Ch. 10 Test, Assessment of Respiratory Function

Question 1

1. A pulse oximeter differentiates oxyhemoglobin from deoxygenated hemoglobin by which of the following methods?
   a. Relating cyclical changes in light transmission through the sampling site.
   b. Shining and comparing two wavelengths of light through the sampling site.
   c. Direct measurement by a heated polarographic electrode applied to the skin.
   d. Using a color sensing device that absorbs one wavelength of light through the skin.

Answer 1

ANS: B

A pulse oximeter uses spectrophotometry to differentiate between oxyhemoglobin and deoxygenated hemoglobin. Two wavelengths of light (660 and 940 nm) are shined through a sample site. Oxyhemoglobin absorbs more light at 940 nm (infrared [IR] light) than does deoxygenated hemoglobin. Deoxyhemoglobin absorbs more light at 660 nm. The use of cyclical changes in light transmission measured at the sampling site is the method to determine the pulse rate with a pulse oximeter. A heated polarographic electrode is used for transcutaneous partial pressure of oxygen (PtcO2) measurements. A color sensing device is used to detect the amount of carbon dioxide in exhaled gas.

Question 2

An arterial blood gas should be done to confirm pulse oximetry findings less than a minimum of _____________.

a. 60%
b. 70%
c. 80%
d. 90%

Answer 2

ANS: C

When a patient’s oxygen saturation measured by pulse oximeter (SpO2) is less than 80% an arterial blood gas should be drawn to confirm the patient’s oxygenation status because a pulse oximeter is generally accurate for oxygen saturations greater than 80%.

Question 3

A pulse oximeter reading will be most accurate when used with a patient in which of the following situations?

a. An intensive care unit patient with hyperbilirubinemia
b. A hypotensive patient receiving peripheral vasoconstrictors
c. An emergency department patient with evidence of smoke inhalation
d. An open heart patient receiving extracorporeal membrane oxygenation

Answer 3

ANS: A

Hyperbilirubinemia does not appear to affect pulse oximetry measurements as do low perfusion states, which are caused by the use of peripheral vasoconstrictors or extracorporeal membrane oxygenation (ECMO). Carbon monoxide poisoning will lead to an overestimation of oxygen saturation measured by pulse oximeter (SpO2).

Question 4

A patient arrives in the emergency department via ambulance following rescue from a house fire. The instrument that would be most appropriate to assist the respiratory therapist in assessing this patient’s oxygenation status is which of the following?

a. Capnograph
b. Pulse oximeter
c. Calorimeter
d. CO-oximeter

Answer 4

ANS: D

Laboratory CO-oximeters measure four types of hemoglobin: oxyhemoglobin (O2Hb), deoxygenated hemoglobin (HHb), carboxyhemoglobin (COHb), and methemoglobin (MetHb). This is beneficial for patients who are suffering from smoke inhalation. The CO-oximeter provides the actual O2Hb and the COHb. Carbon monoxide produces an erroneously high oxygen saturation measured by pulse oximeter (SpO2). Therefore, if smoke inhalation is suspected, a CO-oximeter should be used to evaluate the oxygen saturation. Capnography is the measurement of carbon dioxide concentrations in exhaled gases and is used to assess proper airway placement. Calorimetry allows the clinician to estimate energy expenditure from measurements of oxygen consumption (O2) and carbon dioxide production (CO2). This measurement may be useful when weaning a patient from mechanical ventilation.

Question 5

While trying to use a finger probe to assess a patient’s oxygenation status, the respiratory therapist finds that the pulse rate and the ECG monitor heart rate are not consistent and the oxygen saturation measured by pulse oximeter (SpO2) reading is blank. The patient is awake, alert, and in no obvious respiratory distress. The respiratory therapist should first take which of the following actions?

1. Change the probe site.
2. Draw an arterial blood gas.
3. Adjust the probe position on the finger.
4. Remove the probe, and perform a capillary refill test.
   a. 1 and 2 only
   b. 2 and 3 only
   c. 3 and 4 only
   d. 1 and 4 only

Answer 5

ANS: C

The fact that the patient is awake, alert, and in no respiratory distress decreases the likelihood that the problem is with the patient. Therefore, the first action in this case should not be to draw an arterial blood gas (ABG). In cases where the pulse oximeter cannot identify a pulsatile signal, the oxygen saturation measured by pulse oximeter (SpO2) reading may not be present. This could be alleviated by adjusting the probe position on the finger. Absent SpO2 readings could also be due to low perfusion states. Performing a capillary refill test on the finger being used for the probe would show whether or not the finger has adequate blood flow. If this is true, the next step would be to change the site.

Question 6

Pulse oximetry is most useful in which of the following situations?

a. Determining when to extubate an adult
b. Prescribing oxygen therapy for neonates
c. Monitoring patients undergoing chest physical therapy
d. Establishing initial oxygen necessity for home care patients

Answer 6

ANS: C

The oxygen status of a patient being considered for extubation needs to be assessed by an arterial blood gas, not by pulse oximetry, because not only does the patient’s oxygen status need assessment, but the acid-base balance does as well. Pulse oximetry is not used as a basis for prescribing oxygen therapy in neonates. Neonatologists prefer to base oxygen therapy decisions on arterial partial pressure of oxygen (PaO2) rather than oxygen saturation. Pulse oximetry is useful for monitoring the oxygen status of patients undergoing chest physical therapy because it gives immediate results and is used for continuous monitoring. Pulse oximetry may not be as useful in prescribing oxygen therapy for home care patients.

Question 7

The respiratory therapist has just stopped postural drainage for a 24-year-old patient with cystic fibrosis because of shortness of breath and slight cyanosis in the “head-down” position. The respiratory therapist should recommend which of the following adjustments to therapy?

a. Continue postural drainage and monitor patient with capnography.
b. Use only upright or flat postural drainage positions and draw an arterial blood gas (ABG).
c. Administer oxygen via nasal cannula and monitor with pulse oximetry.
d. Use a transcutaneous partial pressure of oxygen (PtcO2) monitor to assess the extent of hypoxemia.

Answer 7

ANS: C

The presence of slight cyanosis and shortness of breath in the “head-down” position is indicative of hypoxemia. The respiratory therapist should administer supplemental oxygen via nasal cannula (possibly 1-2 L/min) and monitor the patient with a continuous pulse oximetry. Capnography is not useful in detecting hypoxemia. Using flat postural drainage positions where the head is not lower than the shoulders has not been proven to be effective.

Question 8

A patient receiving mechanical ventilation is being continuously monitored for oxygen saturation measured by pulse oximeter (SpO2) for the past 48 hours. When initially applied, the SpO2 and the arterial oxygen saturation (SaO2), as well as the pulse on the pulse oximeter, ECG, and manual pulse, were consistent. During clinical rounds, the respiratory therapist notices that although the probe is appropriately placed and capillary refill is normal, the SpO2 reading is down to 90% from 95%. The most appropriate immediate action is to do which of the following?

a. Replace the probe.
b. Reposition the patient.
c. Draw an arterial blood gas.
d. Move the probe to a different site.

Answer 8

ANS: C

The oxygen saturation measured by pulse oximeter (SpO2) has dropped from 95% to 90%. Since the SpO2 and arterial oxygen saturation (SaO2) previously correlated, this situation could mean that the patient is becoming hypoxemic. The probe is appropriately placed, so changing sites is not appropriate. The patient has already been checked for and has adequate circulation to the site of the probe, so moving the probe to a site with more perfusion is not appropriate. Therefore, the patient needs to have an arterial blood gas to ascertain the SaO2 and partial pressure of oxygen (PaO2).

Question 9

A patient in the intensive care unit is receiving mechanical ventilation, has a pulmonary artery catheter in place, and is being monitored continuously with a capnometer. The patient’s arterial partial pressure of carbon dioxide (PaCO2) is 41 mm Hg and the partial pressure of end-tidal carbon dioxide (PetCO2) is 36 mm Hg. There is a sudden decrease in the PetCO2 to 18 mm Hg causing an alarm to sound. The most likely cause of this development is which of the following?

a. Hypovolemia
b. Apneic episode
c. Pulmonary embolism
d. Increased cardiac output

Answer 9

ANS: C

Pulmonary embolism will cause a decrease in blood flow to the lungs. This increases alveolar dead space and leads to a decrease in the partial pressure of end-tidal carbon dioxide (PetCO2). Hypovolemia would also cause a decrease in the PetCO2, but it would not occur as suddenly as it did in this situation. The fact that the patient has an indwelling pulmonary artery catheter increases the risk of developing a pulmonary embolism, which often will have a quick onset. An apneic episode would have increased the PetCO2. An increased cardiac output would increase the PetCO2 because increases in cardiac output result in better perfusion of the alveoli and a rise in PetCO2.

Question 10

The capnogram in the figure is indicative of which of the following conditions?

a. Chronic obstructive pulmonary disease (COPD)
b. Cardiac arrest
c. Hyperventilation
d. Pulmonary embolism

Answer 10

ANS: A

Phase 3 becomes indistinguishable when physiological dead space increases, as in chronic obstructive pulmonary disease (COPD), and causes the capnogram to appear as it does in the figure. A cardiac arrest would lower the graph line to zero. Hyperventilation will decrease the alveolar plateau, but its shape would remain the same as a normal capnogram. A pulmonary embolism would also cause a drop in the alveolar plateau.

Question 11

For a given minute ventilation, partial pressure of end-tidal carbon dioxide (PetCO2) is a function of which of the following?

1. Metabolic rate
2. Cardiac output
3. Alveolar dead space
4. Physiologic shunt
   a. 1 and 3 only
   b. 1, 2, and 3 only
   c. 2, 3, and 4 only
   d. 1, 2, 3, and 4

Answer 11

ANS: B

Changes in metabolic rate cause changes in partial pressure of end-tidal carbon dioxide (PetCO2). For instance, fever and shivering increase the metabolism and increase the PetCO2. A change in cardiac output will change PetCO2 because the heart transports the blood that carries the carbon dioxide (CO2) to the lungs for elimination. Increases in cardiac output will increase PetCO2. A change in dead space ventilation will also cause changes in the PetCO2. Increasing dead space will decrease the PetCO2.

Question 12

The normal range for arterial-to-end-tidal partial pressure of carbon dioxide [P(a-et)CO2] is which of the following?

a. 2-4 mm Hg
b. 4-6 mm Hg
c. 6 -8 mm Hg
d. 8-10 mm Hg

Answer 12

ANS: B

The arterial-to-end-tidal partial pressure of carbon dioxide [P(a-et)CO2] for tidal breathing should be approximately 4-6 mm Hg.

Question 13

During shift report, the day shift respiratory therapist informs the night shift respiratory therapist about a freshly postoperative patient who is receiving full support via mechanical ventilation. At the time of the last patient-ventilator system check the patient had not awaken from anesthesia. During first round on the day shift the respiratory therapist notes the capnography shown in the figure. The most appropriate action to take would be to do which of the following?

a. Administer a bronchodilator.
b. Begin the weaning process.
c. Fix the leak in the sampling line.
d. Reinflate the ET tube cuff.

Answer 13

ANS: B

The figure shows a patient whose capnography is demonstrating spontaneous respiratory efforts during mechanical ventilation. This corresponds to the patient’s waking up from anesthesia. With all else stable, the next step would be to begin the weaning process.

Question 14

The area under the curve of a single-breath carbon dioxide (SBCO2) curve represents which of the following?

a. Tidal volume
b. Alveolar dead space
c. Physiologic dead space
d. Effective alveolar ventilation

Answer 14

ANS: D

The area under the single-breath carbon dioxide (SBCO2) curve represents alveolar volume. This is known as phase 3 on the SBCO2 curve. Phase 1 is the anatomical dead space volume. Phase 2 is a transitional phase between anatomical dead space and alveolar volume.

Question 15

The change in the single-breath carbon dioxide (CO2) curve from “A” to “B” shown in the figure may be a result of which of the following?

a. Hypervolemia
b. Decreased positive end-expiratory pressure (PEEP)
c. Increased mean airway pressure
d. Excessive bronchodilator administration

Answer 15

ANS: C

The change in the figure shows an increase in phase 1 and a decrease in phase 2 of the single-breath carbon dioxide (SBCO2) curve. An increase in phase 1 may be caused by an increase in anatomical dead space. This is possible as a result of increased airway obstruction or excessive positive end-expiratory pressure (PEEP). Therefore, answers “B” and “D” cannot be correct. A decrease in phase 2 means there is a decrease in venous return or an increase in intrathoracic pressure. This could be caused by hypovolemia or an increased intrathoracic pressure as seen with increased mean airway pressures. Therefore, answer “A” cannot be correct. Answer “C” is a measure of increased intrathoracic pressure and is the correct answer.

Question 16

A patient is receiving mechanical ventilation with a fractional inspired oxygen (FIO2) of 0.85 and a positive end-expiratory pressure (PEEP) of 5 cm H2O. His arterial partial pressure of oxygen (PaO2) is 68 mm Hg, arterial oxygen saturation (SaO2) is 88%, and partial pressure of end-tidal carbon dioxide (PetCO2) is 32 mm Hg. Over the next few minutes his PEEP is titrated resulting in the following data:

Time. 0600. 0630. 0650. 0720. 0740.

FIO2 0.85. 0.85. 0.85. 0.80. 0.80

PEEP (cm H2O). 5. 8. 10. 12. 15

SpO2 (%). 88. 88. 90. 93. 90

PetCO2 (mm Hg) 30 30 32. 34. 25

At 0740 the single-breath carbon dioxide (SBCO2) curve shifted to the right. What action should the respiratory therapist take at this time?

a. Increase the FIO2 to 0.90.
b. Reduce the set tidal volume.
c. Continue to increase the PEEP.
d. Reduce the PEEP to 12 cm H2O.

Answer 16

ANS: D

The increase in positive end-expiratory pressure (PEEP) to 15 cm H2O seems to have decreased pulmonary perfusion because of overinflation of the alveoli. This is evident by the decrease in the partial pressure of end-tidal carbon dioxide (PetCO2) to 25 mm Hg and the right shift in the single-breath carbon dioxide (SBCO2) curve. Increasing the fractional inspired oxygen (FIO2) will not address this problem. Reducing the set tidal volume will increase the PetCO2 but will not improve the pulmonary circulation. Continuing to increase the PEEP will further reduce pulmonary perfusion and cause more dead space. Reducing the PEEP back to 12 cm H2O will optimize the PEEP and reduce overinflation.

Question 17

What type of electrode is used by a transcutaneous partial pressure of oxygen (PtcO2) device?

a. Galvanic
b. Polarographic
c. Paramagnetic
d. Stow-Severinghaus

Answer 17

ANS: B

A heated Clark or polarographic electrode is used to monitor the transcutaneous partial pressure of oxygen. The Stow-Severinghaus electrode is used in the measurement of transcutaneous carbon dioxide (CO2) partial pressure. Polarographic and Galvanic electrodes are types of oxygen analyzers that use chemical reactions to measure oxygen concentrations in gas mixtures.

Question 18

To properly operate, the transcutaneous partial pressure of oxygen electrode needs to be at what temperature range?

a. 32-35° C
b. 36-39° C
c. 42-45° C
d. 46-49° C

Answer 18

ANS: C

The transcutaneous partial pressure of carbon dioxide (PtcO2) electrode is heated to between 42° C and 45° C to produce capillary vasodilation below the surface of the electrode. This will improve diffusion of gases across the skin. If the PtcO2 temperature is lower than this range, the results will not be reliable. A temperature higher than this range will produce skin burns.

Question 19

A transcutaneous partial pressure of oxygen (PtcO2) reading is reliable in which of the following situations?

a. Hypothermia
b. Septic shock
c. Infant respiratory distress syndrome
d. Elevated peripheral (cutaneous) resistance

Answer 19

ANS: C

A reduction in cutaneous circulation will dramatically affect the measurement of transcutaneous partial pressure of oxygen (PtcO2). This situation is caused by hypothermia, septic shock, and elevated peripheral resistance. PtcO2 measurements have been shown to be reliable for neonates.

Question 20

What type of electrode is used by a transcutaneous partial pressure of carbon dioxide (PtcCO2) device?

a. Galvanic
b. Polarographic
c. Paramagnetic
d. Stow-Severinghaus

Answer 20

ANS: D

The Stow-Severinghaus electrode is used in the measurement of transcutaneous carbon dioxide partial pressure. A Clark or polarographic electrode is used to monitor the transcutaneous partial pressure of oxygen. Polarographic and Galvanic electrodes are types of oxygen analyzers that use chemical reactions to measure oxygen concentrations in gas mixtures.

Question 21

28. During calibration of a transcutaneous monitor the respiratory therapist notices a signal drift. The respiratory therapist should do which of the following?
    a. Increase the probe temperature.
    b. Replace the monitor and call for repair.
    c. Add more electrolyte gel to the patient’s skin.
    d. Change the electrolyte and sensor’s membrane.

Answer 21

ANS: D

A signal drift on a transcutaneous monitor should be addressed by changing the electrode and sensor’s membrane. The electrode and the sensor’s membrane should be changed weekly due to the evaporation of the electrolyte solution caused by the heating of the electrode. Increasing the probe temperature may cause patient burns if it is over 45° C. The signal drift does not necessarily mean that the monitor itself needs to be taken out of service. Adding more gel to the patient’s skin will help with gas diffusion during measurement only.

Question 22

How often should the respiratory therapist reposition the sensor of a transcutaneous monitor?

a. 30 minutes to 1 hour
b. 1-3 hours
c. 4-6 hours
d. 7-9 hours

Answer 22

ANS: C

Burns can occur because the site of measurement needs to be heated to between 42° C and 45° C. Repositioning the sensor every 4-6 hours will help avoid this problem.

Question 23

The clinical data that should be recorded when making transcutaneous measurements include which of the following?

1. Electrode temperature
2. Skin temperature
3. Probe placement
4. Fractional inspired oxygen (FIO2)
   a. 1 and 3 only
   b. 1 and 2 only
   c. 2, 3, and 4 only
   d. 1, 2, 3, and 4

Answer 23

ANS: D

The electrode temperature must be documented to ensure that the temperature stays within the range of 42-45° C. The skin temperature should be noted to assess the patient’s peripheral perfusion. The probe placement should be noted to ensure that the probe is being moved to different sites every 4-6 hours. The fractional inspired oxygen (FIO2) should be documented to determine the need for an increase or decrease in the amount of supplemental oxygen the patient is receiving.

Question 24

Components of an indirect calorimeter may include which of the following?

1. Pressure manometer
2. Pneumotachometer
3. Pressure-sensitive transducer
4. Oxygen and carbon dioxide analyzers
   a. 1 and 2 only
   b. 2 and 4 only
   c. 2, 3, and 4 only
   d. 1, 2, 3, and 4

Answer 24

ANS: B

Indirect calorimeters contain analyzers for measuring the concentration of inspired and expired gases, oxygen (O2) and carbon dioxide (CO2), pneumotachometers, turbine flowmeters, or ultrasonic vortex flowmeters to measure volume and flow, temperature-sensitive, solid-state transducers to measure barometric pressure and exhaled gas temperatures.

Question 25

A patient whose carbon dioxide (CO2) production is 390 mL/min and oxygen (O2) consumption is 375 mL/min is most likely experiencing which of the following?

a. Ketosis
b. Severe sepsis
c. Hyperventilation
d. Too much carbohydrate intake

Answer 25

ANS: C

The respiratory quotient (RQ) is the ratio of carbon dioxide (CO2) production to oxygen (O2) consumption. This patient has an RQ (390/375) of 1.04. Ketosis causes the RQ to be less than 0.7. Severe sepsis is associated with RQ levels of approximately 0.7. Hyperventilation is associated with RQ levels greater than 1.0. Pure carbohydrate RQ is 1.0.

Question 26

A mechanically ventilated patient with chronic obstructive pulmonary disease is in the process of being weaned from mechanical ventilation. A diet containing which of the following will be most beneficial to this process?

a. High protein, low fats, and carbohydrates
b. Low fats and proteins, high carbohydrates
c. Low carbohydrate with increased fats and proteins
d. Equal amounts of carbohydrates, fats, and proteins

Answer 26

ANS: C

Diets with a high percentage of carbohydrates will raise the amount of carbon dioxide (CO2) a patient produces. This will overburden a patient with limited ventilatory reserves, as with chronic obstructive pulmonary disease (COPD). The added CO2 is greater than the patient’s ventilatory capacity, and when attempting to maintain spontaneous breathing the patient will fail to wean.

Question 27

The newest types of mechanical ventilators use which of the following devices to measure airway pressures?

a. Barometers
b. Aneroid manometers
c. Electromechanical transducers
d. Variable orifice pneumotachometers

Answer 27

ANS: C

Barometers are used to measure atmospheric (barometric) pressure. Older ventilators incorporated an aneroid manometer into the ventilator circuit. Variable orifice pneumotachometers are used to measure flow. The devices that are used in the current ventilators today are the electromechanical transducers, which include piezoelectric transducers, variable capacitance transducers, and strain gauge transducers.

Question 28

Which of the following actions is indicated when a disparity exists between SpO2, SaO2, and the clinical presentation of a patient?

a. Move the probe to an alternate site to check for SpO2.
b. Replace the pulse oximeter probe.
c. Measure arterial oxygen saturation by CO-oximetry.
d. Disregarding the SaO2.

Answer 28

ANS: C

Laboratory CO-oximeters measure all four types of hemoglobin by using separate wavelengths of light to identify each species, whereas pulse oximeters use only two wavelengths to quantify the amount of O2HB and HHB present.

Question 29

To measure plateau pressure, inspiration should be held for how many seconds?

a. 1-2
b. 2-3
c. 3-4
d. 4-5

Answer 29

ANS: A

Plateau pressure requires the establishment of a period of no-flow for 1-2 seconds to allow pressure equilibration by the redistribution of the tidal volume and stress relaxation. This maneuver increases inspiratory time and if held longer than 2 seconds may cause barotrauma.

Question 30

During the application of positive end-expiratory pressure (PEEP), the monitoring of which pressure will alert the respiratory therapist specifically to alveolar overdistention?

a. Peak inspiratory pressure (PIP)
b. Plateau pressure (Pplateau)
c. Mean airway pressure
d. Transairway pressure (PTA)

Answer 30

ANS: B

The plateau pressure (Pplateau) is the pressure required to overcome only elastance. When positive end-expiratory pressure (PEEP) is applied, the alveolar pressure will rise. This will result in a higher Pplateau. If overdistention occurs the Pplateau will rise immediately. Peak inspiratory pressure (PIP) reflects the total force that must be applied to overcome both elastance and airway resistance offered by the patient-ventilator system. The mean airway pressure represents the average pressure recorded during the entire respiratory cycle. It is influenced by PIP, PEEP, inspiratory time, and total cycle time. The mean airway pressure is not a specific monitor for optimizing PEEP. The PIP will increase in the face of alveolar overdistention, but it is not specific enough to rely on as the sole measurement to identify overdistention. The transairway pressure is the difference between the PIP and the Pplateau and represents the amount of pressure needed to overcome airway resistance (all frictional forces). The transairway pressure will not reflect alveolar overdistention because when alveolar overdistention happens both the PIP and the Pplateau will rise, and the difference between the two will remain constant unless there is an unrelated change in airway resistance.

Question 31

A patient-ventilator system check reveals the following information: peak inspiratory pressure (PIP) 27 cm H2O, positive end-expiratory pressure (PEEP) 5 cm H2O, plateau pressure (Pplateau) 14 cm H2O, inspiratory time (TI) 0.75 second, and set frequency 20/minute. Calculate the mean airway pressure.

a. 6.75 cm H2O
b. 7.75 cm H2O
c. 11.75 cm H2O
d. 12.37 cm H2O

Answer 31

ANS: B

Total cycle time (TCT) = 60/frequency = 60/20 = 3 seconds. (P-macron)aw = [(PIP − PEEP) × (TI/TCT)] + PEEP = [(27 − 5) × (0.75/3)] + 5 = (22 × 0.25) + 5 = 7.75 cm H2O.

Question 32

A patient-ventilator system check reveals the following information: peak inspiratory pressure (PIP) 32 cm H2O, positive end-expiratory pressure (PEEP) 12 cm H2O, plateau pressure (Pplateau) 20 cm H2O, inspiratory time (TI) 1 second, and set frequency 12/min. Calculate the mean airway pressure.

a. 4 cm H2O
b. 8 cm H2O
c. 12 cm H2O
d. 14 cm H2O

Answer 32

ANS: D

Total cycle time (TCT) = 60/frequency = 60/12 = 5. (P-macron)aw = [(PIP − PEEP) × (TI/TCT)] + PEEP = [(32 − 12) × (1/5)] + 12 = (20 × 0.2) + 12 = 14 cm H2O.

Question 33

Calculate the dynamic compliance given the following clinical data: tidal volume 500 mL, peak inspiratory time (PIP) 35 cm H2O, plateau pressure (Pplateau) 20 cm H2O, positive end-expiratory pressure (PEEP) 5 cm H2O, and tubing compliance (CT) 2.5 mL/cm H2O.

a. 11.8 mL/cm H2O
b. 14.2 mL/cm H2O
c. 25 mL/cm H2O
d. 46.2 mL/cm H2O

Answer 33

ANS: B

Dynamic compliance = tidal volume (VT) − [(PIP − PEEP) × CT]/(PIP − PEEP) = 500 − [(35 − 5) × 2.5]/(35 − 5) = 14.2 mL/cm H2O

Question 34

Calculate dynamic compliance given the following clinical data: tidal volume 600 mL, peak inspiratory pressure (PIP) 28 cm H2O, plateau pressure (Pplateau) 15 cm H2O, positive end-expiratory pressure (PEEP) 10 cm H2O, and CT 2 mL/cm H2O.

a. 30.2 mL/cm H2O
b. 31.3 mL/cm H2O
c. 38 mL/cm H2O
d. 44.1 mL/cm H2O

Answer 34

ANS: B

Dynamic compliance = tidal volume (VT) − [(PIP − PEEP) × CT]/(PIP − PEEP) = 600 − [(28 − 10) × 2]/(28 − 10) = (600 − 36)/18 = 31.3 mL/cm H2O.

Question 35

Calculate the static compliance given the following clinical data: tidal volume 500 mL, peak inspiratory pressure (PIP) 35 cm H2O, plateau pressure (Pplateau) 25 cm H2O, positive end-expiratory pressure (PEEP) 12 cm H2O, measured unintended positive end-expiratory pressure (auto-PEEP) 3 cm H2O, and tubing compliance (CT) 2.5 mL/cm H2O.

a. 17.5 mL/cm H2O
b. 34 mL/cm H2O
c. 36 mL/cm H2O
d. 47.5 mL/cm H2O

Answer 35

ANS: D

Static compliance = tidal volume (VT) − [(Pplateau − PEEP) × CT]/(Pplateau − PEEP) = 500 − [(25 − 15) × 2.5]/25 − 15 = (500 − 25)/10 = 47.5 mL/cm H2O.

Question 36

Calculate the static compliance given the following clinical data: tidal volume 600 mL, peak inspiratory pressure (PIP) 40 cm H2O, plateau pressure (Pplateau) 30 cm H2O, positive end-expiratory pressure (PEEP) 15 cm H2O, and tubing compliance (CT) 2 mL/cm H2O.

a. 14.5 mL/cm H2O
b. 38 mL/cm H2O
c. 55 mL/cm H2O
d. 58 mL/cm H2O

Answer 36

ANS: B

Static compliance = tidal volume (VT) − [(Pplateau − PEEP) × CT]/(Pplateau − PEEP) = 600 − [(30 − 15) × 2]/30 − 15 = 570/15 = 38 mL/cm H2O.

Question 37

Calculate the airway resistance given the following clinical data: flow rate 60 L/min, peak inspiratory pressure (PIP) 42 cm H2O, plateau pressure (Pplateau) 15 cm H2O, and positive end-expiratory pressure (PEEP) 5 cm H2O.

a. 10 cm H2O/L/sec
b. 30 cm H2O/L/sec
c. 37 cm H2O/L/sec
d. 42 cm H2O/L/sec

Answer 37

ANS: B

60 L/min = 1 L/sec. Raw = (PIP − Pplateau)/(L/sec) = (42 − 15)/1 = 30 cm H2O/L/sec.

Question 38

Calculate the airway resistance given the following clinical data: flow rate 60 L/min, PIP 28 cm H2O, Pplateau 21 cm H2O, and PEEP 8 cm H2O.

a. 7 cm H2O/L/sec
b. 13 cm H2O/L/sec
c. 20 cm H2O/L/sec
d. 28 cm H2O/L/sec

Answer 38

ANS: A

60 L/min = 1 L/sec. Raw = (PIP − Pplateau)/(L/sec) = (28 − 21)/1 = 7 cm H2O/L/sec.

Question 39

The energy required to move gas through the airways and expand the thorax is known as which of the following?

a. Airway resistance
b. Dynamic compliance
c. Intrinsic work of breathing
d. Extrinsic work of breathing

Answer 39

ANS: C

Intrinsic work of breathing is a result of work done to overcome normal elastic and resistive forces and work to overcome a disease process affecting normal workloads in the lungs and thorax. Airway resistance is the opposition to airflow from nonelastic forces of the lung. Dynamic compliance is a measurement of the ease of movement of gas through the airways. The work of breathing is a result of the airway resistance, dynamic compliance, and static compliance.

Question 40

An increase in intrinsic work of breathing due to a decrease in static compliance is caused by which of the following?

a. Emphysema
b. Bronchospasm
c. Pulmonary fibrosis
d. Airway inflammation

Answer 40

ANS: C

Static compliance is influenced by the elastic characteristics of the lungs and thorax. A decrease in static compliance is due to either the lungs becoming stiffer or the thorax’s inability to stretch to accommodate volume in the lungs. Pulmonary fibrosis is a pathophysiologic condition that causes the alveoli to become stiffer due to scarring. Therefore, pulmonary fibrosis will increase a patient’s work of breathing due to decreases in the static compliance. Emphysema causes an increase in static compliance due to the loss of elastic properties of the lungs and also an increase in airway resistance because of bronchospasm, airway inflammation, and airway edema. Bronchospasm and airway inflammation lead to increased airway resistance and decreased dynamic compliance.

Question 41

Which of these two parameters does a pulse oximeter measure?

1. O2Hb
2. Hb
3. COHb
4. MetHb
   a. 1 and 2
   b. 1 and 3
   c. 2 and 3
   d. 3 and 4

Answer 41

ANS: A

Pulse oximetry provides continuous, noninvasive measurements of arterial oxygen saturation. A sensor is placed over a digit, an earlobe, the forehead or the bridge of the nose; this sensor measures the absorption of selected wavelengths of light beamed through the tissue (Fig. 10-1). For example, oxyhemoglobin can be differentiated from deoxygenated hemoglobin by shining two wavelengths of light (660 and 940 nm) through the sampling site. As Figure 10-2 illustrates, at a wavelength of 660 nm (red light), deoxygenated hemoglobin absorbs more light than oxyhemoglobin. Conversely, oxyhemoglobin absorbs more light at 940 nm (infrared light [IR]) than does deoxygenated hemoglobin.