Download MBBS Biochemistry PPT 45 Final Acid Base Balane Lecture Notes

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ACID BASE BALANCE

OR

Homeostasis of Blood pH

OR

Regulation of Blood pH

Synopsis

? Introduction

? Sources of Acids and Bases in body

? What is Acid Base Balance?

? Mechanisms Regulating Blood pH.

? Significance of Maintaining Acid Base

Balance

? Acid Base Imbalance and their

conditions.

? Diagnostic Tests
Introduction

?Acid Base Balance is a

physiological and

biochemical mechanism

associated to body/blood

pH.

What Is pH?

? pH is a Hydrogen ion concentration.
? pH = - log [H+]
? Different compartment of human

body has specific pH.

? pH has role in Enzyme activity.
Why blood pH is Altered?

?Addition of various

acids or alkalies by

metabolic activities

alters body/blood pH.
Sources and Types

of

Acids and Alkalies

Added During

Metabolic Life Processes

?Acids are H+

donors.

?Bases are H+

acceptors, or give

up OH- in solution.8
Acids and Bases can be strong or

weak:

? A strong acid or base is one that dissociates

completely in a solution

- HCl, NaOH, and H2SO4

? A weak acid or base is one that dissociates

partial y in a solution
-H2CO3, C3H6O3, and CH2O, Lactate.
? Acidic Substances of body:

?Carbonic acid(H2CO3)
?Phosphoric acid( H3PO4)
?Sulphuric acid (H2SO4)

? Organic Acids:

?Lactate, Acetoactate, Pyruvate

? Alkaline Substances of body:

?Citrate
?Bicarbonates.

What is Acid Base Balance?
Homeostatic Mechanisms

That

Regulate Blood/Body pH

? Acid Base balance is a

homeostatic mechanism

? Carried out to regulate the

altered pH of blood and other

body compartments to its normal

constant range.
?Maintenance of Acid

Base balance

?Is a prime requisite to

maintain normal

healthy and active life.

Acid-Base Balance

? It is the regulation of HYDROGEN ions.

(The more Hydrogen ions, the more acidic the solution and the

LOWER the pH)

? The acidity or alkalinity of a solution is measured as

pH
Acid Base Balance Regulates pH

Why it is Very Essential To Regulate

pH?

? pH of blood and other body

compartments are precisely

regulated.

? pH is always tried to be

maintained to its normal constant

range.
? Acid Base Balance

maintains the blood pH at

normal constant narrow

range of 7.35-7.45.

? pH of the medium directly

affects the enzyme activities

? Optimum pH is an essential

requisite for enzyme activities

and normal metabolism.


? It is prerequisite for

regulating blood/body pH:

?To maintain normal/optimal

Enzyme activities

?Normal metabolism

?Normal Coordination

?Normal Health

Factors Regulating

Acid Base Balance

22




Acid Base Balance is Regulated By

? First Line of Defense

vBlood Buffer System

? Second Line of Defense

?Respiratory Mechanism

? Third Line of Defense

?Renal Mechanism

1) Chemical Buffers

? React very rapidly (less than a second)

2) Respiratory Regulation

? Reacts rapidly (seconds to minutes)

3) Renal Regulation

? Reacts slowly (minutes to hours)

24
Role of Blood Buffer System

? First line of defense in

mechanism of Acid Base

Balance.

? Acids (H+) added are

neutralized by the salt part of

buffer.

Extracel ular Buffers

? Bicarbonate Buffer

?NaHCO3/H2CO3 (20:1 at 7.4 pH)

? Phosphate Buffer

?Na2HPO4/NaH2PO4 (4:1 at 7.4

pH)

? Protein Buffer

?Na-Protein/H-Protein
Intracel ular Buffers

? Bicarbonate Buffer

?KHCO3/H2CO3

? Phosphate Buffer

?K2HPO4/KH2PO4

? Protein Buffer

?K-Hb/H-Protein

Mechanism Action of Buffer Systems

? Buffers mixture of weak acids

and its salts

? Resist change in pH of blood

when small amount of acids or

alkalis added to the medium.




?Buffers act quickly but not

permanently

Bicarbonate Buffer System

Respiratory Buffer System

? Acid - Base balance is primarily concerned

with Bicarbonate Buffer mechanism :

? H2CO3/ Hydrogen (H+)
? Bicarbonate (HCO - 3) (Alkali Reserve)

H+

HCO -3

30
Bicarbonate Buffer

? Bicarbonate Buffer- Chief Buffer

system of Blood.

? NaHCO3 the salt part of buffer

neutralizes the strong and non

volatile acids added to blood.

? It constitutes Alkali reserve(HCO3-)
Bicarbonate Buffer

? Sodium Bicarbonate (NaHCO3) and carbonic

acid (H2CO3)

? Maintain a 20:1 ratio : HCO -

3 : H2CO3

HCl + NaHCO3 H2CO3 + NaCl

NaOH + H2CO3 NaHCO3 + H2O

33

? Action of Bicarbonate

(NaHCO3) converts strong

dissociable acid into weak

non dissociable acid

(H2CO3) and a neutral salt

without altering the pH.
? Weak acid H2CO3 formed during

buffering action of Bicarbonate

buffer is then expired out by Lungs.

? Thus Bicarbonate buffer is

connected to the respiratory system

? Bicarbonate buffer is also termed as

Respiratory buffer.

? Alkali reserve is represented by the

concentration of NaHCO3 in the blood.

? Alkali reserve concentration(HCO3-)

determines the strength of buffering action

towards added H+ ions by acids.

? More the concentration of Alkali reserve

,more is the buffering action and vice a versa.
? The blood buffers are effective

as long as

?The acid load added is not very

high and

?The alkali reserve (HCO3 -) is not

exhausted.

Phosphate Buffer/Urine Buffer

Na2HPO4/NaH2PO4 (4:1 at 7.4

pH)

? H+ + HPO 2-

4 H2PO4-

? OH- + H

-

2-

2PO4 H2O + H2PO4

38
Phosphate Buffer Mechanism

? When H+ ions added they are

neutralized/fixed by Na2HPO4

(Alkaline Phosphate) and converted

to NaH2PO4 (Acid Phosphates).

? These acid phosphates then

excreted out through kidneys as

acidic urine.

? Thus Phosphate Buffer is

connected to Excretory system .

? Phosphate Buffer also termed as

Urine Buffer.
? When an alkali enters it is

buffered by the acid phosphate

NaH2PO4 which converted to

Na2HPO4 alkaline phosphate.

? Excreted in urine making it

alkaline urine.

Protein Buffers

? Includes hemoglobin, work in blood.
? Carboxyl group gives up H+
? Amino Group accepts H+
? The Imidazole group of Histidine

present in Hb structure has buffering

capacity.

42
Role of Respiratory Mechanisms

? Respiratory system plays

second line of defense

mechanism of Acid Base

Balance.

? Role of respiration in acid base

balance is short term

regulatory process.

? H2CO3 formed from Bicarbonate Buffer, is

exhaled out through respiratory system.

? Increased H2CO3 stimulates the respiratory

centre in Medulla Oblongata.

? This in turn stimulates hyperventilation

which promptly removes H2CO3 from blood

by expiration.
? Exhalation of H2CO3 is as carbon dioxide

by activity of enzyme Carbonic Anhydrase

of Lungs.

? H+ + HCO - 3 H2CO3 CO2 + H20

? Respiratory mechanism is

powerful, but only works with

volatile acids.

? Doesn't affect fixed acids like

lactic acid.
? Blood pH can be adjusted

through respiratory

mechanism

? By changing rate and depth

of breathing.

? Low H2CO3 concentration in

blood depresses respiratory

centre ,causes hypoventilation

i.e slow and shallow respiration.

? This retains H2CO3 in blood.


?If Nervous centre /

Respiratory system

fails.

?Acid Base Balance

fails.

Generation of bicarbonate by RBC

LACK OF AEROBIC ACTIVITY,DIFFUSION OF CARBONDIOXIDE,H+ BUFFERED BY HHb.

50
Events in lungs and tissue

lung

tissue

-

HCO -

HCO

3

3

HHb

HHb

O

O2

2

H+

H+

H2CO3 HbO2

HbO2

H2CO3

H2O CO2

CO H

2

2O

Isohydric transport

EXPIRED AIR

of co2

METABOLISM

51

Role of Renal Mechanism

? Renal mechanism is the third

line of defense mechanism.

? Role of renal mechanism is

long term regulatory process.

52
? The acid and alkaline phosphates

formed during phosphate buffering

mechanism are filtered from blood

and excreted out through urine.

? Thus the phosphate buffer system is

directly connected to renal

mechanism.

? Renal mechanism conserve and

produce Bicarbonate ions ( Alkali

reserve).

? Renal Mechanism is the most

effective regulator of blood pH.

? If kidneys fail, pH balance fails.


? Renal System maintains Acid Base Balance

through:

? Reabsorption of Bicarbonate (HCO3-) ions.

? Excretion of H+ ions

? Excretion of titrable acids(Acid Phosphates)

? Excretion of Ammonium ions

(Glutaminase activity)

REABSORPTION OF BICARBONATE

~Conservation of Bicarbonate
~Urine is free of HCO -3
~Simultaneous excretion of H+

56


EXCRETION OF TITRABLE ACIDS

~measure of acid excreated by kidney
~no. of mil ilitres of N/10 NaOH required to titrate 1 litre of urine to pH 7.4
~role of phosphate buffer

57

Excretion Of H+ ions

~Elimination of nonvolatile acid
~Excretion of H+
~Occurs in PCT
~Regeneration of bicarbonate
~H+ combine with non carbonate base and excreated

58


EXCRETION OF AMMONIUM ION

NH3 is obtained from Deamination of Glutamine
NH +4 cant diffuse back
2/3 of body acid load liberated in the form of NH +4

59

Rates of correction

? Buffers function almost

instantaneously

? Respiratory mechanisms take

several minutes to hours

? Renal mechanisms may take

several hours to days

60


62


63

MECHANISM FOR REGULATION OF

ACID BASE BALANCE

? Buffer system: temporary solution
? Respiratory mechanism provide short time regulation
? Renal mechanism : permanent solution
? Urine pH < plasma pH ,4.5-9.5
? Eliminate nonvolatile acid, buffered by cation

(principal y Na+)

? Maintain alkali reserve
Acid Base Imbalance

OR

Conditions Of Acid Base

Disturbances

The Body and pH

? Homeostasis of blood pH is tightly

control ed by mechanisms of Acid

Base Balance.

? Extracellular fluid = 7.4
? Blood pH regulated to = 7.35 ? 7.45

66




Occurrence of Acid Base Imbalance

? When Factors involved in

homeostatic mechanisms to

regulate Acid Base Balance fails to

work efficiently.

? Does not maintain the altered pH of

blood to normal constant range.

? Results into Acid Base Imbalance.

ACIDOSIS / ALKALOSIS

?Two major disturbances

in Acid-Base balance

?Acidosis
?Alkalosis
Conditions Of Acid Base Imbalance

? Acidosis /Acidemia
( Decreased pH/Increased H+ ions)

? Alkalosis/Alkalemia
(Increased pH/Decreased H+ ions)

? Acidosis (Acidemia) below 7.35
? Alkalosis (Alkalemia) above 7.45
? Blood pH < 6.8 or > 8.0 death

occurs




ACIDOSIS / ALKALOSIS

? Acidosis

? A condition in which the blood has too much acid (or

too little base), frequently resulting in a decrease in

blood pH.

? Alkalosis

? A condition in which the blood has too much

base (or too little acid), occasional y resulting in

an increase in blood pH.

71

72


74
Effect of Altered pH

?Altered pH may seriously

disturbs the vital

processes.

?Might lead to fatality.

? Most enzymes function only

with narrow pH ranges.

? Extremes of pH affects the

enzymatic action by

protonation or deprotonation

at the active sites of Enzymes.

? Makes Enzymes inactive.
? Inactivated Enzymes affect

metabolic reactions and

metabolic pathways.

? Metabolism gets deranged .
? Leads to metabolic syndromes.

pH also affect excitability of

Nerve and Muscle cells

pH

Excitability

pH

Excitability

78






ACID-BASE REGULATION

? Enzymes, Hormones and ion distribution

are all affected by Hydrogen ion

concentrations

79

ACIDOSIS / ALKALOSIS

? pH changes have dramatic effects on normal cell

function

1) Changes in excitability of nerve and muscle

cells

2) Influences Enzyme activity
3) Influences K+ levels/Retention of K+

80


CHANGES IN CELL EXCITABILITY

? pH decrease (more acidic) depresses the

central nervous system

? Can lead to loss of consciousness

? pH increase (more basic)causes over

excitability of nervous system.

? Tingling sensations, nervousness, muscle

twitches

INFLUENCES ON ENZYME ACTIVITY

? pH increases or decreases can alter the shape of

the enzyme rendering it non-functional

? Changes in enzyme structure can result in

accelerated or depressed metabolic actions

within the cell

82








INFLUENCES ON K+ LEVELS

? If H+ concentrations are high (acidosis) than H+ is

secreted in greater amounts

? This leaves less K+ than usual excreted.
? The resultant K+ retention can affect cardiac

function and other systems

K+

K

Na+

Na

N

H+

H

83

Smal changes in pH can produce major

disturbances

? Acid-base balance can also

affect Electrolytes (Na+, K+, Cl-)

? Can also affect Hormones

84
ACID-BASE IMBALANCE

? Derangements of
? Hydrogen/Carbonic

acid (H+/H2CO3)

? Bicarbonate
(HCO3-)

concentrations

In body fluids are

common in

conditions of Acid

Base Imbalance

Acid-Base Imbalances

?pH< 7.35 Acidosis
?pH > 7.45 Alkalosis


4 Types of Primary Acid-Base Disorders

Acid Base Imbalances

Biochemical

Change

Respiratory Acidosis

Increased H2CO3

Respiratory Alkalosis

Decreased H2CO3

Metabolic Acidosis

Metabolic Alkalosis

87


RESPIRATORY ACIDOSIS

90
Respiratory Acidosis

? Primary Carbonic acid excess

? Increased H2CO3/Increased pCO2

? Defect in respiratory centre of brain

? Defect in respiratory organ system

? Decreased elimination of H2CO3 by

the lungs.

? Hypoventilation

? Increased blood levels of

CO2 above 45 mm Hg.

? Hypercapnia ? high levels of

pCO2 in blood

92


RESPIRATORY ACIDOSIS

? Respiratory acidosis

develops when the lungs

don't expel CO2

adequately.

? This can happen in

diseases that severely

affect the lungs.

93

? Chronic conditions:

? Depression of respiratory center in brain that

controls breathing rate ? drugs or head trauma

? Paralysis of respiratory or chest muscles

? Emphysema

? Asthma

? Pneumonia

? Pulmonary edema

? Obstruction of respiratory tract

? Congestive Cardiac Failure


HYPOVENTILATION

Causes Respiratory Acidosis

? Hypo = "Under"

Elimination of CO2

H+

pH

RESPIRATORY ACIDOSIS

CO2

CO2

-

HCO3

CO2

CO2

H CO

2

3

2

:

20

-breathing is suppressed holding CO2 in body

-pH = 7.1
96




RESPIRATORY ACIDOSIS

? 1) Obstruction of air passages

? Vomit, Anaphylaxis, Tracheal Cancer

97

RESPIRATORY ACIDOSIS

? 2) Decreased Respiration

? Shallow, slow breathing

? Depression of the respiratory centers in the brain

which control breathing rates

? Drug overdose

98




RESPIRATORY ACIDOSIS

? 4) Col apse of lung

? Compression injury, open thoracic wound

Left lung

col apsed

99

Respiratory Acidosis

? Acute conditions:

?Adult Respiratory Distress

Syndrome

?Pulmonary edema
?Pneumothorax

100
Compensation for Respiratory Acidosis

?Kidneys eliminate

hydrogen ion and retain

bicarbonate ions.

101

Signs and Symptoms of Respiratory

Acidosis

? Breathlessness
? Restlessness
? Lethargy and disorientation
? Tremors, convulsions, coma
? Respiratory rate rapid, then gradually

depressed

? Skin warm and flushed due to vasodilation

caused by excess CO2

102


Treatment of Respiratory Acidosis

? Restore ventilation
? IV lactate solution
? Treat underlying

dysfunction or disease

103

RESPIRATORY ALKALOSIS

104
Respiratory Alkalosis

? Primary Carbonic acid deficit
? Decreased H2CO3
? pCO2 less than 35 mm Hg (hypocapnea)

? Most common acid-base imbalance
? Primary cause is hyperventilation
? Washes out excessive quantity of H2CO3

through expiration process of lungs.

105

? Stimulation of respiratory

centre in brain

? Hyperventilation


Respiratory Alkalosis

? Conditions that stimulate respiratory center:

? Oxygen deficiency at high altitudes
? Pulmonary disease and Congestive heart failure ?

caused by hypoxia

? Respiratory center lesions
? Acute anxiety
? Fever, anemia
? Early salicylate intoxication
? Cirrhosis
? Gram-negative sepsis/Meningitis

107

RESPIRATORY ALKALOSIS

? Anxiety is an

emotional disturbance

? The most common

cause of

hyperventilation, and

thus respiratory

alkalosis, is noted in

anxiety

108




















RESPIRATORY ALKALOSIS

? Respiratory center lesions

? Damage to brain centers

responsible for

monitoring breathing

rates

? Tumors
? Strokes

109

RESPIRATORY ALKALOSIS

? High Altitude

? Low concentrations of O2 in the arterial blood

reflexly stimulates ventilation in an attempt to

obtain more O2

? Too much CO2 is "blown off" in the process

110




















RESPIRATORY ALKALOSIS

? Fever

? Rapid shallow breathing

blows off too much CO2

111

RESPIRATORY ALKALOSIS

? Salicylate poisoning
(Aspirin overdose)

? Ventilation is stimulated

without regard to the status

of O2, CO2 or H+ in the body

fluids

112




RESPIRATORY ALKALOSIS

? Kidneys compensate by:

? Retaining hydrogen ions
? Increasing bicarbonate excretion

HCO -3

-

H

HCO

+

3H+

HCO -3

HCO -3

H+

H+

H+

HCO -3

HCO - H+

3

HCO -

H+

3

HCO -3

H+

HCO -3

H+ HCO - H+

3

H+

113

HYPERVENTILATION

Causes Respiratory Alkalosis

? Hyper = "Over"

Elimination of CO2

H+

pH

114
Compensation of Respiratory Alkalosis

? If kidneys are functioning normal
? The conditions of respiratory

acidosis or alkalosis are

compensated.

? Kidneys conserve hydrogen ion
? Excrete bicarbonate ion

115

Treatment of Respiratory Alkalosis

? Treat underlying cause
? Breathe into a paper bag
? IV Chloride containing solution

Cl- ions replace lost

bicarbonate ions

116


METABOLIC ACIDOSIS

117

Metabolic Acidosis

? Primary Alkali deficit

? Bicarbonate deficit - blood concentrations of

bicarbonate drop below 22mEq/L

? Causes:

? Loss of bicarbonate through diarrhea or renal

dysfunction.

? Overproduction production of acids (lactic acid or

ketones)

? Failure of kidneys to excrete H+

118








METABOLIC ACIDOSIS

? Occurs when there is a decrease in the normal

20:1 ratio

? Decrease in blood pH and bicarbonate level

? Excessive H+ or decreased HCO -3

H

O - -

2CO3

HHCCO33

H CO

2

3

=

= 7.4

1

:

210

119

METABOLIC ACIDOSIS

? Any acid-base imbalance

not attributable to CO2 is

classified as metabolic

? Metabolic production of

Acids

? Or loss of Bases

120












METABOLIC ACIDOSIS

? The causes of metabolic acidosis can be grouped

into five major categories

? 1) Ingesting an acid or a substance that is

metabolized to acid

? 2) Abnormal Metabolism
? 3) Kidney Insufficiencies
? 4) Strenuous Exercise
? 5) Severe Diarrhea

121

METABOLIC ACIDOSIS

? 1) Ingesting An Acid

? Most substances that cause acidosis when

ingested are considered poisonous

? Examples include

wood alcohol

(methanol) and

antifreeze

(ethylene glycol)

? However, even an overdose

of aspirin (acetylsalicylic acid)

can cause metabolic acidosis

122






METABOLIC ACIDOSIS

? 2) Abnormal Metabolism

? The body can produce excess acid as a result of several

diseases

? Ketoacidosis
? Type I Diabetes Mellitus
? Uncontrol ed Diabetes mellitus
? Prolonged Starvation
? Lacticacidosis
? Shock
? Haemorrhage
? Violent Exercise-

METABOLIC ACIDOSIS

? Unregulated diabetes

mellitus causes

ketoacidosis

? Body metabolizes fat

rather than glucose

? Accumulations of

metabolic acids (Keto

Acids) cause an

increase in plasma H+

124










METABOLIC ACIDOSIS

? 3) Kidney Insufficiencies

? This type of kidney malfunction is called renal

tubular acidosis or uremic acidosis and may

occur in people with kidney failure or with

abnormalities that affect the kidneys' ability

to excrete acid

METABOLIC ACIDOSIS

? 3) Kidney Insufficiencies

? Kidneys may be unable to rid

the plasma of even the

normal amounts of H+

generated from metabolic

acids

? Kidneys may be also unable to

conserve an adequate

amount of HCO -3 to buffer the

normal acid load

126








METABOLIC ACIDOSIS

? 4) Strenuous Exercise

? Muscles resort to anaerobic glycolysis during

strenuous exercise

? Anaerobic respiration leads to the production

of large amounts of lactic acid

C

Enzymes

6H12O6

2C3H6O3 + ATP (energy)

Lactic Acid

127

METABOLIC ACIDOSIS

? 5) Severe Diarrhea

? Fluids rich in HCO -3 are released and reabsorbed

during the digestive process

? During diarrhea this HCO -3 is lost from the body

rather than reabsorbed








METABOLIC ACIDOSIS

? 5) Severe Diarrhea

? The loss of HCO -3 without a corresponding loss of

H+ lowers the pH

? Less HCO -3 is available for buffering H+

? Prolonged deep (from duodenum) vomiting can

result in the same situation

Symptoms of Metabolic Acidosis

? Headache, lethargy
? Nausea, vomiting, diarrhea
? Coma
? Death

130
Compensation for Metabolic Acidosis

? Increased ventilation.
? Renal excretion of hydrogen ions

if possible.

? K+ exchanges with excess H+ in

ECF.

? H+ into cells, K+ out of cells.

131

Treatment of Metabolic Acidosis

? IV lactate solution

132


METABOLIC ALKALOSIS

133

Metabolic Alkalosis

? Bicarbonate Excess - concentration in blood is

greater than 26 mEq/L

? Causes:

? Excess vomiting = loss of stomach acid

? Excessive use of alkaline drugs

? Certain diuretics

? Endocrine disorders

? Heavy ingestion of antacids

? Severe dehydration

? Cushings Syndrome

? Prolonged exposure to x rays and UV rays

134








METABOLIC ALKALOSIS

? Elevation of pH due to an increased 20:1 ratio

? May be caused by:

? An increase of bicarbonate
? A decrease in hydrogen ions

? Imbalance again cannot be due to CO2

? Increase in pH which has a non-respiratory

origin

7.4

135

METABOLIC ALKALOSIS

? Can be the result of:

? 1) Ingestion of Alkaline Substances
? 2) Vomiting ( loss of HCl )

136








METABOLIC ALKALOSIS

? Baking soda (NaHCO3) often used as a remedy

for gastric hyperacidity

? NaHCO

-

3 dissociates to Na+ and HCO3

137

Compensation for Metabolic Alkalosis

? Alkalosis most commonly occurs

with renal dysfunction, so can't

count on kidneys.

? Respiratory compensation

difficult ? hypoventilation limited

by hypoxia.

138
Symptoms of Metabolic Alkalosis

? Respiration slow and shallow

? Hyperactive reflexes ; tetany

? Often related to depletion of

electrolytes

? Atrial tachycardia

? Dysrhythmias

139

Treatment of Metabolic Alkalosis

? Electrolytes to replace

those lost

? IV chloride containing

solution

? Treat underlying disorder

140
Acidosis

? Principal effect of acidosis is depression of the CNS through

in synaptic transmission.

? Generalized weakness

? Deranged CNS function the greatest threat

? Severe acidosis causes

? Disorientation

? Coma

? Death

141

Alkalosis

? Alkalosis causes over excitability of the central and

peripheral nervous systems.

? Numbness

? Light headedness

? Severe Alkalosis causes :

? Nervousness

? muscle spasms or Tetany

? Convulsions

? Loss of consciousness

? Death

142
Compensation Of

Acid Base Imbalance

? The body response to acid-base imbalance is

called compensation

? May be complete compensation if altered pH

brought back within normal limits

? Partial compensation if pH range is still

outside norms.

? Uncompensated if pH range is very out from

norms.

? If underlying problem is respiratory, renal

mechanisms can bring about metabolic

compensation.

? If underlying problem is metabolic,

hyperventilation or hypoventilation can help :

respiratory compensation.


ACIDOSIS

decreased

failure of

metabolic

production

absorption of

prolonged

removal of

kidneys to

acid

of keto acids

metabolic acids

diarrhea

CO2 from

excrete

from GI tract

lungs

acids

accumulation

accumulation

excessive loss

of CO2 in blood

of acid in blood

of NaHCO3

from blood

deep

vomiting

respiratory

metabolic

from

GI tract

increase in

acidosis

plasma H+

acidosis

concentration

kidney

disease

(uremia)

depression of

145

nervous system

ALKALOSIS

anxiety

overdose

high

prolonged

ingestion of

excess

of certain

altitudes

vomiting

excessive

aldosterone

drugs

alkaline drugs

hyperventilation

loss of acid

accumulation

loss of CO2 and

of base

H2CO2 from

blood

respiratory

metabolic

alkalosis

alkalosis

decrease

in plasma H+

concentration

overexcitability

of nervous

146

system
Organ dysfunction

And

Acid Base Imbalance

? CNS ? respiratory acidosis (suppression) and alkalosis

(stimulation)

? Pulmonary ? respiratory acidosis (COPD) and

alkalosis (hypoxia, pulmonary embolism)

? Cardiac ? respiratory alkalosis, respiratory acidosis,

metabolic acidosis (pulmonary edema)

? GIT ? metabolic alkalosis (vomiting) and acidosis

(diarrhea)

? Liver ? respiratory alkalosis, metabolic acidosis (liver

failure)

? Kidney ? metabolic acidosis (RTA) and alkalosis (1st

Aldosterone)

Organ Dysfunction

? Endocrine

? Diabetes mellitus ? metabolic acidosis

? Addisons Disease/Adrenal insufficiency ? metabolic

acidosis.(Decreased H+ ions excretion)

? Cushing's Syndrome ? metabolic alkalosis

(Increased Cortisol- Increased H+ ions excretion)

? Primary aldosteronism ? metabolic alkalosis

? Drugs/toxins

? Toxic alcohols ? metabolic acidosis

? ASA/Aspirin ? metabolic acidosis and respiratory alkalosis(

Causes Hyperventilation)

? Theophylline overdose ? respiratory alkalosis


ACID ? BASE DISORDERS

Clinical State

Acid-Base Disorder

Pulmonary Embolus

Respiratory Alkalosis

Cirrhosis

Respiratory Alkalosis

Pregnancy

Respiratory Alkalosis

Diuretic Use

Metabolic Alkalosis

Vomiting

Metabolic Alkalosis

Chronic Obstructive Pulmonary Disease

Respiratory Acidosis

Shock

Metabolic Acidosis

Severe Diarrhea

Metabolic Acidosis

Renal Failure

Metabolic Acidosis

Respiratory Alkalosis,

Sepsis (Bloodstream Infection)

149

Metabolic Acidosis

150
Anion Gap

? Sum of anion and cations is always equal
? Sodium and Potassium accounts for 95% of

cations

? Chloride and bicarbonate accounts for 68% of

anions

? There is difference between measured anion

and cation

? The unmeasured anions constitute the

ANION GAP.
? They are protein anions ,sulphates ,phosphates

and organic acid(Unmeasured Anions)

? AG can be calculated as (Na+ + K+)--(HCO -3 + Cl-)
? High anion gap acidosis: renal failure, DM
? Normal anion gap acidosis: diarrhea
? Hyperchloremic acidosis

Calculation Of Anion Gap

? Na ++ K+ = Cl- + HCO3 - + A-
? 136+ 4 = 100 + 25
? A- = 15 mEq/L
? Normal AG is typically 12 ? 4

mEq/L.

? If AG is calculated using K+, the

normal AG is 16 ? 4 mEq/L

Significance of Anion Gap Calculation

? Calculation of Anion gap

and its values help in

diagnosing conditions of

Acid Base Balance and

Imbalance.
? The anion gap is increased in conditions

such as metabolic acidosis:

? That result from elevated levels of

metabolic acids (metabolic acidosis)

?Lactic acidosis
?Diabetic Ketoacidosis
?Renal Failure

? A low anion gap occurs in conditions

that cause a fall in unmeasured

anions

? (primarily albumin) OR a rise in

unmeasured cations


Calculate the Anion Gap

? 1. Calculate the anion gap as described.
? 2. An anion gap ,over 25 suggests a severe

metabolic acidosis.

? 3. Causes of an high anion gap: ethylene

glycol, lactic acid, methanol, paraldehyde,

aspirin, renal failure, ketoacidosis (diabetic or

ethanol).
Anion Gap Acidosis:

? Anion gap >12 mmol/L; caused by a decrease

in [HCO3 -]

? Balanced by an increase in an unmeasured

acid ion from either endogenous production

or exogenous ingestion (normochloremic

acidosis).

Me

M t

e abolic

t



abolic Ac

A idos

c

is and t

and he

t

he Anion

A

g

nion ap

g

1. Normal gap

2. Increased gap

1. Acid

1. Renal "HCO

2. Acid

3" 2. GI "HCO3"

prod

losses

elimination

losses

Lactate

Renal disease

Proximal RTA

DKA

Distal RTA

Diarrhea

Ketosis



Toxins

Alcohols

Salicylates

Iron
Henderson Hasselbalch Equation

? pH= pka +log [HCO3-]/[H2CO3]

? At pH 7.4 the ratio of HCO3-/H2CO3

is 1:20.

? A buffer is most effective when

pH=pKa

? When concentration of salt and acid

are equal.
Significance of Henderson Hasselbalch

Equation

? The equation helps in

calculating pH of Buffers.

? The equation helps in

assessing status of Acid

Base balance.

Stepwise Approaches

? History & physical examination

? Arterial blood gas for pH, pCO2, (HCO3)

? Use the HCO3 from ABG to determine compensation

? Serum Na, K, Cl, CO2 content

? Use CO2 content to calculate anion gap

? Calculate anion gap

? Anion gap = {Na - (Cl + CO2 content)}

? Determine appropriate compensation

? Determine the primary cause
DIAGNOSTIC LAB VALUES

&

INTERPRETATION

? Arterial Blood

Gas(ABG )Analyzer

determines Acid Base

Balance and Imbalance.
Diagnosis of Acid-Base Imbalances

1. Note whether the pH is low (acidosis) or high

(alkalosis)

2. Decide which value, pCO

-

2 or HCO3 , is

outside the normal range

3. If the cause is a change in pCO2,/H2CO3 the

problem is respiratory.

4. If the change is in HCO -3 the problem is

metabolic.

169

Normal Arterial Blood Gas (ABG)

Lab Values:

? Arterial pH: 7.35 ? 7.45
? HCO -3: 22 ? 26 mEq/L

? PCO2: 35 ? 45 mmHg

? TCO2: 23 ? 27 mmol/L

? PO2: 80 ? 100 mmHg

? Base Excess: -2 to +2
? Anion Gap: 12 ? 14 mEq/L
Example

? A patient is in intensive care because he

suffered a severe myocardial infarction 3 days

ago. The lab reports the following values from

an arterial blood sample:

? pH 7.3
? HCO3- = 20 mEq / L ( 22 - 26)
? pCO2 = 32 mm Hg (35 - 45)

171

Diagnosis

? Metabolic acidosis
? With compensation

172
Questions

? Long Essays.

? What is acid-base balance? Describe the homeostatic mechanism

by which the blood pH is regulated.

? Short Notes

? Blood Buffer System.

? Role of Kidney in acid-base balance.

? Hb as Buffer system.

? Acid-Base imbalance.

? Metabolic Acidosis.

? Difference between acidosis & alkalosis.

? Anion Gap.

END

ACID - BASE BALANCE

THANKS

174

This post was last modified on 05 April 2022