Mapleson E system.
T-tube whose limbs are connected to (F) the fresh gas supply from
the anesthesia machine, (R) a length of corrugated reservoir tube
and (P) the patient connector.
-The patient inspires fresh gas from the reservoir tube.
Expiration - The patient expires into the reservoir tube.
Although fresh gas is still flowing into the system at this time,
it is wasted as it is contaminated by expired gas.
Expiratory pause - Fresh gas washes the expired gas out of
the reservoir tube, filling it with fresh gas for the next inspiration.
- The volume
of the reservoir tube must be greater than the patient's tidal
volume, otherwise the inspired gas will be contaminated by the
gas flow requirements--see separate article.
positive pressure ventilation may be performed by intermittently
occluding the end of the reservoir tube.
Jackson-Rees' modification of the Ayre's T-piece (somethimes known
as the Mapleson F system) connects a two-ended bag to the expiratory
limb of the circuit, gas escaping via the `tail' of the bag
respiratory movements to be more easily seen and permits intermittent
positive ventilation if necessary. The bag is, however, not essential
to the functioning of the circuit.
positive pressure ventilation may be performed by occluding the
tail of the bag between a finger and thumb and squeezing the bag.
Alternatively, a `bag-tail valve', which employs an adjustable resistance
to gas flow, may be attached to the bag tail. This causes the bag
to remain partially inflated and so facilitates one-handed performance
to IPPV is the Kuhn bag, which has the gas outlet on the side of
the bag, rather than the tail. This allows the outlet to be occluded
with the thumb during IPPV, but leads to difficulties in scavenging
the waste gases.
of different designs of T-piece are available, which function in
essentially the same way.
T-pieces incorporate 15 mm fittings for the reservoir tube and endotracheal
Normal elbow incorporates a right-angle bend which is convenient
for use in human patients but has little advantage in veterinary
of T-piece systems
- No valves
- Low dead-space
- Low resistance
for controlled ventilation
- Some T-pieces
are rather heavy and difficult to keep connected to the endo-tracheal
tube in small animals.
- The bag
may get twisted and impede breathing.
- High gas
flow requirement in larger animals.
- Small animals
under 7 kg body weight.