Bain Circuit Tests | Step by step Guide

Bain circuit, which is a modification of the type D Mapleson circuit, is used frequently in operating rooms. It is used to ventilate the patient when there is anesthesia machine failure or ventilator failure and to transport the intubated patient.

Bain Circuit Tests

Bain Circuit is a co-axial variant of the Type D Mapleson breathing circuit in which a fresh gas tube is inside the expiratory tube. APL valve and reservoir bag are present at the machine end. The length of the Bain circuit is 180 cm and is best for controlled ventilation in adults.

There are two models of the bain circuit but the checking method is same.

Different models of  Bain Circuit

Checkup Guidelines 

Physical examination :

1. The circuit should be clean and adequately disinfected ( ideally it should be sterile )
2. Search for any holes or damage on the surface of the circuit.       
3. examine the inner tube, it should not be kinking and should be properly attached 
4. check the APL valve: Open and close it.          

Physical Examination of Bain Circuit

Tests :

Inner tube occlusion Test :

which is also known as Bobin Dip Test or Foex-Crempton Smith Test or Ampule Test is used to check the patency and intactness of the inner tube.

The inner tube is called Fresh Gas Tube as it carries fresh oxygen from the oxygen source to patient end.

Steps:

1. attach the machine end of the fresh gas tube to the oxygen port 
   
2. open the oxygen flow meter at the rate of 2 L/min ( or 6 L/min if your machine has a small flowmeter )
3. Take out the plunger of the 2 CC disposable syringe.
4. occlude the inner tube ( patient end of the fresh gas tube ) with the plunger.
5. see the Bobin (an indicator of a flowmeter )
6. It should dip down.   

Photos of Steps: 

Inner tube occlusion Test 

1

Bobin Dip Test

2

Foex-Crempton Smith Test

3

inner tube of bain circuit

 

inner tube of bain circuit

Ampule Test

4

Bain Circuit bobin Dip Test 

5

Conclusion: 

• if Bobin dips down it means the inner tube is intact 
• if Bobin doesn't dip down it means there is leakage or any problem in the inner tube of the bain circuit. 

Positive Pressure Test :

This test is used to check the outer corrugated tube of the bain circuit. 

Steps:

1. Attach the fresh gas tube to the ACGO port of the anesthesia machine. ( ET Tube connector of 7-7.5 size can be used as an adapter for connecting fresh gas tube with large bore ACGO port )
2. Close the APL valve.
3. Now occlude the patient end. 
4. Press the oxygen Flush Button till the reservoir bag is fully inflated.
5. Firmly compress the reservoir bag and feel its resistance 
6. Ideally, the reservoir bag should remain inflated for more than 10 seconds. 

Photos of Tests:

Positive Pressure Test

Positive Pressure Test

Positive Pressure Test bain circuit

Positive Pressure Test

Positive Pressure Test bain circuit

Positive Pressure Test bain circuit

Positive Pressure Test bain circuit

Conclusion: 

• If the reservoir bag remains inflated for more than 10 seconds it means the outer tubing and the reservoir bag are okay.
• If it gets deflated it means there is a leak in the outer tubing or reservoir bag.

Oxygen Flush Test : 

which is also known as Pathik Test is used to check the intactness or patency of the inner tube. This test uses the principle of the Venturi effect.

Steps:

1. Attach the fresh gas tube to ACGO port of the anesthesia machine.
2. Close the APL valve
3. Open the patient end.
4. Press the oxygen flush button 
5. Ideally, the reservoir bag should get deflated due to the century effect

Photos of Test :

Oxygen Flush Test bain circuit

Oxygen Flush Test bain circuit

Oxygen Flush Test bain circuit

Oxygen Flush Test bain circuit

Oxygen Flush Test bain circuit

Conclusion:

1. If the reservoir bag gets deflated it means that the inner tube is intact 
2. if the reservoir bag doesn't get deflated it means there is some problem with the inner tube.

Video of Bain Circuit Tests 

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