Clinical presentation and treatment of respiratory failure—January 30, 1994

Clinical presentation and treatment of respiratory failure—January 30, 1994

1. Clinical manifestations of respiratory failure

(1) Hypoxemia PaO2 < 50 mmHg: ① Cyanosis of the lips and nail beds is the most important sign of hypoxemia, but due to factors such as the body’s usual hemoglobin levels, skin pigmentation, and cardiac function, the degree of cyanosis and the degree of hypoxia may not be in direct proportion; ② In addition to cyanosis, irritability, delirium, convulsions, epilepsy, and loss of consciousness may also occur; ③ Hypoxia has a profound impact on the cardiovascular system, initially causing tachycardia and hypertension, followed by arrhythmias and shock. Due to pulmonary vasoconstriction, pulmonary hypertension and right heart failure may develop.

(2) Hypercapnia (respiratory acidosis): Due to the accumulation of CO2, severe central nervous system and cardiovascular symptoms may occur. Central nervous system symptoms include drowsiness, coma, agitation, and convulsions; muscle tone may increase or decrease, meaning tendon reflexes may become stronger or weaker. Due to compensatory dilation of cerebral blood vessels, intracranial pressure rises, and fundoscopic examination reveals papilledema, miosis, and unequal pupil sizes—these are clinical manifestations of severe respiratory failure, sometimes referred to as pulmonary encephalopathy. Cardiovascular symptoms include chest pain, chest tightness, palpitations, tachycardia, and hypertension; in advanced stages, severe hypercapnia may occur, at which point blood pressure begins to drop. Peripheral vasodilation may cause conjunctival congestion, and some patients may experience arrhythmias. Beyond changes in the lungs and heart, all five viscera and six bowels may exhibit symptoms caused by lack of O2 and excess CO2, such as peptic ulcer symptoms, upper gastrointestinal bleeding, liver and kidney dysfunction, and severe electrolyte imbalance. Both metabolic acidosis and respiratory acidosis may occur.

2. Diagnosis of respiratory failure

(1) Hypoxemia: Normal arterial oxygen partial pressure (PaO2) is (90–100) mmHg. (55–60) mmHg indicates mild respiratory failure, (40–55) mmHg indicates moderate, and less than 40 mmHg indicates severe.

(2) Hypercapnia: Normal PaCO2 is (35–40) mmHg. >50 mmHg indicates mild respiratory failure, >70 mmHg indicates moderate, and >90 mmHg indicates severe.

(3) Arterial oxygen saturation (SaO2): 95%–100% is normal, 80%–90% indicates mild hypoxia, 60%–80% indicates moderate hypoxia, and <60% indicates severe hypoxia.

3. Treatment

(1) Control infection.

(2) Non-invasive nasal mask bi-level positive airway pressure ventilation.

(3) Central nervous system stimulants: Nicethiamine is most commonly used, starting with 0.375 g intravenously, followed by 3.75 g added to 500 mL of 5% glucose solution for intravenous drip; this drug strongly stimulates the central nervous system.