okay hi everyone this is lahiru from abc's of anesthesia and today we're going to go through
a blood gas we're going to go through it not in the super detailed way but the way an anaesthetist
looks at a blood gas everything is really time critical so what we have to do is we actually
get a really quick grasp of what's going on at the life-threatening stuff and be able to treat
it straight away so this blood gas was from a fractured enough patient having a hemiarthroplasty
and they were 84 they were pretty unwell overall with some liver disease
and some previous cardiac disease we took it just a standard blood gas just to see what was going on
anyway so i'm here with my reg here and uh she's going to just explain what she goes through with
this gas okay so the first thing i do when i look at a gas is just check that it's the right patient
what time the gas has been taken and so i can compare it with previous gases if they're there
and that's so important isn't it because it's like especially those big multi-trauma cases
where you're getting massive blood loss you're taking gas every 15 minutes and you really want
to have a chronological order and know exactly what you're doing absolutely but also in exams
you want to be mentioning this otherwise you know these marks master jam really yeah absolutely
um just check that it is arterial and what fio2 the patient was on when the gas was taken
or referred to what the patient's on great keep going yeah okay then the next question
i ask myself always is what's going to kill the patient first so i want to know about oxygenation
and if the pao2 i look at the pao2 here which is 290 and i'm very reassured the patient has
safe oxygenation fantastic and i think they were on was an f i of 50 yeah 50 yeah that's actually
really great so how do you know so safe po2 is above 70 technically you know we'd want it
above 100 realistically yep but say it's above 100 but there's you know you how do you know
what to expect so you're looking kind of for an a gradient so you know on the one hand as you said
you're looking for safe so you're on that nice flat part of the oxygen dissociation hemoglobin
curve but you also want to know is this the oxygen i expect for the fio2 that i'm on right so about
the rule of thumb is that three to five times the fio2 the patient's on is what you should expect
so the patient's on 50 i expect you know 250 or above um that's helpful to know that this patient
actually has great oxygenation with no a gradient almost surprising that that's too nice i'm always
thinking maybe we took a gas when the fio2 is actually 70 probably i think we're playing with it
a bit at that time okay so let's say even though the patient's safe but uh so let's say the pa2 is
290 and the patient is completely safe but maybe i was on 100 oxygen so i'm expecting you know three
to 300 to 500. yeah so then i've got a problem i've got an air gradient even though the patient's
sex so what am i thinking of then yeah i mean that would be mild but if the fpao2 is much lower
than what you would expect you're worried about something like vq mismatch or diffusion problem or
the issue with shunt or something so there's a lung issue let's say aspiration atelectasis
a pe or something something bad's happening to the patient's lungs probably
and at least we know something is some process is happening sometimes they've already had that
problem maybe they're already a copd patient they already had lung disease and other times you're
like okay why is that changed suddenly we're going to look into it we're going to do all the other
investigations that you need to do auscultate suctioning chest x-ray and whatever it is getting
ct after the operation yep good so that's probably enough of the po2 that's quickly what we think
about and what we look at yeah keep going so the next would be looking at the ph i want to know if
this ph is grossly abnormal reassuringly this ph is normal it's 7.418. with a range of 7.35 to 7.45
i'm looking to see whether there is any disturbance in the respiratory system
which is the pco2 there isn't it's low exactly and so something we were talking about before
was that if the paco2 is the cause of it if it's you know above 45 if it's quite high
what do you make of that resonance list i'm not that worried about it in an anesthetized patient
because i know that's probably because of me i'm in control of the patient's ventilation if
they're having a general anesthetic generally if it's relaxant ga so i can manage that
by changing the ventilator settings or improving the ventilation of the patient's spot breathing
and that's right so you know uh high respiratory respirators is forgivable you can over ventilate
them later so you can correct this in minutes to hours to days and so even if the pa co2 is 100
because of whatever reason depending on the reason depending on the problem
i can easily fix that yeah so what else yeah so then the next thing that's probably more
concerning is if the patient has a low ph and the bicarbonate or the base excess is really low
then i'm worried that this is a metabolic acidosis and that's something that's usually worth worrying
about there's something not quite right with this patient we need to figure out what it is okay so
look straight away at the base excess the base excess is the pure acid component of your problem
so a really large negative number i'm really worried especially if you've got a really low ph
um and quickly well the causes i think of uh d-u-l-e so diabetic ketoacidosis uremia
lactic acidosis and ethanol and other alcohol type poisonings so immediately go through those things
check for the anion gap it to make sure that that is the cause of it um and then try to solve it as
we as we need to yeah absolutely so that's your blood gas stuff now there's only a few other
sections here and again you can go through blood gas in such detail but again we're about getting
the critical stuff the life threatening stuff and sort and identifying it and sorting it out
so what do you look for next so i'd look at the hemoglobin next especially during surgery just
to check that it hasn't acutely dropped and could be the cause of let's say lactic acidosis from you
know hypovolemia or bleeding sounds good um the next thing i'd look at is generally the potassium
especially looking for hyperkalemia that's obviously a life-threatening problem and something
we should treat and so i guess if the potassium is greater than 5.5 i'm worried that stuff's going
on in anesthesia it's really important because we often give such some methodium and that can
you know increase the potassium you know up to 0.5 to 1 mm per liter but even more if it's a
burns patient or a critical care myopic invasion or any kind of myopic patient um and just quickly
potassium there's many ways to handle it and on the ward you're often getting slow acting stuff
we're all about fast acting treatments very impatient that's right so what would you give so
i'd stabilize the cardiac membrane with calcium chloride unless it was contraindicated yeah um
with you know 10 millimoles of calcium chloride in a big vein that you know with a good drip um
and then i would give salbutamol as a into in line with the as an um as inhaled salbutamol or insulin
and dextrose fantastic you can theoretically also give bicarbonate which i haven't done clinically
and potentially institute dialysis if all that failed that's right and i've never had to do this
but i always think of that situation what happens if you just can't get the potassium under control
is you know maybe it's a circumstance where i've got a i've got to do everything to shift
the potassium but really the treatment is getting the potassium out of the body
and all those treatments so your calcium is to stabilize insulin is to shift potassium
and dextrose as well so albedo is the shift potassium sodium bicarb is to shift potassium i'm
actually removing it from the body so maybe i need to insert a vasculth and get the icu guys to help
the hemidial dialyze the patient yeah uh right what else do you think well i guess the last thing
would be you know glucose really you want to check for significant hypoglycemia which needs treatment
and it's something that shouldn't be ignored and also significant hyperglycemia we're not into
tight glucose control here so something under 10 you know four to ten i'm pretty happy yeah
realistically if you aim for just you know decent control it's far better you get far less hypos
let's see the glucose in this patient it's normal it's 4.5 but if it was say one or two what would
you do yeah so i think i treat this with 50 or 25 dextrose um and uh dextrose and and then
run a dextrous infusion let's say ten or five percent dextrose dexterous infusion and check
very regularly probably pop in an art line right and check that regularly sounds good hey that's
um you know very quick abg reading uh for this patient again with anesthesia it's all about
the stuff that's really life-threatening so all i need to do after identifying the patient and
the time check the ph make sure it's not a metabolic acidosis make sure your o2 is safe
hb potassium and glucose and that's a quick reading of the abg thanks guys see you next time
you