15. High Frequency Oscillator Ventilation (HFOV) Flashcards
What does 1 Hz equal in breaths per minute?
60
Tidal volumes are less than what?
deadspace
What does an oscillator use to displace gas?
piston or loudspeaker…moves air back and forth in the bias flow of the circuit
What are the 4 benefits of HFV?
small tidal volumes with low alveolar a/w pressure, gas exchange at low alveolar a/w pressures, alveolar recruitment and improved oxygenation, constant lung recruitment on insp. and exp. preventing end-exp. collapse
How does HFOV work?
- continuous distending pressure to open the lung (oxygenation)
- oscillation waves to produce tidal volume (ventilation)
Mechanism of gas transport:
What does Taylor dispersion describe?
What does the Pendelluft effect describe?
What does asymmetric velocity profiles describe?
What does cariogenic mixing describe?
What is collateral ventilation?
turbulent flow in the large a/w enhances gas mixing
at high frequencies, gas distribution is strongly influenced by time content inequalities (gas from fast units will empty into the slow units)
air closest to the tracheobronchial wall has a lower velocity than air in the centre of the a/w lumen (bias flow delivers fresh gas high in o2 down the centre of the a/w, co2 rich gas is moving out of the lungs along pressure gradients by traveling along the walls of the a/w)
mechanical agitation from the contracting heart contributes to peripheral gas mixing
through the pores of Cohen
The smaller the ETT thee ______ the pressure attenuation.
By the time the pressure reaches the alveolar surface, it is reduced down to __-__cmH2O with a #3 ETT
greater
0.1-5
List some risk of HFV.
not knowing the device well, not matching strategy to disease pathology, over distension, atelectasis, hyperventilation, cardiovascular effects
What considerations should be made in respect to hemodynamic monitoring on HFOV?
monitor: HR, BP, pulse pressure, cap fill time, U.O
may need to consider fluid bolus to counteract cardiovascular effects
stop oscillation to hear heart/bowel sounds
What is the purpose of the dedicated medical air functions?
How is the FiO2 set?
Which valve is the red, blue, clear, and green?
cool piston external blender blue - limit valve green - control valve red - safety dump valve clear - pressure sensing line
Which parameters are used to manipulate oxygenation? Which parameters are used to manipulate ventilation?
oxygenation - MAP, FiO2, LRM
ventilation - delta P, Hz, % Ti
How is MAP created?
continuous bias flow of gas past the resistance (inflation) of the balloon controlled by the MAP dial
Bias flow:
premature? term? small child? large child? adult?
What circumstance should you increase bias flow?
10-15, 10-20, 15-25, 20-30, 30-40 LPM
if needed to maintain MAP (rare)
When is lung recruitment used? What should you consider with any planned disconnects/transitions? How long does full recruitment take? How often should CXR’s be taken after initiating HFO?
initiating HFO, post-sxning/disconnects, improve oxygenation
clamping ETT
full - 15-30 min, majority within first 5 min
end of first hour, 2-3 hours, Q12-24 hrs
What are the 2 methods for lung recruitment? Appropriate pressures?
- brief sustained increases in MAP with oscillator running (Neo - MAP increased by 1-3 for 2-10 minutes)
- LRM, piston off (Neo - increase MAP 1-5 cmH2O above current for 40 s, peds - 20-30 cmH2O for 30-40 s, adult - 30-40cmH2O for 40 s)
Under what circumstances should you not perform an LRM?
bubbling chest tube, pneumothorax, hypotensive patient
How in ventilation controlled? How is alveolar ventilation defined?
Do changes in tidal volume have an effect on CO2 elimination?
movement of piston (SV)
Ve = f x Vt2
significant effect
Define amplitude. How is it determined? How is it represented?
force the piston moves for a given time (distance)
by POWER
peak-to-trough pressure swing across the MAP
What should the chest wiggle factor by for neonates? children? large children?
Possible causes of stopped/diminished CW?
Possible causes on CW only on one side?
neonate - wiggle to umbilicus
child - wiggle to groin
large child - wiggle to mid-thigh
ETT obstruction/kink (sin and reassess)
ETT too deep, mucus plug, pneumothorax (check ETT position, sun, transilluminate, xray)
What does frequency control?
time allowed (distance) the piston moves
lower the frequency settings, the greater the volume displacement
high the frequency, the smaller the volume displacement
What does frequency establish?
total cycle time
% Ti controls what? What is the recommended Ti? When is increasing % Ti used?
time for movement of the piston (assists with CO2 elimination)
33%
used in larger patients as the third maneuver to control CO2 eliminations
How can a cuff leak improve PaCO2?
allow CO2 in a/w to be washed out by bias flow gas around the leak
High lung volume strategy:
MAP? Hz? delta P?
MAP 1-3 cmH2O above CMV, Hz per weight, delta P 20-25 and adjust for CMF
