Acid Base Balance

Acid-Base Balance M. Rasjad Indra Laboratorium Ilmu Faal FK. 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)

W ha t is Aci d and Base ?  Acid is proton (H+) donor  Base is proton (H+) acceptor  The most important acid in the blood is H2CO3  The most important base is HCO3 H2CO3 <=> HCO3-+H+

Henderson-Hasselbalch Equation 

pH=pK + log kidneys lungs



pH=pK + log [HCO3-] PCO2



pH=6,1 + log [HCO3-] 0.03 * P CO2

[ HCO 3] 1. pH = 6,1 + log PCO 2 2. [ H + ]( nmol / L ) = 24 x

[ HCO 3] 20 = [ H 2CO3] 1

PCO 2 ( mmHg ) HCO 3mEq / L

pH 7.70  [H+] = 20 nmol/L pH7.20 [H+]=60 nmol/L 7.60 25 7.10 80 7.50 30 7.00 100 7.40 40 6.90 125 7.30 50 6.80 160

ACID  Result

of metabolism and digestion  Consist of: volatile and nonvolatile  Volatile – HCl, H2SO4, HNO3, H3PO4, NH4+, H2CO3  H2CO3 (primary)<=>H20 + CO2  Eliminated as CO2 gas via lungs.

 Nonvolatile:

– Small amount. – Lactic acid, acetic acid – Removed via the kidney

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; Globulin Hemoglobin 3. Lung and Kidney

[H2CO3 ]~PaCO2= Respiratory component  [H2CO3]<=>PaCO2  PaCO2

x (0.03)

:

– Provides a measure of H2CO3 – The respiratory component.  Normal:

– PaCO2 = 40 mm Hg. – H2CO3 = 40 x 0.03 = 1.2 mEq/L

HC O 3 - =Met abolic component  Regulated by the kidney.  By modulating the rate of re-absorption

 Metabolic acid-base imbalance:  Kidney-related  Non-kidney-related  Electrolite Disturbance (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 Blood Plasma

Tubular Epithelium

Tubular Urine

Na+ HCO3-

HCO3

Na+ H+

-

H+

+

HCO3-

H2CO3 CA

H2CO3

H2 O + CO2

CO2

CO2

H2 O

FORMATION OF TITRATABLE ACID Blood Plasma

Tubular Epithelium

Tubular Urine

Na+ HCO3-

HCO3

Na+ H+

-

H+

+

H2CO3 CA H2 O + CO2

CO2

H2PO4-2Na

HPO42-2Na

EXCRETION OF AMMONIUM [NH4] Blood Plasma

Tubular Epithelium

Tubular Urine

Glutamine Na+ α-ketoglutarate2-

Glucose or CO2

2H

2NH4+

NH4+

NH3

NH3

H+ 2Na+ HCO3-

2H2CO3

2HCO32H2O + 2CO2

H+ Na+

CA

2CO2

NH4+

+

+

The acidity of blood  

Depend on [H+] Expressed by pH • The [H+] increase -> the pH decrease • pH = -log[H+] • pH = pK + log [HCO3- / H2CO3] 



Henderson Hasselbalch equation

Arterial Blood Gas (ABG): • pH = measured - HCO3- = calculated • PaCO2 = 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 Disturbance Simple : • 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 Respiratory acidosis

Physiol. compensation 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)

Exercise ► pH

= 7.33 ► PaCO2 = 50 mmHg ► HCO3- =25.8 mEq/L Answer: ► Acidemia ► Primary respiratory ► Acute

► pH

= 7.55 ► PaCO2 = 30 mmHg ► HCO3- = 23.4 mEq/L Answer: ► Alkalemia ► Primary respiratory ► Acute

Exercise pH = 7.31 PaCO2 = 29.5 mmHg HCO3- = 14.5 mEq/L Answer: Acidemia Primary metabolic Respiratory compensation

pH = 7.59 PaCO2 = 46.5 mmHg HCO3- = 45 mEq/L Answer: Alkalemia Primary metabolic Respiratory compensation