Patient Education

Proper instruction and observation of the patient are crucial to the success of MDI of therapy. After instructing the patient, the RCP should ask the patient to act out the procedure, observing to see if the patient has really understood the instructions.

 

The particle size of the drug released is controlled by two factors: the vapor pressure of the propellant blend, and the diameter of the actuator’s opening. Particle size is reduced as vapor pressure increases, and as diameter size of the nozzle opening decreases. The majority of the active drug delivered by an MDI is contained in the larger particles, many of which are deposited in the pharynx and swallowed.

 

The advantages of MDI aerosol devices include:

·        They are compact and portable.

·        Drug delivery is efficient.

·        Treatment time is short.

           

On the other hand, the disadvantages of using MDIs to deliver aerosolize medications include:

·        They require complex hand-breathing coordination.

·        Drug concentrations are pre-set.

·        Canister depletion is difficult to ascertain accurately.

·        A small percentage of patients may experience adverse reactions to the propellants.

·        There is high oropharyngeal impaction and loss if a spacer or reservoir device is not used.

·        Aspiration of foreign objects from the mouthpiece can occur.

·        Pollutant CFCs, which are still being used in MDIs, are released into the environment until they can be replaced by non-CFC propellant material.

 

Extension or reservoir devices can be used to modify the aerosol discharged from an MDI. The purposes of these spacers or extensions include:

·        Allow additional time and space for more vaporization of the propellants and evaporation of initially large particles to smaller sizes.

·        Slow the high velocity of particles before they reach the oropharynx.

·        As holding chambers for the aerosol cloud released, reservoir devices separate the actuation of the canister from the inhalation, simplifying the coordination required for successful use.

 

Dry powder inhalers (DPIs) consist of a unit dose formulation of a drug in a powder form, dispensed in a small MDI-sized apparatus for administration during inspiration. Because these devices are breath-actuated, using turbulent air flow from the inspiratory effort to power the creation of an aerosol of microfine particles of drug, they don’t require the hand-breath coordination needed with MDIs.

 

Cromolyn sodium and albuterol are the two primary drugs available in powder form. Cromolyn sodium is dispensed in a device called the Spinhaler, which pokes holes in capsules containing the powdered drug. The albuterol formulation is dispensed in a device called the Rotahaler, which cuts the capsule in half, dropping the powdered drug into a chamber for inhalation. In both cases, a single-dose micronized powder preparation of the drug in a gelatin capsule is inserted into the device prior to inhalation.

 

Powder flow properties in DPIs depend on particle size distribution, with very small particles not flowing as well as the larger ones. A third drug, budesonide, is available in a pre-loaded, multi-dose (up to 200 doses) DPI unit called a Turbuhaler. The advantages of using DPI devices for drug administration include:

·        They are small and portable.

·        Brief preparation and administration time.

·        Breath-actuation eliminates dependence on patient’s hand-breath coordination, inspiratory hold, or head-tilt needed with MDI.

·        CFC propellants are not used.

·        There is not the cold effect from the freon used in MDIs, eliminating the likelihood of bronchoconstriction or inhibited inspiration.

·        Calculation of remaining doses is easy.

 

The disadvantages encountered when relying on DPIs for drug administration include:

·        Limited number of drugs available for DPI delivery at this time.

·        Dose inhaled is not as obvious as it is with MDIs, causing patients to distrust that they’ve received a treatment.

·        Potential adverse reaction to lactose or glucose carrier substance.

·        Inspiratory flowrates of 60Lpm or higher are needed with the currently available cromolyn and albuterol formulations.

·        Capsules must be loaded into the devices prior to use.

 

Small volume nebulizers (SVNs) are gas powered (pneumatic) and are a common method of aerosol delivery to inpatients, and there are a variety of different SVNs available. Each has specific characteristics, especially in regard to output. These nebulizers fall into two subcategories: mainstream and sidestream. The mainstream nebulizer is one in which the main flow of gas passes directly through the area of nebulization. The sidestream nebulizer is one in which the nebulized particles are injected into the main flow or stream of gas as with IPPB circuits. The main difference, based upon their construction, is that the larger particles tend to rain-out with a sidestream nebulizer.

 

The advantage of SVN therapy is that it requires very little patient coordination or breath holding, making it ideal for very young patients. It is also indicated for patients in acute distress, or in the presence of reduced inspiratory flows and volumes. Use of SVNs allows modification of drug concentration, and facilitates the aerosolization of almost any liquid drug.

 

Another advantage of a SVN is that dose delivery occurs over sixty to ninety breaths, rather than in one or two inhalations. Therefore, a single ineffective breath won’t ruin the efficacy of the treatment. Disadvantages of SVNs include:

·        The equipment required for use is expensive and cumbersome.

·        Treatment times are lengthy compared to other aerosol devices and routes of administration.

·        Contamination is possible with inadequate cleaning.

·        A wet, cold spray occurs with mask delivery.

·        There is a need for an external power source (electricity or compressed gas).

 

In a study comparing the effectiveness of MDIs, DPIs, and SVNs, it was found that approximately the same amount of drug is delivered to the lung, regardless of the type of device used, given that all three devices contain the same loading dose. The clinical response measured by the improvement in FEV₁ is also similar among the three devices, although the change with the MDI was statistically significantly greater than with DPI or SVN.

 

The greater response with the MDI correlates with the greater amount of drug delivered by the MDI in that study. However, the study concluded, “The amount of bronchodilation obtained is a reflection of the dose of drug given, and not the method of delivery.”

 

Since mainstream nebulizers are normally used for continuous administration of a bland aerosol (H₂O, normal saline) for airway humidification or secretion mobilization, they are not usually considered as medication delivery systems.

Also in use today is a pneumatic nebulizer that operates on the “Babbington Principle”. This is called the hydrosphere or Babbington nebulizer. In this nebulizer, a source of gas enters a hollow sphere which is covered by a thin film of water. The hollow sphere has small ports in it, where the gas escapes to the outside. These ports act as jets. When the gas moves through these ports (jets), a negative pressure is produced and the flow of water is then drawn into the flow of gas producing an aerosol. A baffle is usually used in this system also. The baffle is placed distal to the atomization process in the flow of gas/aerosol. Particle sizes in these units are usually between three and five micron.

 

Large-Volume Nebulizers - These units also have the capability for entraining room air to deliver a known oxygen concentration. They can deliver varying concentrations of oxygen. When using these units, you should always match or exceed the patient’s peak inspiratory flow rates. This assures delivery of oxygen and nebulized particles. These units produce particle sizes between two and ten microns and may be heated to improve output.

 

Centrifugal Room Nebulizers - This nebulizer works on the principle of a rotating disk that spins on a hollow tube. This action draws water up the hollow tube that acts as a center shaft. Once the water reaches the rotating disk (which is spinning at a rapid rate), it is thrown outward by centrifugal force through comb-like structures that break up the water and produce an aerosol.

 

Although these are in fact nebulizers, they are used as room humidifiers. The aerosol particles are expelled into the room. Since they are very small particles, they evaporate to become humidity. Humidification is more effective if the door to the room is left closed.

 

Small-particle aerosol generator (SPAG) - This is a highly specialized jet-type aerosol generator designed to for administering ribavirin (Virazole), the antiviral recommended for treating high risk infants and children with respiratory syncytial virus infections.

 

Ultrasonic nebulizers - Ultrasonic nebulizers (USN) have been in use and production since the mid 1960s and have gained high popularity. Ultrasonic nebulizers work on the principle that high frequency sound waves can break up water into aerosol particles. This form of nebulizer is powered by electricity and uses the piezoelectric principle. This principle is described as the ability of a substance to change shape when a charge is applied to it.

 

An ultrasonic nebulizer contains a transducer that has piezoelectric qualities. When an electrical charge is applied, it emits vibrations that are transmitted through a volume of water above the transducer to the water surface, where it produces an aerosol. The frequency of these sound waves is between 1.35 and 1.65 megacycles, depending on the model and brand of the unit.

 

Their frequency determines the particle size of the aerosol. The transducers that transmit this frequency are of two types. One type is the flat transducer, which creates straight, unfocused sound waves that can be used with various water levels. The other type is a curved transducer, which needs a constant water level above it because its sound waves are focused at a point slightly above the water surface. if the water level falls below this point, the unit loses its ability to nebulize.

 

As stated earlier, the frequency of an ultrasonic nebulizer determines the particle size of the aerosol. In ultrasonic nebulizers, the particle size falls in the range of .5 to 3 microns. The amplitude or strength of these sound waves determines the output of the nebulizer, which falls in the range of 0 to 3 ml/minute and 0 to 6 ml/minute. Ultrasonic nebulizers also incorporate a fan unit to move the aerosol to the patient. This fan action also helps cool the unit. The gas flow generated by this fan falls in the range of between 21 and 35 liters/minute. This flow of air also depends on the brand and model of the unit.

 

The transducer of an ultrasonic nebulizer is often found in the coupling chamber, which is filled with water. This water acts to cool the transducer and allows the transfer of sound waves needed for the nebulizer, which takes place in a nebulizer chamber. The nebulizer chamber is found just above the coupling chamber. A thin plastic diaphragm that also allows sound waves to pass usually separates these two chambers.

 

When studying ultrasonic nebulizers, remember that output is controlled by amplitude, and particle size is controlled by frequency. The advantages of ultrasonic nebulization are:

·        high aerosol output

·        smaller stabilized particle size

·        deeper penetration into the tracheobronchial tree (alveolar level)

           

Ultrasonic nebulizers are useful in the treatment of thick secretions that are difficult to expectorate, and they can help to stimulate a cough. The therapy can be delivered through a mouthpiece or facemask. Therapy can be given with sterile water, saline or a mixture of the two.

 

Although IPPB has been used to deliver aerosolized drugs from a SVN, the consensus of clinical findings is that IPPB delivery of aerosolized medication is no more clinically effective than simple, spontaneous, unassisted inhalation from SVNs. If the patient is able to breathe spontaneously without machine support, the use of IPPB for delivery of aerosolized is not supported for general clinical or at-home use, and should be reserved for patients who are not capable of taking deep, coordinated breaths.