Acid–base disorder
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Acid–base imbalance | |
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A Davenport diagram illustrates acid–base imbalance graphically. | |
Specialty | Internal medicine |
Acid–base imbalance is an abnormality of the human body's normal balance of acids and bases that causes the plasma pH to deviate out of the normal range (7.35 to 7.45). In the fetus, the normal range differs based on which umbilical vessel is sampled (umbilical vein pH is normally 7.25 to 7.45; umbilical artery pH is normally 7.18 to 7.38).[1] It can exist in varying levels of severity, some life-threatening.
Classification
PaO2 | Arterial oxygen tension, or partial pressure |
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PAO2 | Alveolar oxygen tension, or partial pressure |
PaCO2 | Arterial carbon dioxide tension, or partial pressure |
PACO2 | Alveolar carbon dioxide tension, or partial pressure |
PvO2 | Oxygen tension of mixed venous blood |
P(A-a)O2 | Alveolar-arterial oxygen tension difference. The term formerly used (A-a DO2) is discouraged. |
P(a/A)O2 | Alveolar-arterial tension ratio; PaO2:PAO2 The term oxygen exchange index describes this ratio. |
C(a-v)O2 | Arteriovenous oxygen content difference |
SaO2 | Oxygen saturation of the hemoglobin of arterial blood |
SpO2 | Oxygen saturation as measured by pulse oximetry |
CaO2 | Oxygen content of arterial blood |
pH | Symbol relating the hydrogen ion concentration or activity of a solution to that of a standard solution; approximately equal to the negative logarithm of the hydrogen ion concentration. pH is an indicator of the relative acidity or alkalinity of a solution |
An excess of acid is called acidosis or acidemia, while an excess in bases is called alkalosis or alkalemia. The process that causes the imbalance is classified based on the cause of the disturbance (respiratory or metabolic) and the direction of change in pH (acidosis or alkalosis). This yields the following four basic processes:
process | pH | CO2 | compensation |
---|---|---|---|
metabolic acidosis | respiratory | ||
respiratory acidosis | renal | ||
metabolic alkalosis | respiratory | ||
respiratory alkalosis | renal |
Mixed disorders
The presence of only one of the above derangements is called a simple acid–base disorder. In a mixed disorder, more than one is occurring at the same time.[2] Mixed disorders may feature an acidosis and alkosis at the same time that partially counteract each other, or there can be two different conditions affecting the pH in the same direction. The phrase "mixed acidosis", for example, refers to metabolic acidosis in conjunction with respiratory acidosis. Any combination is possible, as metabolic acidosis and alkalosis can co exist together.
Calculation of imbalance
The traditional approach to the study of acid–base physiology has been the
Causes
There are numerous reasons that each of the four processes can occur (detailed in each article). Generally speaking, sources of acid gain include:
- Retention of carbon dioxide
- Production of organic molecules
- Loss of bicarbonate in feces or urine
- Intake of acids or acid precursors
Sources of acid loss include:
- Use of hydrogen ions in the metabolism of various organic anions
- Loss of acid in the vomitus or urine
- Gastric aspiration in hospital
- Severe diarrhea
- Carbon dioxide loss through hyperventilation
Compensation
The body's
Acid–base imbalances that overcome the buffer system can be compensated in the short term by changing the rate of
The
References
- PMID 3919587.
- ^ "Mixed Acid Base Disorders: Acid Base Tutorial, University of Connecticut Health Center". Archived from the original on 2009-04-26. Retrieved 2009-05-09.
- PMID 27857.
External links
- On-line text at AnaesthesiaMCQ.com
- Nosek, Thomas M. "Section 7/7ch12/7ch12lin". Essentials of Human Physiology. Archived from the original on 2016-03-24.
- Overview at kumc.edu
- Overview at mcgill.ca
- Stewart's original text at acidbase.org
- Overview at med.utah.edu
- Overview at anaesthetist.com
- Overview at anst.uu.se
- Tutorial at acid-base.com
- Online acid–base physiology text
- Diagnoses at lakesidepress.com
- Interpretation at nda.ox.ac.uk
- Acid Base Tutorial