hypoxemia



OVERVIEW

Definition of Hypoxemia

Hypoxemia is a condition in which the blood does not contain enough oxygen and the partial pressure of oxygen in the arterial blood (PaO2) is lower than the lower limit of normal for a person of the same age, which is characterized by a decrease in the partial pressure of oxygen in the blood and in the oxygen saturation of the blood.

Arterial partial pressure of oxygen (PaO2) refers to the tension generated by physically dissolved oxygen molecules in arterial blood, which is a sensitive indicator reflecting hypoxia in the organism, and is mainly used to determine whether the organism is hypoxic and its degree. Normal arterial partial pressure of oxygen (PaO2) in adults is 83-108 mmHg [1-3].

Hypoxemia affects the body differently depending on the degree, speed of occurrence and duration of hypoxemia.

Hypoxemia is one of the common critical illnesses in respiratory medicine, and is also one of the important clinical manifestations of respiratory failure.

Classification

According to the degree of onset, it can be divided into acute hypoxemia and chronic hypoxemia.

Acute hypoxemia

The onset of the disease is rapid and the symptoms are severe.

Most common in trauma, shock, acute airway obstruction, acute myocardial infarction, carbon monoxide poisoning, pneumothorax, severe pneumonia and other diseases.

Because the body can not compensate quickly, if not rescued in time, the patient’s life will be jeopardized.

Chronic hypoxemia

Long duration of the disease, symptoms gradually aggravated.

It can be seen in chronic obstructive pulmonary disease, chronic bronchitis, bronchial asthma, congenital heart disease, anemia and other diseases.

In the early stage, the organism can adapt through compensation, and the symptoms are not obvious. Continuous hypoxia or acute aggravation of the condition can develop into respiratory failure, and even life-threatening.

Morbidity

Hypoxemia is prevalent in the elderly with underlying respiratory diseases [2].

It can occur in all seasons, with a high prevalence in winter [2].

Etiology

Causes

There are many causes of hypoxemia, the most common of which is hypoxemia caused by respiratory diseases; followed by diseases of the cardiovascular system and the central nervous system, which can also lead to the occurrence of hypoxemia.

Obstructive lesions of the airway

For example, inflammation of trachea-bronchus, chronic obstructive pulmonary disease, spasm, tumor, foreign body, fibrotic scar can cause airway obstruction, hypoxemia and even respiratory failure [9].

Lung tissue lesions

Lesions involving alveoli and/or interstitium, such as pneumonia, emphysema, severe tuberculosis, diffuse pulmonary fibrosis, pulmonary edema, silicosis, etc., can lead to hypoxemia.

Pulmonary vascular disease

Such as pulmonary embolism and pulmonary vasculitis can cause imbalance in ventilation/blood flow ratio, leading to hypoxemia.

Heart disease

Various ischemic heart diseases, severe cardiac valvular disease, cardiomyopathy, pericardial disease, and severe cardiac arrhythmias can lead to ventilation and gas exchange dysfunction, resulting in hypoxemia.

Thoracic and pleural lesions

Thoracic trauma resulting in flail chest, severe spontaneous or traumatic pneumothorax, severe spinal deformity, massive pleural effusion, pleural hypertrophy and adhesions, and ankylosing spondylitis can limit thoracic movement and lung expansion, leading to inadequate ventilation and thus hypoxemia.

Neuromuscular diseases

Cerebrovascular disease, craniocerebral trauma, encephalitis, and sedative-hypnotic poisoning can directly or indirectly inhibit the respiratory center.

Injury to the cervical or high thoracic segments of the spinal cord (tumor or trauma), poliomyelitis, polyneuritis, myasthenia gravis, organophosphorus poisoning, tetanus, and severe potassium metabolism disorders can involve the respiratory muscles, resulting in respiratory muscle weakness, fatigue, paralysis, and insufficient ventilation due to decreased respiratory drive, resulting in hypoxemia.

Pathogenesis

The pathogenesis of hypoxemia is mainly related to insufficient pulmonary ventilation, diffusion disorder, ventilation/blood flow ratio imbalance, increased arterio-venous anatomical shunt in the lungs, and increased oxygen consumption, etc., and often a variety of mechanisms coexist or participate in the role of the disease with the development of the disease successively [1,4].

Symptoms

The clinical manifestations of hypoxia vary, depending on the severity of the underlying disease, the urgency of the onset of hypoxia, the patient’s activity level and metabolic status, and his/her adaptive and compensatory capacity to hypoxia.

Patients with chronic hypoxia have often adapted to this state and have no obvious clinical manifestations. The following describes the symptoms associated with acute hypoxia.

Main Symptoms

Effects on the respiratory system

Breath-holding and dyspnea: patients with less severe hypoxia may show shortness of breath, chest tightness, breath-holding and shortness of breath, and severe cases may have dyspnea.

Cyanosis: a manifestation of cyanosis of the skin and mucous membranes, which often occurs in the parts of the skin that are thinner, less pigmented and richer in capillaries, such as the lips, fingers (toes), nail beds and so on.

Effects on the cardiovascular system

Mild hypoxemia can cause reflex increase in heart rate, increase in myocardial contractility, increase in cardiac output, palpitations and tachycardia.

Severe hypoxemia can directly inhibit the cardiovascular center, causing inhibition of cardiac activity and vasodilation, resulting in decreased blood pressure, arrhythmia, angina pectoris, shock and other manifestations.

Effects on the central nervous system

In mild hypoxemia, patients may experience euphoria, lethargy, poor concentration and other manifestations.

In severe hypoxemia, patients may have headache, sluggishness, irritability, optic disc edema, retinal hemorrhage, convulsions, drowsiness, sensory dullness and coma.

Effects on the musculo-neurological system

Hypoxemia may cause neurologic weakness, tremor, fluttering tremor, hyperreflexia and ataxia.

Effects on digestive system

It manifests as dyspepsia, lack of appetite, and even gastrointestinal mucosal erosion, necrosis, ulceration and bleeding.

Hypoxia can directly or indirectly damage liver cells and increase alanine aminotransferase. If hypoxia can be corrected in time, liver function can be gradually normalized.

Consultation

Department of Medicine

Respiratory medicine

When cyanosis, breathlessness, irritability, dyspnea and other symptoms occur, please go to the Department of Respiratory Medicine.

Emergency Department

If acute hypoxemia occurs, which may lead to respiratory failure or even cardiac arrest, patients are advised to consult the Emergency Department promptly.

Preparation for medical treatment

Preparation for medical consultation: registration, preparation of documents, common problems

Tips for Medical Consultation

Patients may need to be examined during the visit, so please choose clothes that are easy to put on and take off so that the doctor can conduct a physical examination.

Record the symptoms, duration and other relevant information for the doctor’s reference.

Preparation Checklist for Doctor’s Visit

When the symptoms occur, the special performance, etc., which need to be concerned

Are there any signs of bruising on the lips, fingers (toes), nail beds, etc.?

Is there any manifestation of breath-holding, chest tightness or even dyspnea?

Any palpitations or tachycardia?

Any unexplained headache, tiredness, poor concentration, etc.?

Are there any underlying respiratory diseases such as chronic obstructive pulmonary disease, pneumonia, pulmonary embolism, etc.?

Are there any cardiac diseases such as ischemic heart disease, severe heart valve disease, etc.?

Are there any neurological diseases such as cerebrovascular disease, craniocerebral trauma, etc.?

Are there any drug or food allergies?

Test results in the last six months, which can be carried to the doctor

Laboratory tests: blood routine, urine routine, stool routine, blood biochemistry tests.

Imaging examination: ultrasound, X-ray, CT, MRI, etc.

Specialized tests: arterial blood gas analysis, pulmonary function tests.

Diagnosis

Diagnosis is based on

Medical history

The patient may have the following medical history:

Respiratory diseases such as chronic obstructive pulmonary disease, pneumonia, pulmonary embolism, etc.

Cardiac diseases such as ischemic heart disease, severe heart valve disease, etc.

Neurologic diseases such as cerebrovascular disease, craniocerebral trauma, etc.

Clinical manifestations

Patients may present with cyanosis, breath-holding, chest tightness, irritability, dyspnea and other symptoms.

Laboratory examination

Blood routine: to find out whether there is infection, anemia, etc.

Urine routine: observe whether there is hematuria, proteinuria, tubular pattern and other abnormalities, combined with renal function tests to determine the kidney condition.

Stool routine + occult blood: to determine whether there are red blood cells, white blood cells and other abnormalities. It is valuable for the diagnosis of small amount of gastrointestinal bleeding.

Biochemical tests: help to determine whether the liver and kidney functions are abnormal, whether there are electrolyte disorders, dyslipidemia and other conditions, and guide the next step of treatment.

Typical changes are decreased arterial partial pressure of oxygen (PaO2) and decreased arterial oxygen saturation (SaO2).

According to the arterial blood gas analysis and inhaled oxygen concentration can be calculated pulmonary oxygenation function index, such as oxygenation index (PaO2/FiO2), alveolar-arterial oxygen partial pressure difference, intrapulmonary shunt and other indexes, which are important for establishing the diagnosis, severity grading and efficacy evaluation.

Imaging examination

Chest imaging examination includes plain X-ray chest film, chest CT and radionuclide lung ventilation/perfusion scan, pulmonary angiography and ultrasonography.

Lung Function Test

Pulmonary function tests can determine the nature of ventilation dysfunction (obstructive, restrictive or mixed) and whether it is combined with ventilatory dysfunction, as well as the severity of ventilation and ventilatory dysfunction.

Respiratory muscle function tests can indicate the cause and severity of respiratory muscle weakness.

Grading

The grading of hypoxemia is mainly based on the presence or absence of cyanosis, PaO2 and SaO2 [6,8].

50～80

80%＞80

Moderate 30～5060%～80

Moderate

Yes

30～50

60%～80

Severe Significant <30＜60％

Severe

Significant

<30

＜Less than 60%

Differential Diagnosis

Hypoxemia is often caused by other diseases, and the differential diagnosis is mainly between the diseases that cause hypoxemia.

Acute respiratory distress syndrome

Similarity: both may present with shortness of breath and dyspnea.

Differences: Acute or progressive dyspnea that occurs within 1 week more often than not due to causative factors such as pulmonary contusion, severe pneumonia, shock, sepsis, and severe non-thoracic trauma [2].

Massive pulmonary atelectasis

Similarities: patients may have symptoms of shortness of breath and dyspnea.

Differences: there are many causes of massive pulmonary atelectasis, such as pneumothorax, pleural effusion, and tumors, which can usually be relieved or definitively diagnosed by thoracentesis drainage and bronchoscopy [7].

Massive pleural effusion

Similarities: Patients may have symptoms of shortness of breath and dyspnea.

Differences: Common causes of massive pleural effusion include infection, tumor, trauma, cardiac insufficiency, or hypoproteinemia. Chest radiographs may show blunting of the rib-diaphragm angle and loss of the rib-diaphragm angle.

Diffuse alveolar hemorrhage

Similarity: Patients may have shortness of breath and dyspnea.

Differences: patients with diffuse alveolar hemorrhage may have hemoptysis, anemia, and hypoxemia, which is a typical clinical triad of diffuse alveolar hemorrhage; chest imaging shows nonspecific patchy or diffuse infiltrating shadows in both lungs, and bronchoalveolar lavage shows persistent hemorrhage in multiple lung segments, which is an important basis for the diagnosis of diffuse alveolar hemorrhage [5].

Treatment

Treatment purpose: to improve the state of hypoxia in patients, relieve related symptoms, and reduce secondary organ damage caused by severe hypoxemia.

Therapeutic principle: choose the appropriate way of improvement according to the degree of hypoxia in patients, actively search for the cause of the disease, only when the cause of the disease is controlled and improved, in conjunction with the appropriate oxygen therapy, the therapeutic effect can be improved.

Oxygen therapy

Oxygen therapy aims to improve the partial pressure of arterial blood oxygen, oxygen saturation and oxygen content to correct hypoxemia, ensure the oxygen supply to the tissues, and achieve the purpose of relieving tissue hypoxia. The main types include the following.

Nasal catheter or nasal plug

The main advantage is that it is simple, convenient and does not affect the patient’s coughing and eating.

The disadvantage is that the oxygen concentration is not constant and is easily affected by the patient’s breathing.

Mask

It mainly includes simple mask, non-repeatable breathing mask with storage bag and Venturi mask.

The main advantages are that the oxygen concentration is relatively stable, can be adjusted according to the need, and less irritation to the nasal mucosa.

The disadvantage is that it affects the patient’s sputum and food intake to a certain extent.

Transnasal high flow oxygen therapy (HFNC)

Transnasal main flow oxygen therapy is a new type of respiratory support technology emerged in recent years, which can increase end-expiratory lung volume, improve gas exchange and reduce respiratory power consumption; reduce physiological ineffective lumen and improve the efficiency of ventilation; strengthen the airway humidification, promote the ciliated mucus system’s sputum removal ability and improve the patient’s tolerance of treatment; and promote the homogeneity of gas distribution.

Positive Pressure Mechanical Ventilation and Extracorporeal Membrane Oxygenation

Positive Pressure Mechanical Ventilation (PPMV) is a technique that utilizes devices (mainly ventilators) to restore effective ventilation and improve oxygenation when the patient’s natural ventilation and/or oxygenation is impaired.

Extracorporeal membrane oxygenation (ECMO) is the ultimate form of respiratory support for severe respiratory failure, with the primary goal of partially or completely replacing cardiopulmonary function, allowing adequate rest, reducing the incidence of ventilator-associated lung injury, and buying more time for the treatment of the primary disease [10].

General treatment

Etiologic treatment

There are various primary diseases causing hypoxemia, under the premise of solving the harm caused by hypoxia itself, it is necessary to clarify and take appropriate therapeutic measures according to different etiologies, which is fundamental to the treatment of hypoxemia.

General supportive therapy

Hypoxemia is often accompanied by electrolyte disorders and acid-base imbalance, which will further aggravate the dysfunction of the respiratory system and even other organs and interfere with the therapeutic effect of hypoxemia, and therefore should be corrected in time.

The type of electrolyte disorder and acid-base balance imbalance should be judged according to the patient’s clinical manifestations and the results of various examinations, and fluid management should be strengthened to prevent blood volume insufficiency and fluid loading, and to ensure that the hematocrit is at a certain level, which is of great significance for maintaining the oxygen delivery capacity and preventing excessive lung water [4].

Pharmacologic treatment

Drugs that relieve bronchospasm are often applied, mainly phosphodiesterase inhibitors such as aminophylline and dihydroxypropyl theophylline, which have the effect of relaxing airway smooth muscle and inhibiting histamine release.

It is best to monitor the heart rate, heart rhythm and blood concentration when using the drug. Other anticholinergics such as ipratropium bromide (ipratropium atropine), selective β2 agonists such as salbutamol and adrenocorticotropic hormones are also available.

Note: The choice of medication needs to be determined by the clinician on a patient-by-patient basis.

Prognosis

Cure

Cure of patients with hypoxemia depends on the cause and severity of the disease.

If the underlying disease can be ameliorated or cured, the patient’s outcome is generally good with appropriate oxygen therapy.

However, if severe hypoxemia is not properly treated, severe hypoxia can involve multiple systems throughout the body and can be life-threatening.

Hazards

Hypoxemia can affect the metabolism and function of organs throughout the body and even cause changes in tissue structure.

In the initial stage of respiratory failure, the function and metabolism of each organ can undergo a series of compensatory reactions to improve tissue oxygen supply, regulate acid-base balance and adapt to changes in the internal environment.

When respiratory failure enters a serious stage, there is compensatory incompleteness, which is manifested by serious functional and metabolic disorders of various organs until failure.

Daily

Daily Management

Dietary management

Reasonable arrangement of diet, pay attention to eat more nutritious and easily digestible food.

More vitamin-rich fresh fruits and vegetables can be consumed to supplement the vitamins needed by the body and promote recovery.

Eat more protein-rich foods, such as eggs, milk, lean meat and fish.

Cold, raw, stimulating, pickled, fried and deep-fried foods, such as fried chicken and chili peppers, should be avoided.

Life management

Avoid exertion, regular work and rest, and ensure sufficient sleep.

Proper exercise is needed in daily life to improve physical fitness and avoid low immunity.

Maintain a healthy body weight and take appropriate activities, such as slow walking, tai chi, qigong and breathing exercises.

Psychological support