Cairo: Pilbeam's Mechanical Ventilation, 6th Edition

Chapter 03: How a Breath Is Delivered

WorkBook Answer Key

Key Terms Crossword Puzzle

Chapter Review Questions
1. Muscle pressure + Ventilator pressure = (Volume/compliance) + (Resistance/flow)
2. (a) Contraction of the respiratory muscles (Pmus) during a spontaneous breath, (b) generated by the ventilator (Pvent) during a mechanical breath
(a) Muscle pressure and (b) ventilator pressure
3. The left side of the equation of motion represents the two forces that can provide ventilation: the patient’s muscles and the ventilator. The result of this work is represented on the right side of the equation as flow and volume delivery. In this equation, both compliance and resistance stay constant during any single breath. The right side of the equation represents the impedance that must be overcome to deliver a breath. This impedance is produced by the interaction between lung and thoracic compliance and the pressure within the thorax, as well as the resistance to the flow of gases through the conductive airways.
4. (a) The structural design of the ventilator and (b) the ventilator mode set by the clinician
5. (a) Pressure-targeted ventilation and (b) pressure ventilation
6. (a) Volume-targeted ventilation and (b) volume ventilation
7. (a) Pressure, (b) volume, (c) flow, and (d) time
8. The control variable
9. Volume and flow vary based on the patient’s lung characteristics during pressure-controlled ventilation.
10. It will increase.
11. During volume-controlled breathing, the volume and flow waveforms remain unchanged, but the pressure waveform varies with changes in lung characteristics. With decreasing compliance, it will require more pressure to obtain the same tidal volume.
12 Time control
13. High-frequency jet ventilators and oscillators control time.
14. Flow = Volume change per unit of time (liters/minute or liters/second)
15. (any of the following) At the upper, or proximal airway, where the patient is connected to the ventilator, internally near where the main circuit lines connect to the ventilator, and near the exhalation valve.
16. (a) Rectangular, also called square or constant, (b) exponential, may be increasing (rising) or decreasing (decaying), (c) sinusoidal, also called sine wave, (d) ramp, available as ascending or descending (decelerating)
17. (a) Change from exhalation to inspiration, ( b) inspiration, (c) change from inspiration to exhalation, and (d) exhalation.
18. Trigger variable
19. Pressure, flow, and volume
20. Time triggering
21. Limits the value of pressure, volume, flow, or time during inspiration.
22. The cycle variable will end inspiration.
23. The baseline variable establishes the baseline during expiration before inspiration is triggered.
24. If the ventilator is too sensitive, it will trigger on its own, without the patient making an effort.
25. 1 cm H2O, 2 L/min
26. Baseline flow  Flow sensitivity = Flow sensed at exhalation by the ventilator to trigger a breath; 6 L/min  2 L/min = 4 L/min.
27. Flow triggering
28. Volume triggering occurs when the ventilator detects a small drop in volume in the patient circuit during expiratory time.
29. Time trigger
30. 3 seconds
31. 1 second
32. 5 cm H2O
33. Time trigger
34. Time trigger
35. Pressure trigger, patient initiated
36. 10 cm H2O
37. Limit or cycle. Depends on the mode and setup.
38. Assisted
39. Assisted
40. Mandatory
41. Spontaneous
42. Assisted
43. By definition, no.
44. The ventilator will alarm, pressure will be limited, and inspiration will end.
45. (any of the following) Normal pressure limit, pressure limit, high pressure limit, or upper pressure limit.
46. The maximum safety pressure should be set at 10 cm H2O above the average peak inspiratory pressure during volume or pressure ventilation.
47. 120 cm H2O
48. Most ICU ventilators measure the gas flow that has left the ventilator over a specific time and convert it to a volume reading (Flow × Inspiratory time = Tidal volume).
49. 1-3 mL of gas is lost to tubing compressibility for every 1 cm H2O that is measured by the airway pressure sensor.
50. PIP × Compressibility factor = Volume lost = 25 × 2.5 = 62.5 mL
51. (a) When the machine is volume cycling, less volume may return from the patient because of tubing compressibility, (b) system leaks.
52. The ventilator will time cycle between 3 and 5 seconds.
53. Flow cycled
54. A pressure-cycled ventilator can be used for short-term ventilation of patients with stable lung conditions, such as the postoperative patient.
55. Flow termination occurs when the flow reaches a percentage of the peak inspiratory flow.
56. No answer is given. 0.6/1 = x/60x = 36 L/min
57. During an inflation hold, the inspired volume remains in the patient’s lungs and the expiratory valve remains closed for a brief period.
58. (a) Inspiratory pause, (b) end-inspiratory pause, and (c) inspiratory hold
59. If expiratory time is reduced and there is insufficient time for full exhalation of gas to occur
60. The expiratory phase encompasses the period from the end of inspiration to the beginning of the next breath.
61. Baseline pressure
62. Positive end-expiratory pressure (PEEP)
63. High-frequency oscillatory ventilator
64. Expiratory hold (end-expiratory pause), auto-PEEP
65. Ventilator circuits, expiratory valves, and bacterial filters
66. CPAP or bilevel positive pressure
67. (a) IPAP and (b) EPAP
Critical Thinking Questions
1. Pressure
2. Pressure control, pressure support, or BiPAP
3. Flow is the trigger mechanism.
4. Flow is the cycling mechanism.
5. 1 second
6. 2 seconds
7. The trigger for “A” is time.
8. The trigger for “B” is patient (pressure).
9. The transairway pressure is 35  20 = 15 cm H2O.
10. The baseline is 5 cm H2O.
Case Studies
Case Study 1

1. The primary area of concern for this patient is hypoxemia. While receiving oxygen from a non-rebreathing mask, the patient has a PaO2 of only 42 mm Hg. The patient’s acid-base status is acceptable at this time.
2. The most appropriate type of support at this time is continuous positive airway pressure via mask with supplemental oxygen.
3. The patient is receiving mechanical ventilatory support using volume control.
4. The limit variables are volume and flow.
5. The trigger variable is patient (pressure).
6. Yes, the pressure-time curve.
7. The patient is pulling too hard to trigger the ventilator. The pressure-time curve shows that the patient has to deflect from a PEEP of +10 cm H2O down to about +3 cm H2O. That means that the machine is not sensitive enough to the patient’s effort.
8. The respiratory therapist must adjust the sensitivity to approximately 1 cm H2O below the baseline of 10 cm H2O.

Case Study 2

1. Tidal volume, ventilator rate, FIO2, baseline, flow rate, and sensitivity
2. Set the maximum safety pressure at 38 cm H2O.
3. To prevent excessive amounts of pressure from building up in the lungs
4. The maximum safety pressure, when reached, will cycle the ventilator, thereby stopping the ventilator from delivering all the set volume. The maximum safety pressure may be reached because of problems such as excessive mucus, bronchospasm, tension pneumothorax, or stiffening lungs.
5. Loss of volume due to tubing compressibility, a leak in the system, or air trapping
NBRC-Style Questions
1. B
2. C
3. A
4. D
5. B
6. C
7. A
8. B
9. B
10. A
11. A
12. B
13. C
14. C
15. C