2026-07-17 12:03中午
關於缺氧, Hypoxia 與 hypoxemia 差異可以參考這篇
Hypoxia and Hypoxemia (from StatPerls)
名詞解釋
Oxygen saturation 血氧飽和度. 是指血紅素中有攜帶氧氣的比例
Hypoxia, 可翻譯為缺氧. 是指血流所攜帶的氧氣不足以供應組織氧氣需求. 是組織層面的缺氧, 原因可以是血流不足或血中氧氣不足引起
hypoxemia 可翻譯為低血氧. 是指血中氧氣濃度降低.
PaO₂ 動脈血中氧分壓 (the partial pressure of oxygen in arterial blood.)
Pulse oximetry 血氧機. 測得的是血氧氣飽和度. 人體的氧氣輸送主要是靠血紅素(印象是97%靠血紅素. 3% 靠血漿), 貧血的人. 即使血氧飽和度正常. 因同量血流能攜帶的氧氣量下降. 比一般人容易發生組織缺氧
同樣的原因. 動脈血中氧分壓即使正常. 在貧血的狀況仍會降低血液攜帶氧氣能力. 發生組織缺氧的機率也會增加
Hypoxia occurs when oxygen is insufficient at the tissue level to maintain adequate homeostasis, stemming from various causes such as hypoventilation, ventilation-perfusion mismatch, or right-to-left shunting. Hypoxia can manifest acutely or chronically, with varying presentations from dyspnea to tachypnea. Evaluation methods include pulse oximetry, arterial blood gas analysis, imaging, and PaO2:FiO2 ratio calculation for acute hypoxia. Conversely, pulmonary function tests, overnight oximetry, and other relevant assessments.
Introduction
Hypoxia occurs when oxygen is insufficient at the tissue level to maintain adequate homeostasis, stemming from various causes such as hypoventilation, ventilation-perfusion (V/Q) mismatch, or right-to-left shunting. This condition can arise from inadequate oxygen delivery to the tissues due to either low blood supply or low oxygen content in the blood, also known as hypoxemia.
Hypoxia can manifest across a spectrum of intensity, ranging from mild to severe, and present in acute, chronic, or mixed acute and chronic forms. The response to hypoxia varies among tissues—while some tissues can tolerate certain forms of hypoxia or ischemia for extended periods, others are significantly impaired by low oxygen levels
Etiology
At the tissue level, 2 primary causes of hypoxia arise—low blood flow to the tissue or low oxygen content in the blood (hypoxemia).[4][5][6] Hypoxemia should be differentiated as a cause of hypoxia. Oxygen is transported by hemoglobin within red blood cells, and efficient ventilation relies on the direct contact between red blood cells and alveoli, facilitating diffusion. This process may be compromised at any of the following 3 points—blood flow to the lung (perfusion), airflow to the alveoli (ventilation), and gas exchange through the interstitial tissue (diffusion).
As mentioned below, hypoxia can arise from various underlying causes, each with distinct etiologies and mechanisms.
Reduced oxygen tension: As in cases of high altitude.
Hypoventilation: Hypoventilation can result from various factors, including:
- Proximal airway obstruction, such as laryngeal edema or foreign body inhalation.
- Distal airway obstruction, as seen in bronchial asthma or chronic obstructive pulmonary disease (COPD).
- Impaired respiratory drive, as observed in cases of deep sedation or coma.
- Restricted chest wall movement, which is evident in conditions such as obesity hypoventilation syndrome, circumferential burns, massive ascites, or ankylosing spondylitis.
- Neuromuscular diseases include myasthenia gravis, muscular dystrophy, amyotrophic lateral sclerosis, or phrenic nerve injuries.
V/Q mismatch: This imbalance also leads to hypoxia in 2 ways, as mentioned below.
- Decreased V/Q ratio: Decreased V/Q ratio, caused by impaired ventilation or high perfusion, as seen in conditions such as chronic bronchitis, obstructive airway disease, mucus plugs, and pulmonary edema, results in compromised ventilation and a reduction in the V/Q ratio.
- Increased V/Q ratio: In cases of increased V/Q ratio, characterized by impaired perfusion as seen in conditions such as pulmonary embolism, or increased ventilation such as in emphysema with large bullae in the lungs, the available surface area for gas exchange diminishes. This results in higher ventilation than perfusion, leading to a high V/Q ratio.
Right-to-left shunt: Right-to-left shunt occurs when blood bypasses the lungs without oxygenation by crossing from the right to the left side of the heart. Causes include:
- Anatomic shunts: Blood bypasses the alveoli, as seen in intracardiac shunts such as atrial septal defect (ASD), a ventricular septal defect (VSD), or a patent ductus arteriosus (PDA), pulmonary arteriovenous malformations, fistulas, and hepato-pulmonary syndrome.
- Physiologic shunts: Blood passes through non-ventilated alveoli, such as pneumonia, atelectasis, and acute respiratory distress syndrome (ARDS).
Impaired diffusion of oxygen: Oxygen diffusion between the alveolus and the pulmonary capillaries is hindered, typically due to interstitial edema, inflammation, or fibrosis. Clinical examples encompass conditions like pulmonary edema and interstitial lung disease.
