Arterial Blood Gases (ABGs)| Interpretation

[Music] welcome to this short lecture on arterial blood gases or ABG's this particular lecture will firstly will revise how we regulate our pH then we'll look at some examples of what would cause your pH to go out of balance and then we'll look at when you get an arterial blood gas within your clinical notes how to read it understand it and make sense of what's happening so let's have a look on the board firstly so there's a few things going on here firstly we've got an equation which is your bicarbonate buffering system equation if you're not familiar with this I I suggest you go and have a look at Mike's video who has done a number of videos on this but we will go back to it very briefly to show how it fits in with regulating your pH in your arterial blood gases over here we've got some states that you could be in so respiratory acidosis alkalosis metabolic acidosis and alkalosis so we'll talk about them what would cause these states took her and how it impacts this equation well here are your normal values of how your blood gases should normally look and we'll give basically we'll go through some examples of an arterial blood gas and have an approach a full step approach of how when you get your blood gases how you should approach it to make sense of it so let's firstly just revise very quickly the the bicarbonate buffering system this is essentially a system to regulate your hydrogen ions in your body which is essentially your pH your pH or the power of hydrogen is the amount of hydrogen ions in your blood and this is a range of 7.35 to 7.45 so this is an equation that essentially demonstrates how in the our body regulates through homeostasis that the hydrogen levels so firstly let's start at this end we've got carbon dioxide and water carbon dioxide is basically May by every single cell in your body it's it's made by the use of glucose and oxygen to make ATP and as a by-product we make co2 co2 then quickly meets up with water so about 70% of your carbon dioxide will form with water to give you this thing called carbonic acid now this will go into your blood and then I'll get transported to your lungs here where it'll get breathed out so carbon dioxide although it can be made in every cell in your body it can only be exhaled or lost or excreted by your lungs so essentially anything to do with carbon dioxide levels is a respiratory thing so carbon dioxide should be an arranged partial pressure of carbon dioxide in your arterial blood should be in the range of 35 to 45 millimeters of mercury it's an easy way to remember this is look at your pH if you get rid of the sevens if you get rid of both sevens it will give you 35 45 which is essentially your partial pressure of carbon dioxide so any state where carbon dioxide is out of range with your blood gases it's a respiratory cause because your lungs is regulating your carbon dioxide levels so it should be in that range if you've got high carbon dioxide which would be above the 45 because carbon dioxide in your blood with water is an acid it would actually make the pH to go down okay and we'll get to that in a second go into this end so with this carbonic acid which you can see is made by carbon dioxide and water another reversible way you could look at it is down in your body and particularly a kidney end it can reversibly dissociate into hydrogen which we know is an acid and bicarbonate which we know is a base now hydrogen can be made in the body or ingested in the body so this can be moved around quite a bit as can by covenant but by covenant is only regulated by the kidney so the kidney is the only organ in the body that can really play around with bicarbonate levels so for that reason we call the bicarbonate levels a metabolic okay because the kidney essentially regulating the by covenant levels so what's happening with the acid will determine what the kidney is doing with it so if you're in a state where you're produced more hydrogen so you've ingested things that are acid like or you're in States so you are producing acid like if you're producing ketones or lactic acid that would make more of this that would mean your kidney has to make more of this to try and buffer this out so your pH doesn't go out of whack so it's important to note if your bicarbonate levels are out of whack that would mean it it's a kidney thing which means it's a metabolic thing so wherever you see the bicarbonate levels which should be in a range of 22 to 26 millimoles of mercury sorry millimoles per liter anything too high so it's above 26 would mean this excessive base so you would be in a alcoholic or a colossus state whereas if you have low by covenant so less than 22 that would suggest that either you've got a lot of acid and your base is trying to buffer it or you've just lost a lot of base like for instance with diarrhea so hopefully you can see now that the carbon dioxide is regulated by the lungs the bicarbonate is regulated by the kidneys which would equate to a metabolic okay and the purpose of this is just to keep your pH in a normal range okay the other thing that I've got here is just the partial pressure of oxygen which is 75 to 100 millimeters of mercury and this is just an another important aspect to an ABG particularly with the rest the respiratory aspect to it so here are some examples that we'll go through now to make sense of how an ABG is read so the way that it's sometimes written in the clinical notes is a number / number / number / number so the first number is your pH the second is the carbon oxide the third is the oxygen and the fourth is a by cabinet so if you see this you need to understand what it means and this is the approach so step one you look at the pH so you look at this number so the pH as we know should be 7.35 to 7.45 that's the first step the second step is to look at the carbon dioxide levels it should be 35 to 45 so that's the second number okay that's the second step third step is the bicarbonate so you actually look at this number that should be 22 to 26 millimoles per liter and then finally we have this acronym known as Rome just like the city in Italy and the RO okay the arrow stands for respiratory opposite ma metabolic equal now what that means is with if it's a respiratory caused issue the number between here and here will go the opposite direction so if the pH goes down the if it's a respiratory problem these co2 will go up that's why it's called respiratory opposite whereas if it's a metabolic issue if the pH goes down the by carbon all go down which is why it's metabolic equal so if you're still not sure let's do an example and we'll make sense so let's start with example one seven point two nine pH should be seven point three five to some point five so we know that this is down arrow down having a look at now the co2 it's 35 to 45 we know that is up so that's an arrow up the 60 is actually low so I'll just put a cross here and then finally the bicarbonate is 28 which means it's high so now going to the Rome we know that so we've got two arrows going up the carbon dioxides up the bicarbonate up the pH is down so which one is the opposite respiratory opposite metabolic Egor so that means it has to be arrest Kri issue and we've got so what do we got here we got high co2 so this co2 levels are high okay pH is low and we know that if you have high co2 it adds with the water which then might bicarbonate acid but carbonic acid which then would equate to a high amount of hydrogen and this is why this particular person has got a low pH because we know as the hydrogen goes up the pH goes look down so this person would be in respiratory acidosis which is this one here now why is the by covenant hi this one here well we know that the hydrogen's high hence why the pH is low but the kidney is trying to compensate so it's making more bicarbonate so this is why this is high it's trying to make more of this to buffer this to drop the pH but it hasn't done it well enough so because the pH is still out of whack so we say it is in this case partially compensated so this wouldn't be this if you saw this in your notes it would be considered partially compensated respiratory acidosis now what are some of the reasons why a person may have respiratory acidosis a big one is they a hypo they've got hypoventilation hypo ventilation that means they aren't getting rid of enough co2 some causes of hyperventilation would be maybe some drugs sedatives or opiates can change your respiratory drive making it slower than it should therefore you're not getting rid of your co2 okay other things that might cause it intrinsic lung issues so if you have things like pneumonia which changes the gas exchange or pulmonary edema which would also change that or if you have poor flowing so you have trap in which could be obstructive issues like COPD or asthma all these things cause co2 to increase which ultimately would cause hydrogen to increase and if your kidneys can't buffer it you would end up with an acidosis which we've seen but in this case it's partially common so that the kidneys trying to do it so that's the first one done let's move to the next one we've got seven point three seven point five so that's going to be high so arrow up 41 this is normal so I'll just put a tick a tick so that's normal 98 is normal and 29 is high so we've got two arrows going up normal normal so if it was respiratory or the opposite like we saw there but it's gone the same direction so it's equal so we know it's a metabolic so we know it is metabolic because it's in the same direction okay now is an acid or a base well at seven point five it's above four five so we know it is and alkalosis alkalosis now the so this is good this is essentially meaning there's a lot of this relative to this okay which could mean so we're focusing on metabolic alkalosis here so what are some reasons for maybe why you have high high amounts of bicarbonate to hydrogen well maybe Lee maybe you've just lost your hydrogen so ways you could lose your hydrogen is lots of vomiting so if your patients vomiting a lot they're gonna lose a lot of HCl which is the hydrogen if you lose them lots of hydrogen therefore you've got a lot more base compared to the acid that means you have the alkalosis other things that could cause it if a person's taking lots of antacid okay for problems with their stomach like reflux or ulcers or they might be try think another example if you've never suction their stomach can pull on our acid that could be also a cause now we've we know it's a metabolic alkalosis what should happen if that is excessive you would expect to see the carbon dioxide trying to compensate but it's still in a 41 range which means it is not compensating so the lungs aren't compensating for this alkalosis so it is uncompensated okay so this would be an uncompensated metabolic alkalosis and we said some of the causes for metabolic alkalosis would be vomiting antacid use or maybe stomach suctioning so that's the second one done okay let's move on to this one so we've got 7.49 okay so that's again high okay 24 that should be 35 at the low margin so that's low 105 so that's actually high but it's good and 22 which is okay so we know the person's got alkalosis the co2 is going down the other two are normal so it's opposite respiratory opposite so we know it's a respiratory cause so we now know it's respiratory alkalosis because the pH is actually high now the bicarbonate is a normal range which means it's not buffering so again so it's not trying to bug it's not buffering so that would mean it's uncompensated now what essentially is happening here because the co2 is low that means you're getting rid of lots of co2 okay and because you're getting rid of lot of co2 you have less to make with water less acid okay so less of this but you would expect the kidney to try and counter this by getting rid of bicarbonate in the urine but it hasn't done so because it's still in the normal range so what would cause arrest tree alkalosis warts basically the opposite of the respiratory acidosis so it would be not hypoventilation but hyper hyper ventilation so what would cause your patients to hyperventilate well they could be in pain or they could be anxious having a panic attack that would cause too much to get released another thing would be if you go to altitude you have less oxygen partial pressure of oxygen in the atmosphere is less that means you got to breathe more to keep your blood oxygen out that means as you're breathing more you're blowing more co2 off and that could also cause you to get respiratory alkalosis or if you've got problems with your heart like heart failure that could also lead to numbness see co2 again and blown off but you would expect because you got less with water to make carbonic acid you'd expect the is to essentially compensate by urinating out the excessive amounts of bicarbonate but at this point in time the kidney is not doing so remember the kidneys does takes hours to do this this is probably why it's a bit slower finally the last one is 7.38 so this is normal so that's a tick 30 that's low so that's actually a low 93 that's good and 15 is very low so this is down so this seems a bit odd because what we've got here is we've got low co2 low co2 which would actually make you our qalaat ik whereas you've got low by covenant so low bicarbonate which suggests you've got a lot of acid there for some reason which is buffered a lot of the bicarbonate which is a slow because that's there's less free amounts of bicarbonate because it's presumably buffering lots of hydrogen so what this one would be even though the pH is normal but because the by cover is much more out of whack than the co2 we would say it is a metabolic acidosis so it's metabolic so doses but because the pH is in a good range it's a normal range it's fully compensated which means we've got lots of acid we've lost a lot of base to buffer it that's why it's 15 which would suggest there's still lots of acid which means it's going to be more of this which means that the carbon dioxide will try to get rid of that by blowing more of this off right more of out here which would actually make the co2 levels drop which we did see so that's a good thing which means the pH is in a normal range so even though we've got an acid forming condition high amounts of hydrogen it's compensated the lung has compensated which it will probably do because your lungs work within minutes seconds two minutes to come to try and compensate so this is why we've got a metabolic acidosis fully compensated now what are the what are some of the reasons for a person to get metabolic acidosis these are states that would cause lots of this to be produced or if you ingest acid like things or you lose lots of that so metabolic acidosis for example if you are producing lactic acid so you could get that if a person's going into shock because their tissues aren't being perfused therefore they're having got oxygen therefore they go into an anaerobic state therefore that produced lactic acid therefore they've got more hydrogen ions they're pulled up or lose the bicarbonate another one would be ketogenesis ketones Cato Genesis so a person with diabetes ketoacidosis would get these and if you have lots of hydrogen or ketones that means you're going to lose your bicarbonate and what would you expect to see with these two particularly with DKA their respiratory rate increases to get rid of the co2 another thing that you might have is diarrhoea so diarrhea because bicarbonate is produced by the pancreas to buffer the hydrochloric acid in your stomach it would also hope to be reabsorbed in your intestine that if you get diarrhea you prune out lots and lots of bicarbonate and that would also lose that more more hydrogen ions freely therefore and metabolic acidosis in terms of ingestion finally just alcohol or aspirin are actually acid forming metabolites which if you ingest lots of alcohol or aspirin that could also put you into a metabolic acid aaalac state so hopefully now what you've seen is how the bicarbonate system will regulate your ph your kidneys do it with over essentially days your lungs can do it within minutes with co2 your kidneys do it with bicarbonate hopefully you can see how you should approach an ABG and some examples of when they do work we know that it's fully compensated when they try to work it's partially compensated if they've made no attempt it is uncompensated and then finally hopefully you can see conditions or processes that would lead to a pH being out of range and that would hopefully get you to think clinically so when you are looking after your patient and you've taken that AVG you know is what exactly is happening

Channel: Dr Matt & Dr Mike

Views: 115,845

Keywords: ABGs, Arterial Blood Gases, NCLEX, USMLE, 4Step ABG, Metabolic Acidosis, Metabolic Alkalosis, Respiratory Acidosis, Respiratory Alkalosis, Compensated, Uncompensated, Partially Compensated, Fully Compensated, how to measure abg, what are abgs, abg interpretation, arterial blood gas interpretation, arterial blood gas

Id: K1qReVoragU

Length: 21min 39sec (1299 seconds)

Published: Sun Aug 18 2019