Acidosis is a process causing increased
acidity
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a ...
in the blood and other body tissues (i.e., an increase in
hydrogen ion
A hydrogen ion is created when a hydrogen atom loses or gains an electron. A positively charged hydrogen ion (or proton) can readily combine with other particles and therefore is only seen isolated when it is in a gaseous state or a nearly particle ...
concentration
In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', ''molar concentration'', '' number concentration'', ...
). If not further qualified, it usually refers to acidity of the
blood plasma
Blood plasma is a light amber-colored liquid component of blood in which blood cells are absent, but contains proteins and other constituents of whole blood in suspension. It makes up about 55% of the body's total blood volume. It is the intr ...
.
The term ''acidemia'' describes the state of low blood pH, while ''acidosis'' is used to describe the processes leading to these states. Nevertheless, the terms are sometimes used interchangeably. The distinction may be relevant where a patient has factors causing both acidosis and
alkalosis
Alkalosis is the result of a process reducing hydrogen ion concentration of arterial blood plasma (alkalemia). In contrast to acidemia (serum pH 7.35 or lower), alkalemia occurs when the serum pH is higher than normal (7.45 or higher). Alkalosis ...
, wherein the relative severity of both determines whether the result is a high, low, or normal pH.
Acidemia is said to occur when arterial
pH falls below 7.35 (except in the fetus – see below), while its counterpart (
alkalemia) occurs at a pH over 7.45.
Arterial blood gas
An arterial blood gas (ABG) test, or arterial blood gas analysis (ABGA) measures the amounts of arterial gases, such as oxygen and carbon dioxide. An ABG test requires that a small volume of blood be drawn from the radial artery with a syringe an ...
analysis and other tests are required to separate the main causes.
The rate of cellular metabolic activity affects and, at the same time, is affected by the pH of the body fluids. In mammals, the normal pH of arterial blood lies between 7.35 and 7.50 depending on the species (e.g., healthy human-arterial blood pH varies between 7.35 and 7.45). Blood pH values compatible with life in mammals are limited to a pH range between 6.8 and 7.8. Changes in the pH of arterial blood (and therefore the extracellular fluid) outside this range result in irreversible cell damage.
[Needham, A. 2004. Comparative and Environmental Physiology. Acidosis and Alkalosis.]
Signs and symptoms
Nervous system
In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes ...
involvement may be seen with acidosis and occurs more often with respiratory acidosis than with metabolic acidosis. Signs and symptoms that may be seen in acidosis include
headaches, confusion,
feeling tired,
tremors,
sleepiness
Somnolence (alternatively sleepiness or drowsiness) is a state of strong desire for sleep, or sleeping for unusually long periods (compare hypersomnia). It has distinct meanings and causes. It can refer to the usual state preceding falling asleep ...
,
flapping tremor, and dysfunction of the
cerebrum
The cerebrum, telencephalon or endbrain is the largest part of the brain containing the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb ...
of the brain which may progress to coma if there is no intervention.
Metabolic acidosis
Metabolic acidosis may result from either increased production of metabolic acids, such as lactic acid, or disturbances in the ability to excrete acid via the
kidney
The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...
s, such as either
renal tubular acidosis or the acidosis of
kidney failure
Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as eit ...
, which is associated with an accumulation of
urea
Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid.
Urea serves an important ...
and
creatinine
Creatinine (; ) is a breakdown product of creatine phosphate from muscle and protein metabolism. It is released at a constant rate by the body (depending on muscle mass).
Biological relevance
Serum creatinine (a blood measurement) is an importa ...
as well as metabolic acid residues of protein
catabolism.
An increase in the production of other acids may also produce metabolic acidosis. For example,
lactic acidosis
Lactic acidosis is a medical condition characterized by a build-up of lactate (especially -lactate) in the body, with formation of an excessively low pH in the bloodstream. It is a form of metabolic acidosis, in which excessive acid accumulates d ...
may occur from:
#severe (
PaO2 <36mm Hg)
hypoxemia
Hypoxemia is an abnormally low level of oxygen in the blood. More specifically, it is oxygen deficiency in arterial blood. Hypoxemia has many causes, and often causes hypoxia as the blood is not supplying enough oxygen to the tissues of the bod ...
causing a fall in the rate of oxygen diffusion from arterial blood to tissues.
#
hypoperfusion
Perfusion is the passage of fluid through the circulatory system or lymphatic system to an organ or a tissue, usually referring to the delivery of blood to a capillary bed in tissue. Perfusion is measured as the rate at which blood is delivere ...
(e.g.,
hypovolemic shock) causing an inadequate blood delivery of oxygen to tissues.
A rise in lactate out of proportion to the level of
pyruvate, e.g., in mixed venous blood, is termed "excess lactate", and may also be an indicator of
fermentation due to
anaerobic metabolism
Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O2). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain.
In aerobic organisms undergoing r ...
occurring in muscle cells, as seen during strenuous exercise. Once oxygenation is restored, the acidosis clears quickly. Another example of increased production of acids occurs in
starvation and
diabetic ketoacidosis
Diabetic ketoacidosis (DKA) is a potentially life-threatening complication of diabetes mellitus. Signs and symptoms may include vomiting, abdominal pain, deep gasping breathing, increased urination, weakness, confusion and occasionally loss of ...
. It is due to the accumulation of ketoacids (via excessive
ketosis) and reflects a severe shift from
glycolysis to
lipolysis
Lipolysis is the metabolic pathway through which lipid triglycerides are hydrolyzed into a glycerol and free fatty acids. It is used to mobilize stored energy during fasting or exercise, and usually occurs in fat adipocytes. The most important ...
for energy needs.
Acid consumption from
poisoning such as
methanol ingestion, elevated levels of
iron
Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
in the blood, and chronically decreased production of
bicarbonate
In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula .
Bicarbonate serves a crucial biochem ...
may also produce metabolic acidosis.
Metabolic acidosis is compensated for in the lungs, as increased exhalation of carbon dioxide promptly shifts the buffering equation to reduce metabolic acid. This is a result of stimulation to
chemoreceptor
A chemoreceptor, also known as chemosensor, is a specialized sensory receptor which transduces a chemical substance (endogenous or induced) to generate a biological signal. This signal may be in the form of an action potential, if the chemorecept ...
s, which increases
alveolar ventilation
Breathing (or ventilation) is the process of moving air into and from the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring in oxygen.
All aerobic creatures need oxygen for cellular ...
, leading to respiratory compensation, otherwise known as
Kussmaul breathing
Kussmaul breathing is a deep and labored breathing pattern often associated with severe metabolic acidosis, particularly diabetic ketoacidosis (DKA) but also kidney failure. It is a form of hyperventilation, which is any breathing pattern that red ...
(a specific type of
hyperventilation). Should this situation persist, the patient is at risk of exhaustion leading to
respiratory failure
Respiratory failure results from inadequate gas exchange by the respiratory system, meaning that the arterial oxygen, carbon dioxide, or both cannot be kept at normal levels. A drop in the oxygen carried in the blood is known as hypoxemia; a rise ...
.
Mutations to the
V-ATPase
Vacuolar-type ATPase (V-ATPase) is a highly conserved evolutionarily ancient enzyme with remarkably diverse functions in eukaryotic organisms. V-ATPases acidify a wide array of intracellular organelles and pumps protons across the plasm ...
'a4' or 'B1' isoforms result in distal renal tubular acidosis, a condition that leads to metabolic acidosis, in some cases with sensorineural
deafness
Deafness has varying definitions in cultural and medical contexts. In medical contexts, the meaning of deafness is hearing loss that precludes a person from understanding spoken language, an audiological condition. In this context it is written ...
.
Arterial blood gas
An arterial blood gas (ABG) test, or arterial blood gas analysis (ABGA) measures the amounts of arterial gases, such as oxygen and carbon dioxide. An ABG test requires that a small volume of blood be drawn from the radial artery with a syringe an ...
es will indicate low
pH, low blood
HCO3, and normal or low PaCO
2.
In addition to arterial blood gas, an
anion gap
The anion gap (AG or AGAP) is a value calculated from the results of multiple individual medical lab tests. It may be reported with the results of an electrolyte panel, which is often performed as part of a comprehensive metabolic panel.
The an ...
can also differentiate between possible causes.
The
Henderson-Hasselbalch equation is useful for calculating blood pH, because blood is a
buffer solution
A buffer solution (more precisely, pH buffer or hydrogen ion buffer) is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or vice versa. Its pH changes very little when a small amount of strong acid or base is ...
. In the clinical setting, this equation is usually used to calculate
HCO3 from measurements of pH and PaCO2 in
arterial blood gas
An arterial blood gas (ABG) test, or arterial blood gas analysis (ABGA) measures the amounts of arterial gases, such as oxygen and carbon dioxide. An ABG test requires that a small volume of blood be drawn from the radial artery with a syringe an ...
es. The amount of metabolic acid accumulating can also be quantitated by using buffer base deviation, a derivative estimate of the metabolic as opposed to the respiratory component. In hypovolemic shock for example, approximately 50% of the metabolic acid accumulation is
lactic acid
Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as nat ...
, which disappears as blood flow and oxygen debt are corrected.
Treatment
Treatment of uncompensated metabolic acidosis is focused upon correcting the underlying problem. When metabolic acidosis is severe and can no longer be compensated for adequately by the lungs or kidneys, neutralizing the acidosis with infusions of
bicarbonate
In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula .
Bicarbonate serves a crucial biochem ...
may be required.
Fetal metabolic acidemia
In the
fetus
A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal dev ...
, the normal range differs based on which umbilical vessel is sampled (
umbilical vein
The umbilical vein is a vein present during fetal development that carries oxygenated blood from the placenta into the growing fetus. The umbilical vein provides convenient access to the central circulation of a neonate for restoration of blood v ...
pH is normally 7.25 to 7.45;
umbilical artery
The umbilical artery is a paired artery (with one for each half of the body) that is found in the abdominal and pelvic regions. In the fetus, it extends into the umbilical cord.
Structure Development
The umbilical arteries supply deoxygenated b ...
pH is normally 7.18 to 7.38).
Fetal metabolic
acidemia
Acidosis is a process causing increased acidity in the blood and other body tissues (i.e., an increase in hydrogen ion concentration). If not further qualified, it usually refers to acidity of the blood plasma.
The term ''acidemia'' describes t ...
is defined as an umbilical vessel pH of less than 7.20 and a
base excess
In physiology, base excess and base deficit refer to an excess or deficit, respectively, in the amount of base present in the blood. The value is usually reported as a concentration in units of mEq/L (mmol/L), with positive numbers indicating an ...
of less than −8.
Respiratory acidosis
Respiratory acidosis results from a build-up of carbon dioxide in the blood (
hypercapnia
Hypercapnia (from the Greek ''hyper'' = "above" or "too much" and ''kapnos'' = "smoke"), also known as hypercarbia and CO2 retention, is a condition of abnormally elevated carbon dioxide (CO2) levels in the blood. Carbon dioxide is a gaseous pro ...
) due to
hypoventilation
Hypoventilation (also known as respiratory depression) occurs when ventilation is inadequate (''hypo'' meaning "below") to perform needed respiratory gas exchange. By definition it causes an increased concentration of carbon dioxide (hypercapni ...
. It is most often caused by
pulmonary
The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of ...
problems, although
head injuries
A head injury is any injury that results in trauma to the skull or brain. The terms ''traumatic brain injury'' and ''head injury'' are often used interchangeably in the medical literature. Because head injuries cover such a broad scope of inju ...
, drugs (especially
anaesthetic
An anesthetic (American English) or anaesthetic (British English; see spelling differences) is a drug used to induce anesthesia — in other words, to result in a temporary loss of sensation or awareness. They may be divided into two ...
s and
sedatives), and
brain tumor
A brain tumor occurs when abnormal cells form within the brain. There are two main types of tumors: malignant tumors and benign (non-cancerous) tumors. These can be further classified as primary tumors, which start within the brain, and seconda ...
s can cause this acidemia.
Pneumothorax
A pneumothorax is an abnormal collection of air in the pleural space between the lung and the chest wall. Symptoms typically include sudden onset of sharp, one-sided chest pain and shortness of breath. In a minority of cases, a one-way valve i ...
,
emphysema, chronic
bronchitis
Bronchitis is inflammation of the bronchi (large and medium-sized airways) in the lungs that causes coughing. Bronchitis usually begins as an infection in the nose, ears, throat, or sinuses. The infection then makes its way down to the bronchi. ...
,
asthma
Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, co ...
, severe
pneumonia
Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severi ...
, and
aspiration are among the most frequent causes. It can also occur as a compensatory response to chronic
metabolic alkalosis
Metabolic alkalosis is a metabolic condition in which the pH of tissue is elevated beyond the normal range (7.35–7.45). This is the result of decreased hydrogen ion concentration, leading to increased bicarbonate, or alternatively a direct res ...
.
One key to distinguish between respiratory and metabolic acidosis is that in respiratory acidosis, the CO
2 is increased while the
bicarbonate
In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula .
Bicarbonate serves a crucial biochem ...
is either normal (uncompensated) or increased (compensated). Compensation occurs if respiratory acidosis is present, and a chronic phase is entered with partial buffering of the acidosis through renal bicarbonate retention.
However, in cases where chronic illnesses that compromise pulmonary function persist, such as late-stage emphysema and certain types of
muscular dystrophy, compensatory mechanisms will be unable to reverse this acidotic condition. As metabolic bicarbonate production becomes exhausted, and extraneous bicarbonate infusion can no longer reverse the extreme buildup of carbon dioxide associated with uncompensated respiratory acidosis,
mechanical ventilation
Mechanical ventilation, assisted ventilation or intermittent mandatory ventilation (IMV), is the medical term for using a machine called a ventilator to fully or partially provide artificial ventilation. Mechanical ventilation helps move a ...
will usually be applied.
Fetal respiratory acidemia
In the
fetus
A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal dev ...
, the normal range differs based on which umbilical vessel is sampled (
umbilical vein
The umbilical vein is a vein present during fetal development that carries oxygenated blood from the placenta into the growing fetus. The umbilical vein provides convenient access to the central circulation of a neonate for restoration of blood v ...
pH is normally 7.25 to 7.45;
umbilical artery
The umbilical artery is a paired artery (with one for each half of the body) that is found in the abdominal and pelvic regions. In the fetus, it extends into the umbilical cord.
Structure Development
The umbilical arteries supply deoxygenated b ...
pH is normally 7.20 to 7.38).
In the fetus, the lungs are not used for ventilation. Instead, the
placenta
The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mate ...
performs ventilatory functions (
gas exchange
Gas exchange is the physical process by which gases move passively by diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid, a gas-permeable membrane, or a ...
). Fetal respiratory acidemia is defined as an umbilical vessel pH of less than 7.20 and an umbilical artery
PCO2 of 66 or higher or umbilical vein PCO
2 of 50 or higher.
See also
*
Acid–base homeostasis
Acid–base homeostasis is the homeostatic regulation of the pH of the body's extracellular fluid (ECF). The proper balance between the acids and bases (i.e. the pH) in the ECF is crucial for the normal physiology of the body—and for cellu ...
*
Acid–base imbalance
*
Alkalinizing agent
Alkalinizing agents are drugs used to manage disorders associated with low pH. For example, they may be used to treat acidosis due to kidney failure.
Used for oral or parenteral therapy, sodium bicarbonate is the commonly preferred alkalinizin ...
*
Alkaline diet
*
Arterial blood gas
An arterial blood gas (ABG) test, or arterial blood gas analysis (ABGA) measures the amounts of arterial gases, such as oxygen and carbon dioxide. An ABG test requires that a small volume of blood be drawn from the radial artery with a syringe an ...
*
Chemical equilibrium
In a chemical reaction, chemical equilibrium is the state in which both the Reagent, reactants and Product (chemistry), products are present in concentrations which have no further tendency to change with time, so that there is no observable chan ...
*
Lactic acidosis
Lactic acidosis is a medical condition characterized by a build-up of lactate (especially -lactate) in the body, with formation of an excessively low pH in the bloodstream. It is a form of metabolic acidosis, in which excessive acid accumulates d ...
*
pCO2
''p''CO2, pCO2, or P_\ceis the partial pressure of carbon dioxide (CO2), often used in reference to blood but also used in meteorology, climate science, oceanography, and limnology to describe the fractional pressure of CO2 as a function of its ...
*
pKa
References
;Notes
*Hobler KE, Carey LC. Effect of acute progressive hypoxemia on cardiac output and plasma excess lactate. ''Ann. Surg.'' 1973 Feb;177(2):199-202.
*Hobler KE, Napodano RJ. Tolerance of swine to acute blood volume deficits. ''J Trauma.'' 1974 Aug;14(8):716-8.
*Rose, BD, Post TW.
Clinical Physiology of Acid-Base and Electrolyte Disorders, 5th ed.' (No content available.) 2000. New York: McGraw Hill Professional.
External links
{{Authority control
Acid–base disturbances