Basics of Mechanical Ventilation

Question 1

What are the indications for intubation/mechanical ventilation?

Answer 1

1) airway protection 2) hypoxemic and/or hypercarbic respiratory failure 3) elective procedures

Question 2

What is the control variable in assist control pressure control (ACPC) ventilation?

Answer 2

The clinician sets the designated pressure delivered with every breath

Question 3

What is the control variable in assist control volume control (ACVC) ventilation?

Answer 3

The clinician sets the tidal volume of each breath

Question 4

What are conditional variables?

Answer 4

They are the dependent variables in mechanical ventilation (e.g. in volume control, tidal volume is the set paramter and the pressure is the conditional variable (as it varies from breath to breath while tidal volume remains constant)

Question 5

What is the trigger?

Answer 5

The factor that initiates inspiration (pressure-trigerred, flow-triggered, vs time-triggered)

Question 6

What is the cycle?

Answer 6

The determination of the end of inspiration, and the beginning of exhalation (the vent can be volume, pressure, or time cycled)

Question 7

What is airway resistance, and the normal value?

Answer 7

Resistive forces encountered during mechanical respiratory cycle. Normal airway resistance is <5 cmH2O

Question 8

What is lung compliance?

Answer 8

Elasticity of the lungs, or the ease with which they stretch and expand to accomodate a change in volume or pressure

Question 9

What is an example of poor lung compliance?

Answer 9

Difficulty with INHALATION process from HIGH elastic recoil (restrictive lung disease, such as pulmonary fibrosis)

Question 10

What is an example of high lung compliance?

Answer 10

Difficulty with EXHALATION process from LOW elastic recoil (obstructive lung disease, COPD/asthma)

Question 11

What is decruitment?

Answer 11

Loss of gas exchange surface 2/2 atelectasis, minimized by increasing PEEP

Question 12

What is recruitment?

Answer 12

Restoration of gas exchange surface area by applying PEEP to re-open collapsed or atelectatic areas of lung

Question 13

What patient factor should be used in determining ventilator settings?

Answer 13

PREDICTED body weight

Question 14

T/F - ventilator settings are determined using actual body weight

Answer 14

FALSE – never use actual body weight to determine vent settings

Question 15

What is the formula for predicted body weight (PBW) for men?

Answer 15

PBW (kg) = 50+2.3 (height(in)–60)

Question 16

What is the formula for predicted body weight (PBW) for women?

Answer 16

PBW (kg) = 45.5+2.3 (height(in)–60)

Question 17

what is the initiation phase of mechanical breathing?

Answer 17

start of the mechanical breath, triggered by the patient or the machine (with a patient triggered breath, you will notice a slight negative deflection)

Question 18

What is the inspiratory phase of a mechanical breath?

Answer 18

portion of mechanical breathing during which there is a flow of air into the pt’s lungs to achieve PIP (peak inspiratory pressure, or Ppeak) and TV (tidal volume)

Question 19

What is the plateau phase?

Answer 19

can be checked as a diagnostic maneuver to assess the plateau pressure, but does not routinely occur in mechanically ventilated breaths

Question 20

What is mechanical exhalation?

Answer 20

The passive process in mechanical breathing, can be volume cycled (when a maximum TV is achieved), time cycled (after a set number of seconds), or flow cycled (after achieving a certain flow rate)

Question 21

What is PIP (or Ppeak), and the target value?

Answer 21

Peak Inspiratory Pressure, the maximum pressure in the airways at the end of the inspiratory phase. Determined by both airway resistance and compliance. Target is <35 cmH20

Question 22

What is Pplat, and the target value?

Answer 22

Plateau pressure, the amount of pressure that remains in the alveoli during the plateau phase during which there is a cessation of air flow, or with a breath-hold. It reflects compliance in the airways. Target is <30 cmH2O

Question 23

What is PEEP?

Answer 23

Positive End Expiratory Pressure, the positive pressure that remains at the end of exhalation, prevents atelectasis. Target is 5 cmH20 or greater

Question 24

What is instrinsic PEEP?

Answer 24

The pressure that remains in the lungs due to incomplete exhalation (air trapping). Also called auto-PEEP

Question 25

How can intrinsic PEEP be measured on the vent?

Answer 25

Press the "expiratory pause" or "expiratory hold" button on the ventilation

Question 26

What is driving pressure? delta P

Answer 26

the pressure exerted to expand the lungs (delta P = Pplat - PEEP)

Question 27

What is iTime?

Answer 27

Inspiratory time, the time allotted to deliver the set VT or pressure

Question 28

What is eTime?

Answer 28

Expiratory time, the time allotted to fully exhale the delivered mechanical breath

Question 29

What is I:E ratio?

Answer 29

Inspiratory to expiratory ratio, usually expressed as 1:2, 1:3, etc. Can be set directly on the vent, or indirectly by changing the inspiratory time, the inspiratory flow rate, or RR

Question 30

How does one decrease the I:E ratio?

Answer 30

Increasing the expiratory time by convention (e.g. divide by a greater number)

Question 31

What is peak inspiratory flow, and a common target?

Answer 31

the rate at which the breath is delivered expressed in L/min, usually 60L/min. Can indirectly affect I:E ratio -- increasing the flow rate delivers the breath faster, leaving more time for exhalation

Question 32

What is VT, or TV?

Answer 32

Tidal volume, the volume of gas delivered to the pt with each breath, expressed in both mL and mL/kg of PDW

Question 33

What is RR, or f?

Answer 33

Respiratory rate, the mandatory number of breaths delivered by the vent per minute which can vary from actual pt's respiratory rate and both should be reported on rounds

Question 34

What is VĖ, Vė, or MV, and the target?

Answer 34

Minute ventilation, the ventilation the pt receives in one minute calculated by VT x RR expressed in L/min. Target is 4-6L/min in normal healthy adults, but may require 12-15L/min in critical illness

Question 35

What is FiO2?

Answer 35

Fraction of inspired O2 delivered during inspiration, expressed as a percentage, the vent can deliver up to 100% FiO2 (room air is 21%)

Question 36

What is AC ventilation?

Answer 36

Assist control (either AC/PC or AC/VC), one of the safest modes of ventilation, the patient receives the same breath each time determined by clinician parameters. The patient can over-breathe the set rate

Question 37

What is SIMV?

Answer 37

Synchronized intermittent mandatory ventilation, can be volume or pressure controlled (SIMV-VC vs SIMV-PC). Unlike AC, additional breaths triggered by the patient will only receive pressure support or CPAP (vs AC where additional pt breaths they receive what the vent gives)

Question 38

What s PRVC?

Answer 38

Pressure Regulated Volume Control, type of assist control that combines the best attributes of volume control and pressure control to reduce lung injury from excessive pressure. Tidal volume is set at the lowest possible pressure. If pressure reaches a predefine maximum level, the vent will stop airflow and cycle into exhalation. Pressure target is adjusted based on lung compliance

Question 39

What is Pressure Support?

Answer 39

Patient triggered breaths, partial support mode in which the pts receives a constant PEEP as well as a supplemental "supporting" pressure set by the clinician, dependent variables are peak inspiratory flow, RR, and TV determined by pt effort

Question 40

What is NIPPV?

Answer 40

Noninvasive positive pressure ventilation, either CPAP or BiPAP and pt's airway is not secured with an endotracheal tube but given either by facemask or nasal prongs

Question 41

What is CPAP?

Answer 41

Continuous Positive Airway Pressure, a partial support mode of ventilation, the pt receives a constant airway pressure throughout the respiratory cycle. Driven by pt effort, thus pt must be awake, minimally sedated, and able to take spontaneous breaths

Question 42

What is BiPAP?

Answer 42

Bilevel Positive Airway Pressure, in which pt receives two levels of airway pressure throughout the respiratory cycle. The higher pressure IPAP (inspiratory) is similar to the peak airway pressure setting, and the lower pressure EPAP (expiratory) is similar to PEEP and helps maintain alveolar distention