|
VORTRAN
Automatic Resuscitator™ (VAR). Unique single patient,
multiple-use disposable emergency resuscitator.
How
does VAR function?
The
gas-powered VAR provides constant flow, pressure cycled automatic
ventilatory support for both breathing and non-breathing patients. The
primary working mechanism of the VAR is the [1] modulator with [a]
peak inspiratory pressure (PIP) and [b] breathing rate adjustment
dials, which is an exhalation valve that opens at one pressure (PIP)
and closes at another lower pressure (PEEP). The remaining components
of the VAR consist of the [2] pressure manometer, [3] inlet for supply
gas flow, [4] patient connection port, [5] redundant pressure pop-off
valve, and [6] one-way valve for entraining additional air (Figure 1).
The pulmonary
modulator provides the actual ventilatory support. The primary working
mechanism of the pulmonary modulator is the piston. The piston is
spring loaded, designed like a pressure pop-off valve except the
spring force is adjustable (the [a] PIP Dial).
Figure
1
VAR Component Description
Figure
2
VAR Dimensional Profile
Clinical
Considerations
The VAR provides short term, pressure cycled, and constant flow
ventilatory support for either breathing or non-breathing patients.
This allows the patient to receive consistent, and reliable
ventilatory support. The VAR is pressure cycled on inhalation and
exhalation (PIP and PEEP) which minimizes the possibility of gas
trapping. During inhalation, exhalation will not start until PIP is
reached. During exhalation, inhalation will not begin until pressure
drops to PEEP. For spontaneously breathing patient, the rate dial of
the VAR is set so that the base line pressure is above the intrinsic
PEEP allowing the patient to initiate inhalation by drawing the base
line pressure down to the set PEEP. Because the VAR is a constant flow
pressure cycled device, changes in patient compliance will result in
changes in the respiratory rate (stiffer or smaller compliances
produce faster rates). The advantage of this minimizes the danger of
barotrauma. However, it should be emphasized that the VAR is to be
used only by trained personnel who continuously monitor the patient.
The VAR is not an ICU stand-alone ventilator with multiple monitoring
features.
Setup and use of the VAR is simple (refer to Setup Instructions in
Section 3). Set desired flow (Q), adjust PIP pressure dial to obtain
desired inspiratory time (ti) to attain tidal volume (TV = Q X ti),
see Tidal Volume Table below. The gas flow, patient's lung compliance
and PIP settings control the inspiratory time and tidal volume. Then
adjust rate dial to obtain desired breathing rate.
Table
Estimated Tidal Volume (mL) at Various Flow Rate (LPM)
The VAR runs
on a continuous gas flow (inspiratory flow) of 15 to 40 L/min
depending on patients' inspiratory flow demand. When connected to a 50
PSIG gas source, the VAR will automatically deliver 40 L/min (667 mL/second)
per ASTM guideline[1].
Delivered tidal volume may be determined by multiplying the flow in mL/second
and the inspiratory time in seconds, or using the estimated tidal
volume table.
The rate dial controls exhalation time (te),
and when dialed down enough will cause the VAR to stop cycling
automatically (infinite exhalation time). Under these circumstances
the VAR is delivering pressure supported ventilatory support and the
patient must trigger the VAR to begin subsequent full inhalations. If
the patient is apneic or pressure control ventilation is desired
restart automatic cycling of the VAR by adjusting the rate dial
counter clockwise until cycling begins again. Whenever the VAR stops
cycling, the first step, in the absence of obvious clinical factors,
is to check if it is in pressure support mode by rotating the rate
dial counter clockwise (out). If rotating the rate dial counter
clockwise substantially (3 or 4 turns) does not start automatic
cycling, the patient's airway may be occluded or a very large leak
exists.
PIP may be adjusted from 20 and 50 cm H2O.
PEEP is typically 1/10th of PIP. Inspiratory time and rate are
adjustable over a wide range. Changes in the PIP setting or flow will
also affect the respiratory rate. It is important to check all
settings when making a change to any of these three variables (flow,
PIP and rate). For example: reducing the PIP setting may cause the VAR
to go into spontaneous breathing mode. Adjust the rate dial out
(counter-clockwise) to restart automatic cycling.
The VAR is equipped with an air entrainment valve which allows the
patient to entrain additional air and respond to the demands of the
patient. Patient entrainment of outside air is normally audibly
detectable and the percent oxygen delivered to the patient will be
reduced. Specific concentrations of oxygen may be delivered to the
patient with the use of an oxygen blender.
Although the design of the modulator is similar to that of a pop-off
valve and is inherently safe, the VAR is also equipped with a
redundant pop-off valve that relieves pressure at 60 cm H2O.
When the pop-off valve is activated, the pop-off valve piston will be
seen to open slightly and excess pressure released.
The duration of an "E" cylinder when using a VAR will depend
on the flow. An "E" cylinder contains 625 L of gas. At 40
L/min, 625 L will last up to 15 minutes; at 20 L/min, 625 L will last
up to 30 minutes. 15 L/min orifice type flowmeters used on many
"E" cylinders will not be able to deliver more than 15
L/min. When clinicians decide that 15 L/min is not sufficient flow,
the VAR can be attached to a regulator that has a high flow port
(50PSIG) to deliver 40 L/min.
Although peak
pressures are listed on the side of the pressure dial, they are only
approximate. Clinicians using the VAR are still required to use good
clinical judgment and monitor the patient appropriately. A manometer
may be connected between the modulator and the patient connector tee.
The VAR is pressure cycled on PEEP as well as PIP. In the pressure
control mode there is no prolonged stage where the flow of exhalation
gas stops for a significant duration of time (in the pressure support
mode, exhalation time is determined by the patient). This occurs
because the exhalation time is set with the rate dial by varying the
exhalation resistance so that the patient just finishes exhalation
with the beginning of the subsequent inhalation. The volume of gas
with which the patient's lungs are inflated with when reaching PEEP is
the same as with any other means of obtaining PEEP. As with all
ventilatory support modes, short exhalation times on patients with
high airway resistance may lead to gas trapping which is not
detectable in the patient's external airways. Upon occlusion of the
patient's airways, the VAR will stop cycling or may sometimes cycle
rapidly.
The VAR will work with any mask that provides a good seal with the
patient. All clinicians should receive adequate training with a VAR
with mask prior to use. In the presence of a small leak, the VAR will
still cycle between PIP and PEEP. Noticeable changes in the presence
of a leak are increased inspiratory times and decreased expiratory
times. The VAR works very well with an endotracheal tube.
Inhalation may be initiated by briefly removing the mask from the
patient or briefly disconnecting the modulator from the patient
adapter tee. In either event, inhalation begins because pressure has
dropped down to PEEP and the VAR is pressure cycled.
Upon contamination of the VAR with vomitus, it may be cleared by
disconnecting the modulator from the patient connector tee (see
enclosed instructions) and tapping out vomitus on a hard surface.
Additionally, if needed, the rate dial may also be removed to
facilitate removal of vomitus from modulator. This operation should
take less then 20 seconds, and in a lab setting has consistently been
shown to take approximately 11 seconds. Alternatively, upon
contamination with vomitus, the clinician may choose to discard the
device and use a new one.
Inhalation and
exhalation are audibly detectable and easily recognizable during
operation of the VAR.
The VAR may be controlled remotely by connecting any length of 22-mm
corrugated tubing between the patient connector tee and the modulator.
The attached tubing will not increase the dead space, the modulator is
an exhalation control valve, inspiratory gas is delivered through the
patient connector tee.
The primary advantage of the VAR, as compared to manual resuscitators
is the ability to deliver consistent, reliable, hands free
resuscitation. Manual resuscitators may have adverse effects on
patients as a result of inconsistent ventilation (see Clinical
Reference in Section 5).
Figure
3
1.
PIP-Set by PIP Dial, control Inspiratory TIME (Itime)
2. PEEP _ Approximately 1/10th of PIP setting
3. Inspiratory Flow Rate (Q) _ Maximum 40 L/min (= 667 mL/sec)
4. Inspiratory Time (Itime) _ Time required to reach PIP
5. Exhalation Time (Etime) _ Time required to drop from PIP to
PEEP
6. Tidal Volume = Q X Itime
7. Respiratory Rate (RR) = 60 / (Itime + Etime )
8. RATE DIAL _ Set exhalation resistance and change RR
[1] Standard
Specification for Minimum Performance and Safety requirements for
Resuscitators Intended for Use with Humans, ASTM Designation: F 920 _
93.
|
