View source for Acid–base disorder

{{Short description|Abnormality of the human body's normal balance of acids and bases}}
{{More citations needed|date=December 2010}}
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|  image          = Davenport fig 10.jpg
|  caption        = A [[Davenport diagram]] illustrates acid–base imbalance graphically.
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'''Acid–base imbalance''' is an abnormality of the human body's normal [[acid–base homeostasis|balance of acids and bases]] that causes the [[blood plasma|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).<ref name="Yeomans">{{Cite journal |last=Yeomans |first=ER |last2=Hauth, JC |last3=Gilstrap, LC III |last4=Strickland DM |year=1985 |title=Umbilical cord pH, PCO2, and bicarbonate following uncomplicated term vaginal deliveries (146 infants) |journal=Am J Obstet Gynecol |volume=151 |issue=6 |pages=798–800 |doi=10.1016/0002-9378(85)90523-x |pmid=3919587}}</ref> It can exist in varying levels of severity, some life-threatening.

==Classification==
{{Blood gas, acid-base, & gas exchange terms}}
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:
{| class="wikitable"
! process || [[pH]] || {{CO2|link=yes}}  || compensation
 |-
 | style="text-align:right;" | [[metabolic acidosis]] || style="text-align:center;" |{{down}} || style="text-align:center;" | {{down}} || respiratory
 |-
 | style="text-align:right;" | [[respiratory acidosis]] || style="text-align:center;" |{{down}} || style="text-align:center;" |{{up}} || renal
 |-
 | style="text-align:right;" | [[metabolic alkalosis]] || style="text-align:center;" |{{up}} || style="text-align:center;" |{{up}} || respiratory
 |-
 | style="text-align:right;" | [[respiratory alkalosis]] || style="text-align:center;" |{{up}} || style="text-align:center;" |{{down}} || 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.<ref name="urlMixed Acid Base Disorders: Acid Base Tutorial, University of Connecticut Health Center">{{Cite web |title=Mixed Acid Base Disorders: Acid Base Tutorial, University of Connecticut Health Center |url=http://fitsweb.uchc.edu/student/selectives/TimurGraham/Mixed_Acid_Base_Disorders.html |url-status=dead |archive-url=https://web.archive.org/web/20090426054258/http://fitsweb.uchc.edu/student/selectives/TimurGraham/Mixed_Acid_Base_Disorders.html |archive-date=2009-04-26 |access-date=2009-05-09}}</ref> 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 [[empirical]] approach. The main variants are the [[base excess]] approach and the [[bicarbonate]] approach. The [[Quantitative analysis (chemistry)|quantitative]] approach introduced by [[Peter A Stewart]] in 1978<ref>{{Cite journal |last=Stewart P |year=1978 |title=Independent and dependent variables of acid-base control |journal=Respir Physiol |volume=33 |issue=1 |pages=9–26 |doi=10.1016/0034-5687(78)90079-8 |pmid=27857}}</ref> is newer.

==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 [[nonvolatile acid]]s from the metabolism of proteins and other [[organic molecule]]s
# 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==
{{Acids and bases}}
The body's [[acid–base balance]] is tightly regulated. Several [[buffering agent]]s exist which reversibly bind hydrogen ions and impede any change in pH. [[Extracellular]] buffers include [[bicarbonate]] and [[ammonia]], while [[protein]]s and [[phosphate]] act as [[intracellular]] buffers. The [[bicarbonate buffering system]] is especially key, as [[carbon dioxide]] (CO<sub>2</sub>) can be shifted through [[carbonic acid]] (H<sub>2</sub>CO<sub>3</sub>) to hydrogen ions and [[bicarbonate]] (HCO<sub>3</sub><sup>−</sup>) as shown below.
:<chem>HCO_3^- + H+ <=> H2CO3 <=> CO2 + H2O</chem>

Acid–base imbalances that overcome the buffer system can be compensated in the short term by changing the rate of [[Ventilation (physiology)|ventilation]]. This alters the concentration of [[carbon dioxide]] in the blood, shifting the above reaction according to [[Le Chatelier's principle]], which in turn alters the pH. For instance, if the blood pH drops too low (''acidemia''), the body will compensate by increasing breathing, expelling CO<sub>2</sub>, and shifting the reaction above to the right such that fewer hydrogen ions are free–thus the pH will rise back to normal. For ''alkalemia'', the opposite occurs.

The [[kidneys]] are slower to compensate, but [[renal physiology]] has several powerful mechanisms to control pH by the excretion of excess acid or base. In responses to acidosis, [[renal tubule|tubular]] cells reabsorb more bicarbonate from the tubular fluid, [[collecting duct]] cells secrete more hydrogen and generate more bicarbonate, and [[ammoniagenesis]] leads to increased formation of the NH<sub>3</sub> buffer. In responses to alkalosis, the kidney may excrete more bicarbonate by decreasing hydrogen ion secretion from the tubular epithelial cells, and lowering rates of [[glutamine]] metabolism and ammonia excretion.

==References==
{{Reflist}}

==External links==
{{Medical resources|
  DiseasesDB     = |
  ICD10          = {{ICD10|E|87|2|e|70}}-{{ICD10|E|87|4|e|70}} |
  ICD9           = {{ICD9|276.2}}-{{ICD9|276.4}} |
  ICDO           = |
  OMIM           = |
  MedlinePlus    = |
  eMedicineSubj  = |
  eMedicineTopic = |
  MeshID         = D000137 |
}}
* [http://www.anaesthesiamcq.com/AcidBaseBook/ABindex.php On-line text at AnaesthesiaMCQ.com]
* {{Cite book |last=Nosek |first=Thomas M. |title=Essentials of Human Physiology |chapter=Section 7/7ch12/7ch12lin |chapter-url=http://humanphysiology.tuars.com/program/section7/7ch12/7ch12lin.htm |archive-url=https://web.archive.org/web/20160324124828/http://humanphysiology.tuars.com/program/section7/7ch12/7ch12lin.htm |archive-date=2016-03-24}}
* [https://web.archive.org/web/20061217055347/http://www2.kumc.edu/ki/physiology/course/nine/9_1.htm Overview at kumc.edu]
* [https://web.archive.org/web/20071024002625/http://sprojects.mmi.mcgill.ca/nephrology/presentation/presentation4.htm Overview at mcgill.ca]
* [http://www.acidbase.org Stewart's original text at acidbase.org]
* [http://umed.med.utah.edu/ms2/renal/Word%20files/h)%20Acid_Base%20Physiology.htm Overview at med.utah.edu]
* [http://www.anaesthetist.com/icu/elec/ionz/Findex.htm#acid.htm Overview at anaesthetist.com]
* [https://web.archive.org/web/20091114092125/http://www.anst.uu.se/magnroos/Some%20notes%20on%20human%20acid.htm Overview at anst.uu.se]
* [http://www.acid-base.com/physiology.php Tutorial at acid-base.com]
* [http://www.anaesthesiamcq.com/AcidBaseBook/ABindex.php Online acid–base physiology text]
* [http://www.lakesidepress.com/pulmonary/ABG/MixedAB.htm Diagnoses at lakesidepress.com]
* [https://web.archive.org/web/20040618202049/http://www.nda.ox.ac.uk/wfsa/html/u16/u1602_01.htm Interpretation at nda.ox.ac.uk]
* [http://www.anaesthesiamcq.com/AcidBaseBook/ABindex.php Acid Base Tutorial]

{{Fluid, electrolyte, acid base metabolic pathology}}
{{Renal physiology}}
{{Human homeostasis}}

{{DEFAULTSORT:Acid-Base Imbalance}}
[[Category:Human homeostasis]]
[[Category:Acid–base physiology]]
[[Category:Acid–base disturbances]]
[[Category:Equilibrium chemistry]]
[[Category:Respiratory therapy]]