From the Guidelines
Hypoxia is primarily caused by respiratory disorders, cardiovascular issues, environmental factors, and other mechanisms that impair oxygen delivery to tissues, as highlighted in the BTS guideline for oxygen use in adults in healthcare and emergency settings 1. The primary causes of hypoxia include:
- Respiratory disorders like pneumonia, asthma, COPD, and pulmonary edema, which impair oxygen exchange in the lungs
- Cardiovascular issues such as heart failure, cardiac arrest, and severe anemia, which reduce oxygen delivery to tissues
- Environmental factors like high altitude, where oxygen partial pressure is lower, can induce hypoxia
- Carbon monoxide poisoning, which prevents hemoglobin from carrying oxygen effectively
- Hypoventilation from drug overdoses, brain injuries, or sleep apnea, which decreases oxygen intake
- Ventilation-perfusion mismatch, which occurs when air reaches lung areas with poor blood supply or vice versa
- Diffusion impairment in conditions like pulmonary fibrosis, which hinders oxygen transfer across the alveolar-capillary membrane
- Shunting, where blood bypasses the lungs, preventing proper oxygenation
Other mechanisms of hypoxia include:
- Anaemic hypoxia, which results from a reduced oxygen-carrying capacity due to anemia or carbon monoxide poisoning 1
- Stagnant hypoxia, which occurs when there is a low cardiac output state, reducing oxygen delivery even in the absence of hypoxaemia
- Histotoxic hypoxia, which is due to an inability to metabolise oxygen at the mitochondrial level, often seen in severe sepsis or certain types of poisoning 1
It is essential to identify and manage the underlying cause of hypoxia to prevent tissue damage and organ dysfunction, and treatment may include oxygen therapy, addressing the primary condition, and in severe cases, mechanical ventilation, as suggested in the BTS guideline 1.
From the Research
Causes of Hypoxia
- Hypoxia can be caused by various factors, including chronic obstructive pulmonary disease (COPD) 2, 3, high-altitude exposure 4, and carbon monoxide poisoning 5, 6
- In COPD, severely reduced lung function can limit adequate oxygen uptake, leading to hypoxia 2, 3
- High-altitude exposure can also cause hypoxia due to lower oxygen levels in the air 4
- Carbon monoxide poisoning can cause tissue hypoxia-ischemia secondary to carboxyhemoglobin formation and direct CO-mediated damage at a cellular level 5, 6
- Other factors that can contribute to hypoxia include malnutrition, which can worsen the condition in COPD patients 4
Mechanisms of Hypoxia
- Hypoxia can induce gene expression for fructose-2-6-biphosphatase, an enzyme that switches glucose metabolism towards glycolysis, allowing energy production in anaerobic conditions 4
- Hypoxia inducible factor 1 (HIF-1) is pivotal in the adaptation to chronic hypoxia and is involved in the development of anorexia 4
- HIF-1 polymorphism and interaction with other molecules, especially estrogens, can also play a role in the clinical evolution of disease 4
Clinical Implications
- Supplemental oxygen therapy can be used to treat hypoxia in COPD patients 2, 3 and carbon monoxide poisoning 5, 6
- Automated oxygen administration devices may help to optimize supplemental oxygen therapy in COPD patients 2
- Hyperbaric oxygen can also be used to treat carbon monoxide poisoning, but its exact indications are controversial 5, 6