Mechanical Ventilation

Question 1

Purpose of mechanical ventilation

Answer 1

Elimination and control of carbon dioxide
Improves oxygenation
- reduces work of respiration
- reduces oxygen demand by the body
Can open collapsed alveoli by raising pressure during inspiration and maintaining pressure during expiration

Question 2

Possible complications of mechanical ventilation

Answer 2

Barotrauma - pneumothorax, pneumomediastinum and surgical emphysema
Cardiovascular - reduced venous return secondary to higher intra-thoracic pressure
Increased pulmonary vascular resistance
Gastric dilation/ileus
Accidental disconnection/wrong ventilator setting
Sodium and water retention - leads to increased ADH and ANP
Atrophy of respiratory muscles
Infection/pneumonia

Question 3

What is positive end-expiratory pressure (PEEP)

Answer 3

Pressure prevents alveolar collapse at the end of expiration and recruits collapsed alveoli

Question 4

Advantages and disadvantages of positive end-expiratory pressure (PEEP)

Answer 4

Advantages
- increases lung volume and improves oxygenation
- can be used in spontaneous breathing (CPAP/BiPAP) or with mechanical ventilation
Disadvantages
- reduces physiological shunting, but further reduces venous return and increases barotrauma

Question 5

What is continuous positive airway pressure (CPAP)

Answer 5

Same pressure of air administered during inspiration and expiration
Used in spontaneously ventilating patients (need to be conscious and making good respiratory effort)

Question 6

What is bi-level positive airway pressure (BiPAP)

Answer 6

Less airflow during expiration makes expiration easier for the patient
Allows lower overall airway pressures to be used - less barotrauma

Question 7

What is intermittent mandatory ventilation

Answer 7

Delivers a mandatory minute volume and allows spontaneous breaths between mechanical breaths
Often synchronised with spontaneous breaths (mechanical breaths imposed after a spontaneous breath to prevent stacking of breaths)

Question 8

What are the features of mandatory-type ventilators

Answer 8

Determines how breaths are delivered (set volume or set pressure)
Volume control - can set the tidal volume that is to be delivered
Pressure control - tidal volume depends on compliance, as ventilation will stop when the inspiratory pressure is reached (prevents barotrauma)

Question 9

What are the features of spontaneous-type ventilators

Answer 9

Pressure support
- adjunct to support spontaneous breaths with set pressure to increase the tidal volume (aid to weaning off ventilation)
- breath detection is triggers by decreased pressure or flow
Can be used to assist control (trigger) ventilation

Question 10

How can weaning from ventilation be achieved

Answer 10

Must have recovered from original problem
Spontaneous, intermittent mandatory ventilation and pressure support can be used to aid weaning
- as patient takes spontaneous breaths, the SIMV rate is reduced until all the breaths are spontaneous
- pressure setting is then reduced