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Acid and Base Balance Acid and Base Balance and Imbalanceand Imbalance

pH ReviewpH Review

pH = - log [HpH = - log [H++]] HH+ + is really a proton is really a proton Range is from 0 - 14Range is from 0 - 14 If [HIf [H++] is high, the solution is ] is high, the solution is

acidic; pH < 7acidic; pH < 7 If [HIf [H++] is low, the solution is basic ] is low, the solution is basic

or alkaline ; pH > 7or alkaline ; pH > 7

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Acids are HAcids are H+ + donors.donors. Bases are HBases are H+ + acceptors, or give up OHacceptors, or give up OH-- in in

solution.solution. Acids and bases can be:Acids and bases can be:

– Strong – dissociate completely in Strong – dissociate completely in solution solution HCl, NaOHHCl, NaOH

– Weak – dissociate only partially in Weak – dissociate only partially in solutionsolution Lactic acid, carbonic acidLactic acid, carbonic acid

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The Body and pHThe Body and pH

Homeostasis of pH is tightly Homeostasis of pH is tightly controlledcontrolled

Extracellular fluid = 7.4Extracellular fluid = 7.4 Blood = 7.35 – 7.45Blood = 7.35 – 7.45 < 6.8 or > 8.0 death occurs< 6.8 or > 8.0 death occurs Acidosis (acidemia) below 7.35Acidosis (acidemia) below 7.35 Alkalosis (alkalemia) above 7.45Alkalosis (alkalemia) above 7.45

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Small changes in pH can Small changes in pH can produce major produce major disturbancesdisturbances Most enzymes function only with Most enzymes function only with

narrow pH rangesnarrow pH ranges Acid-base balance can also affect Acid-base balance can also affect

electrolytes (Naelectrolytes (Na++, K, K++, Cl, Cl--)) Can also affect hormonesCan also affect hormones

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The body produces more The body produces more acids than basesacids than bases

Acids take in with foodsAcids take in with foods Acids produced by metabolism of Acids produced by metabolism of

lipids and proteinslipids and proteins Cellular metabolism produces Cellular metabolism produces

COCO22..

COCO2 2 + H + H220 0 ↔↔ H H22COCO33 ↔↔ H H++ + + HCOHCO33

--

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Control of Control of AcidsAcids

1.1. Buffer systemsBuffer systems

Take up H+ or release H+ as Take up H+ or release H+ as conditions changeconditions change

Buffer pairs – weak acid and a baseBuffer pairs – weak acid and a base

Exchange a strong acid or base for a Exchange a strong acid or base for a weak oneweak one

Results in a much smaller pH changeResults in a much smaller pH change

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Bicarbonate bufferBicarbonate buffer

Sodium Bicarbonate (NaHCOSodium Bicarbonate (NaHCO33) and ) and carbonic acid (Hcarbonic acid (H22COCO33))

Maintain a 20:1 ratio : HCOMaintain a 20:1 ratio : HCO33- - : H: H22COCO33

HCl + NaHCOHCl + NaHCO33 ↔ ↔ HH22COCO3 3 + NaCl + NaCl

NaOH + HNaOH + H22COCO3 3 ↔ ↔ NaHCONaHCO33 + H + H22OO

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Phosphate bufferPhosphate buffer

Major intracellular bufferMajor intracellular buffer HH++ + HPO + HPO44

2-2- ↔↔ H H22PO4PO4--

OHOH-- + H + H22POPO44-- ↔↔ H H22O + HO + H22POPO44

2-2-

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Protein BuffersProtein Buffers Includes hemoglobin, work in Includes hemoglobin, work in

blood and ISFblood and ISF Carboxyl group gives up HCarboxyl group gives up H++ Amino Group accepts HAmino Group accepts H++

Side chains that can buffer HSide chains that can buffer H++ are are present on 27 amino acids.present on 27 amino acids.

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Respiratory Respiratory mechanismsmechanisms Exhalation of carbon dioxideExhalation of carbon dioxide Powerful, but only works with Powerful, but only works with volatile volatile

acidsacids Doesn’t affect Doesn’t affect fixed acidsfixed acids like lactic like lactic

acidacid COCO2 2 + H + H220 0 ↔↔ H H22COCO33 ↔↔ H H++ + HCO + HCO33

--

Body pH can be adjusted by changing Body pH can be adjusted by changing rate and depth of breathingrate and depth of breathing

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Kidney excretionKidney excretion

Can eliminate large amounts of Can eliminate large amounts of acidacid

Can also excrete baseCan also excrete base Can conserve and produce bicarb Can conserve and produce bicarb

ionsions Most effective regulator of pHMost effective regulator of pH If kidneys fail, pH balance failsIf kidneys fail, pH balance fails

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Rates of correctionRates of correction

Buffers function almost Buffers function almost instantaneouslyinstantaneously

Respiratory mechanisms take Respiratory mechanisms take several minutes to hoursseveral minutes to hours

Renal mechanisms may take Renal mechanisms may take several hours to daysseveral hours to days

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Acid-Base ImbalancesAcid-Base Imbalances

pH< 7.35 acidosispH< 7.35 acidosis pH > 7.45 alkalosispH > 7.45 alkalosis The body response to acid-base The body response to acid-base

imbalance is called imbalance is called compensationcompensation May be May be completecomplete if brought back if brought back

within normal limitswithin normal limits Partial compensationPartial compensation if range is if range is

still outside norms.still outside norms.1818

CompensationCompensation

If underlying problem is If underlying problem is metabolic, hyperventilation or metabolic, hyperventilation or hypoventilation can help : hypoventilation can help : respiratory compensationrespiratory compensation..

If problem is respiratory, renal If problem is respiratory, renal mechanisms can bring about mechanisms can bring about metabolic compensation.metabolic compensation.

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AcidosisAcidosis Principal effect of acidosis is depression of the Principal effect of acidosis is depression of the

CNS through CNS through ↓↓ in synaptic transmission. in synaptic transmission. Generalized weaknessGeneralized weakness Deranged CNS function the greatest threatDeranged CNS function the greatest threat Severe acidosis causes Severe acidosis causes

– DisorientationDisorientation– coma coma – deathdeath

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AlkalosisAlkalosis Alkalosis causes over excitability of the Alkalosis causes over excitability of the

central and peripheral nervous systems.central and peripheral nervous systems. NumbnessNumbness LightheadednessLightheadedness It can cause :It can cause :

– NervousnessNervousness– muscle spasms or tetany muscle spasms or tetany – Convulsions Convulsions – Loss of consciousnessLoss of consciousness– DeathDeath

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Respiratory AcidosisRespiratory Acidosis Carbonic acid excess Carbonic acid excess caused by blood caused by blood

levels of COlevels of CO22 above 45 mm Hg. above 45 mm Hg. HypercapniaHypercapnia – high levels of CO – high levels of CO2 2 in in

bloodblood Chronic conditions:Chronic conditions:

– Depression of respiratory center in brain Depression of respiratory center in brain that controls breathing rate – drugs or head that controls breathing rate – drugs or head traumatrauma

– Paralysis of respiratory or chest musclesParalysis of respiratory or chest muscles– EmphysemaEmphysema

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Respiratory AcidosisRespiratory Acidosis

Acute conditons:Acute conditons:– Adult Respiratory Distress SyndromeAdult Respiratory Distress Syndrome– Pulmonary edemaPulmonary edema– PneumothoraxPneumothorax

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Compensation for Compensation for Respiratory AcidosisRespiratory Acidosis

Kidneys eliminate hydrogen ion Kidneys eliminate hydrogen ion and retain bicarbonate ionand retain bicarbonate ion

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Signs and Symptoms of Signs and Symptoms of Respiratory AcidosisRespiratory Acidosis BreathlessnessBreathlessness RestlessnessRestlessness Lethargy and disorientationLethargy and disorientation Tremors, convulsions, comaTremors, convulsions, coma Respiratory rate rapid, then gradually Respiratory rate rapid, then gradually

depresseddepressed Skin warm and flushed due to Skin warm and flushed due to

vasodilation caused by excess COvasodilation caused by excess CO22

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Treatment of Respiratory Treatment of Respiratory AcidosisAcidosis

Restore ventilationRestore ventilation IV lactate solutionIV lactate solution Treat underlying dysfunction or Treat underlying dysfunction or

diseasedisease

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Respiratory AlkalosisRespiratory Alkalosis

Carbonic acid deficitCarbonic acid deficit pCOpCO22 less than 35 mm Hg less than 35 mm Hg

(hypocapnea)(hypocapnea) Most common acid-base Most common acid-base

imbalanceimbalance Primary cause is hyperventilationPrimary cause is hyperventilation

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Respiratory AlkalosisRespiratory Alkalosis Conditions that stimulate respiratory Conditions that stimulate respiratory

center:center:– Oxygen deficiency at high altitudesOxygen deficiency at high altitudes– Pulmonary disease and Congestive heart Pulmonary disease and Congestive heart

failure – caused by hypoxia failure – caused by hypoxia – Acute anxietyAcute anxiety– Fever, anemiaFever, anemia– Early salicylate intoxicationEarly salicylate intoxication– CirrhosisCirrhosis– Gram-negative sepsisGram-negative sepsis

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Compensation of Compensation of Respiratory AlkalosisRespiratory Alkalosis

Kidneys conserve hydrogen ionKidneys conserve hydrogen ion Excrete bicarbonate ionExcrete bicarbonate ion

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Treatment of Respiratory Treatment of Respiratory AlkalosisAlkalosis

Treat underlying causeTreat underlying cause Breathe into a paper bagBreathe into a paper bag IV Chloride containing solution – IV Chloride containing solution –

ClCl- - ions replace lost bicarbonate ions replace lost bicarbonate ionsions

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Metabolic AcidosisMetabolic Acidosis Bicarbonate deficit Bicarbonate deficit - blood - blood

concentrations of bicarb drop below concentrations of bicarb drop below 22mEq/L22mEq/L

Causes:Causes:– Loss of bicarbonate through diarrhea Loss of bicarbonate through diarrhea

or renal dysfunctionor renal dysfunction– Accumulation of acids (lactic acid or Accumulation of acids (lactic acid or

ketones)ketones)– Failure of kidneys to excrete H+Failure of kidneys to excrete H+

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Symptoms of Metabolic Symptoms of Metabolic AcidosisAcidosis

Headache, lethargyHeadache, lethargy Nausea, vomiting, diarrheaNausea, vomiting, diarrhea ComaComa DeathDeath

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Compensation for Compensation for Metabolic AcidosisMetabolic Acidosis

Increased ventilationIncreased ventilation Renal excretion of hydrogen ions Renal excretion of hydrogen ions

if possibleif possible KK++ exchanges with excess H exchanges with excess H++ in in

ECFECF ( H( H++ into cells, K into cells, K++ out of cells) out of cells)

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Treatment of Metabolic Treatment of Metabolic AcidosisAcidosis

IV lactate solution, producing an IV lactate solution, producing an alkalizing effect alkalizing effect

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Metabolic AlkalosisMetabolic Alkalosis Bicarbonate excessBicarbonate excess - concentration in - concentration in

blood is greater than 26 mEq/Lblood is greater than 26 mEq/L Causes:Causes:

– Excess vomiting = loss of stomach acidExcess vomiting = loss of stomach acid– Excessive use of alkaline drugsExcessive use of alkaline drugs– Certain diureticsCertain diuretics– Endocrine disordersEndocrine disorders– Heavy ingestion of antacidsHeavy ingestion of antacids– Severe dehydrationSevere dehydration

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Compensation for Metabolic Compensation for Metabolic AlkalosisAlkalosis

Alkalosis most commonly occurs Alkalosis most commonly occurs with renal dysfunction, so can’t with renal dysfunction, so can’t count on kidneyscount on kidneys

Respiratory compensation difficult Respiratory compensation difficult – hypoventilation limited by – hypoventilation limited by hypoxiahypoxia

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Symptoms of Metabolic Symptoms of Metabolic AlkalosisAlkalosis

Respiration slow and shallowRespiration slow and shallow Hyperactive reflexes ; tetanyHyperactive reflexes ; tetany Often related to depletion of Often related to depletion of

electrolyteselectrolytes Atrial tachycardiaAtrial tachycardia Dysrhythmias (aka arrhythmia)Dysrhythmias (aka arrhythmia)

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Treatment of Metabolic Treatment of Metabolic AlkalosisAlkalosis

Electrolytes to replace those lostElectrolytes to replace those lost IV chloride containing solutionIV chloride containing solution Treat underlying disorderTreat underlying disorder

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Diagnosis of Acid-Base Diagnosis of Acid-Base ImbalancesImbalances

1.1. Note whether the pH is low (acidosis) Note whether the pH is low (acidosis) or high (alkalosis)or high (alkalosis)

2.2. Decide which value, pCODecide which value, pCO22 or HCO or HCO33-- , ,

is outside the normal range is outside the normal range andand could be thecould be the cause cause of the problem. If of the problem. If the cause is a change in pCOthe cause is a change in pCO2, 2, the the problem is respiratory. If the cause is problem is respiratory. If the cause is HCO HCO33

-- the problem is metabolic. the problem is metabolic.

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3. Look at the value that doesn’t 3. Look at the value that doesn’t correspond to the observed pH correspond to the observed pH change. If it is inside the normal change. If it is inside the normal range, there is no compensation range, there is no compensation occurring. If it is outside the normal occurring. If it is outside the normal range, the body is partially range, the body is partially compensating for the problem.compensating for the problem.

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ExampleExample A patient is in intensive care A patient is in intensive care

because he suffered a severe because he suffered a severe myocardial infarction 3 days ago. myocardial infarction 3 days ago. The lab reports the following values The lab reports the following values from an arterial blood sample:from an arterial blood sample:– pH 7.3pH 7.3– HCO3- = 20 mEq / L ( 22 - 26)HCO3- = 20 mEq / L ( 22 - 26)– pCO2 = 32 mm Hg (35 - 45)pCO2 = 32 mm Hg (35 - 45)

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DiagnosisDiagnosis

Metabolic acidosisMetabolic acidosis With compensationWith compensation

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