Respiratory Acidosis Definition
Respiratory acidosis can be defined as a medical condition in which hypoventilation or decreased ventilation leads to an increase in the concentration of blood carbon dioxide and decreased pH or acidosis.
What Happens in Respiratory Acidosis?
CO2 is constantly produced as the cells of the body respire. However, carbon dioxide can rapidly accumulate if the lungs are unable to expel it adequately through alveolar ventilation. Hence, alveolar hypoventilation leads to increased levels of PaCO2, a condition which is referred to as hypercapnia. Increased levels of PaCO2 reduce the HCO3−/PaCO2 ratio as well as decrease the pH levels.
Respiratory Acidosis ICD-9 Code
The ICD-9 Code for this disorder is 276.2.
Respiratory Acidosis Types
The condition is subdivided into the following two types:
Acute Respiratory Acidosis
In this form, the PaCO2 levels are elevated above 47 mm Hg or 6.3 kPa reference mark along with accompanying acidemia (pH levels less than 7.35).
Chronic Respiratory Acidosis
In this type, the PaCO2 levels are elevated above upper limit of reference range, with normal blood pH levels (between 7.35 and 7.45) or near normal pH that is secondary to the renal compensation and elevated levels of serum bicarbonate (HCO3− greater than 30 mm Hg).
Respiratory Acidosis Causes
There are a number of factors which might be responsible for the development of this disorder. The causes responsible for both types of respiratory acidosis might differ from each other. These causes have been mentioned below:
Acute Respiratory Acidosis
It occurs due to an abrupt or sudden failure of ventilation. This can occur due to the following factors:
- Exacerbation of chronic obstructive pulmonary disease or COPD
- Depression of central respiratory center caused by drugs or cerebral disease
- Airway obstruction caused by asthma, emphysema, bronchitis or pneumonia
- Inadequate ventilation caused by neuromuscular diseases, such as amyotrophic lateral sclerosis, myasthenia gravis, muscular dystrophy and Guillain-Barré syndrome
Chronic Respiratory Acidosis
It can occur alongside to many disorders, such as chronic obstructive pulmonary disease, or be secondary to them. Hypoventilation in chronic obstructive pulmonary disease involves a number of mechanisms, such as:
- Decreased responsiveness to hypercapnia and hypoxia
- Decreased diaphragm function that is secondary to hyperinflation and fatigue
- Increased ventilation-perfusion mismatch that results in an additional dead space ventilation
This form may also be caused by:
- Neuromuscular disorders like amyotrophic lateral sclerosis
- Obesity hypoventilation syndrome or Pickwickian syndrome
- Severe restrictive ventilatory deficiencies that can be observed in thoracic deformities and interstitial fibrosis
Lung diseases that mainly cause abnormalities in the alveolar gas exchange process generally do not lead to hypoventilation. However, they might result in stimulation of ventilation as well as hypocapnia that is secondary to the hypoxia. Hypercapnia can only develop under the influence of severe respiratory muscle fatigue or disease.
Other probable causes of the disorder include problems like:
- Tetanus
- Aspiration
- Poliomyelitis
- Pneumothorax
- Laryngospasm
- Bronchospasm
- Pulmonary edema
- Various myopathies
- Respiratory alkalosis
- Restrictive lung disease
- Malignant Hyperthermia
- Upper Airway obstruction
- High central neural blockade
- Inadequate mechanical ventilation
- Diaphragmatic splinting or paralysis
- Adult respiratory distress syndrome
- Cardiac arrest along with cerebral hypoxia
- Toxins like organophosphates and snake venom
- Cervical cord traumas or lesions at C4 level or above
- Trauma of the CNS, such as hemorrhage, tumor or infarct
- Chest trauma, such as flail chest, hemothorax or contusion
- Drug depression of the respiratory center by sedatives, opiates, or anesthetics
Respiratory Acidosis Symptoms
The condition is characterized by a number of common signs and symptoms. These include:
- Coma
- Stupor
- Seizures
- Lethargy
- Cyanosis
- Azotemia
- Confusion
- Headache
- Wheezing
- Warm skin
- Irritability
- Sleepiness
- Easy fatigue
- Flushed skin
- Papilledema
- Hypercapnia
- Chronic cough
- Hallucinations
- Cor pulmonale
- Combativeness
- Breathlessness
- Myoclonic jerks
- Bounding pulse
- Flapping tremor
- Gait disturbance
- Peripheral edema
- Constricted pupils
- Shortness of breath
- Low blood pressure
- Transient psychosis
- Abnormal heart rhythm
- Reduced cardiac output
- Pulmonary hypertension
- Reduced tendon reflexes
- Dilated cerebral blood vessels
- Increased pressure the inside skull
Respiratory Acidosis Diagnosis
The clinical manifestations of this condition are generally of the underlying disorders. A doctor is likely to first conduct a thorough medical checkup of the patient. Thoracic examination of the patients may reveal the following signs:
- Wheezing
- Decreased breath sounds
- Hyperinflation
- Hyperresonance on percussion
- Prolonged expiration
Rhonchi sounds might also be heard. The mental status of the patient might be depressed due to higher levels of PaCO2 and may have signs of myoclonus, asterixis and seizures. A drug screen test is advisable for patients who do not have any obvious source of respiratory acidosis and hypoventilation. This is because drugs like narcotics and benzodiazepines might have an adverse effect on such patients.
The various diagnostic tests, that are carried out to evaluate if a person is having respiratory acidosis, include the following:
- Chest X-rays
- Thyroid tests
- MRI scanning
- Chest radiography
- Serum electrolytes
- Fluoroscopy of the chest
- Pulmonary function tests
- Complete blood count (CBC)
- Arterial blood gas (ABG) levels
- Electromyography or EMG tests
- Computed Tomography (CT) scanning
- Nerve conduction velocity or NCV tests
- Transdiaphragmatic pressure measurement
Respiratory Acidosis Differential Diagnosis
There are a number of respiratory disorders that show signs and symptoms similar to that of respiratory acidosis. Some of them are even closely related to this condition. Hence, while carrying out the diagnosis of this condition, its symptoms should be differentiated from those of such similar disorders. The differential diagnoses of respiratory acidosis include distinguishing its signs from those of conditions such as:
- Asthma
- Obesity
- Botulism
- Flail chest
- Emphysema
- Opioid Abuse
- Pneumothorax
- Kyphoscoliosis
- Pleural effusion
- Pulmonary edema
- Myasthenia gravis
- Chronic Bronchitis
- Muscular dystrophy
- Diaphragm Disorders
- Severe kyphoscoliosis
- Diaphragmatic Paralysis
- Obstructive sleep apnea
- Guillain-Barré syndrome
- Amyotrophic lateral sclerosis
- Chronic Obstructive Pulmonary Disease
Respiratory Acidosis Treatment
The treatment of the condition is mostly dependent on its underlying causative factors. The primary methods of treatment involve administration of medications as well as carrying out surgical operations whenever required.
Medications
The various types of medications used for curing this disease include:
Beta2 Antagonists
These medications can decrease the muscle tone in small as well as large airways within the lungs, which facilitates ventilation. The short acting beta2 antagonists such as albuterol, levalbuterol, and metaproterenol can be used to treat the symptoms of bronchospasm. The long acting beta2 antagonists like arformoterol, formoterol and indacaterol are normally used for managing more persistent symptoms.
Anticholinergics medications
The anticholinergic medicines facilitate bronchodilation and releases bronchial restrictions. They can be used along with beta2 antagonists to create a synergistic effect. Examples of these drugs include Ipratropium and Tiotropium.
Xanthine Derivatives
Xanthine derivatives help to increase the amounts of cyclic adenosine monophosphate or cAMP by inhibiting phosphodiesterase. This increase in cAMP relaxes the bronchial smooth muscles. Examples of Xanthine derivatives include theophylline and aminophylline. Theophylline is taken orally whereas aminophylline can be administered intravenously. Theophylline also facilitates diaphragmatic muscle contractility as well as initiates the stimulation of CNS respiratory center.
Corticosteroids
Glucocorticosteroids help to manage inflammations that are frequently seen in asthma and chronic obstructive pulmonary disease. Glucocorticosteroid medications such as budesonide, fluticasone, and mometasone can be inhaled directly into the airways. They improve airflow in patients of asthma. Systemic use of glucocorticosteroids like methylprednisolone, prednisone and prednisolone help in efficient treatment of COPD exacerbations.
Benzodiazepine Toxicity Antidotes
Benzodiazepine antagonists like Flumazenil can be used to reverse the depressing effects of a benzodiazepine overdose in the central nervous system.
Opioid Antagonists
Opioid abuse, overdose or toxicity can give rise to respiratory acidosis and hypoventilation. Opioid antagonists can help to reverse the ill effects of opiates along with improving ventilation. Examples of opioid antagonists include Naloxone.
Surgery
Patients with severe kyphoscoliosis should be treated with spine fusion operation if thoracic spine angle is greater than 40°.
Individuals having obesity-related hypoventilation syndrome can find benefit from weight-reducing surgeries. Bariatric surgical techniques, such as vertical banded gastroplasty, roux-en-Y gastric bypass and adjustable gastric banding, can be used to treat these patients. According to US NIH (National Institutes of Health) consensus, if an individual has a body mass index greater than 35kg/m2 along with an obesity-related co-morbid condition, he or she should be treated with the above-mentioned surgical procedures. Alternatively, an individual having BMI greater than 40kg/m2 is also eligible for a surgery.
Primary alveolar hypoventilation can be treated with a procedure known as diaphragmatic pacing. This method is also quite useful in treating congenital central alveolar hypoventilation syndrome.
Other forms of treatment include oxygen therapy and noninvasive ventilation.
Respiratory Acidosis Complications
Patients having chronic form of the disorder can have complications related to alveolar hypoventilation. They suffer from amplified partial arterial pressure caused by the levels of carbon dioxide (PaCO2) and bicarbonates. They also have reduced partial arterial pressure of oxygen or PaO2.
Chronic hypoxemia can lead increased erythropoiesis which results in secondary polycythemia. Chronic hypoxia frequently progresses to pulmonary vasoconstriction. In long-term, this can give rise to problems like:
- Pulmonary hypertension
- Cor pulmonale
- Right ventricular failure
The apneas and hypopneas can result in impaired sleep quality as well as cerebral vasodilation which can cause:
- Daytime fatigue
- Morning headaches
- Somnolence
High quantities of PaCO2 can give rise to confusion and a condition known as Carbon Dioxide Narcosis.
Respiratory Acidosis Prognosis
The outcome of the condition depends on the severity of the underlying conditions and their management. Complete recovery is probable, although patients have also been reported to suffer from recurrence of certain symptoms and complications.
