Vol. 15 •Issue 4 • Page 18
Matchmaking in Asthma
Use this review of delivery devices to choose the right one for your patient.
Asthma is best treated with inhaled medications that must be effectively delivered to the lower airways. But our bodies’ natural protection of our lungs from potentially harmful foreign materials works against this process.
Various inhalation methods have been developed to overcome this protection.1 The effectiveness of an inhalation delivery method depends on the agent to be delivered to the lungs and the patient.2 It’s important to match asthma prescriptions with the proper delivery device.
When deciding which device to use, we may need to ask a series of questions: Does the provider or patient prefer one device over another? In which devices is the medication available? What device is the patient able to use properly, depending on factors such as age and setting? Once the device is selected, patient education is crucial in asthma management, and reinforcement of technique should be performed at each visit.
Nuances of nebulizers
One type of delivery device is the compressed-gas or jet nebulizer. This is the most familiar delivery device due to its frequent use in emergency departments and hospitals.
This type of delivery takes advantage of the Venturi effect, which is a special case of Bernoulli’s principle. When air flows through a tube with a constriction in it, the air must speed up in the restriction, reducing its pressure and producing a partial vacuum. This rapidly flowing gas draws a liquid into it due to the negative pressure.
The source of flowing gas in institutional settings usually is oxygen, while at home a medication compressor delivers room air. The gas travels through tubing to the nebulizer cup with a small amount of liquid in which the medication to be delivered is placed. As the gas passes into the cup, the liquid is drawn into the flow.
Most nebulizers have a barrier a short distance above the liquid surface onto which the flowing gas/liquid mixture impacts, creating a mist of fine particles of liquid. Larger particles generally rain back into the nebulizer cup while fine particles travel around the barrier and out to the patient where they’re inhaled.
Most nebulizers provide a continuous flow to the patient while others provide a patient-activated valve for stopping the outflow during exhalation which improves the efficiency of delivery. To optimize medication deposition, patients should always use a mask or mouthpiece because holding the tube in front of the patient’s face “blow by” decreases delivery significantly.
With jet nebulizers, patients of any age can use them, coordination isn’t required, and delivery of high drug dosages including continuous administration are possible. Jet nebulizers require no organic propellant to deliver the medication and can be used with supplemental oxygen.
However, most jet nebulizers aren’t very portable, they require a source of electricity, and they require 10 to 15 minutes to deliver the medication. In addition, medication delivery is device-dependent.
To overcome some of these disadvantages, ultrasonic devices have been developed that are small, portable and battery powered.3 These create a mist of fine particles using a membrane in the nebulizer cup that vibrates at ultrasonic frequencies. The mist flows through a mouthpiece where it’s easily inhaled.
In general, delivery of medications by ultrasonic nebulizer has similar clinical effect to that of jet nebulizers, though there may be variations in some situations.4-6 Ultrasonic nebulizers are convenient to use, but they tend to be more expensive. Also, the ultrasonic frequency disrupts the chemistry of certain suspensions such as budesonide nebulizer solution, so they shouldn’t be used to deliver those types of medication.
Pressurized metered dose inhalers
Pressurized metered dose inhalers (pMDIs) are the most frequently used type of device for asthma treatment. Typical pMDIs consist of an aluminum cylinder containing a mixture of medication and a volatile organic liquid such as Freon™ or hydrofluoroalkane (HFA) under high pressure.
Because drugs generally aren’t soluble in the liquid, particles of the medication tend to settle on the bottom of the cylinder between uses. The cylinder should be shaken to create a uniform suspension of medication prior to each use.
When a smaller valve consisting of a hollow tube in the center of the canister is depressed, a measured amount of this suspension is exposed to atmospheric pressure allowing it to expand and escape in the form of a fine mist. The organic liquid evaporates rapidly leaving behind particles of medication that can be inhaled.
The advantages of using pMDIs over nebulizers are that they’re compact, portable, require a shorter delivery time, don’t require a power source, and they have a higher dose reproducibility. The disadvantage of pMDIs is that they’re more difficult to use correctly; therefore, it may be difficult to teach the elderly and young children to use them. These devices must be used correctly, or they won’t be effective.7
The Montreal Protocol banned the production of chlorofluorocarbons (CFCs) such as Freon. This international agreement was designed to protect the Earth’s stratospheric ozone layer. The treaty was originally signed in 1987 and substantially amended in 1990 and 1992.
The Montreal Protocol stipulates that the production and consumption of compounds that deplete ozone in the stratosphere — CFCs, halons, carbon tetrachloride and methyl chloroform — were to be phased out by 2000 (2005 for methyl chloroform). Certain compounds such as those used in pMDIs received a waiver until safe alternatives could be developed.8
With the widespread introduction of HFA, which doesn’t contain chlorine and is safer for the ozone layer, Freon will be phased out by Dec. 31, 2008. Besides being environmentally safer, HFA has additional benefits. It has a lower vapor pressure at room temperature; therefore, the spray tends to be slower leading to the delivery of smaller particles that can be more easily inhaled into the lower airways.
Open- vs. closed-mouth techniques
pMDIs can be used either with the closed-or open-mouth technique. With the closed-mouth technique, the pMDI is inserted into the mouth, the lips are closed around it, and the patient is instructed to inhale at the same time the inhaler is actuated. This causes the particles to impact onto the posterior pharynx rather than making the turn down into the airways leading to an increased risk of oral candidiasis and lowered effectiveness of the medication.
That leads to the open-mouth technique in which the pMDI is held two fingers in front of the open mouth. When actuated, the particles have to travel several centimeters farther than with the closed-mouth technique. This allows them to slow down and the organic solvent to evaporate leading to smaller particles that can more easily follow the inspired air into the lower airways. The main difficulty is the inhaler must be aimed correctly, and coordination between actuation and inhalation is more difficult.
Spacers and holding chambers
Spacers and holding chambers were developed to improve the delivery efficiency of pMDIs and to mitigate the difficulty of using them correctly.9 A spacer is simply a tube through which the aerosol travels before it’s delivered into the mouth. It serves the same purpose as the open-mouth technique except aiming the pMDI is facilitated by the tube. With holding chambers, particles slow down, and evaporation causes them to be smaller. This decreases oropharyngeal drug deposition and reduces the risk of candidiasis. Coordination between actuation and inhalation still is necessary because the aerosol isn’t contained in the tube.
Holding chambers, in contrast to simple spacers, are designed to contain the aerosol for several seconds making synchronization between inhaler actuation and inhalation unnecessary. Most holding chambers have one-way valves that permit the patient to inhale and exhale through the same mouthpiece. For young children, masks are available to facilitate delivery. Holding chambers can be used either by having the patient take a deep breath and holding it for 10 seconds after each actuation, or by having them breathe normally for 10 breaths.
Spacers and holding chambers are easy to maintain, requiring a simple rinsing with drying after each use. With the introduction of HFA, a problem with static charge on the finer particles has become apparent. Chambers that develop an electrostatic charge will tend to attract oppositely charged particles preventing them from being delivered to the lower airways. Newer tubing materials have a coating that prevents buildup of static charge.
Another approach is to rinse the tube with a dilute soap solution and permit a fine film of soap to remain on the inside of the tube. This effectively prevents buildup of static charge.
Regular use of spacers or holding chambers reduces the problems associated with pMDIs. They reduce impaction of aerosol on the posterior pharynx, and holding chambers reduce the necessity of synchronizing actuation and inhalation.
Recent systematic reviews of the use of inhalers with holding chambers and nebulizers found that they’re equally effective.10,11 It’s reasonable to offer patients a choice of which one they prefer to use because that’s likely to result in the greatest adherence to treatment.
Dry powder inhalers
With the impending removal of CFCs as propellants for pMDIs and a desire for breath-actuated inhalation delivery devices, dry powdered inhalers (DPIs) were an obvious solution.
Inhalation of powders for treatment of asthma has been around for a long time. The problem with the older devices was that the powders tended to clump, necessitating addition of a propeller in the device to break the clumps apart. They also required a fairly brisk flow to work effectively, and the large particles tended to have a gritty taste that caused coughing in some individuals.
Newer devices include finer powders than was possible before because of advances in their production and prevention of electrostatic charges. Smaller particles permit delivery at lower flow rates than was possible with earlier devices avoiding the problems of taste and cough. In addition, most new devices have counters that allow the patient to tell when the DPI is almost empty.12
Today’s DPIs are portable, quick, breath-actuated and easy to use. Unfortunately, they also add complexity to care because each must be used in a different way. Also, the efficiency of delivery varies with each device, so they’re not interchangeable either with other DPIs or with their pMDI counterparts.13
Given variations in the inspiratory flow required for effective particle delivery, patients should be given a device they can use. As with pMDIs, it’s critical that patients be instructed on the correct use of each device.
Choosing the right device
When considering the large variety of available inhalation devices, how do you decide which to recommend? Because beta-agonists and inhaled corticosteroids are available as pMDIs, nebulizer solutions and DPIs, patients who are to use these classes of medications have a choice of all three. Long-acting beta-agonists are only available as DPIs.
Though there are no set-in-stone rules, in general it’s desirable to give the patient and/or their parents information about the advantages and disadvantages of each type and let them choose which fits into their lifestyle.14,15
Unfortunately, this doesn’t always happen in certain situations such as when providers insist that very young children must use nebulizers because of a false belief that they’re unable to use pMDIs. In reality, most infants can effectively take medications delivered by pMDI with a holding chamber with mask.16
Limiting a patient to a single type of delivery system because of provider preference doesn’t permit patients to make fully informed decisions about their treatment options and should be avoided.
Candace Ramos, BHS, RRT, AE-C, is a community health educator for the health management department at the Children’s Mercy Hospitals and Clinics in Kansas City, Mo. Jay M. Portnoy, MD, is the chief of allergy, asthma and immunology, and director of health management at the same facility.
For a list of references, please call Sharlene George at (610) 278-1400, ext. 1324, or visit www.advanceweb.com/respmanager.