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Respiratory Acidosis Compensation Formula

Acid Base Disorders

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 >>

Perfecting Your Acid-base Balancing Act

Perfecting Your Acid-base Balancing Act

When it comes to acids and bases, the difference between life and death is balance. The body’s acid-base balance depends on some delicately balanced chemical reactions. The hydrogen ion (H+) affects pH, and pH regulation influences the speed of cellular reactions, cell function, cell permeability, and the very integrity of cell structure. When an imbalance develops, you can detect it quickly by knowing how to assess your patient and interpret arterial blood gas (ABG) values. And you can restore the balance by targeting your interventions to the specific acid-base disorder you find. Basics of acid-base balance Before assessing a patient’s acid-base balance, you need to understand how the H+ affects acids, bases, and pH. An acid is a substance that can donate H+ to a base. Examples include hydrochloric acid, nitric acid, ammonium ion, lactic acid, acetic acid, and carbonic acid (H2CO3). A base is a substance that can accept or bind H+. Examples include ammonia, lactate, acetate, and bicarbonate (HCO3-). pH reflects the overall H+ concentration in body fluids. The higher the number of H+ in the blood, the lower the pH; and the lower the number of H+, the higher the pH. A solution containing more base than acid has fewer H+ and a higher pH. A solution containing more acid than base has more H+ and a lower pH. The pH of water (H2O), 7.4, is considered neutral. The pH of blood is slightly alkaline and has a normal range of 7.35 to 7.45. For normal enzyme and cell function and normal metabolism, the blood’s pH must remain in this narrow range. If the blood is acidic, the force of cardiac contractions diminishes. If the blood is alkaline, neuromuscular function becomes impaired. A blood pH below 6.8 or above 7.8 is usually fatal. pH also reflects the balance between the p Continue reading >>

Simple Method Of Acid Base Balance Interpretation

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 >>

Assessment Of Compensation In Acute Respiratory Acidosis - Deranged Physiology

Assessment Of Compensation In Acute Respiratory Acidosis - Deranged Physiology

Assessment of Compensation in Acute Respiratory Acidosis Mechanisms and classification of metabolic acidosis This chapter is concerned with the changes in pH and serum bicarbonate which result from acute fluctuations in dissolved CO2, as a consequence of acute changes in ventilation. It is a more detailed look at the wayCO2interacts with the human body fluid, and the resulting changes which develop in theserum bicarbonate concentration and pH. The discussion which follows builds upon and benefits from someof thebackground knowledgeoffered in otherchapters: Let us consider the favoured model of acute respiratory acidosis, the patient who has stopped breathing. Conventional wisdom dictates that so long as the oxygen supply continues to mass-transfer its way into the patient, then the patient will continue to produce CO2, and as a result of this metabolic activity the PaCO2will rise at a rate of around 3mmHg every minute. This technique of "apnoeic anaesthesia" is well known to anaesthetists, and has enjoyed a fluctuating level of interest since the sixties. With a high PEEP and a sufficient attention to detail one may go through the entire hour-long case without any breaths being taken by the patient. But, let us consider a situation where the airway isnotpatent, and a constant supply of oxygen is not available. The patient has stopped exhaling CO2. What will happen? Well, the PaCO2will rise by about 12mmHg over the first minute, and by about 3.4 mmHg per minute for every minute after that. How do we know this? Because in 1989, 14 volunteers consented to having their tube clamped during an anaesthetic. The clamps were released after 5 minutes, or if the patients became dangerously hypoxic. Magnitude of pH change due to pCO2increase Knowing the change in PaCO2,one can att Continue reading >>

Abg Interpreter

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 >>

Respiratory Acidosis

Respiratory Acidosis

Respiratory acidosis is a medical emergency in which decreased ventilation (hypoventilation) increases the concentration of carbon dioxide in the blood and decreases the blood's pH (a condition generally called acidosis). Carbon dioxide is produced continuously as the body's cells respire, and this CO2 will accumulate rapidly if the lungs do not adequately expel it through alveolar ventilation. Alveolar hypoventilation thus leads to an increased PaCO2 (a condition called hypercapnia). The increase in PaCO2 in turn decreases the HCO3−/PaCO2 ratio and decreases pH. Terminology[edit] Acidosis refers to disorders that lower cell/tissue pH to < 7.35. Acidemia refers to an arterial pH < 7.36.[1] Types of respiratory acidosis[edit] Respiratory acidosis can be acute or chronic. In acute respiratory acidosis, the PaCO2 is elevated above the upper limit of the reference range (over 6.3 kPa or 45 mm Hg) with an accompanying acidemia (pH <7.36). In chronic respiratory acidosis, the PaCO2 is elevated above the upper limit of the reference range, with a normal blood pH (7.35 to 7.45) or near-normal pH secondary to renal compensation and an elevated serum bicarbonate (HCO3− >30 mm Hg). Causes[edit] Acute[edit] Acute respiratory acidosis occurs when an abrupt failure of ventilation occurs. This failure in ventilation may be caused by depression of the central respiratory center by cerebral disease or drugs, inability to ventilate adequately due to neuromuscular disease (e.g., myasthenia gravis, amyotrophic lateral sclerosis, Guillain–Barré syndrome, muscular dystrophy), or airway obstruction related to asthma or chronic obstructive pulmonary disease (COPD) exacerbation. Chronic[edit] Chronic respiratory acidosis may be secondary to many disorders, including COPD. Hypoventilation Continue reading >>

Metabolic Acidosis

Metabolic Acidosis

Patient professional reference Professional Reference articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use. You may find one of our health articles more useful. See also separate Lactic Acidosis and Arterial Blood Gases - Indications and Interpretations articles. Description Metabolic acidosis is defined as an arterial blood pH <7.35 with plasma bicarbonate <22 mmol/L. Respiratory compensation occurs normally immediately, unless there is respiratory pathology. Pure metabolic acidosis is a term used to describe when there is not another primary acid-base derangement - ie there is not a mixed acid-base disorder. Compensation may be partial (very early in time course, limited by other acid-base derangements, or the acidosis exceeds the maximum compensation possible) or full. The Winter formula can be helpful here - the formula allows calculation of the expected compensating pCO2: If the measured pCO2 is >expected pCO2 then additional respiratory acidosis may also be present. It is important to remember that metabolic acidosis is not a diagnosis; rather, it is a metabolic derangement that indicates underlying disease(s) as a cause. Determination of the underlying cause is the key to correcting the acidosis and administering appropriate therapy[1]. Epidemiology It is relatively common, particularly among acutely unwell/critical care patients. There are no reliable figures for its overall incidence or prevalence in the population at large. Causes of metabolic acidosis There are many causes. They can be classified according to their pathophysiological origin, as below. The table is not exhaustive but lists those that are most common or clinically important to detect. Increased acid Continue reading >>

Acid Base Calculation Made Easy !

Acid Base Calculation Made Easy !

Posted by Ash from IP 74.138.144.66 on October 12, 2006 at 17:50:13: 6 steps to ABG analysis, go step by step in the very same order:- 1.Chk whether the pt is academic or alkalemic,by looking at the arterial pH (NL = 7.38 7.42) 2. Chk whether the ABG abnormality is due to a primary repiratory or metabolic disorder by chking the PCo2 levels( NL 38-42) and HCO3 levels (NL 22-26) 3. Now if there is respiratory component identified,chk whether this is acute or chronic respiratory acidosis or alkalosis. 4. Now if u identify a metabolic component ,chk whether it is high anion or normal anion gap M.Acidosis 5. Chk wether the respiratory system is adequetly compensating for this primary metabolic disorder. 6. Now u identify a high anion gap M.A,chk the corrected HCO3 level,y we do this coz to know wether there was a intial primary disorder ,before this new metabolic disorder developed. VERY IMPO FORMULAS :- U have to learn the formulas byheart) In Metabolic acidosis pH and HCO3 (DECREASES) So to compensate for every 1 mmol/l of drop in HCO3 , 1.2mmhg of PCO2 shld decrease So to compensate for every 1 mmol/l of increase HCO3, 0.07 mmhg of pco2 will increase. In Resp .Acidosis (PH - DECREASED and PCO2 AND HCO3 INCREASED) Acute R.acidosis:- For every 10 mmhg increase in pco2 , 1 mmol/l Hco3 shld increase Chronic R acidosis:- for every 10 mmhg increase in pco2, Hco3 increases by 3.5mmol/l In Respiratory Alkalosis pH INCREASED, pco2 and Hco3 DECREASED Acute R.alkalosis :- for every 10 mmhg decrease in PCO2 , hco2 decreases by 2meq/l Chronic :- for very 10 mmhg decrease in PCO2 ,hco3 decreases by 10mmol/l Winters equation :- this equation helps u to determine ,what the expected PCO2 lloks like when there is a metabolic acidosis:- Anion GAP :- done always when the disorder is metabol Continue reading >>

How To Compute Expected Pco2 In Chronic Metabolic Acidosis ?

How To Compute Expected Pco2 In Chronic Metabolic Acidosis ?

How to compute PaCO2 during chronic metabolic acidosis? We dont have to compute for chronic metabolic acidosis (CMA) since the PaCO2 value in mmHg is equal to the two digits of the pH value For instance IF pH = 7.25, PaCO2 should be about 25 mmHg, With this formula, we can immediately focus on the respiratory compensation: If PaCO2 is significantly greater than 25 mmHg, the respiratory compensation is inadequate, thus a respiratory insufficiency is associated; If PaCO2 is largely lower than 25 mmHg, the respiratory is higher than CMA required, therefore a respiratory alkalosis is associated to CMA. Furthermore, according to the alveolar gas equation (Fi02 of 21%): Pa02 + PaCO2= 140 mmHg; in this case, in absence of pulmonary disease, PaO2 should be elevated, near 115 mmHg FG Brivet, FM Jacobs: Anomalies de lEquilibre Acido-basique dOrigine Mtabolique in Ranimation Mdicale ; Collge National des Enseignants de Ranimation Mdicale, Masson Paris 2009 PP 1356-1365. In the same way for ACUTE Metabolic Acidosis, instead of using Narinss formula: It is easier to use Schlichtigs formula: Delta PaCO2 (mmHg) = Standard base excess (2) Thus in case of acute metabolic acidosis, with the same value of pH (7.25) and an SBE of 18, for instance (SBE value being systematically reported by lab but rarely used.), PaC02 should be near 22 mmHg (40- 18). If PaCO2 value is greater than the expected value, respiratory compensation is inadequate, the patient is at risk of respiratory failure, whereas if PaCO2 is lower than 18 we can claim that a respiratory alkalosis is associated. With this approach I can say goodbye Mr. Davenport, you are too sophisticated for me at 5 in the morning 1/ Narins RG, Emmet M. Simple and mixed acid-base disorders: a practical approach. Medicine, 1980, 59: 161-167. Continue reading >>

Response To Disturbances

Response To Disturbances

The body tries to minimize pH changes and responds to acid-base disturbances with body buffers, compensatory responses by the lungs and kidney (to metabolic and respiratory disturbances, respectively) and by the kidney correcting metabolic disturbances. Body buffers: There are intracellular and extracellular buffers for primary respiratory and metabolic acid-base disturbances. Intracellular buffers include hemoglobin in erythrocytes and phosphates in all cells. Extracellular buffers are carbonate (HCO3–) and non-carbonate (e.g. protein, bone) buffers. These immediately buffer the rise or fall in H+. Compensation: This involves responses by the respiratory tract and kidney to primary metabolic and respiratory acid-base disturbances, respectively. Compensation opposes the primary disturbance, although the laboratory changes in the compensatory response parallel those in the primary response. This concept is illustrated in the summary below. Respiratory compensation for a primary metabolic disturbance: Alterations in alveolar ventilation occurs in response to primary metabolic acid-base disturbances. This begins within minutes to hours of an acute primary metabolic disturbance. Note that complete compensation via this mechanism may take up to 24 hours. Renal compensation for a primary respiratory disturbance: Here, the kidney alters excretion of acid (which influences bases as well) in response to primary respiratory disturbances. This begins within hours of an acute respiratory disturbance, but take several days (3-5 days) to take full effect. Correction of acid-base changes: Correction of a primary respiratory acid-base abnormality usually requires medical or surgical intervention of the primary problem causing the acid-base disturbance, e.g. surgical relief of a colla Continue reading >>

Common Laboratory (lab) Values - Abgs

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 >>

Assessment Of Compensation: Boston And Copenhagen Methods - Deranged Physiology

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 >>

Acid-base Disorders - Endocrine And Metabolic Disorders - Merck Manuals Professional Edition

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 >>

Additional Step In Abg Analysis

Additional Step In Abg Analysis

Michelle Kirschner , RN, MSN, APRN, CNP, CCRN The article Assessing Tissue Oxygenation (June 2002:2240) contains a comprehensive overview of arterial blood gas analysis, which will prove to be a valuable resource for nurses and other healthcare professionals in the intensive care environment. The steps outlined are useful in determining an acid-base imbalance involving either the metabolic or respiratory systems and the effectiveness of attempted compensation. However, severely ill patients who develop multiple organ failure frequently present with several acid-base abnormalities occurring simultaneously. Therefore, I routinely add an additional step in the analysis of arterial blood gases to determine if another primary acid-base process is present. The purpose of the additional step is to determine the expected compensation for the primary disorder. If the actual compensation falls within the calculated range, then a second disorder does not coexist. If the calculated value does not match the measured value, then a mixed disorder is present or compensation has not had time to occur. The expected compensation is calculated by using one of 4 formulas based on the primary process: metabolic acidosis, metabolic alkalosis, respiratory acidosis, or respiratory alkalosis. Metabolic conditions are generally compensated fairly quickly by the respiratory system by eliciting an alteration in the Pco2 level. The Winters formula predicts the expected degrees of compensation in a stable, steady-state metabolic disorder: If the actual Pco2 is higher than calculated with Winters formula, then a respiratory acidosis is mostly likely present in addition to the metabolic acid-base disorder. If the Pco2 is greater than 50 to 55 mm Hg, then respiratory acidosis is almost certainly presen Continue reading >>

Rules For Respiratory Acid-base Disorders

Rules For Respiratory Acid-base Disorders

Rule 1 : The 1 for 10 Rule for Acute Respiratory Acidosis * For every 10 mmHg increase in pCO2 (above 40 mmHg) Comment:The increase in CO2 shifts the equilibrium between CO2 and HCO3 to result in an acute increase in HCO3. This is a simple physicochemical event and occurs almost immediately. Example: A patient with an acute respiratory acidosis (pCO2 60mmHg) has an actual [HCO3] of 31mmol/l. The expected [HCO3] for this acute elevation of pCO2 is 24 + 2 = 26mmol/l. The actual measured value is higher than this indicating that a metabolic alkalosis must also be present. Rule 2 : The 4 for 10 Rule for Chronic Respiratory Acidosis The [HCO3] will increase by 4 mmol/l for every 10 mmHg elevation in pCO2 above 40mmHg. Expected [HCO3] = 24 + 4 { (Actual pCO2 - 40) / 10} Comment: With chronic acidosis, the kidneys respond by retaining HCO3, that is, renal compensation occurs. This takes a few days to reach its maximal value. Example: A patient with a chronic respiratory acidosis (pCO2 60mmHg) has an actual [HCO3] of 31mmol/l. The expected [HCO3] for this chronic elevation of pCO2 is 24 + 8 = 32mmol/l. The actual measured value is extremely close to this so renal compensation is maximal and there is no evidence indicating a second acid-base disorder Rule 3 : The 2 for 10 Rule for Acute Respiratory Alkalosis * For every 10 mmHg decrease in pCO2 (below 40 mmHg) Comment: In practice, this acute physicochemical change rarely results in a [HCO3] of less than about 18 mmol/s. (After all there is a limit to how low pCO2 can fall as negative values are not possible!) So a [HCO3] of less than 18 mmol/l indicates a coexisting metabolic acidosis. The arterial pCO2 at maximal compensation has been measured in many patients with a metabolic acidosis. A consistent relationship between bicar Continue reading >>

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