1. A Simple Circuit to Deliver Bubbling CPAP Charanjit Kaur, Akatoli Sema, Rajbir S. Beri and Jacob M. Puliyel Department of Pediatrics, St Stephens Hospital, Tis Hazari, Delhi 110 054, India. Correspondence to: J M Puliyel, Department of Pediatrics, St Stephens Hospital, Tis Hazari, Delhi 110 054, India. Email:puliyel@gmail.com Open access: Indian Pediatr. 2008 Apr;45(4):312-4. http://jacob.puliyel.com

2. Abstract Nasal CPAP, especially ‘bubbling CPAP’, can reduce the need for more invasive ventilation.

3. Abstract We here describe a simple circuit that delivers bubbling CPAP. We describe how the oxygen concentration can be altered from 98% to 21% oxygen using this system. Addition of a humidifier in the circuit has the effect of reducing the oxygen concentration by 1 to 5%. The cost of putting together the system is approximately Rs 5000 – Rs 10,000 (US$ 120 to US$ 240).

4. The bubbling CPAP system results in waveforms similar to those produced by high-frequency ventilation. The chest vibrations produced contribute to gas exchange by facilitated diffusion.

5. Basic Form In it’s most basic form pressurized oxygen from an oxygen cylinder is delivered to the nasopharynx of the baby.

6. Basic form

7. Basic Form An under water ‘T tube’ that acts as a blow off valve. Height of the water column above the exit of the ‘T tube’ regulate the amount of CPAP delivered to the baby. The constant bubbling of gas through the blow off mechanism delivers the bubbling CPAP effect.

8. Gas Delivery System for Baby Nasal prongs may be used. A cut down endotracheal tube or a large bore suction tube (8F) reaching the oropharynx is as comfortable for the baby. Mouth closure is not essential although it can raise pharyngeal pressure.

9. Drawback of basic form This system however delivers 100% oxygen and can harm premature babies. Addition of a Y tube allows Air and Oxygen to be mixed and delivered to the baby

10. Saturations of Oxygen Achieved With Different Flow Rates for Oxygen and Air Flow rate of Oxygen (L) Flow rate of air (L) Theoretical O 2 concentration (%) (without humidity) Theoretical O 2 concentration (%) (humidity saturated at 37 0 C ) Mean saturation achieved in experiments (%) 8010095.098.7 719086.584.5 628076.072.5 537066.561.3 446057.053.6 355047.538.8 264038.023.5 173028.521.2 082019.021.2

11. In centers where it is available, a pulse oxymeter can be used and adjust the air: oxygen mix (to maintain saturations of 92 to 98% in the baby,) and minimize the risk of oxygen toxicity.

12. Humidification A humidifier can also be added so the gas mixture is not dry and it does not irritate the airway.

13. Humidifiers available Humidifiers are chambers with water warmed to body temperature. The air oxygen mixture is run over this water to saturate it with moisture Ordinarily these units can cost around $2500

14. Low Cost Humidifier We have designed an autoclavable glass humidifier unit that costs $100 to $200. The design incorporates an automatic refill mechanism It can incorporate an external heating system to prevent condensation within the tubing.

15. Y Tube for Air:Oxygen mixture and Humidifier Unit

16. Advantages: New Model Humidifier The CPAP unit sans the humidifier can be put together for around Rs 500 to Rs 1000 (US$ 12 to 24). The humidifier adds an additional Rs 5000 to Rs 10,000 to the cost (US$ 100 to 200). This however is a tenth of the cost of conventional commercially available humidifiers

17. Advantages (continued) The conventional humidifier holds water in a Perspex and metal chamber with a rubber gasket between them. This make heat sterilization difficult and there is potential that the chamber with water at 37 o C may culture harmful organisms. The new all glass chamber overcomes this problem

18. Availability The low cost humidifier is available in India from: Appropriate Technologies (JSS) 1626/33 First Floor Naiwala Karol Bhagh, Delhi India Ph 9212459844 We seek partners to manufacture and distribute this overseas

19. Complete Circuit

20. The corresponding author may be contacted on email for clarifications