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ACID-BASE DISORDERS

ACID-BASE DISORDERS. NITIN BHATT, M.D. DIRECTOR, I.C.U. VAMC, RENO . ACID_BASE DISORDERS. 12000 to 15000 mEq of volatile acids are produced daily by body and excreted as CO2 by lungs

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ACID-BASE DISORDERS

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  1. ACID-BASE DISORDERS NITIN BHATT, M.D. DIRECTOR, I.C.U. VAMC, RENO

  2. ACID_BASE DISORDERS • 12000 to 15000 mEq of volatile acids are produced daily by body and excreted as CO2 by lungs • 1 mEq / kg / day of non-volatile acids (sulfuric and phosphoric acids) are produced daily by body and excreted by the kidneys • The pH of body fluids is determined by the amount of acid produced, the buffering capacity and the acid excretion by lungs and the kidneys • The most important buffers in the body are, hemoglobin, plasma proteins and bicarbonate

  3. Addition of acid • First the acid binds to extracellar buffers, then intracelluar buffers and finally to alkaline salts in bones. • PCO2 is lowered by stimulation of respiratoty center • Finally, the kidneys increase the excretion of acids. • If all these mechanisms fail, patient develops acidemia

  4. ACID-BASE DISORDERS • ACIDEMIA: lower than normal arterial blood pH • ALKALEMIA: higher than normal arterial blood pH • ACIDOSIS: a process that tends to acidify body fluids and may lead to acidemia. Could result from metabolic or respiratory dysfunction or compensatory response. • ALKALOSIS: a process that tends to alkalinize body fluids and may lead to alkalemia. Could result from metabolic or respiratory dysfunction or compensatory response. • Acidosis and alkalosis may or may not be associated with abnormal pH in the same direction..

  5. ACID_BASE DISORDERS • SIMPLE ACID BASE DISORDER: when there is only one primary disorder • MIXED ACID BASE DISORDER: when there are two or more primary disorders present at the same time

  6. ACID-BASE DISORDERS • NORMAL ANION GAP = 12 • NORMAL PH = 7.40 • NORMAL PCO2 = 40 • NORMAL HCO3 = 24

  7. ACID-BASE DISORDERS DEFINITIONS METABOLIC ACIDOSIS = HCO3 <24 OR Anion Gap >12 METABOLIC ALKALOSIS = HCO3 >24 RESPIRATORY ALKALOSIS = PCO2 <40 or PCO2 less than expected for primary metabolic abnormality. RESPIRATORY ACIDOSIS = PCO2 >40 or PCO2 higher than expected for primary metabolic abnormality. HIGH ANION GAP (>12-20) always indicates primary metabolic acidosis. We do not compensate for abnormality of one system with compensation by the same system( MET OR RESP).

  8. ACID BASE DISORDERS • PRIMARY PRIMARYCOMPENSATORY DISORDERABNORMALITYCHANGE MET. ACIDOSIS LOWER HCO3 LOWER PCO2 MET. ALKALOSIS HIGHER HCO3 HIGHER PCO2 RESP. ACIDOSIS HIGHER PCO2 HIGHER HCO3 RESP. ALKALOSIS LOWER PCO2 LOWER HCO3 REMEMBER: compensatory response never brings the pH back to normal, therefore, if the pH is in acidic direction, it tells you that the process or processes in acidic direction are the primary disorders.

  9. ACID_BASE DISORDERS Compensatory Process • Tends to return ratio of HCO3 to PCO2 back toward normal and therefore normalize the arterial pH • Does not return pH to normal except in primary respiratory alkalosis of chronic duration. • Require normal function of kidneys and lungs • Lack of appropriate compensation suggests second primary disorder • Compensatory response creates second lab abnormality • Appropriate degree of compensation can be predicted.

  10. ACID_BASE DISORDERS Metabolic Acidosis • Caused by excess acid production which overwhelms renal capacity to excrete acids ( DKA ) , loss of alkali (diarrhea) or renal failure • Tissues and RBCs act to increase the serum HCO3 by exchanging intracellular Na & K for extracellular H , resulting in increased serum K and HCO3 • Increased pulmonary ventilation leads to decreased PaCO2 and change in pH toward normal • HCO3 <10 OR Anion Gap > 12 always suggest primary metabolic acidosis

  11. ACID_BASE DISORDERS Urinary Anion-Gap • Useful in differential diagnosis of hyperchloremic acidosis • Calculated as U. Na + U. K – U. Cl • A negative U. Anion Gap ie Cl >> Na + K suggests appropriate urinary NH4 excretion and G.I. loss of HCO3 • A positive U. Anion Gap ie. Cl << Na + K suggests RTA with distal acidification defect and inadequate NH4 excretion in urine

  12. ACID-BASE DISORDERS: EQUATIONS

  13. ACID-BASE DISORDERS • RESPIRATORY ACIDOSIS ACUTE: 10 INCR. IN PCO2 LEADS TO 1 INCR. IN HCO3 CHRONIC: 10 INCR. IN PCO2 LEADS TO 3-3.5 INCR. IN HCO3 • RESPIRATORY ALKALOSIS ACUTE; 10 DECR. IN PCO2 LEADS TO 2 DECR. IN HCO3 CHRONIC 10 DECR. IN PCO2 LEADS TO 4-5 DECR. IN HCO3 • METABOLIC ACIDOSIS PCO2 = LAST 2 DIGITS OF pH • METABOLIC ALKALOSIS 1 MEQ INCR. IN HCO3 LEADS TO 0.6-0.7 INNCR. IN PCO2

  14. PCO2-HCO3 buffer system • CO2 gas  CO2 dissolved + H2O • CO2 + H2O  H2CO3  H + HCO3 • H= K x H2CO3÷ HCO3 • H2CO3 or PCO2 represents respiratory system function • HCO3 represents kidney or metabolic system

  15. ACID-BASE DISORDERS HENDERSON HASSELBALCH EQUATION Ph = Pk + log HCO3/ H2CO3 Rearranging the above per Kassier and Bliech H = 24 X PCO2/HCO3 ( H= Hydrogen ion conc.) H at normal pH of 7.40 is 40 Nanamol/Liter therefore, 40 = 24 X 40 (PCO2)/24(HCO3)

  16. ACID_BASE DISORDERS • SIMPLE ACID BASE DISORDER: when there is only one primary disorder • MIXED ACID BASE DISORDER: when there are two or more primary disorders present at the same time

  17. ACID-BASE DISORDERS SYSTEMATIC ANALYSIS OF ACID-BASE DISORDER • 1, Find out which one is the primary process or processes. If the pH is abnormal, there has to be a minimum of one primary process ( Acidosis or Alkalosis ). We can not identify more than three primary processes at one time with our current knowledge of acid-base analysis. • 2, Do not apply equations for primary respiratory disorders, if there is also a concurrent primary metabolic disorder present. • 3, Do not try to calculate expected PCO2 for primary metabolic acidosis, if there is also a concurrent primary respiratory disorder or if HCO3 >24. • Use as many equations of acid-base disorders that can be applied in the case, to get the maximum information.

  18. CAUSES OF HYPERCHLOREMIC METABOLIC ACIDOSIS HYPOKALEMIC Proximal RTA, acetazolamide,coumarin/ Distal RTA Post-hypocapnea Diarrhea, Pancreatic fistula, Biliary drainage Ureterosigmoidostomy, Ileal bladder HYPERKALEMIC OR NORMOKALEMIC Type-4 RTA HCl infusion/ingestion Dilutional acidosis

  19. Less than 20 mEq/l ( saline responsive ) Vomiting/NG_Tube suction Chloride wasting diarhhea Colonic villous adenoma Remote diuretic therapy Post hypercapnea Poorly reabsorbed anions Glucose refeeding Greater than 20 mEq/l ( saline unresponsive ) Primary Hyperaldosteronism Cushing`s syndrome Exogenous steroids/ Licorice Adrenal 11 or 17 hydroxylase defects Liddle`s /Barter`s syndromes K and Mg deficiency Milk alkali syndrome Urinary chloride in metabolic alkalosis

  20. DISORDERS OF SERUM CHLORIDE CONCENTRATION

  21. MIXED ACID_BASE DISORDERS

  22. MIXED ACID BASE DISORDERS

  23. Acid-base Disorders An acutely ill 50 yr. old woman with a history of vomiting x 4 days is brought to E.R. P/E shows profound lethargy, P= 120, RR=12, BP 80/50. Lab: Na=140, K=3.3, Cl=85, HCO3=25, PCO2=41 and pH=7.40. Most likely acid-base disorder is A) metabolic acidosis B) metabolic alkalosis C) respiratory acidosis and metabolic alkalosis D) respiratory alkalosis E) metabolic acidosis and metabolic alkalosis

  24. ACID-BASE Q-2 • pH=7.5 • PCO2=27 • HCO3=23

  25. ACID-BASE Q-3 • pH=7.25 • PCO2=60 • HCO3=26

  26. ACID-BASE Q-4 • pH=7.20 • PCO2=21 • HCO3=8

  27. ACID BASE Q-5 • Na=145 • Cl=99 • HCO3=24 • pH=7.4 • PCO2=40

  28. ACID BASE Q-6 • pH=7.10 • PCO2=50 • Na=145 • Cl=100 • HCO3=15

  29. A 65 yr old homeless woman who collapsed in a pub is brought to E.R. P/E: comatose,P=120,BP=58/40.IV N.S. started 10 min.earlier,Pt. Now intubated. I.V. bicarbonate was given with fluids, and Dopamine was started but hypotension persists

  30. Questions related to previous pt. • A) what is the acid base abnormality before intubation? 1, met. Acid. 2, resp acid. 3, met and resp acidosis 4, met acid and met alk 5, met acid, resp acid and met alkalosis. • B) what is the cause of acid-base abnormality 30 min after intubation ? 1, uremia 2, distal RTA 3,resp acidosis 4, lactic acidosis, 5 DKA

  31. ACID-BASE DISORDERS • A 45 yr old man with progressive renal failure x 1 yr., comes to your office because of N/V/ pruritus and weakness. P/E shows P=84,RR=20,BP=180/110 • Lab: Glu=98,Na=138,K=5.5,Cl=100,HCO3=16,BUN=155,Cr= 12.6, PCO2=29,pH=7.30,urine pH=5.0. Most likely DX is • A) metabolic alkalosis • B) respiratory alkalosis • C)metabolic alkalosis and respiratory acidosis • D)metabolic acidosis • E) metabolic acidosis and respiratory alkalosis

  32. ACID-BASE DISORDERS • A 42 YR old alcoholic man presents with hematemesis, anemia and mild orthostatic hypotension. Lab as follows Hct=36%, Glu=85, Na=138, K=3.3, Cl=97, HCO3=35, BUN=25, Cr.=1.2, Urine pH=6.8, Urine Cl=8 meq/L and Urine K=42 meq/L • Most appropriate therapy for this patient is • A, Furosemide or Ethacrynic acid • B, Sodium Chloride • C, Potassium Chloride and Sodium Chloride • D, Potassium Chloride • E, I.V. D5W

  33. ACID-BASE DISORDERS • A patient with DKA has following lab values, • HCO3=12 and PCO2=33 • What is the acid base disorder? • Remember: it takes 12-24 hrs to get optimum response from respiratory system in case of acute metabolic acidosis. And in about 5% of cases,the patient may not fall within the values obtained by applying the rule for expected PCO2 in primary metabolic acidosis

  34. ACID –BASE DISORDERS • A child with a 3-4 hour history of asthma exacerbation has ABG values as follows: pH=7.24, PCO2=65, HCO3=26 • What is the acid base disorder? • A 65 years old man with long standing history of COPD presents with diarrhea x 24 hours. ABG values are: pH=7.24, PCO2=65, HCO3=26 • What is the acid-base disorder?

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