Blood ph regulation new 2016

Department of Biochemistry, Nepalgunj Medical College

Sunday, May 22,

2016Rajesh Chaudhary

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For MBBS I

Acidosis and Alkalosis

If the pH of the body falls below 7.34, it is called acidosis.

If the pH of the body shoots above 7.42, it is called

alkalosis.

Acidemia Vs Acidosis

Alkalemia Vs Alkalosis

Sunday, May 22,

2016Rajesh Chaudhary

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Disturbance of acid-base

Metabolic: Primary disturbance is in [HCO3-]

[HCO3-] Metabolic acidosis

[HCO3-] Metabolic alkalosis

Respiratory: Primary disturbance is in pCO2

pCO2 Respiratory acidosis, Cause: hypoventillation

pCO2 Respiratory alkalosis, Cause: hyperventillation

Sunday, May 22,

2016Rajesh Chaudhary

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Rule of thumb !

If acid-base disturbance is metabolic (HCO3-), then

compensatory response is respiratory (pCO2).

If acid-base disturbance is respiratory (pCO2), then the

compensatory response is renal (to adjust HCO3-).Sunday, May 22,

2016Rajesh Chaudhary

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2016Rajesh Chaudhary

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pH of important biological fluid

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2016Rajesh Chaudhary

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Fluid pHPancreatic juice 7.5 – 8.0

Blood plasma (or whole

blood)

7.35 – 7.45

Cerebralspinal fluid 7.2 – 7.4

Tears 7.2 – 7.4

Interstitial fluid 7.2 – 7.4

Saliva 6.4 – 7.0

Gastric juice 1.5 – 3.0

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Lowry’s-Bronsted concept of Acid-

Base

Acid: Substance that can release hydrogen ion (proton)

upon dissociation.

Base: Substance that can accept hydrogen ion (proton)

Sunday, May 22,

2016Rajesh Chaudhary

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Acid and base can be either strong or weak.

The concept of LEO-GER.

Buffers in our body

Definition: A solution which resists change in pH which might be expected to occur upon addition of acid or base.

Buffers: mixtures of weak acid + it’s corresponding salt

Examples: Blood buffers: Bicarbonates, Phosphate, Proteins, Hemoglobin as a buffer.

Sunday, May 22,

2016Rajesh Chaudhary

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Mechanism of action of buffers

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2016Rajesh Chaudhary

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Reasons for respiratory acidosis-

alkalosis

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Primary acid-base disorders are

recognized by

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Major clinical causes of acid-base

disorder

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2016Rajesh Chaudhary

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Respiratory acidosis Respiratory alkalosis

Severe asthma Hyperventillation

Cardiac arrest Anemia

Obstruction in airways

Salicylate poisoningChest deformities

Depression of respiratory center

by drugs (e.g. opiates)

Mechanism of regulation of pH

Front-line defense

Buffer system

Respiratory mechanism

Second-line defense

Renal mechanism

Dilution factor

Sunday, May 22,

2016Rajesh Chaudhary

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Reabsorption of filtered HCO3-

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Mechanism for excretion of titratable

acid NOTE: Titratable

acid is excreted

throughout the

nephrons but

primarily in the a-

intercalated cells of

the late distal

tubules and

collecting ducts.

Excretion of H+ as NH4+

Sunday, May 22,

2016Rajesh Chaudhary

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Respiratory acidosis

May be acute or chronic.

Acute occurs within minutes and are uncompensated.

Primary problem alveolar hypoventilation.

So, what might be reason behind uncompensated acute case?

Reason: Renal compensation takes 48-72 hours to be effective.

Sunday, May 22,

2016Rajesh Chaudhary

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Why an increased pCO2 causes an

acidosis?

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Examples of acute and

uncompensated respiratory acidosis

Chocking

Bronchopenumonia

Acute exacerbation of asthma / COAD

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2016Rajesh Chaudhary

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Chronic respiratory acidosis

Usually results from chronic obstructive airways disease (COAD)

Usually long-standing condition

Accompanied by maximal renal compensation

Primary problem: impaired alveolar ventilation, but renal

compensation contributes markedly to the acid-base picture.

Compensation may be partial or complete

Kidney increases hydrogen ion excretion and ECF bicarbonate

level rises.

Sunday, May 22,

2016Rajesh Chaudhary

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Respiratory alkalosis

Respiratory alkalosis is much less common than acidosis.

Can occur when respiration is stimulated or is no longer subject to feedback control.

Usually acute with no renal compensation.

Treatment is to inhibit or remove the cause of hyperventilation.

Examples: Hysterical over-breathing, mechanical over-ventilation in an intensive care patient, raised intracranial pressure, or hypoxia – both of which may stimulate respiratory center.

Sunday, May 22,

2016Rajesh Chaudhary

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Mixed acid-base disorder

Not uncommon for a patient to have more than one acid-base disorder.

May have both metabolic and respiratory acidosis.

Example: Chronic bronchitis patient who develops renal impairment.

A patient with COAD (respiratory acidosis) + thiazide-induced potassium depletion and consequent metabolic alkalosis.

Sunday, May 22,

2016Rajesh Chaudhary

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Management of respiratory alkalosis

Increasing the inspired pCO2 by making patient

rebreathe into a paper bag aborts clinical features

of acute hypocapnia in acute hyperventilation

(Drawback: temporary measure; carries risk of

hypoxia)

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2016Rajesh Chaudhary

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Arterial blood gas (ABG) analysis

Why arterial blood is used to blood-gas analysis?

For measuring pH, pCO2 and pO2 in artery.

To measure how well your lungs are able to move oxygen and carbon dioxide between lungs and tissues.

So, what parameters are measured?

pO2, pCO2, pH, bicarbonate, oxygen content and oxygen saturation.

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2016Rajesh Chaudhary

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Why is it done?

For checking severe breathing problems and lungs diseases such as asthma, cystic fibrosis or COPD.

To see how well treatment for lung diseases is working.

To check if you need extra oxygen to help with breathing (mechanical ventilation).

To check if you are receiving right amount of oxygen if you are in oxygen therapy.

Measure acid-base level in the blood of people who have heart failure, kidney failure, uncontrolled diabetes, sleep disorders, sever infections etc.

Sunday, May 22,

2016Rajesh Chaudhary

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A patient has the following arterial

blood values pH, 7.33; [HCO3-], 36

mEq/L; pCO2, 70 mm Hg. What is the

patient’s acid-base disorder? Is it acute or

chronic? Comment on the case.

Sunday, May 22,

2016Rajesh Chaudhary

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Reference ranges

1. pH: 7.37-7.42

pCO2: 40 mmHg

2. [HCO3-]: 24 mEq/L

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2016Rajesh Chaudhary

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