Tuesday, May 19, 2015

Most Aerosolized medicine is wasted

According to the American Association of Respiratory Care's "Guide to Aerosolized Medications," not much of the medicine inhaled by inhalers and nebulizers makes it into airways.

By device, here's how much medicine reaches the lungs?
  • Metered Dose Inhalers:  9%
  • Metered Dose Inhalers with spacer:  15%
  • Small Volume Nebulizer:  12%
  • Dry Powdered Inhaler:  13%
So that means that most of the inhaled medicine, or a whopping 85-91% depending on the device used, "is lost in the oropharynx, the device, the exhaled breath, and the environment," according to the guidelines.

When a patient is intubated the percentage of medicine getting to airways is 2.9%, according to one study. 

It appears that the best distribution into the airway is obtained by inhaler and spacer.  Of course, this would only be possible if good technique is used.  Considering studies show that up to 93% of asthmatics do not correctly use their inhalers (93% to be exact), this kind of knocks inhalers and inhalers with spacers down to a level playing ground with nebulizers.  

While some might panic at these percentages, one should not worry. Pharmaceutical companies are well aware these when the formulate their dosing criteria.  So chances are that, regardless of the route used, most patients get plenty of medicine for maximum effect. 

Plus, it must be considered that 2.5 mg of albuterol solution mixed with 3cc of normal saline contains about twice as much ventolin as in the 200 mcg of albuterol inhaled via an inhaler.  So, again, patients are getting plenty of albuterol, and probably more than enough when an SVN is used. 

So who wins the battle of inhalers vs. nebulizers?  Well, as far as distributing medicine to airways, they all work equally well.

This post was originally published on March 11, 2010.  It has been edited for accuracy by Rick Frea.  

Further reading:

9 comments:

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 reservoir..........how 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...

source*

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