Oscillating ventilation

High frequency oscillatory ventilation (HFOV) simulates the effects of panting: small tidal volumes at a greatly increased rate. This serves to recruit lung tissue by never letting the alveoli completely collapse and it should dramatically improve CO2 removal by maintaining the exposed surface area of the alveoli. The ventilator itself has a piston in the centre of a cone that moves at very high speed to push and pull these tiny tidal volumes into and out of the lung. The patient "wiggles" at the same speed, which is a little disconcerting to watch at first, but the farther down the body the wiggle goes, the more effective the strategy will be.

HFOV is used for refractory ARDS where conventional ventilation has failed to provide improved gas exchange without using excessive pressures or volumes. The mean airway pressure is maintained within a fairly narrow range, the amplitude of the oscillations is adjusted to provide optimal "wiggle" determined by arterial blood gas values and the rate is set in hertz. 1 Hz = 60 oscillations or breaths per minute. The smaller the patient the higher the Hz, in general. My toddler patient yesterday had a mean airway pressure of 26 cm H2O, amplitude of 50 mL/oscillation and 10 Hz (600 "breaths" per minute).

Assessing an HFOV patient is a little different from the usual. You have to assess the wiggle. Breath sounds are assessed based on how clearly you can hear the piston inside the chest. Optimum is that the piston noises are equally heard over all fields. Retained secretions, ongoing atelectasis and pleural effusion are some things that will affect that. It's all but impossible to hear heart tones and bowel sounds over the piston noise and it can be difficult to feel pulses in a limb that's vibrating at 600 oscillations per minute. These patients are often so sick that they don't tolerate large position changes or being "light" without desaturating to alarming degrees. Their intrathoracic pressure will be elevated (reflected in their CVP) and they often will crump when first going on HFOV when venous return to the heart suddenly drops. Being prepared for that is half the battle! Other complications are pneumothorax, gas-trapping and inspissated secretions.

Requiring HFOV for more than about a week is an indication for ECMO, which is a whole other ball of wax.

Check out: http://priory.com/cmol/hfov.htm

Excellent summary, Jan!

Why thank you! We've got a few whumpers going right now, so the review was good!!

Great explanation! Only thing I would add is that it is not used on adults, probably because the adult lung is too large and the little 5-10 cc "puffs", even at a rate of 600, won't ventilate adequately.

Not true, sunny. I've found journal articles dating back to 2003 discussing the efficacy of HFOV for adults with ARDS, others that discuss best practice strategies and


http://ccforum.com/content/7/5/385
It has recently been shown that strategies aimed at preventing ventilator-induced lung injury, such as ventilating with low tidal volumes, can reduce mortality in patients with acute respiratory distress syndrome (ARDS). High-frequency oscillatory ventilation (HFOV) seems ideally suited as a lung-protective strategy for these patients...

http://www.ecu.edu/cs-dhs/pulmonary/...osc%20vent.pdf
Ventilator settings typically used for high-frequency
oscillatory ventilation (HFO) in adults provide acceptable gas
exchange but may not take best advantage of its lung-protective
aspects. We provide guidelines for HFO in adults with acute
respiratory distress syndrome that should optimize the lungprotective
characteristics of this ventilation mode...

http://ajrccm.atsjournals.org/cgi/co...full/166/6/801
Observational studies of high-frequency oscillatory ventilation in adults with the acute respiratory distress syndrome have demonstrated improvements in oxygenation. We designed a multicenter, randomized, controlled trial comparing the safety and effectiveness of high-frequency oscillatory ventilation with conventional ventilation in adults with acute respiratory distress syndrome... We conclude that high-frequency oscillation is a safe and effective mode of ventilation for the treatment of acute respiratory distress syndrome in adults.

The amplitude (tidal volume) of each oscillation is adjustable. We typically use 5-10 mL/kg not 5-10 mL/oscillation. And the Hz is also adjustable. The point of HFOV is to splint the lungs open and it does that quite effectively even in adults.

Oh, thanks for all the great references . . . maybe I should say, I've only seen it used on little ones (when I was an RT). The intensivists in our adult ICU don't think it is effective (but, I don't know if they've ever tried it!!) Actually, we'd have to borrow the oscillator, we don't even have one.

Do they use HFOV on adults at your med center?

Yes we do. We do all sorts of things, orthodox and not so much. We have quite a few oscillators in our vent pool. Actually, none of the new ventilators our health care system purchased for the pandemic are suitable for children in any way, so we'll be sending them across the way to the adult units and keeping the servos for us.

Very cool. When I was an RT, I always thought the theory of high frequency should apply to adults with ARDS, and now especially with the low tidal volume approach. But, the intensivists would never go for it.

I see that you're ECLS . . . you do adult ECMO, too??

At the moment I'm strictly peds, since our unit has the busiest ECLS program in the country. But the rumor is that if the adult ECLS program is swamped we'll be seconded. Their program, I believe, is run by the perfusionists but I may be wrong. The adult program isn't registered with ELSO, only our peds program. We do neonatal and peds pulmonary, cardiac and ECPR. We do some hybrid stuff like cut oxygenators in to VAD circuits (we call it Berl-ECMO), interesting and effective but confusing as heck! Our children's hospital is one of those hospital-within-a-hospital deals and we're the Berlin Heart training center for North America so all of our nurses are also Berlin Heart certified. We currently have 5 circuits running in the PICU. Glad I'm on vacation!