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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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