Acid-base homeostasis

Jump to navigation Jump to search

Acid-base Homeostasis




Blood Gas Analysis

Relationship between pH and H+


Related Chapters

WikiDoc Resources for Acid-base homeostasis


Most recent articles on Acid-base homeostasis

Most cited articles on Acid-base homeostasis

Review articles on Acid-base homeostasis

Articles on Acid-base homeostasis in N Eng J Med, Lancet, BMJ


Powerpoint slides on Acid-base homeostasis

Images of Acid-base homeostasis

Photos of Acid-base homeostasis

Podcasts & MP3s on Acid-base homeostasis

Videos on Acid-base homeostasis

Evidence Based Medicine

Cochrane Collaboration on Acid-base homeostasis

Bandolier on Acid-base homeostasis

TRIP on Acid-base homeostasis

Clinical Trials

Ongoing Trials on Acid-base homeostasis at Clinical

Trial results on Acid-base homeostasis

Clinical Trials on Acid-base homeostasis at Google

Guidelines / Policies / Govt

US National Guidelines Clearinghouse on Acid-base homeostasis

NICE Guidance on Acid-base homeostasis


FDA on Acid-base homeostasis

CDC on Acid-base homeostasis


Books on Acid-base homeostasis


Acid-base homeostasis in the news

Be alerted to news on Acid-base homeostasis

News trends on Acid-base homeostasis


Blogs on Acid-base homeostasis


Definitions of Acid-base homeostasis

Patient Resources / Community

Patient resources on Acid-base homeostasis

Discussion groups on Acid-base homeostasis

Patient Handouts on Acid-base homeostasis

Directions to Hospitals Treating Acid-base homeostasis

Risk calculators and risk factors for Acid-base homeostasis

Healthcare Provider Resources

Symptoms of Acid-base homeostasis

Causes & Risk Factors for Acid-base homeostasis

Diagnostic studies for Acid-base homeostasis

Treatment of Acid-base homeostasis

Continuing Medical Education (CME)

CME Programs on Acid-base homeostasis


Acid-base homeostasis en Espanol

Acid-base homeostasis en Francais


Acid-base homeostasis in the Marketplace

Patents on Acid-base homeostasis

Experimental / Informatics

List of terms related to Acid-base homeostasis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Sadaf Sharfaei M.D.[2]; Priyamvada Singh, M.D. [3]


Acid-base homeostasis is the part of human homeostasis concerning the proper balance between acids and bases, in other words the pH. The body is very sensitive to its pH level. Outside the range of pH that is compatible with life, proteins are denatured and digested, enzymes lose their ability to function, and the body is unable to sustain itself.


The kidneys maintain acid-base homeostasis by regulating the pH of the blood plasma. Gains and losses of acid and base must be balanced. The study of the acid-base reactions in the body is acid base physiology.

Buffering agents

Any substance that can reversibly bind hydrogen ions is called a buffering agent. They function to impede any change in pH. Hydrogen ions are buffered by extracellular (e.g., bicarbonate, ammonia) and intracellular buffering agents (including proteins and phosphate).

Blood Gas Analysis

Blood gas analysis Vessel Range Interpretation
Oxygen Partial Pressure (pO2) Arterial 80 to 100 mmHg Normal
<80  mmHg Hypoxia
Venous 35 to 40 mmHg Normal
Oxygen Saturation (SO2) Arterial >95% Normal
<95% Hypoxia
Venous 70 to 75% Normal
pH Arterial <7.35 Acidemia
7.35 to 7.45 Normal
>7.45 Alkalemia
Venous 7.26 to 7.46 Normal
Carbon Dioxide Partial Pressure (pCO2) Arterial <35 mmHg Low
35 to 45 mmHg Normal
>45 mmHg High
Venous 40 to 45 mmHg Normal
Bicarbonate (HCO3) Arterial <22 mmol/L Low
22 to 26 mmol/L Normal
>26 mmol/L High
Venous 19 to 28 mmol/L Normal
Base Excess (BE) Arterial <−3.4 Acidemia
−3.4 to +2.3 mmol/L Normal
>2.3 Alkalemia
Venous −2 to −5 mmol/L Normal
Osmolar gap = Osmolality – Osmolarity >10 Abnormal
Anion gap = Na+ - [Cl+ HCO3]

Corrected AG = (measured serum AG) + (2.5 x [4.5 − Alb])

<8 Low
8 to 16 Normal
>16 High

Relationship between pH and H+

An inverse relationship between the H+ concentration (nmol/L) and the pH is given as follows:[1]

pH [H+]
7.80 16
7.70 20
7.60 26
7.50 32
7.40 40
7.30 50
7.20 63
7.10 80
7.00 100
6.90 125
6.80 160

Compensation Mechanism

  • There are compensation mechanisms in the body in order to normalizing the pH inside the blood.[2]
  • The amount of compensation depends on proper functioning of renal and respiratory systems. However, it is uncommon to compensate completely. Compensatory mechanisms might correct only 50–75% of pH to normal.
  • Acute respiratory compensation usually occurs within first day. However, chronic respiratory compensation takes 1 to 4 days to occur.
  • Renal compensation might occur slower than respiratory compensation.
Primary disorder pH PaCO2 [HCO3] Compensation Compensation formula
Metabolic acidosis Respiratory
  • Expected paCO2 = 1.5 x serum HCO3 + 8 ± 2 (Winters' formula)
  • Expected paCO2 = Serum HCO3 + 15
Metabolic alkalosis Respiratory
  • Expected paCO2 = 0.5 − 1 increase/ every 1 unit increase in serum HCO3 from 24
Respiratory acidosis Renal
  • Acute: HCO3 increases by 1mEq/L for every 10 mmHg increase in paCO2 above 40
  • Chronic: HCO3 increases by 3.5mEq/L for every 10 mmHg increase in paCO2 above 40
Respiratory alkalosis Renal
  • Acute: HCO3 decreases by 2mEq/L for every 10 mmHg derease in paCO2 above 40
  • Chronic: HCO3 decreases by 5mEq/L for every 10 mmHg decrease in paCO2 above 40

Related Chapters


  1. Rose, Burton David; Post, Theodore W. (2001). Clinical physiology of acid-base and electrolyte disorder. New York: McGraw-Hill. ISBN 0-07-134682-1.
  2. Sood P, Paul G, Puri S (April 2010). "Interpretation of arterial blood gas". Indian J Crit Care Med. 14 (2): 57–64. doi:10.4103/0972-5229.68215. PMC 2936733. PMID 20859488.