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Ch. 26 Fluid, Electrolyte, and Acid-Base Balance
Chapter 25, Problem 21

For each of the following sets of blood values, name the acid-base imbalance (acidosis or alkalosis), determine its cause (metabolic or respiratory), decide whether the condition is being compensated, and cite at least one possible cause of the imbalance. Problem 1: pH 7.63; Pco₂ 19 mm Hg; Hco₃⁻ 19.5 mEq/L Problem 2: pH 7.22; Pco₂ 30 mm Hg; Hco₃⁻ 12.0 mEq/L

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1
Step 1: Identify the normal ranges for pH, Pco₂, and Hco₃⁻. Normal pH is 7.35-7.45, normal Pco₂ is 35-45 mm Hg, and normal Hco₃⁻ is 22-26 mEq/L.
Step 2: Analyze Problem 1. The pH is 7.63, which is above the normal range, indicating alkalosis. Pco₂ is 19 mm Hg, which is below normal, suggesting a respiratory cause. Hco₃⁻ is 19.5 mEq/L, which is below normal, indicating partial compensation.
Step 3: Determine the type of alkalosis in Problem 1. Since Pco₂ is low, it suggests respiratory alkalosis. The low Hco₃⁻ indicates the kidneys are trying to compensate by excreting bicarbonate.
Step 4: Analyze Problem 2. The pH is 7.22, which is below the normal range, indicating acidosis. Pco₂ is 30 mm Hg, which is below normal, suggesting a metabolic cause. Hco₃⁻ is 12.0 mEq/L, which is below normal, confirming metabolic acidosis.
Step 5: Determine the type of acidosis in Problem 2. Since Hco₃⁻ is low, it suggests metabolic acidosis. The low Pco₂ indicates respiratory compensation by hyperventilation to expel CO₂.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Acid-Base Imbalance

Acid-base imbalance refers to the disturbance in the normal pH level of the blood, which is typically maintained between 7.35 and 7.45. An imbalance can manifest as acidosis (pH < 7.35) or alkalosis (pH > 7.45). Understanding the type of imbalance is crucial for diagnosing the underlying cause and determining appropriate treatment.
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Compensation Mechanisms

Compensation mechanisms are physiological responses that help restore normal pH levels in the body. The respiratory system can adjust carbon dioxide levels through changes in breathing rate, while the kidneys can modify bicarbonate and hydrogen ion excretion. Identifying whether compensation is occurring helps assess the severity and duration of the acid-base disturbance.
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Causes of Imbalance

The causes of acid-base imbalances can be classified as metabolic or respiratory. Metabolic causes involve changes in bicarbonate levels or metabolic processes, while respiratory causes relate to carbon dioxide retention or loss. Recognizing the specific cause is essential for effective management and treatment of the imbalance.
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