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Acid Base Disturbance Acid Base Disturbance ภูษิตภูษิต เฟเฟองฟองฟู ู พบพบ.. วววว..ศัศัลยศาตรลยศาตรทั่ทั่วไปวไป,, วววว..เวชบเวชบําบําบัดวัดวิกฤติกฤต กองศกองศัลยกรรมัลยกรรม โรงพยาบาลพระโรงพยาบาลพระมงกมงกุฏุฏเกลเกลาา Overview z BodyBody BufferBuffer SystemSystem z AcidAcid BaseBase disturbancesdisturbances z TreatmentTreatment Definition z AcidsAcids releaserelease HH+ z example:example: HClHCl -->> HH+ ++ ClCl- z BasesBases absorbabsorb HH+ - + z example:example: HCOHCO3 ++ HH -->> HH2COCO3 Introduction z MetabolismMetabolism generatesgenerates HydrogenHydrogen ionsions 4040-- 8080 mmolmmol/day/day z pHpH 7.357.35--7.467.46 retainedretained HH+ withinwithin 3535--4545 nmol/lnmol/l H+ per day = 40-80 x 1,000,000 nmol/l pH is logarithmic z pHpH == loglog 1/[H1/[H+]] == -- loglog [H[H+]] == -- loglog 0.000000040.00000004 EqEq/L/L pHpH == 7.47.4 SmallSmall ΔΔpHpH meansmeans pHpH 7.47.4 == 0.000000040.00000004 largelarge ΔΔ[H[H++]] pHpH 7.17.1 == 0.000000080.00000008 Buffer: pH Guardian H+ Load Distribution and extra- Cellular Cell Respiratory buffering buffering compensation 100 Renal H+ secretion 50 0 61224 72 Hours The ECF accounted for ~43% of total buffering Carbonic acid-Bicarbonate Buffer System - + CO2 + H2O H2CO3 HCO3 + H CO2 Production Dietary protein breakdown 14,000-20,000 mM/day 40-80 mEq/day 40 mmHg [H+] = 24 x pCO2 - [HCO3 ] 40 nEq/L 24 mEq/L 40 mmHg [H+] = 24 x pCO2 - [HCO3 ] 40 nEq/L 24 mEq/L estimated[H+] pH 70 7.10 60 7.20 50 7.30 40 7.40 30 7.50 estimated[H+] pH 70 7.10 60 7.20 CO =11.2 2 50 7.30 + 10 H+ - HCO3 = 14 pH = 6.20 40 7.40 30 7.50 + 10 CO2 lost CO2 = 1.2 - HCO3 = 24 pH = 7.40 CO =1.2 2 CO2 =0.9 - - HCO3 = 14 HCO3 = 14 pH = 7.17 pH = 7.29 Open Compensated Henderson-Hasselbach Equation - + CO2 + H2O H2CO3 HCO3 + H - pH =pK+log [A ] [HA] [HA] = [H2CO3 ] (at equilibrium) = [CO2]dissolved - pH = 6.1 +l og [HCO3 ] [CO2]dissolved SCO2 = 0.03 mmoles CO2/L/mmHg [HCO -] pH = 6.1 +log 3 SCO2 x PCO2 [HCO -] pH = 6.1 +log 3 0.03 x PCO2 pH =pK+log Kidneys Lungs CO2 [Kidney] pH ~ ~ [Lung] - + HCO3 + H - + HCO3 H : Phosphoric + acid, NH4 Respiratory Component PaCO2 & Minute Ventilation PaCO2 PaCO2 = 0.8 VCO2 RR(Vt-Vd) 40 Minute Ventilation Renal Component z Production of “new” bicarbonate via excretion of acid ≈ 70 mEq/day z Reabsorption of filtered bicarbonate ≈ 4,000 mEq/day Acid-base disturbances from Gastrointestinal loss Vomiting: Loss of H+ leading to alkalosis Highly acidic, pH =1.0 - Secretes HCO3 Diarrhea: pH varies from - Loss of HCO3 leading to 4.0 to 8.0 acidosis The Big 3 of pH Guardian H+ Load Distribution and extra- Cellular Cell Respiratory buffering buffering compensation 100 Renal H+ secretion 50 0 61224 72 Hours The Four Cardinal Acid Base Disorders - Disorder pH pCO2 [HCO3 ] M acidosis ↓↓↓ M alkalosis ↑↑↑ R acidosis ↓ ↑ ↑ R alkalosis ↑ ↓ ↓ Boston approach in Systemic ABG analysis 1.1. CheckCheck arterialarterial pHpH - 22.. [[HCOHCO3 ]] && PaCOPaCO2 analysisanalysis 3.3. CalculateCalculate AGAG 4.4. AssessAssess deltadelta ratioratio 5.5. CheckCheck ““cluesclues”” 6.6. AssessAssess compensatorycompensatory responsesresponses 77.. FormulateFormulate acidacid--basebase diagnosisdiagnosis 1. Check arterial pH z pH < 7.4 = acidosis pH > 7.4 = alkalosis z Principle – No over-compensation Boston approach in Systemic ABG analysis √ 1.1. CheckCheck arterialarterial pHpH - 22.. [[HCOHCO3 ]] && PaCOPaCO2 analysisanalysis 3.3. CalculateCalculate AGAG 4.4. AssessAssess deltadelta ratioratio 5.5. CheckCheck ““cluesclues”” 6.6. AssessAssess compensatorycompensatory responsesresponses 7.7. FormulateFormulate acidacid--basebase diagnosisdiagnosis - 2. [HCO3 ]& PaCO2 analysis Respiratory Compensation for Metabolic Changes z Metabolic acidosis - PaCO2 decreases by 1.2 x the drop in [HCO3 ] - PaCO2 ≈≈ 1.51.5 [HCO[HCO3 ]] ++ 88 z Metabolic alkalosis - PaCO2 increases by 0.7 x the rise in [HCO3 ] - PaCO2 ≈ 0.9 [HCO3 ] + 16 Metabolic Compensation for Respiratory Changes z Respiratory Acidosis - Acute: [HCO3 ] increases by 0.1 x the rise in PaCO2 - Chronic: [HCO3 ] increases by 0.35 x the rise in PaCO2 z Respiratory Alkalosis - Acute: [HCO3 ] decreases by 0.2 x the fall in PaCO2 - Chronic: [HCO3 ] decreases by 0.5 x the fall in PaCO2 - [HCO3 ]& PaCO2 analysis z Both are low The last 2-digit if pH = PaCO2 metabolic acidosis respiratory alkalosis Both are high metabolic alkalosis respiratory acidosis - z Opposite directions [HCO3 ]& PaCO2 Mixed disorder must be present • 60-year-old diabetic with a long history of not taking her insulin. She is admitted to the hospital and you receive the following data on her: - pH 7.26, PaCO2 42, HCO3 17... Metabolic acidosis. • A 1st year resident was anxious about her basic sciences examination. She felt numbness around her mouth and tingling in her hands and went to the clinic. - pH 7.48, PaCO2 30, HCO3 23… Respiratory alkalosis A 1st year medical student who did really well on his 1st biochemistry test celebrated too much afterwards. After a weekend of atonement, his lab values are: - pH 7.48, PaCO2 51, HCO3 29… Metabolic alkalosis A 40 year-old man with renal failure for 1 year presents with nausea, vomiting and weakness. His blood chemistry reveals Na 138 mEq/L, K 5.5 mEq/L, Cl 95 mEq/L, HCO3 16 mEq/L ABG: pH 7.31, PaCO2 31 mmHg The most likely acid-base disorder is A. Metabolic alkalosis B. Respiratory alkalosis C. Mixed respiratory alkalosis and metabolic acidosis D. Metabolic acidosis E. Mixed respiratory acidosis and metabolic alkalosis A 40 year-old man with renal failure for 1 year presents with nausea, vomiting and weakness. His blood chemistry reveals Na 138 mEq/L, K 5.5 mEq/L, Cl 95 mEq/L, HCO3 16 mEq/L ABG: pH 7.31, PaCO2 31 mmHg The most likely acid-base disorder is A. Metabolic alkalosis B. Respiratory alkalosis C. Mixed respiratory alkalosis and metabolic acidosis D. Metabolic acidosis E. Mixed respiratory acidosis and metabolic alkalosis - Winter’s formula: PaCO2 = 1.5 [HCO3 ] + 8 = 1.5[16] + 8 = 32 AnAn acutelyacutely--illill 5050--yearyear--oldold womanwoman withwith aa historyhistory ofof severesevere vomitingvomiting forfor thethe pastpast 44 days.days. PhysicalPhysical examinationexamination profoundprofound lethargy,lethargy, aa pulsepulse raterate ofof 120/min,a120/min,a respirationrespiration raterate ofof 12/min,12/min, andand BPBP ofof 80/5080/50 mmHg.mmHg. SerumSerum electrolyteselectrolytes SodiumSodium 140140 meqmeq/L/L PotassiumPotassium 3.33.3 meqmeq/L/L ChlorideChloride 8585 meqmeq/L/L BicarbonateBicarbonate 2525 meqmeq/L/L ArterialArterial bloodblood studiesstudies onon roomroom air:air: pHpH 7.407.40 1 PaCOPaCO2 4141 mmHg,mmHg, AnAn acutelyacutely--illill 5050--yearyear--oldold womanwoman withwith aa historyhistory ofof severesevere vomitingvomiting forfor thethe pastpast 44 days.days. PhysicalPhysical examinationexamination profoundprofound lethargy,lethargy, aa pulsepulse raterate ofof 120/min,a120/min,a respirationrespiration raterate ofof 12/min,12/min, andand BPBP ofof 80/5080/50 mmHg.mmHg. SerumSerum electrolyteselectrolytes SodiumSodium 140140 meqmeq/L/L PotassiumPotassium 3.33.3 meqmeq/L/L ChlorideChloride 8585 meqmeq/L/L BicarbonateBicarbonate 2525 meqmeq/L/L 2 ArterialArterial bloodblood studiesstudies onon roomroom air:air: pHpH 7.407.40 PaCOPaCO2 4141 mmHg,mmHg, 1 Boston approach in Systemic ABG analysis √ 1.1. CheckCheck arterialarterial pHpH √ - 22.. [[HCOHCO3 ]] && PaCOPaCO2 analysisanalysis 3.3. CalculateCalculate AGAG 4.4. AssessAssess deltadelta ratioratio 5.5. CheckCheck ““cluesclues”” 6.6. AssessAssess compensatorycompensatory responsesresponses 7.7. FormulateFormulate acidacid--basebase diagnosisdiagnosis 3. Calculate “Anion Gap” z Unmeasured cations UC UA K+, Ca++, and Mg++ account for about 11 mEq/L. AG z Unmeasured anions 3- 2- HCO - (PO4) , SO4 , albumin and some 3 organic acids, accounting for 20 to 24 mEq/L. Na+ z Typical anion gap is 23 − 11 = 12 mEq/L. z The anion gap can be affected by increases or decreases in the UC or UA. Cl- Decreased anion gap UC UA z ↑ Unmeasured cations K+, Ca++, and Mg++ AG gamma globulin HCO - z ↓ Unmeasured anions 3 (PO4)3- , SO42-, albumin and some organic acids, + Na z The effect of low albumin can be accounted for by adjusting the normal - range for the anion gap 2.5 mEq/L Cl upward for every 1-g/dL fall in albumin. Normal anion gap Metabolic acidosis ~ 10-12 mEq/L ≡ [Na+] - ([Cl-] + [HCO -]) AG 3 HCO - - 3 HCO loss 3 Na+ = Normal AG Metabolic acidosis • Occur in GI tract or Renal Cl- Causes of a “Normal anion gap” (hyperchloremic) metabolic acidosis 1. GI bicarbonate loss: diarrhea villous adenoma pancreatic fistulae uretero-sigmoidostomy obstructed uretero-ileostomy 2. Renal bicarbonate (or equivalent) loss proximal RTA, distal RTA and type IV RTA early renal failure 3. Ingestions & infusions ammonium chloride hyperalimentation (arginine/lysine-rich) - Diarrhea Causes Loss of HCO3 Normal Diarrhea Pancreas Pancreas HCO - HCO - 3 Ileum 3 - HCO3 Ileum Cl- Cl- - Colon + - Colon Cl K HCO3 Normal AG acidosis and Hypo-K Pancreatic fistula or transplant Pancreas - HCO3 Ileum Cl- Skin or urinary bladder Obstructed Uretero-ileostomy Skin - Ureter HCO3 Cl- Cl- Ileal loop Obstructed ileal loop Wide-anion gap Metabolic acidosis ~ 10-12 mEq/L ≡ [Na+] - ([Cl-] + [HCO -]) AG 3 A- เติมกรด HA → H+ + A- HCO - 3 • Organic acid load: Shock, Renal Na+ failure, DKA • Toxic ingextation: ASA, Alcohol etc. Cl- = Wide AG Metabolic acidosis ~ 10-12 mEq/L ≡ [Na+] - ([Cl-] + [HCO -]) AG 3 A- - • AG elevated HCO3 Na+ in either acidosis or alkalosis • AG > 20 Cl- 67% likelihood of metabolic acidosis • AG > 30 ~ 100% likelihood of metabolic acidosis AnAn acutelyacutely--illill 5050--yearyear--oldold womanwoman withwith aa historyhistory ofof severesevere vomitingvomiting forfor thethe pastpast 44 days.days. PhysicalPhysical examinationexamination profoundprofound lethargy,lethargy, aa pulsepulse raterate ofof 120/min,a120/min,a respirationrespiration raterate ofof 12/min,12/min, andand BPBP ofof 80/5080/50 mmHg.mmHg. SerumSerum electrolyteselectrolytes SodiumSodium 140140 meqmeq/L/L PotassiumPotassium 3.33.3 meqmeq/L/L ChlorideChloride 8585 meqmeq/L/L BicarbonateBicarbonate 2525 meqmeq/L/L 2 ArterialArterial bloodblood studiesstudies onon roomroom air:air: pHpH 7.407.40 PaCOPaCO2 4141 mmHg,mmHg, 1 3.
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