Patient parameters

Question 1

Fraction of inspired oxygen (FiO2)

Answer 1

The concentration of oxygen in the inspired gas. It can be set from 0.21 (room air) to 1.0 (100%).

Question 2

Tidal volume (Vt)

Answer 2

The volume of gas, either inhaled or exhaled, during a breath and commonly expressed in milliliters. Vt is generally
set between 8 and 12 mL/kg but may be set lower (eg, 6 mL/kg or lower) to prevent lung over-distension and injury.

Question 3

Respiratory rate (RR) or frequency

Answer 3

The number of breaths per minute that the ventilator delivers. RR is commonly set between 10 and 20 breaths per minute. If the patient is making spontaneous breathing efforts, RR will be higher.

Question 4

Minute ventilation (VE)

Answer 4

The average volume of gas entering, or leaving, the lungs per minute, commonly expressed in liters per minute. The product of Vt and RR = VE. Normal VE is between 5 and 10 L/min.

Question 5

Peak flow rate or peak inspiratory flow

Answer 5

The highest flow, or speed, that is set to deliver the Vt
during inspiration, usually measured in liters per minute. When the flow rate is set higher, the speed of gas delivery is faster and inspiratory time is shorter.

Question 6

Inspiratory(I) and expiratory(E) time and I/E ratio

Answer 6

The speed at which the Vt is delivered. Setting a shorter inspiratory time (I) results in a faster inspiratory flow rate. Average adult I is 0.7 to 1.0 s; I/E ratio is usually 1:2 or 1:3.

Question 7

Peak airway pressure (Paw)

Answer 7

Represents the total pressure that is required to deliver the Vt and depends upon various airway resistance, lung compliance, and chest wall factors. It is expressed in centimeters of water (cm H2O).

Question 8

Plateau pressure (Pplat)

Answer 8

The pressure that is needed to distend the lung, which can be measured by applying an end-inspiratory pause
setting on the ventilator. It is expressed in centimeters of water.

Question 9

Sensitivity or trigger sensitivity

Answer 9

Effort, or negative pressure, required by the patient to trigger a machine breath, commonly set so that minimal effort (-1 to -2 cm H2O) is required to trigger the breath. Some ventilators may have flow triggering, which is more sensitive than pressure triggering if the flow setting is set correctly. A decrease in flow is sensed when the patient makes a spontaneous effort and triggers the machine to deliver the breath.

Question 10

Positive end-expiratory pressure (PEEP)

Answer 10

The amount of positive pressure that is maintained at end-expiration. It is expressed in centimeters of water. The purpose of PEEP is to increase end-expiratory lung volume and reduce air-space closure at end-expirati on.

Question 11

Continuous positive airway pressure (CPAP)

Answer 11

Continuous pressurization
of the breathing circuit when a patient breathes spontaneously. CPAP may be used as a last step in the weaning process or as a noninvasive method of providing a pneumatic splint to the upper airway in obstructive sleep apnea.

Question 12

Mandatory breath

Answer 12

A breath in which the timing and/or size of the breath is controlled by the ventilator; the machine triggers and/or
cycles the breath.

Question 13

Spontaneous breath

Answer 13

A breath in which both the timing and size are controlled by the patient; the patient both triggers and cycles the breath.

Question 14

Functional residual capacity

Answer 14

Volume of gas present in the lungs at the end of passive expiration.