Acid-Base physiology Flashcards
What is le Chatelier’s principle? How does it apply to acid/base physiology? Give an example
H20 + CO2 H2CO3 HCO3- + H+ A change in one of the factors will shift the equation to maintain equilibrium and hemostasis Ex 1: increased CO2 shifts equation right, increases H+ and results in acidosis (respiratory acidosis) Ex 2: Loss of HCO3- through diarrhea will result in increased H+ favoring the right side of the equation, results in metabolic acidosis
What are 2 mechanisms of compensation in acid-base abnormalities?
- Respiratory Drop in pH stimulates respiratory centers in medulla, causing increased ventilation. Increased pH leads to hypoventilation 2. Renal Bicarbonate and H+ handling (excretion or resorption) in the kidneys May be abnormal in renal failure
What is Winter’s formula?
To calculate expected CO2 level for compensation in acidotic states PCO2 = 1.5(HCO3-) + 8
List the 5 step method to ABG interpretation
- Identify pH abnormality 2. Determine amount of CO2 and HCO3- deviation from baseline (identify primary abnormality 3. Determine if primary process is acute or chronic 4. Determine if compensation is adequate 5. Calculate Delta/Delta (if acidosis)
What are the compensation rules for acid base disorders?
Process
PCO2
HCO3-
Metabolic Acidosis
1
1
Metabolic Alkalosis
1
0.7
Respiratory acidosis (acute)
10
1
Respiratory alkalosis (acute)
10
2
Respiratory acidosis (chronic)
10
3
Respiratory alkalosis (chronic)
10
4
DDx of 1. WAGMA, 2. NAGMA, 3. LAGMA
Wide Anion Gap
Metabolic Acidosis
Normal Anion Gap
Metabolic Acidosis
Low Anion Gap
Metabolic Acidosis
Methanol/Ethylene Glycol
Hyperalimentation
Hypoalbuminemia
Uremia
Addison’s
Multiple myeloma
DKA, AKA, malnutrition
Acetazolamide
Lithium toxicity
Paraldehyde
RTA 1, 2, 4
Lab error
Isoniazid, Iron
Diarrhea
Lactic acidosis
Dehydration
ETOH
Diuretics
Salicylates
Uterosignmoidoscopy
Carbon monoxide, cyanide
Pancreatic fistula
Acetate
Pancreatic drainage
Toluene
Saline (large amounts)
MUDPILES CAT
HARDUPS
HILL
DDx of metabolic alkalosis
Either decreased H+ or increased HCO3-
Metabolic Alkalosis
Volume Contraction
Diarrhea
Diuretics
Iron-deficient baby formulat
Normal volume/volume expanded
Hyperaldosteronism
Cushing’s syndrome
Hypokalemia
Adenocarcinoma
DDx of respiratory acidosis
Can’t breathe vs. won’t breathe
Respiratory Acidosis
Airway obstruction
CNS depression (drugs, trauma)
Myasthenia Gravis
Guillan Barre Syndrome
Pneumonia
Pulmonary edema
Pneumothorax
Flail chest
Pulmonary contusions
COPD, Asthma
DDx of respiratory alkalosis
Hyperventilation
Respiratory Alkalosis
High altitude
Anemia
Psychogenic
CVA
Salicylates
Pneumonia
Pulmonary embolism
Pulmonary edema
Sepsis
Hepatic encephalopathy
How do you calculate the delta-delta gap?
Why is it useful?
delta/delta = (calculated AG - 12)/(24 - measured HCO3)
Helps identify if there is a triple disorder
What do the delta/delta gap values mean?
- 1-2 pure WAGMA
- <1 simultaneous NAGMA
- >2 simultaneous metabolic alkalosis or pre-existing chronic compensated respiratory acidosis
What is the base excess
Changes numbers to eliminate respiratory component of ABG - purely metabolic now
This number represents how much base or acid you would have to add to reah pH 7.4
ie: BE -6 = this patient has 6 mmol/L of base that would have to be added to reach pH 7.4 (base deficit)
ie. BE 4 = patient needs 4 mmol/L of acid to reach pH 7.4 (base excess)
What are the 3 types of lactic acidosis
Type A
Type B
D-lactic acidosis
Describe Type A lactic acidosis
Due to tissue hypoperfusion and impaired tissue oxygenation
Ie: shock states
(also consider increased metabolic rate - seizures, exercise)
Describe Type B lactic acidosis
Not due to tissue hypoperfusion
- Toxin induced impairment of cellular metabolism
ie: cyanide, salicylates, - Malignancy
- Decreased hepatic clearance
ie. ETOH, liver disease - Diabetes
- Mitochondrial dysfunction (some congenital)
