Chapter 18 Analysis and Monitoring of Gas Exchange

Chapter 18  Analysis and Monitoring of Gas Exchange

Complete Chapter Questions And Answers
 

Sample Questions

MULTIPLE CHOICE

1. Which of the following is false about invasive versus noninvasive monitoring?
a.
Invasive procedures require insertion of a device into the body.
b.
Laboratory analysis of gas exchange is usually noninvasive in nature.
c.
Physiologic monitoring can be either invasive or noninvasive.
d.
Invasive procedures provide more accurate data but carry greater risks.

ANS: B
Invasive procedures require the insertion of a sensor or collection device into the body, whereas noninvasive monitoring is a means of gathering data externally. Because laboratory analysis of gas exchange requires blood samples, it is usually considered invasive. On the other hand, monitoring can be either invasive or noninvasive. In general, invasive procedures tend to provide more accurate data than do noninvasive methods but carry greater risk.

DIF: Recall REF: p. 382 OBJ: 1

2. Under ideal conditions, electrochemical oxygen (O2) analyzers have approximately what degree of accuracy?
a.
1%
b.
2%
c.
3%
d.
4%

ANS: B
There are two common types of electrochemical oxygen analyzers: (1) the polarographic (Clark) electrode and (2) the galvanic fuel cell. Under ideal conditions of temperature, pressure, and relative humidity, both types are accurate to within ±2% of the actual concentration.

DIF: Recall REF: p. 382 OBJ: 2

3. How does the Clark polarographic O2 electrode function?
a.
It measures the magnetic properties of O2 versus N2.
b.
It measures the electrical potential across a Wheatstone bridge.
c.
It uses O2 to produce a reduction–oxidation reaction.
d.
It measures the comparative cooling effect on a heated wire.

ANS: C
This system typically consists of a platinum cathode and a silver−silver chloride anode (Figure 18-1). Oxygen molecules diffuse through the sensor membrane into the electrolyte, where a polarizing voltage causes electron flow between the anode and cathode. While silver is oxidized at the anode, the flow of electrons reduces oxygen (and water) to hydroxyl ions (OH−) at the cathode. The more O2 molecules that are reduced, the greater is the electron flow is across the poles (current). The resulting change in current is proportional to the PO2, with its value displayed on a galvanometer, calibrated in percent oxygen.

DIF: Recall REF: p. 384 OBJ: 2

4. Which of the following is FALSE about the galvanic fuel cell O2 analyzer?
a.
It actually measures the PO2 and not the O2 concentration.
b.
It requires an external power source (alternating current line or batteries).
c.
It has a slower response time than the Clark electrode.
d.
Its fuel cells deplete and must be periodically replaced.

ANS: B
Most galvanic fuel cells use a gold anode and a lead cathode. Unlike the Clark electrode, current flow across these poles is generated by the chemical reaction itself. Thus, unless accessories such as alarms are included, a galvanic cell needs no external power. Unfortunately, this means that galvanic cells respond more slowly than do Clark electrodes, sometimes taking as long as 60 seconds.

DIF: Recall REF: p. 383 OBJ: 2

5. While checking a polarographic (Clark) electrode, you determine that the device fails to read 100% when exposed to pure O2. Which of the following actions would be the proper first step?
a.
Check the silica crystals.
b.
Send the device out for repair.
c.
Replace the analyzer’s batteries.
d.
Change the analyzer’s fuel cell.

ANS: C
Because a low battery condition is so common with Clark electrode systems, the first step in troubleshooting is to replace the batteries.

DIF: Recall REF: p. 383 OBJ: 3