Question

Homeostatic Case Study

Patient: Mr. Kaunda70-year-old man with respiratory problems

History: A 70-year-old man with chronic renal failure was in the hospital in serious condition recovering from a heart attack. He had just undergone "coronary angioplasty" to redilate his left coronary artery, and was thus on an "npo" diet (i.e. he was not allowed to have food or drink by mouth). He received fluid through an intravenous (IV) line.

Late one night, a new nurse who really did not understand the concept of osmolarity came into the patient's room to replace the man's empty IV bag with a new one. Misreading the physician's orders, he hooked up a fresh bag of IV fluid that was "twice-normal" saline rather than "half-normal" saline (in other words, the patient starting receiving a fluid that was four times saltier than it should have been).

This mistake was not noticed until the following morning. At that time, Mr. Kaunda had marked pitting edema around the hip region. He complained that it was difficult to breathe as well. Blood was drawn, revealing the following:

Na⁺
159 mEq / liter (Normal = 136-145 mEq / liter)
K⁺       
4.9 mEq / liter (Normal = 3.5-5.0 mEq / liter)
C1^-
100 mEq / liter (Normal = 96-106 mEq / liter)

A chest x-ray revealed interstitial edema in the lungs.

Questions:

Will the interstitial fluid increase or decrease the "osmolarity"(concentration) due to the nurse's mistake?Which electrolytes were out of the normal range and in which direction? 

Given your knowledge of osmosis, will the patient’s cells increase or decrease in size? Explain your answer. 

Can you explain why the patient may have edema? 

What is the function of aldosterone and how will the increase in osmolarity affect the blood aldosterone levels? 

Is Mr. Kaunda susceptible to hyponatrenia or hypernatremia? What possible symptoms could Mr. Kaunda develop from his present (osmotic) condition? 

Are there any other normal homeostatic mechanisms that the body has, to control the situation Kaunda faces? How might it react in this situation? 

Answer 1

1. Interstitial fluid osmolarity and volume increase because of nurse's mistake. Blood Na⁺ concentration has increased. Others are in normal range.
2. cells will decrease in size. sodium is an extracellular cation. so increased concentration of sodium outside the cell will result in loss of water from the cell by osmosis.
3. this patient can be having oedema because of multiple reasons. (Renal failure, Fluid overload, Hypertension) let me explain this. patient got extra amount of sodium through his IV line, this will cause intracellular fluid to leak out by osmosis and reach the extracellular and intravascular compartment. Increase in extracellular fluid causes oedema, increase in intravascular compartment fluid cause hypertension which causes further oedema (by increased hydrostatic pressure- read about starlings forces). Also remember that the patient had renal failure, so GFR is less, sodium excretion is less, so more fluid retention and further hypertension and oedema.
4. aldosterone is a hormone which reabsorbs sodium from kidney. since the osmolarity and blood volume in the patient is high, aldosterone levels will be low. ( because RAAS is not activated)
5. he is having hypernatremia. He could develop hypertension and severe oedema. he could also develop weakness, confusion, seizures, dry skin and mucosa etc.
6. because of hypernatremia and hypertension- there will be pressure diuresis and pressure natriuresis. there will be also release of atrial natriuretic peptide and brain natriuretic peptide in response to hypertension and hypernatremia. but given the condition of this patient (renal failure) these mechanisms may not function normally because all these mechanisms require normal kidney to function.