Acid Base Disorders
Arterial blood gas analysis is used to determine the adequacy of oxygenation and ventilation, assess respiratory function and determine the acid–base balance. These data provide information regarding potential primary and compensatory processes that affect the body’s acid–base buffering system. Interpret the ABGs in a stepwise manner: Determine the adequacy of oxygenation (PaO2) Normal range: 80–100 mmHg (10.6–13.3 kPa) Determine pH status Normal pH range: 7.35–7.45 (H+ 35–45 nmol/L) pH <7.35: Acidosis is an abnormal process that increases the serum hydrogen ion concentration, lowers the pH and results in acidaemia. pH >7.45: Alkalosis is an abnormal process that decreases the hydrogen ion concentration and results in alkalaemia. Determine the respiratory component (PaCO2) Primary respiratory acidosis (hypoventilation) if pH <7.35 and HCO3– normal. Normal range: PaCO2 35–45 mmHg (4.7–6.0 kPa) PaCO2 >45 mmHg (> 6.0 kPa): Respiratory compensation for metabolic alkalosis if pH >7.45 and HCO3– (increased). PaCO2 <35 mmHg (4.7 kPa): Primary respiratory alkalosis (hyperventilation) if pH >7.45 and HCO3– normal. Respiratory compensation for metabolic acidosis if pH <7.35 and HCO3– (decreased). Determine the metabolic component (HCO3–) Normal HCO3– range 22–26 mmol/L HCO3 <22 mmol/L: Primary metabolic acidosis if pH <7.35. Renal compensation for respiratory alkalosis if pH >7.45. HCO3 >26 mmol/L: Primary metabolic alkalosis if pH >7.45. Renal compensation for respiratory acidosis if pH <7.35. Additional definitions Osmolar Gap Use: Screening test for detecting abnormal low MW solutes (e.g. ethanol, methanol & ethylene glycol [Reference]) An elevated osmolar gap (>10) provides indirect evidence for the presence of an abnormal solute which is prese Continue reading >>
Acid-base Disorders - Endocrine And Metabolic Disorders - Merck Manuals Professional Edition
(Video) Overview of Acid-Base Maps and Compensatory Mechanisms By James L. Lewis, III, MD, Attending Physician, Brookwood Baptist Health and Saint Vincents Ascension Health, Birmingham Acid-base disorders are pathologic changes in carbon dioxide partial pressure (Pco2) or serum bicarbonate (HCO3) that typically produce abnormal arterial pH values. Acidosis refers to physiologic processes that cause acid accumulation or alkali loss. Alkalosis refers to physiologic processes that cause alkali accumulation or acid loss. Actual changes in pH depend on the degree of physiologic compensation and whether multiple processes are present. Primary acid-base disturbances are defined as metabolic or respiratory based on clinical context and whether the primary change in pH is due to an alteration in serum HCO3 or in Pco2. Metabolic acidosis is serum HCO3< 24 mEq/L. Causes are Metabolic alkalosis is serum HCO3> 24 mEq/L. Causes are Respiratory acidosis is Pco2> 40 mm Hg (hypercapnia). Cause is Decrease in minute ventilation (hypoventilation) Respiratory alkalosis is Pco2< 40 mm Hg (hypocapnia). Cause is Increase in minute ventilation (hyperventilation) Compensatory mechanisms begin to correct the pH (see Table: Primary Changes and Compensations in Simple Acid-Base Disorders ) whenever an acid-base disorder is present. Compensation cannot return pH completely to normal and never overshoots. A simple acid-base disorder is a single acid-base disturbance with its accompanying compensatory response. Mixed acid-base disorders comprise 2 primary disturbances. Compensatory mechanisms for acid-base disturbances cannot return pH completely to normal and never overshoot. Primary Changes and Compensations in Simple Acid-Base Disorders 1.2 mm Hg decrease in Pco2 for every 1 mmol/L decrease in HC Continue reading >>
Common Laboratory (lab) Values - Abgs
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Laboratory VALUES Home Page Arterial Blood Gases Arterial blood gas analysis provides information on the following: 1] Oxygenation of blood through gas exchange in the lungs. 2] Carbon dioxide (CO2) elimination through respiration. 3] Acid-base balance or imbalance in extra-cellular fluid (ECF). Normal Blood Gases Arterial Venous pH 7.35 - 7.45 7.32 - 7.42 Not a gas, but a measurement of acidity or alkalinity, based on the hydrogen (H+) ions present. The pH of a solution is equal to the negative log of the hydrogen ion concentration in that solution: pH = - log [H+]. PaO2 80 to 100 mm Hg. 28 - 48 mm Hg The partial pressure of oxygen that is dissolved in arterial blood. New Born – Acceptable range 40-70 mm Hg. Elderly: Subtract 1 mm Hg from the minimal 80 mm Hg level for every year over 60 years of age: 80 - (age- 60) (Note: up to age 90) HCO3 22 to 26 mEq/liter (21–28 mEq/L) 19 to 25 mEq/liter The calculated value of the amount of bicarbonate in the bloodstream. Not a blood gas but the anion of carbonic acid. PaCO2 35-45 mm Hg 38-52 mm Hg The amount of carbon dioxide dissolved in arterial blood. Measured. Partial pressure of arterial CO2. (Note: Large A= alveolor CO2). CO2 is called a “volatile acid” because it can combine reversibly with H2O to yield a strongly acidic H+ ion and a weak basic bicarbonate ion (HCO3 -) according to the following equation: CO2 + H2O <--- --> H+ + HCO3 B.E. –2 to +2 mEq/liter Other sources: normal reference range is between -5 to +3. The base excess indicates the amount of excess or insufficient level of bicarbonate in the system. (A negative base excess indicates a base deficit in the blood.) A negative base excess is equivalent to an acid excess. A value outside of the normal r Continue reading >>
Simple Method Of Acid Base Balance Interpretation
A FOUR STEP METHOD FOR INTERPRETATION OF ABGS Usefulness This method is simple, easy and can be used for the majority of ABGs. It only addresses acid-base balance and considers just 3 values. pH, PaCO2 HCO3- Step 1. Use pH to determine Acidosis or Alkalosis. ph < 7.35 7.35-7.45 > 7.45 Acidosis Normal or Compensated Alkalosis Step 2. Use PaCO2 to determine respiratory effect. PaCO2 < 35 35 -45 > 45 Tends toward alkalosis Causes high pH Neutralizes low pH Normal or Compensated Tends toward acidosis Causes low pH Neutralizes high pH Step 3. Assume metabolic cause when respiratory is ruled out. You'll be right most of the time if you remember this simple table: High pH Low pH Alkalosis Acidosis High PaCO2 Low PaCO2 High PaCO2 Low PaCO2 Metabolic Respiratory Respiratory Metabolic If PaCO2 is abnormal and pH is normal, it indicates compensation. pH > 7.4 would be a compensated alkalosis. pH < 7.4 would be a compensated acidosis. These steps will make more sense if we apply them to actual ABG values. Click here to interpret some ABG values using these steps. You may want to refer back to these steps (click on "linked" steps or use "BACK" button on your browser) or print out this page for reference. Step 4. Use HC03 to verify metabolic effect Normal HCO3- is 22-26 Please note: Remember, the first three steps apply to the majority of cases, but do not take into account: the possibility of complete compensation, but those cases are usually less serious, and instances of combined respiratory and metabolic imbalance, but those cases are pretty rare. "Combined" disturbance means HCO3- alters the pH in the same direction as the PaCO2. High PaCO2 and low HCO3- (acidosis) or Low PaCO2 and high HCO3- (alkalosis). Continue reading >>
9.3 Bedside Rules For Assessment Of Compensation
The method of assessing acid-base disorders discussed here uses a set of six rules which are used primarily to assess the magnitude of the patients compensatory response. These rules are now widely known and are soundly based experimentally. These rules are used at Step 4 of the method of Systematic Acid-Base Diagnosis outlined in Section 9.2.- (You should read section 9.1 & 9.2 before this section.) These rules are called 'bedside rules' because that can be used at the patient's bedside to assist in the assessment of the acid-base results. The rules should preferably be committed to memory - with practice this is not difficult. A full assessment of blood-gas results must be based on a clinical knowledge of the individual patient from whom they were obtained and an understanding of the pathophysiology of the clinical conditions underlying the acid-base disorder. Do not interpret the blood-gas results as an intellectual exercise in itself. It is one part of the overall process of assessing and managing the patient. A set of blood-gas and electrolyte results should NOT be interpreted without these initial clinical details. They cannot be understood fully without knowledge of the condition being diagnosed. Diagnosing a metabolic acidosis, for example, is by itself, often of little clinical use. What is really required is a more specific diagnosis of the cause of the metabolic acidosis (eg diabetic ketoacidosis, acute renal failure, lactic acidosis) and to initiate appropriate management. The acid-base analysis must be interpreted and managed in the context of the overall clinical picture. The snapshot problem: Are the results 'current'? Remember also that a set of blood gas results provides a snapshot at a particular point in time and the situation may have changed since Continue reading >>
Deciphering Acid-base Disorders
Derangements in acid-base status are commonly discovered on routine emergency department evaluation and often suggest the presence of severe underlying disease. Many acute conditions can disrupt homeostatic mechanisms used to buffer and excrete acid, and these changes may necessitate immediate intervention. When you discover a patient with an abnormal pH, what is your approach to the diagnosis? Large amounts of fixed and volatile acid are produced as normal byproducts of cellular metabolism. In addition to excretion of these byproducts via the lungs and kidneys, physiologic pH is maintained using carbon dioxide and bicarbonate as buffers. The balance of serum PCO2 and HCO3 directly impact pH, and disruption of this ratio results in primary acidemia or alkalemia, depending on the direction of the change. Notably, acidemia and alkalemia describe changes in serum pH, whereas acidosis and alkalosis refer to the clinical conditions underlying those changes. These conditions can be either metabolic or respiratory in etiology, leading to 4 categories of primary acid-base disorders. In response to this primary change, compensatory mechanisms attempt to drive the pH toward normal by keeping the PCO2/HCO3 ratio constant. The degree of compensation is related to the chronicity of the primary disorder, but does not generally restore the pH to normal. To add to the complexity, patients can have more than one primary disorder. Features of each disorder are detailed as follows, which assumes ABGs are used: * Respiratory compensation becomes less effective for chronic metabolic disorders ** There is conflicting data regarding reliable elevation in AG from isolated lactic acidosis *** For isolated respiratory processes only Checklist: Evaluating Acid Base Disturbances Acid-base physiol Continue reading >>
Arterial Blood Gases (abg) Calculator
Enter the Partial Pressure of Carbon Dioxide (PaCO2): The arterial blood gases calculator calculates whether an individual is in metabolic acidosis, metabolic alkalosis, respiratory acidosis, respiratory alkalosis, or is normal. The calculator also determines whether the state is compensated or uncompensated. Arterial blood gases are blood taken from an artery, normally the radial artery, which determines how well oxygenated a person's blood is. Arterial blood gases determine the pH of the the person's blood, the bicarbonatelevel of a person's blood, and the amount of carbon dioxide in a person's blood. It can also tell the amount of oxygen in a person's blood, but we don't use the level of oxygenation to determine the state the person is in. So the first thing an arterial blood gas can tell is the pH of the blood. This is huge and alone determines whether the person is in an acidotic state or an alkalotic state. Normal blood pH ranges from 7.35 to 7.45. If the person's pH is below 7.35, the person is in an acidotic state. If the person's pH is above 7.45, the person is in an alkalotic state. So the pH is the first thing we look at to determine what state- acidotic or alkalotic- aperson is in. Another component of arterial blood gas is the bicarbonate level. Bicarbonateis an alkaline substance produced by the kidneys in order to buffer against acidity in the body. It is the metabolic component of the arterial blood gases. If a person is in a state of respiratory acidosis, to compensate for this acidotic state, the person's kidneys will produce more bicarbonate. This helps to neutralize the acidity. If a person is in a state of respiratory alkalosis, to compensatefor this alkaline state, the person's kidneys will produce less bicarbonate.The normal range of bicarbonate Continue reading >>
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4.5 Respiratory Acidosis - Compensation
Acid-Base Physiology 4.5.1 The compensatory response is a rise in the bicarbonate level This rise has an immediate component (due to a resetting of the physicochemical equilibrium point) which raises the bicarbonate slightly. Next is a slower component where a further rise in plasma bicarbonate due to enhanced renal retention of bicarbonate. The additional effect on plasma bicarbonate of the renal retention is what converts an "acute" respiratory acidsosis into a "chronic" respiratory acidosis. As can be seen by inspection of the Henderson-Hasselbalch equation (below), an increased [HCO3-] will counteract the effect (on the pH) of an increased pCO2 because it returns the value of the [HCO3]/0.03 pCO2 ratio towards normal. pH = pKa + log([HCO3]/0.03 pCO2) 4.5.2 Buffering in Acute Respiratory Acidosis The compensatory response to an acute respiratory acidosis is limited to buffering. By the law of mass action, the increased arterial pCO2 causes a shift to the right in the following reaction: CO2 + H2O <-> H2CO3 <-> H+ + HCO3- In the blood, this reaction occurs rapidly inside red blood cells because of the presence of carbonic anhydrase. The hydrogen ion produced is buffered by intracellular proteins and by phosphates. Consequently, in the red cell, the buffering is mostly by haemoglobin. This buffering by removal of hydrogen ion, pulls the reaction to the right resulting in an increased bicarbonate production. The bicarbonate exchanges for chloride ion across the erythrocyte membrane and the plasma bicarbonate level rises. In an acute acidosis, there is insufficient time for the kidneys to respond to the increased arterial pCO2 so this is the only cause of the increased plasma bicarbonate in this early phase. The increase in bicarbonate only partially returns the extracel Continue reading >>
Arterial Blood Gas Analysis: Example Set 2
Arterial Blood Gas Analysis: Example Set 2 You are working in the emergency room when the paramedics bring in a 45 year-old man who was found down in Pioneer Square. He is somnolent but arouseable. He has emesis on his shirt. He is hypotensive and tachycardic. Labs are drawn and reveal the following: Step 2: The PCO2 is low (respiratory alkalosis) and the bicarbonate is low (metabolic acidosis). Therefore, the metabolic acidosis is the primary process. Step 3: The serum anion gap is elevated at 29. There is, therefore, an elevated anion gap acidosis. Step 4: The respiratory alkalosis is the compensatory process for the metabolic acidosis. The Delta Gap = Measured SAG Normal SAG = 29 12 = 17 Calculate the Delta Delta: Delta Gap + measured bicarbonate = 17 + 12 = 29 Since the Delta Delta is above a normal bicarbonate level, there is a concurrent metabolic alkalosis at work. The patient has a primary elevated anion gap acidosis with respiratory compensation (which is not complete) and a concurrent metabolic alkalosis. You would need to sort through the differential diagnosis for an elevated anion gap acidosis to identify the cause of that problem. The metabolic alkalosis is likely due to vomiting. A 60 year-old man was recently in the hospital for treatment of aspiration pneumonia for which he as treated with levofloxacin and clindamycin. One week later, he presents to the ER with severe diarrhea, abdominal pain and hypotension. Step 2: The PCO2 is low (respiratory alkalosis) and the bicarbonate is low (metabolic acidosis). Therefore, the metabolic acidosis is the primary process. Step 3: The serum anion gap is elevated at 20. There is, therefore, an elevated anion gap acidosis. Step 4: The respiratory alkalosis is the compensatory process for the metabolic acidosis. The Continue reading >>
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Acid-base Disorders
Content currently under development Acid-base disorders are a group of conditions characterized by changes in the concentration of hydrogen ions (H+) or bicarbonate (HCO3-), which lead to changes in the arterial blood pH. These conditions can be categorized as acidoses or alkaloses and have a respiratory or metabolic origin, depending on the cause of the imbalance. Diagnosis is made by arterial blood gas (ABG) interpretation. In the setting of metabolic acidosis, calculation of the anion gap is an important resource to narrow down the possible causes and reach a precise diagnosis. Treatment is based on identifying the underlying cause. Continue reading >>
Compensation Calculator
Respiratory Acidosis Compensation Calculator Severinghaus blood gas calculator. Discussion Kazemi H. Respiratory compensation in metabolic acidosis and alkalosis in normal man. AmRevResp Dis 1980;121:356. 5 van Ypersele de Strihou C, Frans A. Therespiratory response to chronic metabolic alkalosis and acidosis in disease. Clin Sci ... Get Content Here Chapter 19 - The Circulatory System: The Heart Contrast the capacity and the speed of respiratory and renal compensation for acid-base Make sure you can use a calculator to calculate pH from the [H+]. Write down the range of the pH scale, and then, write down Write definitions for respiratory acidosis and alkalosis. In your ... Read Here Mr. Stone - University Of Mississippi Medical Center Mr. Stone Mr. Stone has had severe, continuing diarrhea for about a week. Calculator buttons ( ) pCO2 tends to increase pH, buffering the original metabolic event. This is metabolic acidosis with respiratory compensation. Suppose a respiratory factor, ... Read Content Exam #3 BMB 514 Medical Biochemistry 10/24/11 STEP 1 - NAME A simple calculator is supplied for your use during this exam. No other electronic or respiratory acidosis. Of the following mechanisms, ... Access Full Source Continue reading >>
Arterial Blood Gas (abg) Analyzer
This analyzer should not substitute for clinical context. Sodium and chloride are required for anion gap calculation. While the analyzer can often help with analysis, the history of the patient is critical for accurate interpretation. NOTE: Normal albumin levels are typically 4 g/dL in US units and 40 g/L in SI units. A venous blood gas often correlates well with arterial blood gas findings (except for PaO2) unless values are extremely abnormal, and can often be used successfully as a screening tool. This tool, developed by Jonathan Chen, MD first determines the primary process by looking at the pH and the PCO2. It then calculates compensations to determine chronicity, compensatory, and co-existing acid-base disturbances. Diabetic Ketoacidosis (check serum ketones) Propylene Glycol (in BZD drips) or Paraldehydes Oxoporin (reflects fatty liver damage from glutathione consumption, e.g. acetaminophen toxicity) Renal Tubular Acidosis (Type 1 Distal or Type 2 Proximal) Jonathan Chen, MD, PhD is a research fellow in medical informatics, based at the Veteran Affairs Hospital in Palo Alto and Stanford University. He completed the Stanford Internal Medicine residency program and was in the Medical Scientist Training Program (MSTP) and Biomedical Informatics Training (BIT) program at UC Irvine. Dr. Chen co-founded Reaction Explorer, LLC, which offers a unique system for teaching complex problem-solving in organic chemistry with the aid of expert system technology. To view Dr. Jonathan Chen's publications, visit PubMed Continue reading >>
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Winters Formula For Metabolic Acidosis Compensation Calculator
Winters Formula for Metabolic Acidosis Compensation Calculator This Winters formula for metabolic acidosis compensation calculator checks metabolic and mixed acidosis cases and establishes the level of PCO2 compensation. Discover more about the formula used and the situations that require it below the form. How does this Winters formula for metabolic acidosis compensation calculator work? This is a tool designed to help clinicians and any medical personnel evaluate PCO2 compensation in connection with the level of bicarbonate [HCO3-]. The form is very simple to use and only requires inputting bicarbonate in mEq/L and press calculate. The result will be displayed as an interval with the lower and upper values of partial CO2 pressure in mmHg. The formula used by this metabolic acidosis compensation calculator is explained below: Which means the interval between: 1.5 x HCO3- + 6 and 1.5 x HCO3- + 10 As a rule of thumb, there is a 1.2 mmHg PCO2 reduction for every 1 mEq/L reduction of plasma bicarbonate but only to a minimum of 10 - 15 mmHg. Taking an example, it shows that in order to compensate for a plasma concentration of HCO3- of 9 mEq/L it would be required a partial pressure of CO2 between 19.5 and 23.5 mmHg. The patients data is then compared to the computed value: If the value retrieved in patients data corresponds, this means that the respiratory compensation is adequate. If the value is higher this is indicative of primary respiratory acidosis and if the value is lower than the calculated value, it is indicative of primary respiratory alkalosis. However, the Winters formula is used mostly for metabolic acidosis and in the second case a different set of equations should be used as provided below: PCO2 = 0.7 x HCO3- + 20 +/- 5 mmHg meaning the interval between 0.7 Continue reading >>
Assessment Of Compensation: Boston And Copenhagen Methods - Deranged Physiology
Assessment of Compensation: Boston and Copenhagen Methods This page acts as a footnote to the "Boston vs. Copenhagen" chapter from Acid-Base Physiology by Kerry Brandis. The aforementioned chapter in my opinion remains the definitive resource on the topic. Brandis' chapter explores the epistemology of acid-base interpretation systems by means of which we might be able to determine whether a patient has a single or mixed acid base disorder; i.e. whether there is a purely metabolic or a purely respiratory disturbance, or some mixture of the two. As it happens, there are two well-accepted systems for doing this, each with its own merits and demerits. These are the Boston and Copenhagen methods of acid-base interpretation. There is also another not-so-well accepted system, the physicochemical method proposed by Peter Stewart - which possess a satisfying explanatory power as an instrument of academic physiology. Unfortunately, it is rather complicated, and difficult to apply at the bedside. Furthermore, there does not seem to be much of a difference in hard outcomes, regardless of which system one uses. Thus, this chapter will focus on the Boston and Copenhagen systems, which have equivalent validity as far as acid-base interpretation is concerned. "Which is the system I need to rote-learn to pass my primaries?" Such a question is expected from the fairweather intensivist, who will flee from the ICU as soon as a position opens in a more cushy training program. For the rest, one might remark that these analytical tools are all in common use, and any sufficiently advanced ICU trainee is expected to be intimately familiar with all of these systems. However, the time-poor exam candidate may need to focus their attention on the area which would yield the greatest number of marks Continue reading >>
Abg Interpreter
pH CO2 HCO3 Result appears in here. Normal Arterial Blood Gas Values pH 7.35-7.45 PaCO2 35-45 mm Hg PaO2 80-95 mm Hg HCO3 22-26 mEq/L O2 Saturation 95-99% BE +/- 1 Four-Step Guide to ABG Analysis Is the pH normal, acidotic or alkalotic? Are the pCO2 or HCO3 abnormal? Which one appears to influence the pH? If both the pCO2 and HCO3 are abnormal, the one which deviates most from the norm is most likely causing an abnormal pH. Check the pO2. Is the patient hypoxic? I used Swearingen's handbook (1990) to base the results of this calculator. The book makes the distinction between acute and chronic disorders based on symptoms from identical ABGs. This calculator only differentiates between acute (pH abnormal) and compensated (pH normal). Compensation can be seen when both the PCO2 and HCO3 rise or fall together to maintain a normal pH. Part compensation occurs when the PCO2 and HCO3 rise or fall together but the pH remains abnormal. This indicates a compensatory mechanism attempted to restore a normal pH. I have not put exact limits into the calculator. For example, it will perceive respiratory acidosis as any pH < 7.35 and any CO2 > 45 (i.e. a pH of 1 and CO2 of 1000). These results do not naturally occur. pH PaCO2 HCO3 Respiratory Acidosis Acute < 7.35 > 45 Normal Partly Compensated < 7.35 > 45 > 26 Compensated Normal > 45 > 26 Respiratory Alkalosis Acute > 7.45 < 35 Normal Partly Compensated > 7.45 < 35 < 22 Compensated Normal < 35 < 22 Metabolic Acidosis Acute < 7.35 Normal < 22 Partly Compensated < 7.35 < 35 < 22 Compensated Normal < 35 < 22 Metabolic Alkalosis Acute > 7.45 Normal > 26 Partly Compensated > 7.45 > 45 > 26 Compensated Normal > 45 > 26 Mixed Disorders It's possible to have more than one disorder influencing blood gas values. For example ABG's with an alkale Continue reading >>
