Transcript HCO 3
ACID-BASE BALANCE By: Husnil Kadri Biochemistry Departement Medical Faculty Of Andalas University Padang CARA TRADISIONAL : Hendersen-Hasselbalch (1909) 2 Normal [HCO GINJAL BASA3-] HCO HCO 3 3 pH = 6.1 + log Normal Kompensasi PARU pCO2 ASAM CO CO22 3 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 4 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 5 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- Normal Compensatory Response • Any primary disturbance in acid-base homeostasis invokes a normal compensatory response. • A primary metabolic disorder leads to respiratory compensation, and a primary respiratory disorder leads to an acute metabolic response due to the buffering capacity of body fluids. • A more chronic compensation (1-2 days) due to alterations in renal function. Mixed Acid - Base Disorder • Most acid-base disorders result from a single primary disturbance with the normal physiologic compensatory response and are called simple acid-base disorders. • In certain cases, however, particularly in seriously ill patients, two or more different primary disorders may occur simultaneously, resulting in a mixed acid-base disorder. • The net effect of mixed disorders may be additive (eg, metabolic acidosis and respiratory acidosis) and result in extreme alteration of pH; • or they may be opposite (eg, metabolic acidosis and respiratory alkalosis) and nullify each other’s effects on the pH. 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. INDEPENDENT VARIABLES DEPENDENT VARIABLES Strong Ions Difference pCO2 Protein Concentration pH VARIABEL INDEPENDEN CO2 STRONG ION DIFFERENCE pCO2 SID WEAK ACID Atot DEPENDENT VARIABLES H+ HCO3OH- AH CO3- A- 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 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 KEKURANGAN AIR - WATER DEFICIT Diuretic Diabetes Insipidus Evaporasi Plasma Plasma Na+ = 140 mEq/L Cl- = 102 mEq/L SID = 38 mEq/L 1 liter 140/1/2 = 280 mEq/L 102/1/2 = 204 mEq/L SID = 76 mEq/L SID : 38 76 = alkalosis ALKALOSIS KONTRAKSI ½ liter KELEBIHAN AIR - WATER EXCESS Plasma Na+ = 140 mEq/L Cl- = 102 mEq/L SID = 38 mEq/L 1 Liter H2O 1 liter 2 liter SID : 38 19 = Acidosis ASIDOSIS DILUSI 140/2 = 70 mEq/L 102/2 = 51 mEq/L SID = 19 mEq/L GANGGUAN PD SID: Pengurangan ClPlasma Na+ = 140 mEq/L Cl- = 95 mEq/L SID = 45 mEq/L SID ALKALOSIS ALKALOSIS HIPOKLOREMIK 2 liter GANGGUAN PD SID: Penambahan/akumulasi ClPlasma Na+ = 140 mEq/L Cl- = 120 mEq/L SID = 20 mEq/L SID ASIDOSIS ASIDOSIS HIPERKLOREMIK 2 liter PLASMA + NaCl 0.9% Plasma NaCl 0.9% Na+ = 140 mEq/L Cl- = 102 mEq/L SID = 38 mEq/L Na+ = 154 mEq/L Cl- = 154 mEq/L SID = 0 mEq/L 1 liter SID : 38 1 liter 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 SID : 19 Asidosis 2 liter PLASMA + Larutan RINGER LACTATE Plasma Ringer laktat Laktat cepat dimetabolisme Na+ = 140 mEq/L Cl- = 102 mEq/L SID= 38 mEq/L 1 liter SID : 38 Cation+ = 137 mEq/L Cl- = 109 mEq/L Laktat- = 28 mEq/L SID = 0 mEq/L 1 liter 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 2 liter SID = 34 mEq/L SID : 34 lebih alkalosis dibanding jika NaCl 0.9% diberikan MEKANISME PEMBERIAN NABIKARBONAT 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 35 : Alkalosis, pH kembali normal namun mekanismenya bukan karena pemberian HCO3- melainkan karena pemberian Na+ tanpa anion kuat yg tidak dimetabolisme seperti Cl- sehingga SID alkalosis UA = Unmeasured Anion: Laktat, acetoacetate, salisilat, metanol dll. K K HCO3- HCO3- SID Keto- ANa+ SID ANa+ Cl- ClLactic/Keto asidosis Normal Ketosis GANGGUAN PD ASAM LEMAH: Hipo/Hiperalbumin- atau PK K HCO3 SID Na Cl Normal SID K HCO3 Alb-/P Alb-/P- Na HCO3 Alb/P Na Asidosis hiperprotein/ hiperposfatemi Cl Acidosis SID Alkalosis hipoalbumin Cl /hipoposfate mi Alkalosis 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) If the anion gap is elevated • Then compare the changes from normal between the anion gap and [HCO3 -]. • If the change in the anion gap is greater than the change in the [HCO3 -] from normal, then a metabolic alkalosis is present in addition to a gap metabolic acidosis. • If the change in the anion gap is less than the change in the [HCO3 -] from normal, then a non gap metabolic acidosis is present in addition to a gap metabolic acidosis. Anion Gap Acidosis: • Anion gap >12 mEq/L; caused by a decrease in [HCO3 -] • balanced by an increase in an unmeasured acid ion from either endogenous production or exogenous ingestion (normochloremic acidosis). Non anion Gap Acidosis: • Anion gap = 8-12 mmol/L; caused by a decrease in [HCO3 -] balanced by an increase in chloride (hyperchloremic acidosis). Renal tubular acidosis is a type of non gap acidosis Increased Anion Gap Normal = 8-15 May differ institutionally • Accumulation of organic acids (ketones, lactate) • Toxic Ingestions – methanol, ethylene glycol, salicylates • Reduced inorganic acid excretion – phosphates, sulfates • Decrease in unmeasured cations (unusual) Increased AG Metabolic Acidosis: • Methanol • Uremia/Renal Failure • INH, Iron--lactate • Paraldehyde • Lactic Acidosis – Has many etiologies – Cyanide, CO, Toluene, HS – Poor perfusion • Ethylene glycol • Salicylates – Methyl salicylate • (Oil of wintergreen) – Mg salicylate Levraut J et al. Int Care Med 23:417, 1997 Increased Anion Gap Normal = 8-15 May differ institutionally “ion specific electrodes” • Accumulation of organic acids (ketones, lactate) • Toxic Ingestions – methanol, ethylene glycol, salicylates • Reduced inorganic acid excretion – phosphates, sulfates • Decrease in unmeasured cations (unusual) Decreased or Negative Anion Gap Clin J Am Soc Nephrol 2: 162-174, 2007 • Low protein most important • Albumin has many unmeasured negative charges • “Normal” anion gap (12) in cachectic person – Indicates anion gap metabolic acidosis • Other etiologies of low AG: – Low K, Mg, Ca, increased globulins (Mult. Myeloma), I intoxication • Negative AG – more unmeasured cations than unmeasured anions – Bromide, Iodide, Multiple Myeloma 44 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 Respiratory Compensation for Metabolic Acidosis: • Occurs rapidly • Hyperventilation – “Kussmaul Respirations” – Deep > rapid (high tidal volume) • Is not Respiratory Alkalosis Metabolic Alkalosis: • Calculation not as accurate • Hypoventilation • Not Respiratory Acidosis • Restricted by hypoxemia • PCO2 seldom > 50-55 Reference 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 47