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Year 3 - Preparation for Clinical Practise > ABG > Flashcards

ABG Flashcards

1
Q

What are the poor prognostic factors of asthma

A
  • previous near fatal asthma e.g. previous ventilation or respiratory acidosis
  • previous admission for asthma especially if in the last year
  • requiring three or more classes of asthma medication
  • heavy use of B2 agonist
  • repeated attendances at ED for asthma care especially if in the last year
  • brittle asthma
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2
Q

What is the normal PaCO2 level

A

4.6-6.4kPa

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3
Q

what is the definition of hyperventilation and hypoventilation

A
  • Hyperventilation = less than 4.6 kPa PaCO2

- Hypoventilation = greater than 6.4 kPa

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4
Q

if someone with an asthma attack has normal PaCO2 what does this mean

A
  • a normal CO2 suggests that he is becoming exhausted - alongside hypoxia this would be a worrying sign
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5
Q

What is the normal oxygen level PaO2

A

10.6-13.5KpA

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6
Q

what is oxygenation affected by

A
  • VQ balance
  • inspired oxygen concentration (FiO2)
  • ventilatory efficiency
  • affinity of blood for oxygen
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7
Q

What pH is acidosis and what pH is alkalosis

A
  • less than 7.35 is acidosis

- greater than 7.45 is alkalosis

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8
Q

what is the normal bicarbonate level

A

22-28mmol/l

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9
Q

How long does metabolic compensation take

A
  • takes days
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10
Q

How long does respiratory compensation take

A
  • minutes
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11
Q

How does metabolic compensation happen

A
  1. cellular buffering, this occurs over minutes to hours, this elevates plasma bicarbonate only slightly
    - renal compensation - this occurs over 3-5 days
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12
Q

How does respiratory compensation happen

A
  • respiratory compensation of alkalosis doesn’t tend to happen
  • carbon dioxide is usually the drive to breath unless there is chronic lung disease so it is tough to hyperventilate and increase carbon dioxide
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13
Q

What is the base excess

A
  • the base excess is the quantity of base or acid needed to titrate one litre of blood to pH 7.4 with the pC02 held constant at 5.3kPa
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14
Q

what is the normal base excess

A

-2 - +2 mmol/l

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15
Q

what does negative base excess indicate in an acidosis

A
  • In the context of an acidosis a negative base excess indicates there is a metabolic component
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16
Q

what is the alveolar:arterial gradient

A
  • this estimates the diffusion gradient between alveolus and oxygenated blood
17
Q

what is the normal level for the alveolar: arterial gradient

A
  • the gradient is usually low in normal people
18
Q

How do you calculate the alveolar: arterial gradient

A

= FiO2 - (PaO2 + PaCO2)

- Where FIO2 approximates to the % inspired oxygen (might be the number of breaths per minute)

19
Q

What is the normal range of alveolar: arterial gradient

A
  • 25 years old = 0.2-1.5kPa

- 75 years old = 1.5-3.0 kPa

20
Q

What does it mean when the alveolar: arterial gradient is raised

A
  • this means that there is impaired gas exchange

- oxygen has not diffused form the alveoli to the arterial circulation efficiently

21
Q

what can cause a high alveolar: arterial gradient

A

PE

22
Q

What is the anion gap

A
  • this is the difference between cations and the un-estimated anions
23
Q

what is the anion gap made out of

A
  • fixed acids (such as phosphorous)

- organic acids (ketones, lactate, albumin)

24
Q

Write out the equation of the anion gap

A

(K+ + Na+) - (Cl- + HCO3-)

25
Q

What is the normal anion gap

A

8-16-20

26
Q

what can cause a normal anion gap acidosis

A
  • renal tubular acidosis
  • diarrhoea
  • drugs (acetazolamide)
  • Addison’s disease
  • pancreatic fistulae
27
Q

What does acidosis with a normal anion gap mean

A
  • acidosis with a normal anion gap means that there is no additional acids
28
Q

What causes acidosis with a raised anion gap

A
  • acidosis with a raised anion gap suggests increased fixed or organic acids
    caused by
  • lactic (shock, hypoxia, infection)
  • urate (renal failure)
  • ketones (DM, alcohol)
  • drugs and toxins (salicylates, biguanides like metformin, methanol, ethylene glycol)
29
Q

What is ethylene glycol

A
  • antifreeze - with increasing homelessness and increasing prices of alcohol you will see ethylene glycol poisoning in A and E departments
30
Q

How does albumin affect the anion gap

A
  • the anion gap is reduced by about 2.5 by every 10g/l fall in albumin
31
Q

How do you take an ABG

A

What to have

  • syringe
  • small 23-24g needle
  • rubber stopper
  • syringe cap containing dry lithium heparin or sodium heparin
  • alcohol swabs
  • sterile pieces of gauze
  • tape
  • non sterile gloves and gown
  • lidocaine - for anaesthetic
  • 5 - cc syringe
  • 25 gauge needle
  • rolled towel
  • bag of ice to transport sample to the lab
  • wash your hands
  • extend the patients wrist to bring the radial artery to a more superficial position, it is located between the styloid process of the radius and flexor carpi radials tendon
  • place rolled towel underneath the patients wrist
  • put on a gown and gloves
  • open the ABG kit
  • clean the site with an alcohol swab
  • palpate the radial artery
  • using the 5cc syringe draw up lidocaine
  • inject small amount of analgesia around the artery
  • locate the maximum impulse
  • holding the ABG with the dominant hand
  • 30-45 degree angle
  • advance the needle slowly till the syringe passively fills with blood
  • withdraw the syringe and apply pressure to the syringe for 5 minutes
  • attach the heparin cap and make sure that the blood doesn’t clot
32
Q

What are the indications for an ABG

A

To obtain values for

  • partial pressure of oxygen
  • partial pressure of carbon dioxide
  • arterial pH

co-oximetry to assess for

  • methemoglobinemia
  • carboxyhemoglobin
33
Q

When do you do an ABG

A
  • when the patient is in acute severe respiratory distress
34
Q

When do you not do an radial ABG

A
  • impaired circulation to distal upper extremity - impaired collateral circulations
  • overlying skin infection
  • patients taking anticoagulation’s
  • patients who have coagulopathy
35
Q

What can make it difficult to find the radial artery

A
  • edema

- vasospasm

Year 3 - Preparation for Clinical Practise (33 decks)

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