Difference Between Type 1 And Type 2 Acute Respiratory Failure

Overview

The function of our respiratory system is to supply the body with oxygen and to remove carbon dioxide from the body. A defect in this function results in respiratory failure, which can be classified into type 1 and type 2. Type 1 respiratory failure results when the defect affects oxygen entry and results in low oxygen levels (hypoxemia); Type 2 respiratory failure results when the defect affects the carbon dioxide removal too and results in elevated carbon dioxide levels (hypercapnia).

Another classification of respiratory failure is based on the duration of the disease; acute respiratory failure occurs over a short period of time (a few hours to days); chronic respiratory failure occurs over a longer duration; or acute or chronic respiratory failure. 

Common manifestations of respiratory failure include shortness of breath, increased breathing rate, increased heart rate, sweating, bluish discoloration of skin, and in advanced cases, altered consciousness. The diagnosis of respiratory failure is based on these clinical symptoms, in addition to lab tests of blood levels of oxygen and carbon dioxide, chest x-rays, and other tests accordingly.¹

Early identification of the type of respiratory failure is essential to guide the management, which may include admission to the intensive care unit, use of an oxygen mask, and correction of the underlying disorder. Delayed diagnosis can be life-threatening leading to respiratory arrest, coma, and death.

Type 1 Acute Respiratory Failure (Hypoxemic)

Definition 

In type 1 respiratory failure, there is a reduced oxygen level in the blood (hypoxemia), but it is not associated with elevated carbon dioxide levels, carbon dioxide levels are either normal or reduced. The definition of hypoxemia in lab tests (blood gas analysis) is oxygen levels (PaO2) of less than 50 mmHg (the normal range of PaO2 is above 90 mmHg).²

Pathophysiology

This condition develops when part of the lung's ability to exchange oxygen to the body reduces, other areas of the lung compensate by increasing the amount of carbon dioxide removed so the levels of carbon dioxide remain within normal despite the low oxygen levels. 

Five mechanisms can lead to reduced oxygen levels:

• Reduction in the partial pressure of oxygen inspired, as in high altitudes
• Hypoventilation: reduced ability to breathe normally
• Ventilation-perfusion mismatch: when the ability of the lung to exchange oxygen with the blood is reduced
• Blood shunts from the lung circulation to the body circulation without going through lung alveoli (alveoli are the small units of the lung that are responsible for gas exchange)
• Abnormality in the diffusion of oxygen from the lung alveoli to the blood²

Common causes

• Severe pneumonia: infection affecting the lung can impair its ability to exchange gas and result in respiratory failure
• Acute severe asthma: the inflammation and narrowing of airways associated with asthma can result in respiratory failure, the type of respiratory failure associated with asthma is either type 1 or type  2 in life-threatening conditions
• Pulmonary embolism: blood clots in the blood vessels of the lung can impair the lung’s ability to exchange gasses resulting in respiratory failure
• Pneumothorax: air collection around the lung can cause the lung to collapse and also causes pressure on the heart, impairing the lung’s ability to exchange gasses and resulting in respiratory failure, either type 1 or type 2  
• Pulmonary edema: fluid accumulation in the lung, usually as a result of an associated heart failure, can impair the lung’s ability to exchange gasses resulting in respiratory failure 
• Acute respiratory distress syndrome (ARDS): this is a severe lung condition that results as a complication of other lung conditions³

Clinical features

Patients with type 1 respiratory failure present with symptoms of reduced oxygen levels (hypoxemia) in addition to symptoms of their underlying lung condition. 

The symptoms of hypoxemia include: 

• Shortness of breath
• Rapid breathing
• Bluish discoloration of skin (cyanosis)
• Restlessness and apprehension
• Increased heart rate and sense of heart pulsation
• Confusion and disturbed consciousness

Workup and diagnosis 

We have three objectives in the workup of acute respiratory failure: 

• To confirm clinical suspicion of the condition
• To classify the type of respiratory failure
• To determine the specific underlying cause that led to respiratory failure

The approach includes:

• Clinical history and physical examination
• Lab test: Blood Gas Analysis (BGA) is the most essential as it shows the levels of oxygen and carbon dioxide, in addition to blood pH and acidity
• In cases of type 1 respiratory failure, blood gas analysis shows reduced oxygen levels in the blood (hypoxemia, PaO2 less than 50 mmHg), and the levels of carbon dioxide (PaCo2) are either normal or reduced
• Blood Gas Analysis (BGA) is performed in the beginning and after 20 minutes of starting therapy to monitor progress. In addition to that, monitoring with an oximetry placed on the thumb is essential. Oximetry shows the oxygen saturation in the blood and can be used to reflect oxygen levels in the blood. SaO2 measured by oximetry can reflect PaO2 measured by BGA, and levels of SaO2 less than 90% equal PaO2 less than 60 mmHg
• Chest radiography and other tests aimed at the underlying cause

Management

Oxygen therapy

All patients need to be treated with oxygen to achieve a PaO2 level of 60 mmHg (SaO2 of 90%). Oxygen can be delivered by different methods according to the clinical situation, these methods include the use of a nasal cannula or a face mask.⁴ 

Address underlying cause

Treatment of the underlying infection, reducing pulmonary oedema, pulmonary embolism, and other causes accordingly, 

Mechanical ventilation in severe cases 

Mechanical ventilation is indicated if there is no improvement in the patient's condition and blood oxygen levels, or if the patient is experiencing deterioration.⁴

Type 2 Acute respiratory failure (Hypercapnic)

Definition

In type 2 respiratory failure, there is an elevated level of carbon dioxide in the blood (hypercapnia) in addition to the reduced level of oxygen. The definition of hypercapnia in lab tests (blood gas analysis) is carbon dioxide levels (PaCo2) of more than 50 mmHg (the normal range of PaCo2 is below 35 mmHg).²

Pathophysiology

Impairment in the lung’s ability to exchange gasses and the inability of the lung to remove carbon dioxide out of the body leads to build-up in the blood. The underlying possible mechanisms are similar to those discussed above in type 1 respiratory failure. 

Common causes

• Respiratory centre depression in the brain: this can be due to an overdose of narcotic drugs, opioids, or sedative drugs, or due to brain stem lesions either as a head trauma, brain infection, or tumours²
• Respiratory muscle paralysis: this can be due to lesions affecting the neuromuscular junctions, a variety of diseases like Myasthenia gravis, and Guillain-Barré syndrome²
• Chest wall dysfunction: either due to chest wall deformities (in cases of abnormal spine curvature; kyphosis, scoliosis), chest wall trauma causing multiple rib fractures (flail chest), burn injuries to the chest wall resulting in scarring and limiting the chest ability to exchange gasses with breathing and resulting in respiratory failure²
• Severe lower airway obstruction: in severe asthma and cases of Chronic obstructive pulmonary disease (mostly in smokers)²
• Upper airway obstruction with foreign body inhalation, larynx oedema, and acute epiglottitis³

Clinical features

Similar to symptoms of type 1 respiratory failure, which may include: 

• Shortness of breath
• Rapid breathing
• Bluish discoloration of skin (cyanosis)
• Restlessness and apprehension
• Increased heart rate and sense of heart pulsation
• Confusion and disturbed consciousness

These symptoms are associated with symptoms of the underlying disease. However, in type 2 respiratory failure the shortness of breath is usually severe and the patient rapidly turns blue, with rapid breathing and marked restlessness, apprehension, confusion, and then coma.

Workup and diagnosis 

The approach to type 2 respiratory failure is similar to that of type 1 respiratory failure, depending on three parameters:

1. Clinical history and physical examination
2. Lab test: Blood Gas Analysis (BGA) to show the levels of oxygen, and carbon dioxide, in addition to blood pH and acidity

Cases of type 2 respiratory failure, show elevated carbon dioxide levels in the blood (hypercapnia, PaCo2 more than 45 mmHg), and usually reduced levels of oxygen (PaO2). 

3. Chest radiography and other tests aimed at the underlying cause

Management

Reversal of the underlying cause and oxygen therapy

Treatment aims at Immediate or very rapid reversal of the precipitating event along with the use of high-flow oxygen therapy at the same time. 

• Removal of any foreign body or the use of a tracheostomy
• Fixation of the fractured ribs in cases of chest injury
• Reversal of narcotic drugs used 
• Use of bronchodilator and steroid therapy for severe asthma patients 
• Use of chest tube when indicated³

Mechanical ventilation 

In some cases when the underlying cause can not be reversed immediately, it is important to support ventilation temporarily by breathing intubation and mechanical ventilation.³

Conclusion 

Respiratory failure is not a disease by itself but is a consequence of an underlying pathology either in the lung, the chest and respiratory muscles, or the respiratory centre in the brain. Respiratory failure is classified into type 1 and type 2 according to the underlying levels of oxygen and carbon dioxide in the blood; type 1 is associated with low oxygen levels (hypoxemia) without elevation in carbon dioxide levels; while type 2 is associated with elevated carbon dioxide levels (hypercapnia). The symptoms associated with respiratory failure include shortness of breath, rapid breathing, bluish discolouration of skin, rapid heart rate, apprehension, confusion, and in advanced cases, coma. The management of respiratory failure includes correcting the underlying cause and the use of oxygen therapy.