Acid Base DDx - Kleinschmidt

Question 1

When evaluating Acid/Base disorders what is the first rule or step?

Answer 1

#1 Look at pH using ABG.

• normal pH = 7.35–7.45
• whichever side of 7.40 is the primary abnormality
  
  • acidosis or alkalosis
  • body never fully compensates

Question 2

When evaluating Acid/Base disorders what is the second rule or step?

Answer 2

#2 Calculate Anion Gap

Anion Gap = Na⁺ – (Cl^- + HCO₃^-)

• Normal Anion Gap = 8-12 mEq/L
• Need to explain if metabolic acidosis is with anion gap or normal gap

Question 3

When evaluating Acid/Base disorders what is the third rule or step?

Answer 3

#3 If elevated anion gap → Calculate Osmol Gap!

2(Na⁺) + Glucose/18 + BUN/2.8 = Calculated Osms

• Measured osmolarity – calculated osms = Osmol Gap
  
  • Normal Osmol Gap = <10 or 10
  • elevated with certain ingestions
    
    • methanol
    • ethylene glycol

Question 4

When evaluating Acid/Base disorders what is the fourth rule or step?

Answer 4

#4 Calculate excess anion gap (Delta Gap)

Calculated anion gap – 12 = Delta Gap

• Excess Anion Gap + bicarb = normal bicarb
  
  • normal bicarb = 24-26
  • if lower than normal bicarb → non-anion gap acidosis is also occuring
  • if higher than normal bicarb → underlying metabolic alkalosis

Question 5

When evaluating Acid/Base disorders what is the fifth rule or step?

Answer 5

#5 Interpret clinical picture!

• Thorough history of present illness
• Physical exam
• Past medical hx

Question 6

What are the possible primary disturbances for an acidemia?

Answer 6

increased pCO₂ (respiratory)

OR

decreased [HCO₃^-] (metabolic)

Question 7

What are the possible primary disturbances for an alkalemia?

Answer 7

decreased pCO₂ (respiratory)

OR

increased [HCO₃^-] (metabolic)

Question 8

What is the primary disturbance in metabolic acidosis?

Answer 8

• Retention of acid
  
  • decrease in [HCO₃^-]
    
    • using up all the bicarb to attempt to buffer retained acid

Question 9

What is the compensatory response to metabolic acidosis?

Answer 9

• Increase ventilation
  
  • decreased pCO₂

Question 10

What is a metabolic acidosis caused by?

Answer 10

• Overproduction of acid
• Loss of alkali stores
• Failure of renal mechanisms to:
  
  • synthesize base
  • excrete acid

Question 11

What is the DDx for Metabolic Acidosis with anion gap?

Answer 11

• M = Methanol
• U = Uremia
• D = Diabetic ketoacidosis/Alcoholic ketoacidosis
• P = Paraldahyde
• I = Iron or Isoniazid
• L = Lactic acid
• E = Ethylene glycol, Ethanol
• S = Salicylates

Question 12

What diagnosis on the DDx for Metabolic Acidosis with anion gap creates a Osmol gap and is seen in alcoholics using other volatiles to get intoxicated?

Answer 12

Methanol

Question 13

What diagnosis on the DDx for Metabolic Acidosis with anion gap is seen in patients with sepsis, hypotension, CO poisoning, or cyanide poisoning?

Answer 13

Lactic Acid

Question 14

What diagnosis on the DDx for Metabolic Acidosis with anion gap causes Osmol gap, causes renal failure and oxalate urine crystils, is seen in overdoses or ingestion of antifreeze, and is treated with alcohol or dialysis?

Answer 14

Ethylene Glycol or Ethanol

Question 15

What diagnosis on the DDx for Metabolic Acidosis with anion gap has multiple presentations, can cause coagulopathy or seizures, and tends to be seen with a primary respiratory alkalosis/acidosis?

Answer 15

Salicylates

Question 16

What is the DDx for Metabolic Acidosis with normal anion gap?

Answer 16

• H = Hyperalimentation/Post-hyperventilation
• A = Addison’s disease (chronic adrenal insufficiency)
• R = Renal tubular acidosis
• D = Diarrhea
• A = Acetazolamide (carbonic anhydrase inhibitor)
• S = Spironolactone (aldosterone receptor antagonist)
• S = Saline infusion

***Taken from 2014 First Aid

Question 17

What is the primary disturbance in metabolic alkalosis?

Answer 17

increased plasma [HCO₃^-]

Question 18

What is the compensatory response to metabolic alkalosis?

Answer 18

Hypoventilating

(limited response)

Question 19

What is the DDx for Metabolic Alkalosis?

Answer 19

• Chloride responsive (urine Cl^- <10)
  
  • Vomiting
  • Loop diuretics
  • NG suction
• Chloride unresponsive
  
  • Hyperaldosteronism (Barter’s)
  • Antacid use
  • Cushings

Question 20

What is the primary disturbance in Respiratory Acidosis?

Answer 20

increase in pCO₂

Question 21

What is the compensatory response to Respiratory Acidosis?

Answer 21

• Elevate HCO₃^- (metabolically)
  
  • Acute Compensation
    
    • HCO₃^- rises 1 mEq for each rise of 10 pCO₂
  • Chronic Compensation
    
    • HCO₃^- rises by 3 mEq for each rise of 10 pCO₂

Question 22

What are the causes of Respiratory Acidosis?

Answer 22

• Airway obstruction
• Lung pathology
  
  • COPD
  • Asthma
  • Infection
  • Pneumothorax
• CNS tumor
• Drugs - sedative, opioids, hypnotics, drugs
• Weakening of respiratory muscles (Quadraplegia)

Question 23

What is the primary disturbance in Respiratory Alkalosis?

Answer 23

decrease in arterial pCO₂

Question 24

What is the compensatory response to Respiratory Alkalosis?

Answer 24

• decrease HCO₃^-
  
  • Acute compensation:
    
    • HCO₃^- falls by 2 mEq for each drop of 10 in PCO₂
  • Chronic compensation:
    
    • HCO₃^- falls by 4 mEq for each drop of 10 in PCO₂

Question 25

What are the causes of Respiratory Alkalosis?

Answer 25

• Hyperventilation
• Anxiety/Hysteria
• High altitudes
• Causes of tachypnea
  
  • Sepsis
  • fever
  • PE
  • Pneumonia
  • Pregnancy
• Alcohol or narcotic withdrawal
• Tumor