Blood Gases.pptx

Blood Gases, pH and Buffer Systems



1. Definitions: Acid, Base, Buffer2. Acid-Base Balance3. Assessment of Acid-Base Homeostasis


1. Definitionsa. Acid – substance that can yield H+ in waterb. Base – substance that can yield OH- in water


1. Definitionsc. pK – pH in which protonated and unprotonated

forms are equal E.g: Bicarbonate-carbonic acid system - 6.1

d. Buffer – combination of weak acid or weak base and its salt

e. pH – Negative log of H+ concentration Inversely proportional to H+ concentration Venous blood = 7.35 : Arteries = 7.45

H2CO3 ↔ HCO3- + H+




2. Acid-Base Balancea. Maintenance of H+

b. Buffer Systems: regulation of H+

c. Regulation of Acid-Base Balance: Lungs and Kidneys



H+ concentration: 36-44 nmol/L (pH 7.34-7.44) Excess can lead to alterations in consciousness,

tetany, coma and death Acidosis (<7.34) and Alkalosis (>7.44) Maintained by the lungs and the kidneys



b. Buffer Systems: Acid-Base Balance


2. Acid-Base Balanceb. Buffer Systems: Acid-Base Balance

1. The Bicarbonate-Carbonic Acid System Weak Acid: Carbonic acid (H2CO3 ) Conjugate Base: Bicarbonate (HCO3

-)



1. The Bicarbonate-Carbonic Acid System H2CO3 dissociate into CO2 and H2O CO2 modify the ventilation rate HCO3 can be altered by the kidneys



1. The Bicarbonate-Carbonic Acid System

Blood Gases


2. Hemoglobin (Hb) Second most

Important buffer system

Found inside RBC Most effective single

system



3. Plasma Protein Ampholyte contains (+) and (-) part Free Carboxyl terminal and amino groups bind H+

4. PO4 Buffer System (Monohydrogen Phosphate - Dihydrogen Phosphate) Least important in buffering capacity

NaH2PO4 Weak Acid Na2HPO4 Conjugate Base



1. The Bicarbonate-Carbonic Acid System2. Hemoglobin (Hb)3. Plasma Protein4. PO4 Buffer System

(Monohydrogen Phosphate- Dihydrogen Phosphate)



b. Buffer Systems: Acid-Base Balance




3. Assessment of Acid-Base Homeostasisa. The Bicarbonate Buffering System and

Henderson –Hasselbalch Equationb. Organs in Acid-Base Balancec. Acid-Base Disorders: Acidosis and Alkalosis



Henderson –Hasselbalch Equation

Reference Range at 37°CpH 7.35-7.45pCO2 (mmHg) 35-45HCO3

- (mmol/L) 22-26H2CO3 (mmol/L) = 0.0307 x PCO2





3. Assessment of Acid-Base Homeostasisb. Organs in Acid Base Balance

1. Lungs (Respiratory mechanism)i. H2CO3 ↔ H2O + CO2

ii. Hyperventilation ↑ CO2 release = ↓ pCO2 (↓ H2CO3 )iii. Hypoventilation ↓ CO2 release = ↑ pCO2 (↑ H2CO3 )

H2CO3 (mmol/L) = 0.0307 x PCO2

pH 7.35-7.45pCO2 (mmHg) 35-45HCO3

- (mmol/L) 22-26



2. Kidneys (Renal mechanism)i. H2CO3 ↔ H++ HCO3

ii. Excretion of H+ (H + + NH 3 = NH 4+ / H + + HPO4

- = H2PO4-)

iii. Reabsorption of filtered HCO3 (↓ HCO3 - ↓pH) vice-versa


pH 7.35-7.45pCO2 (mmHg) 35-45HCO3

- (mmol/L) 22-26






Blood Gases

3. Assessment of Acid-Base Homeostasisc. Acid-Base Disorders: Acidosis and Alkalosis

1. Respiratory Origini. Acidosisii. Alkalosis

2. Metabolic Origini. Acidosisii. Alkalosis

Blood Gases


1. Respiratory Origin - Alteration in H2CO3 or CO2

i. Acidosis (Excess H2CO3 or CO2) Causes:

a. Asthma, Emphysemab. Bronchopneumoniac. Depression of respiratory centerd. Hypoventilation due to drugs (E.g. Barbiturates)e. Congestive heart failuref. OPD (Obstructive pulmonary disease)

Blood Gases



i. Acidosis (Excess H2CO3 or CO2) Compensation (Renal)

a. ↑ Na+/H+ exchangeb. ↑ NH3 productionc. ↑ resorption of HCO3

d. ↑ excretion of acid (H+)

Blood Gases




Blood Gases



ii. Alkalosis Excessive reduction in H2CO3 or CO2

Causes:a. High feverb. Hysteria (Hyperventilation)c. Pulmonary emboli and fibrosisd. Drugs (salicylates)

Blood Gases



ii. Alkalosis Renal Compensation

a. ↓ Na+/H+ exchangeb. ↓ NH3 productionc. ↓ resorption of HCO3

d. ↓ excretion of acid (H+)

Blood Gases



2. Metabolic (Nonrespiratory) Origini. Acidosisii. Alkalosis

Blood Gases


2. Metabolic Origin - Alteration in HCO3

i. Acidosis (Primary Bicarbonate Deficit: <24 mmol/L) Causes:

a. Addition Acidosis (diabetic ketoacidosis)b. Subtraction acidosis (diarrhea - ↓H2O and Na)c. Renal tubular acidosis, Acid salt (NH3Cl, CaCl)d. Starvation, Lactic acidsosise. Toxins (methanol, ethanol, ethylene glycol)f. Excessive loss of electrolytes and intestinal fluids

Blood Gases



i. Acidosis (Primary Bicarbonate Deficit: <24 mmol/L) Compensation (Respiratory)

a. Hyperventilation

Blood Gases




Blood Gases



i. Alkalosis Bicarbonate Excess Causes:

a. Addition Alkalosis (ingestion of alkali - NaHCO3 Na Lactate, citrate or acetate

b. Subtraction alkalosis (vomiting - ↓H2O, Na and K)c. Diuretics, Excessive gastric suctioningd. Intestinal obstruction

Blood Gases



i. Alkalosis Bicarbonate Excess Compensation (Respiratory)

a. Hypoventilation

Blood Gases




Blood Gases



pH 7.35-7.45pCO2 (mmHg) 35-45HCO3

- (mmol/L) 22-26


HCO3 (mmol/L) = Total CO2 - H2CO3

pH 7.35-7.45pCO2 (mmHg) 35-45HCO3

- (mmol/L) 22-26

1) HCO3 = 25 H2CO3 = 32

2) HCO3 = 25 pCO2 = 35

3) Total CO2 = 27 pCO2 = 31






End of Part I

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Blood Gases.pptx