Arterial Blood Gas Analysis

Views:
 
     
 

Presentation Description

Our first brain storming presentation

Comments

Presentation Transcript

BRAIN STORMING PROGRAMME: 

BRAIN STORMING PROGRAMME Medicine I

WHAT IS ABG?: 

WHAT IS ABG? MEASURES 3 PARAMETERS— PH P O2 P CO2 OTHERS ARE DERIVED

PowerPoint Presentation: 

Why an ABG instead of Pulse oximetry? Pulse oximetry does not assess ventilation (pCO2) or acid base status. Pulse oximetry becomes unreliable when saturations fall below 70-80%. Technical sources of error (ambient or fluorescent light, hypoperfusion, nail polish, skin pigmentation) Pulse oximetry cannot interpret methemoglobin or carboxyhemoglobin.

PROCEDURE-POINTS TO PONDER: 

PROCEDURE-POINTS TO PONDER PREFERRED ARTERY- ?? RADIAL PRECAUTION- ??? DO A MODIFIED ALLENS TEST BEFORE POKING PREFERRED NEEDLE SIZE-?? 20-26 GAUGE PRE HEPARINISED SYRINGE –DRY Vs LIQUID HEPARIN

PowerPoint Presentation: 

HEPARIN---?? (1000U/ML) AT DEAD SPACE ENOUGH FOR 2-3 ML OF BLOOD DILUTIONAL EFFECT IF <2-3 ML OF BLOOD COLLECTED

PowerPoint Presentation: 

ANGLE –PREFERABLY <30 DEGREES CAPPING IS MUST AVOID AIR BUBBLE- IF PRESENT AT BASE DON’T DISTURB INVIVO LEVELS CAN BE MAINTAINED FOR??? 10 MIN IN UN-ICED SAMPLE 60 MIN IN ICED SAMPLE

PRE ANALYTICAL ERRORS: 

PRE ANALYTICAL ERRORS EXCESS HEPARIN –??? MORE THAN JUST DILUTIONAL EFFECT-AS IT’S A WEAK ACID PH - decreased PO2- increased PCO2- decreased

AIR BUBBLES: 

AIR BUBBLES CAUSE THE SAME EFEECT AS EXCESS HEPARIN EXCEPT THAT BUBBLES DON’T CHANGE PH CAN CHANGE PO2 BY AS MUCH AS 30MM HG

STORING TOO LONG: 

STORING TOO LONG DUE TO RBC METABOLISM PO2- DECREASES PCO2-INCREASES

THE ASSUMED PARAMETERS: 

THE ASSUMED PARAMETERS HEMOGLOBIN- DOES NOT AFFECT PO2 FIO2- MOST COMMONLY FORGOTTEN PARAMETER TO BE MODIFIED RQ- 0.8

EFFECT OF FIO2: 

EFFECT OF FIO2 THE PARAMETER AFFECTED IF FIO2 IS NOT CHANGED? Aa D O2 PHSYIOLOGICAL BASIS AaDO 2= PA O2-p O 2 PA 02= FIO2 ( PB – PH2O)– PCO2/R

Terminology..: 

Terminology.. pO2 pCO2 pH HCO3A HCO3S BE SBE TCO2 BB O2 Sat O2 CT P50 A-a DO2

SOME DEFINITIONS IN PLAIN TERMS: 

SOME DEFINITIONS IN PLAIN TERMS PH= NEGATIVE LOG OF H+ CONCENTRATION PO2= PARTIAL PRESSURE OF OXYGEN IN ARTERIAL BLOOD PCO2= PARTIAL PRESSURE OF CO2 IN ARTERIAL BLOOD HCO3 A = MEASURED BICARBONATE IN ARTERIAL BLOOD

How to evaluate respiratory failure?: 

How to evaluate respiratory failure? PaO 2 : Arterial blood oxygenic partial pressure. Normal: 95-100mmHg (12.6-13.3kPa) Estimate formula of age: PaO 2 =100mmHg-(age×0.33) ±5mmHg

Hypoxia: 

Hypoxia Mild: 80-60mmHg Mediate: 60-40mmHg Severe: <40mmHg

Respiratory Failure: 

Respiratory Failure PaO 2 <60mmHg respiratory failure Notice: sea level, quiet, inspire air rule off other causes ( heart disease)

Classification of Respiratory Failure: 

Classification of Respiratory Failure PaCO 2 : The carbon dioxide partial pressure of arterial blood Normal: 35-45mmHg (4.7-6.0kPa) mean: 40mmHg

Classification of Respiratory Failure: 

Classification of Respiratory Failure Type Ⅰ TypeⅡ PaO2 (mmHg) <60 <60 PaCO2 (mmHg) ≤50 >50

PowerPoint Presentation: 

Alveolar Gas Equation PAO 2 = PIO 2 - 1.2 (PaCO 2 ) where PIO 2 = FIO 2 (P B – 47 mm Hg) P A-a O 2: Difference of alveoli-arterial blood oxygenic partial pressure. Normal: 15-20mmHg (<30mmHg in the old) Significance: a sensitive parameter in gas exchange

PowerPoint Presentation: 

AaDO2—MAXIMUM VALUE FOR YOUNG ADULTS BREATHING ROOM AIR? 20 mm Hg AFFECTED BY AGE REFLECTS THE GAS TRANSPORT BTW LUNGS AND PULM CAPILLARIES UPPER LIMIT OF NORMAL FOR ANY AGE IS 38mmHG

SP02, C A 02 AND PO2: 

SP02, C A 02 AND PO2 PO2 = AMOUNT OF DISSOLVE D OXYGEN- NOT A GOOD MEASURE OF O2 IN BLOOD SP O2- CAN BE MEASURED OR CALCULATED.NOT A GOOD MEASURE OF O2 IN BLOOD CA O2-BEST MEASURE OF O2 IN BLOOD AS IT TAKES IN TO ACCOUNT HB AND SATURATION

Oxygen Content(CaO2/O2CT) and Saturation(SaO2): 

Oxygen Content(CaO2/O2CT) and Saturation(SaO2) O 2 content = 1.34 x Hb x Saturation + 0.0031xPO 2 Normal: 16-22 ml/dl Significance: a comprehensive parameter to evaluate arterial oxygen

SaO2: 

SaO2 Saturation of arterial blood oxygen Normal: 0.95-0.98 Significance: a parameter to evaluate hypoxia, but not sensitive. Calculated value, prone for errors if PaO2 false reading. (Co-oximeters)

PowerPoint Presentation: 

Which value gives the best measure of O2 content in blood?? PaO2 SaO2 CaO2 Ans– © A condition where the PaO2 may be normal but patient severely hypoxemic??

Oxygen dissociation curve: SaO2 vs. PaO2 Also shown are CaO2 vs. PaO2 for two different hemoglobin contents: 15 gm% and 10 gm%. CaO2 units are ml O2/dl. P50 is the PaO2 at which SaO2 is 50%. Point ‘X’ is discussed on later slide.: 

3/13/2013 26 Oxygen dissociation curve: SaO 2 vs. PaO 2 Also shown are CaO 2 vs. PaO 2 for two different hemoglobin contents: 15 gm% and 10 gm%. CaO 2 units are ml O 2 /dl. P 50 is the PaO 2 at which SaO 2 is 50%. Point ‘X’ is discussed on later slide.

Normal Arterial Blood Gas Values*: 

Normal Arterial Blood Gas Values* pH PaCO 2 PaO 2 SaO 2 HCO 3 - 7.35-7.45 35-45 mm Hg 80-100 mm Hg** 93-98% 22-26 mEq/L * At sea level, breathing ambient air ** Age-dependent

PowerPoint Presentation: 

HCO 3 - (bicarbonate) : SB (standard bicarbonate) AB (actual bicarbonate) SB : the contents of HCO 3 - of serum of arterial blood in 38℃, PaCO2 40mmHg, SaO 2 100%. Normal: 22-27mmol/L mean: 24mmol/L AB : The contents of HCO 3 - in actual condition. In normal person: AB=SB

PowerPoint Presentation: 

AB and SB are parameters to reflect metabolism, regulated by kidney. Difference of AB-SB can reflect the respiratory affection on serum HCO 3 - . Respiratory acidosis: AB>SB Respiratory alkalosis: AB<SB Metabolic acidosis: AB = SB<Normal Metabolic alkalosis: AB=SB>Normal

Base excess: 

Base excess Refers to the amount of acid required to return the blood pH of an individual to the normal value (pH 7.4). The value is usually reported in units of (mEq/L). The normal value is somewhere between -2 to +2. The term and concept were first introduced by Astrup and Siggard-Anderson in 1958.

Actual and standard : 

Actual and standard Actual base excess is the base excess in the blood. Standard base excess is the value of base excess when the hemoglobin-value is 5g/dl. This gives a better view of the base excess of the entire ECF.

Calculation : 

Calculation Base Excess = (Actual pH – predicted pH) x 67 Calculate predicted pH based on PaCO2 Interpretation Positive (Base Excess) Metabolic alkalosis Negative (Base Deficit) Metabolic acidosis

PowerPoint Presentation: 

PaCO2 variance : (Measured PaCO2 -40)/100 Eg: PaCO2-74, variance= 34/100=0.34 Predicted pH: If PaCO2 > 40 : Predicted pH : 7.40- ½ (PaCO2 variance) If PaCO2 < 40 Predicted pH : 7.40 + PaCO2 variance

PowerPoint Presentation: 

Buffer bases ( BB) : is the total of buffer negative ion of blood. BB: HCO 3 - hemoglobin plasma proteins HPO42- (phosphate) Normal: 45-55mmol/L mean: 50mmol/L Significance: Metabolic acidosis: BB Metabolic alkalosis: BB

PowerPoint Presentation: 

Total plasma CO 2 (T-CO 2 ) : total content of the CO 2 . Normal: HCO 3 - >95%

Stepwise approach to interpreting the arterial blood gas.: 

Stepwise approach to interpreting the arterial blood gas. 1 . H&P. – idea of underlying disorder 2. Look at the pH. Is there an acid base disorder present? - If pH < 7.35, then acidemia -  if pH > 7.45, then alkalemia -  If pH within normal range, then acid base disorder not likely present. -   pH may be normal in the presence of a mixed acid base disorder,  particularly if other parameters of the ABG are abnormal.

PowerPoint Presentation: 

3 . Look at PCO2, HCO3- Are both values normal or abnormal? In simple acid base disorders, both values are abnormal and direction of the abnormal change is the same for both parameters. One abnormal value will be the initial change and the other will be the compensatory response.

Classification of Acid-basic Disorder: 

Classification of Acid-basic Disorder PH PaCO2 HCO 3 - Resp. acidosis Resp. alkalosis Meta. acidosis Meta. alkalosis

PowerPoint Presentation: 

3a . Distinguish the initial change from the compensatory response. - The initial change will be the abnormal value that correlates with the abnormal pH. - If Alkalosis, then PCO2 low or HCO3- high -  If Acidosis, then PCO2 high or HCO3-  low. Once the initial change is identified, then the other abnormal parameter is the compensatory response if the direction of the change is the same. If not, suspect a mixed disorder.

PowerPoint Presentation: 

3b . Once the initial chemical change and the compensatory response is distinguished, then identify the specific disorder . - If PCO2 is the initial chemical change, then process is respiratory. -  if HCO3- is the initial chemical change, then process is metabolic.

Compensatory Mechanisms: 

Compensatory Mechanisms Respiratory compensation Complete within 24 hrs Metabolic compensation Complete within several days Both the respiratory or renal compensation almost never over-compensates

PowerPoint Presentation: 

Prediction of Compensatory Responses on Simple Acid-Base Disturbances Disorder Prediction of Compensation Metabolic acidosis PaCO2 = (1.5x HCO3-) + 8 (Winter ’ s formula) or PaCO2 will ↓ 1.25 mmHg per mmol/L ↓ in [HCO3-] or PaCO2 = [HCO3-] + 15 Metabolic alkalosis PaCO2 will ↑ 0.75 mmHg per mmol/L ↑ in [HCO3-] or PaCO2 will ↑ 6 mmHg per 10-mmol/L ↑ in [HCO3-] or PaCO2 = [HCO3-] + 15 Respiratory alkalosis Acute [HCO3-] will ↓ 2 mmol/L per 10-mmHg ↓ in PaCO2 Chronic [HCO3-] will ↓ 4 mmol/L per 10-mmHg ↓ in PaCO2 Respiratory acidosis Acute [HCO3-] will ↑ 1 mmol/L per 10-mmHg ↑ in PaCO2 Chronic [HCO3-] will ↑ 4 mmol/L per 10-mmHg ↑ in PaCO2

PowerPoint Presentation: 

COMPENSION LIMITS METABLIC ACIDOSIS PaCO2 = Up to 10 METABOLIC ALKALOSIS PaCO2 = Maximum 6O RESPIRATORY ACIDOSIS BICARB = Maximum 40 RESPIRATORY ALKALOSIS BICARB = Up to 10 No click

PowerPoint Presentation: 

4.If respiratory process, is it acute or chronic? - An acute respiratory process will produce a compensatory response that is due primarily to rapid intracellular buffering. - A chronic respiratory process will produce a more significant compensatory response that is due primarily to renal adaptation, which takes a longer time to develop. To assess if acute or chronic, determine the extent of compensation.

PowerPoint Presentation: 

5.If metabolic acidosis, then look at the Anion Gap .

Anion Gap: 

Anion Gap AG = Na + - (Cl - + HCO3 - ) Unmeasured anions in plasma (normally 10 to 12 mmol/L) Anionic proteins, phosphate, sulfate, and organic anions

Anion Gap: 

Anion Gap Increase Increased unmeasured anions Decreased unmeasured cations (Ca ++ , K + , Mg ++ ) Increase in anionic albumin Decrease Increase in unmeasured cations Addition of abnormal cations Reduction in albumin concentration Decrease in the effective anionic charge on albumin by acidosis Hyperviscosity and severe hyperlipidemia ( underestimation of sodium and chloride concentration)

PowerPoint Presentation: 

Causes of High-Anion-Gap Metabolic Acidosis Lactic acidosis Toxins Ketoacidosis Ethylene glycol Diabetic Methanol Alcoholic Salicylates Starvation Renal failure (acute and chronic)

PowerPoint Presentation: 

Causes of Non-Anion-Gap Acidosis I. Gastrointestinal bicarbonate loss A. Diarrhea B. External pancreatic or small-bowel drainage C. Ureterosigmoidostomy , jejunal loop, ileal loop D. Drugs 1. Calcium chloride (acidifying agent) 2. Magnesium sulfate (diarrhea) 3. Cholestyramine (bile acid diarrhea) II. Renal acidosis A. Hypokalemia 1. Proximal RTA (type 2) 2. Distal (classic) RTA (type 1) B. Hyperkalemia 1. Generalized distal nephron dysfunction (type 4 RTA) a. Mineralocorticoid deficiency b. Mineralocorticoid resistance c. Ø Na + delivery to distal nephron d. Tubulointerstitial disease e. Ammonium excretion defect III. Drug-induced hyperkalemia (with renal insufficiency) A. Potassium-sparing diuretics ( amiloride , triamterene, spironolactone) B. Trimethoprim C. Pentamidine D. Angiotensin-converting enzyme inhibitors and AT-II receptor blockers E. Nonsteroidal anti-inflammatory drugs F. Cyclosporine IV. Other A. Acid loads (ammonium chloride, hyperalimentation ) B. Loss of potential bicarbonate: ketosis with ketone excretion C. Expansion acidosis (rapid saline administration) D. Hippurate E. Cation exchange resins

PowerPoint Presentation: 

6 . If metabolic process, is degree of compensation adequate ? Calculate the estimated PCO2, this will help to determine if a separate respiratory disorder is present

PowerPoint Presentation: 

7.If anion gap is elevated, then calculate the Delta-Ratio (∆/∆) to assess for other simultaneous disorders. Delta ratio = ∆ Anion gap/∆ [HCO3-] or ↑anion gap/ ↓ [HCO3-] = ( Measured anion gap – Normal anion gap)/ Normal [HCO3-] – Measured [HCO3-] =(AG – 12) / (24 - [HCO3-] )

PowerPoint Presentation: 

If ratio approx.1, then pure elevated anion gap acidosis -  If < 1, then there is a simultaneous normal anion gap acidosis present. - if > 2, then there is a simultaneous metabolic alkalosis present or a compensated chronic respiratory acidosis.

PowerPoint Presentation: 

8.If normal anion gap and cause is unknown, then calculate the Urine Anion gap This will help to differentiate RTAs from other causes of non elevated anion gap acidosis. - In RTA, UAG is positive. -  In diarrhea and other causes of metabolic acidosis, the UAG is negative

Mixed Acid Base Disorders: 

Mixed Acid Base Disorders Primary Secondary Respiratory acidosis Respiratory alkalosis Metabolic acidosis Metabolic alkalosis Respiratory acidosis   Respiratory alkalosis   Metabolic acidosis    Metabolic alkalosis   

PROBLEMS….: 

PROBLEMS…. A 48 yr old male ,MICU pt , severe sepsis on ventilatory support. PaO2 – 68 mm Pa CO2 – 38 mm pH- 7.3 Na- 140 K : 4 Cl :102 HCO3 : 18 Interpretation???

PowerPoint Presentation: 

Acidemia Metabolic Anion gap: 20 Expected PaCO2 – 35 Associated respiratory acidosis Delta ratio : approx 1 Inference: Metabolic acidosis(? Lactic) with Respiratory acidosis.

PowerPoint Presentation: 

Interpret this ABG of a chronic Liver disease pt. on diuretics admitted with c/o respiratory distress. PaO2 : 76 mm PaCO2 : 38 mm pH- 7.55 Na :140 K : 4.0 Cl : 91 HCO3 : 33 Interpretation??

PowerPoint Presentation: 

Alkalosis Metabolic Predicted PaCO2 : 48 mm Here value lower – 33 mm INFERENCE: So , metabolic alkalosis with respiratory alkalosis

PowerPoint Presentation: 

Interpret this ABG of a CRF pt. who presented with recurrent episodes of vomiting?? PaO2 : 86 mm Pa CO2 : 40 mm pH: 7.42 Na : 140 K : 3.0 Cl : 95 HCO3 : 25

PowerPoint Presentation: 

Apparently Normal!! Suspect metabolic acidosis Anion gap – 20 ( increased) So , possible Anion gap metabolic acidosis Delta ratio = 8/1 = 8(raised) Coexisting metabolic alkalosis INFERENCE : Metabolic acidosis+ alkalosis

PowerPoint Presentation: 

Interpret the ABG of ICU pt. admitted with AGE in shock.. PaO2 :86 mm PaCO2 : 25 mm pH: 7.20 Na : 135 K : 3.0 Cl: 110 HCO3 : 10

PowerPoint Presentation: 

Acidosis Metabolic Expected PaCO2 : 25 mm Anion gap : 15(high) High anion gap acidosis Delta ratio : 3/14 , INFERENCE : Coexistent hyperchloremic NAG acidosis

Arterial Blood Gases – test your overall understanding: 

3/13/2013 65 Arterial Blood Gases – test your overall understanding A 23-year-old man is being evaluated in the emergency room for severe pneumonia. His respiratory rate is 38/min and he is using accessory breathing muscles. FIO 2 .90 Na + 154 mEq/L pH 7.29 K + 4.1 mEq/L PaCO 2 55 mm Hg Cl - 100 mEq/L PaO 2 47 mm Hg HCO3 22 mEq/L SaO 2 86% HCO 3 - 23 mEq/L Hb 13 gm% CaO 2 15.8 ml O 2 How would you characterize his state of oxygenation, ventilation and acid-base balance?

PowerPoint Presentation: 

Hypoxia ++ ( low PaO2 and SaO2) PaCO2 high (Type II Respiratory failure) A-a DO2 : Increased Severe V-P imbalance Acidosis+ Respiratory Expected HCO3: 26 meq/l Associated Metabolic acidosis

PowerPoint Presentation: 

Anion gap : 32 High anion gap metabolic acidosis Is there a third problem? Delta AG : 20 Delta HCO3 : 2 Delta ratio – 10 INFERENCE: Respiratory acidosis + Metabolic acidosis + Metabolic alkalosis

PowerPoint Presentation: 

Analyse following ABG of post op peritonitis patient on ventilatory support?? PaO2 : 96 mm PaCO2 : 26 mm pH: 7.39 Na : 140 K : 4 Cl : 106 HCO3 : 14

PowerPoint Presentation: 

pH : normal HCO3 : 14, decreased Anion gap – 20 High AG acidosis Expected PaCO2 : 29 mm INFERENCE: Coexistent Respiratory alkalosis with metabolic acidosis