Oxygen therapy is a treatment method used to correct hypoxia. The modern view is that oxygen is also a “drug”, the use of which should be indicated, to master the application method, dose, treatment course, and monitor its efficacy. If oxygen therapy is not applied properly, it can cause oxygen toxicity.
Hazards of hypoxia
The tolerance of each part of the brain tissue to hypoxia varies, with the cerebral cortex being the least tolerant and the brainstem being the most tolerant. When the body temperature is 37, the brain tissue may be irreversibly damaged if the circulation is stopped for 3-4 min. Patients with moderate hypoxia can have mental symptoms such as fatigue, apathy, drowsiness, euphoria and incoherence. The aggravation of hypoxia may cause blurred vision, dysfunction of supply and even cerebral edema, increased intracranial pressure, coma and brain cell death.
Huang Tiequn, Department of Cadre Diagnosis and Treatment, China-Japan Friendship Hospital
2. Cardiovascular effects The heart muscle is one of the organs sensitive to hypoxia. Mild to moderate hypoxia can cause heart rate to increase and blood pressure to rise; aggravated hypoxia can cause myocardial contractility to decrease, heart rate to slow down, blood pressure to drop, cardiac blood displacement to decrease, and even cause arrhythmia and cardiac arrest.
3, the effect on respiration Acute hypoxia stimulates the aortic body and carotid sinus chemoreceptors, causing respiration to increase and deepen. Severe hypoxia inhibits the respiratory center. Hypoxia can cause pulmonary edema and pulmonary atelectasis. Long-term hypoxia causes vasoconstriction of tissue and increases pulmonary artery pressure, leading to right ventricular hypertrophy and pulmonary heart disease.
4. Effects on liver and kidney Acute hypoxia causes edema, degeneration and necrosis of hepatocytes, renal vasoconstriction, reduced renal blood flow, turbidity, watery degeneration and even necrosis of renal tubular epithelial cells, leading to renal insufficiency.
5. Effects on tissue cells Anaerobic glycolysis is enhanced during hypoxia, and a large amount of lactic acid, ketone bodies and inorganic phosphorus accumulation causes metabolic acidosis. ATP decreases during hypoxia, and the Na+-K+-ATP pump fails. Na+ and H+ enter the cells and K+ is released from the cells, causing intracellular edema and extracellular hyperkalemia.
Laboratory tests for tissue hypoxia
1.Mild No cyanosis PaO2>6.67kPa(50mmHg), SaO2>80%.
2.Moderate With cyanosis PaO24.00~6.67kPa(30~50mmHg), SaO2 60%~80%.
3.Severe Significant cyanosis PaO2<4.00kPa(30mmHg), SaO2<60％.
Indications for oxygen therapy
Any hypoxemia is an indication for oxygen therapy. However, because the organism has certain compensatory and adaptive mechanisms, oxygen therapy should be limited to patients with moderate or higher levels of hypoxia and clinical manifestations. The more recognized standard of oxygen therapy is PaO2<8.00kPa (60mmHg).
1. Those with reduced alveolar ventilation, when there is mostly CO2 retention, have attention to oxygen therapy while improving ventilation.
2, those with ventilation/blood flow ratio disorders. The normal ratio is about 0.8, but an increased ratio means alveolar collapse and a decreased ratio means a right-to-left shunt, both of which can cause clinical hypoxemia.
3. Those with reduced diffusion function. Oxygen inhalation can increase the oxygen content in the alveoli, thus increasing the diffusion of alveolar oxygen.
4.Other conditions: reduced cardiac output, severe anemia, CO poisoning, shock, metabolic disorders, etc. Arterial PaO2 in these diseases may be normal, or tissue hypoxia occurs due to decreased oxygen-carrying capacity of blood, or slow circulatory cycle, or decreased oxygen utilization capacity of tissues. However, there is a lack of ideal clinical indicators to reflect tissue hypoxia, and it is more difficult to evaluate the efficacy of oxygen therapy.
Devices and methods of oxygen therapy
(I) Nasal catheter or nasal plug
It is the most commonly used method in clinical practice, which is simple, inexpensive, convenient and comfortable, and does not affect coughing, eating and talking, and is easily accepted by most patients. Its inhalation oxygen concentration (FiO2) and inhalation oxygen flow are roughly related as follows.
FiO2=21+4×inhaled oxygen flow rate(L/min)
In fact, FiO2 is also influenced by tidal volume and respiratory rate, the greater the patient’s ventilation, the lower the FiO2. The disadvantages of applying nasal catheter or nasal plug are: in addition to the fact that FiO2 is not constant and is affected by the patient’s breathing, there is also the fact that the catheter is easily blocked and is locally irritating.
(II) Simple mask
Generally made of plastic or rubber, lighter in weight, the mask needs to be attached around the mouth and nose, and fixed with a strap after the head and face. Simple mask generally consumes more oxygen (oxygen flow rate 5-6L/min), has a higher concentration of inhaled oxygen (FiO2 can reach 40%-50%), can provide better humidification, and is suitable for patients with severe hypoxia and no CO2 retention. Disadvantages: affects coughing and eating, and the mask is easy to shift or fall off during sleep position change.
(C) Mask with storage bag
A latex or rubber storage bag is fitted to a simple mask to deliver high concentrations of oxygen to patients without tracheal intubation or tracheotomy. If there is no one-way flap between the mask and the storage bag is called a partial repeat breathing mask, if there is no single flap, that is, no repeat breathing mask. At this time, the patient can only inhale gas from the storage bag, exhale gas from the air hole overflow, and can not re-enter the storage bag. This mask has a lower oxygen consumption than a simple mask and can provide high FiO2 with a lower flow of oxygen.
(D) Venturi mask
According to the Venturi principle, the oxygen flow is used to generate negative pressure, inhale air to dilute oxygen, adjust the air intake, and control the FiO2 in the range of 25% to 50%, the oxygen concentration in the mask is more stable, the oxygen consumption is more stable, the oxygen consumption is less, no wetting is needed, and basically no repeat breathing. The Venturi mask has been widely used clinically, especially in the treatment of patients with type II respiratory failure, and is therefore particularly beneficial.
(E) Hyperbaric oxygen chamber
The chamber is filled with pure oxygen at a certain pressure, exceeding atmospheric pressure. It is used for a variety of diseases, such as CO poisoning, pulmonary edema, neonatal asphyxia, ARDS, etc. Hyperbaric oxygen bin can improve the amount of physically dissolved oxygen in the blood, which can rapidly correct hypoxemia and tissue hypoxia is improved.
(vi), mechanical ventilation to give oxygen Patients with severe hypoxia and respiratory failure need to be treated with non-invasive ventilation or establish an artificial airway and perform mechanical ventilation.
(vii), simple respirator.
Oxygen therapy monitoring and precautions
1.Check the oxygen administration equipment, whether there is any malfunction in the process of oxygen therapy.
2.Oxygen concentration and oxygen administration route should be different according to the disease.
3.Monitor SaO2, blood gas analysis, prevent CO2 retention, check the improvement of symptoms, etc. during oxygenation.
4.Wetting of airway.
5.Long-term oxygen therapy (LTOT) is very important for patients with chronic respiratory insufficiency (e.g. COPD). Low-flow oxygenation for more than 15h per day can improve quality of life, increase survival rate and reduce pulmonary hypertension.
6.Oxygen therapy safety guidance Strictly implement the four preventions: namely, fire prevention, shock prevention, oil prevention and heat prevention. Always pay attention to check the oxygen meter, when the remaining oxygen is found close to 20 oxygen pressure, should immediately stop using oxygen, replace the new cylinder, so as to avoid the danger of inflation. Instruct patients not to adjust the oxygen flow casually by themselves, and explain the importance of low-flow O2 inhalation to patients.
7.Pay attention to the infection factor in oxygen inhalation Prevent infection Oxygen wetting bottle and oxygen inhalation tube need to be sterilized and used, wetting bottle with saline or sterilized distilled water should be replaced once a day, and wetting bottle for long-term users should be sterilized and replaced once a day, use disposable oxygen connection tube and disposable nasal catheter, oxygen connection tube should be replaced twice a week and nasal catheter should be replaced once a day.
8.Oxygen therapy environment protection Strengthen air disinfection, ventilation in general wards every day, various operations such as bed making, sheet changing, etc., rapid and agile, gentle movements, reduce dust flying, for serious patients with serious lung infections in the ward, the ward is disinfected with ultraviolet light twice a day for 30-60 minutes each time; wet sweeping 2-3 times a day, mopping with disinfectant water 2 times a week; strengthen ward management, limit the number of accompanying visitors The bacteriological monitoring of air and oxygenated water should be carried out regularly, and problems should be dealt with promptly.
Prevention and treatment of oxygen therapy complications
Control the time and concentration of oxygen therapy to prevent oxygen toxicity – long time and high concentration of oxygen inhalation can lead to changes in lung parenchyma, such as alveolar wall thickening and bleeding. Patients with oxygen toxicity often show a burning sensation behind the sternum, dry cough, nausea and vomiting, irritability, progressive dyspnea, and continued increase in oxygen concentration still cannot keep the patient’s partial pressure of blood oxygen at the ideal level. The key to prevent oxygen toxicity is to avoid prolonged high concentration oxygen therapy. If the oxygen concentration is <30%, no side effects and danger will occur even if the oxygen is inhaled for a long time; if the oxygen concentration is >50% and the oxygen is inhaled for more than 24 hours, oxygen toxicity can occur. There are few treatment methods for oxygen poisoning, and the key is prevention. It is best not to inhale pure oxygen for more than 4-6 hours, and the maximum safe value of oxygen concentration is at 40%.
Strengthen primary care to prevent the occurrence of pulmonary atelectasis – Absorptive pulmonary atelectasis can occur when the patient’s airway is completely blocked by secretions and the air in the lower segment of the obstruction is gradually absorbed. In addition, when the patient inhales high concentrations of oxygen, the main gas in the alveoli changes from nitrogen to oxygen, which is more easily absorbed than nitrogen, accelerating the formation of absorptive atelectasis. For this reason, we should strictly control the concentration of oxygen inhalation, and when treating respiratory tract infections, encourage patients to cough and breathe deeply, instruct them to turn more often, give back patting, and enhance sputum excretion, which can reduce the occurrence of aspiration atelectasis.
Strengthen the wetting of oxygen to prevent the drying of respiratory secretions or tracheotomy patients have lost the wetting effect of the upper respiratory tract on the inhaled gas, such as continuous inhalation of oxygen without wetting and high concentration, more than 24 hours, the bronchial mucosa can be damaged by the direct stimulation of dry gas, so that the secretions become dry, sticky, crusty and not easy to cough out, at this time, the method of heating and wetting can be used, so that the oxygen wetting bottle in the Water temperature is kept at 60-70℃ to promote sputum discharge and keep the respiratory tract unobstructed.
Strictly grasp the indications for neonatal oxygen therapy to prevent post-ocular fibrous tissue hyperplasia Neonates who inhale high concentrations of oxygen can be complicated by post-ocular fibrous tissue hyperplasia, which can occur as long as the partial pressure of oxygen exceeds 140 mmHg for several hours and can lead to blindness. Therefore, we should strictly grasp the indications for neonatal oxygen therapy, maintain the oxygen concentration below 40% and PaO2 at 100-120mmHg, so that this complication can be avoided.
Oxygen inhalation therapy is one of the common clinical treatment methods. Nurses live in the first line of clinical, is not only the implementation of oxygen therapy, but also the guardian during oxygen therapy, so they must strengthen the knowledge of oxygen therapy, closely observe and actively prevent the occurrence of side effects of oxygen therapy, to ensure that the patient reasonable oxygen, safe use of oxygen, in order to achieve the purpose of curing the disease and saving lives.