Short answers, pulled from the story.
Respiratory failure results from inadequate gas exchange by the respiratory system, meaning arterial oxygen, carbon dioxide, or both cannot be kept at normal levels. A drop in blood oxygen is called hypoxemia, and a rise in arterial carbon dioxide is called hypercapnia. Typical reference values are oxygen partial pressure above 80 mmHg (11 kPa) and carbon dioxide below 45 mmHg (6.0 kPa).
Type 1 respiratory failure is a failure of oxygenation, with PaO2 below 60 mmHg and a normal or low carbon dioxide level. Type 2 respiratory failure is caused by inadequate alveolar ventilation, with PaCO2 rising above 50 mmHg and pH falling below 7.35, so both oxygen and carbon dioxide are affected.
Type 1 respiratory failure is caused by conditions that affect oxygenation, including low ambient oxygen such as at high altitude, ventilation-perfusion mismatch, alveolar hypoventilation, diffusion problems, and right-to-left shunt. Examples include pulmonary embolism, acute respiratory distress syndrome, pneumonia, and severe pulmonary edema.
Type 3 respiratory failure is a form of Type 1 associated with an operation or surgery, often called perioperative respiratory failure, and it commonly involves lung atelectasis after general anesthesia. Type 4 respiratory failure occurs when metabolic oxygen demands exceed what the cardiopulmonary system can provide, often from hypoperfusion of respiratory muscles in patients in shock.
Arterial blood gas assessment is the gold standard diagnostic test for respiratory failure because it measures blood oxygen levels, and all types are characterized by a low blood oxygen level. Supporting methods include capnometry, which measures carbon dioxide in exhaled air, pulse oximetry, which measures oxygen-saturated hemoglobin, and imaging such as ultrasonography and radiography.
Treatment of respiratory failure requires addressing the underlying cause when possible, with high-flow nasal oxygen as first-line therapy for acute hypoxic cases when intubation is not indicated. Medications include bronchodilators, antibiotics, glucocorticoids, and diuretics, while naloxone reverses opioid overdose. Type 1 may need oxygen therapy or mechanical ventilation, and Type 2 often requires non-invasive ventilation.
The prognosis for respiratory failure is highly variable and depends on the underlying cause and the availability of appropriate treatment and management. One of every three hospitalized cases of acute respiratory failure is fatal.