Board Review Acid Base Disorders 7/2/2013

1. Board ReviewAcid Base Disorders7/2/2013

2. Metabolic Acidosis • Anion Gap Acidosis = decrease in bicarbonate due to presence of unmeasured acid (lactate) • Non-Anion Gap Acidosis = lack of bicarbonate in which chloride increases to maintain neutrality (Diarrhea)

3. Metabolic Acidosis • Mixed Picture • Calculate corrected bicarbonate Corrected Bicarbonate = 24 – Δ Anion Gap Measured > Corrected = Metabolic Alkalosis Measured < Corrected = Normal Anion Gap Acidosis

4. Anion Gap Metabolic Acidosis • Examples: • Lactic Acidosis, DKA, Alcoholic Ketoacidosis, Ethylene Glycol Toxicity, Methanol Toxicity, Proylene Glycol Toxicity, Salicylate Toxicity

5. Anion Gap Metabolic Acidosis • Propofol-Related Infusion Syndrome • IV dosing > 4 mg/kg/h for more than 48 hours can induce lactic acidosis • Also leads to rhabdomyolysis, hyperlipidemia, and J-point elevation on EKG • D-Lactic Acidosis • Occurs in short bowel syndrome after bowel resection; secondary to carbohydrate conversion to D-lactate by flora in the colon • Symptoms include: confusion, slurred speech, and ataxia

6. Non-Anion Gap Metabolic Acidosis • Use the Urine Anion Gap • AG = Na + K – Cl • AG Negative = presence of ammonium and appropriate kidney response to metabolic acidosis (Diarrhea) • AG Positive = no ammonium and inadequate kidney response to acidosis (RTA)

7. Type I RTA • Impaired excretion of hydrogen ions • Leads to urine pH > 6.0 and nephrocalcinosis

8. Type II RTA • Reduction of bicarbonate reabsorption • Bicarbonate eventually becomes reabsorbed once serum level falls low enough • Urine eventually becomes devoid of bicarbonate and pH becomes < 5.5 (chronically)

9. Type IV RTA • Usually associated with hypoaldosteronism • Hyperkalemia • Urine pH < 5.5

10. Metabolic Alkalosis • Saline Responsive with decreased ECF and intravascular volume (Vomiting, Diuretic use) • Use normal saline • Saline Responsive with Increased ECF and decreased intravascular volume (CHF, Cirrhosis) • Use acetazolamide (blocks carbonic anhydrase leading to blocked secretion of hydrogen ions and increased excretion of bicarbonate)

11. A 56-year-old man is evaluated in the emergency department after his wife found him unconscious. She reports that he has a history of alcohol abuse. He is treated with lorazepam, thiamine and 1 L of D5/NS. Upon arrival, he has a generalized seizure that resolves spontaneously. Which of the following is the most appropriate next step in management? A Fomepizole B Hemodialysis C Sodium bicarbonate D Supportive care

12. AG acidosis with respiratory acidosis (normal PCO2 in setting of acidosis) • Seizure related lactic acidosis with alcoholic ketoacidosis • Respiratory Acidosis secondary to postictal state • Improves with volume repletion and supplemental glucose

13. No osmolal gap when you add ethanol • 320-314 = 6 (no gap) • No indication for fomepizole if no osmolar gap (methanol or ethylene glycol ingestion) • HD not indicated as no toxic ingestion is suspected • Sodium bicarb used only to keep pH > 7.15

14. A 42-year-old man hospitalized for recurrent variceal bleeding is evaluated for severe metabolic alkalosis. He has a 4-year history of alcoholic cirrhosis. He required six units of packed red blood cells and four units of fresh frozen platelets to maintain hemodynamic stability. On physical examination, temperature is normal, BP is 100/70 mm Hg, and HR is 96/min. Cardiopulmonary examination is normal. Ascites is noted. There is 2+ presacral edema and 2+ leg edema. Which of the following is the most appropriate management? A Add acetazolamide B Add furosemide C Add isotonic saline D Discontinue octreotide

15. Metabolic alkalosis from metabolism of citrate in blood products (increase bicarbonate) • Impaired excretion of bicarbonate due to poor renal perfusion from cirrhosis because of increased proximal reabsoprtion of bicarbonate • Acetazolamide will improve both alkalosis and volume retention

16. Furosemide facilitates sodium chloride excretion, not bicarbonate excretion • Saline would worsen fluid status as patient has increased ECF

17. A 23-year-old woman is evaluated in the emergency department for a 2-month history of progressive leg weakness. She reports no diarrhea or weight loss. Medical history is remarkable for Sjögren syndrome. She takes no medications. On physical examination, vital signs are normal. Diffuse weakness is noted most prominently in the legs, graded at 3/5. Which of the following is the most likely diagnosis? A Gitelman syndrome B Distal (type 1) renal tubular acidosis C Laxative abuse D Proximal (type 2) renal tubular acidosis

18. Normal AG and hypokalemia • Inability to secret hydrogen ions = pH > 6.0 • Calcinosis • Positive urine AG (no ammonium in the urine)

19. Gitelman syndrome leads to metabolic alkalosis and is associated with hypomagnesemia • Laxative abuse would have a negative urinary AG (appropriate kidney response to acidosis) • RTA Type II has urine pH < 5.5 (bicarbonate is eventually reabsorbed once serum level has fallen enough)

20. An 18-year-old woman is evaluated for a 6-month history of progressive weakness and a 11-lb weight loss. She reports increased fatigue and myalgia following exercise during the past 2 months. On physical examination, the patient is thin. Temperature is 97.6 °F, BP is 110/60 mm Hg, HR is 96/min. BMI is 18. The remainder of the examination is unremarkable. Which of the following is the most likely cause of this patient's acid-base disorder? A Diuretic abuse B Distal (type 1) renal tubular acidosis C Laxative abuse D Surreptitious vomiting

21. Normal anion gap metabolic acidosis • Urine anion gap is negative ( 22 + 15 – 45) = -8 • Bicarbonate loss exceeds increased ammonium excretion

22. Diuretic abuse and vomiting leads to metabolic alkalosis • RTA Type I would expect a positive urine anion gap

23. A 42-year-old man is evaluated in the emergency department for increased confusion. He has psoriasis and was treated with cream and a body wrap for 1 hour. He subsequently developed nausea and vomiting. He reports hearing water in his ears. He also has hypertension and type 2 diabetes mellitus complicated by proteinuria. Medications are enalapril and metformin. On physical examination, the patient is irritable, anxious, and intermittently somnolent but easily aroused. Temperature is 99.7 °F, BP is 160/100 mm Hg, HR is 106/min standing, and RR is 20/min. Which of the following is the most likely cause of this patient's clinical presentation? A Metformin toxicity B Methanol toxicity C Salicylate toxicity D Sepsis

24. Respiratory alkalosis • Excessive decrease in bicarbonate (decrease of more than 2 in bicarb when only 5 drop in PCO2) • AG Metabolic acidosis also present • Used oil of wintergreen (methyl salicylate) • Mental status changes, nausea, fever, vomiting and tinnitus

25. Metformin Toxicity leads to lactic acidosis (normal lactic acid level (6-16)) • Methanol poisoning leads to increased osmolal gap (308-304 =4) • Sepsis unlikely based on clinical picture and absence of leukocytosis

26. A 41-year-old woman is evaluated during a follow-up visit for high blood pressure. On physical examination, blood pressure is 162/100 mm Hg, which is similar to the values measured at her initial visit. Other vital signs are normal. BMI is 21. Laboratory studies are normal. Which of the following is the most appropriate next step in the management of this patient's hypertension? A Combination drug therapy B Lifestyle modifications C Single-drug therapy D Reevaluate patient in 2 weeks

27. Stage 2 HTN ( SBP > 160 or DBP > 100) • Goal for this patient is 140/90 • If require reduction of SBP > 20 or DBP > 10, combination therapy is recommended • Can shorten time for needed for medication adjustment • Can increase likelihood of BP goal

28. An 81-year-old man is evaluated for progressive fatigue. Nine months ago, he was diagnosed with giant cell arteritis; at that time, prednisone, omeprazole, risedronate, and vitamin D were initiated. His symptoms improved, and the prednisone was tapered. Five months ago he began to feel more fatigued. Evaluation was unremarkable other than the urinalysis, which was positive for leukocytes and leukocyte esterase. He was treated with ciprofloxacin without improvement of his symptoms. A subsequent urine culture was negative. Which of the following is the most likely diagnosis? A Acute interstitial nephritis B Acute tubular necrosis C Glomerulonephritis D Thrombotic thrombocytopenic purpura

29. Hypersensitivity to medication • PPI is common • Eosinophils on differential • Leukocytes and possibly leukocytes casts with negative culture

30. ATN presents with muddy brown casts • Can be induced by bisphosphonates • Giant cell arteritis affects large blood vessels, not usually small vessels of kidneys • Would expect dysmorphic erythrocytes and erythrocyte casts • TTP would see thrombocytopenia and microangiopathic hemolytic anemia

31. A 26-year-old man is evaluated in the emergency department after being found on the floor in his apartment by friends who had not seen him in several days. On physical examination, the patient is somnolent and minimally responsive. Temperature is 37.2 °C (98.9 °F), blood pressure is 92/54 mm Hg, pulse rate is 118/min, and respiration rate is 14/min with 97% oxygen saturation on ambient air. BMI is 25. Skin is mottled and edematous on the posterior surface of the legs, buttocks, and back. Neurologic examination reveals no focal or lateralizing findings. The remainder of the examination is normal. Which of the following is the most appropriate treatment for this patient? A Hemodialysis B Intravenous mannitol C Rapid infusion of intravenous 0.9% saline D Rapid infusion of intravenous 5% glucose