Acid-Base Balance Summary PDF

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Summary

helps a lot. use it in grad school now. ...

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Acid-Base Balance Acid-base balance is critical for maintaining the narrow pH range that is required for various enzyme systems to function optimally in the body. - Normal blood pH ranges from 7.3-7.4. o Slightly basic - Decreased pH is termed ACIDEMIA and is caused by an increase in the concentration of hydrogen ions ([H+]). - Increased blood pH is termed ALKALEMIA and is caused by a decrease in the [H+]. The buffer systems that maintain this pH balance are bicarbonate, phosphates, and proteins. - Bicarbonate is the most important extracellular buffer, while phosphates and proteins contribute mostly to intracellular acid-base balance. - The bicarbonate system is the only buffer measured for the calculation of acid-base status in patients and is represented by the equilibrium equation: CO2 + H2O H2CO3 H+ + HCO3-.

o This equation allows one to visualize what effects the addition of carbon dioxide (CO2) or bicarbonate (HCO3-) will have on the buffer system and the blood pH. o Addition of CO2 to the system will cause the equation to shift to the right, increasing the [H+] and, therefore, lowering the pH. o Addition of HCO3- to the system will cause the equation to shift to the left, lowering the [H+] and increasing the pH. o Another way to conceptualize this information is to simply think of CO2 as an acid and HCO3- as a base.  If CO2 is increased it will tend to cause acidemia.  If HCO3- is increased, then alkalemia is the expected result. In addition to buffers, the lungs and kidneys play a major role in acid-base homeostasis. - The lungs function in ventilation and they are responsible for regulating the amount of CO2 present in plasma.

- The kidneys are responsible for controlling the amount of HCO3- in the blood by resorbing or excreting it in the proximal tubule. - Abnormalities in acid-base status are classified as to whether the primary abnormality lies with the CO2 concentration or the HCO3concentration ([HCO3-]). o If CO2 is primarily affected, then a respiratory disturbance is present. o If HCO3- is primarily affected, then a metabolic disturbance is present.

Acid-base Disorder

[H+]

pH

Primary Disturbance

Respiratory Acidosis

Increased

Decreased Increased pCO2

Metabolic Acidosis

Increased

Decreased Decreased [HCO3-]

Acid-base Disorder

Respiratory Alkalosis

[H+]

pH

Primary Disturbance

Decreased Increased Decreased pCO2

Metabolic Alkalosis

Decreased Increased Increased [HCO3-]

Etiology Respiratory acidosis is caused by any condition which increases the pCO2 (hypercapnia). While increased production of CO2 (hyperthermia, cardiopulmonary arrest) is a possible cause of hypercapnia, the vast majority of cases are due to impaired removal of CO2 through the lungs. [COPD] Respiratory alkalosis is caused by conditions that will decrease the pCO2 (hypocapnia). Hyperventilation will lead to hypocapnia, and it can be caused by hypoxemia, pulmonary disease, direct activation of the respiratory center in the brainstem, overzealous mechanical ventilation, or situations causing pain, fear, or anxiety. There are two types of metabolic acidosis. Both are characterized by a decrease in the [HCO3-] but they differ in how that decrease occurs.

- Secretional metabolic acidosis is caused by a direct loss of bicarbonate-rich fluid [such as diarrhea or saliva]. - Titrational metabolic acidosis is caused by the presence of non-CO2 acids that titrate bicarbonate causing a decreased [HCO3-].

Acid-Base Disturbance

Primary Disturbance

Compensatory Response

Compensatory Mechanism

Respiratory acidosis

Increased pCO2

Increase [HCO3-]

Acidic urine

Respiratory alkalosis

Decreased pCO2

Decreased [HCO3-]

Alkaline urine

Metabolic acidosis

Decreased [HCO3-]

Decrease pCO2

Hyperventilation

Metabolic alkalosis

Increased [HCO3-]

Increased pCO2

Hypoventilation...