This document describes the Bain's circuit breathing system. It has a 6mm inner tube to deliver fresh gas from the machine to the patient and a wider outer corrugated tube attached to a reservoir bag. During inspiration, fresh gas flows from the machine through the inner tube and outer tube to the patient. During expiration, fresh gas continues flowing into the system while expired gas gets mixed with it and flows back into the reservoir bag and outer tube. The APL valve vents excess gas to prevent overpressurization of the system. Tests are described to check the functionality of the Bain's circuit.

1. •Bains circuit (Mapelson D)
• Dr.zikrullah mallick

2. Breathing system
• An assembly of components,which connect the patients airway to the
anaesthetic machine creating an artificial atmosphere,from and into
which the patient breathes.

3. CLASSIFICATION
• Bidirectional flow
Afferent reservoir systems
• Mapelson A
• Mapelson B
• Mapelson C
• Efferent reservoir system
• Mapelson D
• Mapelson E
• Mapelson F
• Bain’s system

4. Bain’s circuit
• They have a 6 mm diameter tube as afferent and carries fresh gas
from machine end to patient end
• Reservoir bag is attached to efferent limb which is a wide bore
corrugated tube

5. APL valve is placed near the reservoir bag
In bain’s modification afferent and efferent limbs are
coaxially place
Inner tube 6mm
Outer tube 22 mm
Length 180 cm

7. Bain’s circuit

9. • During inspiration fresh gas from machine, reservoir
bag and corrugated tube flow to the tube
• During expiration, fresh gas to the system at the
patient and expired gas gets continuously mixed with
fresh gas as it flows back into corrugated tube and
reservoir bag

10. • Once the system is full, the excess gas is vented to the atmosphere
through the APL valve during expiratory pause fresh gas continues to
flow and fill the proximal portion of corrugated tube while mixed gas
is vented through the valve
• During next inspiration, patient breaths fresh gas and mixed gas

12. • During inspiration the patient gets ventilated with fresh gas flow from
the machine, corrugated tube and reservoir bag
• During expiration the expired gas gets mixed with the fresh gas that is
flowing into the system at patient end
• During expiratory pause the fresh gas continues to enter the system
and pushes the mixed gas towards reservoir bag

13. • When next ventilation is initiated patient gets ventilated with the gas
in the corrugated tube. As the pressure in the system increases APL
valve opens and contents of reservoir bag are released into the
atmosphere

14. FGF requirement
• Spontaneus : 1.5 to 3 times minute ventilation
• (100 to 300 ml/kg/min)
• Controlled : 1 to 2 times minute ventilation

15. Test for Mapelson D
• By occluding the patient end and closing APL valve, pressurizing the
system
• Open the APL valve
• Bag deflates easily

16. Tests for BAINS system
• Occlude the inner tube at the patient end after setting a low flow
oxygen
• If the inner tube is intact the flow meter indicator will fall

17. Pethick test
• Activate oxygen flush and observe the bag
• Venturi effect caused by high flow oxygen at the patient end will
create a negative pressure at the outer tube
• Bag deflates

18. Advantages
• Can be used in controlled / spontaneous respiration
• Adults and paediatrics
• Portable, light weight
• Scavenging of exhaled gases

19. Hazards
• Accidental disconnection of inner tube from machine end
• Double back itself and cause obstruction to fresh gas flow