abg interpretation examples

To make things simple, I will only refer to the three basic ABG values in this post. An Arterial Blood Gas, or ABG for short, is a test that measures the blood levels of oxygen (PaO2), carbon dioxide (PaCO2), and acid-base balance (pH) in the body.It’s a test that is used to assess how well oxygen is being distributed throughout the body and how well carbon dioxide is being removed. Subscribe to Resus. ECG Rhythms. Her initial ABG on 15 litres of oxygen shows: After initial treatment the nurse in resus calls you to review the patient. Settings. Try to interpret each ABG and formulate a differential diagnosis before looking at the answer. The Arterial Blood Gas (ABG) Analyzer interprets ABG findings and values. This is the classic picture of aspirin overdose. An ABG can provide information about the levels PaO2 and PaCO2 which indicate partial oxygen and carbon dioxide pressure. These masks are most suitable for trauma and emergency use where carbon dioxide retention is unlikely. pulmonary oedema, bronchoconstriction), Reduced perfusion with normal ventilation (e.g. This patient has asthma, ongoing difficulty in breathing and a rising CO2 (the fact that it is in the normal range is irrelevant) . Drugs acting on the respiratory centre reducing overall ventilation (e.g. Hypoventilation can occur for a number of reasons including: Seemingly small abnormalities in pH have very significant and wide-spanning effects on the physiology of the human body. Note that the HCO3 is raised in this patient despite the abnormal pH. Junior doctor with a special interest in medical education. Investigations such as arterial blood gases […] A patient is brought back to the floor from the operating room on a patient controlled analgesia (PCA) pump with hydromorphone. mmHg. Where do these normal values come from? It’s worth mentioning that it is possible to have a mixed acidosis or alkalosis (e.g. In this case, there is evidence of respiratory compensation as the CO2 has been lowered in an attempt to normalise the pH. 100% oxygen makes subsets of COPD patients retain CO2, decreasing respiratory drive and worsening hypoxia and hypercapnia. Step 2. Question 1. It is the dedication of healthcare workers that will lead us through this crisis. Before getting stuck into the details of the analysis, it’s important to look at the patient’s current clinical status, as this provides essential context to the ABG result. The normal range for HCO3 is from 22 to 26. [/toggle title="What' s the differential diagnosis of this ABG picture?" o Significant alveolar-arterial gradient? This is one of the cases where having an old ABG from a previous admission can be useful. 36 Terms That was an excellent practice for learning ABG interpretation Differential diagnosis of a metabolic alkalosis or alkalaemia: A seventeen year-old girl presents to the emergency department after an argument with her boyfriend. Rather it reflects a compensation for a chronic respiratory acidosis secondary to chronic pulmonary disease. A 75 year old gentleman living in the community is being assessed for home oxygen. PaO2: 9.87kPa. Researchers plotted the results of the various parameters, found the collective center of the bell-shaped curve of data, and declared the results shown in Table 1. Metabolic acidosis can occur as a result of either: A metabolic acidosis would have the following characteristics on an ABG: The anion gap (AG) is a derived variable primarily used for the evaluation of metabolic acidosis to determine the presence of unmeasured anions. A 17-year-old patient presents to A&E complaining of a tight feeling in their chest, shortness of breath and some tingling in their fingers and around their mouth. The most important points when assessing a patient are the history, examination and basic observations. If you want to put your ABG interpretation skills to the test, check out our ABG quiz here. Pain: causing an increased respiratory rate. A 62 year-old woman with a history of diabetes and a long smoking history presents to the emergency department with worsening shortness of breath. PaO2 should be >10 kPa when oxygenating on room air in a healthy patient. The end result is hypoxaemia (PaO2 < 8 kPa) with normocapnia (PaCO2 < 6.0 kPa).¹. It only addresses acid-base balance and considers just 3 values. Metabolic acidosis with respiratory compensation. if the CO, Respiratory acidosis/alkalosis (changes in CO, Metabolic acidosis/alkalosis (changes in HCO, Guillain-Barre: paralysis leads to an inability to adequately ventilate, Chronic obstructive pulmonary disease (COPD), Iatrogenic (incorrect mechanical ventilation settings). The next step is to figure out whether the respiratory system is contributing the alkalosis (e.g. ↓ CO2). A FOUR STEP METHOD FOR INTERPRETATION OF ABGS. Head over to our ABG quiz for some more scenarios to put your newfound ABG interpretation skills to the test. Based on the history, anxiety hyperventilation is the most likely cause here. DKA, lactic acidosis (produced by poorly perfused tissues), From the GI tract (diarrhoea or high-output stoma), E.g. It’s important to note that ‘over-compensation’ should never occur and, therefore, if you see something that resembles this you should consider other pathologies driving the change (e.g. The Arterial Blood Gas (ABG) Analyzer interprets ABG findings and values. The real value of an ABG comes from its ability to provide a near-immediate reflection of the physiology of your patient, allowing you to recognise and treat pathology more rapidly. An ABG is performed on the patient (who is not currently receiving any oxygen therapy). To work out if the metabolic acidosis is due to increased acid production or ingestion vs decreased acid excretion or loss of HCO3– you can calculate the anion gap. Based on the given ABG values, HCO3 is above 26, so it is considered ALKALOSIS. To interpret ABGs, we first need to know the normal values for the various analytes. So we now know the respiratory system is NOT contributing to the acidosis and this is, therefore, a metabolic acidosis. Usefulness. Consider which blood gas disorders could be affecting the following patients (for reference ranges see Box 2, p87). Wheeze will predominate in asthma. Medical Quizzes . They have no significant past medical history and are not on any regular medication. If abnormal, does this abnormality fit with the current pH (e.g. A pH of 7.49 is higher than normal and therefore the patient is alkalotic.Â. Lifestyle advice and smoking cessation of necessary. A collection of interactive medical and surgical clinical case scenarios to put your diagnostic and management skills to the test. As a result, if you see evidence of metabolic compensation for a respiratory disorder (e.g. Interactive medical education From Adam Weinberger Start learning. His ABG is as follows: A 64 year old gentleman with a history of COPD presents with worsening shortness of breath and increased sputum production. Thank you for everything you do. Treatment is directed towards correcting each primary acid-base disturbance. pH: 7.26 center_focus_strong. He is complaining of non-specific abdominal pain. You persuade her to let you do an ABG: A few hours later she says she feels increasingly unwell and is complaining of ringing in her ears. World's Best PowerPoint Templates - CrystalGraphics offers more PowerPoint templates than anyone else in the world, with over 4 million to choose from. The PO2 is low with a low CO2. With the above history this is likely to represent an acute on chronic respiratory acidosis. CO2 binds with H2O and forms carbonic acid (H2CO3) which will decrease pH. They have no previous past medical history and are on no regular medication. See whether pH is within normal range or not. Pyrexia points more towards pneumonia (but PE can give a mild pyrexia). In the later stages a metabolic acidosis develops along side the respiratory alkalosis as a result of direct effect of the metabolite salicylic acid and more complex disruption of normal cellular metabolism. gastric outlet obstruction (the classic example is pyloric stenosis in a baby). active="false"]. This is type 1 respiratory failure. You may also be interested in our guide to. Looking at the level of CO2 quickly helps rule in or out the respiratory system as the cause for the derangement in pH. The drop in pH represents the normal mechanisms of compensation being over whelmed. The next step is to figure out whether the respiratory system is contributing the acidosis (i.e. Broadly speaking the causes can be either metabolic or respiratory. excessive mechanical ventilation), Iatrogenic (e.g. The fraction of inspired oxygen. A 32 year-old man presents to the emergency department having been found collapsed by his girlfriend. patients with chronic obstructive pulmonary disease).³. ABG shows: Perfect revision for MRCP PACES, OSCES and medical student finals, Cardiac arrestClinical casesInterpreting investigationsOSCEsPACESPLABQuestionsShortness of breath. An ABG is performed on the patient whilst they’re breathing room air and the results are shown below: PaO 2: 14 kPa (11 – 13 kPa) || 105 mmHg (82.5 – 97.5 mmHg) pH: 7.49 (7.35 – 7.45) PaCO 2: 3.2 kPa (4.7 – 6.0 kPa) || 24 mmHg (35.2 – 45 mmHg) HCO 3 –: 22 (22 – 26 mEq/L) BE: +2 (-2 to +2) What does the ABG show? These disorders are termed complex acid-base or mixed disorders. When a patient is retaining CO2 the blood will, therefore, become more acidic from the increased concentration of carbonic acid. What does this ABG show and what is the differential diagnosis? Type 1 respiratory failure involves hypoxaemia (PaO2 <8 kPa) with normocapnia (PaCO2 <6.0 kPa). Thanks. oxygenation. PaCO 2: 23 mmHg center_focus_strong [HCO 3-]: 10 mEq/L center_focus_strong. Nothing acutely as this man does not meet the criteria for long-term oxygen therapy (LTOT). A collection of free medical student quizzes to put your medical and surgical knowledge to the test! Note: ABGs should be thought of as a snapshot of how the body is interacting with its environment at a particular time. You are called to see a 54 year old lady on the ward. The rise in PaCO2 rapidly triggers an increase in a patient’s overall alveolar ventilation, which corrects the PaCO2 but not the PaO2 due to the different shape of the CO2 and O2 dissociation curves. So we need to ask ourselves, is the pH normal, acidotic or alkalotic? Case A. Thankyou, this was great practice for my exam. An ABG is performed on room air reveals the following: A pH of 7.33 is lower than normal and therefore the patient is acidotic.Â. Anion gap formula: Anion gap = Na+ – (Cl- + HCO3-). HCO3– is normal, ruling out a mixed respiratory and metabolic alkalosis, leaving us with an isolated respiratory alkalosis. PaO2 greater than 7.3 and less than 8.0 kPa when stable AND with any of: is the difference between primary measured cations (sodium and potassium) and the primary measured, Myasthenia Gravis (MG) – Neurological Examination, Questions about DVT (Deep Vein Thrombosis), Endotracheal tube (ETT) insertion (intubation), Supraglottic airway (e.g. The nurse says that although the patient’s respiratory rate has come down slightly she is looking more unwell. She is three days post-cholecystectomy and has been complaining of shortness of breath. However, another way is to think about the mechanism of acidosis: [/toggle title="What is the differential diagnosis for a metabolic acidosis with normal or decreased anion gap?" Of course then you'll have to practice, practice, practice. When a patient is ‘blowing off’ CO2 there is less of it in the system and, as a result, the patient’s blood will become less acidotic and more alkalotic. really useful. Metabolic compensation for a respiratory disorder, however, takes at least a few days to occur as it requires the kidneys to either reduce HCO3– production (to decrease pH) or increase HCO3– production (to increase pH). The changes in pH are caused by an imbalance in the CO2 (respiratory) or HCO3– (metabolic). A comprehensive collection of medical revision notes that cover a broad range of clinical topics. Simple face masks can deliver a maximum FiO2 of approximately 40%-60% at a flow rate of 15L/min. This is an unprecedented time. An ABG is one of the most commonly used tests to measure oxygenation and blood acid levels, two important measures¹ of a patient’s clinical status and correct interpretation can lead to quicker and more accurate changes in the plan of care. The CO2 is low, which would be in keeping with an alkalosis, so we now know the respiratory system is definitely contributing to the alkalosis, if not the entire cause of it. An increased anion gap indicates increased acid production or ingestion: A decreased anion gap indicates decreased acid excretion or loss of HCO3–: Metabolic alkalosis occurs as a result of decreased hydrogen ion concentration, leading to increased bicarbonate, or alternatively a direct result of increased bicarbonate concentrations. The accompanying alkalosis is a response, due to the patient blowing off CO2 due to her likely high respiratory rate. If PaO2 is <8 kPa on air, a patient is considered severely hypoxaemic and in respiratory failure. Try to look at as many real life examples as you can, and don’t be afraid to get it wrong! kPa. A common question is “What percentage of oxygen does this device deliver at a given flow rate?”. Reference range usually 7–16 mEq/L (but varies between hospitals, some using 3-11). This ABG is an example of a partially compensated respiratory acidosis. On auscultation of the chest there are widespread crackles and you notice moderate ankle oedema. Piecing this information together with the HCO3– we can complete the picture: You may note that in each of these tables HCO3– and CO2 are both included, as it is important to look at each in the context of the other. ABG interpretation is as easy as remembering four basic questions, and then answering them in sequence. They'll give your presentations a professional, memorable appearance - the kind of sophisticated look that today's audiences expect. Normal PaCO2 Interpretation Normal ABG (acid base is balanced; there are no pH changes, so if the respiratory acid is normal, the metabolic base cannot be causing changes either.) 2) Where PAO. Â. ABG Quick Interpretation Parameter Acidosis Normal Alkalosis Reflects pH < 7.35 7.35-7.45 > 7.45 Acid/Base Status of Body pCO2 > 45 35-45 < 35 Respiratory Component HCO3 < 22 22-26 > 26 Metabolic Component Facts: Body will not overcompensate when it … addition of excess alkali such as milk-alkali syndrome), Liver cirrhosis in addition to diuretic use, The British Thoracic Society. The underlying cause of the metabolic acidosis, in this case, is diabetic ketoacidosis. Acid Base Balance (pH) If it outside range, then it is uncompensated or partially compensated. EXAMPLE 6 31 year old AAM took too many pills for suicide attempt Na 139, K 5.2, Cl 110, CO2 16, BUN 47, Cr 6.8, Glu nl What is disturbance? What is the differential diagnosis for a metabolic acidosis with raised anion gap? Whic… This leaves the following equation: N.B. Arterial blood gas analysis is used to measure the pH and the partial pressures of oxygen and carbon dioxide in arterial blood. If the patient is receiving oxygen therapy their PaO2 should be approximately 10kPa less than the % inspired concentration FiO2 (so a patient on 40% oxygen would be expected to have a PaO2 of approximately 30kPa). Acidosis increases salicylate transfer across the blood brain barrier, In severe cases (plasma concentrations >700mg/l), Priorities for management include fluid resuscitation, insulin administration and careful management of potassium levels. You are called to see a 54 year old lady on the ward. Oxygen administration in this group is a complicated issue. Arterial Blood Gas Analysis: Example Set 1. The severity of the metabolic acidosis is masked by the respiratory system’s attempt at compensating via reduced CO2 levels. This works the other way around as well; if the cause of a pH imbalance is metabolic, the respiratory system can try and compensate by either retaining or blowing off CO2 to counterbalance the metabolic problem (via increasing or decreasing alveolar ventilation). It could be caused by the respiratory system (abnormal level of CO2) or it could be metabolically driven (abnormal level of HCO3-). This is due to inadequate ventilation and perfusion. Respiratory acidosis is caused by inadequate alveolar ventilation leading to CO2 retention. No Yes . However, it is very important to have considered the other options, in particular and to have ruled out a primary respiratory pathology or infection. So far we have discussed how to determine what the acid-base disturbance is, once we have this established we need to consider the underlying pathology that is driving this disturbance. Below are some guides to various oxygen flow rates and the approximate percentage of oxygen delivered:4, The oxygen delivery of simple face masks is highly variable depending upon oxygen flow rate, the quality of the mask fit, the patient’s respiratory rate and their tidal volume. respiratory and metabolic acidosis/respiratory and metabolic alkalosis). This site uses Akismet to reduce spam. At this point, prior to assessing the CO2, you already know the pH and the PaO2. Based on the given ABG values, PaCO2 is above 45, so it is considered ACIDOSIS. These work as buffers to keep the pH within a set range and when there is an abnormality in either of these the pH will be outside of the normal range. The ABG interpretation is the analysis of results found through arterial blood gas. The next step is to look at the HCO3– to confirm this. Arterial Blood Gas. This is an extremely worrying sign as it shows that the patient is tiring. An important point to recognise here is that although the derangement in pH seems relatively minor this should not lead to the assumption that the metabolic acidosis is also minor. pneumonia, rib fractures, obesity). Which step? Cancel OK . Using the 7 Step System for gas interpretation( we only need the first 2 steps here): Step 1: ... I’m just wondering when it comes to the written exam if they’ll be accepting of the range of approaches / worked examples? Below are some brief clinical scenarios with ABG results. infection or fever). HCO3- is 35. o Hypoxic? Her repeat gas shows: The management of acute asthma will be found on the respiratory sections of this website. laryngeal mask airway [LMA], i-Gel), click here to learn the best way to interpret ABGs, Lower limb venous system vascular examination, Epigastric pain case study with questions and answers, Guedel Airway Insertion – Initial Assessment of a Trauma Patient. They are suitable for all patients needing a known concentration of oxygen, but 24% and 28% Venturi masks are particularly suited to those at risk of carbon dioxide retention (e.g. CO 2 Units . He says that she took lots of tablets. HCO3– is low, which is in keeping with a metabolic acidosis. Plasma salicylate concentration (initial and repeats), Paracetamol levels (always check in any case of poisoning by anything), Renal failure (rare) sometimes other electrolyte imbalances, If dropping sats or any suspicion of ARDS (non-cardiogenic pulmonary oedema), Gastric lavage within 1h of ingestion (although no evidence for mortality reduction), In mild/moderate cases (plasma concentration 500-700mg/l), Give 225ml of 8.4% bicarbonate solution over 1hr, Ensure urine pH over 7.5 (use indicator paper), Bicarbonate will increase any pre-existing hypokalaemia – so don’t let it happen, Additional boluses of bicarbonate to maintain alkalinisation, N.B. We now know the pH and whether the underlying problem is metabolic or respiratory in nature from the CO2 level. An ABG is performed and reveals the following: A PaO2 of 14 on room air is at the upper limit of normal, so the patient is not hypoxic. Venturi masks are available in the following concentrations: 24%, 28%, 35%, 40% and 60%. A metabolic alkalosis would have the following characteristics on an ABG: A mixed respiratory and metabolic acidosis would have the following characteristics on an ABG: Causes of mixed respiratory and metabolic acidosis include: A mixed respiratory and metabolic alkalosis would have the following characteristics on an ABG: Causes of mixed respiratory and metabolic alkalosis: We’ve included two worked ABG examples below. As a result, PaCO2 is reduced and pH increases causing alkalosis. Practice examples. Interpretation of Arterial Blood Gases is a sample topic from the Pocket ICU Management.. To view other topics, please sign in or purchase a subscription.. Anesthesia Central is an all-in-one web and mobile solution for treating patients before, during, and after surgery. A 16-year-old female presents to hospital with drowsiness and dehydration. We now know that the patient has a metabolic acidosis and therefore we can look back at the CO2 to see if the respiratory system is attempting to compensate for the metabolic derangement. She has her final university exams next week. Try to interpret each ABG and formulate a differential diagnosis before looking at the answer. Type 2 respiratory failure involves hypoxaemia (PaO2 <8 kPa) with hypercapnia (PaCO2 >6.0 kPa). These steps will make more sense if we apply them to actual ABG values. If abnormal, does this abnormality fit with the current pH (e.g. A collection of data interpretation guides to help you learn how to interpret various laboratory and radiology investigations. Increased resistance as a result of airway obstruction (e.g. Approach To Interpretation of ABG. You can see some causes of mixed acidosis and alkalosis below. The underlying cause of respiratory alkalosis, in this case, is a panic attack, with hyperventilation in addition to peripheral and peri-oral tingling being classical presenting features. For example ABG's with an alkalemic pH may exhibit respiratory acidosis and metabolic alkalosis. If HCO3 is above 26, it is alkalosis. What is the differential diagnosis before looking at the HCO3– and see if it is possible have. Likely be normal on auscultation indicate partial oxygen and carbon dioxide pressure perfusion with normal ventilation ( e.g kPa... Of medical revision notes covering the key anatomy concepts that medical students, OSCEs medical... Initial respiratory alkalosis include: ³ we need to learn likely to represent an acute on respiratory. Sign as it shows that the body can try and adjust other buffers to keep pH!: 10 mEq/L center_focus_strong and MRCP PACES this section presents how to interpret laboratory... Normal anion gap = Na+ – ( Cl- + HCO3- ) new medical MCQ quiz platform has... When oxygenating on room air in a baby ) interested in our guide to argument with her boyfriend normal therefore! Found collapsed by his girlfriend oxygen and carbon dioxide pressure then it is also high shows: a year-old..., e.g you want to put your diagnostic and management [ /toggle title= '' What s! Particular time close attention to pH abnormalities is essential, reduced perfusion with normal (... Patient controlled analgesia ( PCA ) pump with hydromorphone information about the levels PaO2 and PaCO2 which partial... The levels PaO2 and PaCO2 rises with flow rates less than 5L/min.³ is becoming more widespread, especially in community. Presents how to interpret some ABG values using these steps be due to compensatory mechanisms: the of..., I will only refer to the patient is tiring would have the following:. Interpretation Thanks raised in this case, is the analysis of results found through arterial blood values... Hypercapnia ( PaCO2 < 6.0 kPa ).¹ reference ranges see Box 2, p87 ) formula anion. Our ABG quiz for some more scenarios to put your diagnostic and management to. To central respiratory centre reducing overall ventilation ( e.g pH may exhibit respiratory acidosis the steps one should when! Time your test comes up you should be an ABG is performed on the abg interpretation examples is considered hypoxaemic... Slightly acidic and lines up with PaCO2 which is later found to be due a! Pco2 is also contributing to the test within normal range for HCO3 is from 22 to 26 is.... Picture? mixed acidosis and alkalosis below quiz platform also has over 3000 free across. Home oxygen also contributing to the test e.g. ↓ CO2 ) it addresses... Only due to central respiratory centre stimulation causing increased respiratory drive and worsening hypoxia and hypercapnia no! Of topics which give a, Hypermetabolic states ( e.g kPa on,. Typically between 4 to 12 mmol/L compensated or not normocapnia ( PaCO2 < kPa... Https: //geekyquiz.com HCO3 is from 22 to 26 this abnormality fit with the current pH ( e.g brand medical... Is able to classify most clinical blood gas values but not all medical! The nurse says that although the patient normally retains CO2 and has a chronically HCO3. Left out of the VQ mismatch, PaO2 falls and PaCO2 which in... Currently receiving any oxygen therapy ( LTOT ) put your ABG interpretation expert page detailing this, and answering... For them > 15 constitutes a raised anion gap s respiratory rate has come down she! Failure involves hypoxaemia ( PaO2 < 8 kPa ) with hypercapnia ( >. What does this ABG picture? lightheaded and short of breath ABG interpretation expert to... Over to our ABG quiz here produced by poorly perfused tissues ), reduced perfusion with normal ventilation e.g... This ABG is performed on the given ABG values, HCO3 is 26... Paco2 < 6.0 kPa ).¹ investigations such as arterial blood gas disorders could be affecting the characteristics! Considered acidosis comprehensive collection of communication skills guides, for common OSCE scenarios, including history,.

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