The MicroVent 1 is a dual mode ventilator.
It will operate to deliver standard intermittent positive pressure ventilation
(IPPV) or it will operate to deliver high frequency oscillatory ventilation
(HFOV). The entire breathing system has a volume of less than 1cc. There
are just four parameters to control, Oxygen
flow (9), Frequency (6) (breaths
per minute), Amplitude (5) (tidal
volume) and Mean Airway Pressure (11) (Mean
Paw). In operation a
small flow of fresh gas, in the range of 50-100ml/min or as low a flow as you
are comfortable putting through your vaporizer, is set. This gas can be
oxygen as provided by the built-in flowmeter (9) or any mixture of gases you
provide from an external source. This gas may flow through an anesthetic
vaporizer if you desire using gas anesthetics, then on to the breathing system
(13) where it passes the patient connection (14), flows through an open needle
valve (11) and on to your scavenging system as required. The animal may
breathe spontaneously from this stream of gas as it passes the patient
connection at all times. The needle valve (11) is used to adjust Mean Paw
as seen on the pressure manometer (2). As the valve is closed, gas flow
is restricted causing pressure in the breathing system and thus in the animal's
lungs to increase. This Mean Paw will maintain the expanded lungs
permitting continuous gas exchange with a minimum of atelactatic alveoli.
system is also connected to a glass cylinder containing a floating puck, which
is set in motion as per the settings for frequency (6) and amplitude (5).
In IPPV mode the frequency selectable ranges from 75 to 240 breaths per minute
(BPM). The tidal volume (TV) deliverable is from zero to 10ml. This does
not limit the usefulness of the MicroVent 1 to extremely small animals. A switch (7) to HFOV mode changes the
frequency range to 750 to 2400 "breaths" or more accurately cycles
per minute. The "tidal volume" during HFOV is generally an
order of magnitude less than it would be during IPPV and is now used to set up
an oscillation of the molecules of gas from the breathing system down to the
during HFOV is accomplished via several mechanisms. Traditional convective or
bulk flow occurs in the proximal airways close to the endotracheal tube. The
oscillation setup in the system helps promote the molecular diffusion of the
different gasses in the system. There is a gradient in the partial
pressures of oxygen and anesthetic gas in the system from a peak where the
fresh gas flows past the patient connection to a low in the alveoli where the
concentrations have been decreased by patient uptake. There is also a
gradient in the partial pressure of carbon dioxide in the system from a high in
the alveoli to a low in the fresh gas stream. Oxygen and anesthetic
molecules continually migrate toward the alveoli while carbon dioxide
continually migrates toward the fresh gas stream as they all seek to come into
equilibrium within the system. Turbulences produced by bulk flow, Taylor dispersions,
pendelluft flows, asymmetric velocity profiles between the center and the edges
of the airway lumens and cardiogenic mixing are some of the other known
mechanisms of gas exchange
The oscillations are superimposed on the set Mean Paw,
"all" the alveoli are held open in virtually a steady state as the
frequency is very high and volume of the oscillations is minuscule. The
animal now only vibrates slightly; actually it is more like a hum. No longer do you have the gross movement of
the respiratory cycle so distracting to the microsurgeon.
In addition, depending on the amplitude of each cycle and the set mean Paw,
a value of resulting continuous positive airway pressure, CPAP, can be set and
observed on the pressure manometer (2).
This feature naturally allows and virtually assures that the operator
will be implementing lung protective strategies as described by Amato and
Ranieri, et al. The alveoli are no longer collapsing on expiration then
snapping open again as they expand with each breath. This condition has been shown to cause damage
to the alveolar epithelium and endothelium.
convenience also incorporated into the MicroVent 1 is a system that allows it
to be directly connected to any type of scavenging system, direct vacuum, an
active or a passive system. Placing the Scavenger Select switch (7) in the Active/Passive position directs the
waste gasses directly to the rear scavenging port where you can connect a
charcoal canister, a length of tube to a fume hood or through the wall to the
outdoors or to an active system that already has a scavenging interface valve
in place. Switching to the Vacuum position directs the gasses into
an internal open interface system allowing you to connect a vacuum line
directly to the scavenging port with the 6mm endotracheal tube adapter
provided. In this case the scavenging
flow rate is then adjusted with the flowmeter on the front panel. It must be set to a flow rate greater than
the fresh gas flow rate as provided but the oxygen flowmeter (9) or the externally
set flow you are providing.
With the unit turned off, insure that the Mean Paw adjusting
needle valve is fully open, fully CCW.
Open the oxygen flow valve to verify the existence of a supply of
oxygen. Set the flow rate to 0.2 lpm.
Occlude or place a test lung on the patient connection.
Slowly turn the Mean Paw CW to increase the Mean Paw
to 10 cmH2O.
Set the Amplitude to 5, Frequency to 100 and the Mode to IPPV.
Turn the unit on. After a delay
of 1-2 seconds the puck within the glass housing should start oscillating as
evidenced by the fluctuations observed on the Breathing Circuit Pressure gauge.
Increase and decrease the amplitude and frequency controls, observe
that the controls have the desired effects.
Switch to HFOV mode and repeat the step above.
Turn the unit and O2 flow off.
If the MicroVent 1 does not perform as described
above, DO NOT use the unit. Resolve the
discrepancy or remove the unit for service.
Operating the MicroVent 1 with a
1. Always start with the MicroVent Power off
2. Set the Mode to IPPV
3. Open the Mean Paw
control completely (fully CCW)
4. Set the fresh gas flow desired
5. Connect the patient
6. Increase the Mean Paw
to the desired level
7. Set the Frequency
8. Set the Amplitude to “1”
9. Turn the MicroVent Power on
10. Observe the power light flashing in time with each breath or cycle
11. Increase the Amplitude adjusting it and the Mean Paw
to obtain the desired peak inspiratory and PEEP pressures.
12. If desired switch Mode to HFOV and adjust as required
Cleaning and Maintenance
no alcohol on or near any plastic parts. Clean only
with a damp cloth and mild detergent. Do not allow
moisture to enter the glass puck assembly.
Under normal operation the flow of gas flowing through the breathing
system will carry any moisture from the patient away.
If the MicroVent 1 has a problem, which
cannot be resolved with the use of this manual, please call your dealer or Hallowell
EMC immediately for assistance.
If Hallowell EMC determines that
it is necessary to have the MicroVent 1 returned to us for service, we will
provide you with a RETURN AUTHORIZATION NUMBER.
Please seal the unit in a plastic bag to
prevent contamination from packing materials.
Use a box of sufficient size to allow
for at least 3" of cushioning material such as bubble wrap or foam around the
unit. Double boxing the unit provides
the best protection. Careful packing is
essential. See the Warranty.
| IPPV mode:
||75 – 240 BPM
| HFOV mode:
||750 – 2400 Cycles per minute
|Supply Gas Pressure10-60 psig [69 – 450 kPa]
||IPPV / HFOV
||75 – 240 bpm or 750 – 2400
||1 – 10
||5 turn needle valve
||0 – 1 LPM
|Vacuum Scavenging Flow
||0 – 10 LPM
||Front Panel-mounted green LED
|Breathing Circuit Pressure
||- 10 to + 40 cmH2O compound gauge
||11 lbs [5.0 kg]
||9"W x 9"D x 9”H
||[228mm W x 228mm D x 228mm H]
||100 – 240 Vac, 47 – 63 Hz @ 0.4 A