Cairo: Pilbeam's Mechanical Ventilation, 6th Edition

Chapter 02: How Ventilators Work

WorkBook Answer Key

Key Terms Crossword Puzzle

Chapter Review Questions
1. Electrically powered, pneumatically powered
2. Bird Mark 7—Pneumatic power
Intermed Bear 33 Homecare Ventilator—Electric power
Life-care PLV-102—Electric power
Servoi—Combined power
LTV 800, 900, and 1000—Electric power
Bio-Med MVP-10—Pneumatic power
3. An open loop system is an unintelligent system in which the ventilator delivers what is set by the operator but does not have the ability to automatically change its operation.
4. A closed loop system is called an “intelligent system,” because it has the ability to compare a set of control variables and make adjustments to the system.
5. Gas flow into the lungs can be accomplished by using two different methods of changing the transrespiratory pressure gradient (pressure at the airway opening minus pressure at the body surface [Pawo − Pbs]). A ventilator can change the transrespiratory pressure gradient by altering either the pressure applied at the airway opening (Pawo) or the pressure around the body surface (Pbs). With positive-pressure ventilators, gas flows into the lung because the ventilator establishes a pressure gradient by generating a positive pressure at the airway opening. In contrast, a negative-pressure ventilator generates a negative pressure at the body surface that is transmitted to the pleural space and then to the alveoli.
6. User interface (control panel)
7. (a) Tidal volume, (b) rate (or frequency), (c) inspiratory time, (d) alarms, and (e) FIO2
8. (a) Flow, (b) volume, (c) pressure, and (d) time
9. Internal pneumatic circuit
10. External (pneumatic) circuit (patient circuit)
11. Single circuit
12. If the ventilator’s internal circuit allows the gas to flow directly from its power source to the patient, the machine is called a single-circuit ventilator. The source of the gas may be either externally compressed gas or an internal pressurizing source, such as a compressor. Most ICU ventilators manufactured today are classified as single-circuit ventilators.
Another type of internal pneumatic circuit ventilator is the double-circuit ventilator. In these machines, the primary power source generates a gas flow that compresses a mechanism such as a bellows or “bag-in-a-chamber.” The gas in the bellows or bag then flows to the patient.
13. (a) Main inspiratory line connecting the ventilator output to the patient connector
(b) Patient adapter or Y-connector
(c) Expiratory tubing, through which gas moves from the patient to the exhalation valve
(d) Expiratory valve, through which the patient’s exhaled gas is expelled from the expiratory tubing into the room
14. (a) Internally mounted exhalation valve
(b) Main expiratory line
(c) Main inspiratory line
(d) Patient connector (Y-connector)
15. Older ventilators used externally mounted exhalation valves. These valves had a separate exhalation valve line that powered the exhalation valve. When inspiration began, gas flowed through the main inspiratory tube and also through the separate exhalation valve line. The gas in the exhalation valve line closed the exhalation valve. During exhalation, the flow from the ventilator to the main inspiratory tube and to the exhalation valve line stopped. This allowed the patient to passively exhale through the expiratory port.
16. Inside the ventilator
17. A mechanical device that produces gas flow to the patient.
18. (a) Proportional solenoid valves and (b) digital valves with on-off configurations.
19. The proportional solenoid valve has a plunger, a valve seat, an electromagnet, a diaphragm, a spring, and two electrical contacts. When an electrical current flows, the electromagnet creates a magnetic field, which pulls the plunger and opens the valve. The amount of electrical current determines the strength of the magnetic field and thus the position of the plunger. Digital valves are grouped together, opening or closing specifically sized openings. The amount of flow can be varied, depending on which valves are open.
20. Compressor (blowers)
21. (a) Bellows, (b) pistons, (c) concertina bags, and (d) “bag-in-chamber” systems.
22. An adjustable spring is attached to the top of a bellows, where it applies pressure to force the gas mixture (air and oxygen) out of the ventilator and into the patient. The tighter the spring, the greater the force and the greater the pressure.
23. A linear drive piston uses an electrical motor connected by special gearing (rack and pinion) to a piston rod. The rod moves the piston forward, pushing volume to the patient.
24. A rotating wheel is connected to a rod and piston. An electric motor rotates the drive wheel, causing the gas to flow to the patient, slowly at first, reaching its greatest speed at midinspiration, and then tapering off at end inspiration. This pattern is called a sinusoidal waveform.
25. Today’s ventilators are microprocessor controlled, closed looped, single circuit, positive-pressure ventilators.
Critical Thinking Questions
1. Inspiratory gas flow would not go to the patient. The flow would bypass the patient, taking the course of least resistance into the room.
2. Pneumatic (or fluidic)
Case Studies
Case Study 1

DC battery powered or pneumatically powered

Case Study 2

This would be a closed loop system, because the ventilator detects the period of apnea and is able to adjust how it functions by switching to full ventilatory support.
NBRC-Style Questions
1. C
2. A
3. C
4. C
5. D
6. A
7. B
8. C
9. A
10. C