Critical Care: Acid-base Disorders

Question 1

Changes in what molecule drive metabolic acid-base disturbances?

Answer 1

Bicarbonate (HCO3-)

Question 2

Changes in what molecule drive respiratory acid-base disturbances?

Answer 2

Partial pressure of carbon dioxide (PCO2)

Question 3

A metabolic acidosis is a ______ HCO3-

Answer 3

Decreased

Question 4

A respiratory acidosis is a _______ PCO2

Answer 4

Increased

Question 5

A metabolic alkalosis is a ________ HCO3-

Answer 5

Increased

Question 6

A respiratory alkalosis is a ________ PCO2

Answer 6

Decreased

Question 7

List two kinds of acid-base compensation

Answer 7

1. Respiratory compensation

2. Metabolic compensation

Question 8

What is a mixed acid-base disorder?

Answer 8

When patients have more than one primary disorder

Question 9

On what time frame does respiratory compensationn develop? How?

Answer 9

Immediately with changes in respiratory rate

Question 10

On what time frame (in general) does metabolic compensation develop? How?

Answer 10

Slowly by regulating the excretion and reasbroption of HCO3- and H+

Question 11

What is the compensation for metabolic acidosis? How?

Answer 11

1. The compensation for metabolic acidosis is respiratory alkalosis (i.e. decrease in PCO2).
2. This is achieved by increasing the respiratory rate to eliminate more CO2, thus making pH more basic (i.e. higher pH).

Question 12

What is the compensation for metabolic alkalosis?

Answer 12

1. The compensation for a metabolic alkalosis is a respiratory acidosis (i.e. increase in PCO2).
2. This is achieved by slowing the respiratory rate to retain more CO2, thus making the pH more acidic (i.e. lower pH).

Question 13

What is the compensation for respiratory acidosis?

Answer 13

The compensation for a respiratory acidosis is a metabolic alkalosis (i.e. an increase in HCO3-)

Question 14

What is the compensation for respiratory alkalosis?

Answer 14

The compensation for respiratory alkalosis is metabolica cidosis (i.e. a decrease in HCO3-)

Question 15

Normal value for pH, and range?

Answer 15

7.40 (range: 7.35-7.45)

Question 16

Normal range for PCO2?

Answer 16

Normal: 40, range 35-45 mmHg

Question 17

Normal range for PO2?

Answer 17

80-100 mm Hg

Question 18

Normal range for HCO3-

Answer 18

Normal: 24, range 22-26 mEq/L (or mmol/L)

Question 19

Normal range for SaO2?

Answer 19

95%-100%

Question 20

In metabolic acidosis, a primary disturbance of HCO3 _____ by 1 mmol/L can be compensated by a decrease in PCO2 by ____ mmHg

Answer 20

1. A primary disturbance of HCO3- decrease by 1 mmol/L

2. can be compensated by a decrease in PCO2 by 1.2 mmHg

Question 21

In metabolic alkalosis, a primary disturbance of HCO3 _____ by 1 mmol/L can be compensated by a increase in PCO2 by ____ mmHg

Answer 21

1. A primary disturbance of HCO3- increase by 1 mmol/L

2. Can be compensated by an increase in PCO2 by 0.7 mmHg

Question 22

Respiratory acidosis compensation: An increase in PCO2 by 10 mm Hg can be acutely compensated by a degree of _____ mmol/L. Chronic compensation can achieve _____ mmol/L

Answer 22

1. A respiratory acidosis caused by an increase in PCO2 by 10 mm Hg
2. can be acutely compensated by increased HCO3- by 1 mmol/L
3. And chronically compensated by an increased HCO3- by 3.5 mmol/L

Question 23

Respiratory alkalosis compensation: An decrease in PCO2 by 10 mm Hg can be acutely compensated by a degree of _____ mmol/L. Chronic compensation can achieve _____ mmol/L

Answer 23

1. A respiratory alkalosis caused by a decrease in PCO2 by 10 mm Hg
2. can be acutely compensated by a decreased HCO3 of 2 mmol/L
3. And chronically compensated by a decreased HCO3 of 4 mmol/L.

Question 24

If ____ is more than 12, there is a primary metabolic acidosis regardless of pH or HCO3.

Answer 24

Anion Gap

Question 25

How to calculate anion gap? What does it represent?

Answer 25

1. (Sodium and Potassium) minus (Chloride + Bicarbonate) | 2. It represents unmeasured anions (i.e. organic acids)

Question 26

What is an excess anion gap?

Answer 26

1. Also known as a delta gap. 2. In non-anion gap acidosis, bicarbonate is lost, and chloride is increased to compensate. This is a hyperchloremic acidosis. 3. In anion gap acidosis, there is an increase in organic acids which consume bicarbonate. 4. There should be an equimolar increase in chloride and bicarbonate. 5. Excess anion gap represents whether this equimolar increase is occuring. It can help determine whether chloride is being lost through a primary alkalosis.

Question 27

How to calculate excess anion gap? How to interpret?

Answer 27

1. Excess AG = Total aG - Normal AG. Add excess AG to HCO3- 2. If this sum is greater than 30 mEq/L, there is also a primary AG metabolic alkalosis (e.g. chloride is also being lost.) 3. If the sum is less than a normal serum bicarbonate (e.g. there is a proportional increase in Cl- relative to HCO3- decrease) there is an underlying non-AG metabolic acidosis (e.g. hyperchloremic acidosis).

Question 28

When should an anion gap be calculated?

Answer 28

Any time you are evaluating an acid-base disturbance

Question 29

When should an excess anion gap be calculated?

Answer 29

When evaluating AG Metabolic acidosis

Question 30

What is the first step in evaluating an acid base disorder?

Answer 30

1. Assess pH, PCO2 and HCO3-. 2. pH helps you determine if there is an alkemia or a acidemia. 3. PCO2 derangement determines if it's respiratory. 4. HCO3- derangement determines if it's metabolic.

Question 31

What is the second step in evaluating an acid-base disorder?

Answer 31

1. Calculate an Anion Gap. | 2. If the AG is more than 12, there is a primary metabolic acidosis regardless of pH or HCO3-.

Question 32

What is the third step in evaluating an acid-base disorder?

Answer 32

1. Calculate and interpet an EAG. | 2. The purpose is help determine mixed acid-base disorders.

Question 33

List three principal causes of respiratory acidosis

Answer 33

1. Pulmonary 2. Cardiovascular 3. Neurological

Question 34

List four causes of "pulmonary" respiratory acidosis

Answer 34

1. Pulmonary edema 2. Pulmonary embolus 3. Pneumonia 4. Bronchospasm

Question 35

List two causes of "cardiovascular" respiratory acidosis

Answer 35

1. Cardiac arrest | 2. Stroke

Question 36

List three causes of "neurological" respiratory acidosis

Answer 36

1. CNS depression 2. Spinal cord injury 3. Sedatives

Question 37

How to treat a respiratory acidosis?

Answer 37

1. Invasive-noninvasive ventilation | 2. Correct cause

Question 38

List three broad classes of respiratory alkalosis

Answer 38

1. psychiatric/neurological 2. traumatic/neurological 3. respiratory/mechanical

Question 39

List four "psychiatric/neurologic" causes of respiratory alkalosis

Answer 39

1. Anxiety 2. Pain 3. Stimulant drugs 4. Respiratory rate stimulation

Question 40

List three "traumatic/neurologic" causes of respiratory alkalosis

Answer 40

1. CNS tumor 2. Head injury 3. Stroke

Question 41

List four "respiratory/mechanical" causes of respiratory alkalosis

Answer 41

1. Hypoxia 2. reduced oxygen-carrying capacity 3. Reduced alveolar oxygen extraction 4. Extracorporeal CO2 removal

Question 42

How to treat respiratory alkalosis?

Answer 42

1. Correct cause 2. Oxygen supplementation/Noninvvasive ventilation (in decreased oxygen states) 3. Hypoventilation/sedation (in excessive CO2 removal states)

Question 43

List 8 causes of AG metabolic acidosis

Answer 43

1. MUDPILES 2. Methanol 3. Uremia 4. DKA 5. Propylene glycol 6. Intoxication or infection 7. Lactic acidosis 8. Ethylene glycol 9. Salicylate

Question 44

List 9 causes of non-AG metabolic acidosis

Answer 44

1. F-USED CARS 2. Fistula (pancreatic) 3. Uteroenteric conduits 4. Saline excess 5. Endocrine (hyperparathyroid) 6. Diarrhea 7. Carbonic anhydrate inhibitors 8. Arginine, lysine, Cl- 9. Renal tubular acidosis 10. Spironolactone

Question 45

How to treat AG metabolic acidosis

Answer 45

1. Correct cause 2. Use of bases may be considered (sodium bicarbonate or THAM) in non-AG metabolic acidosis 3. Base use in AG metabolic acidosis is controversial.

Question 46

What are the two types of metabolic alkalosis?

Answer 46

1. Chloride resistant - increased aldosterone action causing excess secretion. 2. Chloride responsive - increased loss.

Question 47

List two causes of chloride resistant metabolic alkalosis

Answer 47

1. Hyperaldosteronism | 2. Increased mineralocorticoid

Question 48

List three causes of chloride responsive metabolic alkalosis

Answer 48

1. Vomiting 2. NG suction 3. Diuretic

Question 49

How to evaluate a metabolic alkalosis?

Answer 49

1. Look at urine chloride. 2. Urine Cl- > 25 indicates chloride resistant (e.g. excess excretion). 3. Urine Cl- < 25 indicates chloride resistant (e.g. non-renal loss of chloride.)

Question 50

What is the relationship between albumin and anion gap?

Answer 50

1. Low albumin can cause a normal anion gap despite clinically significant AG metabolic acidosis. 2. Hypoalbuminemia decreases the AG by 2.5-3 mEq/L for every 1 g/dL decrease in serum albumin less than 4 g/dL. 3. Measured albumin - 4 g/dl (normal albumin) * 2.5 is the correction amount.