ABG Flashcards
(35 cards)
What are the poor prognostic factors of asthma
- previous near fatal asthma e.g. previous ventilation or respiratory acidosis
- previous admission for asthma especially if in the last year
- requiring three or more classes of asthma medication
- heavy use of B2 agonist
- repeated attendances at ED for asthma care especially if in the last year
- brittle asthma
What is the normal PaCO2 level
4.6-6.4kPa
what is the definition of hyperventilation and hypoventilation
- Hyperventilation = less than 4.6 kPa PaCO2
- Hypoventilation = greater than 6.4 kPa
if someone with an asthma attack has normal PaCO2 what does this mean
- a normal CO2 suggests that he is becoming exhausted - alongside hypoxia this would be a worrying sign
What is the normal oxygen level PaO2
10.6-13.5KpA
what is oxygenation affected by
- VQ balance
- inspired oxygen concentration (FiO2)
- ventilatory efficiency
- affinity of blood for oxygen
What pH is acidosis and what pH is alkalosis
- less than 7.35 is acidosis
- greater than 7.45 is alkalosis
what is the normal bicarbonate level
22-28mmol/l
How long does metabolic compensation take
- takes days
How long does respiratory compensation take
- minutes
How does metabolic compensation happen
- cellular buffering, this occurs over minutes to hours, this elevates plasma bicarbonate only slightly
- renal compensation - this occurs over 3-5 days
How does respiratory compensation happen
- respiratory compensation of alkalosis doesn’t tend to happen
- carbon dioxide is usually the drive to breath unless there is chronic lung disease so it is tough to hyperventilate and increase carbon dioxide
What is the base excess
- the base excess is the quantity of base or acid needed to titrate one litre of blood to pH 7.4 with the pC02 held constant at 5.3kPa
what is the normal base excess
-2 - +2 mmol/l
what does negative base excess indicate in an acidosis
- In the context of an acidosis a negative base excess indicates there is a metabolic component
what is the alveolar:arterial gradient
- this estimates the diffusion gradient between alveolus and oxygenated blood
what is the normal level for the alveolar: arterial gradient
- the gradient is usually low in normal people
How do you calculate the alveolar: arterial gradient
= FiO2 - (PaO2 + PaCO2)
- Where FIO2 approximates to the % inspired oxygen (might be the number of breaths per minute)
What is the normal range of alveolar: arterial gradient
- 25 years old = 0.2-1.5kPa
- 75 years old = 1.5-3.0 kPa
What does it mean when the alveolar: arterial gradient is raised
- this means that there is impaired gas exchange
- oxygen has not diffused form the alveoli to the arterial circulation efficiently
what can cause a high alveolar: arterial gradient
PE
What is the anion gap
- this is the difference between cations and the un-estimated anions
what is the anion gap made out of
- fixed acids (such as phosphorous)
- organic acids (ketones, lactate, albumin)
Write out the equation of the anion gap
(K+ + Na+) - (Cl- + HCO3-)
