Since the late 1950's, the Bag-Valve-Mask resuscitator, (originally developed by Ambu in Denmark), has been the mainstay of the healthcare provider for emergency ventilation of the patient in respiratory and/or cardiac arrest.

These self inflating balloons (a development from the anaesthesia machine "black breathing bag" ) have proliferated into an industry estimated to be worth some 60 million dollars in the U.S. alone. But what of the effectiveness of these devices?

Certainly, in the early days of CPR (first truly defined in 1961¹) the "Ambu Bags" (as all BVMs have now become known) were the only available adjuncts for the rescuer which did not require the use of exhaled breath to ventilate the patient. As such, they were a significant advance in emergency respiratory care. However, considering the major advances in medicine that have taken place over the last 35 years, we are still, in the most part, relying on old technology to perform the key task of oxygenating the respiratory/cardiac arrest patient.

That technology has not only been superseded by superior equipment during this time but has also been proven to be ineffective in the way in which it provides ventilation and potentially dangerous (especially in some non-protected airway situations). The American Heart Association "Guidelines for CPR" published in the Journal of the American Medical Association, October 28th 1992², quite clearly identified that these devices were generally ineffective in providing adequate ventilations to the patient.

A wealth of clinical evidence to support these claims has been accumulated over the past 30 years and this evidence has , for the most part, been ignored as die-hard "baggers" continue to utilize these devices. This continued use is not based on sound clinical evidence that they provide good ventilation, but because - " it has always been done this way". Some claim that the "feel" they get from the BVM allows them to make clinical judgements on the patient's lung condition. In reality what they are probably feeling is the back pressure created by the high flowrates generated when squeezing the bag too hard or for too short an inspiratory time. This masks the actual compliance and resistance of the patient's airway. Fuerst, Banner and Melker³ in their paper showed that flowrates which are too high and inspiratory times which are too short end up not ventilating the patients lungs but more often than not producing significant gastric distension which can lead to aspiration of stomach contents and severe complications (if not death) for the patient.

In the 1960's, the first of the manually triggered, oxygen powered resuscitators came onto the market and enabled healthcare providers, primarily in the EMS environment, to provide 100% oxygen under positive pressure to their patients. At the time it was felt that high flowrates were required to allow for the leakage of oxygen from around the mask and for the distension of the soft tissues in the neck and respiratory tract that occur when gas is forced into the patient under pressure. In the American Heart Association "Guidelines for CPR" published in the Journal of the American Medical Association 1986⁴, these flowrates were lowered to 40 litres per minute as a way of reducing the inspiratory pressures created and reducing gastric distension as well as the significant risk of barotrauma they created. To further reduce the risks to the patient the maximum delivery pressure these devices can produce was also limited to 60 cmH²O.

Considerable research undertaken at the University of Florida, Department of Anesthesia by Melker and Banner , has further shown that a maximum flowrate of 27 lpm, combined with a 2 second inspiratory time and an Inspiration/Expiration ratio of 1 : 2 produces the best ventilation with the least risk of gastric distension.

To provide these parameters with a Bag-Valve-Mask device, even in the best trained hands, is not only impossible but also impractical. So what do we do instead? Since 1992 the American Heart Association2 has been recommending the use of "Automatic Transport Ventilators" (ATVs) as the most effective method of ventilation in the emergency prehospital market.

These guidelines clearly define the ATV in terms of both it's function and physical characteristics. Surprisingly, these devices have been available for some 17 years. They have not however, seen any great success in captivating the imagination of the healthcare providers they are designed to assist although there is a wealth of information to support their use^5,6,7,8,9,10.

The modern, state of the art, devices now available offer functions which are normally only seen on hospital ventilators. The size, weight and low cost of these products makes them available to all healthcare providers. The controlled automatic ventilations they provide reduce the risks commonly associated with BVMs and assist in freeing the healthcare provider to perform other tasks.

Conclusions

With this advanced, user friendly, technology available in the form of ATVs why do we persist in using outdated devices? Especially as BVMs have been proven to:

• generate high inspiratory flows and pressures.
• produce severe gastric distension in the unintubated patient.
• not provide adequate ventilation in even the most skilled hands.

When considering your next purchase of emergency respiratory equipment, take a good look at your "old bag" and consider, in the light of all the evidence, whether it's time to put it out to pasture.

References

1.Elam JO, Greene DG. Mission accomplished: successful mouth-to-mouth resuscitation. Anesth Analog. 1961;40:578-580.
2. A.H.A Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiac Care - J.A.M.A Oct.28, 1992:2171-2295
3.Fuerst RS, Banner MJ, Melker RJ. Inspiratory time influences the distribution of ventilation to the lungs and stomach: implications for c.p.r. Ann Emerg Med. In press.
4.American Heart Asociation "Guidelines for CPR" published in the Journal of the American Medical Association in 1986.
5. Hess D, Baran C. Ventilatory volumes using mouth to mouth, mouth to mask and bag-valve-mask techniques Am J Emerg Med 1985;3:292-296
6. Branson RD, McGough EK. Transport ventilators Probl Crit Care. 1990;4:254- 274
7. Hurst JM, Davis K Jr, Branson RD, Johannigman JA. Comparison of blood gases of ventilated patients during transport. J Trauma. 1989;29:1637-1640.
8. Jesudian MC, Harrison RR, Keenan RL, Maull KI. Bag-valve-mask ventilation: two rescuers are better than one: preliminary report. Crit Care Med. 1985;13:122-123
9. Braman SS, Dunn SM, Amico CA, Millman RP. Complications of intra-hospital transport in critically ill patients .Ann Intern Med. 1987;107:469-473
10. Gervais HW, Eberle B, Konietzke D, Hennes HJ, Dick W. Comparison of blood gases of ventilated patients during transport. Crit Care Med 1987;15:761-763