Biphasic Cuirass Ventilation

Biphasic Cuirass Ventilation (BCV) is a method of ventilation which requires the patient to wear an upper body shell or cuirass, so named after the body-armour worn by medieval soldiers. The ventilation is biphasic because the cuirass is attached to a pump which actively controls both the inspiratory and expiratory phases of the respiratory cycle. This method has also been described as 'Negative Pressure Ventilation' (NPV), 'External Chest Wall Oscillation' (ECWO), 'External Chest Wall Compression' (ECWC) and 'External High Frequency Oscillation' (EHFO). BCV may be considered a refinement of the iron lung ventilator.

As the ventilation provided by the cuirass is biphasic, it is possible to achieve both large breaths (tidal volumes) and a high respiratory rate (from 6 to 1200 breaths per minute). The biphasic function allows control over the I:E ratio, which is the ratio between the time allowed for inspiration (pumping air out of the cuirass and creating a negative pressure around the chest) and experation (pumping air into the cuirass and creating an increase in pressure around the chest.) Most other types of ventilation depend on the passive recoil of the patient's chest, which limits the respiratory rate.

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Advantages

BCV is non-invasive and therefore avoids some of the problems associated with invasive ventilation such as infection and barotrauma. Unlike intermittent positive pressure ventilation (IPPV), BCV is active in both the inspiratory and expiratory phases (biphasic). This allows greater control over the tidal volumes and respiratory rate. BCV may also help to maintain and redevelop the respiratory muscles which may weaken with respiratory failure and mechanical ventilation^{[citation needed]}, this allows patients to be weaned from a ventilator. BCV also does not impair cardiac function as much as IPPV does. ^[1]. The oscillations caused by BPV assist in the removal of secretions which are a symptom of many respiratory diseases. Lastly, because BCV does not require the patient to be intubated or to have a tracheostomy, patients can have BCV at home.

Disadvantages

Although the end-expiratory chamber pressure can be set to below atmospheric pressure, which aims to prevent a decrease in functional residual capacity, most studies on anaesthetised humans have had to use a positive end-expiratory pressure in order to allow the removal of harmful carbon dioxide from the patients' lungs. ^[2]. BCV may also be difficult to maintain in patients who are obese. ^[3]. Lastly, unlike endotracheal intubation, BCV does not provide any protection for the lungs from contaminants such as vomit.

Uses

BCV has been successfully used in a case of failed fibreoptic intubation ^[4], in microlaryngeal surgery ^[5] and after paediatric cardiac operations ^{[6] [7]}.

References

1. ^ Lockhat D., Langleben D. and Zidulka A. (1992). "Hemodynamic differences between continual positive and two types of negative pressure ventilation.". American Review of Respiratory Disease 148: 677-80.
2. ^ Scholz S.E., Sticher J., Haufler G., Muller M., Boning O. and Hempelmann G. (2001). "Combination of external chest wall oscillation with continuous positive pressure". British Journal of Anaesthesia 87 (3): 441-6.
3. ^ Scholz S.E., Sticher J., Haufler G., Muller M., Boning O. and Hempelmann G. (2001). "Combination of external chest wall oscillation with continuous positive pressure". British Journal of Anaesthesia 87 (3): 441-6.
4. ^ Broomhead C. J., Dilkes M. G. and Monks P.S. (1995). "Use of the Hayek oscillator in a case of failed fibreoptic intubation". British Journal of Anaesthesia 74 (6): 720-1.
5. ^ Dilkes M.G., McNeill J.M., Hill A.C., Monks P.S., McKelvie P. and Hollamby R.G. (1993). "Use of the Hayek oscillator in a case of failed fibreoptic intubation". Annals of Otology, Rhinology and Laryngology 102: 455-8.
6. ^ Penny D., Hayek Z. and Redington A. (1991). "The Effects of Positive and Negative Extrathoracic Pressure Ventilation on Pulmonary Blood Flow after Total Cavolpulmonary Shunt Procedure". International Journal of Cardiology 30 (1): 128-30.
7. ^ Shekerdemian L.S., Bush A., Lincoln C., Shore D.F., Petros A.J. and Redington A.N. (1997). "Cardiopulmonary interactions in healthy children and children after simple cardiac surgery: the effects of positive and negative pressure ventilation". Heart 78 (6): 587-93.