ABG Flashcards
Indications for ABG
• To obtain & interpret oxygenation levels
• To assess for potential respiratory derangements
• To assess for potential metabolic derangements
• To monitor acid-base status (renal failure)
• To assess carboxyhaemoglobin in CO poisoning
• To assess lactate (sepsis)
• To gain preliminary results for electrolytes and Haemoglobin
• Can be conducted as a one off sample or repeated sampling to
determine response to interventions
CI to ABG
- Local infection
- Distorted anatomy
- Presence of arterio-venous fistulas
- Peripheral vascular disease of the limb to be sampled
- Severe coagulopathy or recent thrombolysis – relative CI, not absolute – coagulopathy only prob if cant control the flow out if you were to puncture it, usually puncture from distal Radius/femoral artery so not problem because can press on these areas
sampling errors in ABG
• Presence of air in the sample - CO2 and O2 will be altered
• Collection of venous rather than arterial blood - O2 different, pH and base excess fine
• An improper quantity of heparin in the syringe, or improper
mixing after blood is drawn
• Delay in specimen transportation - CO2 increase and O2 decrease because metabolising cells
complications of ABG
- Haematoma
- Nerve damage
- Arteriospasm or involuntary contraction of the artery
- Aneurysm of artery
- Fainting or a vasovagal response
goals of oxygen therapy
• Relieve hypoxaemia & maintain oxygenation of tissues
Assessed by SpO2
/SaO2 monitoring and clinical signs (or NEWS2)
Oxygen therapy in a way which prevents excessive CO2
accumulation
(selection of the appropriate flow rate and delivery device)
Reduce the work of breathing E.g. CPAP
Ensure adequate clearance of secretions and limit the adverse events of
hypothermia and insensible water loss by use of optimal humidification and warmth
(dependent on mode of oxygen delivery)
consideration with oxygenation and COPD
if hypoxic and v unwell that comes first – give ox as need to get sats to appropriate level (in emergency) then address flow rate later.
In controlled setting - incrementally increase according to CO2 accumulation
CPAP
cont positive airway pressure – reduce work pf breathing – look at pressure volumes – initial amount of air have blow balloon up to before get stretch – CPAP keeps airways open in stretchy elastic phase of hysteresis curve– so don’t have to repeat work
Muscles of abdo – difficult to maintain normal resp if in pain, so higher work of breathing and open up lungs all time = atelectasis and reduced breathing
sats clinical target
94-98%, COPD (small pop) 88-92% may be appropriate
modes of deliver of oxygen
o Nasal cannulae
o Facemask – Hudsen, venturi
nasal cannulae
Deliver 24-30% oxygen • Flow rate 1-4L/min • Uses: • non-acute situations • mild hypoxia
hudsen mask
-Delivers 30-40% oxygen
-Flow rate 5-10L/min
o Adjust flow rate accordingly
o holes to ventilate
venturi mask
-Delivers 24-60% oxygen
-Different colours deliver different
rates
-Flow rate: fixed, Varies with colour
o Whatever FiO2 is it will tell you what flwo rate should be to get that – and get specific % ox
-often used in COPD adn want specific amount of oxygen
non-rebreather mask
-Used for acutely unwell patients
-Delivers 60-90% oxygen
-15L/min flow rate, has oxygen reservoir
o Normal peak insp flow 15-30 flow/min
o Insp demand not met by simple mask
o So can hit 60-90% with this device
-valve stops rebreathing of expired air
o Higher ox delivery mechanism for spont breathing pt
when is CPAP used
• High pressure oxygen with tight-fitting mask
• Positive pressure all the time (to splint airways open)
• Used in type 1 respiratory failure e.g. pulmonary
oedema/OSA
BiPAP
(bilevel positive airways pressure)
• High positive pressure on inspiration and lower positive
pressure on expiration
• Used in type 2 respiratory failure e.g. COPD
exacerbation
