| Silent hypoxia | |
|---|---|
 | |
| Specialty | Critical care medicine, infectious disease, pulmonology |
| Risk factors | COVID-19, altitude sickness |
Silent hypoxia (also known as happy hypoxia) [1] [2] is generalised hypoxia that does not coincide with shortness of breath. [3] [4] [5] This presentation is known to be a complication of COVID-19, [6] [7] and is also known in walking pneumonia, [8] altitude sickness, [9] [10] [11] and rebreather diving. [12] [13]
One theory relating to COVID-19 presentation suggests the impaired processing of severe hypoxia and resumption of normal breathing may be due to the neurological pathway by which the virus spreads from the oral cavity to the brain. [14] It is speculated that this condition is caused by SARS-CoV-2 affecting the blood flow of the lungs' airways, in addition to the blood vessels within the lungs, which must match in order to allow proper airflow, but not affecting them enough to cause shortness of breath. [15] [16] It is also speculated that silent hypoxia may be caused by the formation of small blood clots within the lungs. [17] [18] [19] [ clarification needed ] It has been shown that the breathing rates of patients with COVID-19 gradually increase, which in turn leads to silent hypoxia. [20] It has also been shown that COVID-19 patients experience lesser levels of shortness of breath after exercise than non-COVID-19 patients. [21]
In healthy people this presentation can occur when the person breathes a gas which has a low oxygen content, and also a low carbon dioxide content, so there is no hypercapnic alarm response.[ citation needed ]
In COVID-19, the arterial and general tissue oxygen levels can drop without any initial warning. The chest x-ray may show diffuse pneumonia. Cases of silent hypoxia with COVID-19 have been reported for patients who did not experience shortness of breath or coughing until their oxygen levels had depressed to such a degree that they were at risk of acute respiratory distress (ARDS) and organ failure. [22] [ medical citation needed ] In a New York Times opinion piece (April 20, 2020), emergency room doctor Richard Levitan reported: "A vast majority of Covid pneumonia patients I met had remarkably low oxygen saturations at triage—seemingly incompatible with life—but they were using their cellphones as we put them on monitors." [22]
A tool used to diagnose silent hypoxia is the six-minute walk test, (6MWT), wherein a patient walks at a normal pace for six minutes, in order to monitor their physiological response. [23] It has been proven that, after performing the 6MWT, COVID-19 patients were more likely to develop exercise-induced hypoxia without symptoms than non-COVID-19 patients who had idiopathic pulmonary fibrosis. [24] [ clarification needed ] The condition can also be first detected by using prehospital pulse oximetry. [25] [26]
Treatment depends on the cause. In some cases supplementary oxygen is needed, in severe cases artificial ventilation may be necessary. In mild cases where the cause was hypoxic breathing gas, it may only be necessary to return to a normally oxygenated environment. Underlying medical problems may require assessment and treatment.
The prognosis for silent hypoxia in COVID-19 is generally poor, [27] [28] [ clarification needed ] as oxygen levels in the blood can drop below 50 percent without being noticed. [29] In cases where a healthy person was exposed to a hypoxic environment, the outcome will usually depend on the extent of associated tissue damage incurred. In mild cases a quick return to normal follows reversion to normally oxygenated breathing gas.
Known to be associated with:
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Hypoxia is a condition in which the body or a region of the body is deprived of adequate oxygen supply at the tissue level. Hypoxia may be classified as either generalized, affecting the whole body, or local, affecting a region of the body. Although hypoxia is often a pathological condition, variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise.
Shortness of breath (SOB), also medically known as dyspnea or dyspnoea, is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing discomfort that consists of qualitatively distinct sensations that vary in intensity", and recommends evaluating dyspnea by assessing the intensity of its distinct sensations, the degree of distress and discomfort involved, and its burden or impact on the patient's activities of daily living. Distinct sensations include effort/work to breathe, chest tightness or pain, and "air hunger". The tripod position is often assumed to be a sign.
Mechanical ventilation or assisted ventilation is the medical term for using a machine called a ventilator to fully or partially provide artificial ventilation. Mechanical ventilation helps move air into and out of the lungs, with the main goal of helping the delivery of oxygen and removal of carbon dioxide. Mechanical ventilation is used for many reasons, including to protect the airway due to mechanical or neurologic cause, to ensure adequate oxygenation, or to remove excess carbon dioxide from the lungs. Various healthcare providers are involved with the use of mechanical ventilation and people who require ventilators are typically monitored in an intensive care unit.
Atypical pneumonia, also known as walking pneumonia, is any type of pneumonia not caused by one of the pathogens most commonly associated with the disease. Its clinical presentation contrasts to that of "typical" pneumonia. A variety of microorganisms can cause it. When it develops independently from another disease, it is called primary atypical pneumonia (PAP).
Hypercapnia (from the Greek hyper = "above" or "too much" and kapnos = "smoke"), also known as hypercarbia and CO2 retention, is a condition of abnormally elevated carbon dioxide (CO2) levels in the blood. Carbon dioxide is a gaseous product of the body's metabolism and is normally expelled through the lungs. Carbon dioxide may accumulate in any condition that causes hypoventilation, a reduction of alveolar ventilation (the clearance of air from the small sacs of the lung where gas exchange takes place) as well as resulting from inhalation of CO2. Inability of the lungs to clear carbon dioxide, or inhalation of elevated levels of CO2, leads to respiratory acidosis. Eventually the body compensates for the raised acidity by retaining alkali in the kidneys, a process known as "metabolic compensation".
Pulse oximetry is a noninvasive method for monitoring a person's blood oxygen saturation. Peripheral oxygen saturation (SpO2) readings are typically within 2% accuracy of the more accurate reading of arterial oxygen saturation (SaO2) from arterial blood gas analysis. But the two are correlated well enough that the safe, convenient, noninvasive, inexpensive pulse oximetry method is valuable for measuring oxygen saturation in clinical use.
Generalized hypoxia is a medical condition in which the tissues of the body are deprived of the necessary levels of oxygen due to an insufficient supply of oxygen, which may be due to the composition or pressure of the breathing gas, decreased lung ventilation, or respiratory disease, any of which may cause a lower than normal oxygen content in the arterial blood, and consequently a reduced supply of oxygen to all tissues perfused by the arterial blood. This usage is in contradistinction to localized hypoxia, in which only an associated group of tissues, usually with a common blood supply, are affected, usually due to an insufficient or reduced blood supply to those tissues. Generalized hypoxia is also used as a synonym for hypoxic hypoxia This is not to be confused with hypoxemia, which refers to low levels of oxygen in the blood, although the two conditions often occur simultaneously, since a decrease in blood oxygen typically corresponds to a decrease in oxygen in the surrounding tissue. However, hypoxia may be present without hypoxemia, and vice versa, as in the case of infarction. Several other classes of medical hypoxia exist.
Bacterial pneumonia is a type of pneumonia caused by bacterial infection.
High-altitude pulmonary edema (HAPE) is a life-threatening form of non-cardiogenic pulmonary edema that occurs in otherwise healthy people at altitudes typically above 2,500 meters (8,200 ft). However, cases have also been reported between 1,500–2,500 metres or 4,900–8,200 feet in more vulnerable subjects.
Pulmonary fibrosis is a condition in which the lungs become scarred over time. Symptoms include shortness of breath, a dry cough, feeling tired, weight loss, and nail clubbing. Complications may include pulmonary hypertension, respiratory failure, pneumothorax, and lung cancer.
Hyperoxia occurs when cells, tissues and organs are exposed to an excess supply of oxygen (O2) or higher than normal partial pressure of oxygen.
Viral pneumonia is a pneumonia caused by a virus. Pneumonia is an infection that causes inflammation in one or both of the lungs. The pulmonary alveoli fill with fluid or pus making it difficult to breathe. Pneumonia can be caused by bacteria, viruses, fungi or parasites. Viruses are the most common cause of pneumonia in children, while in adults bacteria are a more common cause.
Neuroendocrine hyperplasia is rare and poorly understood lung condition which is characterized by an abnormal growth of pulmonary neuroendocrine cells in the lungs. It is a non-progressive disease of the interstitial tissues of the lungs. Prior to the findings of the hyperplasia of neuroendocrine cells it was known as tachypnea of infancy, as most children outgrow the need for oxygen supplementation within two to seven years. It is characterized by tachypnea, hypoxemia, and retractions. It is typically diagnosed in infants and children younger than one year of age. There is no currently recognized treatment, infants and children are given oxygen supplementation until they outgrow the need; since neuroendocrine cells do not multiply or get larger in size while the lungs continue to grow. This allows the lung disease to have less effect on lung function with age, although they will always have the same amount of neuroendocrine cells as they were born with.
Pneumonitis describes general inflammation of lung tissue. Possible causative agents include radiation therapy of the chest, exposure to medications used during chemo-therapy, the inhalation of debris, aspiration, herbicides or fluorocarbons and some systemic diseases. If unresolved, continued inflammation can result in irreparable damage such as pulmonary fibrosis.
Respiratory diseases, or lung diseases, are pathological conditions affecting the organs and tissues that make gas exchange difficult in air-breathing animals. They include conditions of the respiratory tract including the trachea, bronchi, bronchioles, alveoli, pleurae, pleural cavity, the nerves and muscles of respiration. Respiratory diseases range from mild and self-limiting, such as the common cold, influenza, and pharyngitis to life-threatening diseases such as bacterial pneumonia, pulmonary embolism, tuberculosis, acute asthma, lung cancer, and severe acute respiratory syndromes, such as COVID-19. Respiratory diseases can be classified in many different ways, including by the organ or tissue involved, by the type and pattern of associated signs and symptoms, or by the cause of the disease.
An amniotic fluid embolism (AFE) is a life-threatening childbirth (obstetric) emergency in which amniotic fluid enters the blood stream of the mother, triggering a serious reaction which results in cardiorespiratory collapse and massive bleeding (coagulopathy). The rate at which it occurs is 1 instance per 20,000 births and it comprises 10% of all maternal deaths.
Oxygen saturation is the fraction of oxygen-saturated haemoglobin relative to total haemoglobin in the blood. The human body requires and regulates a very precise and specific balance of oxygen in the blood. Normal arterial blood oxygen saturation levels in humans are 97–100 percent. If the level is below 90 percent, it is considered low and called hypoxemia. Arterial blood oxygen levels below 80 percent may compromise organ function, such as the brain and heart, and should be promptly addressed. Continued low oxygen levels may lead to respiratory or cardiac arrest. Oxygen therapy may be used to assist in raising blood oxygen levels. Oxygenation occurs when oxygen molecules enter the tissues of the body. For example, blood is oxygenated in the lungs, where oxygen molecules travel from the air and into the blood. Oxygenation is commonly used to refer to medical oxygen saturation.
Richard Mark Levitan is an American emergency medicine physician and businessperson. He is a clinical professor of medicine at Dartmouth College and a practicing physician at the Littleton Regional Hospital. He also runs a company that creates materials and runs events to teach emergency airway management.
The symptoms of COVID-19 are variable depending on the type of variant contracted, ranging from mild symptoms to a potentially fatal illness. Common symptoms include coughing, fever, loss of smell (anosmia) and taste (ageusia), with less common ones including headaches, nasal congestion and runny nose, muscle pain, sore throat, diarrhea, eye irritation, and toes swelling or turning purple, and in moderate to severe cases, breathing difficulties. People with the COVID-19 infection may have different symptoms, and their symptoms may change over time. Three common clusters of symptoms have been identified: one respiratory symptom cluster with cough, sputum, shortness of breath, and fever; a musculoskeletal symptom cluster with muscle and joint pain, headache, and fatigue; and a cluster of digestive symptoms with abdominal pain, vomiting, and diarrhea. In people without prior ear, nose, or throat disorders, loss of taste combined with loss of smell is associated with COVID-19 and is reported in as many as 88% of symptomatic cases.
The treatment and management of COVID-19 combines both supportive care, which includes treatment to relieve symptoms, fluid therapy, oxygen support as needed, and a growing list of approved medications. Highly effective vaccines have reduced mortality related to SARS-CoV-2; however, for those awaiting vaccination, as well as for the estimated millions of immunocompromised persons who are unlikely to respond robustly to vaccination, treatment remains important. Some people may experience persistent symptoms or disability after recovery from the infection, known as long COVID, but there is still limited information on the best management and rehabilitation for this condition.