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ACID/BASE DISORDERS

ACID/BASE DISORDERS. Resident Rounds Rob Hall PGY3 April 24, 2003. Objectives. Approach to A/B disorders Clinical examples of each disorder Differential dx of each disorder Combined disorders. Should we even do ABGs?.

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ACID/BASE DISORDERS

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  1. ACID/BASE DISORDERS Resident Rounds Rob Hall PGY3 April 24, 2003

  2. Objectives • Approach to A/B disorders • Clinical examples of each disorder • Differential dx of each disorder • Combined disorders

  3. Should we even do ABGs? • MANY studies showing that venous gases have similar pH and pC02 to ABGs • MANY studies show that ABGs rarely change management

  4. How to interpret an ABG • What is the pH? • Is there an acidemia or alkalemia? • Is it respiratory or metabolic? • Is there any compensation? • Is the compensation appropriate? • What is the anion gap?

  5. Took some pills • ABG • pH 7.25 • PC02 22 • HC03 15 • Interpretation? • Is there a second acid base disorder? • Metabolic acidosis + respiratory alkalosis • Think ASA!!

  6. ACIDOSIS Respiratory Acute 1:10 Chronic 1:3 Metabolic 1:1 ALKALOSIS Respiratory Acute 1:10 Chronic 1:2 Metabolic 0.6:1 Compensation:the clue to mixed disorders

  7. 80 female with suspected ischemic gut…… pH 6.9, PC02 35, HCO3 8 Why is the acidemia important?

  8. Severe Acidemia Negative ionotropy Arrythmias Reduced response to catecholamines Hyperkalemia Muscle weakness Altered LOC and seizures Poor enzyme function Severe Alkalemia Reduced coronary blood flow Arrythmias Hypokalemia Altered LOC and seizures Poor enzyme function Consequences of SevereAcid Base Disorders

  9. 75 yo female Altered LOC Fever Sinus tachycardia Tachypnea ABG: pH 7.50, pC02 30, HC03 23 Interpretation? Diagnosis? Differential dx of the acid/base disorder? Case

  10. Respiratory Alkalosis • Pain • Anxiety • Pregnancy • Pulmonary disease/hypoxia • CNS disorder • Thyrotoxicosis • ASA

  11. Cases • 70yo smoker since birth • COPD exacerbation • pH 7.15, pC02 60, HC03 26 • Is he a chronic CO2 retainer? • pH 7.35, pC02 60, HC03 32 • Interpretation? • pH 7.05, pC02 100, HC03 32 • What is his “normal” pC02?

  12. Chronic Respiratory Acidosis • You know that the HC03 increases in a 1:3 ratio to the increase in pC02 • If the HC03 is up by 7, the pC02 is chronically up by about 20 • What is the differential dx of respiratory acidosis?

  13. HYPOVENTILATION Brain stem Spinal Cord Motor neuron Peripheral nerve NMJ Muscle Chest wall Obesity hypoventilation IMPAIRED GAS EXCHANGE Airway obstruction Bronchospasm Pneumonia Pulmonary edema PE Aspiration COPD Respiratory Acidosis

  14. ANION GAP • What is the anion gap? • What is the formula? • What is a “normal” anion gap? • What could cause a LOW anion gap?

  15. Na+ K+ Ca++ Mg++ Cl- HCO3- P04- S04- Albumin Organic acids ANION GAP

  16. Low Anion Gap • Hypoalbuminemia • Increased Ca, Mg, K • Lithium intoxication • Multiple myeloma

  17. What is the Delta Gap? • Delta Gap • Change in AG – change in HC03 • (AG – 12) – (24 – HC03) • Essentially looks for similar changes in anion and drop in bicarb as a marker for additional acid base disorders • Questionable validity

  18. Case • 55yo male, street person, found lying in snow by CPS, confused, no history, denies ingestions, no PMHx or meds • Temp 33, HR 72, BP 120/60, RR 28, sats 98%, GCS 13 • Exam unremarkable except shivering • ABG: pH 7.26, pC02 13, HC03 5 • Na 129, K 4.7, Cl 88, C02 7 • What is the A/B disorder? • What other labs do you want?

  19. BUN 15, Cr 136 ASA –ve Lactate 1.2 CarboxyHb 0.8% EtOH –ve Toxic alcohols –ve Glucose 2 Urine ketone +ve What is the dx? What is the ddx of an increased AGMA? Case

  20. A ASA M Methanol, Metformin U Uremia D DKA P Paraldehyde, Phenformin I Isoniazid, Iron L Lactate E Ethylene glycol C CO, CN A AKA, alcohol T Toluene, Theophylline O Other H2S Any toxin that leads to lactic acidosis (essentially all severe overdoses with hypotension, seizures) Increased AGMA:AMUDPILECATO

  21. How to narrow the ddx with an increased AGMA • Normal glucose rules out DKA • BUN, Creatinine • ASA level • ABG for carboxyHb, lactate • Toxic alcohol level

  22. Which toxins cause an increased AGMA independent of lactate? Methanol Ethylene glycol ASA

  23. 10yo girl, DKA, pH is 6.9 • Would you give bicarb? • What is the theoretical reason to give bicarb for acidemia? • What are the complications? • What are indications for bicarb? • Is there any evidence for or against bicarb?

  24. Complications Paradoxical CSF acidosis Hypokalemia Hypocalcemia Hypernatremia Volume overload Overshoot alkalosis Indications for Bicarb pH < 7.10 ASA Methanol Ethylene glycol NOT DKA (increased rates of cerebral edema): Glaver NEJM 2001 Metabolic Acidosis and bicarbonate therapy:

  25. Gain acid Acid ingestion Obstructive uropathy Pyelonephritis Distal renal tubular acidosis Bicarb loss GI Diarrhea Bowel fistual Pancreatic, biliary, or intestinal drains Ureteroenterostomy Renal Proximal RTA Acetazolamide Ddx of Normal AGMA

  26. Chloride Responsive Vomiting NG drainage Diuretics Vilous adenoma Chloride Resistant Primary hyperaldosteronism Cushing’s Steroids Ectopic ACTH Barter’s syndrome Ddx of Metabolic Alkalosis

  27. A mud pile cat! SSSSSuffering ssssssucatash: look at the size of those………

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