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8/9/2019 Acid and Base Imbalance
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Acid and Base Balance andImbalance
8/9/2019 Acid and Base Imbalance
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pH Review
pH = - log [ H+]H+ is really a proton
Range is from 0 - 14If [H+] is high, the solution is acidic; pH < 7If [H+] is low, the solution is basic or
alkaline ; pH > 7
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Acids are H+ donors.Bases are H+ acce p tors, or give u p OH- insolution.Acids and bases can be: ± Strong ± dissociate com p letely in
solutionHC l, NaO H
± Weak ± dissociate only partially insolution
Lactic acid, carbonic acid
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T he Body and pH
Homeostasis of pH is tightly controlledExtracellular fluid = 7.4
Blood = 7. 35 ± 7.4 5< 6 .8 or > 8.0 death occursAcidosis (acidemia) below 7. 35
Alkalosis (alkalemia) above 7.4 5
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Small changes in pH can produce
major disturbancesMost enzymes function only with narrowpH ranges
Acid-base balance can also affectelectrolytes (Na +, K+, C l-)Can also affect hormones
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T he body produces more acids
than basesAcids take in with foodsAcids p roduced by metabolism of li p ids
and p roteinsCellular metabolism produces CO 2.CO 2 + H20 H2CO 3 H+ + HC O 3
-
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Control of Acids
1. Buffer systemsT ake u p H+ or release H+ as conditions
changeBuffer pairs ± weak acid and a baseExchange a strong acid or base for a
weak oneResults in a much smaller pH change
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Bicarbonate buffer
Sodium Bicarbonate (Na HC O 3 ) andcarbonic acid ( H2CO 3 )
Maintain a 20:1 ratio : HC O 3-
: H2CO 3
HC l + Na HC O 3 H2CO 3 + Na C l
NaO H + H2CO 3 Na HC O 3 + H2O
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P hos phate buffer
Major intracellular buffer H+ + HP O 4
2 - H2P O4 -
OH- + H2P O 4- H2O + H2P O 4
2 -
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P rotein Buffers
Includes hemoglobin, work in blood and ISFCarboxyl grou p gives u p H+
Amino Grou p acce p ts H+
Side chains that can buffer H+ are p resent on27 amino acids.
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2 . Res p iratory mechanisms
Exhalation of carbon dioxideP owerful, but only works with volatile
acidsDoesn¶t affect fixed acids like lactic acidCO 2 + H20 H2CO 3 H+ + HC O 3
-
Body pH can be adjusted by changing rateand de p th of breathing
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3 . Kidney excretion
Can eliminate large amounts of acidCan also excrete base
Can conserve and p roduce bicarb ionsMost effective regulator of pHIf kidneys fail, pH balance fails
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Rates of correction
Buffers function almost instantaneouslyRes p iratory mechanisms take several
minutes to hoursRenal mechanisms may take severalhours to days
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Acid-Base Imbalances
pH < 7. 35 acidosispH > 7.4 5 alkalosis
T he body res ponse to acid-baseimbalance is called compensationMay be complete if brought back within
normal limitsPartial compensation if range is stilloutside norms.
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Com pensation
If underlying problem is metabolic,hyperventilation or hy poventilation canhel p : respiratory compensation .If problem is res p iratory, renalmechanisms can bring about metaboliccompensation.
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Alkalosis
Alkalosis causes over excitability of the centraland peripheral nervous systems.NumbnessLightheadedness
It can cause : ± Nervousness ± muscle s pasms or tetany ± Convulsions ± Loss of consciousness ± Death
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Res p iratory Acidosis
C arbonic acid excess caused by bloodlevels of CO 2 above 4 5 mm Hg.Hypercapnia ± high levels of CO 2 in bloodChronic conditions: ± De pression of res p iratory center in brain that
controls breathing rate ± drugs or head
trauma ± P aralysis of res p iratory or chest muscles ± Em physema
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Res p iratory Acidosis
Acute conditons: ± Adult Res p iratory Distress Syndrome
± P ulmonary edema ± P neumothorax
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Com pensation for Res p iratory Acidosis
Kidneys eliminate hydrogen ion and retainbicarbonate ion
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Signs and Sym p toms of Res p iratory Acidosis
BreathlessnessRestlessness
Lethargy and disorientationT remors, convulsions, comaRes p iratory rate ra p id, then graduallyde pressedSkin warm and flushed due to vasodilationcaused by excess CO 2
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T reatment of Res p iratory Acidosis
Restore ventilationIV lactate solution
T reat underlying dysfunction or disease
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Res p iratory Alkalosis
Carbonic acid deficitpC O 2 less than 35 mm Hg (hy poca pnea)
Most common acid-base imbalanceP rimary cause is hy perventilation
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Com pensation of Res p iratory Alkalosis
Kidneys conserve hydrogen ionExcrete bicarbonate ion
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T reatment of Res p iratory Alkalosis
T reat underlying causeBreathe into a pa per bag
IVChloride containing solution ± C l-ions
re p lace lost bicarbonate ions
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Metabolic Acidosis
B icarbonate deficit - blood concentrations of bicarb dro p below 22 mEq/L
Causes: ± Loss of bicarbonate through diarrhea or renaldysfunction
± Accumulation of acids (lactic acid or ketones) ± Failure of kidneys to excrete H+
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Sym p toms of Metabolic Acidosis
Headache, lethargyNausea, vomiting, diarrhea
ComaDeath
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Com pensation for Metabolic Acidosis
Increased ventilationRenal excretion of hydrogen ions if
possibleK+ exchanges with excess H+ in E CF(H+ into cells, K + out of cells)
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T reatment of Metabolic Acidosis
IV lactate solution
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Metabolic Alkalosis
B icarbonate excess - concentration inblood is greater than 26 mEq/LCauses: ± Excess vomiting = loss of stomach acid ± Excessive use of alkaline drugs ± Certain diuretics
± Endocrine disorders ± Heavy ingestion of antacids ± Severe dehydration
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Com pensation for Metabolic Alkalosis
Alkalosis most commonly occurs withrenal dysfunction, so can¶t count onkidneysRes p iratory com pensation difficult ±hypoventilation limited by hy poxia
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Sym p toms of Metabolic Alkalosis
Res p iration slow and shallowHyperactive reflexes ; tetany
Often related to de p letion of electrolytesAtrial tachycardiaDysrhythmias
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T reatment of Metabolic Alkalosis
Electrolytes to re p lace those lostIV chloride containing solution
T reat underlying disorder
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Diagnosis of Acid-Base Imbalances
1. Note whether the pH is low (acidosis) or high (alkalosis)
2 . Decide which value, pC O 2 or HC O 3
-
, isoutside the normal range and could bethe cause of the p roblem. If the cause isa change in pC O 2 , the p roblem isres p iratory. If the cause is HC O 3 - thep roblem is metabolic.
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3 . Look at the value that doesn¶t corres pondto the observed pH change. If it is insidethe normal range, there is nocom pensation occurring. If it is outside thenormal range, the body is partially
com pensating for the p roblem.
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Exam p le
Apatient is in intensive care because hesuffered a severe myocardial infarction 3 days ago. T he lab re ports the followingvalues from an arterial blood sam p le: ± pH 7. 3
± HC O 3 - = 20 mEq / L ( 22 - 26 )
± pC O2 = 3 2 mm Hg ( 35 - 45 )
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Diagnosis
Metabolic acidosisWith com pensation