Acid-Base Balance Practice Questions

Q: A 40-year-old male presents with hyperventilation and dizziness. Which acid-base disturbance is he most likely experiencing?

Respiratory alkalosis. ***Respiratory alkalosis (hyperventilation)*** - **Hyperventilation** directly leads to an excessive exhalation of **carbon dioxide (CO2)**, causing a decrease in blood pCO2, which is the primary characteristic of respiratory alkalosis. - The drop in CO2 reduces the amount of **carbonic acid** in the blood, leading to an increase in pH (alkalosis) and symptoms like **dizziness and lightheadedness**. *Metabolic acidosis (compensatory hyperventilation possible)* - While metabolic acidosis can lead to **compensatory hyperventilation** to blow off CO2, the primary cause here is the hyperventilation itself, not a metabolic derangement. - In metabolic acidosis, there would be a **low bicarbonate level** and often a primary metabolic cause like DKA or lactic acidosis, which are not suggested by the isolated hyperventilation. *Metabolic alkalosis (typically associated with hypoventilation)* - **Metabolic alkalosis** is characterized by an elevated bicarbonate level, often due to vomiting or diuretic use. - It would typically lead to **compensatory hypoventilation** to retain CO2 and lower pH, which is the opposite of the patient's presentation. *Respiratory acidosis (hypoventilation)* - **Respiratory acidosis** results from **hypoventilation**, leading to CO2 retention and an increase in blood pCO2. - The patient is actively hyperventilating, which would decrease CO2, making respiratory acidosis an incorrect diagnosis.

Q: In a patient with severe diarrhea, what is the expected change in the blood acid-base balance?

Metabolic acidosis. ***Metabolic acidosis*** - Severe diarrhea leads to excessive loss of **bicarbonate (HCO3-)** from the gastrointestinal tract, primarily from the small intestine and colon [1], [2]. - The loss of this principal buffer results in a decrease in blood pH, causing **metabolic acidosis** [1], [2]. *Metabolic alkalosis* - This condition is characterized by an increase in blood pH due to an excess of bicarbonate or a loss of hydrogen ions [3]. - It is typically caused by conditions like **vomiting** (loss of gastric acid) or diuretic use, not diarrhea [2], [3]. *Respiratory alkalosis* - This occurs when there is a decrease in the partial pressure of carbon dioxide (PCO2) due to **hyperventilation**. - While diarrhea can lead to compensatory hyperventilation, the primary disturbance is metabolic, not respiratory [1]. *Respiratory acidosis* - This is characterized by an increase in PCO2 due to **hypoventilation** or impaired gas exchange in the lungs. - Diarrhea does not directly cause respiratory acidosis; in fact, the body might try to compensate for metabolic acidosis by increasing ventilation [2].

Q: A patient with chronic obstructive pulmonary disease (COPD) exhibits signs of respiratory acidosis. What is the primary cause?

Increased carbon dioxide retention. ***Increased carbon dioxide retention*** - In **COPD**, impaired gas exchange (due to airway obstruction and lung damage) leads to inefficient elimination of **carbon dioxide** from the body via exhalation. - The buildup of **CO2** in the blood, an acidic gas, results in a decrease in pH, causing **respiratory acidosis**. - This is the primary mechanism underlying respiratory acidosis in COPD patients. *Decreased carbon dioxide retention* - **Decreased CO2 retention** would imply efficient or excessive CO2 elimination, which would lead to **respiratory alkalosis**, the opposite of what is seen in this patient. - This scenario would be characterized by a **low PCO2**, not the elevated PCO2 found in respiratory acidosis. *Decreased bicarbonate reabsorption* - **Decreased bicarbonate reabsorption** by the kidneys would lead to a loss of bicarbonate, a base, from the body. - This would result in **metabolic acidosis**, not respiratory acidosis, and is not a primary respiratory issue. *Increased bicarbonate reabsorption* - **Increased bicarbonate reabsorption** is a compensatory mechanism by the kidneys in response to **respiratory acidosis**. - While it occurs to buffer the excess CO2, it is not the primary cause of the acidosis itself; rather, it is the body's attempt to correct it.

Q: A patient with diabetic ketoacidosis (DKA) presents with Kussmaul breathing. Which compensatory mechanism is he demonstrating?

Increased CO2 elimination. ***Increased CO2 elimination*** - Kussmaul breathing is a deep, rapid breathing pattern that represents the body's attempt to **compensate for metabolic acidosis** by expelling more carbon dioxide [1], [3]. - By increasing the rate and depth of breathing, the lungs remove more **acidic CO2**, thereby raising the blood pH [2]. *Increased CO2 retention* - **Increased CO2 retention** would worsen the patient's acidosis, as CO2 forms carbonic acid in the blood when combined with water, lowering the pH [4]. - This mechanism is characteristic of **respiratory acidosis**, not respiratory compensation for metabolic acidosis. *Decreased bicarbonate reabsorption* - **Bicarbonate reabsorption** primarily occurs in the kidneys and affects acid-base balance over a longer period, rather than being a rapid respiratory compensatory mechanism [2]. - **Decreased bicarbonate reabsorption** would lead to a loss of base, which would exacerbate acidosis, not compensate for it. *Increased bicarbonate excretion* - Similar to decreased bicarbonate reabsorption, **increased bicarbonate excretion** by the kidneys would result in a loss of base from the body. - This would further acidify the blood and is not a compensatory response for metabolic acidosis; instead, the kidneys would typically try to **conserve bicarbonate**.

Q: Respiratory acidosis is recognized primarily by an increase in which of the following?

PaCO2. ***PaCO2*** - **Respiratory acidosis** is directly caused by **hypoventilation**, leading to impaired **carbon dioxide (CO2)** elimination from the lungs. - The accumulation of **CO2** in the blood increases its partial pressure (**PaCO2**), which then reacts with water to form **carbonic acid**, lowering the blood **pH**. *PaO2* - **PaO2** (partial pressure of oxygen) usually decreases in conditions causing hypoventilation, but its increase is not the primary indicator of **respiratory acidosis**. - While both can be affected in respiratory compromise, **PaCO2** is the defining determinant of the respiratory component of acid-base balance. *HCO3-* - **HCO3-** (bicarbonate) is primarily involved in **metabolic acid-base balance** and acts as a buffer against acidity. - In **respiratory acidosis**, bicarbonate levels might increase as a compensatory mechanism (renal compensation) over time to buffer the excess acid, but an initial increase is not the primary hallmark of respiratory acidosis itself. *pH* - **pH** measures the overall acidity or alkalinity of the blood. In acidosis, the **pH** decreases. - While a low pH is present in acidosis, it is a *result* of the increased **PaCO2**, not the primary driver for recognizing respiratory acidosis.

Q: What is the most likely cause of metabolic acidosis in a patient with a pH of 7.2, HCO3- levels of 10 or 12, and pCO2 of 35 mmHg?

Loss of bicarbonate by the kidneys. ***Loss of bicarbonate by the kidneys*** - A pH of 7.2 (acidosis) and low **HCO3- (10-12 mEq/L)**, with a near-normal **pCO2 (35 mmHg)**, indicates an uncompensated **metabolic acidosis** [1], [3]. - Renal tubular acidosis (RTA), particularly **Type 2 RTA**, is characterized by impaired bicarbonate reabsorption by the proximal renal tubules, leading to excessive loss of bicarbonate in the urine, resulting in metabolic acidosis [2]. *Increased potassium excretion by the kidneys* - While certain renal conditions can lead to **potassium wasting**, this directly contributes to **hypokalemia**, not primarily to the observed metabolic acidosis. - While some **RTAs (Type 1 and Type 2) are associated with hypokalemia**, the direct cause of acidosis is bicarbonate loss or impaired acid excretion [2]. *Increased hydrogen ion excretion by the kidneys* - **Increased hydrogen ion excretion** would typically help correct acidosis, not cause it. - This process is crucial for acid-base balance, and its effective functioning would lead to **alkalosis** or normalization of pH, not acidosis. *Increased carbon dioxide expiration by the lungs* - **Increased CO2 expiration** would lead to a decrease in **pCO2**, which is a **respiratory alkalosis** or a compensatory mechanism for metabolic acidosis, not the cause of the acidosis itself [1]. - The given pCO2 of 35 mmHg is within or near the normal range, indicating the lungs are either not compensating fully or not the primary cause of the acidosis.

Q: Which of the following is considered the most important intracellular buffer in human physiology?

Phosphate buffer. ***Phosphate buffer*** - The **phosphate buffer system (H₂PO₄⁻/HPO₄²⁻)** is the most important intracellular buffer due to relatively high concentrations of inorganic phosphates within cells - The pKa₂ of approximately **6.8 is close to intracellular pH** (~7.0-7.2), providing optimal buffering capacity - Plays a crucial role in buffering acids and bases generated by metabolic processes within cells and is also important in renal tubular buffering *Albumin protein* - **Proteins**, including albumin, are important **extracellular buffers** in plasma due to their abundant ionizable amino acid residues - While proteins do contribute to intracellular buffering (especially hemoglobin in RBCs), the **phosphate system is more significant** for general intracellular pH regulation *Ammonia buffer* - The **ammonia buffer system (NH₃/NH₄⁺)** is primarily a **renal buffer system** that plays a crucial role in acid excretion via urine - It is not considered the primary intracellular buffer for metabolic acid-base balance within cells *Bicarbonate buffer* - The **bicarbonate buffer system (HCO₃⁻/H₂CO₃)** is the **most important extracellular buffer system**, critical for maintaining blood pH - Although present intracellularly, its buffering capacity is less prominent than phosphate within cells due to lower intracellular bicarbonate concentration and its pKa of 6.1 being further from intracellular pH

Q: Metabolic change in severe vomiting is

Metabolic alkalosis due to loss of gastric acid. **Metabolic alkalosis due to loss of gastric acid** - Severe vomiting leads to the loss of **hydrochloric acid (HCl)** from the stomach, causing an increase in plasma bicarbonate and subsequently **metabolic alkalosis** [1], [3]. - This condition is often accompanied by **hypokalemia** due to renal compensation and increased aldosterone activity [1]. *Respiratory alkalosis due to hyperventilation* - **Hyperventilation** causes a decrease in arterial partial pressure of carbon dioxide (PaCO2), leading to **respiratory alkalosis** [2]. - While vomiting can sometimes cause mild hyperventilation due to discomfort, the primary metabolic derangement from severe vomiting is related to acid loss, not CO2 expulsion [4]. *Hyperkalemia due to renal dysfunction* - **Hyperkalemia** is an elevated potassium level, typically associated with **renal failure** or certain medications. - In severe vomiting, the loss of gastric fluid and subsequent fluid shifts tend to cause **hypokalemia** as the kidneys try to conserve hydrogen and excrete potassium [1]. *Metabolic acidosis due to renal failure* - **Metabolic acidosis** is characterized by a decrease in blood pH and bicarbonate, often caused by the accumulation of acids or loss of bicarbonate [3]. - **Renal failure** is a common cause of metabolic acidosis due to impaired acid excretion, which is not the primary issue in severe vomiting.

Question 1

A 40-year-old male presents with hyperventilation and dizziness. Which acid-base disturbance is he most likely experiencing?

Accepted Answer

Respiratory alkalosis

Answer

Metabolic acidosis

Answer

Metabolic alkalosis

Answer

Respiratory acidosis

Question 2

In a patient with severe diarrhea, what is the expected change in the blood acid-base balance?

Accepted Answer

Metabolic acidosis

Answer

Metabolic alkalosis

Answer

Respiratory alkalosis

Answer

Respiratory acidosis

Question 3

Which buffer system is most effective in regulating the pH of blood during exercise?

Accepted Answer

Hemoglobin buffer

Answer

Phosphate buffer

Answer

Protein buffer

Answer

Carbonic acid-bicarbonate buffer

Question 4

A patient with chronic obstructive pulmonary disease (COPD) exhibits signs of respiratory acidosis. What is the primary cause?

Accepted Answer

Increased carbon dioxide retention

Answer

Decreased carbon dioxide retention

Answer

Decreased bicarbonate reabsorption

Answer

Increased bicarbonate reabsorption

Question 5

A patient with severe burns is at risk for metabolic acidosis. Which buffer system is primarily involved in compensating for this condition?

Accepted Answer

Bicarbonate buffer system

Answer

Phosphate buffer system

Answer

Protein buffer system

Answer

Ammonia buffer system

Question 6

A patient with diabetic ketoacidosis (DKA) presents with Kussmaul breathing. Which compensatory mechanism is he demonstrating?

Accepted Answer

Increased CO2 elimination

Answer

Increased CO2 retention

Answer

Decreased bicarbonate reabsorption

Answer

Increased bicarbonate excretion

Question 7

Respiratory acidosis is recognized primarily by an increase in which of the following?

Accepted Answer

PaCO2

Answer

pH

Answer

HCO3-

Answer

PaO2

Question 8

What is the most likely cause of metabolic acidosis in a patient with a pH of 7.2, HCO3- levels of 10 or 12, and pCO2 of 35 mmHg?

Accepted Answer

Loss of bicarbonate by the kidneys

Answer

Increased potassium excretion by the kidneys

Answer

Increased hydrogen ion excretion by the kidneys

Answer

Increased carbon dioxide expiration by the lungs

Question 9

Which of the following is considered the most important intracellular buffer in human physiology?

Accepted Answer

Phosphate buffer

Answer

Albumin protein

Answer

Ammonia buffer

Answer

Bicarbonate buffer

Question 10

Metabolic change in severe vomiting is

Accepted Answer

Metabolic alkalosis due to loss of gastric acid

Answer

Respiratory alkalosis due to hyperventilation

Answer

Hyperkalemia due to renal dysfunction

Answer

Metabolic acidosis due to renal failure

Acid-Base Balance — MCQs

Acid-Base Balance — MCQs

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