Interpreting ABG 1 Flashcards
What is T1RF
Hypoxia without hypercapnia due to high A-a gradient
What is T2RF
Hypoxia without hypercapnia - involves hyperventilation
Hypoxia
Insufficient oxygen in tissues
Hypoxaemia
Low PaO2
Will you be hypoxic if you are hypoxaemic
Yes
VBG not ABG
- FiO2 = 21%
- pO2 = 8%
- SO2 = 98%
- Hb = 150
Stroke
- FiO2 = 21%
- pO2 = 11
- SO2 = 98%
- Hb = 130
COPD
- FiO2 = 21%
- pO2 = 9.6
- SO2 = 88%
- Hb = 155
Anaemia
- FiO2 = 21%
- pO2 = 11
- SO2 = 98%
- Hb = 58
What is FiO2
Fraction of inspired oxygen - normally 21%
What is Pi
Pressure of inspired air
What is PAO2
How well Hb attaches to RBCs
What is PAO2
PP of oxygen in alveoli
What is PaO2
PP of oxygen in arteries
Alveolar-arterial gradient
PAO2 - PaO2
What is SO2
Oxygen bound to Hb
Does CO2 or O2 diffuse more easily
CO2
Are PACO2 and PaCO2 equal?
Assumed to be
Function of chemoreceptors
detect increase in PaCO2 and correct any rise by increasing ventilation but PaO2 is not so quickly corrected
What is PaCO2 proportional to
(VCO2 x k) / VA
PAO2
(FiO2(Pi-PH2O)) - (PaCO2/RER)
PaO2
(FiO2(Pi-PH2O)) - (PaCO2/RER) - (A-a gradient)
How does poor diffusion from lung to blood occur?
Thick membrane, small SA and increased circulation time
Examples of poor diffusion from lung to blood
Pulmonary fibrosis
Exercise
How does V/Q mismatch occur?
Blood not getting to lung or/and air not getting to alveoli
Examples of V/Q mismatch
PE
Atelectasis
Pulmonary oedema
How does shunt occur?
Blood bypassing lungs
Examples of V/Q mismatch
Ventricular septal defect
How is oxygen saturation increased
Increase in FiO2
Where is ventilation regulated
Respiratory centre in brainstem
SO2
Oxygen saturation in blood
SaO2
Saturation in arterial blood
How is PaO2 dictated
Alveolar ventilation, matching ventilation with perfusion and concentration of o2 in air
V/Q mismatch
Not all blood in lungs meets well-ventilated alveoli and not all alveoli are perfused with blood
Why is hyperventilating good?
Shifting more air in and out of alveoli to blow off CO
More blood passing through can offload more CO
Lowers CO
Non-shunted blood compensates for high CO
Nasal prongs
Fio2< 40%. Comfortable and convenient.Fio2non-specific: depends on flow rate (1–6 L/min) and ventilation.
Standard face mask
Fio230–50% at flow rates 6–10 L/min but imprecise. May cause CO2retention at flows less than 5 L/min (rebreathing) and, therefore, not useful for providing lowerFio2.
high-flow face mask
Fio224–60%. Delivers fixed, predictableFio2. Ideal for providing controlled, accurate O2therapy at low concentrations.
Face mask with reservoir
Fio260–80%. Can achieve even higherFio2with a tight-fitting mask. Useful for short-term use in respiratory emergencies.
Endotracheal intubation
Fio221–100%. Used in severely unwell patients with very high O2requirements, especially in patients with ventilatory failure. The patient is sedated and mechanically ventilated.
Metabolic acidosis
any process other than rise in PaCO2 that lowers blood pH - caused by too much metabolic acid or too much base excretion - hyperventilation big symptom
Raised anion gap
lactic acidosis, ketoacidosis, renal failure, poisoning, rhabdomyolysis
Normal anion gap
renal rube acidosis, diarrhoea, adrenal insufficiency, ammonium chloride ingestion, urinary diversion, drugs - normally caused by loss of HCO3-
What do kidneys do with reduced HCO3-
Retain Cl-
DKA triad
High anion gap metabolic acidosis
Elevated plasma glucose
Ketone presence
Metabolic alkalosis causes
gastric secretions, potassium depletion, Cushing syndrome, Conn syndrome, diarrhoea
