Acid-Base Balance/ Imbalance
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Acid-base balance is the balance between the body’s acidity and alkalinity. An acid is a hydrogen ion or proton donor. A base is a hydrogen ion or proton acceptor. Acidity and alkalinity are measured using the pH (power of hydrogen) scale. The scale ranges from 0 – 14. 0 represents the most acidic, 14 represents the most alkaline, and 7 represents neutral. The human body is slightly alkaline, with a pH ranging from 7.35 – 7.45. If the pH value in the human body differs from this range, it can be very detrimental. The hydrogen ion and the pH of the body are directly related. If hydrogen ion concentration in the body increases, the pH decreases. If the hydrogen ion concentration decreases, the pH value increases.
Changes in the body’s acidity can occur from an increase in the intake of acidic compounds, increased production, or a decrease in the elimination of acidic compounds. It can also be caused by a decreased level of base production. The human body tries to maintain a 1:20 ratio between acids and bases. This is done through several mechanisms that compose the buffer system. The three buffer systems are the carbonic acid-bicarbonate, protein buffering, and the renal buffering system.
The carbonic acid-bicarbonate buffer system is the fastest action of all the compensatory mechanisms. As a byproduct of metabolism, hydrogen and other acids are produced. The carbonic acid-bicarbonate buffer system works by combining acids with bases to create a weaker acid. Hydrogen (H+) will combine with bicarbonate (HCO3–) which forms H2CO3. Carbon dioxide (CO2) will combine with water (H2O) to form carbonic acid. This is formed with the help of carbonic anhydrase represented by H+ + HCO3– ßà H2O + CO2. This equation can work in both directions. CO2 elevation moves the equation balance to the left, where hydrogen ion elevation moves it to the right.
Hemoglobin easily binds to hydrogen and carbon dioxide. The protein buffering system mainly uses hemoglobin to eliminate acid. As blood is circulated through the body, gas exchange occurs at the capillary level. Oxygen is dropped off, and carbon dioxide and hydrogen are bound with hemoglobin. This then returns to the lungs where another gas exchange occurs. Carbon dioxide and hydrogen are released into the lung tissue. Hydrogen gets bound with bicarbonate, which creates carbonic acid. This is then dissociated into carbon dioxide and water which is exhaled. The respiratory system is mainly driven by blood pH levels, not oxygen levels.
The renal buffering system is the slowest compensatory mechanism for maintaining acid-base balance. The kidneys eliminate hydrogen and reabsorb bicarbonate within the tubules of the nephrons. This is the process by which the kidneys regulate the pH. If acidity is too high, more hydrogen will be excreted in the urine. If alkalosis is present, the kidneys will retain hydrogen and excrete bicarbonate.
Acid-base imbalances can also be caused by respiratory or metabolic issues. Lactic acidosis, diabetic ketoacidosis or renal failure are all causes of metabolic acidosis. Diarrhea and vomiting can cause a loss of base within the body. In metabolic acidosis, the pH decreases but the carbon dioxide levels remain normal. Patients with this type of imbalance present with poor perfusion or renal failure. Treatment is usually direct towards the underlying cause.
Metabolic alkalosis is less common and usually occurs from excessive vomiting and long term diuretic use. More acids are lost through vomiting, where more bases are lost through diarrhea. In metabolic alkalosis, the pH increases, but the carbon dioxide levels remain normal. This condition is usually related to an electrolyte imbalance which may present as hypokalemia or hypocalcemia. Treatment is directed at the cause. If dehydration is present, replace fluids with IV sodium chloride solution. If vomiting persists, administer an anti-emetic. In patients who have fluid overload, a diuretic may be necessary.
Respiratory acidosis and alkalosis are directly linked with the respiratory system's ability to eliminate carbon dioxide. Normal ranges of arterial blood gases are as follows;
- PaO2 = 80 – 100 mm Hg
- PaCO2 = 35 – 45 mm Hg
- pH = 7.35 – 7.45
- HCO3 = 22 – 26 mmol/L
Respiratory acidosis occurs from any condition that decreases respiratory rate or volume. Without the ability of the lungs to eliminate carbon dioxide, the body must rely on the renal system to do so. This can take days to do, which can result in a lethal acidosis state. In this condition, the carbon dioxide levels will be increased and the pH decreased. Treatment for this is directed at correcting the ventilatory status of the patient.
Respiratory alkalosis occurs when too much carbon dioxide is eliminated via the respiratory system. This can occur in patients who have hyperventilation syndrome, anxiety, hysteria. Also, metabolic causes such as a fever can cause respiratory alkalosis. In this situation, carbon dioxide levels are decreased and the pH is elevated. Signs and symptoms range from; paresthesia, circumoral numbness, chest tightness, dyspnea, dizziness, confusion, and tetany. Treatment for this ranges from coaching the patients breathing, having to administer a sedative, and the most extreme, having to take control of the patient’s airway for them.
Question and Answers
- If the human body has a pH value of 7.27, it is considered:
- If acid levels in the body are too high, more ______ will be excreted in the urine.
- Which system has the fastest action of all of the compensatory mechanisms within the human body?
- The carbonic acid-bicarbonate buffer system
- The renal buffering system
- The protein buffering system
- The circulatory system
- In metabolic alkalosis, the pH _______, but the carbon dioxide levels remain normal.
- True or False; respiratory alkalosis occurs when too much carbon dioxide is eliminated via the respiratory system.
- In respiratory acidosis, carbon dioxide levels will increase and pH levels will _____.
- What is considered the normal range for PaCO2?
- 7.35 – 7.45
- 22 – 32 mm Hg
- 55-65 mm Hg
- 35-45 mm Hg
- If the human body has a pH value of 7.27, is it:
The correct answer is 1. The pH scale ranges for 0-14. 0 represents the most acidic state and 14 represents the most alkalotic state. 7 is considered neutral.
2. If acid levels in the body are too high, more ______ will be excreted in the urine.
The correct answer is 3. The kidneys eliminate hydrogen and reabsorb bicarbonate within the tubules of the nephrons. If acidity is too high, more hydrogen will be excreted in the urine.
3. Which system has the fastest action of all of the compensatory mechanisms within the human body?
The correct answer is 1. The carbonic acid-bicarbonate buffer system is the fastest action of all the compensatory mechanisms.
4. In metabolic alkalosis, the pH _______, but the carbon dioxide levels remain normal.
The correct answer is 2. The pH will increase but carbon dioxide levels remain normal. The pH is increasing because the body has become alkalotic from a metabolic disturbance.
5. True or False; respiratory alkalosis occurs when too much carbon dioxide is eliminated via the respiratory system.
The correct answer is True. When too much carbon dioxide is retained, your body becomes acidotic. In this case, respiratory alkalosis is caused when too much carbon dioxide is eliminated as seen in patients with hyperventilation syndrome.
6. In respiratory acidosis, carbon dioxide levels will increase and pH levels will _____.
The correct answer is 2. Excess carbon dioxide levels will create an acidic environment which makes the pH levels decrease. Remember, anything less than 7 on the pH scale is considered acidic.
7. What is considered the normal range for PaCO2?
The correct answer is 4. 35-45 mm Hg. Anything above 45 mm Hg is considered hypercarbic, anything below 35 mm Hg is considered hypocarbic.