Case History 14: Acid-Base Physiology

Return to Main Page

Normal Levels of Substances in the Arterial Blood:

pH 7.40 + 0.05
pCO2 (partial pressure of carbon dioxide)       40 mm Hg
pO2 (partial pressure of oxygen) 90 - 100 mm Hg
Hemoglobin - O2 saturation 94 - 100 %
[HCO3-] 24 meq / liter

Vignette #1:

A 14-year-old girl with cystic fibrosis has complained of an increased cough productive of green sputum over the last week. She also complained of being increasingly short of breath, and she is noticeably wheezing on physical examination. Arterial blood was drawn and sampled, revealing the following values:

pH 7.30
pCO2 50 mm Hg
pO2 55 mm Hg
Hemoglobin - O2 saturation 45 %
[HCO3-] 24 meq / liter

Questions:

1. What causes cystic fibrosis? Describe the pathophysiologic mechanisms of the disease.

Answer

2. How would you classify this girl's acid-base status?

Answer

3. How does cystic fibrosis cause this acid-base imbalance?

Answer

4. How would the kidneys try to compensate for the girl's acid-base imbalance?

Answer

5. This girl has also had a long history of diarrhea and poor weight gain. Explain why.

Answer

6. List some other causes of this type of acid-base disturbance.

Answer


Vignette #2:

A 76-year-old man complained to his wife of severe sub-sternal chest pains that radiated down the inside of his left arm. Shortly afterward, he collapsed on the living room floor. Paramedics arriving at his house just minutes later found him unresponsive, not breathing, and without a pulse. CPR and electroconvulsive shock were required to start his heart beating again. Upon arrival at the Emergency Room, the man started to regain consciousness, complaining of severe shortness of breath (dyspnea) and continued chest pain. On physical examination, his vital signs were as follows:

Systemic blood pressure 85 mm Hg / 50 mm Hg
Heart rate 175 beats / minute
Respiratory rate 32 breaths / minute
Temperature 99.2oF

His breathing was labored, his pulses were rapid and weak everywhere, and his skin was cold and clammy. An ECG was done, revealing significant "Q" waves in most of the leads. Blood testing revealed markedly elevated creatine phosphokinase (CPK) levels of cardiac muscle origin. Arterial blood was sampled and revealed the following:

pH 7.22
pCO2 30 mm Hg
pO2 70 mm Hg
Hemoglobin - O2 saturation      88 %
[HCO3-] 2 meq / liter

Questions:

1. What is the diagnosis? What evidence supports your diagnosis?

Answer

2. How would you classify his acid-base status? What specifically caused this acid-base disturbance?

Answer

3. How has his body started to compensate for this acid-base disturbance?

Answer

4. What would his blood pH be if his body had not started compensating for the acid-base disturbance? Show your work.

Answer

5. List some other causes of this type of acid-base disturbance.

Answer

 

Vignette #3:

An elderly gentleman is in a coma after suffering a severe stroke. He is in the intensive care unit and has been placed on a ventilator. Arterial blood gas measurements from the patient reveal the following:

pH 7.50
pCO2 30 mm Hg
pO2 100 mm Hg
Hemoglobin - O2 saturation       98%
[HCO3-] 24 meq / liter

Questions:

1. How would you classify this patient's acid-base status?

Answer

2. How does this patient's hyperventilation pattern raise the pH of the blood?

Answer

3. How might the kidneys respond to this acid-base disturbance?

Answer

4. List some other causes of this type of acid-base disturbance.

Answer


Vignette #4:

A 28-year-old woman has been sick with the flu for the past week, vomiting several times every day. She is having a difficult time keeping solids and liquids down, and has become severely dehydrated. After fainting at work, she was taken to a walk-in clinic, where an IV was placed to help rehydrate her. Arterial blood was drawn first, revealing the following:

pH 7.50
pCO2 40 mm Hg
pO2 95 mm Hg
Hemoglobin - O2 saturation       97%
[HCO3-] 32 meq / liter

Questions:

1. How would you classify her acid-base disturbance?

Answer

2. Why might excessive vomiting cause her particular acid-base disturbance?

Answer

3. How would the kidneys compensate for this acid-base disturbance?

Answer

4. List some other causes of this type of acid-base disturbance.

Answer

Return to Main Page

Copyright ©2000 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use and Privacy Policy.
McGraw-Hill Higher Education is one of the many fine businesses of The McGraw-Hill Companies.

If you have a question or a problem about a specific book or product, please fill out our Product Feedback Form.
For further information about this site contact mhhe_webmaster@mcgraw-hill.com
or let us know what you think by filling out our Site Survey.

Corporate Link