ACID BASE ACID BASE BALANCEBALANCE

ACID BASE BALANCE ACID BASE BALANCE General PrinciplesGeneral Principles

– Dynamic relationship which reflects the Dynamic relationship which reflects the concentration of hydrogen (H+) ionsconcentration of hydrogen (H+) ions

– Hydrogen ions are acids which must be maintained Hydrogen ions are acids which must be maintained within strict limitswithin strict limits

» Any deviation from norm affects biochemical eventsAny deviation from norm affects biochemical events

– Measured in a negative log (pH) which is inversely Measured in a negative log (pH) which is inversely proportional to the hydrogen ion concentrationproportional to the hydrogen ion concentration

» High H+ ion concentration = Low pHHigh H+ ion concentration = Low pH

» Low H+ ion concentration = High pHLow H+ ion concentration = High pH

THE pH SCALETHE pH SCALE

Most frequently used measure of acid base balanceMost frequently used measure of acid base balance Ranges from 1-14Ranges from 1-14

– 1 means only hydrogen ions present1 means only hydrogen ions present– 14 means no hydrogen ions present14 means no hydrogen ions present– pH of water is 7.0 (neutral)pH of water is 7.0 (neutral)

pH of human body is 7.35-7.45pH of human body is 7.35-7.45 pH compatible with life = 6.9-7.8pH compatible with life = 6.9-7.8

– pH of < 7.35 indicates a state of acidosispH of < 7.35 indicates a state of acidosis– pH of > 7.45 indicates a state of alkalosispH of > 7.45 indicates a state of alkalosis– Variation of 0.4 in either direction can be fatalVariation of 0.4 in either direction can be fatal

Acid-Base BalanceAcid-Base Balance

A pH below 7.35 is A pH below 7.35 is referred to as referred to as acidosisacidosis

A pH above 7.45 is A pH above 7.45 is referred to as referred to as alkalosisalkalosis

Body constantly produces acids through metabolismBody constantly produces acids through metabolism– Carbon dioxideCarbon dioxide– Metabolic acids (lactic and pyruvic acid)Metabolic acids (lactic and pyruvic acid)

Acids must be constantly eliminated from the bodyAcids must be constantly eliminated from the body– As acids increase, bodily functions decreaseAs acids increase, bodily functions decrease– ExampleExample

» Diminishes myocardial contractilityDiminishes myocardial contractility» Reduces vascular response to catecholaminesReduces vascular response to catecholamines» Interferes with the actions of pharmacological Interferes with the actions of pharmacological

agentsagents

BUFFER SYSTEMBUFFER SYSTEM Fastest acting defense mechanism (seconds)Fastest acting defense mechanism (seconds) Chief buffer is bicarbonateChief buffer is bicarbonate

– Bicarbonate combines with excess hydrogen ions to form Bicarbonate combines with excess hydrogen ions to form carbonic acid in a dynamic relationship:carbonic acid in a dynamic relationship:

HCO3 + H+ <--------> H2CO3HCO3 + H+ <--------> H2CO3

– For every molecule of carbonic acid, there are 20 molecules For every molecule of carbonic acid, there are 20 molecules of bicarbonateof bicarbonate

– Any change in 20:1 ratio is immediately corrected to Any change in 20:1 ratio is immediately corrected to maintain pHmaintain pH

» An increase in H+ causes an increase in H2CO3An increase in H+ causes an increase in H2CO3

» A decrease in H+ causes a decrease in H2CO3A decrease in H+ causes a decrease in H2CO3

Bicarbonate Buffer SystemBicarbonate Buffer System

Fastest mechanism Fastest mechanism Hydrogen will bind with bicarbonateHydrogen will bind with bicarbonate Results in formation of carbonic acidResults in formation of carbonic acid

acidcarbonicionebicarbonationHydrogen

COHHCOH 323

Carbonate Buffer SystemCarbonate Buffer System

An increase in hydrogen ions leads to an An increase in hydrogen ions leads to an increase in carbonic acid. increase in carbonic acid.

A deficit in hydrogen ions (alkalosis); carbonic A deficit in hydrogen ions (alkalosis); carbonic acid will dissociate into bicarbonate ion and acid will dissociate into bicarbonate ion and hydrogen ion hydrogen ion

323

323

COHHCOH:AcidDecreased

COHHCOH:AcidIncreased

BUFFER SYSTEM (CONT.)BUFFER SYSTEM (CONT.) Carbonic acid is a weak, volatile acid Carbonic acid is a weak, volatile acid

which must be eliminatedwhich must be eliminated Enzyme carbonic anhydrase catalyzes Enzyme carbonic anhydrase catalyzes

the carbonic acid to convert to carbon the carbonic acid to convert to carbon dioxide and water: H2CO3--------->CO2 dioxide and water: H2CO3--------->CO2 + H2O+ H2O

CO2 and H2O are easily eliminated by CO2 and H2O are easily eliminated by the lungs and kidneysthe lungs and kidneys

Functions within minutes (1-3)Functions within minutes (1-3) Lungs eliminate excess CO2 by Lungs eliminate excess CO2 by

increasing respirations, causing a increasing respirations, causing a decrease in H+ ion and an increase in pHdecrease in H+ ion and an increase in pH

Lungs can retain more CO2 by Lungs can retain more CO2 by decreasing respirations, causing an decreasing respirations, causing an increase in H+ ions and a decrease in pHincrease in H+ ions and a decrease in pH

Respiratory MechanismsRespiratory Mechanisms Increased respirations cause increased elimination of COIncreased respirations cause increased elimination of CO2 2

and Hand H22O.O.– An increase in pHAn increase in pH

Decreased respirations cause retention of CODecreased respirations cause retention of CO2 2 and Hand H22O. O. – Decreasing pHDecreasing pH

Slowest onset and generally important in Slowest onset and generally important in long term maintenance of acid-base long term maintenance of acid-base balance (hours to days)balance (hours to days)

FunctionFunction– Kidneys retain bicarbonate, causing a Kidneys retain bicarbonate, causing a

decrease in H+ ions and an increase in pHdecrease in H+ ions and an increase in pH– Kidneys excrete bicarbonate, causing an Kidneys excrete bicarbonate, causing an

increase in H+ ions and a decrease in pHincrease in H+ ions and a decrease in pH

Respiratory AcidosisRespiratory Acidosis

Caused by abnormal retention of COCaused by abnormal retention of CO22 from from

impaired ventilation due to problems impaired ventilation due to problems occurring in the lungs or respiratory center occurring in the lungs or respiratory center of the brainof the brain

Respiration = CO2 + H2O H2CO3 H+ + HCO3-

Caused by increased respiration and excessive elimination of CO2

The CO2 level is decreased and the pH is increased.

Respiratory AlkalosisRespiratory Alkalosis

Respiration = CO2 + H2O H2CO3 H+ + HCO3-

ACID-BASE ACID-BASE DERANGEMENTS (CONT.)DERANGEMENTS (CONT.)

Metabolic acidosisMetabolic acidosis

– Increased production of acids (lactic and pyruvic)Increased production of acids (lactic and pyruvic)

– Can also result from diarrhea, vomiting, diabetes and Can also result from diarrhea, vomiting, diabetes and medications (ASA)medications (ASA)

– pH is decreased and CO2 level is normalpH is decreased and CO2 level is normal

– Treatment is aimed at improving ventilations to eliminate Treatment is aimed at improving ventilations to eliminate CO2CO2

– Sodium bicarbonate with documented metabolic acidosisSodium bicarbonate with documented metabolic acidosis

» Rarely administered during initial resuscitative Rarely administered during initial resuscitative strategiesstrategies

ACID-BASE ACID-BASE DERANGEMENTS (CONT.)DERANGEMENTS (CONT.)

Metabolic alkalosisMetabolic alkalosis– Caused by increased vomiting, overdosing on Caused by increased vomiting, overdosing on

antiacids, diureticsantiacids, diuretics– pH is increased and CO2 remains normalpH is increased and CO2 remains normal– Treatment is aimed at underlying causeTreatment is aimed at underlying cause

CombinationsCombinations– Any combination of acid-base derangementsAny combination of acid-base derangements– Only ABG can accurately diagnose problemOnly ABG can accurately diagnose problem

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