ABG and Oxygen Flashcards
what is hypoxia
lack of oxygen in the tissues
what is hypoxaemia
low oxygen levels in the blood
what causes anaemic hypoxia
lack of Hb
what causes perfusion hypoxia
poor CO (cardiac output)
what causes toxic hypoxia
failure to release O2 at tissue level
what causes hypoxaemic hypoxia
low pO2 and SaO2
what is pO2
partial pressure of oxygen- oxygen saturation in blood plasma
what range of pH is classed as acidaemia
<7.35
define acidosis
process causing excess acid to be present in the blood
what does acidosis not necessarily cause
acidaemia
what pH range is classified as alkalaemia
> 7.45
define alkanosis
process causing excess base to be present in the blood
what are CO2 changes related to
respiratory changes
what are HCO3 changes related to
metabolic changes
which compensation is slow and which is fast
respiratory compensation fast, met slow
which out of CO2 and HCO3 is an acid and which is a base
CO2 acid, HCO3 base
what do opposite codes (high/low) mean
compensation
what do matched codes mean
primary abnormality
what can cause resp acidosis with metabolic compensation
chronic type 2 resp failure; COPD, CF, Kyphoscoliosis
what can cause metabolic acidosis with resp compensation
sepsis, poisoning, drugs, lactate
what causes uncompensated resp acidosis
acute type 2 resp failure
what causes decompensated resp acidosis
acute or chronic type 2 resp failure
what is the anion gap
difference between primary measured cations (Na+ and K+) and primary measured anions (CL- and HCO3-)
what is the commonest cause of a high anion gap
infection
what organ controls bicarbonate
kidneys
what organs control CO2
lungs
how does the body react to acidosis
breathing fast- hyperventilating- to get rid of CO2
what is metabolic compensation for resp acidosis
kidney stores bicarbonate
what is the resp compensation for metabolic alkanosis
maintain CO2 and reduce resp rate
what is type 2 resp failure
hypoxia and hypercapnia
what is hypercapnia
too much CO2
what is SpO2
percutaneous oxygen saturation (detected with a pulse oximeter)
what is SaO2
arterial blood oxygen saturation
why is venous blood darker than arterial
as deoxygenated haemoglobin in darker in colour
what is PaO2
amount of oxygen dissolved in arterial blood plasma
what is the amount of oxygen dissolved in the blood proportional to
the partial pressure of oxygen
what is FiO2
fraction of inspired oxygen
what is the only cause of hypoxia
hypoxaemia
why is too much oxygen a bad thing
poisons people, unable to detect changes in pO2, can develop into hypercabia (CO2 retention)
in what type of patient should you suspect type two resp failure
COPD
who else is at risk of type 2 resp failure
scoliosis, neuromuscular deficiency, hyper obese
how does excess oxygen cause V/Q mismatching
reverses reactive vasoconstriction in areas of poor ventilation, improves perfusion but not ventilation
what is the haldane effect
when CO2 occupies the empty binding sites on Hb (acidotic)
what happens when patients with the haldane effect are given high FiO2
pushes CO2 out of Hb and into system
what is normal respiration driven by
CO2 chemoreceptors
what does chronic hypercarbia lead to
desensitisation of these receptors- making oxygen chemoreceptors control respiration
why should COPD patients (with chronically compensated CO2 levels) not be put on
as they are not dependant on hypoxic drive and when in resp failure and put on high oxygen the CO2 in their blood will rise via the haldane effect, V/Q mismatch, and via the removal/reduction of the hypoxic drive
patients with chronically poor localised ventilation can be sensitive to what
oxygen- V/Q mismatch
what is a good marker for oxygen sensitivity
CO2 retention
what are the symptoms of hypoxaemia
altered mental state, cyanosis, dyspnoea, tachypnoea, arrhythmias
when does hypoxaemia cause death
around 2.7 kPa
what is the bets SaO2
sepsis= 85-95%
critical care= 100%
what causes anaemic hypoxia
deficiencies (iron, vit b, folate)
what causes toxic hypoxia
toxins- cyanide, CO, arsenic, alcohol, popper
what is hypoxic hypoxaemia caused by
low inspired oxygen concentration; alveolar hypoventilation, impaired diffusion, shunt, dead space, V/Q mismatch
what causes low inspired oxygen concentration
anaesthetic gases, altitude
what causes alveolar hypoventilation
opiates, anaphylaxis, obesity, kyphoscoliosis, anaesthetic, foreign body in lung
what is impaired diffusion
failure of the alveolar-endothelial interface
what can cause impaired diffusion
interstitial thickening (pulmonary fibrosis, lymphangitis, sarcoidosis), vascular dysfunction (pulmonary vasculitis, endothelial malignancy)(blood vessels to big/damaged)
what is shunting
perfusion without ventilation
what is dead space
ventilation with perfusion
what causes dead space
PE, po vasculitis, po hypertension
describe the V and Q in lug apex
good v poor q
describe the V and Q in lug base
poor v good q
what is DO2
global oxygen delivery (total amount of oxygen delivered to tissues per minute)
what conditions are patients given all the oxygen
cardiac arrest, severe trauma, severe sepsis, anaphylaxsis
