Module A: Basic Terms and Concepts of Mechanical Ventilation

Question 1

Ventilation

Answer 1

The movement of air into and out of the lungs

Question 2

external respiration

Answer 2

the exchange of oxygen and carbon dioxide between the alveoli and the pulmonary capillaries

Question 3

Internal respiration

Answer 3

occurs at the cellular level and involves the movement of oxygen from the systemic blood into the cells

Question 4

Transairway pressure

Answer 4

the pressure difference between the air opening and the alveolus:

Pta = Paw - Palv

represents the pressure that must be generated to overcome resistance to gas flow in the airways

Question 5

Transpulmonary pressure

Answer 5

the difference between the pressure in the alveoli and the pleural space, and is responsible for maintaining alveolar inflation

Ptp = Palv - Ppl.

Ptp is the pressure req’d to maintain alveolar inflation and is therefore sometimes called the alveolar distending pressure

Question 6

Trans-respiratory pressure

Answer 6

the pressure difference between the airway opening and the body surface

two components: transthoracic pressure (the pressure req’d to overcome elastic recoil of the lungs and chest wall) and transairway pressure (the pressure req’d to overcome airway resistance).

Ptr = Pawo - Pbs

Ptr = Ptt + Pta or (Pawo - Pbs) = (Palv - Pbs) + (Paw - Palv).

responsible for the actual flow of gas into and out of the alveoli during breathing

Question 7

Transthoracic pressure

Answer 7

the difference between the pressure in the pleural space and the pressure at the body surface

Pw = Palv - Pbs

represents the total pressure required to expand or contract the lungs and chest wall

Question 8

Mouth pressure

Answer 8

pressure at the upper airway (mouth);

also called

• airway opening pressure (Pawo),
• airway pressure (Paw),
• upper airway pressure,
• mask pressure, or
• proximal airway pressure.

Question 9

Airway opening pressure

Answer 9

pressure at the upper airway (mouth);

also called

• airway opening pressure (Pawo),
• airway pressure (Paw),
• upper airway pressure,
• mask pressure, or
• proximal airway pressure.

Question 10

Airway pressure

Answer 10

pressure at the upper airway (mouth);

also called

• airway opening pressure (Pawo),
• airway pressure (Paw),
• upper airway pressure,
• mask pressure, or
• proximal airway pressure.

Question 11

Alveolar pressure

Answer 11

Alveolar pressure (Palv or Pa) also called intrapulmonary pressure or lung pressure.

Alveolar pressure normally changes as the intrapleural pressure changes.

During spontaneous inspiration, Palv is about -1 cm H20, and during exhalation it is about +1 cmH20

Question 12

calculate compliance

Answer 12

For patients receiving mechanical ventilation, compliance measurements are made during the static or no-flow stat

Cs = (exhaled Vt)/(Pplat - PEEP)

Question 13

calculate resistance

Answer 13

Resistance is a measurement of the frictional forces that must be overcome during breathing

Raw = (Pip - Pplat)/flow, or Raw = Pta/flow

Example: Raw = 40 (pip) - 25 (pplat)/1 (flow in lpm) = 15cmh20/(L/sec)

Question 14

Baseline pressure

Answer 14

Airway pressures are measured relative to a “baseline value”

Typically the baseline value will be zero, which indicates that no additional pressure is applied at the airway opening during expiration and before inspiration

Increases with PEEP

Question 15

Plateau pressure

Answer 15

Measured after a breath has been delivered to a patient, and before exhalation begins

reflects the effect of elastic recoil on the gas volume inside the alveoli and any pressure exerted by the volume in the ventilator circuit that is acted upon by the recoil of the plastic circuit

Question 16

Peak pressure

Answer 16

highest pressure recorded at the end of inspiration (also called PIP or peak airway pressure

The pressures measured during inspiration are the sum of two pressures: the pressure req’d to force the gas through the resistance of the airways (Pta) and the pressure of the gas volume as it fills the alveoli (Palv)