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Metabolic Acidosis Acid Base Disorders in Medicine For The Primary Care Provider Jonathan J. Taliercio, DO, FASN Program Director, Nephrology and Hypertension Fellowship Assistant Professor, CCLCM Cleveland Clinic JonTaliercio_DO 2 Faculty Disclosure . No conflicts of interest . The presentation will not include discussion of unapproved or investigational uses of products or devices. 3 Case 1 A hospitalized 62-year-old woman has a 2 day history of SBO manifesting with profuse vomiting requiring NGT suction. Exam BP 80/50, HR 115/min, ↓ skin turgor, and diffuse abdominal pain. The BMP indicates serum Na 135 mEq/L, K 3.5 mEq/L, Cl 85 mEq/l, HCO3 25 mEq/l, BG 90 mg/dl, BUN 110 mg/dl, creatinine 4.5 mg/dl. ABG: pH 7.40, pCO2 40 mm Hg. Which one of the following best applies to this patient? A.There is no significant disorder because the blood pH and HCO3 are normal B.The patient does not have metabolic acidosis because of the normal blood pH C.The patient has metabolic alkalosis D.The patient has metabolic acidosis and respiratory acidosis E.The patient has a mixed metabolic acidosis and metabolic alkalosis 4 Case 1 A hospitalized 62-year-old woman has a 2 day history of SBO manifesting with profuse vomiting requiring NGT suction. Exam BP 80/50, HR 115/min, ↓ skin turgor, and diffuse abdominal pain. The BMP indicates serum Na 135 mEq/L, K 3.5 mEq/L, Cl 85 mEq/l, HCO3 25 mEq/l, BG 90 mg/dl, BUN 110 mg/dl, creatinine 4.5 mg/dl. ABG: pH 7.40, pCO2 40 mm Hg. Which one of the following best applies to this patient? A.There is no significant disorder because the blood pH and HCO3 are normal B.The patient does not have metabolic acidosis because of the normal blood pH C.The patient has metabolic alkalosis D.The patient has metabolic acidosis and respiratory acidosis E.The patient has a mixed metabolic acidosis and metabolic alkalosis 5 What We Will Be Talking About . Relevant, High Yield information for clinical practice . Basic Concepts . Acid Base Nomenclature . Stepwise Approach to Acid Base Problem Solving . Questions and Answers . Conclusions 6 Basic Concepts . Carbohydrate and fat metabolism generates 15,000 mmol/day of CO2 + . CO2 is a volatile acid due to its ability to producing a H after hydration with H2O slow fast + CO2 + H20 H2CO3 H + HCO3 . Under normal conditions, the lungs eliminate ALL the CO2 produced from CHO and fat metabolism and thus CO2 has NO impact on acid base balance 7 Basic Concepts . Dietary protein (amino acids) metabolize into nonvolatile acids – Sulfuric, phosphoric, hydrochloric acid . 1 mmol H+/kg ~ (50-100 mmol/day) . In order to maintain acid-base balance, the kidney’s must – Excrete ALL the metabolized nonvolatile acids with urinary buffers – Replenish ALL the HCO3 that is consumed via the neutralization of the nonvolatile acids – Must prevent ALL urinary loss of HCO3 8 Net non- volatile Net non- acid: Metabolism Diet volatile acid: ECF 40 mmol 30 mmol Lungs pH 7.4 CO2 (volatile acid): 15,000 mmol Reabsorbed - Filtered HCO3 : - New HCO3 : - HCO3 : 4320 mmol 70 mmol 4320 mmol Kidneys 30 mmol titratable acids Urine + 40 mmol NH4 Boron & Boulpaep (2009) courtsey of Sarmey 9 Consequences of Acidosis Acute Chronic . Kidney . Cardiovascular – Stone disease – ↓ Cardiac contractility and arterial vasodilatation leading to ↓ BP – CKD – ↑ Risk for dysrhythmias – Bone disease . Respiratory . MSK – Hyperventilation (metabolic) – Growth retardation (children) – Sarcopenia . Cerebral – albumin synthesis – Obtundation and coma (respiratory) . Endo . Metabolic – Insulin Resistance – Hyperkalemia, ↓ATP synthesis 10 Normal Values for Acid-Base Parameters in Arterial and Venous Blood + pH [H ] PCO2 [HCO3] nanoEq/L mmHg mEq/L Arterial 7.35-7.45 37-43 35-45 21-27 Venous .03 to .04 42-48 ↑ 3- 8 ↑ 1-2 Central .03-.05 42-48 ↑ 4-5 21-27 11 Florence Agnes Henderson David Michael Hasselhoff 12 Henderson Hassalbalch Hasselhoff Equation 13 Henderson-Hasselbalch What is the expected pH in a patient with HCO3 15 and PCO2 40? HCO3 (BASE) pH = pK + log (α) PCO2 (ACID) 15 pH = 6.1 + log 0.03 (40) pH = 7.2 14 Clinical Use What is the expected pH in a patient with HCO3 15 and PCO2 40? PCO2 (ACID) pH [H+] [H+] nEq/L = 24 x HCO3 (BASE) 7.0 100 7.1 80 40 7.2 63 [H+] nEq/L = 24 x 15 7.3 50 7.4 40 [H+] nEq/L = 63 7.5 31 7.6 25 15 Basic Concept . A simultaneous ABG and a BMP is required for the determination of an acid base disorder – HCO3 measurement on the ABG is calculated using the henderson-hasselbalch equation – Total PCO2 on a venous sample is a true measurement of HCO3 fast slow + – H + HCO3 H2CO3 CO2 + H20 16 Acid-base Nomenclature . Simple (primary) acid-base disturbance – The presence of one primary abnormality coupled with its anticipated secondary response . Mixed acid-base disturbance – The simultaneous presence of two or more primary abnormalities 17 Acid Base Nomenclature . Acidemia - pH < 7.35 ↑ [ H+ ] (↓ pH) . Alkalemia- pH > 7.45 ↓ [ H+ ] (↑ pH) . Acidosis- a pathophysiological process which decreases extracellular fluid pH – Metabolic acidosis initial disturbance ↓ [HCO3] – Respiratory acidosis initial disturbance ↑ [PCO2] . Alkalosis - a pathophysiological process which increases extracellular fluid pH – Metabolic alkalosis initial disturbance ↑ [HCO3] – Respiratory alkalosis initial disturbance ↓ [PCO2] 18 Patterns of Simple Acid Base Disorders Compensatory Primary Primary Disorder pH Change Change (PCO2) (HCO3) Metabolic Acidosis ↓ ↓ ↓↓ Metabolic Alkalosis ↑ ↑ ↑↑ Primary Compensatory Primary Disorder pH Change Change (PCO2) (HCO3) Respiratory Acidosis ↓ ↑↑ ↑ Respiratory Alkalosis ↑ ↓↓ ↓ 19 Key Concept In primary acid base disorders, the compensatory response does not fully correct the underlying disorder but rather reduces the magnitude of the change in pH 20 Patterns of Mixed Acid Base Disorders Change Change Disorder pH (PCO2) (HCO3) Mixed Respiratory ↑ ↓ ↑ Alkalosis and Metabolic or Alkalosis WNL Mixed Respiratory ↓ ↑ ↓ Acidosis and Metabolic or Acidosis WNL 21 Key Concept .If the pH is normalized than a mixed disorder is present .It is impossible to have a simultaneous respiratory acidosis and respiratory alkalosis 22 Respiratory Compensation for Metabolic Acidosis Primary Compensatory Disorder Change Response Metabolic ↓ [HCO3] * Expected ↓ PCO2 : 1.2 mmHg ↓ in PCO2 Acidosis for every 1 mmol/L fall in HCO3 (Winters Formula) * Expected ↓ PCO2 : 1.5 X HCO3 + 8 (+/- 2) * Expected ↓ PCO2 : HCO3 + 15 * Expected ↓ PCO2: Last 2 digits of pH Time adaptation ~ 30 mins - 24 hours 23 Respiratory Compensation for Metabolic Alkalosis Primary Compensatory Disorder Change Response Metabolic ↑ [HCO3] * Expected ↑ PCO2 : 0.7 mmHg ↑ in PCO2 - Alkalosis for every 1 mmol/L rise in HCO3 * Expected ↑ PCO2 : HCO3 + 15 - * Expected ↑ PCO2 : 1.2 [HCO3 ] + 6 (+/-2) - * Expected ↑ PCO2 : 0.9 [HCO3 ] + 9 (+/-3) HINT: * PCO2 should > 40 and usually is <55 Time adaptation ~ 30 mins - 24 hours 24 Metabolic Compensation for Respiratory Disturbances Disorder Compensatory Response - Acute Respiratory Acidosis 1 mEq/L increase in [HCO3 ] for (mins- hours) every 10 mmHg rise in PCO2 - Acute Respiratory Alkalosis 2 mEq/L decrease in [HCO3 ] for (mins- hours) every 10 mmHg fall in PCO2 - Chronic Respiratory Acidosis 3.5 mEq/L increase in [HCO3 ] for (3-5 days) every 10 mmHg rise in PCO2 - Chronic Respiratory Alkalosis 4 mEq/L decrease in [HCO3 ] for (3-5 days) every 10 mmHg fall in PCO2 25 Metabolic Compensation for Respiratory Disturbances Disorder Compensatory Response - Acute Respiratory Acidosis 1 mEq/L increase in [HCO3 ] for (mins- hours) every 10 mmHg rise in PCO2 - Acute Respiratory Alkalosis 2 mEq/L decrease in [HCO3 ] for (mins- hours) every 10 mmHg fall in PCO2 - Chronic Respiratory Acidosis 3.5 mEq/L increase in [HCO3 ] for (3-5 days) every 10 mmHg rise in PCO2 - Chronic Respiratory Alkalosis 4 mEq/L decrease in [HCO3 ] for (3-5 days) every 10 mmHg fall in PCO2 26 A Few Words on Metabolic Acidosis 27 Metabolic Acidosis Primary defect is fall in serum HCO3 Accumulation of metabolic acids caused by: 1. Excess acid production which overwhelms renal capacity for acid excretion (ex. DKA) 2. Renal excretory failure: normal total acid production in face of poor renal function (ex. CKD) 3. Loss of alkali: leaves un-neutralized acid behind (ex. diarrhea) 28 Serum Anion Gap + - . Anion Gap = Na - (Cl + HCO3) – Normal range 8-12 meq/L . The gap simply reflects the differences between the unmeasured anions and unmeasured cations . The expected anion gap should be reduced by 2.5 meq/L for every 1 g/dl reduction in albumin below 4 g/dl – Example: Expected AG is 5 in a patient with a albumin of 2 g/dl (10 – (2 x 2.5) = 5) 29 Unmeasured Unmeasured Anions Cations - SO4 = 2 4 - HPO4 = 3 Protein = 16 Mg++= 2 Cl- = 105 Cl- = 105 30 Causes of AGMA . Methanol . Glycols (ethylene, propylene) . Uremia . Oxoproline . Diabetic (ETOH starvation . L-lactate ketosis) . D-lactate . Propylene glycol . Methanol . Isoniazid . Aspirin . Lactic acidosis . Renal failure . Ethylene glycol . Ketosis (ETOH or DKA) . Salicylates 31 Causes of a Low Serum Anion Gap ↓ AG = ↑ UC - ↓ UA - SO4 = 2 4 - HPO4 = 3 Unmeasured Unmeasured Anions Cations Protein = 16 Mg++= 2 Low AG due to ↑ UC Low AG due to ↓ UA Cationic proteins of Myeloma Cl- = 105 Hypoalbuminemia Hypercalcemia Hypermagnesiemia Lithium 32 Case 1 A hospitalized 62-year-old woman has a 2 day history of SBO manifesting with profuse vomiting requiring NGT suction. Exam BP 80/50, HR 115/min, ↓ skin turgor, and diffuse abdominal pain. The BMP indicates serum Na 135 mEq/L, K 3.5 mEq/L, Cl 85 mEq/l, HCO3 25 mEq/l, BG 90 mg/dl, BUN 110 mg/dl, creatinine 4.5 mg/dl. ABG: pH 7.40, pCO2 40 mm Hg. Which one of the following best applies to this patient? A.There is no significant disorder because the blood pH and HCO3 are normal B.The patient does not have metabolic acidosis because of the normal blood pH C.The patient has metabolic alkalosis D.The patient has metabolic acidosis and respiratory acidosis E.The patient has a mixed metabolic acidosis and metabolic alkalosis 33 Step Wise Approach to Acid Base Problem Solving 1.
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