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[+] .

: 36 43 nmol/I (pH 7,35 7,46)

120 nmol/l 20 nmol/I

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3

4

Small changes in pH can produce

major disturbances

Most enzymes function only with narrow pH ranges

Acid-base balance can also affect electrolytes (Na+, K+, Cl-)

Can also affect hormones

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n n

( ) , ( ).

n n n .

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n ( , i ) n n n ( n nv )

n ~ 60 mmoles ( [] = 4 mmoles/l ECF) n nn,

nv n n , nv oo H2C03 n C02 20.

To n n .

o, n n nn,

n 2 [+]. n

, n

( , , )

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9

10

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Bohr: pH 2 2

+ + bO2 HHb+ + O2

30%

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, + .

HP42- + + 24

:

3 + + 4

+

:

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:

( [HC03-] )

() .

n H2C03

n C02 ( )

:

Henderson-Hasselbach

pH = 6,1 + log [HCO3-]/[H2CO3]

( [HCO3-]/[H2CO3] = 20)

[2C03] = .PC02

pH [HCO3-] / PC02

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20

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CO2 and bicarbonate are the components of

the bicarbonate buffer.

Because the pCO2 depends on the rate of

respiration, it is called the

respiratory component of

the acid-base balance.

In contrast, because the plasma concentration of

bicarbonate is

maintained by the kidney,

and is affected by the

amount of nonvolatile

acids produced in

tissues, it is called the

metabolic component of

the acid-base balance.

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, PCO2 [+]

, PCO2 [+]

.

: [+]

[+] .

( ). + & HCO3

-

-

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25

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

26

Alkalosis

Alkalosis causes over excitability of the central and peripheral nervous systems.

Lightheadedness

It can cause :

Nervousness

muscle spasms or tetany

Convulsions

Loss of consciousness

Death

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p, pC02 p02

M

n n CO2 n CO2 n

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pH electrode

mV

External

reference

electrode

Non-conducting

glass body

Internal reference

electrodeH+-responsive

glass membrane

Shielded connecting

cable

pCO2 electrode

mV

External

reference

electrode

CO2(g)

Flow Cell

Electrode

assembly

Gas-permeable

membrane

(silicone rubber)

NaHCO3/H2O

CO2 + H2O HCO3- + H+

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Gas-permeable

membrane

Platinum wire

(cathode)

-0.65V

Reference electrode

(anode)

Oxygen (pO2) electrode (Clark)

Flow cell O2

Reaction at the platinum

electrode

The amount of current (e-) is proportional to

the concentration of O2

O2 + 2H+ + 2e

- H2O2Pt

-0.6 V

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-

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35

Metabolic Acidosis

Bicarbonate deficit - blood concentrations of bicarb drop below 22mEq/L

Causes:

Loss of bicarbonate through diarrhea or renal dysfunction

Accumulation of acids (lactic acid or ketones)

Failure of kidneys to excrete H+

36

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)

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3838

Treatment

of Metabolic

Acidosis

IV lactate solution

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X

= Na+ - [CI- + HC03-]

B

[HC03-] , . .

, .

:

: - ..

:. & ( [] )

( , , ).

" ". : .

. .

. +

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Headache, lethargy Nausea, vomiting, diarrhea

( Kussmaul)

[+]

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44

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

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,

Respiration slow and shallow

Often related to depletion of electrolytes

Atrial tachycardia

Dysrhythmias

,

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47

Treatment of

Metabolic

Alkalosis

Electrolytes to replace those lost

IV chloride containing

solution

Treat underlying disorder

-

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PC02 .

:

(),

( )

. & .

52

Respiratory Acidosis

Carbonic acid excess caused by blood levels of CO2 above 45 mm Hg.

Hypercapnia high levels of CO2 in blood

Chronic conditions: Depression of respiratory center in brain that

controls breathing rate drugs or head trauma

Paralysis of respiratory or chest muscles

Emphysema

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53

Respiratory Acidosis

Acute conditons:

Adult Respiratory Distress Syndrome

Pulmonary edema

Pneumothorax

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Compensation for Respiratory

Acidosis

Kidneys eliminate hydrogen ion and retain bicarbonate ion

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( v) :

, ,

:

,

[+] , PC02.

.

2

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57

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

58

Treatment of Respiratory Acidosis

Restore ventilation

IV lactate solution

Treat underlying dysfunction or disease

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59

60

Respiratory Alkalosis

Carbonic acid deficit

pCO2 less than 35 mm Hg (hypocapnea)

Primary cause is hyperventilation

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.

, ,

.

62

Respiratory Alkalosis

Conditions that stimulate respiratory center:

Oxygen deficiency at high altitudes

Pulmonary disease and Congestive heart failure caused by hypoxia

Acute anxiety

Fever, anemia

Cirrhosis

Gram-negative sepsis

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63

Compensation of Respiratory

Alkalosis

Kidneys conserve hydrogen ion

Excrete bicarbonate ion

64

Treatment of Respiratory Alkalosis

Treat underlying cause

Breathe into a paper bag

IV Chloride containing solution Cl- ions replace lost bicarbonate ions

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65

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( )

,

: ( )

( ), - ( )

.

( )

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69

Diagnosis of Acid-Base Imbalances

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

high (alkalosis)

2. Decide which value, pCO2 or HCO3- , is

outside the normal range and could be

the cause of the problem. If the cause is

a change in pCO2, the problem is

respiratory. If the cause is HCO3- the

problem is metabolic.

70

3. Look at the value that doesnt correspond to the observed pH change. If it is inside

the normal range, there is no

compensation occurring. If it is outside the

normal range, the body is partially

compensating for the problem.

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72

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)

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73

Diagnosis

Metabolic acidosis

With compensation

74

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