acid base disorder.pdf

7/26/2019 Acid base disorder.pdf

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Acid base disorder

Tim dosen patologi


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The concept of acid base balance

Acid-base balance refers to the mechanisms

the body uses to keep its fluids close to neutral

pH (that is, neither basic nor acidic) so that thebody can function normally.

Arterial blood pH is normally closely

regulated to between 7.35 and 7.45.


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Any ionic or molecular

substance that can act as a

proton donor.

Strong acidHCl, H2SO4, H3PO4.Weak acidH2CO3, CH3COOH.

acids?? bases??

Any ionic or molecular

substance that can act as a

proton acceptor.

Strong alkaliNaOH, KOH.Weak alkaliNaHCO3, NH3,CH3COONa.


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Lactic acidKetone bodies

Sulfuric acid

Phosphoric acid

Intracellular metabolism

Volatileacids

300~400L CO2 (15molH+)

Fixedacids

50~100 mmol H+

NH3, sodium citrate, sodium lactate

Origin of acids Much more

Origin of bases less

CO2+H2O=H2CO3


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ACID BASE BALANCE ANDREGULATION


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pH

pH of ECF is between 7.35 and 7.45.Deviations, outside this range affectmembrane function, alter protein function,etc.

You cannot survive with a pH 7.7 Acidosis- below 7.35 Alkalosis- above 7.45

CNS function deteriorates, coma, cardiacirregularities, heart failure, peripheralvasodilation, drop in BP.


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Given that normal body pH is slightly alkaline and thatnormal metabolism produces acidic waste productssuch as carbonic acid (carbon dioxide reacted withwater) and lactic acid, body pH is constantlythreatened with shifts toward acidity.

In normal individuals, pH is controlled by two majorand related processes pH regulation and pHcompensation.

Regulation is a function of the buffer systems of thebody in combination with the respiratory and renalsystems, whereas compensation requires furtherintervention of the respiratory and/or renal systems torestore normalcy.


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buffering

HA H+ + A

Ka =[ H+ ] [ A

]

[ HA ]

[ H+ ] = Ka

[ HA ]

[ A ]

pH = pKa + lg[ HA ]

[ A

]


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ACID-BASE

BUFFERING

by the body fluids thatimmediately combine with acidsor base to prevent excessive changes in pH

RESPIRATORY

which regulates the removal of volatile CO2as a gas inthe expired air from the plasma and therefore alsoregulates bicarbonate (HCO3

-) from the body fluids viathe pulmonary circulation.

KIDNEYS

which can excrete either acid or alkaline urine, therebyadjusting the pH of the blood.


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H load

ECF Lung ICF Renal Bone

Buffers RBC Respiratoryc

ontrol

Buffers

H+excretion

bicarbonate

reabsorption

Release

bone salt

H K

exchange

Hb

buffers

others

Ca2 H2PO4

In chronic

metabolic

acidosis

H2CO3CO2

Acid

excretion

Expiration

Immediately minutes hours days Very slow


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Buffers system extracellular


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Renal control of acid-base balance

The kidneys control acid-base balance by excretingeither an acidic or basic urine.

The kidney filters large volumes of HCO3-and the extent to

which they are either excreted or reabsorbed determines

the removal of base from the blood. The kidney secretes large numbers of H+into the tubule

lumen, thus removing H+from the blood.

The gain of the adjustment of pH by the kidney and

the acid base balance it regulates is nearly infinite,which means that while it works relatively slowly, it canCOMPLETELY correct for abnormalities in pH.


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The kidneys regulate extracellular fluid pH by secreting H +,reabsorbing HCO3

-, and producing new HCO3-

During alkalosis, excess HCO3- is not bound by H+, and is

excreted, effectively increasing H+in the circulation and

reversing the alkalosis. In acidosis, the kidneys reabsorb all the HCO3

-and produceadditional HCO3

-, which is all added back to the circulationto reverse the acidosis.

H

+

is secreted and HCO3-

reabsorbed in all segments of thekidney except for the thin limbs of the loop of Henle.(however, HCO3

-is not readily permeable through theluminal membrane).


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plasma RBC

Cl transfer

Primarychanging

b buffering

CO2

CO2+ H2O

H2CO3

H+

C l

CAcarbonic anhydrase

CA

CA

C l

HCO3 HCO3

The compensation effect of RBC


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u

Buffers only provide a temporarysolution.

uLung: responds rapidly to altered

plasma H+

concentrations, and keepblood levels under control until thekidneys eliminate the imbalance.

uKidney: are the ultimate H+ions balance.Slow acting mechanisms can eliminateany imbalance in H+levels.


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ACID BASE DISTURBANCE


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An acid base disorder is a change in the normal

value of extracellular pH

When is it happen??

renal or respiratory function is abnormal

an acid or base load overwhelms excretory capacity

Definition of acid-base disorders


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Simple acidbase disorders

Clinical disturbances of acid base metabolism

classically are defined in terms of the

HCO3 /CO2 buffer system.

Acidosis: process that increases[H+]

increasing PCO2or by reducing [HCO3-]

Alkalosis: process that reduces[H+]

reducing PCO2or by increasing [HCO3-]


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Since PCO2 is regulated by respiration,abnormalities that primarily alter the PCO2are referred to as respiratory acidosis (high

PCO2) and respiratory alkalosis (low PCO2). In contrast, [HCO3] is regulated primarily by

renal processes. Abnormalities that primarily

alter the [HCO3] are referred to as metabolicacidosis (low [HCO3]) and metabolicalkalosis (high [HCO3]).


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PaCO2

(Partial Pressure of Carbon Dioxide)

The amount of carbon dioxide dissolved in arterial blood.

Normal: 4.396.25kPa3545 mmHg

Average: 5.32 kPa40 mmHg

Respiratory acidosis: > 45 mmHg

Respiratory alkalosis:


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HCO3-

Normal: 2126 mmHg

Average:24 mmHg

Metabolic acidosis: < 21 mmHg

Metabolic alkalosis: > 26 mmHg


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pH

pH is a measurement of the acidity of the blood, reflectingthe number of hydrogen ions present.

pH = - log [H+]

pH7.45alkalosis

pH7.35acidosis

pH 7.35 - 7.45

Acid-base balance.

Acidosis or alkalosis with complete compensation.A mixed acidosis and alkalosis, both events have opposite

effects on pH, may also have a normal pH.


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assessment of the arterial blood gasprofile >> penilaian pH

appraisal of the pCO2 and [HCO3-] toidentify the primary derangementand compensatory response

assessing the adequacyof thecompensatory response by applyingthe rules of compensation

examine the serum electrolytes andanion gap (AG) and to decidewhether additional testing is required

Step

analisis

kasus


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Compensation

The body response to acid-base imbalance is called

compensation

Complete if brought back within normal limits

Partial compensation if range is still outside norms.

If underlying problem is metabolic, hyperventilation or

hypoventilation can helprespiratory compensation.

If problem is respiratory, renal mechanisms can bring

about metabolic compensation.


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Asidosis

pCO2

HCO3??N : belum terjadi kompensasi

: kompensasi renal (parsial)

: mixed (respiratory &metabolic disorder)

HCO3

PCO2??

N : belum terjadi kompensasi

: kompensasi paru (parsial)

: mixed disorder


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Alkalosis

pCO2

HCO3??N : belum terjadi kompensasi

: mixed (respiratory &metabolic disorder)

: kompensasi renal (parsial)

HCO3

PCO2??

N : belum terjadi kompensasi

: mixed disorder

: kompensasi paru (parsial)


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Metabolic

acidosis

generate

intake

In

creasedAG

Acids Fixed acids

Source

Exclusion

Lactic acidosis

ketoacidosis

Salicylic acidosis

renal failure

Bases

Source

impossible

Loss

From GIdiarrhea

From kidneyproximal/distal tubular acidosis

Consume ammonium chloride have been administered

Primary [HCO3]

NormalAG

AG : anion gap


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Metabolic Acidosis occurs when the kidneys fail to excrete

acids formed in the body, or there is excess ingestion of acids,

or the loss of bases from the body

Renal Tubular Acidosis: due to a defect in H+secretion or

HCO3-reabsroption.

Diarrhea: Excess HCO3-loss into the feces without time to

reabsorb (most common cause).

Diabetes mellitus: In the absence of normal glucose

metabolism the cells metabolize fats and form acetoacetic

acid, reducing pH, and inducing renal acid wasting.

Chronic renal failure: decreased renal function results in acid

build-up in the circulation and reduced HCO3- reabsorption.

Acid ingestion: toxins such as aspirin or methyl alcohol result

in excess acid formation.


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Metabolicalkalosis

Fixed acids

Source

Loss

impossible

From GI vomiting, gastric suction

From kidney

K+or Cldeficiency

Hyperaldosteronism

Cushings syndrome

Diuretic therapy

Bases

Source Alkali administrationNaHCO3sodium lactate .

Exclusion impossible

Primary [HCO3]


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Metabolic Alkalosis: occurs when there is excess retention

of HCO3-or excess loss of H+from the body

Diuretic therapy: many diuretics increase tubular flow,

resulting in increased Na load, increased Na reabsorption

and therefore increased HCO3-reabsorption.

Excess Aldosterone: which promotes excess Nareabsorption and stimulates H+secretion.

Vomiting:loss of the acidic contents of the stomach

creates a depletion of H+which is compensated for by

removing more H+from the circulation.

Ingestion of alkaline drugssuch as NaHCO3-used for

upset stomachs and ulcers.


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Severe

vomiting

Loss of H+

Loss of Cl

Loss of K+

Loss body fluid


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Respiratory Acidosisis the inability of the lungsto eliminate CO2efficiently; so the equilibrium

shifts toward increased H+and HCO3-; therefore,

pH decreases.

Respiratory Alkalosisis excessive loss of CO2

through ventilation driving the equilibrium to theleft away from H+therefore, pH increases.

Respiratory Acidosis: CO2 + H2O H+ + HCO3-

Respiratory Alkalosis: CO2+ H2O H+ + HCO3-


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Respiratoryalkalosis

Respiratoryacidosis

Volatile acid

Exhalationfailure of ventilation

inhalation

inhale CO2 at high concentration

Volatile acidhypoxemia, anxiety, hysteria,

Salicylate intoxication

CNS diseases

Exhalation

Primary [H2CO3 or CO2 ]

Primary [H2CO3 or CO2 ]


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The metabolic or renal regulation of the balance of H+ or

HCO3- excreted will determine if there is a net loss of H+ or

HCO3-, and will determine the pH of the urine.

CO2+ H2O H+ + HCO3

-

Filtered

Secreted

Urine (excreted)

Nephron

Reabsorbed

Note: the renal regulation of the

equilibrium between H+ and CO2takes

place on the right side of the

equation


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Overall, the kidneys must

excrete H+and prevent

the loss of HCO3-.

Filtered HCO3-must react

with secreted H+in order

to be reabsorbed as

H2CO3


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Mixed acidbase disorder

Acidosis + alkalosis in a patient

More than one acid base disturbance present

pH may be normal or abnormal.


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