Exam 2: Clinical Metabolic Acidosis

Question 1

žCalculate the Anion Gap

Answer 1

• Anion Gap = Serum Na⁺ - (Cl^- + HCO₃^-)
• Normal = 6 - 12 mEq/ L
• Helpful in differential diagnosis of metabolic acidosis.
  
  • High AG: associated with addition of endogenously or exogenously generated acids
  • Normal AG: associated with loss of HCO₃^- or failure to excrete H⁺ from the body

Question 2

žžList causes of high anion gap acidosis

Answer 2

• Associated with addition of endogenously or exogenously generated acids
• Some causes of high anion gap acidosis:
  • Lactic Acidosis - Lactate
  • Ketoacidosis - Beta-hydroxybutyrate, acetoacetate
  • Renal Failure - Sulfate, phosphate, urate
  • Ingestions - Salicylate, methanol, ethylene glycol, metformin/phenformin
  • Massive rhabdomyolysis - release of H+ and organic anions from damaged muscle

Question 3

Mnemonic for causes of high anion gap acidosis

Answer 3

• Associated with addition of endogenously or exogenously generated acids
• DR MAPLES
  • D - DKA
  • R - Renal
  • M - Methanol
  • A - Alcoholic ketoacidosis
  • P - Phenformin
  • L - Lactic
  • E - Ethylene glycol
  • S - Salicylates

Question 4

žžList causes of normal anion gap acidosis

Answer 4

• Associated with loss of HCO₃^- or failure to excrete H⁺ from the body
• Some causes of normal anion gap acidosis:
  • GI loss of HCO3 - diarrhea
  • Ureteroileostomy
  • Renal diminished H+ secretion - type 1 RTA (Distal RTA)
  • Renal HC03 loss - type 2 RTA (Proximal RTA)
  • Hypoaldosteronism - Type 4 RTA
  • Ingestions - ammonium chloride

Question 5

žDiabetic ketoacidosis

Answer 5

• Relative insulin deficiency
• Accelerated lipolysis and ketogenesis
• Alcoholic ketoacidosis and starvation ketoacidosis
  
  • suppression of endogenous insulin secretion
  • inadequate carbohydrate ingestion
  • glucose levels normal

Question 6

žDiscuss the clinical features of diabetic ketoacidosis

Answer 6

• Clinical Features
  
  • Nausea, vomiting
  • Diffuse abdominal pain
    
    • air in stomach!
  • Evidence for dehydration
  • Hyperventilation- Kussmaul respirations
  • Shock
  • Coma

Question 7

žDiscuss the Labs of diabetic ketoacidosis

Answer 7

• Laboratory Evaluation
  
  • Anion gap acidosis
  • Serum Ketones
  • Hyperglycemia
  • Urine ketones correlate poorly with Ketonemia
  • Electrolyte abnormalities:
    
    • HypoNa⁺
    • HyperK⁺
    • Azotemia
      
      • abnormally high levels of nitrogen-containing compounds
    • Hyperosmolality

Question 8

žžDiscuss the causes of lactic acidosis

Answer 8

• Results from impaired cellular respiration
• Lactate produced from reduction of pyruvate in muscle, RBCs from anaerobic glycolysis
• Overproduction of lactic acid from tissue hypoperfusion or impaired oxygenation
  
  • Cardiopulmonary arrest
  • Shock
  • Severe hypoxemia
  • Carbon monoxide poisoning
  • Vascular insufficiency (mesenteric or limb ischemia)
• Frequently occurs during strenuous exercise in healthy people - with no consequence

Question 9

žžDiscuss the lactate assay of lactic acidosis

Answer 9

Normal: 1- 0.5 mmol/L

Critical illness: < 2 mmol/L (normal)

Lactic Acidosis: > 5 mmol/L

Question 10

žžDiscuss the signs of impaired tissue perfusion

Answer 10

• Hypotension
• Deteriorating mental status
• Peripheral vasoconstriction
• Anuria or Oliguria

Question 11

Renal Failure and High Anion Gap Acidosis

Answer 11

• Inorganic compounds
  
  • phosphates and sulfates contribute to Anion Gap
• Organic compounds
  
  • accumulate as renal failure progresses.
• Acidosis with GFR < 20-30 ml/min
• Acidosis also related to decreases NH_4⁺ excretion by kidneys.

Question 12

žList the features / labs of ethylene glycol poisoning

Answer 12

• Laboratory Tests
  
  • Electrolytes - for anion gap
  • Arterial blood gas determination
  • Woods lamp (Ultraviolet light) to urine or clothing
    
    • green-colored glow in dark room (Fluorescin)
  • Urinalysis - Ca²⁺ oxalate crystals

Question 13

žList the treatment of ethylene glycol poisoning

Answer 13

• Goal: Prevent neurologic sequelae
• Administer Alcohol (ethanol)
  
  • to saturate alcohol dehydrogenase and inhibit metabolism of EG to toxic metabolites
• Bicarbonate therapy
  
  • to correct acidosis < 7.2
• Give IV thiamine and pyridoxine-cofactors
• Hemodialysis to clear EG

Question 14

Identify the crystals

Answer 14

A) Oxalate

B) Triple Phosphate

C) Cystine

Question 15

žList the metabolic effects of salicylate poisoning

Answer 15

• Initial respiratory alkalosis
• Progresses to mixed respiratory alkalosis and metabolic acidosis
  
  • More rapid progression in children
• Uncoupling of oxidative phosphorylation
• Derangement in Krebs cycle and carbohydrate metabolism
• Accumulation of organic acids = metabolic acidosis
  
  • pyruvate, lactate, acetoacetate

Question 16

žList the clinical effects of salicylate poisoning

Answer 16

• CNS
  
  • confusion to coma
• Ototoxicity
  
  • tinnitus, deafness, dizziness
• GI
  
  • nausea, vomiting, bleeding
• Pulmonary edema
  
  • noncardiogenic
• Hem
  
  • inhibit vitamin K dependent factors
• Mortality
  
  • Acute overdose - 2%
  • Chronic overdose - 25%

Question 17

Dx Type 1,2,4 RTA

(renal tubular acidosis)

Answer 17