Medical term: Primary hypercapnia

When the lungs are unable to expel enough of the carbon dioxide (CO2) that the body creates, respiratory acidosis results. The pH level of your blood falls below 7.35 and other body fluids become overly acidic due to an excess of CO2. ² This potentially fatal illness can be brought on by an acute illness, a drug overdose, or a chronic lung ailment. Acidic blood can cause progressively severe symptoms, such as drowsiness that eventually leads to a coma. As a medical emergency, respiratory acidosis needs to be diagnosed and treated right away. This article explores types of respiratory acidosis, causes, diagnosis, the course of treatment and prevention.

Types of respiratory acidosis

Currently there are two types of respiratory acidosis, acute or chronic.

Acute respiratory acidosis is characterised by an acidemia (pH less than 7.35) and an increased PaCO2 over the top limit of the reference range (>45 mm Hg) while Chronic respiratory acidosis is characterised by elevated serum bicarbonate levels (>30 mEq/L), normal or almost normal pH due to renal compensation, and elevated PaCO2 over the upper limit of the reference range.

Causes of respiratory acidosis

Hypoventilation is the state in which breathing becomes too difficult for you to expel carbon dioxide from your blood. Blood carbon dioxide levels rise as a result of hypoventilation, making your blood more acidic. These changes may result in acute or chronic respiratory acidosis or a combination of both depending on the factors.

The following factors can result in acute respiratory acidosis. These are:

On the other hand, chronic respiratory acidosis occurs as a secondary symptom in long term illnesses or as a complication in lifestyle choices such as:

• chronic obstructive pulmonary disease (COPD)
• Obesity hypoventilation syndrome
• Skeletal defects especially in the chest and abdomen region such as fibrosis
• Neuromuscular disorders e.g Amyotrophic Lateral Sclerosis. At this stage there is severe decrease in response to low oxygen levels and high PaCO2

Understanding the acid-base balance

To understand the body’s acidity or alkalinity, the pH scale is used. It is more acidic when the number is lower and more alkaline when the number is higher. The pH range of the body's acid-base equilibrium is typically 7.35 to 7.45. A value of less than 7.35 is referred to as acidosis. It is referred to as alkalosis if it rises above 7.45.5.

The PH balance in the body can be affected by:

• Exhaling carbon dioxide (or not being able to)
• Alterations in metabolism that affect the generation of acid or carbon dioxide
• Excretion of bicarbonate via the kidneys

The following illnesses can result in or aggravate respiratory acidosis:

• Inadequate blood or air flow via the lungs (perfusion or ventilation)
• A malfunctioning brainstem that prevents regular breathing.
• Conditions that obstruct the airways, such as asthma and COPD

Inadequate blood or air flow via the lungs (perfusion or ventilation)

The blood must carry carbon dioxide to functional, well-ventilated alveoli in order for the body to expel it. This function is impacted by both impaired blood flow and inadequate air filling of the lung tissue. 

Dead space ventilation is a phenomenon caused by an imbalance between blood flow (perfusion) and airflow (ventilation). Respiratory acidosis can be exacerbated by this lack of function, which may result from:

• Pulmonary edema (secondary to heart failure)
• Pneumonia
• Pneumothorax (a rupture that leads air to escape and external collapse of the lung)
• Pulmonary fibrosis (scarring and thickening of the lung tissue)
• Obesity hypoventilation syndrome (severe obesity restricts how much the lungs can expand).

Airway blockage

Before it reaches your lungs, air can become stopped at a number of locations. It can be restricted in the trachea, the windpipe. Alveoli, which are tiny, grape-shaped sacs found in the lungs, can become mucus-filled or stiff. Respiratory failure and acidosis may develop gradually as a result of an airway blockage. 

Among the causative factors are:

• Aspiration (e.g choking)
• Allergy e.g COPD
• Breathing difficulties such as coughing, wheezing, and shortness of breath may be linked to these illnesses

Malfunctioning brainstem

Breathing is controlled by a brainstem. In order to accomplish this, it transmits signals to the diaphragm and other respiratory muscles, causing the lungs to expand during inhalation and contract during exhalation.

The diaphragm draws downward as it contracts, allowing the lungs to fill with air. The lungs slowly empty as it relaxes.

Breathing becomes difficult if the respiratory centre of the brainstem is destroyed since these signals aren't sent. This type of disability may result from:

• Drugs that inhibit breathing (alcohol, benzodiazepines, and opioids)
• Overdose on drugs
• Spinal cord damage
• Trauma 
• Stroke 
• Tumour(s)

These anomalies usually cause additional symptoms, which frequently impair consciousness and in extreme situations induce a coma.

Musculoskeletal defects

The diaphragm which is a muscle is principally in charge of your lungs' expansion and filling. The ability to breathe may be compromised if this muscle gives up. Respiratory acidosis can develop gradually as a result of conditions that limit lung expansion or impair the muscles that support breathing. 

Possible reasons consist of:

• Malfunction of the diaphragm (typically caused by a damaged phrenic nerve)
• Scoliosis
• Myasthenia gravis
• ALS
• Guillain-Barre syndromes
• Muscular dystrophy

Diagnosis of respiratory acidosis

People with respiratory acidosis are usually diagnosed when they exhibit breathing difficulties or experience a shift in consciousness, such as fainting or disorientation.

Sudden show of symptoms will require immediate medical attention. Gradual signs are typically less serious. The goal of diagnostic testing is to test for pH imbalance, determine its severity and discover the condition behind it. During a physical exam, the doctor will assess blood circulation, listen to heart and lungs, look for airway blockages.

Preliminary blood tests

The results of blood tests for respiratory acidosis show the blood's pH and carbon dioxide concentrations. The most crucial diagnostic procedure is the measurement of arterial blood gas which determines the blood's levels of carbon dioxide and oxygen.

PaCO2, or arterial CO2 tension: measures blood acidity, partial pressure of oxygen, and carbon dioxide levels.

Electrolytes

Electrolyte testing is a method of testing used to measure body's concentrations of specific salts and minerals, such as:

• Sodium 
• Bicarbonate 
• Potassium
• Chloride

People with respiratory acidosis will have one or more of the electrolytes higher or lower than normal.

Lung function test

Lung function is often decreased in people with respiratory acidosis. A doctor can assess the efficiency of the lungs when they perform the following tasks using a variety of tests:

Spirometry: A patient is asked to breathe into and out of a spirometer by a medical practitioner. This measures the volume of air that enters and exits your lungs as well as the volume of air that is moved during the process.

Lung volume: This determines how much air the lungs can hold(air pressure) by amount of air that is breathe in.

Gas diffusion. By use of a mouthpiece connected to a machine,a safe concentration of carbon monoxide is inhaled .This is used to gauge how well your lungs are able to transfer gases into your circulation.

Exercise test. This entails using an exercise bike or running on a treadmill while blood pressure, blood oxygen level, and heart rate are monitored by monitors. The activity demonstrates how your lungs work during physical exertion.

Testing and Imaging

To identify the root cause of the respiratory acidosis, these tests are used:

• Basic metabolic panel(blood test).
• Chest X-ray which helps to see injuries, muscular issues, or skeletal problems that can cause acidosis.
• Computed tomography (CT) scan of the chest
• Pulmonary function testing (to measure breathing and lung function)

Other tests

There may be additional tests based on the outcomes of preliminary tests in order to assist identify the underlying cause of the acidosis.

Differential diagnosis conditions such as metabolic acidosis could also affect the tests as they have similar symptoms to that of respiratory acidosis. To make sure the issue is only peculiarly limited to respiratory issues, the doctor could request other testing. These tests evaluate the quantity of acid (glucose, lactate, and ketones) in the body, which can be brought on by diabetes, kidney failure, or other illnesses. Some tests consist of urinary testing, such as a urine test or CBC (complete blood count).

Treatment for respiratory acidosis

 If severe respiratory acidosis lasts for more than 12 hours, the kidneys will try to compensate by decreasing the blood acidity. This procedure typically takes three to five days. However, it may not be enough to restore your acidity hence the need for therapy. The primary therapy for respiratory acidosis is to enhance breathing and address the underlying reason.

Oxygen booster

Extra oxygen is given if your blood oxygen level is low. However, oxygen therapy alone is not an effective treatment—in certain situations, it may inhibit breathing, exacerbating the acidity.

Non-invasive Positive Pressure Ventilation

A continuous positive airway pressure (CPAP) or bilevel (BiPAP) equipment may help patients to breathe better. These devices are most commonly used to treat obstructive sleep apnea (OSA), but they can also be used to treat severe respiratory acidosis.²

CPAP and BiPAP use a face mask over the nose and occasionally mouth to provide compressed air. This aids in the expulsion of carbon dioxide from your lungs.

When pulmonary acidity is caused by OSA, obese hypoventilation syndrome, or neuromuscular failure, this medication is extremely beneficial.

Intubation

If breathing problems worsen, it is essential to insert a breathing tube into the airway so that it may directly ventilate the lungs. The patient is rendered unconscious to prevent them from accidently ripping out the tube. The tube is then attached to a ventilator, which assists the lungs in taking in oxygen and expending carbon dioxide. This is usually the last choice of treatment.

Other treatments

These treatments depend on Medications: Bronchodilators and corticosteroids may be used to treat airway blockage caused by asthma or COPD.

Quitting smoking: Smokers will be urged to do so. Smoking adds to airway dysfunction, and preventing further damage may help to prevent future issues.

Significant weight reduction in obesity hypoventilation syndrome may relieve improper lung compression. If diet and exercise are insufficient, weight loss surgery may be recommended.

Sedatives should be avoided: Avoid narcotic pain relievers and benzodiazepines (anxiety medications). If you must take one (with your doctor's clearance), never mix the medication with alcohol.⁴

Treatment for sleep apnea: If OSA is the cause, using CPAP or BiPAP to treat it can help prevent respiratory acidosis. To diagnose OSA, you may be referred for a sleep study.

Summary

Respiratory acidosis is a potentially fatal disorder in which your blood gets too acidic. This is frequently caused by a respiratory issue.

Breathing issues can be caused by issues with brain signals that govern breathing, a blocked airway (aspiration, asthma), decreased lung function (pneumonia, pulmonary fibrosis), and musculoskeletal issues (diaphragm dysfunction, nerve or muscle illnesses).

A physical exam, blood testing for carbon dioxide and acid levels, lung function tests, and imaging are all used to make a diagnosis.

Treatment entails assisting with breathing and treating or controlling the underlying cause(s).