Acid-Bases Disorders & ABGs

Question 1

Define acidemia vs acidosis

Answer 1

• acidemia: increase in blood H+ (pH <7.35)
• acidosis: pathophysiologic process that acidifies body fluids

Question 2

Define alkalemia vs alkalosis

Answer 2

• alkalemia: decrease in blood H+ (pH >7.45)
• alkalosis: pathophysiologic process that alkalinizes body fluids

Question 3

Define acid-base disorders

Answer 3

changes on CO2 partial pressure (pCO2) or serum bicarbonate (HCO3-) that produces abnormal arterial pH values

Question 4

Which is the acid and which is the base: CO2, HCO3

Answer 4

CO2 = acid

HCO3 = base

Question 5

Which organ compensates for metabolic acidosis/alkalosis

Answer 5

Lungs - manages CO2 levels via hypo/hyperventilation

• takes minutes to compensate
• CAN’T have respiratory acidosis & alkalosis at the same time

Question 6

Which organ compensates for respiratory acidosis/alkalosis

Answer 6

Kidneys - manages HCO3 levels via excretion/absorption

• takes days to compensate
• CAN have metabolic acidosis/alkalosis at the same time

Question 7

What is an anion gap

Answer 7

measure of the difference between negatively charged and positively charged electrolytes in the blood (cations = positive, anions = negative)

Question 8

why does chloride loss result in metabolic alkalosis?

Answer 8

less chloride ions are available to exchange with bicarb so the ability to excrete excess bicarb from kidney is impaired

Question 9

Describe the pathophys of respiratory acidosis

Answer 9

Question 10

Describe the etiology of respiratory acidosis

Answer 10

low pH and high pCO2

Question 11

What is the presentation of respiratory acidosis

Answer 11

somnolence, confusion, AMS, asterixis, seizures or coma if severe

Question 12

What test should be done before getting an ABG from the radial artery

Answer 12

Allen’s test to check for good flow of the ulnar artery to continue hand perfusion

Question 13

Describe the pathophys of respiratory alkalosis

Answer 13

Question 14

Describe the etiology of respiratory alkalosis

Answer 14

high pH and low pCO2

Question 15

Describe the presentation of respiratory alkalosis

Answer 15

Question 16

Why is respiratory alkalosis usually self limited

Answer 16

because muscle fatigue/weakness will suppress ventilation

Question 17

Describe the etiology of metabolic acidosis

Answer 17

Question 18

Describe the presentation of metabolic acidosis

Answer 18

Question 19

Describe the diagnosis of metabolic acidosis

Answer 19

Question 20

Describe the treatment of metabolic acidosis

Answer 20

admit! treat underlying cause

Question 21

Describe the pathophys of HAGMA and NAGMA

Answer 21

Question 22

Describe the etiology of metabolic alkalosis

Answer 22

Question 23

Describe the treatment of metabolic alkalosis

Answer 23

Question 24

What are the components of an ABG measurement

Answer 24

• pH 7.35-7.45
• PaO2 (generally >80 mmHg)
• PaCO2 (35-45 mmHg)
• HCO3 (21-27 mEq/L)

Sometimes:
- carboxyhemoglobin (<3%)
- methemoglobin (<1%)

Question 25

Describe the use of VBG over ABG

Answer 25

- less invasive/painful - convenient - not useful for oxygenation - different values

Question 26

Describe the approach to ABG analysis

Answer 26

1. determine acidemia vs alkalemia 2. determine primary disorder (respiratory - acute vs chronic, metabolic - HAGMA v NAGMA) 3. is there appropriate compensation 4. what is the clinical diagnosis

Question 27

How do you determine if there is metabolic vs respiratory acidosis on ABG?

Answer 27

**relationship of pH and pCO2 with HCO3*** - ROME: respiratory opposite, metabolic equal

Question 28

How do you determine appropriate compensation on ABG analysis?

Answer 28

**pCO2 and HCO3 should move in the SAME direction** compensation always moves in the SAME direction as the primary disorder (if the compensation is higher/lower than expected pCO2 or HCO3 values using given equations - think mixed disorder like resp acidosis with metabolic alkalosis)

Question 29

What element of an ABG are you looking at to determine expected compensation for respiratory vs metabolic processes

Answer 29

- respiratory: expected HCO3 - metabolic: expected pCO2

Question 30

Define partial compensation on ABG

Answer 30

compensatory mechanism tried but failed to bring the pH back to normal (pH still out of range and pCO2 & HCO3 both high or both low)

Question 31

Define uncompensated on ABG

Answer 31

no change in compensatory mechanism (pH still out of range and either pCO2 or HCO3 out of range while other is normal)

Question 32

Define full compensation on ABG

Answer 32

compensatory mechanism brought pH back to normal (pH within normal limits while pCO2 and HCO3 both high or both low)

Question 33

How do you determine an acute vs chronic process on ABG analysis

Answer 33

look at clinical picture