CVR - ABGs, O2 therapy and drains

Question 1

What are arterial blood gases (ABGs)?

Answer 1

Blood test that measures the acidity (pH) and the levels of O2 and CO2 from an artery

Question 2

Define the following:
PO2
PaO2
PvCO2

Answer 2

PO2 = partial pressure of oxygen in the air
PaO2 = partial pressure of oxygen in plasma of arterial blood
PvCO2 = partial pressure of carbon dioxide dissolved in the plasma of venous blood

Question 3

How does the level of CO2 affect the acidity and alkalinity of the blood?

Answer 3

CO2 = H+ in the blood plasma
increased CO2 = increased H+ = decreased pH = acidic
decreased Co2 = decreased H+ = increased pH = alkali

Question 4

Give the ABG normal values for:

• pH
• PaO2
• PaCO2
• HCO3-
• Base excess (BE)

Answer 4

pH = 7.35-7.45
 PaO2 = 10.7-13.3 kPa
PaCO2 = 4.7-6.0 kPa
HCO3- = 22-26 mmol/l
BE = -2 to +2

Question 5

With regards to H+ when is there a respiratory and metabolic mechanism?

Answer 5

Respiratory mechanism:
- if CO2 production is altered, breathing is adjusted to exhale more or less CO2
- increase CO2 = increase H+ = decrease pH = increased depth & rate of breathing
Metabolic mechanism:
- kidneys are responsible for excreting metabolic acids
- they secrete H+ ions in the urine and reabsorb HCO3- from the urine = reduce H+ in the blood

Question 6

When would the following occur:

1. Respiratory acidosis
2. Respiratory alkalosis
3. Metabolic acidosis
4. Metabolic alkalosis

Answer 6

1. Respiratory acidosis = increase in PaCO2
2. Respiratory alkalosis = decrease in PaCO2
3. Metabolic acidosis = decrease HCO3- or BE
4. Metabolic alkalosis = increase HCO3- or BE

Question 7

Define respiratory failure

Answer 7

Failure of the respiratory system to provide adequate gaseous exchange for metabolic requirements

Question 8

What are type I and type II respiratory failure?

Answer 8

Type I RF (hypoxaemic) = failure of oxygenation

Type II RF (hypercapnic) = failure of ventilation

Question 9

What causes type I RF?

Answer 9

Failure of oxygenation
PaO2 < 8kPa
Result of only one problem - low PaO2

Question 10

What causes type II RF?

Answer 10

Failure of ventilation
PaO2 < 8kPa AND PaCO2 > 6.0
Result of two problems - low PaO2 AND high PaCO2

Question 11

What COPD problems can lead to RF?

Answer 11

• lung hyperinflation
• increased V/Q mismatch
• loss of elasticity
• increased sputum production

Question 12

What is oxygen therapy?

Answer 12

Therapeutic administration of O2 at a concentration greater than that of sea level, to increase alveolar O2 concentration

Question 13

What can oxygen therapy be used to correct?

Answer 13

1. Hypoxia (insufficient O2 available to the tissues to meet metabolic needs)
2. Hypoxaemia (abnormally low oxygenation of arterial blood)

Question 14

What is FiO2 and how is it measured?

Answer 14

The fraction of inspired air (%)
‘the % of inspired O2 delivered to the patient’
measured using oximetry (measurement of oxyhemoglobin)

Question 15

What are the target O2 saturations?

Answer 15

Normal = 94-98%

TYPE II RF or COPD = 88-92%

Question 16

What % of oxygen does a nasal cannula deliver and at what flow, and what are some pros and cons?

Answer 16

low flow rate - 1-4 l/min
24-40% oxygen
pros:
 - possible to eat, drink and communicate
 - well-tolerated
 - low cost
cons:
 - dry nasal passage
 - nasal congestion

Question 17

What % of oxygen does an oxygen face mask deliver and at what flow, and what are some pros and cons?

Answer 17

Flow rate = 5-10l/min, must be at least 5l/min to avoid CO2 build-up
Delivers variable O2 conc between 35-60%
pros:
- good for mouth breathers
cons:
- less convenient for eating and breathing
- requires supervision

Question 18

What questions can you ask your patient to check they are receiving enough O2?

Answer 18

• Do you think you are getting enough O2?
• Can you feel the O2?
• Do you feel ‘hungry’ for air?

Question 19

What should happen to the respiratory rate as oxygen flow is increased?

Answer 19

RR should decrease as you increase the flow, as they will have to try less hard to get sufficient O2.

Question 20

What are chest drains also known as, what do they drain and what do they do?

Answer 20

Also known as under water-sealed drains (UWSD)
Inserted to allow draining of the pleural spaces of air, blood or fluid
They allow expansion of the lungs and restoration of negative pressure in the thoracic cavity. The underwater seal also prevents backflow of air or fluid into the pleural cavity.

Question 21

When are wound drains used, what do they remove and why would they be used?

Answer 21

Used post-surgery
Used to remove pus, blood or other fluids from a wound
Reasons to drain:
- allow the wound to heal
- reduce pain, as build-up of fluid can cause discomfort
- reduce the risk of infection
- minimise bruising

Question 22

What do nasogastric feeding tubes do?

Answer 22

Carries food and medicine to the stomach through the nose

Question 23

What are nasogastric aspiration tubes used for?

Answer 23

Drains the stomachs contents
Remove gastrointestinal secretions
Removes any swallowed air