Acid Base DDx - Kleinschmidt Flashcards
When evaluating Acid/Base disorders what is the first rule or step?
#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
When evaluating Acid/Base disorders what is the second rule or step?
#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
When evaluating Acid/Base disorders what is the third rule or step?
#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
When evaluating Acid/Base disorders what is the fourth rule or step?
#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
When evaluating Acid/Base disorders what is the fifth rule or step?
#5 Interpret clinical picture!
- Thorough history of present illness
- Physical exam
- Past medical hx
What are the possible primary disturbances for an acidemia?
increased pCO2 (respiratory)
OR
decreased [HCO3-] (metabolic)
What are the possible primary disturbances for an alkalemia?
decreased pCO2 (respiratory)
OR
increased [HCO3-] (metabolic)
What is the primary disturbance in metabolic acidosis?
- Retention of acid
-
decrease in [HCO3-]
- using up all the bicarb to attempt to buffer retained acid
-
decrease in [HCO3-]
What is the compensatory response to metabolic acidosis?
- Increase ventilation
- decreased pCO2
What is a metabolic acidosis caused by?
- Overproduction of acid
- Loss of alkali stores
- Failure of renal mechanisms to:
- synthesize base
- excrete acid
What is the DDx for Metabolic Acidosis with anion gap?
- M = Methanol
- U = Uremia
- D = Diabetic ketoacidosis/Alcoholic ketoacidosis
- P = Paraldahyde
- I = Iron or Isoniazid
- L = Lactic acid
- E = Ethylene glycol, Ethanol
- S = Salicylates
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?
Methanol
What diagnosis on the DDx for Metabolic Acidosis with anion gap is seen in patients with sepsis, hypotension, CO poisoning, or cyanide poisoning?
Lactic Acid
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?
Ethylene Glycol or Ethanol
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?
Salicylates
What is the DDx for Metabolic Acidosis with normal anion gap?
- 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
What is the primary disturbance in metabolic alkalosis?
increased plasma [HCO3-]
What is the compensatory response to metabolic alkalosis?
Hypoventilating
(limited response)
What is the DDx for Metabolic Alkalosis?
- Chloride responsive (urine Cl- <10)
- Vomiting
- Loop diuretics
- NG suction
- Chloride unresponsive
- Hyperaldosteronism (Barter’s)
- Antacid use
- Cushings
What is the primary disturbance in Respiratory Acidosis?
increase in pCO2
What is the compensatory response to Respiratory Acidosis?
- 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
- Acute Compensation
What are the causes of Respiratory Acidosis?
- Airway obstruction
- Lung pathology
- COPD
- Asthma
- Infection
- Pneumothorax
- CNS tumor
- Drugs - sedative, opioids, hypnotics, drugs
- Weakening of respiratory muscles (Quadraplegia)
What is the primary disturbance in Respiratory Alkalosis?
decrease in arterial pCO2
What is the compensatory response to Respiratory Alkalosis?
- 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
- Acute compensation:
