respiratory acidosis

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.

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acidosis /ac·i·do·sis/ (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, decreasing the pH.

2. a pathologic condition resulting from this process. Cf. alkalosis. acidot´ic

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compensated acidosis  a condition in which the compensatory mechanisms have returned the pH toward normal.

diabetic acidosis  metabolic acidosis produced by accumulation of ketones in uncontrolled diabetes mellitus.

hypercapnic acidosis  respiratory a.

hyperchloremic acidosis  metabolic acidosis accompanied by elevated plasma chloride.

lactic acidosis  a metabolic acidosis occurring as a result of excess lactic acid in the blood, due to conditions causing impaired cellular respiration.

metabolic acidosis , nonrespiratory acidosis a disturbance in which the acid-base status shifts toward the acid because of loss of base or retention of noncarbonic, or fixed (nonvolatile), acids.

renal hyperchloremia acidosis , renal tubular acidosis (RTA) metabolic acidosis resulting from impairment of renal function.

respiratory acidosis  acidosis due to excess retention of carbon dioxide in the body.

starvation acidosis  metabolic acidosis due to accumulation of ketone bodies which may accompany a caloric deficit.

uremic acidosis  metabolic acidosis seen in chronic renal disease when the ability to excrete acid is decreased.

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respiratory acidosis

n.

Acidosis that is caused by retention of carbon dioxide, due to inadequate pulmonary ventilation or hypoventilation, and that results in a decrease in blood pH unless compensated for by renal retention of bicarbonate.

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respiratory acidosis,

an abnormal condition characterized by a low plasma pH resulting from reduced alveolar ventilation. The hypoventilation inhibits the excretion of carbon dioxide, which consequently combines with water in the body to produce carbonic acid, thus reducing plasma pH. Respiratory acidosis can result from disorders such as airway obstruction, medullary trauma, neuromuscular disease, chest injury, pneumonia, pulmonary edema, emphysema, and cardiopulmonary arrest. It may also be caused by the suppression of respiratory reflexes with narcotics, sedatives, hypnotics, or anesthetics. Also called carbon dioxide acidosis. Compare metabolic acidosis. See also metabolic alkalosis, respiratory alkalosis.

observations Some common signs and symptoms of respiratory acidosis are headache, dyspnea, fine tremors, tachycardia, hypertension, and vasodilation. Confirming diagnosis is usually based on a PaCO₂ over the normal 45 mm Hg and an arterial pH below 7.35.

interventions Ineffective treatment of acute respiratory acidosis can lead to coma and death. Treatment seeks to remove or inhibit the underlying causes of associated hypoventilation. Any airway obstructions are immediately removed. Mechanical ventilation and oxygen therapy may be used, and IV bronchodilators and sodium bicarbonate may be administered.

nursing considerations The patient with respiratory acidosis is carefully monitored for any changes in arterial blood gas pressures, electrolyte concentrations, and respiratory, cardiovascular, and central nervous system functions. In patients requiring mechanical ventilation, patent airways are maintained and tracheal tubes are suctioned as needed. Adequate hydration is also important.

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acidosis (as´idō´sis),

n a pathologic disturbance of the acid-base balance of the body characterized by an excess of acid or inadequate base. Causes include acid ingestion, increased acid production such as that seen in diabetes mellitus or starvation, or loss of base through the kidneys or intestine.

acidosis, compensated,

n a condition of acidosis in which the body pH level is maintained within the normal range through compensatory mechanisms involving the kidneys or lungs.

acidosis, respiratory,

n an acidemia resulting from retention of an excess of CO₂ caused by hypoventilation.

acidosis, uncompensated,

n an acidosis in which compensatory mechanisms are unable to maintain the body pH level within the normal range.

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acidosis

a pathological condition resulting from accumulation of acid or depletion of the alkaline reserve (bicarbonate content) in the blood and body tissues, and characterized by increase in hydrogen ion concentration (decrease in pH).

The optimal acid-base balance is maintained by chemical buffers, biological activities of the cells, and effective functioning of the lungs and kidneys. The opposite of acidosis is alkalosis.

It is rare that acidosis occurs in the absence of some underlying disease process. The more obvious signs of severe acidosis are muscle twitching, involuntary movement, cardiac arrhythmias, disorientation and coma.

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compensated acidosis

a condition in which the compensatory mechanisms have returned the pH toward normal.

diabetic acidosis

a metabolic acidosis produced by accumulation of ketones in uncontrolled diabetes mellitus.

hypercapnic acidosis

respiratory acidosis.

iatrogenic acidosis

may result from administration of drugs, such as urinary acidifiers, or anesthetic agents which depress respiration.

lactic acidosis

the accumulation of lactate in the rumen in ruminants and the stomach of horses, and hence in the blood, as a result of overfeeding with readily fermentable carbohydrate. See also carbohydrate engorgement.

metabolic acidosis

acidosis resulting from accumulation in the blood of keto acids (derived from fat metabolism) at the expense of bicarbonate, thus diminishing the body's ability to neutralize acids. This type of acidosis can occur when there is an acid gain, as in diabetic ketoacidosis, lactic acidosis, poisoning and failure of the renal tubules to reabsorb bicarbonate. It can also result from bicarbonate loss due to diarrhea or a gastrointestinal fistula.

mixed alkalosis and acidosis

characterized by low serum chloride, normal or slightly elevated plasma bicarbonate and a very high anion gap.

organic acidosis

accumulation of organic anions occurs in uremia, diabetic acidosis and lactic acidosis, and ingestion of salicylates, ethylene glycol or methanol.

renal tubular acidosis

renal tubular malfunction leads to faulty resorption of bicarbonate or excretion of acid and the production of alkaline urine; types I (distal tubular acidosis) and II (proximal tubular acidosis) are identified.

respiratory acidosis

acidosis resulting from ventilatory impairment and subsequent retention of carbon dioxide.

ruminal acidosis

acidosis caused by an altered metabolic state, usually lactic acidosis, in the rumen.

starvation acidosis

a metabolic acidosis due to accumulation of ketones following a severe caloric deficit.

uncompensated acidosis

a condition in which the compensatory mechanisms have not been applied sufficiently to return the pH of the blood to normal.

uremic acidosis

see metabolic acidosis (above).

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respiratory acidosis

Metabolism A condition caused by alveolar hypoventilation, tissue accumulation of CO₂, and ventilatory failure leading to ↑ PaCO₂–ie, hypercapnia; this leads, in turn to ↓ HCO₃^–/PaCO₂ and ↓ pH Lab pH < 7.35, HCO₃- > 26 mEq/L–if 'compensating', PaCO₂ > 45 mm Hg Etiology Hypoventilation due to drugs, CNS depression, heart disease, lung disease–eg, COPD, neuromuscular disease–eg, ALS, diaphragm paralysis, major kyphoscoliosis, Guillain-Barré syndrome, myasthenia gravis, muscular dystrophy, obesity hypoventilation syndrome Clinical Cyanosis, diffuse wheezing, hyperinflation–ie, barrel chest, ↓ breath sounds, hyperresonance on percussion, prolonged expiration; depressed mental status due to ↑ CO₂, accompanied by asterixis, myoclonus, seizures, papilledema,  dilated conjunctival or facial blood vessels. See Metabolic acidosis, Metabolic alkalosis, Respiratory alkalosis.