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Arterial blood gases > arterial blood gases > Flashcards

arterial blood gases Flashcards

1
Q

What are the normal ranges?

A 
pH: 7.35 – 7.45
PaCO2: 4.7 – 6.0 kPa || 35.2 – 45 mmHg
PaO2: 11 – 13 kPa || 82.5 – 97.5 mmHg
HCO3–: 22 – 26 mEq/L
Base excess (BE): -2 to +2 mmol/L
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2
Q

Why is a normal PaO2 for a patient on oxygen flow a bad thing?

A

You would expect PaO2 to be higher/above normal they are receiving oxygen.

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3
Q

What does a normal PaCO2 in a hypoxic asthmatic signal?

A

Tiring

Maybe need ITU

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4
Q

What does a very low PaO2 and normal everything else mean?

A

It’s a venous sample

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5
Q

Healthy oxygen?

A

> 10kPa

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6
Q

What should oxygen saturation be for someone on oxygen?

A

Should be 10kPa less than the concentration of the inspired oxygen.

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7
Q

What is considered hypoxaemic and severely hypoxaemic?

A

<10kPa hypoxia

<8kPa is severe

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8
Q

Type 1 vs type 2 resp failure?

A

Type one is hypoxia but normocapnia whereas, type 2 is hypoxia and hypercapnia.

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9
Q

What causes type 1 failure?

A

Ventilation perfusion mismatch, volume of air flow is not matched by blood flow. Initial increase in PaCO2 is is compensated by increased alveolar ventilation hence normocapnia

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10
Q

What are some examples of V/Q mismatch?

A

Reduced ventilation and normal perfusion (e.g. pulmonary oedema, bronchoconstriction)
Reduced perfusion with normal ventilation (e.g. pulmonary embolism)

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11
Q

Why does type 2 occur?

A

Alveolar hypoventilation

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12
Q

What are some reasons for alveolar hypoventilation?

A

Resistance due to airway obstruction - COPD
Less compliance of lung tissue and chest wall - pneumonia and rib fracture
reduced strength of resp muscles - MND
Drugs acting on resp centre - opioids

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13
Q

What are the two driving forces for changes in pH?

A

metabolic (HCO3-) and respiratory (CO2)

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14
Q

What is PaCO2 like for resp acidosis/alkalosis?

A

CO2 increased in acidosis with a decrease in pH and vice versa for alkalosis.
There is compensation when HCO3- is involved and the pH can be returned to normal/slightly abnormal.

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15
Q

What does a high base excess show?

A

Higher than normal HCO3- which indicates primary metabolic alkalosis or compensated resp acidosis and vice versa for low base excess.

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16
Q

How is compensation achieved for a metabolic change?

A

Quickly by either blowing off more CO2 or reducing respiratory rate, all with the idea of increasing alveolar ventilation (getting rid of CO2) or reducing alveolar ventilation to retain CO2.

17
Q

How is a metabolic compensation different?

A

Takes a few days

Kidneys are required to increase/reduce HCO3- production.

18
Q

What should never happen?

A

Overcompensation, if this is the case there is a pathology causing it.

19
Q

What is mixed acidosis/alkalosis and how is it corrected?

A

The PaCO2 and HCO3- will be moving in opposite directions. You need to correct each disturbance individually.

20
Q

What is the basis for the cause of resp acidosis?

A

Alveolar hypoventilation

21
Q

What are some causes of resp acidosis?

A

Asthma, COPD, Resp depression by opiates,

Guillain Barre which is paralysis that leads to inability to ventilate.

22
Q

What are some causes of resp alkalosis?

A

Excessive alveolar ventilation

anxiety, pain, hypoxia, PE, pnuemothorax

23
Q

What is the basis of metabolic acidosis?

A

Increased acid production/ingestion or decreased excretion/HCO3-

24
Q

What is an anion gap?

A

Tells you how to differentiate the causes of metabolic acidosis.
Anion gap = Na+ – (Cl- + HCO3-)

25
Q

What does increased anion gap indicate?

A

increased acid production or ingestion

Diabetic ketoacidosis (↑ production)
Lactic acidosis (↑ production)
Aspirin overdose (ingestion of acid)
26
Q

What is a normal anion gap?

A

4 to 12 mmol/L

27
Q

What does decreased anion gap indicate?

A

decreased acid excretion or loss of HCO3–

Gastrointestinal loss of HCO3– (e.g. diarrhoea, ileostomy, proximal colostomy)
Renal tubular acidosis (retaining H+)
Addison’s disease (retaining H+)

28
Q

What is a cause of mixed resp and metabolic acidosis?

A

Cardiac arrest

Multi-organ failure

29
Q

What is a cause of mixed resp and metabolic alkalosis?

A

Liver cirrhosis in addition to diuretic use
Hyperemesis gravidarum (severe vomitting in preg)
Excessive ventilation in COPD

30
Q

What is classic presentation of a panic attack

A

hyperventilation

peripheral and peri-oral tingling.

31
Q

How does hyperventilation lead to perioral and peripheral parasthesia?

A

When you become alkalotic your freely ionised calcium concentration decreases.
Also H+ bound to albumin comes off due to alkalosis and calcium therefore increases its binding due to more slots. Further decreasing free active concentration.
hypocalcaemia causes muscle spasms

Arterial blood gases (1 decks)

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