Acid-Base and the Renal System Flashcards Preview

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Flashcards in Acid-Base and the Renal System Deck (69)
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1

pH is determined by what?

Henderson-Hasselbach equation?

the ratio of CO2 to HCO3

pH = 6.10 + log ([HCO3] ÷ [0.03 X PCO2])

2

1. Each day the body generates acids that must be what? 2

2. How much CO2 produced daily?

3. Cellular metabolism generates organic acids which are metabolized to what?

1. buffered or excreted

2. 15,000 mmol of CO2 produced daily

3. metabolized to
-glucose,
-CO2 or
-water

3

Acid base balance is maintained by what? 3

1. Respiratory: CO2 is exhaled via the respiratory system
2. Metabolism: Metabolic utilization of organic acids
3. Renal: excretion of nonvolatile acids

4

Renal excretion of acid is accomplished how?

1. H+ ions combined with urinary buffers

5

H+ ions combined with urinary buffers are excreted by the urine. Which buffers are we talking about?
4

Give an example of a major adaptive response that happens due to this process?

1. Phosphate (HPO4 = H → H2PO4)
2. Urate
3. Creatinine
4. Ammonia (NH3 + H → NH4)

Major adaptive response is an increase in ammonium excretion in the urine

6

What are the three kinds of buffers we talked about?

1. Respiratory
2. Renal
3. Carbonic acid-bicarbonate buffer

7

Describe the physiology of the Respiratory Buffer system?



How soon may compensation occur?

pH will trigger an increase or decrease in the rate and depth of ventilation until the appropriate amount of CO2 has been re-established

Compensation may occur within minutes

8

Respiratory compensation

Within an intact respiratory system there is a prediactable amount of buffer for CO2. Describe this for:
1. Metabolic acidosis?
2. Metabolic alkalosis?

Metabolic acidosis
1. PCO2 will decrease by 1.3 mmHg for every 1 mEq/L drop in the serum HCO3

Metabolic alkalosis
2. PCO2 will increase 0.7mmHg for every 1 mEq/L increase in HCO3

9

Bicarbonate HCO3-:
1. Is what kind of ion?
2. What is it a buffer for?

3. What maintains the balance of HCO3- and H+?

4. There is a small immediate change due to what?

5. Kidneys affect changes in the pH which take how long?

1. Base
2. Buffer for hydrogen ions
3. Renal system maintains the
4. whole body buffering system

5. 3-5 days

10

Bicarbonate buffer: How much will HCO3- change in the following settings:

1. Acute respiratory acidosis

2. Chronic respiratory acidosis

3. Acute respiratory alkalosis

4. Chronic respiratory alkalosis

1. HCO3 will increase 1 mEq/L per 10mmHg increase in PCO2

2. HCO3 will increase 3.5 mEq/L per 10mmHg increase in PCO2

3. HCO3 will decease by 2 mEq/L per 10mmHg decrease in PCO2

4. HCO3 will decrease by 5 mEq/L per 10mmHg decrease in PCO2

11

Carbonic acid-bicarbonate buffer system
1. Whats the chemical equation again?

2. If there is an increase in the H+ concentration in the blood it can be converted into what?

3. If H+ concentrations in the blood drop below the desired level then carbonic acid will do what?

4. When CO2 levels increase it is converted into?

1. CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-

2. carbonic acid

3. dissociate

4. carbonic acid

12

The end goal of blood gas analysis is what?

What are the 4 etiologies?

Determine if the acid base disturbance is metabolic or respiratory in etiology

1. Respiratory acidosis
2. Respiratory alkalosis
3. Metabolic acidosis
4. Metabolic alkalosis

13

Respiratory acidosis
1. What is the main problem?
2. What is this caused by?

3. How do we correct this?

1. too much CO2.
2. something wrong with ventilation (rib fractures, something wrong with the pulmonary cap membrane)

3. Ventilator, meds etc

14

Respiratory acidosis occurs at what levels:
pH?
PaCO2?

pH less than 7.35 with a PaCO2 > than 45 mm Hg

15

Causes of Respiratory Acidosis
4

1. Central nervous system depression
2. Impaired respiratory muscle function
3. Pulmonary disorders
4. Hypoventilation

16

Describe what could cause the following resulting in respiratory acidosis?
1. Central nervous system depression 2
2. Impaired respiratory muscle function 3

1.
-medications (narcotics, sedatives, or anesthesia)
-head injury

2.
-spinal cord injury,
-neuromuscular diseases
-neuromuscular blocking drugs



17

Describe what could cause the following resulting in respiratory acidosis?
1. Pulmonary disorders 7
2. Hypoventilation 5

1.
-Atelectasis
-Pneumonia
-Pneumothorax
-Pulmonary edema
-Bronchial obstruction
-Massive pulmonary embolus
-Respiratory failure

2.
-Pain
-Chest wall injury/deformity
-Abdominal distension
-Obesity
-Trauma

18

Respiratory Alkalosis
1. What is the main problem?

2. How do you correct that?

1. Hyperventilation

2. Correct the underlying cause
(fever, sepsis, anxiety, pain)

19

Respiratory Alkalosis
pH at?
PaCO2 at?

pH >7.45 with a PaCO2 less than 35 mm Hg

20

Causes of respiratory alkalosis?
4

1. Psychological responses (anxiety, fear)
2. Increased metabolic demands
3. Medications, such as respiratory stimulants
4. Central nervous system lesions

21

What would cause increased metabolic demands that lead to respiratory alkalosis?
4

1. Fever,
2. sepsis,
3. pregnancy
4. thyrotoxicosis

22

What is the problem in Metabolic acidosis?

Not enough HCO3- to buffer the acidic state of the body (not enough bicarb to buffer or too much acid)

23

Metabolic acidosis:
How can bicarb be lost? 1

Or too much acid can build up? How? 3

1. GI or renal losses

1. Excretion problem- Renal disease
2. Intake - Overdose
3. Metabolism issues – anaerobic, ketone bodies

24

Metabolic Acidosis
HCO3- level at?
pH at?

The presence of metabolic acidosis should spur a search for what?

bicarbonate level of less than 22 mEq/L with a pH less than 7.35

hypoxic tissue somewhere in the body.

25

Metabolic Acidosis can be caused by?
6

1. Renal failure
2. Diabetic ketoacidosis
3. Diarrhea
4 Anaerobic metabolism
--from tissue hypoxia
5. Starvation
6. Salicylate intoxication

26

1. The anion gap can be used for what?

2. Whats the equation?

3. Whats the nromal range?

1. Can be used to narrow down the etiology of the metabolic acidosis

2. AG = Na – (HCO3 + Cl)

3. Traditionally normal range 12 +/- 4 mEq/L
(if measured automatically the reference range may be different)

Just the difference between the cations and anions

27

Non acid base disorders that may cause errors in AG interpretation?

1. Low albumin

2. Hypernatremia
3. Hyponatremia
4. Certain antibiotics

28

For every __mEq/L decrease in serum albumin the AG will decrease by __mEq/L

1

2

29

Major unmeasured cations? 4

Major unmeasured anions? 4

Why dont we measure these?

So if the Anion Gap is altered how does this inform us there is abnormalities in these?

1. Ca++
2. Mg++
3. Gamma-glubulins
4. K+

1. Albumin
2. Phosphate
3. Sulfate
4. Lactate (sepsis, hypoxemia, exercise)

Because they dont change

Because these readily change and if one is elevated then it will dump the opposite anion or cation to compensate.
(ex. dump Cl- if K+ is low)

30

Why the AG should always be calculated
2

1. It is possible to have an abnormal AG even if the sodium, chloride and bicarbonate levels are normal

2. A large AG (>20) suggests a primary metabolic acid-base disturbance regardless of the pH or serum bicarbonate levels (respiratory system would never get that out of range)