Respiratory failure

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Respiratory failure
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Respiratory system
Specialty Pulmonology, Intensive care medicine

Respiratory failure results from inadequate gas exchange by the respiratory system, meaning that the arterial oxygen, carbon dioxide, or both cannot be kept at normal levels. A drop in the oxygen carried in the blood is known as hypoxemia; a rise in arterial carbon dioxide levels is called hypercapnia. Respiratory failure is classified as either Type 1 or Type 2, based on whether there is a high carbon dioxide level, and can be acute or chronic. In clinical trials, the definition of respiratory failure usually includes increased respiratory rate, abnormal blood gases (hypoxemia, hypercapnia, or both), and evidence of increased work of breathing. Respiratory failure causes an altered mental status due to ischemia in the brain.

Contents

The typical partial pressure reference values are oxygen Pa O2 more than 80 mmHg (11 kPa) and carbon dioxide Pa CO2 less than 45 mmHg (6.0 kPa).. [1]

Cause

Several types of conditions can potentially result in respiratory failure:

Diagnosis

Type 1

Type 1 respiratory failure is defined as a low level of oxygen in the blood (hypoxemia) with either a standard (normocapnia) or low (hypocapnia) level of carbon dioxide (PaCO2) but not an increased level (hypercapnia). It is typically caused by a ventilation/perfusion (V/Q) mismatch; the volume of air flowing in and out of the lungs is not matched with the flow of blood to the lungs. The fundamental defect in type 1 respiratory failure is a failure of oxygenation characterized by:

PaO2decreased (< 60 mmHg (8.0 kPa))
PaCO2normal or decreased (<50 mmHg (6.7 kPa))
PA-aO2increased

This type of respiratory failure is caused by conditions that affect oxygenation, such as:

Type 2

Hypoxemia (PaO2 <8kPa or normal) with hypercapnia (PaCO2 >6.0kPa).

The basic defect in type 2 respiratory failure is characterized by:

PaO2decreased (< 60 mmHg (8.0 kPa))or normal
PaCO2increased (> 50 mmHg (6.7 kPa))
PA-aO2normal
pH<7.35

Type 2 respiratory failure is caused by inadequate alveolar ventilation; both oxygen and carbon dioxide are affected. Defined as the buildup of carbon dioxide levels (PaCO2) that has been generated by the body but cannot be eliminated. The underlying causes include:

Some also refer to type 3 (peri-operative; generally a subset of type 1 failure, but is sometimes considered separately) and type 4 (shock; secondary to cardiovascular instability) acute respiratory failure; however, type 1 and 2 are the most widely accepted. [3] [4] [5]

Treatment

Mechanical ventilator VIP Bird2.jpg
Mechanical ventilator

Treatment of the underlying cause is required, if possible. The treatment of acute respiratory failure may involve medication such as bronchodilators (for airways disease), [6] [7] antibiotics (for infections), glucocorticoids (for numerous causes), diuretics (for pulmonary oedema), amongst others. [8] [9] [10] Respiratory failure resulting from an overdose of opioids may be treated with the antidote naloxone. In contrast, most benzodiazepine overdose does not benefit from its antidote, flumazenil. [11] Respiratory therapy/respiratory physiotherapy may be beneficial in some cases of respiratory failure. [12] [13]

Type 1 respiratory failure may require oxygen therapy to achieve adequate oxygen saturation. [14] Lack of oxygen response may indicate other modalities such as heated humidified high-flow therapy, continuous positive airway pressure or (if severe) endotracheal intubation and mechanical ventilation. .[ citation needed ]

Type 2 respiratory failure often requires non-invasive ventilation (NIV) unless medical therapy can improve the situation. [15] Mechanical ventilation is sometimes indicated immediately or otherwise if NIV fails. [15] Respiratory stimulants such as doxapram are now rarely used. [16]

There is tentative evidence that in those with respiratory failure identified before arrival in hospital, continuous positive airway pressure can be helpful when started before conveying to hospital. [17]

See also

Related Research Articles

Hypoxia (medical) Medical condition caused by lack of oxygen in the tissues

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 hypoventilation training or strenuous physical exercise.

Meconium aspiration syndrome Medical condition affecting newborn infants

Meconium aspiration syndrome (MAS) also known as neonatal aspiration of meconium is a medical condition affecting newborn infants. It describes the spectrum of disorders and pathophysiology of newborns born in meconium-stained amniotic fluid (MSAF) and have meconium within their lungs. Therefore, MAS has a wide range of severity depending on what conditions and complications develop after parturition. Furthermore, the pathophysiology of MAS is multifactorial and extremely complex which is why it is the leading cause of morbidity and mortality in term infants.

Mechanical ventilation, assisted ventilation or intermittent mandatory ventilation (IMV), is the medical term for artificial ventilation where mechanical means are used to assist or replace spontaneous breathing. This may involve a machine called a ventilator, or the breathing may be assisted manually by a suitably qualified professional, such as an anesthesiologist, Registered Nurse, paramedic or other first responder, by compressing a bag valve mask device.

Obesity hypoventilation syndrome Condition in which severely overweight people fail to breathe rapidly or deeply enough

Obesity hypoventilation syndrome (OHS) is a condition in which severely overweight people fail to breathe rapidly or deeply enough, resulting in low oxygen levels and high blood carbon dioxide (CO2) levels. The syndrome is often associated with obstructive sleep apnea (OSA), which causes periods of absent or reduced breathing in sleep, resulting in many partial awakenings during the night and sleepiness during the day. The disease puts strain on the heart, which may lead to heart failure and leg swelling.

Pulmonary edema Fluid accumulation in the air spaces and parenchyma of the lungs tissue

Pulmonary edema, also known as pulmonary congestion is liquid accumulation in the tissue and air spaces of the lungs. It leads to impaired gas exchange and may cause respiratory failure. It is due to either failure of the left ventricle of the heart to remove blood adequately from the pulmonary circulation, or an injury to the lung tissue or blood vessels of the lung. Treatment is focused on three aspects: firstly improving respiratory function, secondly, treating the underlying cause, and thirdly avoiding further damage to the lung. Pulmonary edema, especially when sudden (acute), can lead to respiratory failure or cardiac arrest due to hypoxia. It is a cardinal feature of congestive heart failure. The term edema is from the Greek οἴδημα, from οἰδέω.

Acute respiratory distress syndrome Human disease

Acute respiratory distress syndrome (ARDS) is a type of respiratory failure characterized by rapid onset of widespread inflammation in the lungs. Symptoms include shortness of breath (dyspnea), rapid breathing (tachypnea), and bluish skin coloration (cyanosis). For those who survive, a decreased quality of life is common.

Hypercapnia Abnormally high tissue carbon dioxide levels

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). Inability of the lungs to clear carbon dioxide leads to respiratory acidosis. Eventually the body compensates for the raised acidity by retaining alkali in the kidneys, a process known as "metabolic compensation".

Infant respiratory distress syndrome Human disease affecting newborns

Infantile respiratory distress syndrome (IRDS), also called respiratory distress syndrome of newborn, or increasingly surfactant deficiency disorder (SDD), and previously called hyaline membrane disease (HMD), is a syndrome in premature infants caused by developmental insufficiency of pulmonary surfactant production and structural immaturity in the lungs. It can also be a consequence of neonatal infection and can result from a genetic problem with the production of surfactant-associated proteins. IRDS affects about 1% of newborns and is the leading cause of death in preterm infants. Notably, data has shown the choice of elective caesarean sections to strikingly increase the incidence of respiratory distress in term infants; dating back to 1995, the UK first documented 2,000 annual caesarean section births requiring neonatal admission for respiratory distress. The incidence decreases with advancing gestational age, from about 50% in babies born at 26–28 weeks to about 25% at 30–31 weeks. The syndrome is more frequent in males, Caucasians, infants of diabetic mothers and the second-born of premature twins.

Respiratory acidosis Medical condition

Respiratory acidosis is a state in which decreased ventilation (hypoventilation) increases the concentration of carbon dioxide in the blood and decreases the blood's pH.

Non-invasive ventilation

Non-invasive ventilation (NIV) is the use of breathing support administered through a face mask, nasal mask, or a helmet. Air, usually with added oxygen, is given through the mask under positive pressure; generally the amount of pressure is alternated depending on whether someone is breathing in or out. It is termed "non-invasive" because it is delivered with a mask that is tightly fitted to the face or around the head, but without a need for tracheal intubation. While there are similarities with regards to the interface, NIV is not the same as continuous positive airway pressure (CPAP), which applies a single level of positive airway pressure throughout the whole respiratory cycle; CPAP does not deliver ventilation but is occasionally used in conditions also treated with NIV.

Permissive hypercapnia is hypercapnia in respiratory insufficient patients in which oxygenation has become so difficult that the optimal mode of mechanical ventilation is not capable of exchanging enough carbon dioxide. Carbon dioxide is a gaseous product of the body's metabolism and is normally expelled through the lungs.

Hypoxemia Abnormally low level of oxygen in the blood

Hypoxemia is an abnormally low level of oxygen in the blood. More specifically, it is oxygen deficiency in arterial blood. Hypoxemia has many causes, and often causes hypoxia as the blood is not supplying enough oxygen to the tissues of the body.

Bronchopulmonary dysplasia Medical condition

Bronchopulmonary dysplasia is a chronic lung disease in which premature infants, usually those who were treated with supplemental oxygen, require long-term oxygen. The alveoli that are present tend to not be mature enough to function normally. It is more common in infants with low birth weight (LBW) and those who receive prolonged mechanical ventilation to treat respiratory distress syndrome (RDS). It results in significant morbidity and mortality. The definition of BPD has continued to evolve primarily due to changes in the population, such as more survivors at earlier gestational ages, and improved neonatal management including surfactant, antenatal glucocorticoid therapy, and less aggressive mechanical ventilation.

The Alveolar–arterial gradient, is a measure of the difference between the alveolar concentration (A) of oxygen and the arterial (a) concentration of oxygen. It is an useful parameter for narrowing the differential diagnosis of hypoxemia.

Restrictive lung diseases are a category of extrapulmonary, pleural, or parenchymal respiratory diseases that restrict lung expansion, resulting in a decreased lung volume, an increased work of breathing, and inadequate ventilation and/or oxygenation. Pulmonary function test demonstrates a decrease in the forced vital capacity.

Pulmonary contusion Internal bruise of the lungs

A pulmonary contusion, also known as lung contusion, is a bruise of the lung, caused by chest trauma. As a result of damage to capillaries, blood and other fluids accumulate in the lung tissue. The excess fluid interferes with gas exchange, potentially leading to inadequate oxygen levels (hypoxia). Unlike pulmonary laceration, another type of lung injury, pulmonary contusion does not involve a cut or tear of the lung tissue.

Persistent fetal circulation is a condition caused by a failure in the systemic circulation and pulmonary circulation to convert from the antenatal circulation pattern to the "normal" pattern. Infants experience a high mean arterial pulmonary artery pressure and a high afterload at the right ventricle. This means that the heart is working against higher pressures, which makes it more difficult for the heart to pump blood.

In some individuals, the effect of oxygen on chronic obstructive pulmonary disease is to cause increased carbon dioxide retention, which may cause drowsiness, headaches, and in severe cases lack of respiration, which may lead to death. People with lung ailments or with central respiratory depression, who receive supplemental oxygen, require careful monitoring.

Respiratory compromise describes a deterioration in respiratory function with a high likelihood of rapid progression to respiratory failure and death. Respiratory failure occurs when inadequate gas exchange by the respiratory system occurs, with a low oxygen level or a high carbon dioxide level.

Pathophysiology of acute respiratory distress syndrome

The pathophysiology of acute respiratory distress syndrome involves fluid accumulation in the lungs not explained by heart failure. It is typically provoked by an acute injury to the lungs that results in flooding of the lungs' microscopic air sacs responsible for the exchange of gases such as oxygen and carbon dioxide with capillaries in the lungs. Additional common findings in ARDS include partial collapse of the lungs (atelectasis) and low levels of oxygen in the blood (hypoxemia). The clinical syndrome is associated with pathological findings including pneumonia, eosinophilic pneumonia, cryptogenic organizing pneumonia, acute fibrinous organizing pneumonia, and diffuse alveolar damage (DAD). Of these, the pathology most commonly associated with ARDS is DAD, which is characterized by a diffuse inflammation of lung tissue. The triggering insult to the tissue usually results in an initial release of chemical signals and other inflammatory mediators secreted by local epithelial and endothelial cells.

References

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