Alterations in Fluids and Electrolytes and Acid-Base Balance

Reading:

Porth, C.M. (2007)  Essentials of Pathophysiology:  Selected portions of chapters 6.

Purposes:

Identify the general functions of electrolytes in homeostasis and recognize the significance of different electrolyte concentrations in different body fluid compartments;

Discuss the effects of excess and deficits of key electrolytes;

Understand the importance of maintaining the pH of body fluids within a narrow range;

Identify and contrast the principal buffer systems which minimize changes in body fluid pH;

Describe the four main acid-base imbalances (respiratory acidosis, metabolic acidosis, respiratory alkalosis, metabolic alkalosis) and the ways the body compensates;

Identify selected clinical conditions which predispose the individual to acid-base imbalance;

Comprehend the difference between compensation and correction of acid-base disturbances.

Reading Guide:

Again, as in the last module, to help you determine which parts of the chapters are to be emphasized, refer to the written syllabus for guidance on included topics and for page references to the textbook.. 

Also, review the textbook website at http://thePoint.LWW.com/PorthEssentials for links to chapter-related resources with animations and chapter review questions.

Terminology:

Study Questions:

1. Why would it be unwise to give an individual with hyperkalemia an acidic solution intravenously? (What is the relationship between potassium and acid-base balance)? What effect does acidosis or alkalosis have on serum potassium levels?
2. Which of two mechanisms (ADH and renin-angiotensin-aldosterone) is the primary control of serum sodium levels and which control H₂O levels?
3. Can you think of an example where hypernatremia (true sodium excess) would occur without water excess occurring as well?
4. Why can insulin be used to treat hyperkalemia?
5. What substance is formed by the combination of CO₂ and water? Does this substance contribute to the acidity or alkalinity of the plasma?
6. How does a buffer work? Where are the buffer systems in the body? Can you name several?
7. What is the normal ratio of the carbonic acid/bicarbonate buffer system pair? Which of the two compounds is the larger if pH is normal?
8. In acidosis and alkalosis, what are the compensatory mechanism which restore pH toward normal? Which of these is fastest (do the lungs or the kidneys react most quickly to try to correct an acid/base imbalance)? Which is most complete?
9. What is the relationship between ionized calcium and acid-base balance? Why does someone with alkalosis tend toward tetany and convulsions?
10. In interpreting blood gases and pH, ask yourself the following questions:
    Is the pO₂ above or below 50? The gives some idea of the normalcy of respiratory function.
    Is the pH in the range of acidosis or alkalosis?
    If abnormal, is pH compensated (between 7.35 and 7.45)?
    Is pCO₂ high or low (normal = 38-42 mm Hg)?
11. What are the normal blood values for sodium, potassium, calcium, chloride, pCO₂, bicarbonate?
12. What effect does hypokalemia have on neuromuscular excitability? What effect does hyperkalemia have on neuromuscular excitability?
13. What effect do hypernatremia and hyponatremia have on blood pressure?
14. What are Chvostek's and Trousseau's signs? Would they be positive in a condition of hypocalcemia or hypercalcemia?
15. Would alveolar hypoventilation be more likely to cause respiratory acidosis or alkalosis?

Exercises:

A. First indicate whether the answer is True or False for Module 6 Exercise. To challenge yourself a little more, if the answer is false, think about what is needed to correct the statement to make it true. Exercise 6 is one of the extra-credit opportunities. Go to Angel at https://elearning.kumc.edu/angel/frames.aspx to complete Exercise 6.

This next exercise is just for fun!

B. Your syllabus lists a table much like the following one. Without referring to that table, test yourself by carefully placing your cursor right on the appropriate sign in the parentheses for each of the cells below for PH, Problem, and Compensation to fit the acid-base abnormality listed in the first column. (When you put your cursor on a sign, a box will pop up to tell you if your answer is correct or incorrect. The box will disappear when you move your cursor away from a sign. Also, if you put your cursor on a correct sign for more than 1 time, the score will be either unavailable or inaccurate. So please be careful moving your cursor around. To do this exercise again, be sure to click the "Reset " button first.)

 Acid-Base Summary 

Category	pH	Problem	Compensation
Metabolic Acidosis	( or ) 7.35	( or ) HCO3-	( or ) pCO2
Metabolic Alkalosis	( or ) 7.45	( or ) HCO3-	( or ) pCO2
Respiratory Acidosis	( or ) 7.35	( or ) pCO2	( or ) HCO3-
Respiratory Alkalosis	( or ) 7.45	( or ) pCO2	( or ) HCO3-

Discussion Group:

The deadline for participation in the discussion group for this module is midnight, Sunday, Oct. 22nd.

This module should be finished by Oct. 20 to give you time to study for the exam on Oct. 26, 2006, from 3-5 p.m. in 1050 SON.