Download High Frequency Ventilation

High Frequency Ventilation
Level 1
Mark Willing, RRT-NPS
Indications for High Frequency
Ventilation



Failure of conventional mechanical ventilation
to relieve respiratory acidosis
Those patients at risk for or have developed a
pneumothorax, pulmonary interstitial
emphysema, pneumomediastinum, or other
air-leak syndrome
A general “lung protective” ventilator strategy
General Concepts




Low tidal volumes (less than 2ml/kg)
Rapid rates (up to 900 breaths/min)
May be “lung protective” due to decreased
volutrauma
May be more efficient at ventilation than
conventional ventilation methods
Enhanced Efficiency of Ventilation

Ventilation during high frequency ventilation is
achieved by a combination of factors
contributing to enhanced removal of CO2
–
–
–
Simultaneous inspiration and expiration due to
unique gas flow pattern
Dependent upon maintaining as many open alveoli
as possible
Enhanced mixing of gases in the airways and
between alveoli
Gas entering the lungs travels centrally, while
gas leaving the lungs swirls around it
Minute Ventilation





The amount of gas that is exchanged within the lung in one minute is
called minute ventilation
As minute ventilation is increased, the amount of CO2 in the blood may
decrease
Minute ventilation during conventional ventilation and spontaneous
breathing is calculated as:
– Respiratory Rate X Tidal Volume
Minute ventilation during high frequency ventilation is calculated as:
– (Respiratory Rate)0.5 X (Tidal Volume)2
Therefore, tidal volume is the primary determinant of minute ventilation
during high frequency ventilation
High Frequency Jet Ventilation
High Frequency Jet Ventilation
Concepts



The inhalation valve is placed as close to the patient as possible
to deliver a “crisp” jet stream of fresh gas deep into the lungs.
A conventional ventilator is used in tandem to assist in
oxygenation. Through manipulation of inspiratory time, PEEP,
PIP, and rate, the mean airway pressure can be adjusted for
optimal oxygenation and alveolar recruitment.
Passive exhalation requires a “lower” set rate (320-480
breaths/minute)
High Frequency Jet Ventilator
Adjustments


Increasing the PIP setting may increase the
delivered tidal volume, therefore lowering the
CO2 in the blood…and vice-versa
Oxygenation is primarily influenced by the
conventional ventilator through manipulation of
the PEEP, PIP, inspiratory time, and rate
Servo Pressure




Respiratory therapists and nurses, alike, will be
charting the servo pressure
Servo pressure is an indirect measurement of the
delivered tidal volume
Changes in servo pressure give the bedside
practitioner information regarding changes in
compliance and resistance
As the servo pressure increases, it may be indicative of
improving compliance and resistance…and vice-versa.
Common Alarms

“Cannot meet PIP” and/or “Loss of PIP”
–
–
–
–
Leaks in the circuit (associated with an acute increase in servo
pressure and high servo alarm). Little or no chest wiggle and breath
sounds.
Excessive respiratory effort by the patient (associated with
repeated high/low servo and mean airway pressure alarms).
Recent disconnect for suctioning or repositioning (associated
with a high/low servo and mean airway pressure alarm).
Near or complete extubation (associated with a high servo pressure
and alarm). Loud upper airway noises, little to no chest wiggle, air
escaping out the mouth.
What To Do





These two alarms are commonly associated with circuit disconnects and
suctioning, which may be associated with severe, and perhaps lifethreatening, alveolar collapse and oxygen desaturation.
The RN must notify the RRT and have this person available at the
bedside prior to position changes, suctioning, and surfactant
administration.
In the event that the RRT is currently unavailable, it is best to leave such
“elective” procedures until such time an RRT can assist with or perform
the procedure without the RN.
If at any other time, if the ventilator fails to establish the set PIP,
immediately notify the respiratory therapist.
Hand-bagging a patient with a manual resuscitator bag may be very
dangerous to certain premature infants, therefore immediate response
from a respiratory therapist is critical.
Positioning the Circuit



The small bore, clear tubing coming off the jet adapter must not be
in a dependent position. Any secretions or water obstructing the
tube will result in inaccurate pressure readings, damage the
pressure transducer in the patient box, and/or will cause
inaccurate pressure delivery to the patient.
The elbow on the in-line suction catheter should be positioned in
such a manner that water condensation is not injected or lavaged
down the airway.
The green jet tubing should be as straight as possible to reduce
any dampening of the jet stream into the airway.
High Frequency Oscillatory
Ventilation
High Frequency Oscillatory
Ventilation Concepts




Open as many alveoli as possible without over
distending the lung
May create blood pressure problems due to high lung
volume, therefore volume expanders and/or vasoactive
drugs may be needed
Active exhalation…pulls the gas out of the lungs on the
expiratory cycle
Active exhalation allows for higher set ventilatory rates
(up to 900 breaths/min)
The SensorMedics high frequency oscillator
pushes and pulls gas above and below a set
mean airway pressure
Settings



Frequency (Hertz, Hz)
Mean Airway Pressure (MAP)
Amplitude (Delta P, change in pressure)
Hertz (Hz)






60 cycles in a minute = 1 Hertz
120 breaths/min = 2 Hz, and so on
15Hz on an oscillator is 900 breaths/min
The smaller the patient, the higher the Hz
setting,…and vice-versa
Less than 2kg patient = 12-15Hz
Children in the PICU may be on 6-10Hz
Mean Airway Pressure (MAP)


Primary determinant of alveolar lung volume
and critical to the efficiency of ventilation and
oxygenation
Use chest X-rays to determine over/underinflation of lung and then adjust MAP
accordingly
Amplitude



Amplitude = Delta P = Change in pressure
As the change in pressure increases, it may
increase the tidal volume, therefore decrease
the CO2 in the blood…and vice-versa
For example, on conventional ventilation, a PIP
of 24 and a PEEP of 4 results in a change in
pressure of 20, and corresponds to a certain
tidal volume…no different with high frequency
ventilation
Circuit Positioning


The circuit should be tilted upward a few
degrees to allow for water condensation to
drain backward towards the ventilator.
The endotracheal tube should be kept as
straight as possible to reduce any dampening
of the pressure.
What do I do if the ventilator turns
off?




The ventilator will automatically stop if there is a disconnect in the
circuit, and may create profound, and perhaps life-threatening,
alveolar collapse and oxygen desaturation.
Notify the RRT immediately.
Gently hand-bag the patient using appropriate inspiratory
pressures (manometer), rate, and PEEP (PEEP valve) until the
respiratory therapist arrives.
As with all patients receiving high frequency ventilation, any
“elective” procedures such as suctioning, surfactant
administration, and position changes require the presence of an
RRT.
What’s that “chirping” noise?


“Chirping” or an intermittent alarm from the ventilator
commonly occurs when the mean airway pressure has
come close to the upper and lower alarm limits.
This is as a result of:
–
–
–
–
–
An improper alarm setting
Water spitting out of the control valve
Excessive respiratory effort from the patient
The MAP setting has been allowed to wander
Inadequate flow to meet the inspiratory demands of the
patient.
Summary





High frequency ventilation can provide enhanced gas exchange beyond
what is capable with conventional ventilation.
The open-lung or high-volume lung strategies have recently proven to be
most successful with and without the presence of active air-leaks.
High frequency ventilation may provide a means of a lung “protective”
strategy for ventilating patients with poor lung compliance at risk for
developing air-leak syndromes.
High lung volume strategy coupled with the relatively stable intrathoracic
volume may reduce venous return to the heart and decrease blood
pressure. Some patients may benefit from an increase in intravascular
volume and/or administration of medications that increase blood
pressure.
Procedures such as suctioning, position changes, and surfactant
administration are to be left for some time at which an RRT can be
present, even if it means before or after the designated “stim” time.