Blood Gases/ Acid-Base Balance Unit 2 MLT

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Medical Education and Training Campus Program: Medical Laboratory Technician Course: CHEM 201 Chemistry 2

pH

Indicator of the acidity or basicity of a solution, Measure of the hydrogen ion concentration, (H+)

pH Ranges

0 (acidic) to 14 (basic) and 7.0 is neutral

Normal Blood pH

7.35 - 7.45; values slightly above and below these values may be compatible with life, but can cause serious acidosis or alkalosis.

Effects of Altered pH in the Blood

Enzymes that are constructive can become destructive, oxygen delivery can be comprised as well as oxygen delivery to organs and food digestion and absorption.

Acidosis (Academia)

High hydrogen ion concentration when blood pH is <7.35.

Alkalosis (Alkalemia)

Low hydrogen ion concentration when blood pH is > 7.45.

Plasma Total CO2 (TCO2)

Estimate of the sum of the plasma concentration of bicarbonate (HCO3), carbonic acid (H2CO3), and dissolved gaseous carbon dioxide (CO2).

Oxygen (O2)

This measures the partial pressure of oxygen (Po2) dissolved in the blood and how well oxygen is able to move from airspace of the lungs into the blood.

Carbon Dioxide (Pco2)

This measures how much gaseous carbon dioxide is dissolved in the blood and how well carbon dioxide is able to move out of the body.

Oxygen Saturation Point (SO2)

A measure of the capacity of oxygen transport. This is the percentage of hemoglobin binding sites in the bloodstream occupied by oxygen (oxyhemoglobin)

Formulas to Calculate pH

pH = -log [H+] (for any solution)
pH = pKa + log [HCO3-]/[H2CO3] (body fluids and blood)
(HCO3-)/(H2CO3)=20/1 (for healthy individuals)
Ka = [H+][Cl-]/[HCl] (dissociation constant)
pKa = -log Ka (the negative log of the dissociation constant)

Henderson-Hasselbach

pH = pKa + log [HCO3]/[H2CO3]
[HCO3] is represented by the pH from the kidneys
[H2CO2] is represented by the pH from the lungs

Ka (Dissociation Constant)

Represents the concentration of ions that dissociate when an acid is placed into a solution.

Buffers

Solution of weak acids or bases and their associated salt (conjugated acid or base).

Weak Acid (Bronsted-Lowry)

A substance that separates less rapidly into ions. It gives up H+ ions with difficulty.

Weak Base (Bronsted-Lowry)

A substance that has slight affinity to gain hydrogen ions (H+).

Strong Acid is Added to a Buffer

Hydrogen ions (H+) of the strong acid will react with the conjugate base of the buffer system.

Strong Base is Added to a Buffer

Hydroxide ions (OH-) of the strong base will react with the weak acid of the buffer system.

Acid-Base Balance

The amount of acid or base produced and absorbed equals the amount of acid or base excreted and expired.

Acid-Base Balance Systems

Intracellular Buffers
Extracellular Buffers
Respiratory Mechanisms (lungs)
Renal Mechanisms (kidneys)

Extracellular Buffers

Blood, Interstitial fluid, urine, CSF.
Reacts with seconds with the lungs to change the pH.
Helps maintain normal blood pH.
Types of Buffers: Bicarbonate - Carbonic Acid, Proteins, and Phosphate.

Intracellular Buffers

Found inside all cell of the body.
Types of buffers: Bicarbonate - Carbonic Acid, Hemoglobin (Hb), and Phosphate.

Properties of Extracellular and Intracellular Buffers

Bicarbonate-Carbonic Acid, Hemoglobin, Protein, and Phosphate Buffer.

Bicarbonate-Carbonic Acid [ HCO3- (proton acceptor) / H2CO3 (proton donor) ]

Buffer system of both ECF and ICF. it reacts quickly to changes in the amount of (H2CO3) or (HCO3-) present in the body fluid.

Hemoglobin (Hb)

The main buffer system inside the red blood cell (RBC). Can bind with either carbon dioxide (CO2) or hydrogen ions (H+) produced from cell metabolism.

Reduced Hemoglobin (Hydrogenated Hemoglobin)

Biological function of hemoglobin is the exchange of blood gases. Hb + H+ > HHb.

Carbaminohemoglobin (HbCO2)

The compound formed by the union of carbon dioxide with hemoglobin.

Protein

One of the main buffers inside the cells and plasma. Albumin is one of the main protein buffers in the plasma and has a 7.4 pH level.

Phosphate (HPO4 2-/ H2PO4-) Buffer

Important for the ECF in RBCs and plasma, ICF and the Kidneys(urine). Helps maintain the pH in the ECF and ICF.

Respiratory Mechanisms (Lungs)

Involves to processes: Internal (cell/tissue) production of gaseous CO2 and External (lungs) diffusion of gaseous CO2.

Partial Pressure

The force exerted by a single gas that is present in a mixture of several gases.

Respiratory Center

Made up of several neurons located in the brain stem, responds to carbon dioxide (CO2) and hydrogen ion (H+) levels in the blood.

Blood Gas Exchanges in Respiratory Mechanisms

Supply oxygen (O2) to tissue cells for normal metabolism.
Maintain normal pH by excreting or retaining CO2.

Increased Ventilation (Hyperventilation)

Faster and deeper breathing. This decreases [CO2] and [H+] in the ECF.

Decreased Ventilation (Hypoventilation)

Shower and shallow breathing. This increases [CO2] and [H+] in the ECF.

Internal Respiration CO2 Cells/Tissues

Formed continuously as an end product of aerobic glucose metabolism.

Internal Respiration CO2 Plasma Transport

Increased partial pressure causes CO2 to be push out of the interstitial fluid and into the plasma.

Internal Respiration CO2 Metabolism

89% of the CO2 is diffused into the red blood cells.
11 % of the gaseous CO2 will stay in plasma.

11% of CO2 in Internal Respiration

1% bound to free amino groups (-NH2) of plasma proteins.
5% converted to bicarbonate (HCO3-).
5% converted to carbonic acid (H2CO3).

89% of CO2 in Internal Respiration

5% is dissolved gaseous CO2
21% of gaseous CO2 is bound to globin in Hb.
63% reacts with water to form carbonic acid (H2CO3) in the presence of enzyme carbonic anhydrase.

Carbonic Anhydrase

An enzyme present in the plasma of erythrocytes that catalyzes the conversion of CO2 and H2O into carbonic acid (H2CO3).

Chloride Shift

In Internal respiration chloride ions diffuse into RBCs as bicarbonate ions leaves; this compensates to keep a PCO2 balance in charge; in External respiration blood reaches lungs, bicarb ions are converted back to CO2, which is then exhaled.

Transporting CO2

Is mostly transported to the lungs in plasma as Bicarbonate ions.

External Respiration (Lungs).

11% of the dissolved CO2 is transported in the plasma.
89% inside the RBC into the alveoli.

11% of CO2 in External Transport

1% attached to plasma protein.
5% is handled by the bicarbonate buffer system.
5% remains dissolved in the plasma.

89% of CO2 in External Transport

5% of the dissolved gaseous CO2 is exhaled.
21% of gaseous CO2 comes from Carbaminohemoglobin.
63% of gaseous CO2 comes from plasma HCO3- ions.

Transport of O2

Oxygen does not easily dissolve in water. 1.5% of inhaled O2 is dissolved in plasma. 98.5% of blood oxygen is bonded to hemoglobin.

Oxyhemoglobin

Primary form of Oxygen transport. The bright red hemoglobin that is a combination of hemoglobin and oxygen from the lungs.

Total Amount of Oxygen

1L of arterial blood has 200mL of oxygen. 3mL (1.5%) is dissolved in plasma and 197mL (98.5%) of oxygen is bound to Hb to form Oxyhemoglobin.

100% Saturation

All four iron-heme binding sites in all hemoglobin molecules present are bound by oxygen.

Partial Saturation

Not all four iron-heme binding sites in all hemoglobin molecules are bound by oxygen.

Higher PO2

Leads to plenty of oxygen available to bind to every single iron-heme site in all blood.

Lower PO2

Leads to not having enough oxygen available to bind to every single iron-heme site in all blood.

PO2 as it Travels through the Body

95mm Hg in the blood vessels, 40mm Hg in the interstitial fluid and 5-40mm Hg in the blood cells.
When oxygen diffuses into the cells, the capillaries decreases to 40mm Hg. remains this way up to the lungs.

Factors that Affect Oxygen Binding

Partial Pressure, Bohr Effect, Temperature and 2, 3 Diphosphoglycerate.

Bohr Effect

Changes in pH, [CO2], [H+], acids produced from cell metabolism and excretion of acids as CO2 in the lungs.

Temperature

Generated from cell metabolism and muscle contraction.
Elevated temp increases metabolism and decreases temp decreases metabolism.

2, 3 Diphosphoglycerate (2, 3 DPG)

It is a metabolic byproduct of glucose metabolism. Regulated by high altitudes and body hormones.

Renal Mechanisms in Acid-Base Balance

Another mechanisms resisting in pH. Reacts slowly to changes in pH. Helps maintain the pH of urine between 4.5 to 8.0.

Acids Excretion in Renal Mechanisms

Hydrogen excretion in urine, generation and reabsorption of bicarbonate into blood and buffers (Phosphate Buffer and Ammonia-Ammonium Buffer)

Phosphate Buffer

CO2 diffuses from blood into the renal tubular cells where it forms N2CO3 and then dissociate into HCO3-. Then further reabsorbed into plasma along with Na+ ions.

Ammonia-Ammonium Buffer

Accounts for 60% of Hydrogen ions from acids in the form of ammonium ion (NH4+).

Glutamine

Diffuses from both blood and urine. Creates two new H2CO3 and NH4+ from the degradation.

Kidney Control Changes in Blood pH

Increasing excretion of acids and reabsorption of HCO3- (base) when the blood pH is decreased (acidic).
Decreasing excretion of acids and increasing excretion of HCO3- (base) when the blood pH is increased (basic).

Serum Electrolytes

Routine test are used to screen or monitor electrolyte or acid-base imbalances and measures the concentration of key electrolytes in the body. Ordered along with ABG.

Anion Gap

It is a direct measurement of the concentration of unmeasured acid anions in the blood.

Increased Anion Gap

Decreased unmeasured cations from Hypokalemia, Hypocalcemia, and Hypomagnesium. Indicates metabolic Acidosis (anion gap > 12mmol/L).

Arterial Blood Gases (ABGs)

Measures acid-base balance and oxygenation status in the blood and evaluates gas exchange in the lungs.

Measuring Arterial Blood Gases

pH, Bicarbonate (HCO3-), Oxygen (PO2), Carbon Dioxide (PCO2), and Oxygen Saturation (SO2). Samples should be analyzed immediately.

Arterial Blood Gases Drawbacks

Painful procedure due to puncture site, preanalytical errors: air bubbles, too much anticoagulant, improper mixing, storage calibration.

Base Excess (Base Deficit)

Measures all buffers in the blood: Hb, protein, phosphate, and bicarbonate-carbonic acid. measures the deviation of all blood buffers in a patients sample.

Base Excess Values

A negative value indicates acidosis. A positive base indicates alkalosis, also a postive value is called "base deficit".

Clinical Significance of Acidosis/Acidemia

Increased acid production from metabolism, decreased acid excretion via the lungs or kidneys and increased excretion of base (HCO3-) via the kidney. Arterial pH falls below 7.35.

Clinical Significance of Alkalosis

Decreased excretion of base (HCO3) by the kidneys.
Increased excretion of acids via the lungs or kidney.
pH of the blood exceeds 7.45.

Respiratory Acidosis

Excess carbon dioxide retention. Caused by CNS depression from drugs, injury and/or disease, Asphyxia, and hypoventilation due to disease.

Respiratory Alkalosis

Excess carbon dioxide excretion. Caused by Hyperventilation, Respiratory stimulation by drugs, disease, hypoxia, fever, and gram-negative bacterial infections.

Metabolic Acidosis

Kidney increase excretion of bicarbonate<24mEq/L which causes the retention of acids in the blood. pH <7.35.

Metabolic Acidosis Causes

Bicarbonate depletion due to renal disease, diarrhea, Excessive production of H2CO3 due to liver disease and Endocrine disorders including diabetes mellitus, hypoxia.

Hypoxia

A very strong drive resulting from a deficiency of available oxygen in the blood and bodily tissues (short of anoxia).

Metabolic Alkalosis

Kidney decreases excretion of bicarbonate >24mEq/L which causes the excretion of acids in the blood. pH >7.45.

Metabolic Alkalosis Causes

Excessive excretion of acids due to renal disease, loss of gastric hydrochloric acid from prolonged vomiting or gastric suctioning. Excessive alkali ingestion (antacids)

Lactic Acidosis

The most common type of metabolic acidosis. Excess production or diminish removal of lactic acid from the blood.

Type A Lactic Acidosis

Inadequate oxygen (O2) delivery. Caused by; shock, cardiac arrest, severe anemia, carbon monoxide poisoning, and hypoxia.

Type B Lactic Acidosis

Has adequate oxygen (O2) delivery. Caused by epileptic seizure, cyanide poisoning, stroke, uncontrolled diabetes mellitus, and liver failure.

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