Ch. 26 Fluid, Electrolyte, and Acid-Base Balance

Marieb - Human Anatomy & Physiology 11th Edition

Marieb, Hoehn11th EditionHuman Anatomy & PhysiologyISBN: 9780136874034Not the one you use?Change textbook

Marieb, Hoehn 11th Edition

Ch. 26 Fluid, Electrolyte, and Acid-Base Balance

Problem 21

Chapter 26, 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

Verified step by step guidance

Step 1: Analyze the pH value to determine if the condition is acidosis or alkalosis. A pH less than 7.35 indicates acidosis, while a pH greater than 7.45 indicates alkalosis.

Step 2: Compare the Pco₂ and Hco₃⁻ values to normal ranges (Pco₂ normal: 35-45 mm Hg; Hco₃⁻ normal: 22-26 mEq/L) to identify whether the cause is respiratory or metabolic. If Pco₂ is abnormal and correlates with pH changes, the cause is respiratory. If Hco₃⁻ is abnormal and correlates with pH changes, the cause is metabolic.

Step 3: Determine if the condition is compensated by checking if the non-primary parameter (either Pco₂ or Hco₃⁻) is moving in the opposite direction to partially correct the pH. Compensation means the body is attempting to restore normal pH by adjusting the other parameter.

Step 4: For each problem, summarize the acid-base imbalance (acidosis or alkalosis), specify whether it is metabolic or respiratory based on the values, and state if compensation is present or absent.

Step 5: Identify at least one possible cause for each imbalance. For example, respiratory alkalosis can be caused by hyperventilation, metabolic acidosis by diabetic ketoacidosis, respiratory acidosis by hypoventilation, and metabolic alkalosis by excessive vomiting.

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Key Concepts

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

Acid-Base Imbalance (Acidosis and Alkalosis)

Acid-base imbalances occur when the blood pH deviates from the normal range (7.35-7.45). Acidosis refers to a pH below 7.35, indicating excess acidity, while alkalosis is a pH above 7.45, indicating excess alkalinity. Identifying whether the imbalance is acidosis or alkalosis is the first step in diagnosis.

Metabolic vs Respiratory Causes

Acid-base imbalances can originate from metabolic or respiratory causes. Metabolic imbalances involve changes in bicarbonate (HCO₃⁻) levels due to kidney function or metabolic processes, while respiratory imbalances involve changes in carbon dioxide (Pco₂) levels due to lung function. Differentiating these helps pinpoint the underlying cause.

Compensation Mechanisms

The body attempts to restore normal pH through compensation: respiratory compensation adjusts breathing to change Pco₂, and renal compensation adjusts HCO₃⁻ reabsorption or excretion. Determining if compensation is occurring involves checking if the non-primary parameter is altered in the opposite direction to partially correct pH.

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Related Practice

Textbook Question

Mr. Jessup, a 55-year-old man, is operated on for a cerebral tumor. About a month later, he appears at his physician's office complaining of excessive thirst. He claims to have been drinking about 20 liters of water daily for the past week and says he has been voiding nearly continuously. A urine sample is collected and its specific gravity is reported as 1.001.

What is your diagnosis of Mr. Jessup's problem?

What connection might exist between his previous surgery and his present problem?

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Textbook Question

Explain how the chemical buffer systems resist changes in pH.

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Textbook Question

Explain how emphysema and congestive heart failure can lead to acid-base imbalance.

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Textbook Question

Explain the relationship of the following to renal secretion and excretion of hydrogen ions:

Plasma carbon dioxide levels

Phosphate

Sodium bicarbonate reabsorption

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Textbook Question

During a routine medical checkup, Shelby, a 26-year-old physiotherapy student, is surprised to hear that her blood pressure is 180/110. She also has a rumbling systolic and diastolic abdominal bruit (murmur) that is loudest at the mid-epigastric area. Her physician suspects renal artery stenosis (narrowing). She orders an abdominal ultrasound and renal artery arteriography, which confirm that Shelby has a small right kidney and the distal part of her right renal artery is narrowed by more than 70%. Her physician prescribes diuretics and calcium channel blockers as temporary measures, and refers Shelby to a cardiovascular surgeon. Explain the connection between Shelby's renal artery stenosis and her hypertension. Why is her right kidney smaller than her left? What would you expect Shelby's blood levels of K⁺, Na⁺, aldosterone, angiotensin II, and renin to be?

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Textbook Question

Mrs. Bush, a 70-year-old woman, is admitted to the hospital. Her history states that she has been suffering from diarrhea for three weeks. On admission, she complains of severe fatigue and muscle weakness. A blood chemistry study yields the following information: Na⁺ 142 mEq/L; K⁺ 1.5 mEq/L; Cl⁻ 92 mEq/L; Pco₂ 32 mm Hg.

Which electrolytes are within normal limits? Which are so abnormal that the patient has a medical emergency?

Which of the following represents the greatest danger to Mrs. Bush?

a. A fall due to her muscular weakness

b. Edema

c. Cardiac arrhythmia and cardiac arrest.

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