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Evaluation and Analysis of Acid-Base Disorders. Acid-Base Analysis, What do You Need? Blood gas (pH, CO 2 ) Serum chemistry (Na, Cl, HCO 3 ) Calculator.

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Presentation on theme: "Evaluation and Analysis of Acid-Base Disorders. Acid-Base Analysis, What do You Need? Blood gas (pH, CO 2 ) Serum chemistry (Na, Cl, HCO 3 ) Calculator."— Presentation transcript:

1 Evaluation and Analysis of Acid-Base Disorders

2 Acid-Base Analysis, What do You Need? Blood gas (pH, CO 2 ) Serum chemistry (Na, Cl, HCO 3 ) Calculator 30 seconds

3 ABG: 7.40 / 40 / 80 / 24 – pH – PaCO 2 – PaO 2 – HCO 3

4 Acid-Base Normals: pH= 7.40 (7.35 - 7.45) PCO 2 = 40 (35 - 45) HCO 3 = 24 (22 - 26)

5 Acidemic vs. Alkalemic pH < 7.35 = Acidemic pH > 7.45 = Alkalemic

6 Rule 1 Look at the pH. Whichever side of 7.40 the pH is on, the process (CO 2, HCO 3 ) that caused it to shift that way is the primary abnormality. Principle: The body does not fully compensate for a primary acid-base disorder

7 Keep It Simple: CO 2 = Acid –  CO 2 =  pH (acidemia) –  CO 2 =  pH (alkalemia) HCO 3 = Base –  HCO 3 =  pH (alkalemia) –  HCO 3 =  pH (acidemia)

8 Four Primary Disorders: PCO 2 < 35 = respiratory alkalosis PCO 2 > 45 = respiratory acidosis HCO 3 < 22 = metabolic acidosis HCO 3 > 26 = metabolic alkalosis – Can have mixed pictures with compensation – Can have up to 3 abnormality simultaneously (1 respiratory + 2 metabolic) – The direction of the pH will tell you which is primary!

9 Simple Acid-Base Disorders

10 Example # 1: Blood gas: 7.50 / 29 / 22 Alkalemic Low PCO 2 is the primary (respiratory alkalosis) No metabolic compensation = acute process Acute Respiratory Alkalosis

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12 Example # 2: Blood gas: 7.25 / 60 / 26 Acidemic Elevated CO 2 is primary (respiratory acidosis) No metabolic compensation= acute process Acute Respiratory Acidosis

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14 Acidemic Elevated CO 2 is primary (respiratory acidosis) Metabolic compensation has occurred = chronic process Chronic Respiratory Acidosis with Metabolic Compensation* * true metabolic compensation takes 3 days (72hrs) Example # 3: Blood gas: 7.34 / 60 / 31

15 Chronic Respiratory Acidosis with Metabolic Compensation

16 Example # 4: Blood gas: 7.50 / 48 / 36 Alkalemic Elevated HCO 3 is primary (metabolic alkalosis) Respiratory compensation has occurred = acute /chronic ? Metabolic Alkalosis with Respiratory Compensation* *Respiratory compensation takes only minutes

17 Metabolic Alkalosis with Respiratory Compensation

18 Example # 5: Blood gas: 7.20 / 21 / 8 Acidemic Low HCO 3 Is primary (metabolic acidosis) Respiratory compensation is present Metabolic Acidosis with Respiratory Compensation

19

20 Anion Gap (AG): The calculated difference between the positively charged (cations) and negatively charged (anions) electrolytes in the body: AG= Na + - (Cl - + HCO 3 - ) Normal AG = 12 ± 2 (10 – 14)

21 Rule 2 Calculate the anion gap. If the anion gap is  20, there is a primary metabolic acidosis regardless of pH or serum bicarbonate concentration Principle: The body does not generate a large anion gap to compensate for a primary disorder (anion gap must be primary)

22 Rule 3 Calculate the excess anion gap (total anion gap – normal anion gap) and add this value to the measured bicarbonate concentration: – if the sum is > than normal bicarbonate (> 30) there is an underlying metabolic alkalosis – if the sum is less than normal bicarbonate (< 23) there is an underlying nonanion gap metabolic acidosis 1. Excess AG = Total AG – Normal AG (12) 2. Excess AG + measured HCO 3 = > 30 or < 23?

23 Mixed Acid-Base Disorders

24 Remember the Rules 1. Look at the pH: ( 7.40?) whichever caused the shift (CO 2 or HCO 3 ) is the primary disorder 2. Calculate the anion gap: if AG  20 there is a primary metabolic acidosis (regardless of pH or HCO 3 ) 3. Calculate the excess anion gap, add it to HCO 3 : Excess AG = Total AG – Normal AG (12) Excess AG + HCO 3 = ? If sum > 30 there is an underlying metabolic alkalosis If sum < 23 there is an underlying nonanion gap metabolic acidosis

25 Example # 1 Blood gas: 7.50 / 20 / 15 Na= 140, Cl = 103 Alkalemic Low CO 2 is primary (respiratory alkalosis) Partial metabolic compensation for chronic condition? AG = 22 (primary metabolic acidosis) Excess AG (AG – 12) + HCO 3 = 25 (no other primary abnormalities) Respiratory Alkalosis and Metabolic Acidosis The patient ingested a large quantity of ASA and had both centrally mediated resp. alkalosis and anion gap met. Acidosis associated with salicylate overdose

26 Example # 2 Blood gas: 7.40 / 40 / 24 Na= 145, Cl= 100 pH normal AG = 21 (primary metabolic acidosis) Excess AG (AG – 12) + HCO 3 = 33 ( underlying metabolic alkalosis) Metabolic Acidosis and Metabolic Alkalosis This patient had chronic renal failure (met. acidosis) and began vomiting (met. alkalosis) as his uremia worsened. The acute alkalosis of vomiting offset the chronic acidosis of renal failure = normal pH

27 Example # 3 Blood gas 7.50 / 20 / 15 Na= 145, Cl = 100 Alkalemic Low CO 2 is primary (respiratory alkalosis) AG = 30 (primary metabolic acidosis) Excess AG (AG – 12) + HCO 3 = 33 (underlying metabolic alkalosis) Respiratory alkalosis, Metabolic Acidosis and Metabolic Alkalosis This patient had a history of vomiting (met. alkalosis), poor oral intake (met. acidosis) and tachypnea secondary to bacterial pneumonia (resp. alkalosis)

28 How Many Primary Abnormalities Can Exist in One Patient? Three primary abnormalities is the max because a person cannot simultaneously hyper and hypoventilate One patient can have both a metabolic acidosis and a metabolic alkalosis – usually one chronic and one acute

29 Example # 4 Blood gas: 7.10 / 50 / 15 Na= 145, Cl= 100 Acidemic High CO 2 and low HCO 3 - both primary (respiratory acidosis and metabolic acidosis) AG = 30 (metabolic acidosis is anion gap type) Excess AG + HCO 3 = 33 (underlying metabolic alkalosis) Respiratory Acidosis, Metabolic Acidosis and Metabolic Alkalosis This is an obtunded patient (resp. acidosis) with a history of emesis (metabolic alkalosis) and lab findings c/w diabetic ketoacidosis (metabolic acidosis w/ gap)

30 Example # 5 Blood gas: 7.15 / 15 / 5 Na= 140, Cl= 110 Acidemic Low HCO 3 - primary (metabolic acidosis) AG= 25 (metabolic acidosis is anion gap type) Excess AG + HCO 3 = 18 (underlying nonanion gap metabolic acidosis) Anion Gap and Nonanion gap Metabolic Acidosis Diabetic ketoacidosis was present (anion gap met. acidosis). Patient also had a hyperchloremic nonanion gap met. acidosis secondary to failure to regenerate bicarbonate from ketoacids lost in the urine.

31 Conclusions: To do accurate acid-base evaluations you need both blood gas and serum chemistry Use a systematic approach Remember the 3 rules “normal” blood gases may not be normal It is important to identify all the underlying acid- base in order to appropriately treat the patient


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