I. Indications of Oxygen Therapy
Cardiac and Respiratory Arrest: For patients with cardiac or respiratory arrest from any cause, immediate oxygen therapy during resuscitation is crucial. In cases of non - breathing patients, devices like simple respirators, respirators, or anesthesia machines can be used for tracheal intubation with pressurized oxygen.
Hypoxemia
Hypoxemia with Hypercapnia: Caused by insufficient ventilation, accompanied by carbon dioxide retention. Oxygen therapy can correct hypoxemia but may aggravate carbon dioxide retention if misused.
Simple Hypoxemia: Usually due to diffusion dysfunction and ventilation/blood flow imbalance. Increasing inspired oxygen concentration can correct hypoxemia from diffusion dysfunction, but it is less effective for intrapulmonary shunts caused by ventilation/blood flow imbalance.
Tissue Hypoxia: In conditions such as decreased cardiac output, acute myocardial infarction, and anemia, although obvious hypoxemia may not be present, tissue hypoxia can occur. Monitoring mixed venous blood PO2 (should reach > 4.67kPa or 35mmHg when oxygen therapy is effective) can indicate tissue oxygenation.
II. Purposes of Oxygen Therapy
Correcting Hypoxemia: Increases alveolar oxygen partial pressure, diffusion capacity, and pulmonary capillary oxygen partial pressure, raising PaO2.
Reducing the Work of Breathing: Restores normal lung gas exchange, maintaining appropriate alveolar oxygen partial pressure, reducing total ventilation and oxygen consumption.
Reducing the Heart Load: Effectively reduces the work of the heart and its load.
III. Methods of Oxygen Therapy
High - Flow System Oxygen Supply
Principle: Provides the full inspiratory gas volume. The patient breathes only the gas from the system. It can offer a stable oxygen concentration (24% - 70%). The Ventruri mask is a common device, using the Bernoulli principle to control inhaled air volume and adjust oxygen concentration.
Advantages: Can supply a lasting and correct oxygen concentration regardless of patient ventilation changes, control the temperature and humidity of inhaled gas, and monitor inspired oxygen concentration. It must meet at least 4 times the patient's minute ventilation volume to ensure constant oxygen concentration.
IV. Hyperbaric Oxygen Therapy
Uses 100% oxygen at pressures > 101.325kPa (1atm) to improve tissue hypoxia and inhibit anaerobic bacteria growth during anaerobic infection. Increases dissolved oxygen in blood (e.g., at 303.975kPa or 3atm, plasma dissolved oxygen can reach 6.6ml). Indications include hemorrhagic anemia, carbon monoxide poisoning, acute cyanide poisoning, acute gas embolism, gas gangrene, etc.
V. Monitoring the Effect of Oxygen Therapy
Cardiovascular System Response: Observe consciousness, blood pressure, heart rate, rhythm, peripheral tissue perfusion (skin color), and record urine output. Improvement indicates ideal oxygen therapy effect.
Respiratory System Response: Dyspnea and shortness of breath should improve, breathing movement stabilizes, frequency slows, and work of breathing reduces.
Blood Gas Analysis: PaO2 should increase.
VI. Side Effects of Oxygen Therapy and Oxygen Toxicity
Carbon Dioxide Retention: In hypoxemia, high - concentration oxygen inhalation can eliminate the reflex mechanism that stimulates the respiratory center, inhibiting spontaneous breathing and increasing PaCO2, potentially leading to pulmonary encephalopathy. Low - concentration oxygen inhalation is recommended for relevant patients with PaCO2 monitoring.
Absorptive Atelectasis: High - concentration oxygen inhalation flushes out alveolar nitrogen. With bronchial obstruction, alveolar oxygen can be quickly absorbed, causing atelectasis.
Oxygen Poisoning
Symptoms: Early symptoms include tracheal irritation (uncontrollable dry cough, shortness of breath, retrosternal pain), usually within 6 hours of inhaling 100% oxygen. Lung function may be normal initially, then lung capacity and compliance decrease. ARDS, hemoptysis, alveolar cell damage, surfactant decrease, and interstitial fibrosis may occur over time.
Prevention: Oxygen at 60% - 70% at 101.325kPa (1atm) can be used safely for 24 hours; 40% - 50% can be used longer. Oxygen concentration > 40% for 2 - 3 days increases the risk of toxicity. Targeted oxygen therapy is needed, along with other treatments like bronchodilators, expectoration, cardiac diuretics, and PEEP to keep oxygen concentration below the toxic level while maintaining PaO2 at 8.0 - 9.33kPa (60 - 70mmHg).