Acid Base balance

Prince Sattam Bin AbdulAziz University College Of Pharmacy

A 62-year-old woman has been hospitalized in the ICU for several weeks. Her hospital stay has been complicated by aspiration pneumonia and sepsis, requiring prolonged courses of antibiotics.

For the past few days, she has been having high temperatures again, and her stool output has increased dramatically

. Her most recent stool samples have tested positive for Clostridium difficile toxin,

laboratory testsserum Na 138 mEq/L, K 3.5 mEq/L, Cl 115 mEq/L,

albumin 4.4 g/dL, pH 7.32, Paco2 30 mm Hg, and HCO3 − 15 mEq/L.

Which one of the following acid-base disturbances is consistent with this patient’s ABG?

A. AG metabolic acidosis.B. Normal AG metabolic acidosis.C. Saline-responsive metabolic alkalosis.D. Acute respiratory acidosis.

Complete

• The compensation for a respiratory acidosis is metabolic (alkalosis /acidosis )……

• The compensation for a respiratory alkalosis is metabolic ………..(acidosis/Alkalosis)

• The compensation for metabolic acidosis is a respiratory …………. ………..(acidosis/Alkalosis)

• RR in respiratory alkalosis is …… ( increased /decreased )

• Metabolic acidosis Hco3- (increased/decreased)• Respiratory acidosis Pco2 (increased/decreased)

Anion gab facts • Anion gap is reflective of unmeasured acids. ( T/F)

•  An increase in anion gap suggests an increase in the number of negatively charged weak base in the plasma. ( T/F)

• Serum anion gap (SAG) can be used to elucidate cause of metabolic acidosis ( T/F)

• Anion gap  may be elevated in conditions such as renal failure, lactic acidosis, ketoacidosis, and salicylate, methanol, or ethylene glycol toxicity

True

False /weak base

true

True

How to calculate Anion gab

• Calculate the anion gap (AG) = [Na+] − [Cl− + HCO3−].

• Calculate anion gab for in the previous case

Normal AG = 140 − [105 + 24] = 6–12 mEq/L.

If AG is more than 12, there is a primary metabolic acidosis regardless of pH or HCO3−.

• Back to the first question

laboratory testsserum Na 138 mEq/L, K 3.5 mEq/L, Cl 115 mEq/L, albumin 4.4 g/dL, pH 7.32, Paco2 30 mm Hg, and HCO3 − 15 mEq/L. Which one of the following acid-base disturbances is consistent with this patient’s ABG?A. AG metabolic acidosis.B. Normal AG metabolic acidosis. (non anion gabC. Saline-responsive metabolic alkalosis.D. Acute respiratory acidosis.

• The cause of her normal anion gab metabolic acidosis ?

A . Clostridium difficile toxin causing diarrhea

B. Aspiration pneumoniaC. Use of antibiotics

Interpreting ABGs

• Step 1 - check the pH?

• Step 2 - What is the CO2?

• Step 3 - Watch the bicarbonate?

• Step 4 - Look for compensation?

• Step 5 - What is the PaO2 and SaO2?

Respiratory Acidosis

• Carbonic acid excess• Exhaling of CO2

inhibited• Carbonic acid builds up• pH falls below 7.35• Cause = Hypoventilation (see chart)

H2CO3

Acid-Base Imbalances

• Normal

1 20

7.4

H2CO3 ……………… HCO324 mEq/L1.2 mEq/L

Respiratory Acidosis

1 13

7.21

H2CO3 ……………… HCO3

24 mEq/L

1.84 mEq/L

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Signs and Symptoms of Respiratory Acidosis

• Breathlessness• Restlessness• Lethargy and disorientation• Tremors, convulsions, coma• Respiratory rate rapid, then gradually

depressed• Skin warm and flushed due to vasodilation

caused by excess CO2

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Treatment of Respiratory Acidosis

• Restore & improve alveolar ventilation• IV lactate solution (converted to bicarbonate ions

in the liver). • Treat underlying dysfunction or disease e.g. pul odema, Res depression

19

Respiratory Alkalosis

• Carbonic acid deficit• Increased exhaling

of CO2• Carbonic acid decreases• pH rises above 7.45• Cause = hyperventilation (see chart)

H2CO3

Acid-Base Imbalances

• Normal

1 20

7.4

H2CO3 ……………… HCO324 mEq/L1.2 mEq/L

Respiratory Alkalosis

1 40

7.70

H2CO3 ……………… HCO3

24 mEq/L

0.6 mEq/L

23

Respiratory Alkalosis

• Conditions that stimulate respiratory center:– Oxygen deficiency at high altitudes– Pulmonary disease and Congestive heart failure –

caused by hypoxia – Acute anxiety– Fever, anemia– Early salicylate intoxication– Cirrhosis– Gram-negative sepsis

24

Treatment of Respiratory Alkalosis

• Treat underlying cause• Breathe into a paper bag• IV Chloride containing solution (hydrochloric

acid, arginine chloride & ammonium chloride), – Cl- ions replace lost bicarbonate ions

Metabolic Acidosis• Base-bicarbonate deficit• Low pH (< 7.35) • Low plasma bicarbonate (base)• Cause = relative gain in H+

(lactic acidosis, ketoacidosis) or actual loss of HCO3 (renal failure, diarrhea)

Acid-Base Imbalances

• Normal

1 20

7.4

H2CO3 ……………… HCO324 mEq/L1.2 mEq/L

Metabolic Acidosis

• Kidney failure (decrease in bicarbonate)

1 10 7.10

H2CO3 ……………… HCO312 mEq/L

1.2 mEq/L

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Symptoms of Metabolic Acidosis

• Headache, lethargy• Nausea, vomiting, diarrhea• Coma• Death

29

Treatment of Metabolic Acidosis

• Treat the causes• Improve renal perfusion & acid excretion• NaHCO3, Dose = (weight Kg x base deficit x 0.3)• Ensure adequate ventilation

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Metabolic Alkalosis

• Bicarbonate excess• High pH (> 7.45)• Loss of H+ ion or gain of HCO3• Most common causes vomiting, gastric

suctioning (NG tube)• Other: Abuse of antacids, K+

wasting diuretics

Acid-Base Imbalances

• Normal

1 20

7.4

H2CO3 ……………… HCO324 mEq/L1.2 mEq/L

Metabolic Alkalosis

1 30

7.58

H2CO3 ……………… HCO3

36 mEq/L

1.2 mEq/L

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Symptoms of Metabolic Alkalosis

• Respiration slow and shallow• Hyperactive reflexes ; tetany• Often related to depletion of electrolytes• Atrial tachycardia• Dysrhythmias

34

Treatment of Metabolic Alkalosis

• Electrolytes to replace those lost• Treat underlying disorder• IV chloride containing solution e.g saline (Chloride

Responsive)• Aldosterone antagonist (Chloride resistant)

34

Assessing ABGs

• pH 7.35 - 7.45• PaCO2 35 - 45 mmHg• HCO3 22 - 26 mEq/L• Base Excess -2 - +2 mEq/L• PaO2 80 - 100 mm Hg• O2 saturation 95 - 100 %

Interpreting ABGs

Uncompensated• pH abnormal (high or low)• One component abnormal (high or

low CO2 or HCO3)• The other component is normal(The component not causing the acid-base

imbalance is still normal)

Partly compensated• pH not normal (but moving toward

normal)• Both CO2 and HCO3 are outside normal

range• The component that was normal is

changing in order to compensate

Interpreting ABGs

Compensated• pH normal• Other values abnormal in

opposite directions• One is acidotic the other alkaline

Interpreting ABGs

• Determine amount of hypoxemia present• Normal PaO2 (adults - room air)• < 70 years = 80-100 mm Hg

70-79 = 70-100 mm Hg• Drops 10 mm Hg for each decade

Interpreting ABGs

• Hypoxemia = < 70 mm Hg(for adult < 70 years old)

• Mild = 60-80 mm Hg• Moderate = 40-60 mm Hg• Severe = < 40 mm Hg

Interpreting ABGs

• Oxygen saturation (pulse oximetry)

• 95-100%• < 91% confusion• < 70% life threatening

Case 1

• 80 year old female with severe pneumonia, fever

• pH = 7.25• PaCO2 = 55 mm Hg• HCO3 = 24 mEq/L• PaO2 = 65 mm Hg• O2 sat = 80%

Acidosis or alkalosis?Respiratory or metabolic?

Compensated or Uncompensated?Level of hypoxemia?

Case 2:A patient is in intensive care because he suffered a severe myocardial infarction 3 days ago. The lab reports the following values from an arterial blood sample:– pH 7.3– HCO3- = 20 mEq / L ( 22 - 26)– pCO2 = 32 mm Hg (35 - 45)

DiagnosisMetabolic acidosisWith partial compensation

• Case 3: • A 44 year old moderately dehydrated man was

admitted with a two day history of acute severe diarrhea. Electrolyte results: Na+ 134, K+ 2.9, Cl- 108, HCO3- 16,

• Urea 31, Cr 1.5.• ABG

pH - 7.31 pCO2 - 33 mmHgHCO3 - 16 pO2 - 93 mmHg

• ????????? Diagnosis and Anion Gap

CASE 4:

• A 20 year old female with type I DM, presents to the emergency department with a 1 day history of nausea, vomiting, polyuria, polydypsia and vague abdominal pain. P.E. noted for deep sighing breathing, orthostatic hypotension, and dry mucous membranes.

• Lab. Findings are: Na 134 , K 6.0, Cl- 93, HCO3- 11 glucose 720, Urea 38, Cr 2.6. UA: pH 5, ketones negative, glucose positive . Plasma ketones trace. ABG: pH 7.27 HCO3- 10  PCO2 23

• What is the acid base disorder? 47

CASE 5

• A 70 year old man with history of CHF presents with increased shortness of  breath and leg swelling.ABG:

• pH 7.24, • PCO2 60 mmHg, • PO2  52 • HCO3- 27• What is the acid base disorder?

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– Interprete ABG

– pH < 7.35

– PaCO2 >45

– HCO3 Normal

• Uncompensated

– pH < 7.35

– PaCO2 >45

– HCO3 Normal

– Respiratory

Acidosis

• Question: Interprete ABG???– pH Normal

– PaCO2 >45

– HCO3 > 26

• Compensated– pH Normal

– PaCO2 >45

– HCO3 > 26

– Respiratory Acidosis

ABG interprete????

– pH > 7.45

– PaCO2 < 35

– HCO3 Normal

– pH Normal

– PaCO2 < 35

– HCO3 < 22

ABG Results

• Uncompensated– pH > 7.45

– PaCO2 < 35

– HCO3 Normal

– Respiratory Alkalosis

• Compensated– pH Normal

– PaCO2 < 35

– HCO3 < 22

– Respiratory Alkalosis

ABG interprete??

– pH < 7.35

– PaCO2 Normal

– HCO3 < 22

– pH Normal

– PaCO2 < 35

– HCO3 < 22

ABG Results

• Uncompensated– pH < 7.35

– PaCO2 Normal

– HCO3 < 22

– Metabolic Acidosis

• Compensated– pH Normal

– PaCO2 < 35

– HCO3 < 22

– Metabolic Acidosis

ABG interprete???

– pH > 7.45

– PaCO2 Normal

– HCO3 >26

– pH Normal

– PaCO2 > 45

– HCO3 > 26

ABG Results

• Uncompensated– pH > 7.45

– PaCO2 Normal

– HCO3 >26

– Metabolic Alkalosis

• Compensated– pH Normal

– PaCO2 > 45

– HCO3 > 26

– Metabolic Alkalosis