EBME

Clinical Engineering

Biphasic Cuirass Ventilation

bcvBiphasic Cuirass Ventilation (BCV) is a method of ventilation which works using a non-invasive cuirass or shell, attached to a power unit which actively controls both phases of the respiratory cycle (the inspiratory and expiratory phases).

This method has in the past often been described and labelled as 'Negative Pressure Ventilation' (NPV), 'External Chest Wall Oscillation' (ECWO), 'External Chest Wall Compression' (ECWC) and 'External High Frequency Oscillation' (EHFO).

As ventilation is Biphasic, it is possible to achieve both higher tidal volumes (negative inspiratory tidal volume and positive expiratory tidal volume), higher frequencies -from 6 to 1200CPM, and also for the user to have proper and real control over I:E Ratio, without having to depend on passive recoil of the patient.

In addition, the technology used for the cuirass allows for a comfortable fit and seal of the air within the cuirass. These advantages allow for a much higher minute ventilation to be created and thus making complete ventilation possible in both normal and sick lungs.

BCV Ventilation
Your lungs have 2 main parts: bronchial tubes (also called airways) and alveoli (also called airsacs). When you breathe in through your wind pipe, the air moves through your bronchial tubes and into your alveoli. From the alveoli, oxygen goes into your blood while carbon dioxide moves out of your blood.

Biphasic cuirass ventilation (BCV) requires the patient to wear an upper body shell or cuirass, so named after the body armor 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. BCV may be considered a refinement of the iron lung ventilator. Biphasic cuirass ventilation was developed by the late Dr Zamir Hayek, a pioneer in the field of assisted ventilation.

biphasic cuirass overviewAs 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). Breathing consists of two phases, inspiration and expiration. During the inspiration phase, the diaphragm moves downwards, while the rib muscles pull the ribs out expanding the chest. This expands the lungs and generates a lower pressure inside the chest cavity than outside. This decreases the pressure below normal atmospheric pressure, causes air to rush in through our nose and mouth and into our lungs. This is termed negative pressure breathing. When we breathe out the muscle relax, up and in, and this forces the air to move out of our lungs. The ventilator works in the same manner as sucking the ribs down and out and therefore creating a negative pressure in the chest. Expiration is an active pushing the chest and ribs forcing the air out of the lungs.

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 expiration (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.

The BCV Ventilator can be used in a variety of ways to aid breathing -

  • Periods of controlled ventilation to ease the effort/work of breathing
  • Nocturnal ventilation
  • Use of secretion clearance mode to mobilise and expel secretions

Biphasic Cuirass Ventilation (BCV) is often a preferred method of ventilation as it:

  • Provides complete ventilation to patient, is non-invasive and avoids many of the dangers and problems associated with invasive ventilation such as infection and barotraumas.
  • Works in a physiological way, in that it:
  • Works in the way that the lungs work most efficiently by actively controlling both phases of the respiratory cycle
  • Provides even ventilation for patient
  • Helps to maintain and redevelop the respiratory muscles which often wither and waste with respiratory failure and mechanical ventilation
  • Improves cardiac output
  • Provides an efficient method of weaning from PPV
  • Assists patient to remove secretions which are a symptom of most respiratory diseases, aggravating the condition of these patients
  • Can begin to provide treatment for patients before their condition deteriorates and hospitalisation is required
  • Allows for continuity of treatment for patients in hospital, at home, in transport and in emergency situations
  • Is simple to use.

BCV has been successfully used on patients with:
Acute Respiratory Failure Chronic Obstructive Pulmonary Disease (COPD) Neuromuscular (e.g. SMA, Duchennes etc) Head and Spinal Injuries Problems with Weaning from PPV Ventilation during anaesthesia in Ear Nose and Throat (ENT) Procedures Cystic Fibrosis (CF), and those who require physiotherapy Aids Related Lung Disease Asthma Ventilation post-operation Eg. post-coronary bypass, Fontan, Fallot, post-pneumonectomy

patientUnlike 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, this allows patients to be weaned from a ventilator. BCV also does not impair cardiac function, as IPPV does. BCV is often used as an aid in patients with poor cardiac output.

Unlike conventional negative pressure ventilation, biphasic cuirass ventilation is able to quickly reduce any harmful build up of CO2 using its active expiratory phase.

Many published papers and case studies now show how effective BCV is at reducing CO2 build up. It has also now been shown that the most effective ventilation frequency to reduce CO2 when using BCV is 60 cycles per minute. The oscillations caused by BCV 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. BCV has also been successfully used in a case of failed fiberoptic intubation, in microlaryngeal surgery, and after paediatric cardiac operations.


Sources:
http://www.mediventintl.com/05_aboutbcv.html
http://en.wikipedia.org/wiki/Biphasic_cuirass_ventilation
http://askdrwiki.com/mediawiki/index.php?title=Biphasic_Cuirass_Ventilation
http://www.unitedhayek.com/faq

Edited by John Sandham
Jan 2012