Why?
Acidosis and alkalosis are abnormal conditions in which there are excessive amounts of acid or alkali (base) in the blood. In order for the metabolic processes to work correctly and for the proper amount of oxygen delivery to the tissues, the blood pH must be kept in a narrow range such as 7.35 to 7.45. Acidosis refers to the presence of excessive amounts of acid in the blood, which causes the pH to fall below 7.35, while alkalosis refers to the presence of excessive amounts of alkali in the blood, which causes the pH to rise above 7.45. Many ailments and diseases can interfere with pH control in the body and cause the person’s blood pH to go beyond healthy limits.
Metabolism produces large amounts of acid that must be neutralized and/or eliminated to maintain pH balance. Most of the acid is carbonic acid and consists of carbon dioxide (CO 2 ) and water. Smaller amounts of lactic acid, ketoacids and other organic acids are also formed.
The lungs and kidneys are the major organs that regulate blood pH. The lungs expel acid from the body in the form of CO2 . Increasing or decreasing the respiratory rate can affect blood pH within seconds or minutes by changing the amount of exhaled CO2 . The kidneys excrete acids with urine and regulate the level of bicarbonate (HCO 3 – , an alkali) in the blood. Acid-base changes due to decreases or increases in HCO 3 – concentration occur later than changes in CO 2 and these processes take hours or days. Both of these processes are always “at work” and keep blood pH tightly controlled in healthy people.
Buffering systems that resist changes in pH also contribute to the regulation of acid and base levels. The main buffers in the blood are hemoglobin (in erythrocytes), plasma proteins, bicarbonate and phosphates.
The absolute amounts of acids and alkalis are less important than the balance between the two and their effect on blood pH (see Figure 1). Acidosis occurs when blood pH drops below 7.35 . High acid production in the body may be due to consumption of substances metabolized into acids, decreased acid excretion or increased base excretion. Alkalosis occurs when blood pH rises above 7.45 . For example, prolonged vomiting or severe dehydration (dehydration), administration or consumption of alkali, hyperventilation (inhaled CO2 It may be due to electrolyte disturbances caused by excessive acid excretion. Any disease or condition that adversely affects the lungs, kidneys, metabolism or breathing has the potential to cause acidosis or alkalosis. The normal equilibrium between acid and base can be seen in Figure 1.
Figure 1: Fill and Drain cocks
Important points
- The pH of the blood is normally between 7.35 and 7.45.
- The body’s goal is to maintain a constant state of balance between incoming/produced acids and bases (filling tap open) and discarded acids/bases (draining cock open).
- Imbalances lead to acidosis (acid container overflowing) or alkalosis (base container overflowing).
- Balance can be achieved by increasing the rate of elimination (faster discharge) and/or slowing the flow (by closing the fill valve).
Acid-base disorders fall into two broad categories.
- Those that affect respiration and cause changes in CO2 concentration are called respiratory (respiratory) acidosis (low pH) and respiratory alkalosis (high pH). Acid-base disturbances due to changes in respiratory rate are usually due to lung diseases or conditions that adversely affect normal respiration .
- Disorders affecting HCO 3 – concentration are called metabolic acidosis (low pH) and metabolic alkalosis (high pH). Metabolic acid-base disturbances may be due to kidney disease , electrolyte disturbances, severe vomiting or diarrhea, ingestion of certain drugs and toxins, and diseases that adversely affect normal metabolism (eg, diabetes ) .
Results
Acidosis may not cause any symptoms or may be associated with non-specific symptoms such as fatigue, nausea and vomiting. Acute acidosis can also cause increased breathing rate and depth, confusion and headaches. It can lead to seizures, coma, and in some cases, death. Symptoms of alkalosis are often due to potassium (K + ) loss, but may include restlessness, weakness, and cramps.
Usual causes of acid-base disorders
respiratory acidosis
Decreased CO 2 elimination
- Decreased respiratory rate (respiratory impulse) due to medications or central nervous system disorders
- Impaired breathing and lung movements (respiratory and mechanical) due to trauma or abnormal presence of air between the lungs and chest wall (pneumothorax)
- Respiratory muscle/nerve disease (myasthenia gravis, botulismus, amyotropic lateral sclerosis (ALS), Guillain-Barré syndrome )
- Airway obstruction (food or foreign body)
- lung disease
Respiratory Alkalosis
Increased CO 2 elimination
- Rapid breathing (hyperventilation) due to anxiety, pain and shock
- Medications (aspirin)
- Pneumonia (pneumonia) pulmonary congestion (lung blood supply) or embolism
- exercise, fever
- Central nervous system tumor, trauma or infection ( meningitis, encephalitis )
- Liver failure
Metabolic acidosis
HCO 3 – decreased HCO 3 – due to loss or increased acidity
- alcoholic ketoacidosis
- diabetic ketoacidosis
- Kidney failure
- lactic acidosis
- Toxins – Salicylates (aspirin), methanol, ethylene glycol overdose
- Bicarbonate loss from the gastrointestinal tract due to prolonged diarrhea
Metabolic alkalosis Increased HCO 3 –
due to loss of acid or intake of bicarbonate
- Diuretics (diuretics)
- prolonged vomiting
- severe dehydration
- Bicarbonate application, alkali intake
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Results
Acidosis may not cause any symptoms or may be associated with non-specific symptoms such as fatigue, nausea and vomiting. Acute acidosis can also cause increased breathing rate and depth, confusion and headaches. It can lead to seizures, coma, and in some cases, death. Symptoms of alkalosis are often due to potassium (K + ) loss, but may include restlessness, weakness, and cramps.
Usual causes of acid-base disorders
respiratory acidosis
Decreased CO 2 elimination
- Decreased respiratory rate (respiratory impulse) due to medications or central nervous system disorders
- Impaired breathing and lung movements (respiratory and mechanical) due to trauma or abnormal presence of air between the lungs and chest wall (pneumothorax)
- Respiratory muscle/nerve disease (myasthenia gravis, botulismus, amyotropic lateral sclerosis (ALS), Guillain-Barré syndrome )
- Airway obstruction (food or foreign body)
- lung disease
Respiratory Alkalosis
Increased CO 2 elimination- Rapid breathing (hyperventilation) due to anxiety, pain and shock
- Medications (aspirin)
- Pneumonia (pneumonia) pulmonary congestion (lung blood supply) or embolism
- exercise, fever
- Central nervous system tumor, trauma or infection ( meningitis, encephalitis )
- Liver failure
Metabolic acidosis
HCO 3 – decreased HCO 3 – due to loss or increased acidity- alcoholic ketoacidosis
- diabetic ketoacidosis
- Kidney failure
- lactic acidosis
- Toxins – Salicylates (aspirin), methanol, ethylene glycol overdose
- Bicarbonate loss from the gastrointestinal tract due to prolonged diarrhea
Metabolic alkalosis Increased HCO 3 –
due to loss of acid or intake of bicarbonate- Diuretics (diuretics)
- prolonged vomiting
- severe dehydration
- Bicarbonate application, alkali intake
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Tests
The purpose of the tests is to determine whether a person has an acid-base disorder, to determine the severity of the disorder, and to help diagnose underlying diseases or abnormalities that have caused the acid-base disorder (such as diabetic ketoacidosis or ingestion of a toxin). These tests are also performed to monitor critically ill patients, those with chronic lung disease and conditions known to adversely affect acid-base balance .
The main tests used to identify, evaluate and monitor acid-base disorders are:
- blood gases
- electrolytes
Blood gas tests are a group of tests that are usually administered with a blood sample taken from an artery (an artery rather than a vein). The blood pH gives an overall assessment of PO 2 (the amount of oxygen in the blood) and PCO 2 (the amount of carbon dioxide in the blood). Based on these results, bicarbonate (HCO 3 – ) can be calculated.
In most acid-base disorders, both HCO 3 – and PCO 2 are outside the reference range , as the body tries to keep the pH close to normal . Therefore, if one of these substances is abnormally high or low, the other will change in the same direction, returning the pH to the healthy range. This process is called compensation. The table below shows the expected values for each of the four major acid-base disturbances.
Consequences seen in the four main acid-base disorders:
ACID-BASE DISORDER H+ PH HCO3 PCO2 COMPENSATION MECHANISM OF THE BODY metabolic acidosis ↑ ↓ ↓↓ ↓ Respiration is accelerated (hyperventilation) to increase CO2 excretion metabolic alkalosis ↓ ↑ ↑↑ ↑ Respiration is slowed (hypoventilation ) to reduce CO2 excretion respiratory acidosis ↑ ↓ ↑ ↑↑ The kidneys increase the amount of HCO 3 – retained and acid excreted. respiratory alkalosis ↓ ↑ ↓ ↓↓ The kidneys reduce the amount of HCO 3 – retained and acid excreted. ↑ increased level; ↑↑ too many increased levels; ↓ decreased levels; ↓↓ too many reduced levels Electrolyte tests include Na + (sodium), K + (potassium), Cl – (chloride), and bicarbonate (usually measured as total CO 2 content). Fluid levels, electrolyte concentrations, and acid-base balance in the body are interrelated, and in metabolic acid-base disorders, one or more electrolytes usually increase or decrease. Using the results of an electrolyte panel in patients with metabolic acidosis , an anion gap is calculated to help identify which disorders may be responsible for the acid-base abnormality. For example, an increase in anion gap may indicate diabetic acidosis. (For more information on anion gap click here (See Frequently Asked Question #1)
The presence of low chloride (Cl – ) and potassium (K + ) values in patients with metabolic alkalosis also provides clues as to the cause of acid-base disturbance. Based on these results, other tests may be ordered (eg, glucose , lactate , ketones , osmolality , methanol, ethylene glycol) to recognize the disease or abnormalities causing the acidosis or alkalosis.
It is possible for a person to have more than one acid-base disorder at the same time. Examples include aspirin intake (which can cause both respiratory alkalosis and metabolic acidosis) and lung patients taking diuretics ( diuretics ) (respiratory acidosis plus metabolic alkalosis). Using formulas to calculate the expected degree of compensation, it is possible to determine whether mixed acid-base disturbance is present.
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Treatment
Treatment of acidosis and alkalosis involves identifying and addressing the underlying cause(s) of the imbalance and providing any necessary support to the afflicted person. In most cases, high and low pH are not treated directly. However, in some cases, doctors may administer HCO 3 – intravenously (into a vein) to people with dangerously low blood pH levels.