Medicine of the Future in America

Canadian Health and Care Mall: Technical Features of Aerosol Delivery Systems

clinical medicineBecause of the problems associated with delivery of aerosols from MDI devices, such as incorrect administration, excessive deposition of aerosol on the oropharyngeal mucosa, and lack of reproducible dosing, several auxiliary MDI delivery systems have been introduced into clinical medicine. All feature some type of holding chamber to store aerosol after actuation of the MDI. The increased residence time for aerosols released from MDI devices into the holding chamber enhances vaporization of propellant to achieve a smaller particle size and most of the impaction loss occurs in the auxiliary device (Table 4) rather than the oropharynx. At low inspiratory flow, these devices prevent excessive aerosol deposition in the oropharynx but at higher flows, deposition from the spacer devices markedly increases (Table 3). The lesser oropharyngeal deposition protects against potential absorption of aerosolized P-adrenergic agonists through the mucosa to produce systemic side effects and prevents oral thrush associated with aerosolized corticosteroids. A mouthpiece provided on all systems enables the aerosol inhalation to be taken with the mouth closed around the mouthpiece. With the exception of one device (InspirEase), all the auxiliary systems have holding chambers opened to the atmosphere with potential for leakage of aerosol from the holding chamber if not coordinated with inhalation.

It has been shown that deposition in the lungs can be maximized by actuating the MDI (delivered directly) during the course of a slow (<0.5 L/sec), deep inhalation, followed by a 10-second breath-hold. A rapid inhalation without a breath-hold after actuation of the MDI gives inferior results. Visual, tactile, and auditory feedback are provided by the InspirEase auxiliary MDI aerosol system to achieve a targeted volume and a slow inspiratory flow, but not by the other commercially available systems. This is important because rapid inspiratory flow from the spacer device can produce unwanted oropharyngeal aerosol deposition. Finally, as it becomes more recognized that the response of the airways to drugs is highly dependent on the quantity of aerosol deposited, reproducibility of dosing from direct administration of MDI and the various auxiliary systems will come into question. From a theoretical standpoint, the auxiliary devices, paiticularly the closed systems such as InspirEase, should be useful in testing dose responsiveness to bronchodilators and, as yet unavailable in this country, MDI devices containing bronchoprovocating agents. Further, the auxiliary aerosol delivery systems should be useful for potent medications which are absorbed in the lung but destroyed in the GI tract. The majority of definitions are not known for people that’s why it is rather easy to misunderstand the sense in general. To know but in an easy way you may here on Canadian health&care mall news website.

InspirEase: This consists of a 700-ml collapsible, cylindrical plastic bag, 11.5 cm in length and 9 cm in diameter, to which is attached a mouthpiece assembly containing a reed that vibrates and produces a sound at inspiratory flow rates greater than 0.3 Us. The nozzle of the MDl is inserted into inspiratory flow ratean opening of the mouthpiece, and its actuation releases the medication into the collapsible bag. The system is closed and not valved. Patients are instructed to inflate the bag by hand, place their mouth on the mouthpiece, actuate the MDl, inhale slowly from the bag until empty (too rapid an inhalation is signaled by sound from the reed and insufficient inhaled volume by visual and tactile feedback), breath-hold while slowly counting to 5, exhale back into the bag, again inhale slowly and breath-hold while slowly counting to 5 to complete the treatment. The two slow rebreathing and breath-holding maneuvers promote aerosol deposition by sedimentation. Although the inside wall of the holding chamber of this device occasionally becomes contaminated and colonized with bacteria and fungi, these organisms do not become airborne during inhalation maneuvers. Thus, there is no danger of nosocomial infections of the lung with this device.

Aerochamber: This consists of a 145-ml, one-way valved rigid holding chamber, 11 cm in length and 4.1 cm in diameter. In contrast to the InspirEase, which has a closed chamber, this device has vent holes so that room air can be drawn in through the chamber during inspiration. However, aerosol can be lost by leakage from the chamber after the MDl is actuated and prior to inhalation. The patient is instructed to insert the MDl with its mouthpiece into the rear end of the Aerochamber, and within 1 to 3 s after delivering one puff from the MDl to place the lips around the mouthpiece of the device and inhale slowly from FRC to TLC and breath-hold for 10 s. The one-way valve opens during inspiration so that patient does not have to aim, puf£ and inhale at the same time. No means are provided for regulation of inspiratory flow rate. Because the holding chamber has a much smaller volume than the InspirEase and is valved at the mouthpiece end, more aerosol is lost by inertial impaction within this device than in the InspirEase and spacer.

Spacer: This consists of an extension tube which substitutes for the conventional mouthpiece. One model used is 3.2 cm in diameter, 10 cm in length, and 80 ml in volume. This device is non-valved and opened with vents to room air. It limits aerosol deposition onto the oropharynx because the hand-breath coordinationterminal jet velocity is slowed; it does not offer means for enhancing hand-breath coordination of the M DI. If the spacer is used correctly, less impaction loss takes place in the spacer compared to the Aerochamber, because the latter is close-ended, whereas the spacer is open-ended. However, if the mouthpiece is aimed at or contacts at the tongue, its characteristics approach the

Aerochamber. One proprietary corticosteroid aerosol MDI (Azmacort) incorporates a spacer into its design.

Large Spacer Devices: These devices have a 700- to 750-ml opened holding chamber which is valved at the mouthpiece end so that the patient can empty the chamber over several breaths. They are of rigid (Inhal-Aid, Nebuhaler) or collapsible construction. They may be pear-shaped, with the largest dimensions of 25 cmXl3 cm, or relatively conical. They adapt to all MDI devices through an end connection opposite the mouthpiece. The rigid devices do not provide volume indication, but the collapsible device gives tactile and visual volume feedback. The Inhal-Aid has a visual gauge for crude sensing of inspiratory flow.

The rigid holding chambers are not readily portable. The one-way valve in the Nebuhaler may not seat properly during expiration at low flows when held upward at a tilt, so that patients with severe asthma may exhale into the holding chamber and displace aerosol out of the chamber, thereby receiving less medication. Unpublished studies in our laboratory indicate that closure of the one-way valve on Inhal-Aid is not sensitive to the way the device is held. The large spacers have been advocated for MDI aerosol delivery to both pediatric and adults with obstructive airways disea

This entry was posted in Aerosol Penetration and tagged alcohol, bronchospasm, slow deep inhalation, steroid dependent, vaporization.
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