Bains

1. BAINS CIRCUITS
breathing system is defined as an assembly of components, which connect the patient’s airway to
the anesthetic machine creating an artificial atmosphere, from and into which the patient breathes.
It primarily consists of:• A fresh gas entry port or delivery tube through which thegases are
delivered from the machine to the system•
A port to connect it to the patient’s airway•
A reservoir for gas, in the form of a bag or a corrugated tube tomeet the peak inspiratory flow
requirements•
An expiratory port or valve through which the expired gas isvented to the atmosphere• Flow
directing valves and carbon dioxide absorber if total rebreathing is to be allowed,
Corrugated tubes for connecting these component’s

6. Functional Analysis
• During exhalation (Fig. 8.7), exhaled gases mix with fresh gases and move through the corrugated tube
toward the bag. After the bag has filled, gas exits via the APL valve.
• During the expiratory pause, fresh gas pushes exhaled gases down the corrugated tubing.During inspiration,
the patient will inhale gas from the fresh gas inlet and the corrugated tubing. If the fresh gas flow is high, all
the gas drawn from the corrugated tube will be fresh gas. If the fresh gas flow is low, some exhaled gas
containing CO2 will be inhaled.
• The ventilatory pattern will help to determine the amount of rebreathing. Factors that tend to decrease
rebreathing include a high inspiratory:expiratory (I:E) time ratio, a slow rise in inspiratory flow rate, a low
flow rate during the last part of exhalation, and a long expiratory pause, with the long expiratory pause
having the greatest effect .
• As gas containing CO2 is inhaled, the end-tidal CO2 will rise. If the patient's spontaneous respiration then
increases, the end-tidal CO2 will fall while inspired CO2 will increase (49). Provided rebreathing is not
extreme, a normal end-tidal CO2 can be achieved but only at the cost of increased work on the part of the
patient. The end- tidal CO2 tends to reach a plateau. At that point, no matter how hard the patient works,
the end-tidal CO2 cannot be lowered further. If the patient's respiration is depressed, end-tidal CO2 will rise
further (49).
• End-tidal CO2 depends on both the ratio of minute volume and fresh gas flow and their absolute values (49).
If expired volume is greater than fresh gas flow, end-tidal CO2 will be determined mainly by fresh gas flow. If
fresh gas flow is greater than minute volume, end-tidal CO2 will be determined mainly by minute volume.
Recommendations for fresh gas flows based on body weight vary from 100 to 300 mL/kg/minute
• . Most studies have recommended that the fresh gas flow be 1.5 to 3.0 times the minute volume
whileothers have held that a fresh gas flow approximately equal to total ventilation is adequate (57). In
terms of body surface area, fresh gas

10. • Bain System HazardsIf the inner tube of the Bain system becomes detached from its
connections at either end or develops a leak at the machine end, if the fresh gas supply
tube becomes kinked or twisted, if the system is incorrectly assembled (such as using
standard corrugated tubing), or if there is a defect in the metal head so that fresh gas
and exhaled gas mix, the entire limb becomes dead space . In one case, it was reported
that a manufacturing defect caused the inner tube to be blocked .
• Preuse Checks
• The Mapleson D System is tested for leaks by occluding the patient end, closing the APL
valve, and pressurizing the system. The APL valve is then opened. The bag should deflate
easily if the valve and scavenging system are working properly. Either the user or a
patient should breathe through the system to detect obstructions.The Bain modification
of the Mapleson D requires special testing to confirm the integrity of the inner tubing.
This can be performed by setting a low flow on the oxygen flowmeter and occluding the
inner tube (with a finger or the barrel of a small syringe) at the patient end while
observing the flowmeter indicator. If the inner tube is intact and correctly connected, the
indicator will fall
• ) The integrity of the inner tube can also be confirmed by activating the oxygen flush and
observing the bag . A Venturi effect caused by the high flow at the patient end will create
a negative pressure in the outer exhalation tubing, and this will cause the bag to deflate.
If the inner tube is not intact, this maneuver will cause the bag to inflate slightly.
However, this test will not detect a system in which the inner tube is omitted or does not
extend to the patient port or one that has holes at the patient end of the inner tube .

12. ADVANTAGES
• 1. The equipment is simple, inexpensive, and rugged. With the exception of the APL valve, there
are no moving parts. The components are easy to disassemble and can be disinfected or sterilized
in a variety of ways. For these reasons, they continue to be a popular choice to provide positive
pressure ventilation in emergencies .
• 2. Variations in minute volume affect end-tidal CO2 less than in a circle system..
• In coaxial systems (Lack, Bain), the inspiratory limb is heated by the warm exhaled gas in the
coaxial expiratory tubing.
• Resistance is usually low at flows likely to be experienced in practice
• These systems are lightweight and not bulky. They are not likely to cause drag on the mask or
tracheal tube or accidental extubation
• . They are easy to position conveniently. A long Mapleson D system with an aluminum APL valve
may be used to ventilate a patient in the MRI unit (123).
• . Compression and compliance volume losses are less with the Mapleson systems than with the
circle system.8. Changes in fresh gas concentrations result in rapid changes in inspiratory gas
composition.9. Since there is no CO2 absorbent, there will be no production of possibly toxic
products such as carbon monoxide and compound A

13. Disadvantage of Mapleson system