Interpretation of ABG

Please signin to watch the full session

Interpretation of ABG

19 Jun, 5:30 AM

[Music] welcome everyone i dr rucha welcome you all on behalf of team netflix we have dr sally's been bender with us to talk about interpretation of ebg uh series consultant chess physician uh practicing at global hospital hospital and welcome sir as usual i'm sure it will be a blockbuster session today as well uh dr aditya is here with us uh tomorrow in the session so with this i hand it over to sir so good morning everyone on our rainy lazy sunday morning we are all meeting to discuss a very very important topic of arterial blood gas i'm sure all of you have some time or the other interpreted it or maybe even done a abg or on the verge of going in for an exam where you would be asked about interpretation of arterial blood gas so we will not waste more time now we will just focus on why we need to do a abg and what exactly it tells us so remember in uh in science uh it is like whenever you do a test it needs to be justified why you are doing a test everything is justifiable it needs to be answered the object you the reason a patient comes to you obviously abg's are usually done in the hospital not at a home or in the opd is very very unlikely that we do a abg in the opd so we are talking here of a scenario where the patient is either in the casualty or he is admitted and he's breathless so 99 of these patients are having breathing difficulty and they would be needing to know what is the false oxymeter saturation so you would be putting a pulse oximeter saturation and we know that saturation is just the hemoglobin getting saturated by oxygen [Music] okay so it is just telling us the saturation saturated aspect of the hemoglobin it is not even telling us the partial pressure of oxygen in the blood it is not telling the partial pressure of oxygen that is a pao2 so when we put a pulse oximeter which is very often used these days there it's a colorimetric method means it it senses the color of the blood and it tells us whether the saturation is good or saturation is not good so it's a very superficial method of understanding the oxy hemoglobin saturation so to be more specific because we are dealing with life threatening situations we need to know about how much is the papo2 how much is the partial pressure of carbon dioxide we cannot know that from the pulse oximeter we need to know the ph of the blood normally the ph is 7.4 it's a neutral ph it is neither acidic nor alkaline we need to know the bicarbonates in the blood okay so avg tells us many things including the ph the po2 the pco2 the bicarbonate of course it tells us the specific saturation which we have screened from the pulse oximeter and apart from that we also come to know the sodium the chlorides in the blood by which we can know whether there is a acidosis with a reason to it and what could be the possible change in the electrolytes happening in the blood gas so please remember the avg is not only to know about pco2 there is a ph there is a bicarb there is a po2 there is saturation there is sodium there is potassium there is chlorides there are bicarbonate so everything is a comprehensive assessment of the arterial blood gas so coming to this report directly going to the report okay we are going to interpret a few images in the few slides which will come across but we need to know the basics because it is not just an interpretation after you interpret you need to be ready with plan b what to do if there is acidosis what to do if there is alkalosis what to do if there is increase in the carbon dioxide so the normal parameters are supposed to be learned by there is no other method you need to remember them in your memory that 7.35 to 7.45 anything less than 7.35 anything above 7.45 that would mean the acidosis and the alkalosis then of course the pco2 that is 35 to 45 alkalosis and acidosis and the bicarbonate again 22 26 so we have to know these parameters remember these parameters to understand what is the meaning of particular treatment as you can see here the po2 is 8200 and anything which is going below 80 would of obviously classified into hypoxemia and we would give oxygen therapy also try to understand not every patient whose respiratory rate is 34 and 36 and he is having tachypnea and his breathless need not have a respiratory disease all right this statement is important every patient who has breathing problem need not have a lung problem so giving a nebulizer is not the treatment for every patient with breathing difficulty we will try to understand what exactly happens so this slide and the next slide will try to explain now let us see the physiology which happens and the change so physiology is what is normal and the change in the physiology is the pathology so the first and foremost right at the top you can see a ph less than 7.35 if it is less than 7.335 then there are two reasons so what is the reason and you can see the balance on each side the lung diagram and the kidney diagram so it is the lungs and the kidney which are actually balancing the ph so two organs which balance the ph is going to be the lung and the kidney both have to function adequately a problem in either of them will pitch the ph in the upper or lower direction so the most important aspect please remember when you see a ph less than 7.35 bring these two organs in your in your mind in your imagination it could be either the kidney or it could be the lungs it's not necessary always the kidney it's not necessary always the lungs and also remember that it can be both the organs getting affected simultaneously so next time you see acidic ph what will you think this could be lungs or this could be the kidney or both of them now let's consider at this point it is because of the lungs you have a patient who says doctor i'm feeling very breathless since last few weeks i am feeling very breathless i i can't breathe properly and when i walk i feel i am short of breath you do the abg and you find that a ph is less than 7.35 so the report comes as 7.30 patient is having breathlessness now you can see what is happening the diagram which shows that the pco2 is increasing which is causing the acidosis makes the patient to have a physiological increase in the respiratory to wash out the carbon dioxide there is also a washing out of the carbon dioxide because carbon dioxide has increased so the acid has increased and so there is a washout or the patient becomes tachypnic hyperventilation now the interesting thing if you see the other part of the ph that the bicarbs could be going down we know that acid is always neutralized by bicarbonates so if the bicarbonates in the body are less even then there will be acidosis now if the bicarbonate nets are less what does the body do again the patient is becoming tachypnea so there is increase in the respiratory rate now this is what is happening inside his body you are not seeing what's happening inside the body this diagram is trying to explain what's happening inside his body he is coming to you saying doctor i am unable to breathe my respiratory i'm feeling very short on breath he's tacky he's sweating his diaphoresis and you see a baby which shows acidosis so you should be remembering that oh this could be a problem where there is a lung issue which is causing increase in the carbon dioxide retention because we know the normal lung takes oxygen and throws out carbon dioxide so if there is an abnormality in the lung there can be a problem so it could be either less oxygen or more carbon dioxide if there is a problem in the kidney even then there can be acidosis what problem can happen in the kidney is that the bicarbonates are becoming lesser why they are becoming lesser because they are not getting absorbed adequately so there is bicarbonates which are getting lesser and that's why there is acidosis so two mechanisms for for for a ph going less than 7.35 if you have understood here then just look at the center the center is the most important chemical equation carbon dioxide plus water give rise to carbonic acid and it's a either way reaction it's a two way reaction and this can break into h plus and bicarbonates it can break into h plus plus bicarbonates again this is a two-way reaction depending on what is happening in the patient's body so co2 plus h2o give rise to carbonic acid it can break into h and hco3 remember this equation very well because if you know this equation you can very well understand what exactly is happening in the body imagine that the carbon dioxide is increasing so they will combine with the water and form a carbonic acid and acid obviously will make the ph acidic so that would be the equation which works in cases of respiratory ailments respiratory disorders which are possibility ending into a carbon dioxide retention so now you think of your patients with copd exacerbation severe acute asthma exacerbations or they could have interstitial lung disease respiratory failure all these patients as the airways become narrow and narrow and narrow and the carbon dioxide is unable to exhale unable to go out the carbon dioxide in the blood gets retained which means the partial pressure of the car arterial carbon dioxide is more so more carbon dioxide fuses with the water carbonic acid acid increases and the ph drops all right so this would be the way you need to understand the mechanics if you take the other the lower parts about respiratory alkalosis and metabolic alkalosis here the ph will be more than 7.45 the ph will be more than 7.45 and similar equation comes into picture to work in tandem to maintain the normal physiological ph of 7.4 so the word when i am saying it tries to maintain this word is this explanation is put in word in one word and that word is the compensation which happens to maintain the ph so ph is supposed to be maintained by compensation of the other organ so the lung if it is the problematic the kidney comes to compensate to balance the ph if there is a problem in the kidney the lungs come to compensate to maintain the ph so there is a compensation to maintain the ph the physiological ph now we are still as clinicians we need to go into the deeper aspect of what happens at this equation so again see the equation is right in the center a little more broadly explained the co2 plus h2o carbonic acid then h plus and hco3 so if we have a situation where the patient is having airway obstruction the patient is having blockage of the airways because of any reason which we are going to investigate maybe an x-ray may be a ct scan you are going to auscultate you will see that the carbon dioxide is high if the carbon dioxide is high the acidic ph starts and the acidic ph has to be neutralized it has to be neutralized by the kidney and how will the kidney try to neutralize the acidic ph it will do so by reabsorbing or retaining the bicarbonates so the bicarbonate level in the blood starts increasing to compensate the ph which was dropping okay so just try to go through the sequence because when you see the interpretation of abg it may be a little complex so try to imagine few things which are happening a patient of copd or interstitial lung disease ards pneumonia his lungs are not functioning normally when we say lungs are not functioning normally means to be more pathologically oriented the ventilation is not being adequate and the diffusion is not being adequate so the carbon dioxide is not getting washed out these these terminologies are very very very important okay carbon dioxide wash out so carbon dioxide is not getting washed out instead the carbon dioxide is getting retained because of which the pao2 will paco2 will increase and this pseudo increase gives rise to the paco2 plus h2o carbonic acid acid increases the ph drops the moment the ph starts dropping the kidneys come to the rescue this coming to the rescue is explained by by the word compensation so the kidneys come to the rescue by wanting to neutralize the ph and it tries to neutralize the ph by retaining or increasing the bicarbonates if the kidney function is good if the kidney is working well and the bicarbonates are retained the ph will start coming back to 7.4 [Music] okay so this is what exactly happens when we have a disease process happening leading to co2 retention at the same time it may be that the lungs are normal but the patient is have a problem in the kidney or the acids in the blood is increasing because of some metabolic reasons so in that situation the acid is increasing which will be the h plus so h plus is increasing and there is metabolic acidosis and the metabolic acidosis can again stimulate the brain okay so see the arrow from metabolic acidosis is going to the brain and the acid is increasing so now the carbon dioxide has to be brought down by the lung [Music] see the equation backwards okay the equation backwards acids are increasing the kidney is affected or there is excessive acid now acid formation is happening through carbonic acid so if the carbonic acid is reduced if the carbon dioxide is reduced the acid in the blood may come down so the lung comes into work and how does the lung work it has to reduce the carbon dioxide so how will the carbon dioxide reduce by making the patient breathe faster and faster so if a patient comes to you with complaints saying i am having breathlessness okay imagine each of you imagine now patient is sitting in front of you patient's respiratory rate is say 40 per minute he is takipnik you feel that he is having a respiratory problem but chest is clear and on history he mentions that he is having diabetes and he missed his insulin injections so there could be something which is affecting or increasing the acid in the blood because of uncontrolled sugar levels okay so this mechanism which i am explaining is about a scene where the insulin levels are much much less the glucagon levels are much high there is breakdown of the adipose tissue and that forms lot of ketones or ketos which are the acids so this acid gives rise to a metabolic acidosis now the metabolic acidosis makes the ph go down the body senses it that the acids are increasing that the ph is going down the body can't allow the ph to go down because if the ph goes down there will be cell death even myocardial cell death so we can't afford to do that so the lung has to compensate and come to the rescue by increasing the respiratory rate so here in this particular patient the respiratory rate was high to actually compensate the metabolic acidosis now seeing the patient you may not know this of course history will help you in a lot to know what's exactly happening but you need to also understand the values of the blood gas to really know what exactly and how severe is the problem so to go at a micro level in the kidney there is a capillary which is the globular capillaries which have the carbon dioxide if there is high then there is the inflow of carbon dioxide into the proximal tubules forming the carbonic acid then there could be an excretion of the acid so there are mechanisms right from the blood to the proximal tubule and the tubular lumen okay so there are multiple such programs these mechanisms which help in balancing now if you just just think of this diagram and i tell you okay in this particular blue circle there is a disease in the proximal tubular cells of the kidney i don't know the problem but the there is a problem in the proximal tubular cells of the kidney this entire equation will get this function you see so the kidney disease itself can induce lot of abnormalities in the abg so that's how you will have to think about doing a creatinine you'll have to think of knowing the electrolytes which has been mentioned in the arterial blood gas report so let us see these few points so many aspects of an abg we will try to see how much we can learn in the given 60 minutes but ph less than going down pco2 going high and bicarb remaining normal this would be respiratory acidosis very clear you can see the second block ph going high pco2 going down but the bicarbonate is normal this is respiratory alkalosis the third and the fourth blocks are self-explanatory you should be able to understand those as well but i will at this juncture add a small tip to this the first block which you see as respiratory acidosis the bicarbonate is normal which means that the kidney has yet not started helping the lungs hope you are getting the point so in the first block the ph is low tco2 is high so there is a problem in the lungs we are knowing that the carbon dioxide is increasing we know the patient's history also but the kidneys are not helping the lungs means the kidneys are not compensating to allow the ph to come to normal so when it is not complicity the simplest way to explain this in one word is uncompensated respiratory acidosis so abnormal ph means uncompensated similarly the respiratory alkalosis in the second block it is uncompensated respiratory alkalosis metabolic acidosis in the third block is an uncompensated metabolic acidosis i hope you are getting it because in metabolic acidosis the bicarbs are going to go low and the acids are going to increase so the ph is going to come down and if there is metabolic acidosis the lungs will try to help or try to compensate by exhaling or throwing out more carbon dioxide so if the lungs are going to compensate or they are compensated or they are trying to compensate actually the carbon dioxide will also come down in a case of metabolic acidosis but here it is not happening so we would label it the third block as uncompensated metabolic acidosis [Music] so this is like a flow chart system explaining the same i'm putting again and again the same slide because you need to you know sort of refurbish your understanding of the abg reports what exactly we mean by acidemia and alkalosis and here is what i was talking about the compensation because every time you talk of abg you it's the story does not end by saying oh it's respiratory acidosis it doesn't end there because your plan starts after interpreting the abg so whether the kidneys are functioning whether there is a compensation mechanism happening whether it is fully compensated or partially compensated so those things will also be coming gradually but try to understand the basic change which happens in the abg acid-base disorders i have already said now we are talking here as primary disturbance and secondary response is the compensation okay so before we go on actually to interpret an abg please get this into your understanding about compensation and for saying that's a fully compensated acidosis or alkalosis the ph has to be between normal 7.35 to 7.45 all right so let us let us see this particular abg now take some time see the first abg it's just an example it's not a complete abg report it's a just a pictorial image ph is 7.20 so if you go step by step it is acidotic what is happening to the bicarb bicarbs are low so bicarbonates are being low which means that the acid is increased that's why the ph is acidic [Music] okay so it is a metabolic acidosis and it is uncompensated metabolic acidosis it's an uncompensated metabolic acidosis you see the bicarbs in all the three abgs it's the same i have kept the same bicarbs in all the three abg [Music] but in all the three avg's the carbon dioxide is changing [Music] so what is happening the ph is improving as the carbon dioxide goes down so the ph comes to normal the moment it comes to normal we will call it as a fully compensated metabolic acidosis we'll call it as a fully compensated metabolic acidosis [Music] in between the two abgs the bicarbonates are of course decreasing so there is an acidosis happening but at the same time the carbon dioxide has also started decreasing that means the lungs are now coming into play and they are trying to help the the the acidosis to get neutralized so the ph has started improving but not completely compensated so we will terminate as partially compensated metabolic acidosis so there is uncompensated partially compensated and fully compensated this all is very important you should never just give a random description metabolic acidosis or respiratory alkalosis or respiratory alkalosis you should mention whether it is fully compensated or partially compensated for treatment we need to know that i hope everyone is understanding this if yes then we go to importance of each of these parameters and then after maybe five slides we will have a small interpretation of few abg's so let us see what happens the po2 is the most important we very well know but remember low oxygen doesn't kill a person in five minutes or ten minutes there could be hypoxia there will be headache there could be altered sensorium there could be even a hypoxic conversion for that matter if there is prolonged hypoxia so hypoxia is a outcome of improper respiration and when i say respiration means improper ventilation improper diffusion and improper perfusion so there could be a ventilation for future mismatch means the ventilation is becoming less perfusion is normal or there is a defect in the diffusion so there are many aspects towards low oxygen that will interpret as a hypoxia and this is a this is a four five six seven eight nine rule in case there is a pulse oximeter and you want to know how much will be the approximate approximate po2 then this will help you know how much is the po2 by checking the saturation so saturation of 90 means po2 of 60 saturation 80 means po2 of 50 saturation 70 means po2 of 40. so this is the approximate so you have seen in during covet also patients with saturation of 80 now if the saturation is 80 it means that the person is actually having a partial pressure of arterial oxygen of 50 so this is a very important approximation and we should know this now the next part which comes next point which comes in a abg is the ph so death is is the finality of every every existence but when we talk of an abg a ph less than 7 is is virtually heading towards a cardiac arrest and same is the extreme on the other side so extreme is going above 7.8 is again going to have a life threatening consequence so we always want the body rather always wants the ph to be between 7.35 to 7.45 at this juncture i would want to tell you all that abg interpretation is not something which you see a report and say this is what is happening it is happening at that point of time but there is a process there is a progress and there are different stages during the patient's cycle of disease that this abg will change so what you interpret right now say morning now it is today say 11 40 a.m and someone has sent you a abg report of uncompensated metabolic acidosis may be after 4-5 hours at 4 pm if the abg is sent of the same patient it may show compensated metabolic acidosis so these changes are dynamic and that's why we always want to know what is the blood gas report and what was the earlier blood gas report and many times you will hear or you may advise that i want you to repeat the blood gas again after four hours or six hours or after one hour depending on what is the severity of this illness so try to assimilate these few points and let's try to interpret we can say what is happening in this blood gas uh before we go to that just check all the parameters in this there is ph pco2 po2 then the corrected to the temperature which is a tabulated which is a instrumental format then there is a bicarbonate there is base excess there is saturation and the fio2 what is the fr2 at the last point you can see the fio2 what do we mean by fio2 it is a fraction of oxygen in the inspired air normally we breathe so if i ask you first of all let us see do you think this patient is breathing room air let's see how many of you are able to answer that is he on oxygen or is he off oxygen [Music] any one of you would like to put up your answer is this patient on oxygen or of oxygen [Music] is he being given a nasal oxygen or it could be that he is a room air his breathing room air so that is my one ques first question and second is now look at the abg and ask yourself how will you interpret this abg look at the ph look at the pco2 look at the bicarbonates you should remember the normal values without that you will not be able to interpret so so now you tell me two answers to this i need one what do you think about the abg [Music] and second is could this be a patient on oxygen therapy or his breathing room here [Music] anyone is going to attempt or try to answer or it's difficult to answer [Music] so in this let me help for those who are unable to answer is this abg shows a ph of 7.46 means it is above the normal so 7.46 means it is a alkaline ch now look at the pco2 so pco2 is 44 which is normal carbon dioxide so with a normal carbon dioxide we will not be having alkaline ph so the next thing you should be looking is the bicarbonates yes dr rahul you have said correctly that the patient is on oxygen i wanted to highlight that because when we say fio2 of 30 that means the patient is on oxygen normally when we breathe air the oxygen is 21 so fio2 is 21 that is 21 percent of air contains oxygen so when we breathe room air the patient breathing a fio2 of 21 but here so dr ravi on air the fio2 will be 21 but here the fio2 is 30 that means he is given oxygen that's why the fr2 is more than 21 so this person must be on oxygen so that is the first answer and coming back to the abg the ph is alkaline the pco2 is 44 and bicarbs are 31. so how will you label this [Music] so dr neya patient is going to be on oxygen in this apg report because the fyo2 is 31 30 if the patient is off oxygen means breathing room air the fio2 has to be 21 okay so patient is on oxygen from this fio2 which is mentioned at the bottom fio2 you can see the lower most point written there f i o to 30 percent on room air or when we say patient is off oxygen the fio2 is 21 but here the oxygen is high so it is 30 percent that means the f52 is definitely more than room here so patient is on oxygen he may be on one liter two liters that we'll discuss but now coming back to the abg so what do you think this is do you think this is first of all alkalosis or acidosis so i would say it is an alkalosis because the ph is going above 7.45 carbon dioxide is normal and bicarbonate is 31 so the bicarbonate is also high that means the increase in the bicarbonate is giving rise to the increase in the ph so there is a metabolic alkalosis so this blood gas would be defined as having metabolic alkalosis and it is not in the normal ph so we would put it as uncompensated metabolic alkalosis okay so uncompensated metabolic alkalosis so those who have tried to assess this abg i hope they are correct in the assessment if there is a doubt or difficulty please please put up on the chat box so there is on oxygen so doctor sohona this patient would not be off oxygen as i mentioned of oxygen means breathing room air and when the person is breathing room air the fio2 will be 21 but here the entered data is [Music] fio2 of 30 so this patient is on oxygen and dr devendra when you say uncompensated respiratory acidosis first of all if we say acidosis the ph has to be acidic only then we will say acidosis but here the ph is alkaline so this is not acidosis this is alkalosis and when we say alkalosis the ph is going beyond the normal is the ph in the normal range it is not in the normal range use the word compensated we use the word compensated only and only if the ph is brought in the normal range okay please understand this is a very important point that only and only if the ph comes to normal [Music] we will call it as a compensation if the ph is not normal we will use the words either uncompensated or partially compensated so this is uncompensated because the ph is about 7.45 and it's a metabolic alkalosis let's try one more blood gas i will give some more time on this but you try to interpret this so this patient is come with a again breathlessness most of our patients come with breathing problem they are technique they have got tachycardia there could be fever there are many symptoms which come up there could be oliguria aneurya abdominal pain vomiting loose motions all of these symptoms can come up in our patients and as you actually understand more and more interpretation of the metabolic acidosis you will realize that many gi disorders can give rise to metabolic acidosis so look at the ph look at the pco2 and look at the bicarb [Music] so this is the second dbg we are discussing the one which is dated 14th august 2018 so those who are interpreting this remember this abg specific abg 14th august 2018 [Music] so try to interpret this abc now the second abg the one which we are right now seeing the the one which is dated 14th august 2018 so let's let's try to analyze this now one first and foremost ph is 7.183 that means it is acidosis and whatever acid it is definitely uncompensated because the ph has not come to normal so first is we get into our mind that this is uncompensated ph is not normal means uncompensated now let's see the pco2 pco2 is 44.9 means it's almost 45 it's almost 45 so that is also not getting washed out we would have thought that it will be less if the patient's body is compensating bicarbonates are 16.9 so the bicarbonates have reduced so here we will have to put it as yes it is acidosis yes it is uncompensated in yes it is metabolic so it's a metabolic acidosis which is uncompensated so this abg would be labeled as uncompensated metabolic acidosis i hope you are all getting it if if you are not getting it you take time because there are many formulas which are going to come it's going to be a little mathematical there are many formulas will come to know how much is the compensation whether the pco2 has increased in the formula given so try to you know understand this let us let us try to see this abg now let us try to see this abg the third avg we are discussing the third abc abg so try to see this abg now [Music] take some five seconds to note the changes which are happening in this this is the third apg we are discussing [Music] yeah so so one question is why is it not called mixed exactly so that part we will have to discuss in the coming slides where we have formulae to know how much is the rise of the ph depending on how much is the rise in the carbon dioxide and then we can actually decipher whether it's a mixed acidosis whether there is a metabolic as well as respiratory so those are based on the formula so right now we are going a little slow to just understand the concept of acidosis alkalosis uncompensated fully compensated that's why slowly slowly you try to understand so how will we interpret this particular abg the third image is the present abg which are on your screen and the abg where the ph is seven point four nine nine i'm talking [Music] so the ph is alkalotic because it is above 7.45 [Music] the pco2 though it is given in kilopascals if you can see the normal values it is 4.5 to 6 and here it is normal so the pco2 is there remaining normal [Music] and the bicarbonate here is 32. so it is it is definitely alkalosis that is good we know that the ph is not come to the normal seven point three five to seven point four five would be the normal ph so here it is above the normal okay seven point three five to seven 7.45 is the normal ph is this ph normal it is not normal [Music] here the ph is 7.49 that means it is almost 7.5 it is 7.499 so it is a uncompensated metabolic alkalosis and for compensation what would have happened is that the patient would have hyperventilated and the carbon dioxide would have started coming down we discussed in the first few slides that when the acids increase or the bicarb decrease we are talking about h plus to increase the h plus is mixed with the water then the carbon carbonic acid and the patient tries to wash out as much carbon dioxide as possible because the lungs will come into play so this is metabolic alkalosis let us try to see this avg this is the fourth abg i am talking of the abg where the ph is 7.25 [Music] let's see how many of you are able to answer this this particular abg in which the ph is 7.25 we are slowly going to come to the formulae maybe we will have to first understand the basic abg without that i can't just jump to how much compensation and partial compensation and all those things first we need to understand the changes which are happening in the given report [Music] so you see this abg where the ph is 7.25 dr the raj i'm talking about this abg where the ph is 7.25 can you see that abg on your screen the one with ph of 7.25 [Music] so if we are done then i will just discuss this ph is 7.25 so it is an acidotic ph it is not in the normal range so it is uncompensated that is the first thing it's an acidosis it is uncompensated now let's see the bicarbonate the bicarbonate is 14.9 means it is definitely low the bicarbonates are low means the buffer the antacid the bicarbonates are less so it's a metabolic acidosis okay it's a metabolic acidosis and it is not compensated so let's keep this in mind mind at the moment let's take a look at the pco2 what is happening to the pco2 is it normal [Music] it is not normal the pco2 is normally between 35 to 45 but here it is just at the lower end it is just 35 the pco2 will be low when the patient is hyperventilating when the patient is breathing faster so please again try to remember or understand or imagine the things which i'll show in the first slides in this abg there is acidosis [Music] agreed bicarbonates are less agreed now the lung has to come to help the kidney how will the lung help the kidney by breathing faster so the respiratory rate will increase the moment the respiratory increases the carbon dioxide will start coming down now here the carbon dioxide has started coming down which means that it is now just starting to compensate for the metabolic acidosis so we cannot call it compensated because the ph is not normal but we will have to call it as partially compensated so dr neha is correct it is called as partially compensated metabolic acidosis so there is partially compensation of the metabolic acidosis if you do his abg after another two hours you may actually find that the ph is come to normal and the pco2 has gone to 20 so it would be compensation which is full but at this point of time the blood gas has been done and so it says so dr chaitanya what we are trying to explain is that this is a partially compensated why we are saying partially compensated because the carbon dioxide has started coming down which means the patient has started hyperventilating which means that the patient is the lungs are trying to help to neutralize the ph so this would be partially compensated metabolic acidosis go through these abgs whenever you can and now coming to the last i mean it's already one hour but we'll talk for another 5-10 minutes because certain formulae you need to you know remember they are just to be remembered i know max is not a very favorite subject of doctors but we need to remember this winter's formula for metabolic acidosis you can google it out it's it's a it's a it's like almost a standard everywhere in the world entirely about winter's formula for metabolic acidosis why is it used it is to use to evaluate the respiratory compensation when there is metabolic acidosis so some questions which had come up or some confusion was there that is it partially compensated or not compensated so we can use this formula and try to understand whether there is metabolic acidosis and how much is the metabolic alkalosis how much is the compensation which is happening so the formula paco2 is equal to 1.5 into the bicarbonates plus 8 plus or minus 2 so if the paco2 this calculated co2 is more than the predicted means the actual is what is there a stands for the actual if the paco2 is more than the predicted concurrent respiratory acidosis and if the paco2 is less than predicted concurrent respiratory alkalosis so you need to know this i'll give an example uh it would have been easier if you would have actually seen a patient and you would have realized but when a patient is breathless his respiratory is high his muscles also start working and the muscles work and generate lactic acid and that can actually give rise to even a metabolic acidosis so there is respiratory alkalosis because of the hyperventilating hyperventilation but the muscular contractions repeated respiratory efforts give rise to lactic acidosis which can infuse the metabolic acidosis aspect so there will be alkalosis which is because of the lung and metabolic acidosis which is becoming because of the muscle activity so there are certain points which have to be remembered or understood by the formula what is base axis base axis is a calculated value it is not the direct value from the blood what we it's a calculated value means if the bicarbonate is 36 and we consider or the normal value for that report is given as 25 then the one which is above that the subtraction the difference will be the excess of bicarbs the base excess in that particular patient so that is the base axis so please note down this formula because it is important when you are interpreting a patient with a metabolic acidosis so if the actual psco2 is more than predicted concurrent respiratory acidosis that means it will be mixed acidosis at the same time if there is a psu to less than predicted it could be concurrent respiratory alkalosis now these are again the same same uh points which we talked about what compensation and here is the mention of the base axis so if it is uncompensated the base is going to reduce if it is partially compensated even then it is not going to be reducing only in compensation the base excess would be brought back to normal so there would be a difference of all the focus is finally on the ph [Music] this may be getting a little little confusing now because as we come to certain calculations uh there are two phases of compensation okay one is acute and one is a chronic always it is so so we have a patient of copd he's got a chronic respiratory disease similarly there are patients with nephropathy which have got chronic kidney disease so there could be something which is an acute compensation something which is a chronic compensation which happens in both the respiratory acidosis and respiratory alkalosis and thus the third you know block over here the lower most you can see that for every rise of 10 in the pco2 the bicarbonate will rise by one or three so if it's an acute history then for compensation the bicarbonate will rise by one and for if it's a chronic case then the bicarbonates will rise by three you will have to remember this because with every patient every history you will have to think about it so respiratory acidosis let's put it in the example form so if there is a respiratory acidosis which is acute a patient is having acute attack of asthma or acute exacerbation or acute bronchitis or patient is having pneumonia and admitted with breathlessness for every 10 mm hg rise in the pco2 so that's the pco2 increases what will happen there will be pco2 increase so carbonic acid so there is respiratory acidosis which will happen but the body will try to compensate by increasing the bicarbonates so there is a formula for this that for every rise of 10 in the pco2 the bicarbonate will rise by one if it's an acute disease and if it's a chronic compensation that it will rise by three and similarly there is a formula for respiratory alkalosis although always also so there is ten ten is to one ten is to three ten is to two ten is two that easy way to understand so one two three four so you might make four columns one two three four for every ten increase of co2 for every ten entries in co2 for every ten increase in pco to n for every fall in when it comes to respiratory alkalosis we are going to say fallen pco2 by 10. so this way you will be able to uh understand the abg so i think we will have to just perhaps see this slide and then we will take questions uh we'll have to probably dr doctor but i think we'll have to sometime take a abg part two because there are many aspects in the blood gas yeah after one slide then we will uh just let me see what are the things yeah i think this let this be the last slide we can take on from here because there are many formulae in this slide which people have to now take a picture or remember it and then we can apply them to the blood gases which we'll try to see whenever we meet next because every acidosis alkalosis has got a compensation but that is just a very gross statement by saying that there is compensation there could be mixed acidosis there could be mixed alkalosis and how much is the compensation we need to know by this formula so i think i'll leave it at that that let them have a picture of this and whenever we start we start from this point you can check if there are any relevant questions and can pick up i am right here uh so thank you sir for such a wonderful lecture sir uh we have uh actually cleared most of our doubts and the section there is no question i can see uh what are the causes of metabolic alkalosis so dr shivani usually the metabolic alkalosis will be those whereas if we understand it correctly the bicarbonates will increase that will give rise to the metabolic aspect of bicarbonate so certain reasons certain poisonings or certain renal disorders where there is excessive excretion of acids can give rise to a increase in the bicarb or retention of bicarbonates so we will come to that there are many slides which i have kept for the alkalosis and especially metabolic alkalosis so we'll have to wait for that because that needs to be explained but that question is very important uh sure so dr shivani will continue this and so we'll take up uh in later part we'll definitely have part two on this right side and and and yes and one more thing you know what happens is that when we talk i i think we have yet not even touched upon what is called as the anion gap means about sodium potassium chlorides these electrolytes determine us huge extent of the alkalosis and acidosis so we will deal with that so that will help you understand metabolic calcium thank you sir i'll pick up more questions what is hco3 oh a and h3ocf hco3 a and hco3f yes i i personally have not gone through this what he has mentioned or i'm not understanding exactly what what the doctor is trying to say but maybe if you if you said what [Music] yeah so there is again all formula based it is 0.3 into the weight into the deficit that's a formula which is used very often 0.3 into the weight of the patient into the deficit so if there is 10 we are talking of metabolic acidosis so the bicarbs are going to be less and the normal bicarb we consider 25 so it will be at a deficit of 15 so the correction will be 0.3 into the weight into the deficit that will give you a particular number or a value now there are different ways to correct beyond this is that if there is a requirement of xyz correction then 50 of them can be given as a bolus and then after that the remaining can be given in an infusion over a period of 24 hours so that can give rise to a proper correction and you need to monitor it so that will be the way to correct the acidosis metabolic acidosis and correction one question i saw about diabetic ketoacidosis so there is a mechanism for diabetic ketoacidosis i was mentioning initially in fact one of the slides of mine if i really need to go ahead but there is one of my slides which will be talking about exactly what happens in diabetic ketosis or acidosis so this i was about to show in the next one but since you brought up the question so at a cellular level there is a fundamental error in the insulin and decrease insulin increase glucagon and that leads to actually an abnormality because of the osmotic diuresis being increased so more increased glucose more diuresis lack of electrolytes loss of potassium and sodium lipolysis and subsequently what we consider a patient of diabetic ketoacidosis so if this is one of the reasons or mechanisms right so [Music] [Music] so dr bali is asking how is uh clinical how to calculate degree of compensation and how it helps clinically yeah so degree of compensation is important because as i was saying there are certain formulae and when we want to interpret it uh exactly we want to correct you see finally why do we know the apg is to correct the acid or the alkalos how much to correct it is important by knowing whether the body is trying to itself correct corrected or we need to completely give something from externally so if there is a respiratory acidosis and the body started having a mechanism where the bicarbs have started increasing i may not over correct i don't want to over correct so the treatment will depend and please remember these questions are very important what you are asking is because uh how much to treat and how aggressive to treat so we have to repeat abc again after two hours to see whether our treatment is working so i think all these formulae will finally assimilate in uh you know sort of finding out what exactly is the way ahead to treat the patient right so i can see lot of questions on management aspect as well i mean how to correct each and every condition yeah yeah so so what what what i suggest is that let us now this was just a primer to know what is alkalosis how much is the compensation especially the formula this one this like this slide and this and the earlier one so these three the one which was winter's formula so i think each of you have to really understand what is the winter's formula the formula for acute and chronic and the abg interpretation there are many sub formulas in this about bicarbs and pco2 and ph so we need to learn this so that we can move on with the next aspect which is the anion gaps and after you finish those anion gaps then we can come to the management aspect of each disease so dr raj has elaborated his question of hco3 actual and hco3 standard so so if if i am uh able to answer him proper correctly then it it only meets the normal range when we say the actual is what we are having in a patient which we are doing it and the standard will be according to what is given so 22 to 28 will equivalence will be what the standard uh bicarbonates are given and what is seen in the abc if if i am able to explain him correctly if he wants a specific uh thing i think he can give me a call or we can discuss it uh so dr raj if you want to raise hand or come on stage and ask the in elaborative form you can go ahead and do that i'll accept your request so till then dr ayappan is asking can severe metabolic acidosis cause altered sensory severe metabolic acidosis when we say acidosis the acidosis has the reason behind it so it can definitely it can but what happens in acidosis the most important problem is cardiac arrest okay so by the time you have a ph of 7.10 or 1 6 or even 6.8 the major worry would be to prevent respiratory muscle fatigue and to prevent bradycardia so such a patient will obviously go into uh cardiac failure so we need cardiac arrest so we need to ventilate this patient altered sensorium is a major symptom associated with hypoxia with hyponatremia and drowsiness with high carbon dioxide so finally at this end of it everything will come together but there are stepwise changes which happen thank you sir uh so with this i mean uh there's just one request from dr you have shown three apgs today uh could you please just go back to uh any one of them they might want to take screenshots yes yes you can go through this [Music] so what is the importance of lactate in abc yes very it's it's a very important asp part so when we talk of metabolic acidosis or lactic acidosis which will be discussed there is a anion gap there is a high anal gap acidosis so those will be coming up in the next session which is completely dedicated to only the metabolic acidosis where we talk of lactates where we talk of electrolytes where we are going to talk even of diabetic ketoacidosis salicylic acid poisoning [Music] uh so you will elaborate more in detail about iron gap i'm sure but uh an end gap between point eight to two what is the influence that you need to take from that if you could highlight no so and then they have first of all let us see what is a normal animal that is not an anger which which is normal so if if i am putting it rightly so that everyone is listening and seeing the slide so here it is clearly mentioned that anion is 12 plus or minus 2 we are going to calculate it's a calculated gap so there is a normal gap when it comes to up to 12 to 12 or there can be a high energy gap which is more than that so if we are going to calculate it we will be finding it about when it is a high and normal and gap so i don't think at this point you know we should confuse the attendees by discussing too much of that i just found one reference about that actual bicarbonate which talks about standard bicarbonate as a is actually a calculated parameter and is like the plasma carbonate bicarbonate concentration of blood that has been equilibrated with the gas of the normal pco2 so so it's it's a more of a calculated normal doesn't mean that we need to go by the standard one we need to see the value in the blood gas and interpret the images accordingly right perfect so uh so with this we have covered all the questions that uh were based on the basics of interpretation uh and i'm sure uh we will be covering uh into depth about management how to correct it uh and other parts as well uh so thank you so much uh for your time we have already uh exceeded a lot today and thanks everyone for your patience today thank you sir okay thank you so much


Interpreting an arterial blood gas (ABG) is a crucial skill for physicians, respiratory therapists, and other health care personnel. ABG interpretation is especially important in critically ill patients. It is an essential part of diagnosing and managing a patient’s oxygenation status and acid–base balance. In order to analyze blood gases, it is important to understand the associated physiology including the nature of acids and bases, and pH levels. Acid–base imbalances can cause complications in a variety of diseases, and the deviation can sometimes be so extreme that it becomes a life-threatening risk factor. The proper collection, management, and analysis of an ABG specimen are all critical to accurate results. Join us LIVE on Medflix as we comprehend the fundamentals of ABG Interpretation with Dr. Salil Bendre.


About Medflix

Medflix is a new platform by PlexusMD, India's most active and trusted doctor community. On Medflix, you can discover live surgeries, discussions, conferences and courses from some of the top doctors and institutions across the world. Join clubs in your areas of interest and access hundreds of amazing live discussions everyday.

Contact us

+91 9023-729662

Medflix Logo

© 2022 Plexus Professionals Network Pvt Ltd