Introduction:
The respiratory system is divided into upper and lower respiratory zones, respectively. The tracheobronchial tree is divided into 23 generations according to Weber's model. From the trachea to the sixteenth terminal, the bronchioles are called the conducting zone or the anatomical dead space where no gaseous exchange occurs. From the seventeenth terminal, bronchioles, to the twenty-third terminal, alveoli are known as the respiratory zone where gaseous exchange occurs.
There are approximately 300 million alveoli present in both lungs. The alveolar cells line the alveoli. Alveolar cells are of two types- type 1 and type 2. Type 1 alveolar cells or pneumocytes occupy 96-98 % of the surface area of alveoli, whereas type 2 alveolar cells or pneumocytes occupy only two to four percent of the surface area of alveoli.
The major function of these two types of alveolar cells is the gaseous exchange and secreting surfactant, respectively. Terminal bronchioles are the seat of resistance in the respiratory system. The major function of the respiratory system is the gaseous exchange between the environment and the body. It specifically provides oxygen and removes carbon dioxide from the body.
The other non-respiratory functions of the respiratory system are: acid-base balance, secreting surfactant, pulmonary circulation, defense mechanism, articulation and phonation, and serotonin metabolism. Respiratory failure can occur if there is an abnormality in any part of the respiratory tract, including the airways, alveoli, respiratory muscles, central nervous system, peripheral nervous system, and chest wall.
What Are the Types of Respiratory Failure?
Respiratory failure is classified based on blood gas analysis as follows:
Type 1: Hypoxemia without hypercapnia caused by a failure of gas exchange due to mismatching of pulmonary ventilation and perfusion. It is characterized by an arterial oxygen pressure (PaO2) of less than 60 mm Hg and a normal or low arterial carbon dioxide pressure (PaCO2). It is the most common type of respiratory failure and can be associated with acute diseases of the lungs.
Type 2: Hypoxemia with hypercapnia due to alveolar hypoventilation, which occurs when the respiratory muscles cannot perform sufficient work to remove the carbon dioxide produced by the body. It is characterized by arterial carbon dioxide pressure (PaCO2) higher than 50 mm Hg. The blood's pH depends on the bicarbonate levels, which in turn is dependent on the duration of hypercapnia.
Depending on their chronicity, respiratory failure may be further classified into acute and chronic.
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Acute Respiratory Failure: It may develop within minutes to hours and is considered a life-threatening situation with an imbalance in the arterial blood gas and acid-base status.
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Chronic Respiratory Failure: It may develop over several days or more. This allows the time for renal compensation and an increase in bicarbonate levels.
What Are the Causes of Respiratory Failure?
Common causes of respiratory failure in critically ill patients are:
Type 1 Respiratory Failure:
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Pulmonary edema
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Pulmonary embolism.
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Pulmonary fibrosis.
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Pneumothorax.
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Pulmonary contusion or blunt chest trauma.
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Acute respiratory distress syndrome.
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Asthma.
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Aspiration.
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Lung collapse due to retained secretions.
Type 2 Respiratory Failure:
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Reduced respiratory drive, for example, drug overdose or head injury.
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Upper airway obstruction is due to edema, infection, and a foreign body.
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Late severe acute asthma.
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Flail chest injury.
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Chronic obstructive lung disease (COPD).
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Peripheral neuromuscular diseases such as Guillain-Barre disease and myasthenia gravis.
What Are the Symptoms of Respiratory Failure?
Symptoms of respiratory failure depend upon whether there is inadequate oxygen or excessive carbon dioxide in the blood.
Hypoxemic Symptoms Are:
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Shortness of breath or dyspnea.
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Cyanosis or bluish discoloration of the skin and mucous membranes is especially seen in nails, earlobes, and the tongue.
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Increased heart rate or tachycardia. Occurs as a result of compensatory mechanisms to pump more blood to the oxygen-deprived tissues.
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Coughing.
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Severe headache.
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Pulmonary hypertension.
Hypercapnia Symptoms Are:
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Increase in the rate of breathing per minute or tachypnea.
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Confusion or disorientation.
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Flushed skin.
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Fatigue and drowsiness.
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Muscle cramps.
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Elevated blood pressure.
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Headache.
Severe Respiratory Failure Symptoms Include:
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Arrhythmias.
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Seizures.
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Fainting.
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Panic attack.
What Are the Types of Diagnostic Tests That Can Be Carried Out?
Various tests can be carried out to detect respiratory failure, such as:
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Arterial Blood Gas (ABG) Analysis: It helps to identify the type of respiratory failure. It includes the measurement of arterial oxygen, carbon dioxide, and pH. The calculation can be done with the help of the Henderson-Hasselbach equation, where pH is directly proportional to bicarbonate ions and indirectly proportional to carbon dioxide. The normal partial pressure of carbon dioxide is 35-45mmHg; more than 45mmHg is acidosis, whereas less than 35mmHg is alkalosis. The normal partial pressure of bicarbonate ions ranges between 22-26mmHg, where more than 26 is considered alkalosis and less than 22 is acidosis.
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Pulse Oximetry: It is a probe that checks the oxygen saturation level of the blood. It is attached to the fingertips of the patient and continuously monitored on the screen.
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Capnography: It provides a continuous reading of the respiratory system and the end-tidal carbon dioxide.
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Echocardiogram: It helps monitor cardiac function as tachycardia and arrhythmias may occur due to hypoxemia and acidosis.
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Imaging: Chest X-ray or computed tomography (CT) scan can help diagnose infections or certain lung conditions.
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Pulmonary Function Test or Spirometry: It is useful in evaluating chronic respiratory failure.
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Pulmonary Capillary Wedge Pressure: It helps to differentiate between cardiogenic and noncardiogenic edema.
What Is the Management of Respiratory Failure?
Depending on the patient's clinical presentation, interventions should aim to correct hypoxemia, hypercapnia, and respiratory acidosis. The management does not only focus on the supportive treatment but also the treatment of the underlying cause.
Treatment of Respiratory Failure:
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Non-Invasive Ventilation (NIV): Is used as an alternative to invasive ventilation. It is generally indicated in chronic obstructive lung diseases (COPD), cardiogenic pulmonary edema, and pulmonary infiltrates in immunocompromised patients. It improves survival chances and reduces complications for patients with acute respiratory failure.
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Extracorporeal Membrane Oxygenation (ECMO): It is used in critically ill patients, allows the blood to bypass organs such as the heart and lungs, and allows these organs to repair and heal. It is a heart-lung machine that provides oxygen to the tissues in the body and simultaneously removes carbon dioxide from the body.
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Mechanical Ventilation: Mechanical Ventilation or assisted ventilation is a machine that helps a critically ill patient to breathe when they are unable to do so spontaneously. It is used to protect the airways due to mechanical or neurologic causes, to supply adequate oxygenation, or to remove excess carbon dioxide from the body. Prolonged ventilator use can be harmful, damage the lungs and the airways, and lead to infections such as pneumonia.
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Tracheostomy: A surgical incision is made on the front of the neck. A thin-walled, narrow-lumen tube is placed into the trachea to help one breathe enough oxygen to balance the carbon dioxide levels.
Medications Used to Treat Respiratory Failure:
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Bronchodilators: To open up the airways such as short and long-acting beta-agonists.
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Corticosteroids: To reduce the inflammation of the airways and the lungs.
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Antibiotics: Depending on bacterial lung infection, such as pneumonia.
Conclusion:
Respiratory failure is an emergency medical condition that makes it difficult to breathe on their own. It can develop when the body cannot provide sufficient oxygen to the organs and tissues. Accumulating carbon dioxide can lead to irreversible organ damage and slow down oxygen delivery to the body. Hence, it is very important to diagnose the condition as early as possible and intervene immediately to avoid irreversible damage and death.