Transcript Elektrolit & Asam-basa

REGULATION OF ACID-BASE
&
ELECTROLYTES
Oleh:
Dr. Husnil Kadri, M.Kes
Bagian Biokimia Fakultas Kedokteran
Universitas Andalas
Padang
ASAM BASA..
+
[H ]
pH
2
Acid
Base
Notasi pH diciptakan oleh seorang ahli kimia dari Denmark
yaitu Soren Peter Sorensen pada thn 1909, yang berarti log
negatif dari konsentrasi ion hidrogen. Dalam bahasa Jerman
disebutWasserstoffionenexponent (eksponen ion hidrogen)
dan diberi simbol pH yang berarti: ‘potenz’ (power) of
Hydrogen.
3
Acid-Base Balance
• Normal pH of body fluids
– Arterial blood is 7.4
– Venous blood and interstitial fluid is 7.35
– Intracellular fluid is 7.0
• Alkalosis or alkalemia – arterial blood pH
rises above 7.45
• Acidosis or acidemia – arterial pH drops
below 7.35
4
Sources of Hydrogen Ions
• Most hydrogen ions originate from cellular
metabolism
– Breakdown of phosphorus-containing proteins
releases phosphoric acid into the ECF
– Anaerobic respiration of glucose produces
lactic acid
– Fat metabolism yields organic acids and
ketone bodies
– Transporting carbon dioxide as bicarbonate
releases hydrogen ions
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Hydrogen Ion Regulation
• Concentration of hydrogen ions is
regulated sequentially by:
– Chemical buffer systems – act within seconds
– The respiratory center in the brain stem – acts
within 1-3 minutes
– Renal mechanisms – require hours to days to
effect pH changes
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Acid/Base Homeostasis: Overview
7
Regulation of Blood pH
• The lungs and kidneys play important role in
regulating blood pH.
• The lungs regulate pH through retention or
elimination of CO2 by changing the rate and
volume of ventilation.
• The kidneys regulate pH by excreting acid,
primarily in the ammonium ion (NH4+), and by
reclaiming HCO3- from the glomerular filtrate
(and adding it back to the blood).
8
Carbonic acid/bicarbonate buffer system
+ + HCO CO2 + H2O 
H
CO

H
2
3
3
CA
• Carbonic acid is formed when CO2
combines with water. This reaction is
catalysed by carbonic anhydrase
• Carbonic acid dissociates spontaneously
to form a proton and a bicarbonate ion
9
The Lung Regulation
• Normal, unassisted breathing:
– An increase in arterial PCO2 acts through the
respiratory centre to increase the rate of
pulmonary ventilation
– A decrease in arterial PCO2 reduces the rate
of ventilation
• Assisted breathing:
– A respirator is used to assist breathing by
expelling CO2, thus reducing PCO2 in blood
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The Lung Regulation
• When hypercapnia or rising plasma H+
occurs:
– Deeper and more rapid breathing expels more
carbon dioxide
– Hydrogen ion concentration is reduced
• Alkalosis causes slower, more shallow
breathing, causing H+ to increase
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12
The Renal Regulation
• Chemical buffers can tie up excess acids
or bases, but they cannot eliminate them
from the body
• The lungs can eliminate carbonic acid by
eliminating carbon dioxide
• Only the kidneys can rid the body of
metabolic acids (phosphoric, uric, and
lactic acids and ketones) and prevent
metabolic acidosis
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The Renal Regulation
• The most important renal mechanisms for
regulating acid-base balance are:
– Conserving (reabsorbing) or generating new
bicarbonate ions
– Excreting bicarbonate ions
• Losing a bicarbonate ion is the same as
gaining a hydrogen ion; reabsorbing a
bicarbonate ion is the same as losing a
hydrogen ion
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15
Reabsorption of Bicarbonate
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Hydrogen Ion Excretion
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CARA TRADISIONAL :
Hendersen-Hasselbalch
(1909)
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Normal
[HCO
GINJAL
BASA3-]
HCO
HCO 3
3
pH = 6.1 + log
Normal
Kompensasi
PARU
pCO2
ASAM
CO
CO22
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Carbonic acid/bicarbonate buffer system
pKa = 6.1
ECF:
H2CO3  H+
Carbonic acid
+
HCO3Bicarbonate ion
• The pKa of carbonic acid is 6.1
• Carbonic acid is the major buffer in ECF
• The pH of blood can be determined using
the Henderson-Hasselbalch equation
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Henderson-Hasselbalch equation
• pH = pKa + log [HCO3-]/[H2CO3]
• pH = pKa + log [HCO3-]/0.03 x PCO2
• 7.4 = 6.1 + log
20 / 1
• 7.4 = 6.1 + 1.3
• Plasma pH equals 7.4 when buffer ratio is 20/1
• The solubility constant of CO2 is 0.03
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Cara Stewart ;
pH atau [H+] DALAM PLASMA
DITENTUKAN OLEH
DUA VARIABEL
VARIABEL
INDEPENDEN
VARIABEL
DEPENDEN
Stewart PA. Can J Physiol Pharmacol 61:1444-1461, 1983.
VARIABEL INDEPENDEN
CO2
STRONG ION DIFFERENCE
pCO2
SID
WEAK ACID
Atot
CO2
CO2 Didalam plasma berada
dalam 4 bentuk
 sCO2 (terlarut)
 H2CO3 asam karbonat
-
 HCO3 ion bikarbonat
 CO32- ion karbonat
 Rx dominan dari CO2 adalah rx
absorpsi OH- hasil disosiasi air
dengan melepas H+.
 Semakin tinggi pCO2 semakin
banyak H+ yang terbentuk.
 Ini yg menjadi dasar dari
terminologi “respiratory acidosis,”
yaitu pelepasan ion hidrogen akibat
 pCO2
STRONG ION DIFFERENCE
Definisi:
Strong ion difference adalah ketidakseimbangan muatan
dari ion-ion kuat. Lebih rinci lagi, SID adalah jumlah
konsentrasi basa kation kuat dikurangi jumlah dari
konsentrasi asam anion kuat. Untuk definisi ini semua
konsentrasi ion-ion diekspresikan dalam ekuivalensi
(mEq/L).
Semua ion kuat akan terdisosiasi sempurna jika berada didalam
larutan, misalnya ion natrium (Na+), atau klorida (Cl-). Karena
selalu berdisosiasi ini maka ion-ion kuat tersebut tidak
berpartisipasi dalam reaksi-reaksi kimia. Perannya dalam kimia
asam basa hanya pada hubungan elektronetraliti.
STRONG ION DIFFERENCE
Gamblegram
Mg++
Ca++
K+ 4
SID
[Na+] + [K+] + [kation divalen] - [Cl-] - [asam organik kuat-]
Na+
140
Cl102
[Na+]
140 mEq/L
+
[K+]
+
-
4 mEq/L -
KATION
[Cl-]
102 mEq/L
ANION
=
[SID]
=
34 mEq/L
SKETSA HUBUNGAN ANTARA SID,H+ DAN OH-
[H+]
[OH-]
Konsentrasi [H+]
Asidosis
(–)
Alkalosis
SID
(+)
Dalam cairan biologis (plasma) dgn suhu 370C, SID hampir
selalu positif, biasanya berkisar 30-40 mEq/Liter
WEAK ACID
[Protein-] + [H+]
[Protein H]
disosiasi
Kombinasi protein dan posfat disebut asam
lemah total (total weak acid)  [Atot].
Reaksi disosiasinya adalah:
[Atot] (KA) = [A-].[H+]
Gamblegram
Mg++
Ca++
K+ 4
HCO324
Weak acid
(Alb-,P-)
Na+
140
Cl102
KATION
ANION
SID
DEPENDENT VARIABLES
H+
HCO3OH-
AH
CO3-
A-
INDEPENDENT VARIABLES
DEPENDENT VARIABLES
Strong Ions
Difference
pCO2
Protein
Concentration
pH
APLIKASI
H3O+ = H+ = 40 mEq/L
K
Mg
Ca
HCO3- 
HCO3 = 24
HCO
Alb
3 
P
Alb
Laktat/keto=UA
P
Na
140
Alb
P
Keto/laktat
Asidosis
hiperkloremi
asidosis
Cl
CL
Cl
115
95
102
Alkalosis
hipokloremi
KATION
ANION
SID
SID n
SID 
KLASIFIKASI GANGGUAN
KESEIMBANGAN ASAM BASA
BERDASARKAN PRINSIP STEWART
Fencl V, Jabor A, Kazda A, Figge J. Diagnosis of metabolic acid-base disturbances in
critically ill patients. Am J Respir Crit Care Med 2000 Dec;162(6):2246-51
KLASIFIKASI
ASIDOSIS
ALKALOSIS
 PCO2
 PCO2
 [Na+],  SID
 [Na+],  SID
i. Kelebihan / kekurangan Cl-
 [Cl-],  SID
 [Cl-],  SID
ii. Ada anion tak terukur
 [UA-],  SID
I. Respiratori
II. Nonrespiratori (metabolik)
1. Gangguan pd SID
a. Kelebihan / kekurangan air
b. Ketidakseimbangan anion
kuat:
2. Gangguan pd asam lemah
i. Kadar albumin
 [Alb]
 [Alb]
ii. Kadar posphate
 [Pi]
 [Pi]
Fencl V, Jabor A, Kazda A, Figge J. Diagnosis of metabolic acid-base disturbances in
critically ill patients. Am J Respir Crit Care Med 2000 Dec;162(6):2246-51
RESPIRASI
METABOLIK
Abnormal
pCO2
Abnormal
SID
AIR
 Anion kuat
Cl-
Alkalosis
Turun
kekurangan
Hipo
Asidosis
Meningkat
kelebihan
Hiper
Fencl V, Am J Respir Crit Care Med 2000 Dec;162(6):2246-51
Abnormal
Weak acid
Alb
PO4-
UA-
Turun
Positif
meningkat
Anion Gap
• Described by Gamble in 1939
• Electroneutrality
• Na+, Cl-, and HCO3 are measured ions
Na + UC = Cl + HCO3 + UA
UC = Sum of unmeasured cations
UA = Sum of unmeasured anions
Anion Gap
Unmeasured Cations:
• total 11 mEq/L
– Potassium 4
– Calcium
5
– Magnesium 2
Unmeasured Anions:
• total 23 mEq/L
– Sulfates
1
– Phosphates 2
– Albumin
16
– Lactic acid 1
– Org. acids 3
Anion Gap
Na + UC = Cl + HCO3 + UA
140 + 11 = 104 + 24 + 23
151 = 151
UA – UC = Na - (Cl + HCO3);
Anion Gap = Na - (Cl + HCO3)
Change in Anion Gap vs HCO3
• In simple AG Metabolic Acidosis
– decrease in plasma bicarbonate = increase
in AG
Anion Gap = 1
HCO3
• Helpful in identifying mixed disorders
Sources
1.
2.
3.
4.
5.
6.
7.
8.
Achmadi, A., George, YWH., Mustafa, I. Pendekatan “Stewart”
Dalam Fisiologi Keseimbangan Asam Basa. 2007
Beaudoin, D. Electrolytes and ion sensitive electrodes. PPT.
2003.
Ivkovic, A ., Dave, R. Renal review. PPT
Kersten. Fluid and electrolytes. PPT.
Marieb, EN. Fluid, electrolyte, and acid-base balance. PPT.
Pearson Education, Inc. 2004
Rashid, FA. Respiratory mechanism in acid-base homeostasis.
PPT. 2005.
Silverthorn, DU. Integrative Physiology II: Fluid and Electrolyte
Balance. Chapter 20, part B. Pearson Education, Inc. 2004
Smith, SW. Acid-Base Disorders. www.acid-base.com
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