Answer Key to Short Answer Questions for
“The Car Accident: A Case Study in Acid-Base Balance”
1. Define the following terms contained in this case:
a. Bilateral
Bilateral - Bi = two, lateral=side (two sides / both sides)
b. Hypoventilation
Hypoventilation - hypo = below, ventilation = breathing (low breathing rate)
c. Hemothorax
Hemothorax - hemo = blood, thorax = chest (blood in the chest cavity)
d. Arrhythmias
Arrhythmias - a = without, rhythmos = rhythm (irregular heartbeat)
2. What are the normal ranges for the measurements listed in the blood and urine tests?
Aterial Blood Gas (ABG)
pH: 7.35 – 7.45
pCO2: 35 – 45
bicarbonate 22 – 26 mEq/L
Urinalysis
pH 4.5 – 8.0
3. Explain how Mr. Henderson’s rib fractures are related to the suspected hemothorax.
A hemothorax is a condition in which blood collects in the pleural cavity around the lungs. Rib fractures can be severe enough that the fracture can become displaced and produce a penetrating injury. In Mr. Henderson’s case, the broken ribs may have produced the bleeding noted on the chest X-ray.
4. Mr. Henderson’s PCO2 is elevated. Under normal conditions, what would be the PRIMARY mechanism that his body would use to reduce the amount of PCO2 in the blood? Why is this mechanism not working in this case?
The primary compensation in Mr. Henderson’s case would be hyperventilation in order to “blow off” the excess CO2. In this case, there are two conditions which are preventing this from working. Both the hemothorax and the pain associated with the blunt trauma, including the fractured ribs, is preventing normal ventilation from occurring.
5. Describe how the high PCO2 and low pH in Mr. Henderson’s blood are related in this case.
When CO2 combines with water, it produces carbonic acid. Carbonic acid releases hydrogen ions, which leads to a drop in pH.
6. Describe how the high bicarbonate in Mr. Henderson’s blood is related to the low pH in his urine.
In response to the drop in pH, the kidneys increase the reabsorption of bicarbonate, which becomes elevated in the blood. The bicarbonate acts as a buffer to help restore and stabilize blood pH. At the same time, the kidneys secrete more hydrogen ions into the urine. This leads to low urine pH. The elimination of hydrogen ions from the blood also contributes to the restoration of blood pH.
7. What type of intervention might the doctors and nurses initiate in order to address the hemothorax? Explain how this intervention will lead to changes in PCO2 and blood pH.
The blood that is collecting in the pleural cavity around the lungs can be drained (usually done by inserting a chest tube). This will help eliminate one of the issues preventing proper ventilation. If Mr. Henderson can return to a normal or even elevated respiratory rate, he will be able to remove CO2 from the blood. Less CO2 in the blood would mean a reduction in the formation of carbonic acid. This should help to restore blood pH to normal.