic carbon dioxide retention with extreme caution and close monitoring. Because hypoxemia may be the primary stimulus for
respiration in these patients, the lowest possible concentration
of oxygen to avoid serious tissue hypoxia should be used. In
patients with hypercapnia, the sudden increases in PaCO 2
produced by oxygen may result in cessation of respiration.
Types of Respiratory Drugs:
Bronchodilators: B2RAs:
Pharmacotherapeutics: Adverse Drug Reactions:
Dry Nasal Passages
The most common adverse drug reaction reported in patients
who are administered oxygen is dry nasal passages from the
flow of gas through the nasal cannula (NC). This can be
prevented by administering humidified oxygen by mask or
by keeping the flow rate low (less than 5 to 6 L/min)
Toxicity
Oxygen toxicity occurs when inspired concentrations of oxygen exceed those of air for prolonged periods of time. Cell
membrane damage and death are thought to be caused by increased production of reactive species such as superoxide
anion, singlet oxygen, hydroxyl radical, and hydrogen peroxide. Some tissues, including the respiratory tract, the CNS, and
the retina, are more sensitive to high oxygen concentration.
In the respiratory tract, inhalation of 100% oxygen for
6 to 8 hours can lead to decreased movement of tracheal
mucus. In as little as 12 hours of 100% oxygen, the patient
may experience tracheobronchial irritation and complain of
chest tightness. After 17 hours, there is increased alveolar permeability and inflammation. Overall pulmonary function decreases after 18 to 24 hours of continuous 100% oxygen. After
24 hours of 100% oxygen, the patient usually has symptoms
of nausea, vomiting, and anorexia. The patient may survive
1 week on toxic levels of oxygen. Death occurs from pulmonary edema. Oxygen toxicity of the CNS does not occur
until the partial pressure of inspired oxygen (PIO2) is greater
than 2 atm, which usually occurs in a hyperbaric chamber.
The retina of a premature neonate can be damaged by exposure to high levels of oxygen for prolonged periods. The
development of retrolental fibroplasia is thought to be related
to high levels of partial pressure of oxygen in arterial blood
(PaO2) administered to the neonate. Adults rarely have
oxygen-induced retinopathy, even with hyperbaric levels
Types of Respiratory Drugs:
Bronchodilators: B2RAs:
Pharmacotherapeutics: Drug Interactions:
There are no drug interactions with oxygen.
Types of Respiratory Drugs:
Bronchodilators: B2RAs:
Pharmacotherapeutics: Monitoring
Monitoring the patient on oxygen is necessary to treat hypoxia and to avoid toxicity. The most accurate yet invasive
method to monitor blood oxygenation is by arterial or mixed
venous blood gas sampling. This procedure can be painful
for the patient and requires rapid transport of the specimen
to the laboratory. Blood gases have the advantage of providing additional information, besides oxygenation, regarding
the patient’s status that may assist in the treatment of the
underlying cause of hypoxemia. Pulse oximetry is a noninvasive method of monitoring the patient receiving oxygen
therapy. It measures the difference in absorption of light by
oxyhemoglobin and deoxyhemoglobin in an accessible location, such as the finger, toe (in children), or ear. Pulse oximetry measures the hemoglobin saturation and not PO2.
The need for continuing oxygen therapy should be monitored by drawing arterial blood gases after 1, 3, and 6 months
of therapy.
Types of Respiratory Drugs:
Bronchodilators: B2RAs:
Pharmacotherapeutics:
Patient Education:
Administration
The patient who is receiving home oxygen therapy requires
knowledge of the appropriate use of oxygen, as well as education about safe administration. The patient should use the
oxygen as prescribed by the provider. Increasing or decreasing the flow rate of oxygen may have adverse effects. Using
oxygen for fewer hours than prescribed will increase hypoxia
and will have detrimental effects.
The patient should understand that oxygen is a flammable
gas that should be kept away from open flame. Patients who
smoke should be cautioned not to smoke while their oxygen
is running.
Adverse Reactions
There are minimal adverse reactions with the use of oxygen.
The patient should be advised of the potential of developing
dry nasal passages. Increasing hydration and increasing the
humidity of the home will help somewhat.
Oxygen toxicity should be discussed and the patient
advised to use the oxygen only as directed. Patients who begin
to exhibit symptoms that may be related to toxicity should
contact their health-care provider.
Lifestyle Management
Lifestyle management issues related to the disease process
being treated should be discussed. They often include the
following:
1. The patient should avoid or quit smoking.
2. COPD patients should avoid unnecessary exposure to
viral respiratory infections.
3. Patients with COPD or other chronic respiratory
diseases should avoid high altitudes.
4. Before traveling by air, the patient should contact the
provider to formulate a plan of care.
