Unit 3

Question 1

Control circuit

Answer 1

A system of components which measures and directs the output of the ventilator.

Question 2

Control Variable

Answer 2

The control variable is the primary variable the ventilator manipulates to start inspiration
Pressure
Volume
Flow

Question 3

If the machine initiates the breath, the trigger variable is….

Answer 3

time

Question 4

Autocycling

Answer 4

When sensitivity is set at a level which permits exhalation dynamics to trigger the subsequent breath without patient effort

Question 5

What might cause the patient to fail to reach the trigger threshold? (5)

Answer 5

*Diameter of the airway
The smaller the airway, the more effort must be generated to overcome resistance to flow

*Inability of the patient to generate a respiratory effort
Paralysis or heavy sedation

• Secretions in the airway
• Cuffless tubes

*Leaks in the airway / ventilator circuitry
Bronchopleural fistulae

Question 6

Limit Variable

Answer 6

A limit variable is one that can reach and maintain at a preset level, but does not terminate inspiration.

Sets the upper limit

Question 7

Cycle Variable

Answer 7

This parameter terminates inspiration and begins expiration

Question 8

Flow termination graph…

Answer 8

Vertical Axis - Flow

Horizontal Axis - Time

Question 9

Mandatory Breath

Answer 9

The machine sets the start time / tidal volume

Inspiration is initiated by the machine

Question 10

Spontaneous Breath

Answer 10

The patient initiates and terminates breath delivery
Spontaneous breaths may be assisted
Breath initiation by patient but cycled by a “non patient” parameter, such as volume
Spontaneous breaths may be unassisted

Question 11

Three possible sequences of breath

Answer 11

Continuous mandatory ventilation (CMV)
All breaths are mandatory
Continuous spontaneous ventilation (CSV)
All breaths are spontaneous
Intermittent Mandatory Ventilation (IMV)
Breaths can be intermittent or mandatory
Breaths can occur separately, or they can be superimposed on each other
Example: Bi-Level or Airway Pressure Release Ventilation

Question 12

Advantages of Assist-Control (3)

Answer 12

The patient is able to alter minute ventilation by increasing/decreasing the rate / Ve

Patients are more comfortable if they can determine the level of ventilatory support

A minimal minute ventilation is delivered
When a back up rate is set

Question 13

Disadvantages of Assist-Control (2)

Answer 13

The patient is able to alter minute ventilation by increasing/decreasing the rate / Ve

Patients who are tachypneic or who trigger the ventilator rapidly can induce respiratory alkalosis via hypeventilation

Question 14

SIMV

Answer 14

SIMV is an IMV mode during which spontaneous breathing is permitted throughout a “patient sensitive” period of time between mandatory breaths

Most ventilators permit spontaneous breathing within a defined period of time (usually within 75% of the mandatory breath cycle time)

Spontaneous breaths occurring the last 25% of the breath cycle initiate mandatory breath delivery

If no spontaneous effort occurs, the subsequent breath is mandatory and is initiated at the beginning of the time cycle interval

Question 15

Pressure Support is…

Answer 15

Patient initiated
Pressure limited
Flow cycled

Question 16

Optimal PS Level… formula?

Answer 16

Most physicians order between 5-10 cm H2O as a general “rule of thumb”

PSV = (PIP – P plat) x Vi spontaneous
Ventilator inspiratory flowrate

Vi spontaneous and ventilator inspriatory flowrate reported in liters per second. PiP is the peak inspiratory pressure (during mandatory breath), Pplat is the plateau pressure

Question 17

Major disadvantage of PSV

Answer 17

VT is not constant

Question 18

NIPPV is good for patients with… (7)

Answer 18

COPD exacerbation
Asthma
Cardiogenic pulmonary edema
Hypoventilation syndromes
Failure post extubation
Restrictive lung conditions
Upper airway obstruction

Question 19

CPAP is….

Answer 19

pressure controlled, patient triggered, patient cycled, unsupported spontaneous breathing

Question 20

PC IRV

Answer 20

Pressure controlled
Time cycled
Pressure limited
By definition, inspiratory time is longer than expiratory time
All machine delivered breaths are mandatory
The patient is not permitted to breath during inspiration

Question 21

In PC IRV, delivered tidal volume is dependent on…

Answer 21

Resistance and compliance features of the lungs
Pressure gradient (PiP – PeeP) cm H2O
Inspiratory time or I:E ratio
Ti to an extent

Question 22

Advantages of PC IRV

Answer 22

Manipulation of mean airway pressure (map) is possible without having to increase the inspiratory pressure
Inspiratory time is prolonged
As expiratory time is decreased, the potential for gas trapping increases as does the level of auto-PEEP
Auto-PEEP is added to the baseline peep and might provide better ventilation/perfusion matching
Modern ventilators lock the I:E ratio at a maximum of 4:1

Question 23

Disadvantages of PC IRV

Answer 23

Tidal volume delivery is variable
Due to changes in compliance and resistance, the tidal volume may increase or decrease
Unless minute ventilation is carefully monitored, acute hypoventilation / hyperventilation can occur
The patient is not permitted to breath spontaneously
Medical paralytics/heavy sedation is required
Respiratory muscle strength decreases or is lost
Length of stay might be increased
Gas trapping / auto PEEP induced positive pressure in the thorax
Cardiac output may be negatively affected
Ventilator parameter changes must be monitored very carefully
Changes to rate or inspiratory time must be evaluated on the effect to I:E ratio

Question 24

MMV

Answer 24

Mandatory Minute Ventilation is a mode of ventilation which permits spontaneous breathing by the patient, but also ensures a minimal minute ventilation delivery to the patient

Question 25

Closed Loop

Answer 25

Closed loop means the ventilator changes its output based on a measured input variable ex. MMV