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Clin Lab Med Unit 3 > 3 ABGs > Flashcards

3 ABGs Flashcards

1
Q

Arterial blood gases are frequently used to detect and monitor…

A

Oxygenation
Ventilation
Acid/base balance

Also quantify levels of carboxyhemoglobin and methemoglobin

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2
Q

For ABGs, blood is drawn from …

A

Artery, usually the radial artery

Sometimes from brachial or femoral artery

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3
Q

ABG blood is collected with __________, placed on ice, and taken quick to lab

A

Anticoagulant (heparin)

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4
Q

How quickly can you get results from an ABG?

A

5-15 minutes

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5
Q

O2 saturation on ABG correlates to…

A

Pulse Ox

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6
Q

What are the five values you get back with an ABG test?

A 
pH
pO2 
O2 saturation
pCO2 
HCO3
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7
Q

The pO2 is used to determine…

A

How well patient is oxygenating

NOT used in determination of acid-base conditions

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8
Q

The pO2 from an ABG is much more reliable way to check…

A

Oxygenation

Better than the O2 saturation reading from pulse ox

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9
Q

______ are used to keep blood pH in a narrow range

A

Buffer systems

Body maintains precise control of hydrogen ions to maintain homeostasis

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10
Q

Acidemia is defined as pH < _____

A

< 7.35

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11
Q

Alkalemia is defined as pH > _____

A

> 7.45

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12
Q

Acidosis/alkalosis ≠ _____________.

A

Acidemia/Alkalemia

The former are acid/base disorders, the laters refers to pH of blood

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13
Q

Acid-base disturbances indicate …

A

An underlying disease process

Treatment is directed at the management of the underlying disease

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14
Q

You can have up to _____ different acid-base disorders at the same time

A

3

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15
Q

The body tries to compensate for an acid-base disorder by …

A

Using respiratory or metabolic processes that attempt to return a patient’s pH to normal (7.4)

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16
Q

__________ compensation for a __________ process is usually rapid

A

Respiratory compensation for metabolic process

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17
Q

Metabolic compensation can take _________.

A

Days or even a week

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18
Q

A septic patient will start breaking more rapidly because…

A

Their body is trying to compensate for metabolic acidosis by breathing off a bunch of CO2

ALWAYS pay attention if a patient suddenly becomes tachypnic

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19
Q

A primary respiratory problem involves ______ whereas a primary metabolic problem involves _______

A 
Respiratory = pCO2
Metabolic = HCO3
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20
Q

pCO2 >45

A

Acidosis

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21
Q

pCO2 <35

A

Alkalosis

22
Q

HCO3 > 26

A

Alkalosis

23
Q

HCO3 < 22

A

Acidosis

24
Q

What disorder:

pH >7.45
Primary disturbance = decreased pCO2
Compensatory response = decreased HCO3

A

Respiratory Alkalosis

25
Q

What disorder:

pH < 7.35
Primary disturbance = Increased pCO2
Compensatory response = Increased HCO3

A

Respiratory acidosis

26
Q

What disorder:

pH > 7.45
Primary disturbance = Increased HCO3
Compensatory response = Increased pCO2

A

Metabolic alkalosis

27
Q

What disorder:

pH < 7.35
Primary disturbance = Decreased HCO3
Compensatory response = Decreased pCO2

A

Metabolic acidosis

28
Q

How to evaluate an acid-base disorder

A

1) Evaluate pH (decreased, increased, or normal)

2) If decreased pH…
Normal HCO3 —> increased pCO2 = Respiratory Acidosis
Low HCO3 —> Metabolic acidosis —> look at anion gap/chloride

3) If increased pH…
High HCO3 —> metabolic alkalosis
Normal HCO3 —> decreased pCO2 —> respiratory alkalosis

29
Q

If both pCO2 and HCO3 are HIGH —>

A

Respiratory acidosis OR metabolic alkalosis

30
Q

If both pCO2 and HCO3 are LOW —>

A

Respiratory alkalosis OR metabolic acidosis

31
Q

If pCO2 and HCO3 are moving in opposite directions…

A

MIXED DISORDER

32
Q

What is MUDPILES?

A

Conditions that cause high anion gap metabolic acidosis

Methanol
Uremia
DKA
Propylene glycol
Iron/isoniazid
Lactate (lactic acidosis)
Ethanol/ethylene glycol
Salicylate/starvation
33
Q

Metabolic acidosis is

A

low pH and HCO3 <22

34
Q

Conditions that cause non-anion gap metabolic acidosis

A

GI bicarb loss
—> Diarrhea, GI fistula, ureterosigmoidostomy

Renal bicarb loss
• Early renal failure
• Renal tubular acidosis
• Carbonic anhydrase inhibitors
• Aldosterone inhibitors (spironolactone)

Hyperchloremia due to saline resuscitation

35
Q

How to treat metabolic acidosis

A

TREAT UNDERLYING CAUSE

Consider giving sodium bicarb to help in the immediate period until you’ve treated the underlying cause

Allow for normal respiratory compensation - DON’T GIVE MORPHINE

36
Q

What is metabolic alkalosis?

A

High pH and HCO3>26

37
Q

What to check first if you see Metabolic Alkalosis on ABG

A

Urine Chloride - helps to distinguish the etiology

38
Q

If metabolic alkalosis and urine chloride < 25…

A

GI losses like vomiting, NG suction
Diuretics (“contraction alkalosis”)
CF

GIVE FLUIDS TO TREAT

39
Q

If metabolic alkalosis and urine chloride >25…

A 
Barter’s syndrome
Cushing’s 
Hyperaldosteronism
Potassium depletion
Citrate toxicity
Chronic diuretics
Renin secreting tumor

Treat underlying cause, may need potassium

40
Q

What is Respiratory Acidosis?

A

Low pH and pCO2 >45

Essentially you aren’t able to ventilate well enough, leading to an accumulation of CO2

41
Q

Causes of respiratory acidosis

A 
Acute airway obstruction
Lung disease (esp COPD)
CNS depression (ie too much morphine)
Neuromuscular disorder (ie Guillan-Barré)
Impaired lung motion
Inappropriate mechanical ventilation settings
42
Q

Treating respiratory acidosis

A 
Treat underlying cause
Respiratory support (BiPAP can be helpful)

Important to differentiate acute from chronic - acute may need BiPAP but chronic is typically more stable (ie chronic COPD)

43
Q

How to tell acute from chronic respiratory acidosis

A

Look at pH

Chronic will have a normal pH but they are compensatory

44
Q

What is respiratory alkalosis?

A

High pH but low pCO2 (<35)

Excessive elimination of CO2 from the lungs (“blowing off too much CO2”)

45
Q

SSx of respiratory alkalosis

A

Lightheadedness, palpitations, tachypnea, +/- paresthesias

46
Q

Possible causes of respiratory alkalosis

A 
HYPERVENTILATION**** (ie anxiety)
Compensatory mechanism in sepsis
Pain
CNS
Salicylate overdose
Pregnancy
High altitude
Hypoxemia
Hepatic encephalopathy
47
Q

Steps in determining acid/base disturbance…

A

Step 1 - look at pH to determine primary abnormality

Step 2 - Look at pCO2 and HCO3. Whichever change supports the direction of the pH change tells you the primary process
pCO2 reflects respiratory, HCO3 reflects metabolic
If pCO2 and HCO3 go in opposite directions, you likely have multiple disorders - always focus on HCO3 first in that case

Step 3 - determine compensation (if pH close to normal, they are compensating well)

Step 4 - calculate anion gap (very high anion gap —> Primary metabolic acidosis regardless of pH or HCO3)

48
Q

How to calculate Anion gap

A

[Na] - [Cl+HCO3]

Normal range = 8-12

Elevated > 12

49
Q

Anytime you have a very high anion gap (AG >20)…

A

There automatically has to be a primary metabolic acidosis, regardless of the pH or serum bicarbonate concentration

The body does not generate a large anion gap to compensate for a primary disorder

50
Q

You can have both _______ and ______ at the same time but you can only have one __________.

A

Metabolic alkalosis and metabolic acidosis but only one respiratory disorder at a time

B/c you can’t breathe fast and slow at the same time lol

51
Q

A normal pH does not mean…

A

There is not an acid/base disorder!

52
Q

Low ______ is usually pathologic

A

HCO3

Make sure to investigate!

Clin Lab Med Unit 3 (4 decks)

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