Acid Base Balance

pH

Indicator of the acidity or basicity of a solution

 

measure of the hydrogen ion concentration [H+]

Ranges of a pH

ranges from 0-14

 

pH< 7.0 is acidic

 

pH= 7.0 is neutral

 

ph> 7.0 is basic

Normal Blood pH

normal blood pH is 7.35- 7.45

 

values slightly above or below these values may be compatible with life, but can lead to serous acidosis or alkalosis

Effects of altered pH in the Blood

enzymes that are constructive can become destructive or not function properly

 

comprises O2 delivery to cells

 

comprises organ systems

 

food abosrption and digestion can also be affected

acidosis

also known as academis

 

as a high hydrogen ion concentration when blood pH is <7.35

akalosis

also known as alkalemia

 

defined as low hydrogen ion concentration when blood pH is >7.45

Plasma Total CO2 (Tco2)

an estimate of the sum of the plasma concentrations of bicarbonate, carbonic acid, and dissolved gaseous carbon dioxide

 

bicarbonate conc. is the commonly measured index of blood hydrogen ions homeostasis

 

 

advantages of Tco2

venous blood can be used

 

often performed with urea and electrolytes tests

Oxygen (Po2)
measures the partial pressure of oxygen dissolved in blood and how well the oxygen is able to move from the airspace of the lungs into the blood
Carbon Dioxide (Pco2)

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

 

indicates whether or not a respiratory problem exists.

 

high Pco2 indicates hypoventillation (respiratory acidosis).

 

a low Pco2 indicates hyperventillation ( respiratory alkalosis)

Oxygen Saturation Point (SO2)

a measure of the capacity of oxygen transport.

 

percentage of hemoglobin binding sites in the bloodstream occupied by oxygen (oxyhemoglobin)

Formulas to calculate pH

any solution: pH= -log[H+]

 

Henderson-Hasselbach equation: pH= pKa+log[HCO3]/[H2CO3]

 

Henderson-hasselbach used for body fluids and blood

[HCO3]- represents the contribution of pH from the kidneys

[H2CO3]- represents the contribution of pH from the lungs

 

Buffers

soulutions of weak acids or bases and their associated salts( conjugated acid or base)

 

resist changes in pH by reacting with an acid or a base

weak acid (bronstead- lowry definition)

a substance that separates less readily into ions.

 

gives up H+ with difficulty

 

(weak acids are also weak electrolytes)

 

form conjugate bases with the loss of hydrogen ions(H+)

weak base (bronstead-lowry definition)

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

 

form conjgate acids with the additon of hydrogen ions

 

Strong acid and Bases
strong acid and bases separates almost 100% into ions when put into a water solution 
How buffers work with a strong acid

when a strong acid is added to a buffer, hydrogen ions of the strong acid will react with the conjugate base of the buffer system.

This reduces the conc. of hydrogen ions by making a weak acid.

This explains how the ph of 1.2 hydrochloric acid can be increased to a pH of 5.1 to 7.1

how buffers work with strong bases

when a strong base is added to a buffer, hydroxide ions of the strong base will react with the weak acid of the buffer system.

This reduces the conc. of hydroxide ions by making water and the conjugate base of the weak acid.

this explains how the pH of 13 of sodium hydroxide can be decreased to a pH below 7.4

acid-base balance

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

-The amount of acid or base consumed from the diet and absorbed in the intestines as well as that metabolically produced is equal to the amount ofacid or base excreted by the lungs and kidneys.

4 acid-base balance systems

1) intracellular buffers ( inside all the cells in the body)

 

2) extracellular buffers ( Blood, Interstitial fluid, urine, csf)

 

3) respiratory mechanisms (lungs)

 

4) remnal mechanims ( kidneys)

Extracellular Buffers

( blood, interstitial fluid, urine, csf)

 

react very rapidly (w/in seconds) with the lungs to changes in pH

 

Helps maintain the normal blood pH (7.35- 7.45)

 

Types of buffers in the extracellular fluid

1) Bicarbonate- Carbonic Acid

 

2) proteins

 

3) phosphate

intracellular buffers

 found inside all the cells of the body

 

types of buffers in the intracellular fluid

1) bicarbonate- carbonic acid

 

2) hemoglobin (Hb)- found only inside the rbcs

 

3) proteins

 

4) phosphate

Bicarbonate- Carbonic Acid

buffer system of both the extracellular and intracellular fluids.

reacts quickly to changes in the amount of carbonic acid or bicarbonate present in body fluids

 

one of the main buffers of plasma in th extracellular fluid

 

regulated by two organs:

 

– the immediate response of the lings by controlling ventilation and carbon dioxide excretion.

– bicarbonate reabsorption and hydrogen ion excretion by the kidneys.

 

this buffeer system works by using hydrogen ions to react with bicarbonate to form carbonic acid

this minimizes pH changes.

components of the buffer system

carbonic acid; weak acid (proton donor)

 

bicarbonate; conjugate base ( proton acceptor)

hemoglobin (Hb)

main buffer system inside rbcs. present in high concentrations in rbcs.

 

Hb binds either CO2 or hydrogen ions made from cell metabolism to minimize pH changes in the body.

Reduced Hb

exchange of blood gases.

 

binds, transports, and release O2 to the tissues.

 

binds, transports, and releases carbon dixoide in the lungs

proteins

one of the main buffers inside the cells (intracellular fluid) and plasma ( extracellular fluid)

 

made up of a series of amino acids that have side groups. some of these side groups can regulate acid-base balnace.  they have either a positive or neg charge.

 

negatively charged amino acids can then bind hydrogen ions to help minimize pH balance changes.

phosphate

important buffer system of:

 

Extracellular fluid: RBCs and plasma

 

Intracellular fluid: inside all body cells

 

Kidney: Urine

 

help maintain  and regulate the pH in the extracellular fluid and within cells

 

internal respiration (cells/tissues)
the production of gaseous CO2 from metabolism and the diffusion of this gaseous CO2 into plasma and the RBCs for transport to the lungs
External Respiration (lungs)

Diffusion of gaseous CO2 from plasma and the RBCs to teh alveoli for excretion

 

 

Ventilation

the rate of the air exchange between the lungs.

 

O2 is inhaled, and CO2 is exhaled from the lungs

Partial Pressure
the force exerted by a single gas that is present in a mixture of several gases
Physiological Functions of Respiratory Mechanisms
the respiratory mechanism reacts rapidly to changes in pH along with extracellular buffers
Blood Gas Exchanges

supply oxygen to tissue cells for normal metabolism.

 

maintain normal pH by excreting or retaining CO2

Increasing ventilation

hyperventilation- faster and deeper breathing.

this decreases CO2 and H+ in the extracellular fluid.

 

 

decreasing ventilation

hypoventilation: slower and shallow breathing.

this increases CO2 and H+ in the extracellular fluid.

Cells/ Tissues

end products of aerobic glucose metabolism:

CO2, H20, and ATP

 

for one molecule of glucose metabolized:

O2 is consumed

CO2 is produced

Interstitial Fluid
cells facilitates the duffusion of gaseous carbon dioxide out of the cells and into the interstitial fluid.
plasma

fluid facilitates the diffusion of gaseous carbon dioxide out of the interstitial fluid and into the plasma.

 

as CO2 diffuses into plasma, the plasma Pco2 increases.

This increase in the Pco2 facilitates the diffusion of a large amount (89%) of CO2 inside RBC

 

The small amount (11%) of gaseous CO2 stay in plasma

11%  of gaseous CO2

1% – bound to free amino groups of plasma protein

 

5%- converted to bicarbonate

 

5%- converted to carbonic acid

89% of gaseous CO2

5%- dissolved gaseous CO2

 

21%- bound to globin portion of Hb

 

63%- reacts with water to form carbonic acid

Chloride Shift

the simultaneous exchange of chloride ions into the RBC for bicarbonate ions out of the RBC

 

helps decrease the Pco2 inside the RBCs by removing CO2 as bicarbonate ions

How is most carbon dioxide transported
most of the carbon dioxide is transported to the lings in plasma as bicarbonate ions
Carbon Anhydrase
catalyzes the reaction of the dissociation of Carbonic Acid into H20 and CO2
Transport of Oxygen

oxygen doesnt easily dissolve in water

1.5% of inhaled O2 is dissolved in plasma.

 

98.5% of blood O2 is bound to hemoglobin inside the RBC

 

Oxygen binding and release from Hb

oxyhemoglobin is the primary form of transport of oxygen

 

 

Oxygen Saturation

the estent of oxygen binding to hemoglobin

 

 

100% Saturation
all four iron-heme binding sites in all hemoglobin moelcules present are bound by oxygen
Factors that effect the Po2 of blood

Increases in blood flow to the tissues

 

cells use oxygen to carry out metabolic reactions

factors that affect O2 binding to Hb:

 

Bohr Effect

– changes in pH CO2 H+

 

– acids produced from cell metabolism

– excretion of acids as CO2 in the lungs

 

temperture

Acids produced from cell metabolism

Lactic acid from excercise and oxidation of pruvate

 

carbonic acid from glucose metabolism

 

acids produced from metabolism increases both carbon dioxide and hydrogen ion concentrations

Factors that affect oxygen binding to Hb:

 

Temperature

generated from cell metabolism and muscle contraction

 

elevated body temps increases metabolism, delivery of oxygen to the cells, and release of O2 from Hb

 

Lower body temperature decreases metabolism, deliver of oxygen to the cells, and release of O2 from Hb

Factors that affect oxygen binding to Hb:

 

2,3- Diphosphglycerate

found inside RBCs

 

metabolic by product of glucose metabolism

 

regulated by: high altitiudes and body hormones (thryoxine, growth homrone, epinephrine, norepinepherine, and testosterone)

 

facilitates O2 release from Hb by binding two beta chains of Hb

 

more O2 is then readily available to cells

Renal Mechanism Properties

reacts slowly to changes in pH ( min to hrs) and persist longer than the other acid base mechanisms

 

helps maintain the pH of urine between 4.5-8.0

 

excretes acids as hydrogen ions (acidic urine) and base a bicarbonate ions ( basic urine)

Excretion of acids involves:

hydorgen ions neutralized by buffer systems  found in urine: bicarbonate- carbonic acid, ammonia-ammonium, phosphate, urate and citrate

 

reabsorption of bicarbonate into blood

 

generation and reabsorption of bicarbonate into blood

two unrinary buffer systems

phosphate buffer

 

ammonia- ammonium buffer

– account for 60% excretion of hydrogen ions from acids in the form ammonium ion

 

both gaseous ammonia and hydrogen ions aer then excreted into urine

How does kidney’s control changes in pH

increases excretion of acids and reabsorption of bicarbonate when the pH decreases

;

decreasing excretion of acids and increasing excretion of bicarbonate when pH increased

Serum Electrolytes

in acid- base imbalances screening test along with arterial blood gas (ABG)

;

Measures the conc. of key electrolytes in the body: Na+, Cl-, K+, and HCO3-

;

bicarbonate conc. is reported as total CO2 in a serum electrolyte test

Anion Gap

;a drect measure of the conecetration of unmeasured acid anions in blood

;

calucalated as the difference between the measured cations and the measured anions

;

increase in the anion gap result indicates metabolic acidosis

anion gap; 12mmol/L

Arterial Blood Gas

test measures acid-base balance and oxygenation status in the blood.

;

Evaluates gas exchiange in the lungs by measuring the dissolved gases in arterial blood as: pH Po2 and So2

testing pH

screening test

;

reference range: 7.35-7.45

Bicarbonate

caulated from abg results using Henderson Hasselbach equation

;

pH= Pka+log([hco3]/[h2co3])= 6.1+ (log[hco3]/(Pco2 x 0.0301))

;Testing oxygen(Po2)
measuures the amount of oxygen dissolved in the blood as Po2.
Testing Carbon Dioxide
Measures how much gaseous carbon dioxide is dissolved in the blood as Pco2.
Testing Oxygen Saturation;

Measures how much oxygen hemoglobin is carrying as a percentage of the maxium it could carry

;

formula:

;

So2= [Hb-O2]/[Hb-O2]+[Hb] x 100%= [Oxyhemoglobin]/Total Hb x 100%

Timing for running samples

Samples should be analyazed immediately.

;

if it is not analyzed within 30 minutes, it shoul be sotred on ices and analyzed within one hour from collection of sample

Why are arterial blood gases performed less frequently?

painful procedure due to puncture site

;

preanalytical errors due to puncture sites

preanalyticals errors with abgs

air bubbles in sample: increases oxygen adn decreased carbon dioxide

;

too much anticoagulant- dilutes blood and increases Pco2

;

improper mixng of sample with anticoagulant or clotting of sample- incorrect results

;

improper storage during transport lowers the pH due to glycolysis- increase carbon dixoide, decrease oxygen

;

indentification and handling of collected samples

;

improper calibration and maintenance of instrumentation

;

collecting venous blood rather arterial blood

Base excess

measures all buffers in the blood: Hb, proteins, phosphate, and bicarbonate-carbonic acid

;

it measures the deviation of all blood buffers in a patient sample.

;

Base excess is affected by blood lactate and organic acids that accumlulate during and after excercise.

;

a positive value is also called “base deficit”

;

a negative value indicates acidosis

;

A positive value base indicates alkalosis

Clinical Significance

;

Acidosis/ Acidemia

excess amount of acids in the blood is a result of

;

increased acid production from metabolism

;

decreased acid excretion via the lungs or kidneys

;

increased excretion of base via the kidneys

;

*acidosis occurs when arterial pH falls below 7.35*

Clinical Significance:

;

Alkalosis

excess accumulation of base in the blood as a resultof:

;

decreased excretion of base by the kidneys

;

increased excretion of acids via the lings or kidneys

;

*alkalosis occurs when pH of the blood exceeds 7.45*

Respiratory Acidosis

excess carbon dioxide retention

;

disorders prevent normal excretion of CO2

;

pH ;7.35 and Pco2; 40mm Hg

;

HCO3- ;24 mEq/L

Causes of Respiratory Acidosis

central nervous system depression from drugs, injury, and/or disease

;

asphyxia

;

hypoventilation due to pulmonary, cardiac, musculoskeletal or neuromuscular disease

Respiratory Alkalosis

Excess carbon dixoide excretion

;

pH;7.45 and Pco2 ;40mm Hg

;

HCO3- ; 24 mEq/L

Causes of Respiratory Alkalosis

Hyperventilation due to anxiety, pain, or improper ventilation settings

;

Respiratory stimulation by drugs, disease, hypoxia, fever

;

gram-negative bacterial infections

Metabolic Acidosis

kidneys increase excretion of bicarbonate

;

this causes rentention of acids in the blood

pH;7.35 and Pco2;40mm Hg

Causes of Metabolic Acidosis

Bicarbonate depletion due to renal disease, dirrhea

;

Excessive production of organic acids due to liver disease

;

Endocrine disorders including diabetes mellitus, hypoxia, shock, and drug toxicity

metabolic alkalosis

kidneys decrease excretion of bicarbonate

;

this causes excretion of acids from the blood

;

pH;7.45 and Pco2; 40mm Hg

;

HCO3- ;24mEq/L

;

Causes of metabolic Alkalosis

Excessive excretion of acids due to renal disease

;

loss of gastric hydrochloric acid from prolonged vomiting of gastric sunctioning;

;

;loss of potassium due to increase renal excretion as a result of diurectics or steroid use.

;

excessive alkali ingestions (antacid)

Lactic Acidosis

* the most common type of metabolic acidosis*

;

excess production or diminish removal of lactic acid from the blood

;

;

Type A lactic acidosis

caused by inadequate Oxygen delivery

;

caused by: shock, cardiac arrest, severe anemia, carbon monoxide poisoning, and hypoxia

Type B lactic Acidosis

has adequate oxygen delivery

;

caused by: epileptic seizures, cyanide poisoning, strokes, uncontrolled diabetes mellitus, and liver failure

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