View source for Acid-base imbalance

{{Infobox_Disease |
  Name           = Acid-base imbalance |
  Image          = |
  Caption        = |
  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 |
}}

'''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). It can exist in varying levels of severity, some life-threatening.

==Classification==
[[Image:Davenport fig 10.jpg|right|thumb|A [[Davenport diagram]] illustrates acid-base imbalance graphically.]]
An excess of acid is called [[acidosis]] (pH less than 7.35) and an excess in bases is called [[alkalosis]] (pH greater than 7.45). The process that causes the imbalance is classified based on the [[etiology]] 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]]''' || '''[[carbon dioxide]]'''  || '''compensation'''
 |- 
 | [[metabolic acidosis]] || down || down || respiratory
 |- 
 | [[respiratory acidosis]] || down || up || renal
 |- 
 | [[metabolic alkalosis]] || up || up || respiratory
 |- 
 | [[respiratory alkalosis]] || up  || 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 |url=http://fitsweb.uchc.edu/student/selectives/TimurGraham/Mixed_Acid_Base_Disorders.html |title=Mixed Acid Base Disorders: Acid Base Tutorial, University of Connecticut Health Center |work= |accessdate=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 effecting 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, except concurrent respiratory acidosis and respiratory alkalosis, since a person cannot breathe too fast and too slow at the same time. 

===Calculation of imbalance===
The traditional approach to the study of acid-base physiology has been the [[empiric]] 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 |author=Stewart P |title=Independent and dependent variables of acid-base control |journal=Respir Physiol |volume=33 |issue=1 |pages=9–26 |year=1978 |pmid=27857 |doi=10.1016/0034-5687(78)90079-8}}</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]]

==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.
:<math>\rm HCO_3^- + H^+ \leftrightarrow H_2CO_3 \leftrightarrow CO_2 + H_2O</math>

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 following reaction to the right such that less 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==
* [http://www.anaesthesiamcq.com/AcidBaseBook/ABindex.php On-line text at AnaesthesiaMCQ.com]
* {{GeorgiaPhysiology|7/7ch12/7ch12lin}}
* [http://www2.kumc.edu/ki/physiology/course/nine/9_1.htm Overview at kumc.edu]
* [http://sprojects.mmi.mcgill.ca/nephrology/presentation/presentation4.htm Overview at mcgill.ca]
* [http://www.merck.com/mmhe/sec12/ch159/ch159a.html]
* [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]
* [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 On-line Acid-Base Physiology text]
* [http://www.lakesidepress.com/pulmonary/ABG/MixedAB.htm Diagnoses at lakesidepress.com]
* [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]]

[[de:Säure-Basen-Haushalt]]
[[es:Trastornos del equilibrio ácido-base]]
[[el:Ισορροπία οξέων - βάσεων]]
[[fr:Métabolisme acido-basique]]
[[fr:Équilibre acido-basique]]
[[hr:Poremećaji acidobazne ravnoteže]]
[[it:Equilibrio acido base]]
[[pt:Desequilíbrio ácido-básico]]
[[uk:Буферні системи]]
[[Category:2Fix]]