Respiratory acidosis overview

# Overview
Respiratory acidosis is a clinical condition that occurs when the lungs are not able to remove enough of the carbon dioxide (CO2) produced by the body. Respiratory acidosis can be encountered in the inpatient units and emergency department , as well as in intensive care and postoperative units.Respiratory acidosis may become life-threatening if left untreated.

# Historical Perspective
Respiratory acidosis was first described by HendersonHasselbalch and BronstedLowry In the early 1950s.

# Pathophysiology
Respiratory acidosis is an result of  imbalance between acid-base due to alveolar hypoventilation.The normal range is 35-45 mm Hg  for PaCO2.Increase in the production of carbon dioxide due to  failure of ventilation results in sudden increase of the partial pressure of arterial carbon dioxide (PaCO2) above the normal range. Alveolar hypoventilation is one of the cause to increased PaCO2 which is is called hypercapnia. Hypercapnia and respiration acidosis occur while impairment in air flow happens and the elimination of carbon dioxide by the respiratory system is much less than the production of carbon dioxide in the tissues

# Causes
Common causes of respiratory acidosis include chronic obstructive pulmonary disease (COPD), neuromuscular diseases, chest wall disorders, obesity-hypoventilation syndrome, obstructive sleep apnea (OSA), the central nervous system (CNS) depression, lung, airway diseases, laryngeal and tracheal stenosis, Interstitial lung disease. Respiratory acidosis seen with past history of chronic lung disease, sleep problems, neuromuscular disorder, smoking history, travel history and any history of recent trauma.

# Classification
Respiratory acidosis may be classified into two groups: Acute respiratory acidosis and Chronic respiratory acidosis.

# Differential Diagnosis

# Epidemiology and Demographics
The prevalence of respiratory acidosis in patients with acute COPD is approximately  75 (95% CI 61 to 90) per 100 000/year in men aged 45-79 and 57 (95% CI 46 to 69) per 100 000 in women. The incidence of respiratory acidosis increases with age because the range for a normal gradient increases with age.

# Natural History, Complications & Prognosis
Respiratory acidosis (primary hypercapnia), is the acid-base ailment that consequences from an increase in  carbon dioxide in the body. Acute respiratory acidosis happens with respiratory failure, which could result from any unexpected respiratory parenchymal, airways (eg, chronic obstructive pulmonary disease), pleural, chest wall, neuromuscular eg, spinal cord injury, or central nervous system disorders. Chronic respiratory acidosis can result from several procedures and is typified by way of a sustained increase in arterial partial pressure of carbon dioxide, ensuing in renal adaptation, and an extra marked increase in plasma bicarbonate. 
Different mechanisms of respiratory acidosis include increased carbon dioxide production, alveolar hypoventilation, abnormal breathing drive, abnormalities of the chest wall and respiratory muscles. 
Common complications of respiratory acidosis include pulmonary, neurologic and cardiovascular complications such as Anxious, Dyspnea, Daytime somnolence, Alterations in sensorium like delirium and paranoia, Asterixis, Myoclonus, Seizures and Papilledema.
Depending on the level of the carbon-dioxide levels at the time of diagnosis and the disease causing the respiratory acidosis defines the prognosis.

# Diagnosis

## History and Symptoms
Respiratory acidosis or acute hypercapnia is often asymptomatic, leading to delayed diagnosis of the condition. Symptoms may include confusion,  fatigue, lethargy, shortness of breath, sleepiness or daytime somnolence.The medical manifestations of respiratory acidosis are regularly the ones of the underlying disorder.

## Physical Examination
Physical examination may vary, relying on the severity of the disorder and on the rate of development of hypercapnia. Mild to moderate hypercapnia that develops slowly generally has minimum symptoms.

## Laboratory Findings
Laboratory findings consistent with the diagnosis of respiratory acidosis include arterial blood gas (ABG), complete blood count(CBC), toxicology screen, thyroid function tests, creatine phosphokinase which are helpful in the diagnosis of respiratory acidosis.

## X-ray
An x-ray may be helpful in the diagnosis of respiratory acidosis which underlying lung pathology. Findings of an x-ray suggestive respiratory acidosis include hyperinflation, diaphragmatic flattening, Infiltrates, Pneumothorax.

## CT Scan
CT scan may be helpful in the diagnosis of respiratory acidosis. Findings on CT scan help in identifying etiologies of specific condition that include Central nervous system tumor, Stroke,CNS trauma and Brainstem lesions.

## MRI
MRI may be helpful in identifying abnormalities that not found on CT scans, especially in the brainstem.

## Other Diagnostic Studies
Other diagnostic studies for respiratory acidosis include pulmonary function tests, which are necessary for the diagnosis of the chronic obstructive lung disease.

# Treatment
The mainstay of treatment for respiratory acidosis is treating the underlying disorder which is responsible for the condition. While correcting hypercapnia extra care should be taken because rapid correction of the hypercapnia can result in metabolic alkalemia and can result in seizures especially when cerebrospinal fluid (CSF) becomes alkaline. Indications for admitting the patient in intensive care unit (ICU) when a patient presents with a low pH of (< 7.25), confusion, lethargy and respiratory muscle weakness.

## Medical Therapy
Pharmacologic medical therapy is recommended for patients who are taking sedatives. For patients suspected of drug overdose, administration of antidote should be considered. Supportive therapy for respiratory acidosis includes bag-valve-mask ventilation. In patients with severe hypoxemia it is necessary to administer oxygen to avoid life threatening complications.

## Surgery
Surgical intervention is not recommended for the management of respiratory acidosis.

## Prevention
There are no established measures for the primary prevention of respiratory acidosis.