Acid Base Balance



Acid Base Balance

Definitions of Acid, Base and pH

Acids are substances that contain hydrogen ions (H+) that can be released to other substances. Alkalies posses no hydrogen ions of their own but are able to accept them from acids. Together, the acids and alkalies of the body fluids are constantly reacting to keep the body in a normal state. This is called acid-base balance. If this balance is not kept, the body will become either acidic or alkalotic.

pH is a scale which indirectly measures the amount of (H+) in the body fluid (blood). When the body produces more hydrogen ions, the blood becomes more acidic. When the body is able to rid itself of too many hydrogen ions, the blood becomes alkalotic. Too much deviation to either side can be fatal. The pH scale goes from 1 – 14. 1 being the most acidic and 14 the most alkalotic. 7 is neutral and any fluid with a pH of 7 is neither acidic or alkalotic. The scale is shown below.

pH below 7 = acid pH of 7 = neutral pH above 7 = alkaline

pH of extracellular fluid is slightly alkalotic at 7.40. For the purposes of discussion, the normal body pH will be from 7.35 – 7.45.

pH below 7.35 = acidosis pH above 7.45 = alkalosis

Death occurs when the plasma pH is below 6.8 or above 7.8

Acid Base Regulatory System – Regulatory Mechanisms of Acid-Base Balance

There are three ways the body regulates acid base balance. They are listed below starting with the fastest.

Buffer System Respiratory System Renal System

BUFFER SYSTEM:

H2O + CO2 H2CO3 H+ + HCO3

Respiratory Metabolic

How to read an Arterial Blood Gas (ABG)

There are three essential components to the ABG that will give you an indication of what the pH reading is (identifying whether the patient is normal, acidotic or alkalotic), the paCO2 and HCO3 (which will point you to the possible cause – respiratory or metabolic). Two other readings will also help the provider in assessing oxygen levels in the blood sample, paO2 and O2 Saturation.

pH normal = 7.35 – 7.45

paCO2 normal = 35 – 45

HCO3 normal = 22 – 26

paO2 normal = 80 – 100

O2 Saturation normal = 90 – 100 %

Acidotic Conditions

Respiratory Acidosis:

Causes – respiratory/ventilatory failure (CNS depression, obstructive lung disease, arrest)

Signs and symptoms -

Treatment = ventilation with 100% oxygen

Metabolic Acidosis:

Causes – anaerobic metabolism (renal impairment, diabetes)

Signs and symptoms -

Treatment = ventilation with 100% oxygen

Alkalotic Conditions

Respiratory Alkalosis:

Causes – hyperventilation (due to fever, anxiety, pulmonary infections)

Signs and symptoms -

Treatment = increase carbon dioxide levels

Metabolic Alkalosis:

Causes – (medications, baking soda, prolonged vomiting)

Signs and symptoms -

Treatment = correct underlying cause.

| |Acidosis |Alkalosis |

| |Respiratory |Metabolic |Respiratory |Metabolic |

|pH |↓ |↓ |↑ |↑ |

|paCO2 |↑ |~ |↓ |~ |

|HCO3 |~ |↓ |~ |↑ |

|Compensation |HCO3 ↑ |paCO2 ↓ |HCO3 ↓ |paCO2 ↑ |

H2O + CO2 H2CO3 H+ + HCO3

Water carbon dioxide carbonic acid hydrogen bicarbonate ion

Davenport diagram: classic working diagram for studying primary uncompensated acid–base imbalance. The point X represents a normal pH value and normal values for partial pressure of carbon dioxide (PCO2) and bicarbonate (HCO3). Note that as the PCO2 increases toward 60 mmHg the pH decreases (respiratory acidosis), and that as it decreases toward 20 mmHg the pH increases (respiratory alkalosis). Metabolic acidosis develops as the concentration of HCO3 decreases, and metabolic alkalosis develops as the concentration of HCO3 increases.

List Normal Values:

pH ________________ paCO2 ____________ HCO3 _____________ paO2 _____________

Problems to be solved

|Determine Acid or Base |Determine respiratory component |Determine metabolic component |

| pH Circle correct answer | paCO2 Circle the correct answer | HCO3 Circle the correct answer |

|1. |7.32 |acidic |1. |38 |normal high low |

| | |normal | | | |

| | |alkalotic | | | |

|pH |7.41 |pH |7.11 |pH |6.91 |

|paCO2 |35 |paCO2 |53 |paCO2 |66 |

|HCO3 |23 |HCO3 |24 |HCO3 |10 |

| | | |

|4. | |5. | |6. | |

|pH |7.52 |pH |7.60 |pH |7.37 |

|paCO2 |16 |paCO2 |44 |paCO2 |41 |

|HCO3 |25 |HCO3 |32 |HCO3 |26 |

| | | |

|7. | |8. | |9. | |

|pH |7.48 |pH |7.48 |pH |7.42 |

|paCO2 |13 |paCO2 |60 |paCO2 |39 |

|HCO3 |28 |HCO3 |32 |HCO3 |25 |

| | | |

|10. | |11. | |12. | |

|pH |6.70 |pH |7.68 |pH |7.28 |

|paCO2 |66 |paCO2 |23 |paCO2 |38 |

|HCO3 |32 |HCO3 |31 |HCO3 |9 |

| | | |

|13. | |14. | |15. | |

|pH |6.82 |pH |7.38 |pH |7.44 |

|paCO2 |66 |paCO2 |39 |paCO2 |43 |

|HCO3 |8 |HCO3 |25 |HCO3 |22 |

| | | |

|16. | |17. | |18. | |

|pH |7.89 |pH |7.02 |pH |7.37 |

|paCO2 |22 |paCO2 |53 |paCO2 |41 |

|HCO3 |22 |HCO3 |11 |HCO3 |28 |

| | | |

|19. | |20. | |21. | |

|pH |6.98 |pH |6.8 |pH |7.43 |

|paCO2 |48 |paCO2 |46 |paCO2 |32 |

|HCO3 |9 |HCO3 |16 |HCO3 |17 |

| | | |

|22. | |23. | |24. | |

|pH |7.22 |pH |7.52 |pH |7.44 |

|paCO2 |49 |paCO2 |12 |paCO2 |39 |

|HCO3 |25 |HCO3 |22 |HCO3 |25 |

| | | |

Identify which each condition will likely result in (respiratory or metabolic – acidosis or alkalosis) if uncorrected.

|1 |ASA OD | |

|2 |Head injury with respiratory depression | |

|3 |Diabetic hyperglycemia | |

|4 |Acute alcohol intoxication | |

|5 |Renal failure | |

|6 |Cerebral neoplasm causing hyperventilation | |

|7 |Diuresis OD | |

|8 |Antacid OD | |

|9 |Excessive vomiting / bulimia | |

|10 |Cardiac arrest | |

|11 |Exacerbated COPD | |

|12 |Status asthmaticus | |

Normal Values: pH 7.35 – 7.45 paCO2 35 – 45 HCO3 22 – 26 paO2 80 – 100

Answer Key

|pH |paCO2 |HCO3 |

|1 |Acid |1 |Normal |1 |Normal |

|2 |Acid |2 |Low |2 |High |

|3 |Normal |3 |High |3 |Low |

|4 |Acid |4 |High |4 |Low |

|5 |Acid |5 |Low |5 |Low |

|6 |Alkalotic |6 |Low |6 |High |

|7 |Normal |7 |Normal |7 |High |

|8 |Acid |8 |High |8 |Normal |

|9 |Alkalotic |9 |Low |9 |Low |

|10 |normal |10 |normal |10 |Normal |

ABG Problems:

|1 |WNL |13 |Mixed acidosis |

|2 |Respiratory acidosis |14 |WNL |

|3 |Respiratory & metabolic acidosis |15 |WNL |

|4 |Respiratory alkalosis |16 |Respiratory alkalosis |

|5 |Metabolic alkalosis |17 |Mixed acidosis |

|6 |WNL |18 |WNL |

|7 |Respiratory alkalosis |19 |Mixed acidosis |

|8 |Respiratory alkalosis w/ compensation |20 |Mixed acidosis |

|9 |WNL |21 |Respiratory alkalosis w/ comp. (chronic) |

|10 |Respiratory acidosis w/ compensation |22 |Respiratory acidosis |

|11 |Mixed alkalosis |23 |Respiratory alkalosis |

|12 |Respiratory acidosis w/ compensation |24 |WNL |

Medical conditions problems:

|1 |Metabolic acidosis |7 |Metabolic alkalosis |

|2 |Respiratory acidosis |8 |Metabolic alkalosis |

|3 |Metabolic acidosis |9 |Metabolic alkalosis |

|4 |Respiratory acidosis |10 |Respiratory acidosis |

|5 |Metabolic acidosis |11 |Respiratory acidosis |

|6 |Respiratory alkalosis |12 |Respiratory acidosis |

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