Acid Base Disorders and Blood Gas Interpretation

Question 1

What is the Henderson Hasselbach Equation?

Answer 1

pH = pKa + log [A-]/[HA]

Question 2

what does the pKa represent?

Answer 2

the point where the acid and base are equal

Question 3

For calculating the bicarbonate buffering system, what would you put in the HH equation?

Answer 3

pH = pKa + log [HCO3-]/[CO2]

Question 4

what are normal values for [CO2], pKa, and [HCO3-]?

Answer 4

• [CO2] = 0.03
• pKa = 6.1
• [HCO3-] = 24 meq/L

Question 5

What is nl pH for arterial blood?

Answer 5

7.38-7.43 (higher in denver)

Question 6

what is nl pH for venous blood?

Answer 6

7.34-7.37

Question 7

What are the 2 methods of compensation for acid/base disturbances?

Answer 7

Lungs regulate CO2 (minutes)

kidneys regulate HCO3 (hours to days)

Question 8

True or False: Compensation will never completely correct to normal pH nor will it over compensate

Answer 8

True

Question 9

What is respiratory acidosis?

Answer 9

Too much CO2 usually due to ineffective ventilation leads to acidosis

Question 10

What are 2 acute causes of respiratory acidosis?

Answer 10

CNS depression (opiate, benzo, etoh)
Respiratory muscle fatigue (increased work of breathing)

Question 11

What are some causes of chronic respiratory acidosis?

Answer 11

• central hypoventilation (obesity hypoventilation syndrome)
• neuromuscular disease (ALS)
• chronic lung disease (COPD, bronchiectasis)
• hypothyroidism

Question 12

What is respiratory alkalosis?

Answer 12

decreased CO2 results in increased pH due to increase in ventilation

Question 13

What are some acute causes for respiratory alkalosis?

Answer 13

pain,

• anxiety,
• fever,
• mechanical ventilation

Question 14

what are some chronic causes for respiratory alkalosis?

Answer 14

living at altitude

• brain injury
• chronic salicylate toxicity
• pregnancy

Question 15

What is metabolic acidosis?

Answer 15

too much acid results in drop in HCO3 and pH

Question 16

How do you determine if someone is compensating properly?

Answer 16

Winter’s formula

Expected PCO2 = 1.5 [HCO3] +8 +/- 2

Question 17

what are the 2 categories of metabolic acidosis?

Answer 17

anion gap and non anion gap

Question 18

how do you solve for anion gap?

Answer 18

Anion gap = [Na] - ([Cl] - [HCO3-]

Nl is 12-14

Question 19

What does an increased anion gap indicate?

Answer 19

It means that there is an increase in unmeasured anions like ketoacids which is likely causing the acidosis. This is because the bicarb is elevated but too much to just compensate for the measured ions (Cl) so it must be compensating for ions that are not measured

Question 20

What are the main causes of non-anion gap metabolic acidosis?

Answer 20

Due to loss of HCO3 either due to
GI loss (diarrhea)
Renal loss
too much IV saline (increased Cl with loss of bicarb)

Question 21

What are the main causes of anion gap metabolic acidosis?

Answer 21

MUDPILES
Methanol
Uremia
DKA
Propylene glycol (food/anti-freeze)
INH (isoniazid in the tx of TB)
Lactate
Ethylene glycol (anti-freeze)
Salicylates (aspirin)

Question 22

what is metabolic akalosis?

Answer 22

too much HCO3- results in higher pH

Question 23

what is one of the main concerns of metabolic alkalosis?

Answer 23

ventricular arrythmias and seizures can occur

Question 24

what are some causes of metabolic alkalosis?

Answer 24

• vomiting or NG tube suction
• ingestion of NaHCO3
• ingestion of other alkali
• hypovolemia
• diuretics

Question 25

What is the major way to distinguish between metabolic vs respiratory acidosis in regards to PCO2 and pH?

Answer 25

In respiratory acidosis/alkalosis PCO2 and pH move in opposite directions but in metabolic they move in the same direction