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![Step 3-4: Is there appropriate
compensation? Is it acute or chronic ?
Metabolic Acidosis
Winter’s formula: pCO2 = 1.5[HCO3] + 8 ± 2 MEMORIZE
If serum pCO2 > expected pCO2 -> additional respiratory
acidosis
Metabolic Alkalosis
For every 10 increase in HCO3 -> pCO2 increases by 6](https://image.slidesharecdn.com/abgs-130804133323-phpapp01/85/Ab-gs-10-320.jpg)
![Step 5: Calculate the anion gap
AG = Na – Cl – HCO3 (normal 12 ± 2)
AG corrected = AG + 2.5[4 – albumin]
If there is an anion Gap then calculate the
Delta/delta gap (step 6). Only need to calculate
delta gap (excess anion gap) when there is an anion
gap to determine additional hidden metabolic
disorders (nongap metabolic acidosis or metabolic
alkalosis)
If there is no anion gap then start analyzing for
non-anion acidosis](https://image.slidesharecdn.com/abgs-130804133323-phpapp01/85/Ab-gs-12-320.jpg)
Uploaded byRahul Verma
Ab gs
This document outlines the steps for analyzing arterial blood gases (ABGs) and acid-base disorders: 1) Determine if the pH is acidic or alkaline, 2) Identify the primary disorder (respiratory or metabolic), 3) Assess compensation, 4) Determine if compensation is acute or chronic, 5) Calculate the anion gap, 6) If elevated, calculate the delta gap, 7) Consider differentials based on clinical context and lab results. Examples are provided to demonstrate applying the steps to analyze specific acid-base disorders like metabolic acidosis or alkalosis.
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Ab gs
- 1. ABG analysis &Acid-Base Disorders 2012
- 2. Outline 1. Discuss simplesteps in analyzing ABGs 2. Calculate the anion gap 3. Calculate the delta gap 4. Differentials for specific acid-base disorders
- 3. Steps for ABGanalysis 1. What is the pH? Acidemia or Alkalemia? 2. What is the primary disorder present? 3. Is there appropriate compensation? 4. Is the compensation acute or chronic? 5. Is there an anion gap? 6. If there is a AG check the delta gap? 7. What is the differential for the clinical processes?
- 4. Normal Values Variable NormalRange pH 7.35 - 7.45 pCO2 35-45 Bicarbonate 22-26 Anion gap 10-14 Albumin 4
- 5. Step 1: Lookat the pH: is the blood acidemic or alkalemic? EXAMPLE : 65yo M with CKD presenting with nausea, diarrhea and acute respiratory distress ABG :ABG 7.23/17/235 on 50%VM BMP Na 123/ Cl 97/ HCO3 7/BUN 119/ Cr 5.1 ACIDMEIA OR ALKALEMIA ????
- 6. EXAMPLE ONE ABG7.23/17/235 on 50%VM BMP Na 123/ Cl 97/ HCO3 7/BUN 119/ Cr 5.1 Answer PH = 7.23 , HCO3 7 Acidemia
- 7. Step 2: Whatis the primary disorder? What disorder is present? pH pCO2 or HCO3 Respiratory Acidosis pH low pCO2 high Metabolic Acidosis pH low HCO3 low Respiratory Alkalosis pH high pCO2 low Metabolic Alkalosis pH high HCO3 high
- 8. EXAMPLE ABG 7.23/17/235on 50%VM BMP Na 123/ Cl 97/ HCO3 7/BUN 119/ Cr 5. PH is low , CO2 is Low PH and PCO2 are going in same directions then its most likely primary metabolic will check to see if there is a mixed disoder.
- 9. Step 3-4: Isthere appropriate compensation? Is it chronic or acute? Respiratory Acidosis Acute: for every 10 increase in pCO2 -> HCO3 increases by 1 and there is a decrease of 0.08 in pH MEMORIZE Chronic: for every 10 increase in pCO2 -> HCO3 increases by 4 and there is a decrease of 0.03 in pH Respiratory Alkalosis Acute: for every 10 decrease in pCO2 -> HCO3 decreases by 2 and there is a increase of 0.08 in PH MEMORIZE Chronic: for every 10 decrease in pCO2 -> HCO3 decreases by 5 and there is a increase of 0.03 in PH
- 10. Step 3-4: Isthere appropriate compensation? Is it acute or chronic ? Metabolic Acidosis Winter’s formula: pCO2 = 1.5[HCO3] + 8 ± 2 MEMORIZE If serum pCO2 > expected pCO2 -> additional respiratory acidosis Metabolic Alkalosis For every 10 increase in HCO3 -> pCO2 increases by 6
- 11. EXAMPLE ABG 7.23/17/235on 50%VM BMP Na 123/ Cl 97/ HCO3 7/BUN 119/ Cr 5. Winter’s formula : 17= 1.5 (7) +8 = 18.5 So correct compensation so there is only one disorder Primary metabolic
- 12. Step 5: Calculatethe anion gap AG = Na – Cl – HCO3 (normal 12 ± 2) AG corrected = AG + 2.5[4 – albumin] If there is an anion Gap then calculate the Delta/delta gap (step 6). Only need to calculate delta gap (excess anion gap) when there is an anion gap to determine additional hidden metabolic disorders (nongap metabolic acidosis or metabolic alkalosis) If there is no anion gap then start analyzing for non-anion acidosis
- 13. EXAMPLE Calculate Aniongap ABG 7.23/17/235 on 50%VM BMP Na 123/ Cl 97/ HCO3 7/BUN 119/ Cr 5/ Albumin 4. AG = Na – Cl – HCO3 (normal 12 ± 2) 123 – 97 – 7 = 19 No need to correct for albumin as it is 4
- 14. Step 6: Calculatethe different needed formulas Delta gap = (actual AG – 12) + HCO3 Adjusted HCO3 should be 24 (+_ 6) {18-30} If delta gap > 30 -> additional metabolic alkalosis If delta gap < 18 -> additional non-gap metabolic acidosis If delta gap 18 – 30 -> no additional metabolic disorders
- 15. EXAMPLE : DeltaGap ABG 7.23/17/235 on 50%VM BMP Na 123/ Cl 97/ HCO3 7/BUN 119/ Cr 5/ Albumin 4. Delta gap = (actual AG – 12) + HCO3 (19-12) +7 = 14 Delta gap < 18 -> additional non-gap metabolic acidosis So Metabolic acidosis anion and non anion gap
- 16. Metobolic acidosis: Aniongap acidosis
- 17. EXAMPLE: WHY ANIONGAP? 65yo M with CKD presenting with nausea, diarrhea and acute respiratory distress ABG :ABG 7.23/17/235 on 50%VM BMP Na 123/ Cl 97/ HCO3 7/BUN 119/ Cr 5.1 So for our patient for anion gap portion its due to BUN of 119 UREMIA But would still check lactic acid
- 18. Nongap metabolic acidosis Causesof nongap metabolic acidosis - DURHAM Diarrhea, ileostomy, colostomy, enteric fistulas Ureteral diversions or pancreatic fistulas RTA type I or IV, early renal failure Hyperailmentation, hydrochloric acid administration Acetazolamide, Addison’s Miscellaneous – post-hypocapnia, toulene, sevelamer, cholestyramine ingestion For non-gap metabolic acidosis, calculate the urine anion gap UAG = UNA + UK – UCL If UAG>0: renal problem If UAG<0: nonrenal problem (most commonly GI)
- 19. EXAMPLE : NONANION GAP ACIDOSIS 65yo M with CKD presenting with nausea, diarrhea and acute respiratory distress ABG :ABG 7.23/17/235 on 50%VM BMP Na 123/ Cl 97/ HCO3 7/BUN 119/ Cr 5.1 Most likely due to the diarrhea
- 20. Metabolic alkalosis Calculatethe urinary chloride to differentiate saline responsive vs saline resistant Must be off diuretics in order to interpret urine chloride Saline responsive UCL<10 Saline-resistant UCL >10 Vomiting If hypertensive: Cushings, Conn’s, RAS, renal failure with alkali administartion NG suction If not hypertensive: severe hypokalemia, hypomagnesemia, Bartter’s, Gittelman’s, licorice ingestion Over-diuresis Exogenous corticosteroid administration Post-hypercapnia
- 21. Respiratory Alkalosis Causes ofRespiratory Alkalosis Anxiety, pain, fever Hypoxia, CHF Lung disease with or without hypoxia – pulmonary embolus, reactive airway, pneumonia CNS diseases Drug use – salicylates, catecholamines, progesterone Pregnancy Sepsis, hypotension Hepatic encephalopathy, liver failure Mechanical ventilation Hypothyroidism High altitude
- 22. Respiratory Acidosis Causes ofrespiratory acidosis CNS depression – sedatives, narcotics, CVA Neuromuscular disorders – acute or chronic Acute airway obstruction – foreign body, tumor, reactive airway Severe pneumonia, pulmonary edema, pleural effusion Chest cavity problems – hemothorax, pneumothorax, flail chest Chronic lung disease – obstructive or restrictive Central hypoventilation, OSA
- 23. Steps for ABGanalysis 1. What is the pH? Acidemic or Alkalemic? 2. What is the primary disorder present? 3. Is there appropriate compensation? 4. Is the compensation acute or chronic? 5. Is there an anion gap? 6. If there is a AG, what is the delta gap? 7. What is the differential for the clinical processes?
Editor's Notes
- #3 -Objective slide
- #4 Just read the steps off the slides. Quick overview . Determine if you have acidemia or alkalemia based on the PH Here we determine primary disorder is it respiratory or metabolic Check to see if there is appropriate compensation for the primary disorder in order to figure if its simple or mixed disorder Then analyze if this is an acute event or chronic Always look to see if there is an anion gap Due the other calculation depending on the underlying primary source . Such as if AG acidosis check to see if there is also a Delta gap to see if there is also non-anion gap present And lastly then come up with a DDX
- #5 Memorize these values . Just read off slides.
- #8 Just go over the table Then point out the arrows :A quick trick is to determine respiratory versus metabolic is : If PH and PCO2 are going in the opposite direction : then its respiratory, If PH and PCO2 are going in same directions then its metabolic. - Be careful with the mixed disorders using the trick.
- #10 You need to memorize these and know it by heart . Then quickly go over the changes Then summarize : The easiest one is that for acute situations for every change of 10 in the PCO2 there is should be a change of 0.08 in PH and in chronic situation there should be a change of 0.03 . - If there is a different change then know that there is most likely a mixed disorder
- #11 Metabolic acidosis is the disorder you will mostly encounter in the hospital. You must memorize Winter’s formula Winter’s formula calculates the expected pCO2 in the setting of metabolic acidosis. If the serum pCO2 > expected pCO2 then there is additional respiratory acidosis in which the etiology needs to also be determined.
- #13 Always calculate the AG . (fyi most BMP ordered calculate the gap for you but need to memorize the formula) Don’t forget to look at albumin and adjust the calculated gap. If albumin is less than 4 then add 2.5 to your gap for every decrease of 1 Delta/Delta gap needs to be calculated to see if there is other underlying acidosis/alkolosis that are present
- #15 Must memorize how to calculate the delta gap Just read off the slide
- #17 Go over the table One thing to watch out for is Toluene (initially high gap, subsequent excretion of metabolites normalizes gap) Calculate osmol gap to determine if osmotically active ingestions (methanol, paraldehyde) are the cause of the gap metabolic acidosis. Other ingestions are toluene, isopropyl alcohol.
- #19 - Go over the table - Most common cause in the hospital is IV fluids and Diarrhea
- #21 For metabolic alkalosis , check urine cholride (must be off diuretics) Urine chloride < 10 implies responsivenss to saline : extracelluar fluid volume depletion Urine chloride >10 implies resistance to sailne : severe poatssium depletion , mineralcorticoid excees syndrome Etc
- #22 Read the chart then summarize Can divide into three categories 1. systemic : (sepsis , asa , liver failure , endocrine , chf) 2. Central causes (respiratory center, ischmia , CNS tumor ) 3. Lungs (pna, asthma , PE )
- #23 Respiratory acidosis . Read the chart. Can divide into three categories 1. Chest cavity (flail chest , pneumothorax Etc.) 2. Central causes (sedation , CVA etc) 3. Lungs (pna, asthma etc)