Acid-Base BalanceAcid-Base Balance

M. Rasjad IndraM. Rasjad Indra

Laboratorium Ilmu FaalLaboratorium Ilmu Faal

FK. UNIBRAWFK. UNIBRAW

Seorang wanita 34 tahun hamil 32 minggu datang ke rumah sakit dengan keluhan muntah-muntah selama dua hari terakhir.

Penderita adalah peminum alkohol berat. Awal muntah terjadi setelah meneguk alkohol dalam jumlah besar, tetapi segera berhenti minum setelah mengalami muntah.

Hasil pemeriksaan darah:

pH : 7,17 (7,35 – 7,45)

PCO2 : 14 mm Hg (23 – 33)

HCO3 : 7 mmol/L (35 – 45)

What is Acid and Base ?What is Acid and Base ?

Acid is Acid is proton (Hproton (H++)) donordonor Base is Base is proton (Hproton (H++)) acceptoracceptor The most important acid in the blood is The most important acid in the blood is

HH22COCO33

The most important base is The most important base is HCOHCO33--

HH22COCO3 3 <=> HCO<=> HCO33--+H+H++

Henderson-Hasselbalch Henderson-Hasselbalch EquationEquation

pH=pK + log pH=pK + log kidneyskidneys lungslungs

pH=pK + log pH=pK + log [HCO[HCO33--]]

PCOPCO22

pH=6,1 + log pH=6,1 + log [HCO[HCO33--]]

0.03 * P CO0.03 * P CO22

pH 7.70 pH 7.70 [H+] = 20 nmol/L pH7.20 [H+] = 20 nmol/L pH7.20 [H+]=60 [H+]=60

nmol/Lnmol/L 7.60 25 7.10 807.60 25 7.10 80 7.50 30 7.00 1007.50 30 7.00 100 7.40 40 6.90 1257.40 40 6.90 125 7.30 50 6.80 1607.30 50 6.80 160

1.

2.

1

20

]32[

]3[

COH

HCO

2

]3[log1,6

PCO

HCOpH

LmEqHCO

mmHgPCOxLnmolH

/3

)(224)/]([

ACIDACID Result of Result of metabolismmetabolism and and digestiondigestion Consist of: Consist of: volatilevolatile and and nonvolatilenonvolatile VolatileVolatile

– HCl, H2SO4, HNO3, H3PO4, NH4+, HCl, H2SO4, HNO3, H3PO4, NH4+, H2CO3H2CO3 HH22COCO3 3 ((primary)<=>Hprimary)<=>H220 + CO0 + CO22

Eliminated as COEliminated as CO22 gas via gas via lungslungs..

NonvolatileNonvolatile::– Small amount.Small amount.– Lactic acid, acetic acidLactic acid, acetic acid – Removed via the Removed via the kidneykidney

Base :•NaOH: Sodium hydroxide•KOH: Potasium hydroxide•NH3

+: Ammonia

•HCO3-: Bicarbonate

Amphoteric Substance: Can function as both an acid and a base.•Glycine( +H3N-CH2-COO-):

•NaOH++H3N-CH2-COO-=>H2N-CH2-COO-Na+ + H2O

•HCl + +H3N-CH2-COO- => Cl-+H3N-CH2-COOH

Buffer: Minimize the change & promote stability

1. Acid <=> Conjugate base : H2PO4

- <=> HPO42- + H+

H2CO3 <=> HCO3- + H+

NH4+ <=> NH3 + H+

2. Protein :Albumin; GlobulinHemoglobin

3. Lung and Kidney

[H[H22COCO33 ]~PaCO ]~PaCO22= = Respiratory Respiratory componentcomponent

[H[H22COCO33]<=>PaCO]<=>PaCO22 x (0.03) x (0.03)

PaCOPaCO22 : :

– Provides a measure of HProvides a measure of H22COCO33

– The respiratory component.The respiratory component. Normal:Normal:

– PaCOPaCO22 = 40 mm Hg. = 40 mm Hg.

– HH22COCO33 = 40 x 0.03 = 1.2 mEq/L = 40 x 0.03 = 1.2 mEq/L

HCOHCO33--=Metabolic component=Metabolic component

Regulated by the kidney.Regulated by the kidney. By modulating the rate of re-absorptionBy modulating the rate of re-absorption

Metabolic acid-base imbalance:Metabolic acid-base imbalance: Kidney-relatedKidney-related Non-kidney-relatedNon-kidney-related

Electrolite DisturbanceElectrolite Disturbance(Chloride depletion)(Chloride depletion)

Three Process in Urinary Acidification

1.Reabsorption of filtered bicarbonate

2.Formation of titrable acid

3.Excretion of ammonium

REABSORPTION OF FILTERED BICARBONATE

HCO3-

H2CO3

H+

H2O

CO2

Na+

HCO3- H+

H2CO3

HCO3-

+

CO2 CO2 H2O

Blood Plasma Tubular Epithelium Tubular Urine

+

CA

Na+

HCO3-

H2CO3

H+

H2O

CO2

Na+

HCO3- H+ HPO4

2-2Na

+

CO2

Blood Plasma Tubular Epithelium Tubular Urine

+

CA

Na+

H2PO4-2Na

FORMATION OF TITRATABLE ACID

HCO3-

2H2CO3

H+

2H2O

2CO2

2Na+

2HCO3-

H+

+

2CO2

Blood Plasma Tubular Epithelium Tubular Urine

CA

Na+

Glutamine

-ketoglutarate2- 2NH4+

NH3 NH3

NH4+

Na+

2H+Glucose or CO2

NH4+

+

EXCRETION OF AMMONIUM [NH4]

The acidity of bloodThe acidity of blood Depend on [HDepend on [H++]] Expressed by pHExpressed by pH

• The [HThe [H++] increase -> the pH decrease] increase -> the pH decrease• pH = -log[HpH = -log[H++]]

• pH = pK + log [HCOpH = pK + log [HCO33-- / H / H22COCO33]]

Henderson Hasselbalch equationHenderson Hasselbalch equation

Arterial Blood Gas (ABG):Arterial Blood Gas (ABG):• pH = measuredpH = measured - HCO- HCO33

-- = calculated = calculated

• PaCOPaCO22 = measured = measured

Normal Range

• PaCO2 = 38 to 42 mmHg

• HCO3- = 22 to 26 mEq/L

• pH = 7.38 to 7.42

• HCO3- / H2CO3 = 20 : 1

• Acid-base disturbance (blood):– Acidemia: pH< 7.38– Alkalemia: pH> 7.42

Acid-Base DisturbanceSimple :

• Respiratory acidosis: PaCO2 high / HCO3- normal or slightly high

• Respiratory alkalosis: PaCO2 low /HCO3- normal or low

• Metabolic acidosis: HCO3- low / PaCO2 normal or low

• Metabolic alkalosis: HCO3- high / PaCO2 normal or high

Mixed / Combination: • (Respiratory + Metabolic)

Physiologic compensation

Primary disorder Physiol. compensationRespiratory acidosis Kidney – retention of HCO3-

; excretion of H+Respiratory alkalosis Kidney – excretion of

HCO3-; retention of H+Metabolic acidosis Lung – excretion of H+

(CO2).Metabolic alkalosis Lung – possible retention of

H+ (CO2)

ExerciseExercise

► pH = 7.33pH = 7.33► PaCO2 = 50 mmHgPaCO2 = 50 mmHg► HCO3- =25.8 mEq/LHCO3- =25.8 mEq/L

Answer:Answer:► AcidemiaAcidemia► Primary respiratory Primary respiratory ► AcuteAcute

► pH = 7.55pH = 7.55► PaCO2 = 30 mmHgPaCO2 = 30 mmHg► HCO3- = 23.4 HCO3- = 23.4

mEq/LmEq/L

Answer:Answer:► AlkalemiaAlkalemia► Primary respiratoryPrimary respiratory► AcuteAcute

ExerciseExercise

pH = 7.31pH = 7.31

PaCO2 = 29.5 mmHgPaCO2 = 29.5 mmHg

HCO3- = 14.5 mEq/LHCO3- = 14.5 mEq/L

Answer:Answer:

AcidemiaAcidemia

Primary metabolicPrimary metabolic

Respiratory Respiratory compensationcompensation

pH = 7.59pH = 7.59

PaCO2 = 46.5 mmHgPaCO2 = 46.5 mmHg

HCO3- = 45 mEq/LHCO3- = 45 mEq/L

Answer:Answer:

AlkalemiaAlkalemia

Primary metabolicPrimary metabolic

Respiratory Respiratory compensationcompensation