blood ph regulation new 2016
TRANSCRIPT
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
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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
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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)
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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.
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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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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
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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+
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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.
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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.
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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.
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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.
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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.
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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.
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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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