CVR - ABGs, O2 therapy and drains Flashcards
What are arterial blood gases (ABGs)?
Blood test that measures the acidity (pH) and the levels of O2 and CO2 from an artery
Define the following:
PO2
PaO2
PvCO2
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
How does the level of CO2 affect the acidity and alkalinity of the blood?
CO2 = H+ in the blood plasma
increased CO2 = increased H+ = decreased pH = acidic
decreased Co2 = decreased H+ = increased pH = alkali
Give the ABG normal values for:
- pH
- PaO2
- PaCO2
- HCO3-
- Base excess (BE)
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
With regards to H+ when is there a respiratory and metabolic mechanism?
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
When would the following occur:
- Respiratory acidosis
- Respiratory alkalosis
- Metabolic acidosis
- Metabolic alkalosis
- Respiratory acidosis = increase in PaCO2
- Respiratory alkalosis = decrease in PaCO2
- Metabolic acidosis = decrease HCO3- or BE
- Metabolic alkalosis = increase HCO3- or BE
Define respiratory failure
Failure of the respiratory system to provide adequate gaseous exchange for metabolic requirements
What are type I and type II respiratory failure?
Type I RF (hypoxaemic) = failure of oxygenation
Type II RF (hypercapnic) = failure of ventilation
What causes type I RF?
Failure of oxygenation
PaO2 < 8kPa
Result of only one problem - low PaO2
What causes type II RF?
Failure of ventilation
PaO2 < 8kPa AND PaCO2 > 6.0
Result of two problems - low PaO2 AND high PaCO2
What COPD problems can lead to RF?
- lung hyperinflation
- increased V/Q mismatch
- loss of elasticity
- increased sputum production
What is oxygen therapy?
Therapeutic administration of O2 at a concentration greater than that of sea level, to increase alveolar O2 concentration
What can oxygen therapy be used to correct?
- Hypoxia (insufficient O2 available to the tissues to meet metabolic needs)
- Hypoxaemia (abnormally low oxygenation of arterial blood)
What is FiO2 and how is it measured?
The fraction of inspired air (%)
‘the % of inspired O2 delivered to the patient’
measured using oximetry (measurement of oxyhemoglobin)
What are the target O2 saturations?
Normal = 94-98%
TYPE II RF or COPD = 88-92%
What % of oxygen does a nasal cannula deliver and at what flow, and what are some pros and cons?
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
What % of oxygen does an oxygen face mask deliver and at what flow, and what are some pros and cons?
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
What questions can you ask your patient to check they are receiving enough O2?
- Do you think you are getting enough O2?
- Can you feel the O2?
- Do you feel ‘hungry’ for air?
What should happen to the respiratory rate as oxygen flow is increased?
RR should decrease as you increase the flow, as they will have to try less hard to get sufficient O2.
What are chest drains also known as, what do they drain and what do they do?
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.
When are wound drains used, what do they remove and why would they be used?
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
What do nasogastric feeding tubes do?
Carries food and medicine to the stomach through the nose
What are nasogastric aspiration tubes used for?
Drains the stomachs contents
Remove gastrointestinal secretions
Removes any swallowed air
