The Medivent RTX works using a unique Biphasic Cuirass Ventilation (BCV) technique. A negative pressure is generated within the chest cuirass, for inspiration or continuous inspiratory assistance, and applies a positive pressure within the cuirass inducing expiration. This positive expiratory pressure means that expiration is an active phase in the respiratory cycle this makes the RTX particularly efficient at CO2 clearance references 34, 36.

The pressure applied within the cuirass acts uniformly over the thorax. Subsequently, lung expansion is also uniform ventilating all areas of the lungs. In positive pressure ventilation (PPV) the gas pushed into the lungs naturally follows the path of least resistance therefore ventilating the already well ventilated areas. Increase in pressures/volumes to aid ventilation of all areas of the lungs leads to barotrauma, volutrauma and possible development of a pnuemothorax. These complications, along with those of ventilator associated pneumonia, are of no relevance with BCV.

BCV in conjunction with PPV is used as an aid to weaning, to increase right ventricular function and aid in expansion of areas of collapse references 12, 13, 38, 40, 41, 55, 60.

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

Control Mode

This mode provides full control over the patient’s respiration

1. Mandatory respiratory rate is set and delivered; patients do not fight against the mandatory breaths as the RTX uses their own respiratory muscles to breath. This is a unique function of the RTX as it mimics physiological respiration.
   
2. Controls both inspiratory and expiratory phases and you have control over the I:E ratio
   
3. Commence rate at 2 above their own current spontaneous rate, then can slowly decrease the rate as patients breathing controlled by RTX
4. If PaCO2 increases alter I:E ratio to 1:1.2 - 1:1.5
   
5. At frequency’s over 60 the inspiratory pressure and the expiratory pressures should set at the same figures i.e. -15 and +15
6. At frequencies of 240-1200cpm you can only preset frequency and inspiratory pressure parameters
   
7. It is in this mode that you are able to oscillate the patient from 1-20Hz with pressures up to +/- 50 cmH2O
   

There are 2 modes which are triggered by the patients’ respiratory effort. These modes can be used as pressure support modes and an aid to weaning.

 

Respiratory triggered

1. Provides triggered ventilation with the respiratory cycle triggered by the patient’s actual respiratory requirements
   
2. The frequency is determined by either the patients rate or the minimum frequency set by the physician
   
3. The I:E ratio is determined and set by the physician
   
4. The trigger can either be through the cuirass or through the airway tube placed at or near the patients airway e.g. by the patients nose or mouth. Cuirass trigger will pick up more vigorous spontaneous breathing, whereas airway mode can be triggered by smaller, shallower respiratory effort.
   
5. As the respiratory cycle is triggered by the patients own respiration, this allows better adjustment to the patients actual requirements. The respirator will wait for a period for the trigger; this is dependant on the trigger sensitivity set. If no trigger is detected during this period then the respirator will begin another cycle. In the event of apnoea the RTX will deliver the set back up rate.
   
6. Trigger % should be 80-85% if higher you may need to adjust sensitivity, this is to ensure false triggers are prevented
   
7. Minimum backup rate is 6 per minute i.e. 1 every 10 seconds
   
8. Maximum backup rate is 60 per minute i.e.1 per second

 

Respiratory synchronised

1. This mode is fully synchronised with the patients own respiration, automatically adjusting the arte and shape of breathing in sympathy with the natural breathing adjustments being made by the patient themselves.
   
2. The patients’ inspiratory effort creates an initial trigger which is followed by a further trigger by the initial effort of expiration. The trigger can be either through the cuirass or airway.
   
3. Difference between this mode at respiratory triggered is that on this mode the support is timed with patients own respiratory pattern, so no I:E ratio is set by the physician
   
4. The I:E ration will be calculated and displayed
   
5. This mode will allow the patient to breathe both at their own rate and determine their own shape.
   
6. In the event of apnoea the RTX will deliver the set back up rate delivering fully controlled ventilation at the pressures set

 

ECG Triggered

1. This mode takes into account the capability of the RTX to improve both cardiac output and circulation by including the capability of ECG trigger
   
2. Frequency is determined by the patients’ heart rate, and all other parameters are preset.
   
3. Ventilation is synchronised to the patient’s cardiac cycle, augmenting the effect on circulation and cardiac output. If no cardiac activity is detected (e.g. there is a bad contact with the ECG probes) the RTX will alarm and operate at predetermined default settings for frequency set by the physician.
   
4. Inspiration activated on T wave and expiration on R wave
   
5. Clinician set inspiration pressure and this then defaults the exp to the same