Respiratory Acidosis- Types, Etiology, Pathophysiology, Symptoms, Diagnosis, and Treatment

Introduction:

The normal pH of the blood ranges from 7.35 to 7.45, which means that the blood is slightly basic (alkaline). The body's pH balance is essential to maintain homeostasis and is also known as the acid-base balance. The lungs and kidneys play a major role in maintaining this balance. Any abnormalities or disease conditions affecting the lungs and the kidneys would result in a disturbance in the acid-base balance causing either acidosis or alkalosis. Both conditions need to be addressed earlier to prevent further complications. The primary problem in respiratory acidosis is the decreased ratio of arterial bicarbonate to arterial carbon dioxide resulting in decreased pH.

What Is the Normal Physiology of Acid-Base Balance?

The physiological pH buffering is mediated by two main compounds, bicarbonate (HCO3) and carbon dioxide (CO2). Bicarbonate (HCO3) maintains the alkalinity of the blood, while carbon dioxide maintains the acidic nature of the blood and body fluids. The balance between both compounds is mandatory to keep the pH in balance and maintain homeostasis. The respiratory system is responsible for regulating the CO2 levels through a process called respiration, and the renal system is responsible for regulating the HCO3 levels through a process called reabsorption.

What Are the Types of Acid-Base Imbalances?

There are four types of acid-base imbalances. These are as follows:

• Metabolic Acidosis - It is characterized by the presence of excess acid in body fluids.

• Metabolic Alkalosis - It is characterized by elevated serum bicarbonate levels.

• Respiratory Acidosis - This is a condition in which the lungs fail to eliminate the carbon dioxide produced by the body.

• Respiratory Alkalosis - It is characterized by a high level of carbon dioxide in the blood.

What Is Respiratory Acidosis?

Respiratory acidosis is characterized by a decreased blood pH due to the accumulation of carbon dioxide in the blood. It is mainly caused due to the failure of ventilation. Respiratory acidosis is one of the four primary acid-base imbalances.

What Is PaCO2?

PaCO2 refers to the partial pressure of carbon dioxide in the arterial blood. The normal value is between 35 to 45 mmHg. Values above 45 mmHg indicate an increased level of carbon dioxide in the blood.

What Are the Types of Respiratory Acidosis?

There are two types of respiratory acidosis, which include:

• Acute Respiratory Acidosis: It is characterized by elevated PaCO2 levels above the range of 45 mmHg with an accompanying acidemia (pH of the blood less than 7.5). This may occur as a result of sudden failure of ventilation.

• Chronic Respiratory Acidosis: It is characterized by elevated PaCO2 levels above the range of 45 mmHg with a normal or near-normal blood pH. This may be secondary to any other diseases.

• Acute and Chronic Respiratory Acidosis: A few individuals might have long-term (chronic) respiratory acidosis and develop a coexisting illness that could affect ventilation. This could worsen the chronic symptoms even if one does not notice the symptoms before. This is regarded as a combined type.

What Is the Etiology of Respiratory Acidosis?

The main cause of respiratory acidosis is hypoventilation. The conditions which can cause hypoventilation are as follows:

• Cerebrovascular Accidents - These involve loss of blood flow to the tissues as a result of damage to the parts of the brain.

• Central Nervous System Depressants - Medications such as benzodiazepines, sleeping tablets, and barbiturates can cause hypoventilation.

• Myasthenia Gravis - This is an autoimmune type of neuromuscular disease characterized by weakness of the skeletal muscles.

• Guillain Barre Syndrome - This is an autoimmune disorder characterized by the production of autoantibodies against the nerves.

• Muscular Dystrophy - Muscular dystrophy is characterized by the progressive loss of muscle mass and the subsequent weakening of muscles.

• COPD - Chronic obstructive pulmonary disease (COPD) is the inflammation of the lung tissues resulting in obstruction to the airflow from the lungs.

• Hypercapnia - It is characterized by an increase in PaCO2 to levels more than 45 mmHg.

• Hypoxia - Inadequate oxygen levels in the blood cause hypoxia.

• Pneumonia - This is an acute infection of the lungs resulting in the accumulation of pus and fluid in the alveoli.

• Pickwickian Syndrome - Obesity hypoventilation syndrome is characterized by daytime hypercapnia.

• Amyotrophic Lateral Sclerosis - This is a disease that causes damage to the nerve cells in the brain and the spinal cord.

Asthma and sleep apnea (a serious type of sleep disorder in which there is a repeated stop and start in the breathing activity).

What Is the Pathophysiology of Respiratory Acidosis?

Carbon dioxide plays a crucial role in maintaining the blood's pH. The blood’s pH serves as an important factor in initiating ventilation. In the case of respiratory acidosis, hypoventilation occurs as a result of the above-discussed etiologies. This, in turn, results in the overproduction of CO2 by the body than it can eliminate. The increased CO2 levels would, in turn, increase the concentration of hydrogen ions and contribute to the fall in pH, thereby resulting in respiratory acidosis.

The central chemoreceptors in the brain are sensitive to varying pH levels. Depression of the central respiratory center located due to certain drugs and diseases would result in hypoventilation, thereby developing respiratory acidosis. The other cause of hypoventilation is the blocked region of the lung that causes a mismatch between air and blood in the lungs.

What Are the Causes of Acute and Chronic Respiratory Acidosis?

Causes of acute respiratory acidosis are:

• Emphysema (a condition of the lung that results in shortness of breath).

• Asthma.

• Pneumonia.

• COPD.

• Certain conditions can have an influence on the rate of breathing.

• Hindrance in the airways due to choking or other reasons.

• Muscle weakness that can impact breathing or taking a deep breath.

• Drug overuse (like opioids) can affect the central nervous system.

Causes of chronic respiratory acidosis are:

• Asthma.

• Acute pulmonary edema (an abnormal accumulation of fluid in the lungs).

• COPD.

• Excessive obesity could affect the expansion of the lungs.

• Scoliosis (curvature of the spine towards one side).

• Neuromuscular disorders like Guillain-Barre Syndrome, muscular dystrophy, and so on.

What Are the Symptoms of Respiratory Acidosis?

The symptoms of respiratory acidosis include:

• Dizziness.

• Anxiety.

• Weakness.

• Sleep disturbances.

• Cyanosis (it is the bluish discoloration of the skin and mucous membranes).

• Confusion.

• Wheezing.

• Headache.

• Myoclonus (a quick involuntary muscle jerk).

• Hypercapnia (an increase in PaCO2).

• Cerebral vasodilation (an increase in cerebral blood flow).

• Memory loss.

• Papilledema (swelling of the optic nerve).

• Increased intracranial pressure (increase in pressure inside the brain).

• Pulmonary hypertension (a type of blood pressure affecting the lung arteries).

• Polycythemia (increased red blood cell count).

• Apnea (a serious disorder in which the breathing stops and starts while sleeping).

• Somnolence (a state of being drowsy).

How Is Respiratory Acidosis Diagnosed?

Respiratory acidosis is diagnosed in the following ways:

1. History: A thorough medical history would help in understanding the symptoms of the disease and provide a clue in diagnosing the condition. The patient should be enquired about the history of dizziness, wheezing, headache, confusion, and the history of medications such as opioids.

2. Physical Examination: Careful examination of the patient to check for the signs of hypoventilation and acidosis such as respiratory rate, heart rate, temperature, blood pressure, cyanosis, and myoclonus would help in diagnosis and treatment planning.

3. Arterial Blood Gas: It is a type of blood test in which a blood sample from an artery is collected to measure the oxygen and carbon dioxide levels in the blood and also measures the acid-base balance in the blood. In the case of patients with respiratory acidosis, the carbon dioxide levels in the blood would be increased to levels more than 45 mm Hg, bicarbonate levels will be elevated to more than 30 mmHg, and pH will decrease to values less than 7.5.

4. Blood Test:

• Serum Electrolyte Levels - Measurement of the levels of certain salts and minerals like sodium, potassium, chloride, and bicarbonate will be done. The level of one or more of the electrolytes will be low or elevated in individuals with acid-base disorders such as respiratory acidosis.

• Autoantibodies - The presence of autoantibodies in the circulating blood should be screened to rule out the existence of conditions such as myasthenia gravis and Guillain barre syndrome.

5. Pulmonary Function Test: It is done to check the functioning capacity of the lungs in patients with respiratory disorders.

6. Lung Function Tests: The efficacy of the lungs is assessed by evaluating the movement of air into and away from the lungs, the ability to hold enough air in the lungs, and transferring oxygen into the bloodstream. Certain tests that assess the function of the lungs include spirometry, exercise test, gas diffusion test, and lung volume test.

7. Chest X-Ray: It helps rule out the infectious cause and pneumonia.

8. Computed Tomography (CT) and Magnetic Resonance Imaging (MRI): CT and MRI of the head would help to find out whether the underlying cause of the disease is a neurological insult or head injury.

Other tests to diagnose respiratory acidosis include drug testing, complete blood count (CBC), and urine test (urinalysis).

How Is Respiratory Acidosis Managed?

The main aim of management is to treat the underlying cause of the condition and look into it at the earliest. The steps in management are as follows:

• Nasal Ventilation - It is done to treat hypercapnia where the physician asks the patient to wear a mask that blows air into the lungs.

• Mechanical Ventilation - It is done by inserting a tube into the mouth to reach the airway, thereby aiding in breathing.

• Diuretics and Corticosteroids: Diuretics minimize fluid accumulation in the heart and lungs and corticosteroids minimize inflammation.

• Antibiotics - Antibiotics are given to treat infections such as pneumonia.

• Bronchodilators - Bronchodilators are given to dilate the airways, and medications such as anticholinergic drugs, beta-agonists, and methylxanthines can relieve the symptoms.

• Lifestyle Modifications - Modifications in lifestyle such as stopping smoking and limiting exposure to chemicals, dust, and so on should be done to avoid further complications.

Those suffering from acute respiratory acidosis might require a machine called BiPAP which aids in breathing and gas transfer without the requirement of invasive tubing.

Conclusion:

Respiratory acidosis may occur due to a variety of causes, thus making the treatment a bit complex. The main motto of management is to correct the underlying cause. The occurrence of respiratory acidosis due to an underlying condition is called ventilatory failure or respiratory failure. Hypercapnia should be addressed early and reduced slowly, as sudden reduction would result in seizures due to the rapid alkalinization of the cerebrospinal fluid. Patients with severe symptoms should be monitored in the intensive care unit.