Portable Home Ventilators
by: Donnell Cushman, BSRT, RRT
As medical technology continues to advance and the drive
toward cost savings continues, an increased number of critically
ill patients are being discharged from the hospital to the home
setting. One of the most dramatic changes in home care is the sharp
rise in the number of patients being discharged to their home on
portable home ventilators. The home care ventilator patient now
covers all age groups, requiring the Respiratory Therapist to have
a thorough background in the variety of disease processes and ventilator
management techniques, along with a thorough knowledge of the variety
of ventilators and associated equipment required to provide ventilatory
life support in the home.
Negative Pressure Ventilator
The purpose of this article is to review the different portable
ventilators available in the home setting. Ventilators, whether
hospital or home based, can be divided into two categories: Negative
Pressure Ventilators and Positive Pressure (Volume) Ventilators.
Negative pressure ventilators provide assisted or augment spontaneous
breathing or completely regulate a prescribed breathing pattern for
a patient who cannot breathe without assistance. This is achieved
by generating negative extrathoracic pressure. Negative pressure expands
the thorax, producing a negative intra-alveolar pressure and consequent
movement of air into the lungs. Expiration is largely passive. There
are several different types of negative pressure ventilators currently
available in the home care market. These include the iron lung, the
cuirass, and the body wrap.
The iron lung consists of a large metal cylinder with flexible
diaphragm operated by a piston rod at the distal end. This ventilator
has the capacity to develop intra-tank pressure of up to -25 to
-30 cmH2O and a respiratory rate between 10 and 30 breaths per minute.
Although the iron lung is the most effective means of negative pressure
ventilatory support, it is quite large, requiring a considerable
amount of operating space. It prevents easy accessibility to the
patient and is very uncomfortable for many patients.
The cuirass ventilator consists of a rigid shell, some
models consist of shells of either reinforced plastic or fiberglass
which extend from the symphysis pubis to the suprasternal notch.
The cuirass is sealed to the chest and abdominal walls with a flexible
rubber diaphragm. Correct fitting of the cuirass is imperative for
its proper functioning. The cuirass must be connected to a power
source capable of generating -25 to -30 cmH2O pressure. Since the
cuirass only covers the chest area the patient can be ventilated
in either the sitting or supine position, therefore making the cuirass
ventilator the least confining of the negative pressure ventilators.
If the cuirass fits too loosely, poor sealing of the cuirass to
the body surface will result in delivery of inadequate tidal volumes.
However, excessive tightening of the straps or a too small cuirass
can result in patient discomfort, restriction of chest wall motion,
and skin irritation. Due to the small tidal volumes generated by
this unit in patients with normal chest wall and lung compliance,
the cuirass is not capable of providing complete ventilatory support
in apneic patients.
The body wrap consists of a one-piece plastic suit, a flat
rigid plate, and a large plastic grid. The patient lies supine on
the plate which extends the length of the thoracic spine. The grid
is placed over the patient's thorax and the separate power source
is connected to the mid-portion of the suit by a plastic tube. The
grid causes the negative pressure generated within the suit to be
applied predominately to the thorax since the plastic is sucked
tightly against all other body parts. The body wrap is portable,
lightweight and much more comfortable than the iron lung. The body
wrap does not allow access to the patient without interruption of
ventilatory support, and generally only provides modest tidal volumes.
It can only be used on patients who are not totally dependent on
ventilatory support and can maintain unassisted ventilation for
prolonged periods of time.
The major advantage of negative pressure ventilation is
that it eliminates the need for tracheal intubation usually required
for positive pressure ventilatory supports: therefore decreasing
the number of complications and discomforts of tracheal intubation.
The patient is also able to verbally communicate with family and
medical personnel while being mechanically ventilated.
The disadvantages of negative pressure ventilation will
of course depend on the type of negative pressure ventilator being
used. Negative pressure ventilation is not suitable for all patients.
Negative pressure ventilation is not suitable for all patients.
Negative pressure ventilators cannot sustain adequate ventilation
for prolonged periods in apneic patients. Other disadvantages include
the fact that regulation of inspiratory flow rates and cycle duration
is not possible. lncreased thoracic elastance may prevent generation
of adequate tidal volumes. The lack of complete accessibility to
the patient impedes the performance of adequate chest physiotherapy.
The lack of control of the upper airway places patients with disorders
of upper airway function at increased risk of aspiration of gastric
contents and upper airway obstruction. Therefore it is recommended
that negative pressure ventilation only be used on those patients
who do not have excessive secretion, markedly increased thoracic
elastance, or disorders of the upper airway.
Positive Pressure Ventilation
The spectrum of patients requiring positive pressure ventilation
demands that portable volume ventilators have various degrees of
sophistication. Needs may range from occasional ventilatory support
to complete ventilatory use. The patient may range from a child
to an adult. The needs of a ventilator dependent child may vary
greatly from the needs of a ventilator dependent adult. Most modern
portable and critical care ventilators use positive pressure to
inflate the patients lungs. This pressure causes a positive pressure
to inflate the patient's lungs. This pressure causes a positive
intra thoracic and alveolar pressure during inpiration. As with
negative pressure ventilation, expiration is largely passive.
There are a number of home positive pressure ventilators
currently available in the home care market. These include the LP-6
Ventilator, the Bear 33, the PLV-1OO, and the PB-28OO, just to name
a few. Regardless of the name brand, all portable ventilators should
have the blowing features: an internal and external battery source,
a way in which to add oxygen to the patient's breathing circuit,
a way to measure delivered and exhaled volumes and the ability to
alert patient and/or caregivers of low patient pressures.
Portable volume ventilators are often used in locations
that lack emergency AC power. All units should, therefore, have
an external battery and an internal power source that is capable
of running the unit for up to one hour under normal working conditions.
The internal battery should charge automatically whenever the ventilator
is connected to AC power. The ventilator should not have a separate
charging mode, but instead charge while operating in any ventilation
mode. The internal power source should activate automatically when
the line voltage falls below the unit's operating range. A low battery
alarm should sound at least 20 - 45 minutes before operation of
the ventilator is affected. A visual indicator should identify when
the unit is charging. The external battery is often dependent on
the type portable ventilator being used. lf AC power is lost, the
ventilator should switch to the external battery automatically.
Portable volume ventilators should have some means of providing
oxygen-enriched inspired air to the patient. Delivered oxygen concentration
should be within + or - 4% of the set level over the ventilator's
normal range of operation.
Measurements of delivered and exhaled volumes are usually
performed by using a Wright's spirometer to measure the amount of
air coming directly from the ventilator during each inspiratory
breath. The exhaled volume is measured with a Wright's spirometer
by attaching it to the exhalation port on the patients' breathing
circuit. These volumes should be measured periodically to assess
the patients' condition and to ensure proper ventilator functioning.
Monitors and alarms are essential to establishing and maintaining
adequate and safe ventilation. Adjustable alarms should be available
for detecting excessive increases and decreases in patient airway
pressures. Pressure alarms should be adjustable between a minimum
of 5 cmH2O and at least 60 cmH20. Pressure should be monitored just
proximal to the patient's airway.
The disadvantages of positive pressure ventilators, are
the patient usually requires tracheal intubation (Tracheostomy),
therefore increasing the risk for infections and airway obstruction.
With the application of positive pressure directly to the lungs
the incidence for barotrauma is greatly increased.
The advantages of portable positive ventilators are the
fact they are smaller, reliable, and more portable than the hospital
based ventilator. Therefore allowing patients who would otherwise
be confined to the hospital to be discharged to the home setting.
The number of ventilator dependent patients being discharged from
the hospital to the home setting is continuing to increase. It is
imperative that the respiratory therapists, physicians, and discharge
planning nurses are familiar with the different types of portable
positive pressure and negative pressure ventilators available in
the home setting. Manufacturers are continuing to explore methods
of developing ventilators that better meet the needs of the large
spectrum of patients requiring mechanical ventilation in the home