Lecture 3

Question 1

What is the management rationale for use of ventilatory support of patients with hypercapnic RF?

Answer 1

1. Hypercapnic RF d/t high CO2 - this is d/t PUMP and/or LOAD failure
2. Ventilation replaces the PUMP

Question 2

Iron lung - example of negative or positive pressure?

Answer 2

Negative pressure
- used during polio epidemic; pt put in chamber and negative pressure around the chest to suck air in; suction is released and pt passively breathes out

Question 3

Hand bagging - example of negative or positive pressure?

Answer 3

Positive pressure

- use during polio epidemic; bag is squeezed to push air in via tracheostomy

Question 4

CV/CMV (Controlled Ventilation/Controlled Mandatory Ventilation)

Answer 4

Machine has COMPLETE control and pt requires SEDATION (so limited/no respiratory mm activity - deconditioning)

• RR set
• tidal volume set
• PT EFFORT IS IGNORED
• no variation in size or timing of the breath

Question 5

ACV (Assist Control Ventilation)

Answer 5

• RR set - BUT you can add breaths
• tidal volume set - NO variation here
• PT EFFORT TRIGGERS A BREATH (machine can recognize if pt wants to take a breath autonomously)
• risk of breath hyperventilation (if the pt triggers a breath the machine will give the same sized tidal volume)

Question 6

IMV (Intermittent Mandatory Ventilation)

Answer 6

• RR set
• tidal volume set
• unlimited # of breaths in between of any volume
• risk of breath stacking - can overstretch lungs - barotrauma

Question 7

SIMV (Synchronised Intermittent Mandatory ventilation)

Answer 7

• machine can sense a spontaneous breath (unlimited number of breaths of any volume) and will wait till that breath is over before delivering another breath
• set number/size of ventilator breaths per minute
• can be triggered by patient effort
• no breath stacking since machine will wait till pt’s breath is over
• this is why ventilator breaths with SIMV can be at diff time points depending on when the pt takes a spontaneous breath

Question 8

PSV (Pressure Support Ventilation)

Answer 8

• machine delivers flow to PRESSURE limit
• pt has to make continuous resp mm effort - so limits deconditioning
• the actual tidal volume might vary since lower lung and chest wall compliance means the pressure will be reached quicker for a lower volume change
• PS = IPAP - EPAP

Question 9

What are the starting parameters for mechanical ventilation? (Vt, RR, PEEP, FiO2)

Answer 9

Vt = 6-10ml/kg
RR = 10-20 bpm
PEEP = 5cmH2O
FiO2 = 1.0 (started here but quickly dropped down)