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respiratory > blood gas > Flashcards

blood gas Flashcards

1
Q

What can be measured from blood gas?

A 
Oxygen (O2)
•Carbon dioxide (CO2)
•pH
•Oxygen Saturation (SaO2)
•Bicarbonate (HCO3-)
•Base excess (BE)
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2
Q

What are the indications for measuring blood gases?

A

Identification of respiratory, metabolic, and mixed acid-base disorders

  • Measurement of the partial pressures of respiratory gases involved in oxygenation and ventilation, including assessment of severity of impairment
  • Assessment of the response to therapeutic interventions such as mechanical ventilation in a patient with respiratory failure
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3
Q

Give some advantages of capillary blood gas:

A
  • Relatively pain free
  • Simple procedure
  • Physiologists can perform
  • No doctors required for procedure
  • If performed well can reflect PO2from an ABG
  • Only small sample needed (90-150ul)
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4
Q

Give some disadvantages of capillary blood gas:

A
  • Poor arterialisation – misleadingly low PO2
  • Not the gold standard
  • Sample may be exposed to air
  • ## now not recommended for LTOT assessment
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5
Q

What are the contraindications for blood gas testing?

A
  • Patient does not consent to procedure
  • Negative modified Allen’s test (ABG)
  • Abnormal puncture site (e.g. inflammation, infection etc)
  • Aortic valvular incompetence (ABG)**
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6
Q

What needs to be done before taking blood sample?

A

History taking, asking contraindications, consent and adequate skin prep

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7
Q

What are the advantages and disadvantages of ABG?

A

CONS:
•Painful
•Difficult to perform
•If you want to take repeated samples e.g.
LTOT assessment – hard to take
repeated samples
•Risk of arterial occlusion (clot) / damage
Pros:
•Gold standard
•Accurate in acute settings
•Minimal exposure to air

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8
Q

What are the advantages and disadvantages of ABG?

A

CONS:
•Painful
•Difficult to perform
•If you want to take repeated samples e.g.
LTOT assessment – hard to take
repeated samples
•Risk of arterial occlusion (clot) / damage Pros:
•Gold standard
•Accurate in acute settings
•Minimal exposure to air

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9
Q

What is Allen’s test?

A

The Allen test is a first-line standard test used to assess the arterial blood supply of the hand

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10
Q

What are the three different electrodes?

A

Sanz electrode, Severinghaus electrode, Clark electrode

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11
Q

What do the 3 electrodes directly measure?

A
  • pH-Sanz electrode
  • PCO2-Severinghaus electrode
  • PO2-Clark electrode
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12
Q

How often should Blood gas machines be calibrated?

A

•Calibration – normally automatic on modern analysers:
One point calibration – every 1-2 hours (ARTP 2020)
Two point calibration – every 4-6 hours (ARTP 2020)

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13
Q

What is one point Calibration?

A

One point calibration:
•Simplest type
•Corrects sensor for offset errors
•Only one measurement point needed

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14
Q

What is two point calibration?

A

Two point calibration:
•More precise
•Sensor offset is adjusted at 2 different values
•Leads to accurate measurement across the range
•Two point calibration additionally allows slope of calibration curve to be adjusted

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15
Q

What are the normal values for PaO2, PaCO2, pH, HCO3, BE, SaO2?

A

Pa02 – 10-13.5kPa

PaCO2- 4.8-6.0kPA

PH- 7.35-7.45

HCO3- 23-27mmol/L

BE –-3- +3

SaO2- 97-99%

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16
Q

Type 1 respiratory failure is defined as…

A

Low Pa02 along with normal or low PaCO2

17
Q

Type 2 respiratory failure is defined as

A

Low PaO2 along with an Increased PaCO2

18
Q

What other factors does the equation help us to understand?

A

Patient with emphysema with low SPO2

Affect of abnormal hb

Altitude ?

19
Q

The equation for oxygen carrying capacity is…

A

CaO2 (ml/dl) = (SaO2 x Hb x 1.34 ) + (0.003 x PaO2)
(bound to Hb) YOUT (Plasma)

Where:
SaO2 – expressed as a fraction (e.g. 0.99 not 99%)
1.34 – capacity of Hb to carry O2 (g/dl) (Hufner’s constant)
0.003 – derived from oxygen solubility constituents (37oC) ( referred to as aO2)
PaO2 – in mmHg

20
Q

What is the normal Ca02?

A

16-22ml/dl

21
Q

How do you know if it is resp or metabolic?

A

Resp- the PaCO2 will be abnormal

Metabolic- the HCO3 will be abnormal

22
Q

1- When is it alkalosis?

2- When is it acidosis?

A

1- when the pH is greater than 7.45

2-when the pH is smaller than 7.35

23
Q

The mode of action for a sanz electrode

A

oUses AgCl and Calomel reference electrodes

oPotential difference between blood sample and buffer solution is measured

24
Q

The mode of action for servinghaus electrode

A

oCO2 forms H+

oDifference in H+ ions between electrolyte & buffer solution is measured

25
Q

The mode of action for Clark electrode

A

oReduction of O2 at the Pt cathode

oFlow of electrons

respiratory (12 decks)

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