Respiratory Acidosis
Definition
Respiratory acidosis is a condition in which a build-up of carbon dioxide in the blood produces a shift in the body's pH balance and causes the body's system to become more acidic. This condition is brought about by a problem either involving the lungs and respiratory system or signals from the brain that control breathing.
Description
Respiratory acidosis is an acid imbalance in the body caused by a problem related to breathing. In the lungs, oxygen from inhaled air is exchanged for carbon dioxide from the blood. This process takes place between the alveoli (tiny air pockets in the lungs) and the blood vessels that connect to them. When this exchange of oxygen for carbon dioxide is impaired, the excess carbon dioxide forms an acid in the blood. The condition can be acute with a sudden onset, or it can develop gradually as lung function deteriorates.
Causes and symptoms
Respiratory acidosis can be caused by diseases or conditions that affect the lungs themselves, such as
emphysema, chronic
bronchitis, asthma, or severe
pneumonia. Blockage of the airway due to swelling, a foreign object, or vomit can induce respiratory acidosis. Drugs like anesthetics, sedatives, and
narcotics can interfere with breathing by depressing the respiratory center in the brain. Head injuries or brain tumors can also interfere with signals sent by the brain to the lungs. Such neuromuscular diseases as Guillain-Barré syndrome or
myasthenia gravis can impair the muscles around the lungs making it more difficult to breathe. Conditions that cause chronic
metabolic alkalosis can also trigger respiratory acidosis.
The most notable symptom will be slowed or difficult breathing.
Headache, drowsiness, restlessness, tremor, and confusion may also occur. A rapid heart rate, changes in blood pressure, and swelling of blood vessels in the eyes may be noted upon examination. This condition can trigger the body to respond with symptoms of metabolic alkalosis, which may include
cyanosis, a bluish or purplish discoloration of the skin due to inadequate oxygen intake. Severe cases of respiratory acidosis can lead to
coma and
death.
Diagnosis
Respiratory acidosis may be suspected based on symptoms. A blood sample to test for pH and arterial blood gases can be used to confirm the diagnosis. In this type of acidosis, the pH will be below 7.35. The pressure of carbon dioxide in the blood will be high, usually over 45 mmHg.
Treatment
Treatment focuses on correcting the underlying condition that caused the acidosis. In patients with chronic lung diseases, this may include use of a bronchodilator or steroid drugs. Supplemental oxygen supplied through a mask or small tubes inserted into the nostrils may be used in some conditions, however, an oversupply of oxygen in patients with lung disease can make the acidosis worse.
Antibiotics may be used to treat infections. If the acidosis is related to an overdose of narcotics, or a
drug overdose is suspected, the patient may be given a dose of naloxone, a drug that will block the respiratory-depressing effects of narcotics. Use of mechanical ventilation like a respirator may be necessary. If the respiratory acidosis has triggered the body to compensate by developing metabolic alkalosis, symptoms of that condition may need to be treated as well.
Key terms
pH — A measurement of acid or alkali (base) of a solution based on the amount of hydrogen ions available. Based on a scale of 14, a pH of 7.0 is neutral. A pH below 7.0 is an acid; the lower the number, the stronger the acid. A pH above 7.0 is a base; the higher the number, the stronger the base. Blood pH is slightly alkali with a normal range of 7.36-7.44.
Prognosis
If the underlying condition that caused the respiratory acidosis is treated and corrected, there may be no long term effects. Respiratory acidosis may occur chronically along with the development of lung disease or
respiratory failure. In these severe conditions, the patient may require the assistance of a respirator or ventilator. In extreme cases, the patient may experience coma and death.
Prevention
Patients with chronic lung diseases and those who receive sedatives and narcotics need to be monitored closely for development of respiratory acidosis.
Resources
Books
"Fluid, Electrolyte, and Acid-Base Disorders." In Family Medicine Principles and Practices. 5th ed. New York: Springer-Verlag, 1998.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.
acidosis
[as″ĭ-do´sis] 1. the accumulation of acid and hydrogen ions or depletion of the alkaline reserve (bicarbonate content) in the blood and body tissues, resulting in a decrease in pH.
2. a pathologic condition resulting from this process, characterized by increase in hydrogen ion concentration (decrease in pH). The optimal
acid-base balance is maintained by chemical buffers, biologic activities of the cells, and effective functioning of the lungs and kidneys. The opposite of acidosis is
alkalosis. adj.,
adj acidot´ic.
Acidosis usually occurs secondary to some underlying disease process; the two major types, distinguished according to cause, are
metabolic acidosis and
respiratory acidosis (see accompanying table). In mild cases the symptoms may be overlooked; in severe cases symptoms are more obvious and may include muscle twitching, involuntary movement, cardiac arrhythmias, disorientation, and coma.
In general, treatment consists of intravenous or oral administration of sodium bicarbonate or sodium lactate solutions and correction of the underlying cause of the imbalance. Many cases of severe acidosis can be prevented by careful monitoring of patients whose primary illness predisposes them to respiratory problems or metabolic derangements that can cause increased levels of acidity or decreased bicarbonate levels. Such care includes effective teaching of self-care to the diabetic so that the disease remains under control. Patients receiving intravenous therapy, especially those having a fluid deficit, and those with biliary or intestinal intubation should be watched closely for early signs of acidosis. Others predisposed to acidosis are patients with shock, hyperthyroidism, advanced circulatory failure, renal failure, respiratory disorders, or liver disease.
compensated acidosis a condition in which the compensatory mechanisms have returned the pH toward normal.
lactic acidosis a
metabolic acidosis occurring as a result of excess
lactic acid in the blood, due to conditions causing impaired
cell respiration. It occurs most commonly in disorders in which oxygen is inadequately delivered to tissues, such as
shock,
septicemia, or extreme
hypoxemia, but it can also result from exogenous or endogenous metabolic defects. Initially manifesting as
hyperventilation, it progresses to mental confusion and coma.
metabolic acidosis any of the types of acidosis resulting from accumulation in the blood of
keto acids (derived from fat metabolism) at the expense of bicarbonate; this diminishes the body's ability to neutralize acids. This type is contrasted with
respiratory acidosis. It occurs when there is either an acid gain (as in diabetic ketoacidosis, lactic acidosis, poisoning, or failure of the renal tubules to reabsorb bicarbonate) or a bicarbonate loss (as in diarrhea or a gastrointestinal fistula).
The symptoms of metabolic acidosis include weakness, malaise, and headache. As the acid level goes up these symptoms progress to stupor, unconsciousness, coma, and death. The breath may have a fruity odor owing to the presence of acetone, and the patient may experience vomiting and diarrhea. Loss of fluids can deplete body fluid content and aggravate the acidosis. Hyperventilation may occur as a result of stimulation of the hypothalamus.
blood gas analysis will reveal a lowered pH and an elevated Pa
CO2. (See accompanying table.)
Treatment and Patient Care. Treatment of metabolic acidosis is primarily concerned with control of the underlying causes. Diabetic ketoacidosis may be corrected by the administration of insulin and fluids. In acute renal failure the patient requires dialysis, and in chronic uremic acidosis the condition is controlled by restricting sodium intake and buffering with bicarbonate. The patient's vital signs should be checked frequently to assess the progress of compensation. A rising pulse rate and a drop in blood pressure frequently occur as a result of hypovolemia in the diabetic-acidotic patient, and cardiac arrhythmias can be caused by increased calcium levels in the blood. A careful recording of intake and output provides a means of determining the kidneys' ability to regulate the
acid-base balance. Safety measures to avoid injury during involuntary muscular contractions should be carried out. (See also
convulsions.) Nursing measures to relieve discomfort from vomiting and to avoid the hazards of aspiration of vomitus are required. Education of the patient and family in the prevention of acute episodes of metabolic acidosis, particularly diabetic ketoacidosis, is of primary importance.
renal tubular acidosis (RTA) a
metabolic acidosis resulting from impairment of the reabsorption of bicarbonate by the renal tubules, characterized by low plasma bicarbonate and high plasma chloride; the urine is alkaline.
respiratory acidosis acidosis resulting from ventilatory impairment and subsequent retention of
carbon dioxide, in contrast to
metabolic acidosis. The respiratory system has an important role in maintaining
acid-base balance. In response to an increase in the hydrogen ion concentration in body fluids, the respiratory rate increases, causing more carbon dioxide to be released from the lung. When either an acute obstruction of the airways or a chronic condition involving the organs of respiration causes interference with the exhalation of the carbon dioxide produced by metabolic activity, carbon dioxide accumulates in the blood and unites with water to form carbonic acid.
Acute respiratory acidosis occurs when there is a relatively sudden malfunction of respiratory activities, as in upper airway obstruction, acute infections and inflammation of the lung and bronchial tissues, and pulmonary edema. In acute respiratory acidosis the compensatory chemical buffer systems are of limited benefit in restoring the acid-base balance because they depend on normal blood circulation and tissue perfusion for optimal effect. The physiologic regulators, the lungs and kidneys, are of little help because the lungs are malfunctioning and the kidneys require more time to compensate than the acute condition permits.
Chronic respiratory acidosis results from gradual and irreversible loss of ventilatory function, as in
chronic obstructive pulmonary disease (COPD). Although the patient in this condition does have an increased retention of CO
2, there is time for the kidneys to compensate by retaining bicarbonate and thereby maintaining a pH within tolerable limits. If, however, even a minor respiratory infection develops, the patient is subject to a rapidly developing state of acute acidosis because the lungs cannot be depended upon to remove more than a minimal amount of CO
2.
Treatment and Patient Care. The initial treatment for acute respiratory acidosis is to establish an airway immediately and maintain adequate ventilation and hydration. Acute cases may require the use of an
endotracheal tube or
tracheostomy tube. Some form of
intermittent positive pressure breathing is applied through a machine-driven ventilator, essentially to force adequate O
2 delivery and concomitant CO
2 removal from the lungs, thereby avoiding further rises in CO
2 levels to the point that CO
2 narcosis will develop. Beyond a certain point the respiratory center may cease responding to the higher CO
2 levels, and breathing will stop abruptly. Drugs that further depress the respiratory center (narcotics, hypnotics, and tranquilizers) must be avoided. Patients in the acute stage are watched for cessation of breathing and cardiac arrest.
cardiopulmonary resuscitation may be required to revive the patient.
It is recommended that oxygen administration be limited in patients with chronic obstructive pulmonary disease (COPD). In COPD the stimulus to breathe is a hypoxic state, therefore administration of high concentrations of O
2 will remove this needed stimulus. The rate of oxygen flow should be closely correlated with blood gas studies. In patients with acute lung diseases the stimulus to breathe is still dependent on CO
2 concentrations, so that O
2 can be supplied without fear of inhibiting the stimulus to breathe.
Measures that facilitate breathing are essential to patient care during respiratory acidosis. Frequent turning, coughing, and deep breathing exercises to encourage oxygen–carbon dioxide exchange are beneficial, as is suctioning when needed to remove secretions obstructing the airway.
postural drainage, unless contraindicated by the patient's condition, may be effective in promoting adequate ventilation.
starvation acidosis a
metabolic acidosis due to accumulation of ketones following a severe caloric deficit.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.