26. Resuscitation Bags and Valves

Question 1

What type of resuscitation bags do you find on a cardiac arrest trolley?

Answer 1

A self-inflating bag
with a non-rebreathing valve and mask

is found on a cardiac arrest trolley.

This is a compact and
portable ventilating system

that does not require a pressurised
gas supply to work.

It consists of a fresh gas inlet
with a one-way valve

(commonly in communication with an
O2 reservoir bag to increase FiO2),

an entrainment valve at the inlet

(to allow entrainment of air
if oxygen supply does
not meet respiratory demands),

a self-inflating bag
(1500 mL for adults,
500 mL for children and
250 mL for infants),

a nonrebreathing valve
and a
pressure-relieving valve
to prevent barotrauma

Question 2

How does it work

resuscitation bags do you find on a cardiac arrest trolley

Answer 2

The main component in a
self-inflating resuscitation
bag is the nonrebreathing valve

(e.g. Reuben, Ambu E or Laerdal valves).

Their function is to ensure that 
gas flows out of the self-inflating bag 
and into the patient during inspiration 
and that exhaled gases pass 
out through the expiratory port 

and

do not re-enter the self-inflating bag.

Non-rebreathing valves are made up of the following:

> Inspiratory port,
often coloured blue (‘blue to bag’),
supplying fresh gas
for inspiration.

> Expiratory port,
often coloured yellow or gold
(‘gold for go’), allowing the
exit of exhaled gases.

> Patient port that connects to the 
airway adjunct (mask, LMA, OETT).

> One-way valve or valves ensuring
exhaled gases are not rebreathed.

Question 3

Reuben valve:

Answer 3

> This consists of a spring-loaded bobbin.

> During positive pressure ventilation, 
as the bag is squeezed, 
the bobbin is pushed across 
and closes the expiratory port, 
allowing fresh gas to enter
the patient.

> During expiration, 
as the bag relaxes, 
the bobbin shifts to the opposite side 
and closes the inspiratory port, 
allowing exhaled gases to escape
through the expiratory port.

> The bag then self-inflates,
drawing in air from the room and oxygen from
the reservoir bag ready to deliver the next breath.

> The valve can jam,
keeping the inspiratory port continuously open,
which risks hyperinflating the lungs.

> The valves offer resistance 
(0.8 cm H2O during inspiration 
and 1 cm H2O
during expiration) and therefore 
can significantly increase the work of breathing 

and impair passive expiration
in the spontaneously ventilating patient.

Therefore, these devices should be
used cautiously in patients
with respiratory fatigue
(‘assisted’ breaths should be given to such
patients by gently squeezing the bag when they inspire, which helps
open the valves, thereby reducing resistance)

Question 4

Ambu E valve:

Answer 4

> This is a double-leaf valve.

> During positive pressure ventilation, 
the inspiratory port leaf valve is
pushed across and 
seals the expiratory port, 
thereby allowing gases to
enter the patient.

> During expiration,
the inspiratory port leaf valve
gets pushed back,

sealing the inspiratory port while 
the expiratory port leaf valve gets forced
open, 
allowing exhaled gases to 
escape into the atmosphere.

> During low inspiratory gas flow rates,
the inspiratory port leaf valve may
not give a good seal across
the expiratory port and hence some of the
fresh gas can escape across the valve,
reducing the fresh gas supply to
the patient.

> The valve offers resistance and
should be used cautiously in the
spontaneously ventilating patient.

Question 5

What factors determine the oxygen concentration that can be delivered to the patient?

Answer 5

1
> FiO2

2
> Oxygen flow rate

3
> Reservoir bag volume
(adult size approximately 2600 mL)

4> Inspiratory flow rate

5
> Respiratory rate

6
> Valve type