Respiratory failure
Respiratory failure | |
---|---|
ARDS, aspiration pneumonia | |
Treatment | Treatment of underlying cause, non-invasive ventilation |
Frequency | 10–80 per 100,000 |
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 state of consciousness due to ischemia in the brain.
The typical partial pressure reference values are oxygen Pa O
2 more than 80 mmHg (11 kPa) and carbon dioxide Pa CO2 less than 45 mmHg (6.0 kPa).[1]
Cause
A variety of conditions that can potentially result in respiratory failure.[1] The etiologies of each type of respiratory failure (see below) may differ, as well. Different types of conditions may cause respiratory failure:
- Conditions that reduce the flow of air into and out of the lungs, including physical obstruction by foreign bodies or masses and reduced breathing due to drugs or changes to the chest.[1]
- Conditions that impair the lungs' blood supply. These include right heart failure and some myocardial infarctions.
- Conditions that limit the ability of the lung tissue to exchange oxygen and carbon dioxide between the blood and the air within the lungs. Any disease which can damage the lung tissue can fit into this category. The most common causes are (in no particular order) infections, interstitial lung disease, and pulmonary edema.
Types
Respiratory failure is generally organized into 4 types.[citation needed] Below is a diagram that provides a general overview of the 4 types of respiratory failure, their distinguishing characteristics, and major causes of each.
Type 1
Type 1 respiratory failure is characterized by a low level of oxygen in the blood (hypoxemia) (PaO2) < 60 mmHg with a normal (normocapnia) or low (hypocapnia) level of carbon dioxide (PaCO2) in the blood.[1]
The fundamental defect in type 1 respiratory failure is a failure of oxygenation characterized by:
PaO2 decreased (< 60 mmHg (8.0 kPa)) PaCO2 normal or decreased (<50 mmHg (6.7 kPa)) PA-aO2 increased
Type I respiratory failure is caused by conditions that affect
- Low ambient oxygen (e.g. at high altitude).[1]
- Ventilation-perfusion mismatch (parts of the lung receive oxygen but not enough blood to absorb it, e.g. pulmonary embolism, Acute respiratory distress syndrome, Chronic obstructive pulmonary disease, Congestive heart failure.[1]
- Alveolar hypoventilation (decreased minute volume due to reduced respiratory muscle activity, e.g. in acute neuromuscular disease); this form can also cause type 2 respiratory failure if severe.
- Diffusion problem (oxygen cannot enter the capillaries due to parenchymal disease, e.g. in pneumonia or ARDS).
- venous system, e.g. Arteriovenous malformation, Complete atelectasis, Severe pneumonia, Severe pulmonary edema).
Type 2
Hypoxemia (PaO2 <8kPa or normal) with hypercapnia (PaCO2 >6.0kPa).
The basic defect in type 2 respiratory failure is characterized by:
PaO2 decreased (< 60 mmHg (8.0 kPa))or normal PaCO2 increased (> 50 mmHg (6.7 kPa)) PA-aO2 normal 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:
- Increased airways resistance (chronic obstructive pulmonary disease, asthma, suffocation)
- Reduced breathing effort (drug effects, brain stem lesion, extreme obesity)
- A decrease in the area of the lung available for gas exchange (such as in chronic bronchitis)
- Neuromuscular problems (motor neuron disease)
- Deformed (kyphoscoliosis), rigid (ankylosing spondylitis), or flail chest.[2]
Type 3
Type 3 respiratory failure is a type of Type 1 respiratory failure, with decreased PaO2 (hypoxemia) and either normal or decreased PaCO2.[1] However, because of its prevalence, it has been given its own category. Type 3 respiratory failure is often referred to as peri-operative respiratory failure, because it is distinguished by being a Type 1 respiratory failure that is specifically associated with an operation, procedure, or surgery. [3]
The pathophysiology of type 3 respiratory failure often includes lung atelectasis, which is a term used to describe a collapsing of the functional units of the lung that allow for gas exchange. Because atelectasis occurs so commonly in the perioperative period, this form is also called perioperative respiratory failure. After general anesthesia, decreases in functional residual capacity leads to collapse of dependent lung units.[1]
Type 4
Type 4 respiratory failure occurs when metabolic (oxygen) demands exceed what the cardiopulmonary system can provide.
Physical exam
Physical exam findings often found in patients with respiratory failure include findings indicative of impaired oxygenation (low blood oxygen level). These include, but are not limited to, the following:
- respiratory distress[6]
- Altered mental status (eg. confusion, lethargy)[6]
- Clubbing of fingertips (see image right)[6]
- Peripheral cyanosis (eg. bluish color on mucosal membranes or fingers and/or toes)
- Tachypnea (faster breathing rate)[6]
- Pale conjunctiva[6]
People with respiratory failure often exhibit other signs or symptoms that are associated with the underlying cause of their respiratory failure. For instance, if respiratory failure is caused by cardiogenic shock (decreased perfusion due to heart dysfunction, symptoms of heart dysfunction (e.g., pitting edema) are also expected.
Diagnosis
Alternative or supporting diagnostic methods include the following:
- Capnometry: measures the amount of carbon dioxide in exhaled air.[1]
- Pulse Oximetry: measures the fraction of hemoglobin saturated with oxygen (SpO2).[1]
Imaging (eg. ultrasonography, radiography) may be used to assist in the diagnostic workup. For example, it may be utilized to determine the etiology of a person's respiratory failure.
Treatment
Treatment of the underlying cause is required, if possible. The treatment of acute respiratory failure may involve medication such as
Type 1 respiratory failure may require oxygen therapy to achieve adequate oxygen saturation.
Type 2 respiratory failure often requires
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]
Prognosis
Prognosis is highly variable and dependent on etiology and availability of appropriate treatment and management.[18] One of three hospitalized cases of acute respiratory failure is fatal.[18]
See also
References
- ^ PMID 30252383, retrieved 2023-11-15
- ^ .
- ^ "Acute respiratory failure". Department of Critical Care. Retrieved 2023-10-28.
- ^ Katyal P, Gajic O. "Critical Care Medicine, Acute respiratory failure" (PDF). Mayo Clinic. Rochester, MN, USA. Archived from the original (PDF) on 9 April 2021 – via McGill University.
- ^ Melanson P. "Acute respiratory failure". Critical Care Medicine. McGill University.
- ^ a b c d e "Respiratory Failure - Diagnosis". National Heart, Lung and Blood Institute, US National Institutes of Health. 2022-03-24. Retrieved 2023-11-15.
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- ^ PMID 28860265.
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- ^ a b "Respiratory failure". Cleveland Clinic. 15 March 2023. Retrieved 15 November 2023.