Thursday, March 11, 2010

Most Aerosolized medicine is wasted

I thought this was some interesting information. According to the AARC's "Guide to Aerosolized Medications," the following are percentages of medications that actually reach a patients lungs:
  1. MDI: 9%
  2. MDI with spacer 15%
  3. SVN: 12%
  4. DPI: 13%
The rest of the medicine "is lost in the oropharynx, the device, the exhaled breath, and the environment," according to the guidelines.

According to MacIntyre, "Aerosolized delivery in intubated, mechanically ventilated patients," Critical Care Medicine, 1885 (13, 81), the amount of inhaled medicine that gets to the air passages of an intubated patient is even less, about 2.9 percent. This information is according to James Fink.

This is interesting. You can see clearly here that more medicine as a percentage that is taken reaches the lungs of a patient using an MDI with a spacer compared to that of an SVN and even a DPI.

However, we must also consider how much medicine is given. A typical SVN provides 2.5mg of a solution, which is usually twice the amount of medication as 2 puffs, or 200 micrograms (μg) of albuterol.

Still, even while there is more medicine delivered with an SVN, the 2 puffs generated similar results as the SVN. This is interesting. And I imagine this is the proof many hospitals have used in changing to using MDIs in the stead of SVNs.

Also, an MDI is much less expensive than an SVN.

Further reading:
More references:
  1. Hess, Dean, Neil MacIntyre, Shelley Mishoe, William Galvin, editors, "Respiratory Care Principles and practice," 2nd edition, 2012, Jones and Bartlett, page 316


Anonymous said...

(posted this last week, didn't get a reply)

Hey man I have a question that I can't find the answer for:

If a standard nasal cannula isn't high flow because after a certain point we have surpassed the patient's anatomical can a high flow nasal cannula run @ much higher flows and provide much higher FiO2s without a reservoir?

In other words: how does a high flow nasal cannula work in regard to the patient's anatomical reservoir?

-1st yr RT

Anonymous said...

whats ur sorce man?

Anonymous said...


Anonymous said...

oh sorry ,, found it :P

Anonymous said...

I just remember learning about that when I was in school...about our anatomical reservoir being the reason we don't run NCs over a certain flow...but at the hospital I work at we use high flow nasal cannulas without reservoirs fairly often and no one has ever been able to tell me why they work and regular nasal cannulas don't...not even the almost-all-knowing Google. I figured this blog might be my best bet.

Todd, 1st yr RT

Rick Frea said...

Sorry, it's been so busy lately I haven't had time to respond. To be honest, I have no idea. You stumped me too. We'll have to learn about this together.

Heidi said...

If you look at those HFNC they have a larger bore to them then the regular NC. It's larger to create more laminar flow. NEVER ever connect them to regular extension tubing as it will cut the flow down to 6 LPM.

I've been working with them for about 6 years now, and prefer the Heated High Flow, but they work up to 15 liters without drowned the patient. At least that's what our education department has claimed to be true.

Anonymous said...

The therapists in this forum should be commended for their intellectual curiosity. Clearly, it's less safe for our patients when no one can explain why/how the care we provide works. When used in neonates, it has been suggested that the high flow nasal cannula generates some unknown level of CPAP. The makes sense, but the pressure level is widely variable and is influenced by many factors: Flow rate, cannula size, size of the air leak around the nasal prongs to name a few. Many nurses and neonatologists have jumped on the high flow cannula bandwagon when there is no evidence that this therapy is better than low flow nasal cannula. No evidence. All anecdotal. It's a belief that is fueled with lots of hype from manufacturers. I think it's bad practice to deliver unknown, variable CPAP pressures without alarms and monitoring. But it's good to ask questions about therapy with questionable benefits.

Anonymous said...

True, for low flow o2, the anatomical resevoir is a key componant of the FIO2... But, due to newer tecnhology regarding humidification delivery, true "hi-flow" (i.e. flowrates > inspiratory demands) can now be achieved. Thus true high flow / high FIO2's can now be effectively delivered via a high flow cannula