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Acid – Base Balance Stop Think Get anamnesis Physical examination pH Bicarbonate pCO2 Adequacy of compensation
Diagnosis The evaluation always starts with the anamnesis Then determine the pH See if compensation adequate Remember, compensation is never complete Metabolic acidosis, determine anion gap Metabolic alkalosis, determine volume status
Metabolic Acidosis Characterized by a fall in the plasma bicarbonate and a low pH Either by bicarbonate loss Or addition of acid This results in compensatory decrease of pCO2
Metabolic Acidosis Normal anion gap Gastro- intestinal loss of bicarbonate Renal loss: a. Proximal RTA b. Distal RTA c. Type IV RTA (Hypoaldosteronism) d. Ammonium chloride e. Hyperalimentation
Acid – base balance If metabolic acidosis, determine anion gap If metabolic alkalosis, determine volume status
Metabolic acidosis High anion gap Lactic acidosis Ketoacidosis Renal failure - Organic acids Intoxications a. Salicilate b. Methanol c. Ethylene glycol d. Sulfur Rhabdomyolysis
Metabolic Alkalosis How do patients become alkalotic? How do patients remain alkalotic?
Metabolic Alkalosis Results from elevation of plasma bicarbonate associated with high pH May be due to bicarbonate administration May be due to H+ loss Respiratory compensation consists of hypoventilation and pCO2 elevation
Causes of Metabolic Alkalosis Loss of H+: Gastrointestinal loss Renal loss: Diuretics Mineralocorticoid excess Penicillins Hypercalcemia Hydrogen movement into the cells - Hypokalemia Retention of bicarbonate: Blood transfusion Bicarb administration Contraction alkalosis: Diuretics
Metabolic Alkalosis Impaired HCO3 excretion with perpetuation of metabolic alkalosis Decreased GFR Volume depletion Increased tubular reabsorption Volume depletion Chloride depletion Hypokalemia Hyperaldosteronism
DiagnosisMetabolic alkalosis, determine chloride in urine to differentiate volume dependency or not
Urine Cl- in Metabolic Alkalosis Less than 25 mEq/l More than 40 mEq/l Vomiting Mineralocorticoid Diuretics excess Cystic Fibrosis Diuretics (early) Alkali load Severe Hypokalemia
ExampleNa 140K 3.4Cl 77Bicarbonate 9Anion gap 54pH 7.23pCO2 23Ketonuria: tracesCreatinine 2.3 Why do they remain alkalotics
Compensations Metabolic Alkalosis pCO2 = 40+ 0.6 delta BICMetabolic AcidosispCO2 = 2 last numbers of pHpCO2 = 1.5 x ( HCO3) + 8
Compensations?Respiratory Acidosis Respiratory AlkalosisAcute AcuteHCO3 = + 1 mEq/10 mm HCO3 = - 1-2 mEq/10 Hg pCO2 mm Hg pCO2Chronic ChronicHCO3 = + 3.5 mEq/10 HCO3 = - 5 mEq/10 mm mm Hg pCO2 Hg pCO2
Example20 y old vomiting, lethargy, tachypnea, tachycardia BP 150/100. IDDM , no insulin lately. Almost no food last few days, Na 142, K 3.6, Cl 106, Bic 16, Gluc 230, Urea 190 , Creatinine pending, pH 7.28, PCO2 34. Urine Ketones moderately positive-a couple of hours ago. No urine since.
continuation Diabetic ketoacidosis Treated with insulin,2.5 Lt saline and Potassium chloride After 3 hours patient lethargic, Met Ac not improved, Gluc 70, jugular ++ reflux++ Rales +++ Anuria At last, Creatinine results………12…..
continuation LESSONS Consider all possibilities Urine Ketones positive in starvation and vomiting Check urine output before giving IV Control your patient often !!!
Continuation Adequate compensation is ( - ) 5 mEq Bicarbonate / 10 mm Hg If acute, Bic should be 23 Since it is Chronic Respiratory Alkalosis ( more than 48 hours) Bic should be ( 24- 5)= 19 Anion Gap is normal- there is no hidden Met Ac Simple Chronic Respiratory Acidosis
CONTINUATION For Met Alk pCO2 should be 40 = 0.6( 44-24)= 52 pCO2 is to high ( 65 ), so Metabolic Alkalosis + Respiratory Acidosis Why not respiratory acidosis + compensation?
EXERCISE 21 y old IDDM presents with vomiting pH 7.75 pCO2 24 BIC 32 Anion Gap 30
CONTINUATION Adequate Compensation : pCO2 should be 40+ 0.6 ( 32-24 )= 44.8, so Respiratory Alkalosis. Anion Gap is 30 , so Hidden Metabolic Acidosis. Delta Anion Gap 16, Bic should have fallen to + - 6-8, but is 32
CONTINUATION Severe Respiratory Alkalosis + Severe High Anion Gap Metabolic Acidosis+ Severe Metabolic Alkalosis.