Acid-Base Basics

Chemistry of Life

Acid-Base Balance: Basics Chemistry Facts

Acid gives up a hydrogen ion Proton donors [H+]

A base/alkali accepts a hydrogen ion Proton acceptor [H+] Major base in the body: BICARBONATE

(HCO3) Acids react w/carbonates & bicarbonate to

form CARBON DIOXIDE Carbon Dioxide

Major lung chemical [acid]

Acids react with bases to form H2O and a salt = Neutralization reaction because both the Acid and Base are neutralized i.e. Carbonic acid= HCO3 + H+ = Carbon dioxide +

Water2

Release/donate H ions when Dissolved in H2O.

Bases                           

Homeostatic Mechanisms

Ph Body fluid ph:

measure of the body’s fluid free H+ ion level

Buffer systems [chemical] Bicarbonate Phosphate Protein/Hemoglobin

Kidneys Lungs

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pH Concentration of hydrogen (H) in a

solution A chemically neutral solution has a

pH of 7.00 Normal body pH is 7.35–7.45

Below 7.25 or above 7.55 is considered life-threatening

Above 7.8 (alkalosis) or below 6.8 (acidosis) usually is fatal

7.4 indicates a ratio of 20 parts bicarbonate [base] to 1 part carbonic acid

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Buffer Systems Buffers-

Chemically change strong acids into weaker acids or to bind acids to neutralize their effect Primary regulator of acid-base

balance Function:

Minimize effect of acids on blood pH Three other buffer systems in the body include

Phosphate, Protein/Hemoglobin

Acid-Base Regulation: Buffer System Bicarbonate buffer systems

Body’s primary buffer system Buffers blood and interstitial

fluids Bicarbonate-carbonic BS

Buffer system maintains 20:1 ratio between bicarbonate & carbonic acid & normal pH

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Respiratory Buffer: Lungs

Under control of _________: control/regulate blood levels of CO2 & the H2CO3 content

CO2: powerful stimulator of resp. center Chemoreceptors (Brain):

Sense pH change & vary rate & depth of breathing to regulate CO2 levels Hypoventilate & hyperventilate respiratory acidosis and alkalosis

To assess effectiveness of ventilation: PaCO2 (Partial pressure of carbon dioxide in arterial blood) Normal PaCO2 : 35-45 mm Hg7

CO2 & Hyperventilation

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RR

CO2

Blowing off CO2

pH

CO2 & Hypoventilation

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RR

CO2

Body retains

pH

Renal Control: Kidney Kidneys: 3rd line of defense Movement of bicarbonate: 1st renal control

mechanism Change the excretion rate of acids and the

production and absorption of bicarbonate ion Formation of acids: 2nd renal control

[phosphate buffering system] Formation of ammonium: 3rd renal control Slow to compensate but are the most

effective compensating mechanism10

Helping Out: Bicarbonate System

Lungs assist by:

______________________________

Kidneys: __________________________

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Acid – Base Balance

CO2 + H20 H2CO3 H+ + HCO3-

LungsLungs

RespiratoryRespiratory

FastFast

Kidneys Kidneys

MetabolicMetabolic

SlowSlow

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What Happens?• When either the HCO3

- or H2CO3

increases or decreases resulting in 1:20 ratio no longer being maintained:

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Acid-Base Balance

pH: 7.35-7.45PaCO2: 35-45 mm HgHCO3: 22-26 mEq/L

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Acid-Base Balance

Base deficit/Excess:-2 to +2 mEq/L

SaO2 saturation: >95% to 100%

PaO2: 80-100 mm Hg

Factors Affecting Acid-Base/BodyFluids/E-Lytes

Age Gender & body size Illness Medical dx, meds & surgery

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Elevator Effect

Anion Gap

Cation-anion difference Relationship among body cations

(+) & anions (-) Helpful in dx & treating acidotic

conditions Increases in gap = too much acid

in blood (acidosis) due to i.e. DKA, Lactic acidosis

Looking at the “+” & “-” Side of Things

CATIONS

“+” charged ion Types

____, ____ ____ , ____

ANIONS

[-] charged ion Types

______ ______ ______

Anion: A Negative ION

Anion Gap

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140 – (25+105)=

140 - (130) = 12 mEq/L

GAP= 10 (Normal)

Normal value: 8-16 mEq/L

Important in analyzing acid-base disorders

Anion Gap High Anion gap m. acidosis

Too much acid accumulated Seen with Lactic acidosi, DKA,

Hyperchloremia

Normal anion gap [aka as hyperchloremic m. acidosis] Direct loss of HCO3 ion

Diarrhea, fistula (GI) or renal causes

Abnormally low gap: HYPONATREMIA, multiple myeloma [Bone Cancer]