PENDEKATAN ASAM BASA METODA STEWART
Anang Achmadi Department of Anesthesiology & Intensive Care Santosa Hospital Bandung Central
BGA/ AGD
• pH : 7.42 • pCO2 : 35 • pO2 : 100 • BE : -‐2 • HCO3 : 21
?
GANGGUAN KESEIMBANGAN ASAM BASA TRADISIONAL DISORDER
pH
PRIMER
RESPON KOMPENSASI
ASIDOSIS METABOLIK
↓
HCO3- ↓
pCO2 ↓
ALKALOSIS METABOLIK
↑
HCO3- ↑
pCO2 ↑
ASIDOSIS RESPIRATORI
↓
pCO2 ↑
HCO3- ↑
ALKALOSIS RESPIRATORI
↑
pCO2 ↓
HCO3- ↓
7.42 / 35 / 100 / -2 / 21 Menurut H-H à normal
(a) Free water n
Na 140; Cl 102; Alb 1.8
0.3 x (140-140) = 0
(b) Chloride effect n
102-(102 x 140/140) = 0
(c) Albumin effect n
n
(0.148 x 7.42 - 0.818) (42-[18]) = 6.7
UA = - 2 – [(0) + (0) + (6.7)] mEq/L = - 8.7 HIDDEN METABOLIC ACIDOSIS
Am J Respir Crit Care Med Vol 162. pp 2246–2251,2000
Traditional view • • • • •
Problems: 1. Which one is the independent variable? 2. What is the source of hydrogen ions? 3. Does not provide quantitative assessment 4. Does not explain dilutional acidosis or contraction alkalosis • 5. Does not explain hypoalbuminemic alkalosis
Subversive New Concepts in Acid-base Physiology • New paradigms are emerging (Current Opinion Crit Care 1999; 5: 427- 477) in acid base physiology • Based on the work of the late Peter Stewart (Can J Physiol Pharmacol 1983; 61: 1444-1461) • They are subversive because they challenge traditional teaching
Stewart’s Approach • The Henderson-Hesselbach equation describes the relationship of 3 linked variables but does not say which is dependent and which independent • The solvent (H2O) not the solutes is the largest source of hydrogen ions
Menurut Stewart
pH atau [H+] DALAM PLASMA DITENTUKAN OLEH DUA VARIABEL VARIABEL INDEPENDEN
DEPENDENT VARIABLES
Stewart PA. Can J Physiol Pharmacol 61:1444-1461, 1983.
VARIABEL INDEPENDEN
CO2
STRONG ION DIFFERENCE
WEAK ACID
SID
Atot
pCO2 Controlled by the respiratory system
The electrolyte composition of the blood (controlled by the kidney)
The protein concentration (controlled by the liver and metabolic state)
CO2 CO2 Didalam plasma berada • Rx dominan dari CO2 adalah rx absorpsi OH- hasil disosiasi air dalam 4 bentuk – – – –
dengan melepas H+.
sCO2 (terlarut) H2CO3 asam karbonat HCO3- ion bikarbonat CO32- ion karbonat
• Semakin tinggi pCO2 semakin banyak H+ yang terbentuk. • Ini yg menjadi dasar dari terminologi “respiratory acidosis,” yaitu pelepasan ion hidrogen akibat ↑ pCO2
OH- + CO2 ⇔ HCO3- + H+ CA
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 Mg++ Ca++ K+ 4
SID
[Na+] + [K+] + [kation divalen] - [Cl-] - [asam organik kuat-] Na+ 140 Cl102 [Na+]
+
140 mEq/L
[K+] +
-
[Cl-]
4 mEq/L -
KATION
=
102 mEq/L
[SID] = 34 mEq/L
ANION
MENGAPA DISEBUT ION KUAT DAN LEMAH ?
100 80 70 60
% ter-ionisasi
pK
50 40 30 20 10
2
3
4
5
6
7
8
9
pH Suatu ion dikatakan kuat atau lemah tergantung dari pKnya (pH, dimana 50% dari substansi tsb terdisosiasi). Mis; pK Lactate 3.9 (berarti, pada pH normal, hampir 100% laktat terdisosiasi ). H2CO3 dan Alb disebut asam lemah karena pada pH normal hanya 50% substansinya terdisosiasi.
Elektrolit = Ion-ion Ion-ion kuat
Ion-ion lemah
(Strong ions) :
(Weak ions) :
Substansi yang terdisosiasi sempurna di dalam suatu larutan : àKation; Na+,K+,Mg+,Ca++ àAnion; Cl-,SO4-,PO4=, laktat-, keto-.
Substansi yang hanya sebagian terdisosiasi dalam suatu larutan : à Albumin-, Posfat-, H2CO3
Hubungan SID dgn pH/H+ Konsentrasi H+
[H+] ↑↑ [OH-] ↑↑
SID↓
Na
Cl
SID
Asidosis
(–)
Na
Cl
SID
SID↑
Alkalosis
Na Cl
(+)
Dalam cairan biologis (plasma) dgn suhu 370C, SID selalu positif, nilainya berkisar 30-40 mEq/Liter
DEPENDENT VARIABLES
H+
HCO3OH-
AH CO3-
A-
PRINSIP UMUM • Hukum kekekalan massa (Law of Mass): – Jumlah dari suatu zat/substansi akan selalu konstan kecuali ditambahkan atau dikurangi dari luar, atau dibuat/dirusak oleh suatu reaksi kimia.
• Netralitas elektrik (Electroneutrality): – Semua larutan sejati mempunyai muatan listrik yang netral, dimana konsentrasi total kation harus sama dengan konsentrasi anion Σ iones (+) = Σ iones (-) Stewart PA. Modern quantitative acid-base chemistry. Can J Physiol Pharmacol 61:1444-1461, 1983.
Konsep larutan encer (Aqueous solution) • Semua cairan dalam tubuh manusia mengandung air, dan air merupakan sumber [H +] yang tidak habis-habisnya • [H+] ditentukan oleh disosiasi air (Kw), dimana molekul H2O akan berdisosiasi menjadi ion-ion H3O+ dan OH-
WEAK ACID [Protein-] + [H+]
[Protein H] disosiasi
Kombinasi protein dan posfat disebut asam lemah total (total weak acid) à [Atot]. Reaksi disosiasinya adalah:
[Atot] (KA) = [A-].[H+]
INDEPENDENT VARIABLES
DEPENDENT VARIABLES
Strong Ions Difference PHYSICOCHEMICAL Rx
pCO2
Protein Concentration
CONSERVATION of MASS ELECTRONEUTRALITY
H+ HCO3OHtCO2 ACO3=
BLOOD PLASMA H+
Na+
OH-
CO32-
Alb Posfat -
K+ Mg++ Ca++
XA
-
Cl-
CATION
SID
HCO3-
ANION
ATot Unmeasured Anion
Clasification (Fencl et al) ACIDOSIS I. Respiratory
ALKALOSIS
↑ PCO2
↓ PCO2
↓ SID, ↓ [Na+]
↑ SID, ↑ [Na+]
i. Chloride excess/deficit
↓ SID, ↑ [Cl-]
↑ SID, ↓ [Cl-]
ii. Unidentified anion excess
↓ SID, ↑ [XA-]
II. Nonrespiratory (metabolic) 1. Abnormal SID a. Water excess/deficit b. Imbalance of strong anions
2. Non-volatile acids i. Serum albumin
↑ [Alb]
↓ [Alb]
ii. Inorganic phosphate
↑ [Pi]
↓ [Pi]
WORKSHOP ACIDBASE STEWART PERDICI 2006
Advantages of Stewart’s Method • The effect of chloride is explicitly recognized • The effect of plasma proteins and phosphate in appreciated and quantified • The pathogenesis of the acid-base disorder is better understood • More logical therapies can be implemented • Misdiagnoses are decreased, especially if lactate is not immediately available
STOMACH
Alkaline tide
ClNa: 20-80 Cl: 150-180
SID (-)
SID (+) pH ↑ Alkalosis
pH ↓
Kellum JA. Diagnosis and Treatment of Acid-Base Disorders. In: Textbook of Critical Care, W.B. Saunders Co, Philadelphia, PA , 1999. Grenvik A, Shoemaker PK, Ayers S, Holbrook (eds). pp839-853 Magder S. Pathophysiology of metabolic acid-base disturbances in patients with critical illness.In: Critical Care Nephrology. Kluwer Academic Publishers, Dordrecht, The Netherlands, 1998. pp 279-296.Ronco C, Bellomo R (eds).
SMALL INTESTINE INTESTINE GALL BLADDER pH > 7.5 ↑
Cl-
ClPANCREAS pH > 7.7 ↑
CATION
SID (↓) pH ↓
Kellum JA. Diagnosis and Treatment of Acid-Base Disorders. In: Textbook of Critical Care, W.B. Saunders Co, Philadelphia, PA , 1999. Grenvik A, Shoemaker PK, Ayers S, Holbrook (eds). pp839-853 Magder S. Pathophysiology of metabolic acid-base disturbances in patients with critical illness.In: Critical Care Nephrology. Kluwer Academic Publishers, Dordrecht, The Netherlands, 1998. pp 279-296.Ronco C, Bellomo R (eds).
Volume dan komposisi elektrolit cairan gastrointestinal From Miller, Anesthesia, 5th ed,2000.
24 h vol. (mL)
Na+ (mEq/L)
K+ (mEq/L)
Cl- (mEq/ L)
HCO3SID
Saliva
500-2000
6
25
13
18
Stomach
1000-2000
80
15
115
-20
Pancreas
300-800
140
7.5
80
67.5
Bile
300-600
140
7.5
110
37.5
Jejunum
2000-4000
130
7.5
115
22.5
Ileum
1000-2000
115
5
92.5
27.5
Colon
-
60
30
40
-
DILUTIONAL ACIDOSIS NaCl + H2O à Na+ + Cl- + H+ + OH- + H2O
1 L H2O Na+ Na+ = 140 mEq/L Cl- = 110 mEq/L SID = 30 mEq/L
1 liter
= 70 mEq/L Cl- = 55 mEq/L SID = 15 mEq/L
2 liter
CONTRACTION ALKALOSIS 1 Liter
Na+ = 140 mEq/L Cl- = 110 mEq/L SID = 30 mEq/L
1 liter
Na+ = 280 mEq/L Cl- = 220 mEq/L SID = 60 mEq/L
½ liter
Ringer Laktat
Ringer Laktat Plasma
Na
Cl
K
Ca
Osms
bicnat
131
111
5
4
276
29
135
105
4
5
290 +10
24
33
NaCl Na
Cl
Osm
NaCl 0,9%
154
154
308
NaCl 0,45%
77
77
NaCl 3%
513
513
Plasma
135
108
1026 290 +10
34
PLASMA + NaCl 0.9%
Plasma Na+ = 140 mEq/L Cl- = 102 mEq/L SID = 38 mEq/L
NaCl 0.9%
1 liter
Na+ = 154 mEq/L Cl- = 154 mEq/L SID = 0 mEq/L
1 liter
SID : 38 à 35
ASIDOSIS HIPERKLOREMIK AKIBAT PEMBERIAN LARUTAN Na Cl 0.9% Plasma
=
Na+ = (140+154)/2 mEq/L= 147 mEq/L Cl- = (102+ 154)/2 mEq/L= 128 mEq/L SID = 19 mEq/L
2 liter
SID : 19 à Asidosis 36
PLASMA + Larutan RINGER LACTATE
Plasma
Ringer laktat Laktat cepat dimetabolisme
Na+
= 140 mEq/L Cl- = 102 mEq/L SID= 38 mEq/L
1 liter
Cation+ = 137 mEq/L Cl- = 109 mEq/L Laktat- = 28 mEq/L SID = 0 mEq/L
1 liter
SID : 38 37
Normal pH setelah pemberian RINGER LACTATE Plasma
=
Na+ = (140+137)/2 mEq/L= 139 mEq/L Cl- = (102+ 109)/2 mEq/L = 105 mEq/L Laktat- (termetabolisme) = 0 mEq/L SID = 34 mEq/L
2 liter
SID : 34 à lebih kecil perubahan SID dibanding jika diberikan NaCl 0.9% 38
Kesimpulan 0.9% saline = (Ab)normal Saline
Reid et al, Clin Sci, 2003
39
MEKANISME PEMBERIAN NA-BIKARBONAT PADA ASIDOSIS
Plasma;
Plasma + NaHCO3
asidosis hiperkloremik
Na+ = 140 mEq/L Cl- = 130 mEq/L SID =10 mEq/L
25 mEq NaHCO3
1 liter
1.025 liter
Na+
HCO3 cepat = 165 mEq/L dimetabolisme
Cl- = 130 mEq/L SID = 35 mEq/L
SID ↑ : 10 à 35 : à Alkalosis, pH kembali normal à namun mekanismenya bukan karena pemberian HCO3- melainkan karena pemberian Na+ tanpa anion kuat yg tidak dimetabolisme seperti Cl- sehingga SID ↑ à alkalosis
Efek pemberian bikarbonat: CO2 + H2O ⇔ HCO3- + H+ [HCO3- ] ⇔ [CO32-] + [H+] Reaksi pembentukan karbonat Alkalosis à [H+] ↓ à reaksi ke kanan à [CO32-] ↑
• Jika [CO32-] ↑ maka calcium yang terionisasi akan diikat oleh [CO32-] à hipokalsemia akut; sensitifitas membran sel ↑ à tetany, hyperexcitability of muscles, sustained contraction, dan gangguan kontraksi otot jantung. •
Pe↑ natrium secara cepat à SID ↑ secara cepat à alkalosis berat à kompensasi paru dengan cara menahan CO2 à hipoventilasi à CO2 narkosis à apneu Asidosis à [H+] ↑ à reaksi ke kiri à [CO32-] ↓
Pada asidosis kronik; [CO32-]↓↓ à pembentukan CaCO3 << à integritas tulang terganggu à osteoporosis
OTHER FINDINGS : 1. HCO3 doesn t improve hemodynamic in critically ill patients who have lactic acidosis (Cooper; Ann Inter Med. 1990) 2. HCO3 therapy in the treatment of lactic acidosis : Medicine or toxin? (Sing Et Al, J Ann. Osteopath. Assoc. 1995) 3. The Routine use of sodium bicarbonate is no longer recommended. (In 1992, the American National Conference on Cardiopulmonary Resuscitation established current guidelines) 4. CONSENSUS CONFERENCE in FRANCE (June 2000) organized by The French Reanimation Society recommend not to give sodium bicarbonate in any acidosis except in HCO3 loss.
PENILAIAN ANALISA GAS DARAH MENGGUNAKAN KOMBINASI BASE EXCESS DAN STEWART Nilai2 yg diperlukan: 1. AGD (BE) 2. Natrium 3. Klorida 4. Albumin Story DA, Bellomo R. Hendersen-Hasselbach vs Stewart: Another Acid-Base Controversy; Review Article, Crit Care & Shock (2002)2:59-63
BE = (1 - 0.014Hgb) (HCO3 – 24 + (1.43Hgb + 7.7) (pH - 7.4)`
50
PCO2 = 80
40
[HCO3-‐]
40
Alkalosis Metabolik
30
Base Excess/ Base Deficit
"20
Base Excess" Normal
Base Defisit"
"
20
10 7.0
Asidosis Metabolik
7.2
"
7.4
pH
7.6
7.8
UNMEASURED ANION (UA) PADA ASIDOSIS METABOLIK UA = BE – [(efek Na + efek Cl) + efek Alb]
BASE EXCESS DAN STEWART (a) Free water n
0.3 x (Na-140)
(b) Chloride effect n
Jika + à efek alkalinisasi Jika - à efek asidifikasi
102-(Cl x 140/Na)
(c) Albumin effect n
n
(0.148 x pH - 0.818) (42-[alb])
UA = BE/BD – [(a) + (b) + (c)] mEq/L
Magder S. Pathophysiology of metabolic acid-base disturbances in patients with critical illness. In: Critical Care Nephrology.Kluwer Academic Publishers, Dordrecht, The Netherlands, 1998. pp 279-296. Ronco C, Bellomo R (eds).
Clinical Investigations
Strong ions, weak acids and base excess: a simplified Fencl–Stewart approach to clinical acid–base disorders D. A. Story, H. Morimatsu and R. Bellomo . British Journal of Anaesthesia, 2004, Vol. 92,
• SBE(mmol/l=meq/l); – from a blood gas machine
• Na–Cl effect (meq/l)= – [Na+]–[Cl–]–38
• Albumin effect (meq/l)= – 0.25x[42–alb(g/l)]
• Unmeasured ion effect (meq/l)= – SBE–(Na–Cl) effect–alb effect
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