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I & M 441 > Arterial Blood Gas (ABGs) > Flashcards

Arterial Blood Gas (ABGs) Flashcards

1
Q

What sites of placement do we use to insert arterial lines?

A

Radial artery
Brachial artery (watch out for embolis)
Femoral artery
Dorsalis pedis (foot) artery

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2
Q

What are the main components of an ABG analysis?

A 
pH 
pO2
pCO2
HCO3
BE (base excess)
SaO2
AG (anion gap)
Others:
Glucose
Lactate
Hct
Electrolytes (Na+, K+, Ca++, Cl-)
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3
Q

What is the normal range of blood pH?

A

7.35-7.45

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4
Q

What are 3 indicators on an ABG reading that may indicate general acidosis?

A

Blood pH < 7.35
PaCO2 > 45
HCO3 < 22
BE < -3

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5
Q

What are 3 indicators on an ABG reading that may indicate general alkalosis?

A

Blood pH > 7.45
PaCO2 < 35
HCO3 > 26
BE > +3

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6
Q

What is the respiratory buffer response and how long does it take to kick in?

A

Blood pH changes in response to varying levels of H2CO3; body responds by either hypoventilating (compensation for alkalemia) or hyperventilating (compensation for acidemia) –> so PaCO2 will be affected by this response.

This response occurs within 1-3 minutes of blood pH shift in normal physiology.

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7
Q

What is the difference between acidemia and acidotic?

A

AcidEMIA refers to an acid state of blood.

Acidotic refers to a generally acidic state of the patient.

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8
Q

What is the renal buffer response and how long does it take to kick in?

A

The kidney can retain or excrete HCO3 (bicarbonate). It will do either in response to changes in blood pH - for example, if blood pH decreases, kidneys will retain HCO3.

This buffer system takes hours to days to correct the imbalance so cannot be relied on clinically - we must help pt compensate.

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9
Q

What is the difference between respiratory and metabolic acidosis/alkalosis?

Are they mutually exclusive?

A

Respiratory acidosis = pCO2 > 45

Metabolic acidosis = HCO3 < 22

Respiratory alkalosis = pCO3 < 35

Metabolic alkalosis = HCO3 > 26

No, patient can have both respiratory and metabolic acidosis.

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10
Q

What are some causes of respiratory acidosis?

A

CNS depression
Pleural disease (think pleural space of lungs)
COPD
ARDS
Musculoskeletal disorders (that may affect lung function)
Compensation for metabolic alkalosis
Hypoventilation

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11
Q

What is base excess?

A

Indicates the amount of excess or insufficient level of bicarbonate -2 to +2mEq/L

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12
Q

H+ value that corresponds with pH of 7.4? 7.3? 7.5?

A

7.4 = 40, 7.3 = 50, 7.5 = 30

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13
Q

What is the respiratory buffer response?

A

The blood pH changes according to the level of H2CO3 present, triggering the lungs to increase or decrease the rate and depth of ventilation.

This response occurs within 1-3 minutes.

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14
Q

How does the body compensate for chronic respiratory acidosis?

A

Renally via synthesis and retention of HCO3.

Also by excreting more Cl to balance charges (causing hypochloremia).

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15
Q

How does the body respond to acute and chronic respiratory alkalosis?

A

Acute - decreases HCO3 2mEq/L for every 10mmHg decrease PCO2

Chronic - decreases HCO3 4mEq/L for every 10mmHg decrease in PCO2

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16
Q

A 1mEq/L decrease in HCO3 causes how much of a change in PCO2?

A

Decreases PCO2 by 1.2mmHg

17
Q

Causes of Metabolic Gap Acidosis?

A

MUDPILES - Methanol, Uremia, DKA, Paraldehyde, INH, Lactic acidosis, Ethylene glycol, Salicylate

Also non-gap metabolic acidosis - hyperalimentaiton, acetazolamide, RTA, diarrhea, pancreatic fistula

18
Q

Stepwise Approach to ABG

A
  1. Acidemic or alkalemic?
  2. Respiratory or metabolic?
  3. Assess PaO2. Below 80mmHg = hypoxemia. For respiratory, is it acute or chronic?
  4. For metabolic acidosis, is anion gap present?
  5. Assess normal compensation by respiratory system for a metabolic disturbance.
19
Q

How do you tell if hypoxemia is acute?

A

If the change in PaCO2 is associated with a change in pH

20
Q

If pH is acidotic, but the PaCO2 decreases, what does this indicate?

A

The lungs are compensating for a metabolic acidosis by blowing off excess CO2.

21
Q

If pH and HCO3 are moving in opposite directions, what does this indicate?

A

The kidneys are compensating for a respiratory disorder by holding or releasing HCO3

22
Q

What are some possible causes of respiratory acidosis?

A
  • CNS depression
  • Pleural disease
  • COPD/ARDS
  • Musculoskeletal disorders
  • Compensation for metabolic alkalosis
23
Q

What is the effect of respiratory alkalosis on chloride electrolyte levels?

A

Cl- will increase to balance charges

24
Q

What are some possible causes of respiratory alkalosis?

A
  • Intracerebral hemorrhage
  • Anxiety that decreases lung compliance
  • Liver cirrhosis
  • Sepsis
  • Salicylate and progesterone drug usage
25
Q

How does the body compensate in chronic respiratory alkalosis?

A

Decreased bicarb (acid) reabsorption and ammonium excretion to normalize pH

26
Q

How long does it take for complete activation of respiratory compensation (alkalosis) for metabolic acidosis?

A

12-24 hours

27
Q

Causes of non-gap metabolic acidosis?

A
  • Diarrhea
  • Pancreatic fistula
  • Hyperalimentation (overconsumption of food, can be through tube)
  • RTA (renal tubular acidosis)
  • Acetazolamide
28
Q

Causes of metabolic alkalosis?

A
  • Vomiting
  • Chronic diarrhea
  • Diuretics
  • Hypokalemia
  • Renal failure
29
Q

In multiple ABG readings, your patient’s pH is decreasing along with his PaCO2. Is this a primary respiratory or metabolic problem?

A

a primary metabolic problem

30
Q

In multiple ABG readings, your patient’s pH is decreasing and HCO3- is dropping. Is this a primary respiratory or metabolic problem?

A

a primary metabolic problem

31
Q

What does base excess (BE) estimate?

A

Estimates the amount of strong acid or base needed to correct (METABOLIC component) an acid-base abnormality

32
Q

What is the formula for estimating how much HCO3- to give a patient undergoing metabolic acidosis?

A

0.3 x BE x body weight in kg

33
Q

When the pt’s pH and paCO2 moves in the same direction, the problems is primarily metabolic/respiratory?

A

Metabolic

I & M 441 (13 decks)

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