ABGs Flashcards
What are the four abnormalities on an ABG?
Metabolic acidosis
Metabolic alkalosis
Respiratory acidosis
Respiratory alkalosis
Shortcut for interpreting whether metabolic or respiratory
ROME
Resp opposite, metabolic equal
Respiratory- opposite CO2 and pH [eg. high pH=low CO2]
Metabolic- equal CO2 and pH
SBA One pH: 7.2 PaCO2: 9.6 PaO2: 9.2 HCO3- : 26
What abnormality is shown? Metabolic Alkalosis Respiratory Alkalosis Metabolic Acidosis Respiratory Acidosis
Why?
Low ph
High paCO2
Respiratory acidosis
Normal ranges for ABGs
4.7 < kPa < 6.5
10.5 < kPa< 13.5
22 < mEq/L < 26
What does high Co2 mean?
Respiratory acidosis
Or metabolic alkalosis with compensation
What does high bicarb mean?
Metabolic alkalosis
Or respiratory acidosis with compensation
How can metabolic acidosis be compensated?
Low carbon dioxide
How can metabolic alkalosis be compensated?
High carbon dioxide/hyperventilation
How can resp acidosis happen?
High carbon dioxide
pH: 7.55
PaCO2: 3.0
PaO2: 13.6
HCO3-: 24
What abnormality is shown? Metabolic Alkalosis without compensation Metabolic Alkalosis with compensation Respiratory Alkalosis without compensation Respiratory Alkalosis with compensation
Respiratory Alkalosis without compensation
How can respiratory alkalosis be compensated?
Low bicarbonate/base excess
How can respiratory acidosis be compensated?
High bicarbonate
How can respiratory alkalosis happen?
Increased resp rate + over breathing= hyperventilation
Low carbon dioxide
Increased pH
How can metabolic acidosis happen?
Low bicarbonate
How can metabolic alkalosis happen?
High bicarbonate
What is the timeframe of respiratory compensation occurring?
Immediate/acute
What is the timeframe of metabolic compensation occurring?
Chronic= weeks
Which of these is a common cause of respiratory alkalosis?
Opiates Anxiety COPD Norovirus Atelectasis
Anxiety
Causes hyperventilation- blowing off + decrease of carbon dioxide
Breathing into paper bag helps to re breathe in carbon dioxide
NB: panic attacks cause numbness because:
alkalosis causes calcium to bind to albumin in blood
Causes hypocalcaemia and parasthesia
What type of pathology in the lung causes respiratory alkalosis?
Global
Hyperventilation
[Hyperoxaemia, hypocapnia]
What type of pathology in the lung causes respiratory acidosis?
Global
Alveolar hypoventilation
hypoxia, hypercapnic
pH: 7.5
PaCO2: 6.6
PaO2: 11.0
HCO3-: 28
What abnormality is shown? Metabolic Alkalosis without compensation Metabolic Alkalosis with compensation Respiratory Alkalosis without compensation Respiratory Alkalosis with compensation
4.7 < kPa < 6.5
10.5 < kPa< 13.5
22 < mEq/L < 26
Metabolic Alkalosis with compensation
Can the pH abnormality be explained by the patient’s respiratory status?
If no, it’s opposite= must mean this is compensation
If the carbon dioxide does not explain the clinical picture – you should ask yourself whether the pH derangement can explain the change in carbon dioxide as a mechanism of compensation. You should also look for further proof of a metabolic cause by looking at the bicarbonate/base excess
What factors cause metabolic alkalosis?
Vomiting [lose hydrochloric acid]
Drugs- for acid reflux- [have bicarbonate in them, which react with and mop up hydrogen ions, leading to decrease in H+ ions]
pH: 7.32
PaCO2: 7.1
PaO2: 10.8
HCO3-: 30
What abnormality is shown? Metabolic Acidosis without compensation Metabolic Acidosis with compensation Respiratory Acidosis without compensation Respiratory Acidosis with compensation
4.7 < kPa < 6.5
10.5 < kPa< 13.5
22 < mEq/L < 26
Respiratory Acidosis with compensation
pH: 7.21
PaCO2: 3.7
PaO2: 12.9
HCO3-: 15
What abnormality is shown? Metabolic Acidosis without compensation Metabolic Acidosis with compensation Respiratory Acidosis without compensation Respiratory Acidosis with compensation
4.7 < kPa < 6.5
10.5 < kPa< 13.5
22 < mEq/L < 26
Metabolic Acidosis with compensation
Explanation:
If the side with carbon dioxide was the problem, then you would expect the other side to try and compensate as it is in relative excess. Therefore you would expect hydrogen ions to mop up bicarbonate and form carbon dioxide. As a result you would expect the hydrogen ion concentration to drop and an alkalosis.
This would be a respiratory alkalosis. However, the pH in the question is 7.21 meaning an acidosis. The change in carbon dioxide therefore is moving away from the derangement. It is an act of compensation from a healthy set of lungs. Therefore the pH problem must be metabolic in nature.
What are the factors causing metabolic acidosis?
Diarrhoea [loss of bicarbonate]
Renal tubular acidosis
What is an anion gap?
An artificial concept for practicality of measuring ions in blood
When measuring ions in blood:
Only sodium and potassium cations are counted,
and only chloride and bicarbonate anions are counted
Sodium + potassium make up most of the cations, but there are quite a few other anions apart from chloride and bicarbonate [eg. ketones, dissociated acids] that we just can’t be bothered to count
Therefore there is a anion gap
All positive and negative ions have equal quantities- because we are electroneutral
How do you work out the anion gap?
In a e lecture somewhere apparently?
Don’t know if we need to know it
Will add it in when I do the el lecture, sorry lol
How do you work out the osmolality from ion concentrations?
2 [K+ + Na+] + urea + glucose = osmolality
What are the causes of a wide anion gap?
KULT Ketones [DKA] Uraemia Lactate Toxins- paracetamol, aspirin, anti freeze [ethylene glycol], isoniazid
What is a normal anion gap
412
