Acute respiratory distress syndrome in the elderly

　　There are more than 100 causes that can lead to acute respiratory distress syndrome (ARDS) in clinical practice. Common causes include shock, trauma, severe infection, aspiration, inhalation of harmful gases, excessive fluid infusion, DIC, viral pneumonia, fat embolism, and others. According to literature reports, the causes of ARDS will be summarized into 10 categories below:

　　1. Shock infectious, hemorrhagic, cardiogenic.

　　2. Trauma pulmonary or extrapulmonary trauma, pulmonary fat embolism, drowning.

　　3. Severe infection and sepsis bacterial pneumonia, viral pneumonia, fungal infection and fungal pneumonia, rickettsial infection, tuberculosis, and other infections.

　　4. Aspiration of gastric contents.

　　5. Inhalation of harmful gases such as high concentration oxygen, and others.

　　6. Drug anesthetic drug overdose, methadone, colchicine, and others.

　　7. Metabolic diseases such as diabetic acidosis.

　　8. Hematological diseases such as multiple large blood transfusions.

　　9. Obstetric and gynecological diseases such as eclampsia and pre-eclampsia, amniotic fluid embolism.

　　10. Other acute pancreatitis, connective tissue disease, extracorporeal circulation, post-cardioversion, organ transplantation.

　　In addition to its clinical manifestations, acute respiratory distress syndrome in the elderly can also cause other diseases. Common complications include infection (especially Gram-negative bacillary infection), liver and kidney dysfunction, gastrointestinal bleeding, arrhythmia, pneumothorax, etc.

　　Acute respiratory distress syndrome (ARDS) often occurs as a complication of severe trauma, shock, sepsis, aspiration of toxic gases, and severe infection, among other primary diseases. It is characterized by an acute onset, even sudden onset. Specifically, the following are involved:

　　1. Respiratory distress

　　Tachypnea and respiratory distress are the main clinical manifestations of ARDS, usually occurring within 1-2 days of onset, with progressive acceleration, often exceeding 28 times/min. In severe cases, the respiratory rate may reach 60 times/min, with significant difficulty breathing and respiratory distress symptoms.

　　2. Cough, sputum, restlessness, and confusion

　　Coughing up sputum and blood-stained sputum is one of the typical symptoms of ARDS, and due to hypoxia and respiratory distress, most ARDS patients start to show restlessness, confusion, or expressionless in the early stage.

　　3. Signs

　　With the worsening of symptoms, the respiratory rate increases, cyanosis, and inspiratory 'three凹陷 signs' appear. Some patients may have dry and wet rales in the lungs.

　　The prevention of acute respiratory distress syndrome in the elderly mainly involves actively treating the primary disease, preventing complications, and reducing the mortality rate. In cases of traumatic diseases, such as chest trauma, immediate treatment is required to prevent hypoxemia and widespread lung injury. Fracture patients should prevent fat embolism and other complications. Infection is a common complication that worsens the condition and increases the mortality rate. Active prevention and treatment of infection should be carried out, and common complications include pneumothorax, liver and kidney dysfunction, gastrointestinal bleeding. Reasonable use of ventilators during treatment, strict monitoring of clinical and laboratory indicators, in order to prevent the occurrence of complications and correct them in a timely manner.

　　The clinical examination of elderly acute respiratory distress syndrome is as follows:

　　I. Chest X-ray signs Patchy or large areas of shadow present interstitial or alveolar lesions.

　　II. Electrolyte measurement There is often hyperkalemia, HCO3- increases due to acidosis compensation, decreases due to metabolic acidosis, and the results can be high, low, or normal.

　　III. Electrocardiogram There may be sinus arrhythmia, conduction block, atrial and ventricular arrhythmias, and non-specific S-T segment and T wave changes.

　　Elderly patients with acute respiratory distress syndrome should enhance nutrition, choosing easily digestible foods rich in calories, protein, and vitamins. Foods such as congee, milk, soft rice, soy milk, eggs, lean meat, and fresh vegetables and fruits rich in vitamins A, B, and C can enhance the body's resistance.

　　The prognosis of elderly acute respiratory distress syndrome is extremely poor, with a mortality rate of up to 50% to 60%, and there is still no specific therapy. Only targeted or supportive treatment can be performed, actively treating the primary disease, improving ventilation and tissue hypoxia, preventing further lung injury and pulmonary edema, which are the main principles of treatment. Specifically, as follows:

　　I. Treatment of the primary disease

　　In the treatment of the primary disease, special attention should be paid to the control of infection, as infection is not only a common cause of ARDS but also can seriously affect the prognosis once ARDS is complicated by infection. Blood culture should be performed, and sensitive antibiotics should be selected for intravenous, adequate dosing.

　　II. Improve ventilation and tissue hypoxia

　　During ARDS, due to widespread atelectasis and pulmonary edema, lung compliance decreases, and the function of pulmonary ventilation and gas exchange is severely impaired, leading to severe tissue hypoxia, and routine oxygen inhalation cannot effectively correct it. Therefore, mechanical ventilation treatment is required. Indications for mechanical ventilation: if the inhaled oxygen concentration is greater than 50%, the arterial blood oxygen saturation (SaO2)
　　1. High-frequency ventilation (HFV) and high-frequency jet ventilation (HFJV): HFV can reduce peak airway pressure and minimize the lung injury and barotrauma caused by it. However, oxygenation decreases with the decrease in mean airway pressure, which is particularly true for ARDS patients. HFJV can significantly increase oxygenation but also increase mean airway pressure, reduce venous return and cardiac output. Therefore, HFV and HFJV are no longer used for the treatment of ARDS.

　　2. PEEP: It can expand collapsed alveoli and reinflate atelectatic alveoli, thus correcting the ventilation/perfusion (V/Q) ratio disorder, increasing functional residual capacity and lung compliance. It is conducive to the diffusion of oxygen through the alveolar membrane. Therefore, PEEP can effectively increase PaO2. However, experiments show that PEEP cannot prevent lung injury. In summary, PEEP itself cannot prevent or cure ARDS, but it can accelerate the repair process by improving oxygenation, avoid further lung tissue damage from high FiO2, and provide an opportunity for comprehensive treatment as a supportive therapy.

　　3. New mechanical ventilation methods:

　　① Assistive controlled ventilation or intermittent mandatory ventilation is currently recommended, where patients rely on spontaneous breathing while occasionally receiving positive pressure breathing from the ventilator. However, it is not suitable for patients with extremely fatigued respiratory muscles.

　　② Other types of mechanical ventilation, including volume-controlled inverse ventilation; low tidal volume ventilation with appropriate PEEP; extracorporeal membrane oxygenation therapy, etc., have different efficacy, with their own advantages and disadvantages.

　　Third, multi-link reduction of lung and systemic injury

　　1. Glucocorticoids: Adrenal cortical hormones can alleviate allergic, inflammatory, and toxic reactions; relieve bronchospasm; inhibit PMN and platelet aggregation, prevent microthrombosis, and stabilize lysosomal membranes. Reduce the release of lysosomal enzymes and related mediators; increase the synthesis of pulmonary surfactant substances, and alleviate microatelectasis, etc., which are used in the early stage of ARDS, but there is much controversy, mainly about the dose and timing of medication. Delaying medication for too long is not appropriate, and there are also reports that the mortality rate of high-dose methylprednisolone is still higher than that of the control group.

　　2. Vasodilators: Including atropine and PGE1 have a relieving effect on ARDS and experimental RDS, but there is no evidence at present.

　　3. Other: Such as methylxanthines, pentoxifylline can affect intercellular signal transduction, reduce PMN and AM activation, and antagonize TNF, inhibit the production of PIA2 enzyme and IL-1 and their cytokine responses, inhibit OR release, and alleviate lung injury. In addition, there are drugs like Pulmadine, which are currently in the experimental stage.