Hypoxemia: Definition, Causes, and Treatment

Definition of hypoxemia

Hypoxemia (also known as oxygen desaturation) is defined as an abnormally-low partial pressure of oxygen in the arterial blood. Oxygen cascade (or oxygen delivery from the outer air to body cells) is highly sensitive to various abnormalities that can appear anywhere in the air (e.g., reduced oxygen content), airways, lungs, or cardiovascular system. The examples and causes are explained below. Oximeters are commonly used these days in hospitals and by critical-care professionals to define blood oxygen levels and diagnose hypoxemia.

On an average, the normal oxygen levels in our blood stream are about 85 mm Hg. In people suffering from hypoxemia, this falls down to as low as 60 mmHg. During hypoxemia, the oxygen saturation in the body is less than 90 percent. This is the formal definition of hypoxemia. Normal pulse oximeter readings can range from 95 to 100 percent. If the same falls below 80 percent, the condition is referred to as severe hypoxemia.

Hypoxemia has a profound negative effect on quality of life (Nonoyama et al, 2007; Orth et al, 2008; Sans-Torres et al, 1999; Tanni et al, 2007). Even nocturnal hypoxemia (i.e., temporary hemoglobin desaturation during sleep) has negative effects on life quality (Young et al, 2011).

Causes of hypoxemia

1) The inspired air has reduced oxygen content (e.g., at high altitude or due to other causes).

2) Insufficient gas exchange is caused by alveolar hypoventilation (or breathing too little) with chest breathing. It can happen, for example, during sleep or during physical exercise for people with lung diseases.

3) Some parts of the lungs are obstructed, or damaged, or have insufficient ventilation (e.g., as for emphysema, COPD and other conditions).

4) Blood shunting causes the arterial and venous blood to mix and this causes reduced oxygenation of the arterial blood.

5) Impaired alveolar-capillary diffusion (e.g., due to thick mucus during exercise in people with cystic fibrosis).

In many cases, transition into a horizontal position, sleep (especially REM sleep), overeating, slouching (or poor posture) and physical exercise (e.g., in cystic fibrosis and COPD) can cause hypoxemia or greatly worsened hypoxemia. Nocturnal desaturation is common for many conditions, including cystic fibrosis (Coffey et al, 1991), heart disease (Tanigawa et al, 2006) and diabetes (Mahler et al, 2011).

The main cause of chronic hypoxemia

While hypoxemia may occur suddenly, or due to an accident or unusual and exotic situations, most cases of chronic hypoxemia relate to gradual worsening of blood oxygenation due to chronic lung diseases, such as cystic fibrosis, COPD (severe asthma, bronchitis, emphysema, and so on), lung cancers, bronchiectasis and many others. In such cases, gradual deterioration in blood oxygenation is accompanied by hypercapnia (too much CO2 in the arterial blood) and has a simple single cause: an abnormal breathing pattern that is manifested in the following factors:
- hyperventilation
- thoracic (or chest, or shallow) breathing
- mouth breathing.

Minute ventilation rates (chronic diseases)

Condition	Minute ventilation	Number of people	All references or click below for abstracts
Normal breathing	6 l/min	-	Medical textbooks
Healthy Subjects	6-7 l/min	>400	Results of 14 studies
COPD	14 (±2) l/min	12	Palange et al, 2001
COPD	12 (±2) l/min	10	Sinderby et al, 2001
COPD	14 l/min	3	Stulbarg et al, 2001
Asthma	13 (±2) l/min	16	Chalupa et al, 2004
Asthma	15 l/min	8	Johnson et al, 1995
Asthma	14 (±6) l/min	39	Bowler et al, 1998
Asthma	13 (±4) l/min	17	Kassabian et al, 1982
Asthma	12 l/min	101	McFadden & Lyons, 1968
Cystic fibrosis	15 L/min	15	Fauroux et al, 2006
Cystic fibrosis	10 L/min	11	Browning et al, 1990
Cystic fibrosis*	10 L/min	10	Ward et al, 1999
CF and diabetes*	10 L/min	7	Ward et al, 1999
Cystic fibrosis	16 L/min	7	Dodd et al, 2006
Cystic fibrosis	18 L/min	9	McKone et al, 2005
Cystic fibrosis*	13 (±2) l/min	10	Bell et al, 1996
Cystic fibrosis	11-14 l/min	6	Tepper et al, 1983

Hyperventilation, regardless of ventilation-perfusion ratio (or the presence of lung problems during the initial stages), leads to alveolar hypocapnia. This, in turn, causes a cascade of pathological effects that involve drying and overcooling of airways, constriction of airways, inability of the body to heal lung damage, over-production of thick mucus, suppression of the immune system, possible appearance of allergies, over-expression of hypoxia-inducible factor 1, oxidative stress, and many other effects (see the CO2-related links below). Alveolar hyperventilation leads to appearance of 2 other factors: chest breathing and mouth breathing.

Chest breathing immediately leads to reduced-blood oxygenation since lower portions of the lungs get about 6-7 times more blood, due to gravity, in comparison with the top parts of the lungs.

Mouth breathing causes reduction in alveolar CO2 due to reduced-dead volume, possible reduction in absorption of nasal NO (nitric oxide), as in cystic fibrosis, and frequent respiratory infections. Alveolar hypocapnia directly contributes to worsened ventilation-perfusion ratio.

For uneducated and archaic views on hypoxemia, you may check this Wikipedia article: click here.

Treatment for hypoxemia

Note. Severe cases of hypoxemia require the attention of emergency or critical care professionals. Their treatment for hypoxemia may include mechanical ventilation and supplemental oxygen therapy.

Successful treatment of chronic hypoxemia in patients with COPD, cystic fibrosis, emphysema, severe asthma, and other lung diseases has been demonstrated clinically by more than 600 Russian MDs.

Their treatment is based on breathing retraining using either the legendary Buteyko breathing technique or the Frolov breathing device therapy. Breathing exercises with the Amazing DIY Breathing Device often produce a large immediate increase in oximeter readings in comparison with any other breathing device or technique, if this reading was low at rest.

However, one also needs to address lifestyle-risk factors (supine sleep, mouth breathing, overeating, insufficient or incorrect physical exercise, nutritional deficiencies, and many others) in order to achieve permanent changes in automatic breathing patterns. These factors are analyzed in the Section Learn here.

Reference pages: Breathing norms and medical facts:
- Breathing norms: Parameters, graph, and description of the normal breathing pattern
- 6 breathing myths: Myths and superstitions about breathing and body oxygenation (prevalence: over 90%)
- Hyperventilation: Definitions of hyperventilation: their advantages and weak points
- Hyperventilation syndrome: Western scientific evidence about prevalence of chronic hyperventilation in patients with chronic conditions (37 medical studies)
- Normal minute ventilation: Small and slow breathing at rest is enjoyed by healthy subjects (14 studies)
- Hyperventilation prevalence: Present in over 90% of normal people (24 medical studies)
- HV and hypoxia: How and why deep breathing reduces oxygenation of cells and tissues of all vital organs
- Body-oxygen test (CP test) : How to measure your own breathing and body oxygenation (two in one) using a simple DIY test
- Body oxygen in healthy: Results for the body-oxygen test for healthy people (27 medical studies)
- Body oxygen in sick : Results for the body-oxygen test for sick people (14 medical studies)
- Buteyko Table of Health Zones: Clinical description and ranges for breathing zones: from the critically ill (severely sick) up to super healthy people with maximum possible body oxygenation
- Morning hyperventilation: Why people feel worse and critically ill people are most likely to die during early morning hours

References: pages about CO2 effect:
- Vasodilation: CO2 expands arteries and arterioles facilitating perfusion (or blood supply) to all vital organs
- The Bohr effect: How and why oxygen is released by red blood cells in tissues
- Cell oxygen levels: How alveolar CO2 influences oxygen transport
- Oxygen transport: O2 transport is controlled by vasoconstriction-vasodilation and the Bohr effects, both of which rely on CO2
- Free radical generation: Reactive oxygen species are produced within cells due to anaerobic cell respiration caused by cell hypoxia
- Inflammatory response: Chronic inflammation in fueled by the hypoxia-inducible factor 1, while normal breathing reduces and eliminates inflammation
- Nerve stabilization: People remain calm due to calmative or sedative effects of carbon dioxide in neurons or nerve cells
- Muscle relaxation: Relaxation of muscle cells is normal at high CO2, while hypocapnia causes muscular tension, poor posture and, sometimes, aggression and violence
- Bronchodilation: Dilation of airways (bronchi and bronchioles) is caused by carbon dioxide, and their constriction by hypocapnia (low CO2)
- Blood pH: Regulation of blood pH due to breathing and regulation of other bodily fluids
- CO2: lung damage: Elevated carbon dioxide prevents lung injury and promotes healing of lung tissues
- CO2: Topical carbon dioxide can heal skin and tissues
- Synthesis of glutamine in the brain, CO2 fixation, and other chemical reactions
- Deep breathing myth: Ignorant and naive people promote the idea that deep breathing and breathing more air at rest is beneficial for health
- Breathing control: How is our breathing regulated? Why hypocapnia makes breathing uneven, irregular and erratic.

References
Coffey MJ, FitzGerald MX, McNicholas WT, Comparison of oxygen desaturation during sleep and exercise in patients with cystic fibrosis, Chest. 1991 Sep;100(3):659-62.

Lebecque P, Lapierre JG, Lamarre A, Coates AL, Diffusion capacity and oxygen desaturation effects on exercise in patients with cystic fibrosis, Chest. 1987 May;91(5):693-7.

Mahler DA, Gifford AH, Waterman LA, Ward J, Machala S, Baird JC, Mechanism of Greater Oxygen Desaturation during Walking Compared with Cycling in COPD, Chest. 2011 Jan 27.

Neumann C, Martinez D, Schmid H, Nocturnal oxygen desaturation in diabetic patients with severe autonomic neuropathy, Diabetes Res Clin Pract. 1995 May;28(2):97-102.

Nonoyama ML, Brooks D, Guyatt GH, Goldstein RS, Effect of oxygen on health quality of life in patients with chronic obstructive pulmonary disease with transient exertional hypoxemia, Am J Respir Crit Care Med. 2007 Aug 15;176(4):343-9. Epub 2007 Apr 19.

Orth M, Walther JW, Yalzin S, Bauer TT, de Zeeuw J, Kotterba S, Baberg HT, Schultze-Werninghaus G, Rasche K, Duchna HW, Influence of nocturnal oxygen therapy on quality of life in patients with COPD and isolated sleep-related hypoxemia: a prospective, placebo-controlled cross-over trial [German], Pneumologie. 2008 Jan;62(1):11-6.

Sans-Torres J, Domingo C, Rué M, Durán-Tauleria E, Marín A, An assessment of the quality of life of patients with COPD and chronic hypoxemia by using the Spanish version of the Chronic Respiratory Disease Questionnaire [Spanish], Arch Bronconeumol. 1999 Oct;35(9):428-34.

Tanigawa T, Yamagishi K, Sakurai S, Muraki I, Noda H, Shimamoto T, Iso H, Arterial oxygen desaturation during sleep and atrial fibrillation, Heart. 2006 Dec;92(12):1854-5.

Tanni SE, Vale SA, Lopes PS, Guiotoko MM, Godoy I, Godoy I, Influence of the oxygen delivery system on the quality of life of patients with chronic hypoxemia, J Bras Pneumol. 2007 Apr;33(2):161-7.

Young AC, Wilson JW, Kotsimbos TC, Naughton MT, The impact of nocturnal oxygen desaturation on quality of life in cystic fibrosis, J Cyst Fibros. 2011 Mar;10(2):100-6.

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