Bronchodilatory therapy with nebuhaler: how important is the delay between firing the dose and inhaling?

The evolution of spacers and valved holding chambers

Spacers and valved holding chambers (VHCs) are pressurized metered dose inhaler (pMDI) accessory devices, designed to overcome problems that patients commonly experience when administering aerosol via a pMDI. Spacers were developed in direct response to patient-related issues with pMDI technique, particularly, poor coordination between actuation and inhalation, and local side-effects arising from oropharyngeal deposition. Current clinical guidelines indicate the need for widespread prescription and use of spacers, but, despite their apparent ubiquity, the devices themselves are, unfortunately, all too commonly "disused" by patients. An understanding of the background from which spacers developed, and the key factors influencing the optimization of the spacer and the later VHC, is crucial to developing an appreciation of the potential of these devices, both contemporary and future, for improving the delivery of pressurized aerosols to patients. This review, informed by a full patent search and an extensive scientific literature review, takes into account the clinical and laboratory evidence, commercial developments, and the sometimes serendipitous details of scientific anecdotes to form a comprehensive perspective on the evolution of spacers, from their origins, in the early days of the pMDI, up to the present day.

In vitro comparison of the effect of inhalation delay and flow rate on the emitted dose from three valved holding chambers

BACKGROUND

Valved holding chambers (VHCs) are accessory devices for pressurized metered dose inhalers (pMDIs). Use of a VHC may help overcome coordination issues associated with drug delivery via the pMDI alone. Previous work has established that aspects of VHC use, including the time between actuation and inhalation (inhalation delay) and inhalation flow rate, can influence the amount of drug available to inhalation. This study compared the impact of inhalation delay and flow rate on the in vitro delivery of aerosol from different VHC brands.

METHODS

A custom-built inhalation delay test rig, which enabled automation of controlled inhalation delays (0, 5, or 10 sec), was developed. Extraction air flow was set to 5, 15, or 30 L/min. Delivery of albuterol (ProAir HFA 90 μg) to a filter (emitted dose) was assessed using three commercially available VHC brands (one conventional, two antistatic). Emitted dose under 27 different combinations of inhalation delay, flow rate, and VHC brand was determined in order to assess the effects of inhalation delay and flow rate. Pairwise comparisons of the different VHC brands with different inhalation delay/flow rate combinations were conducted to assess in vitro equivalence.

RESULTS

Emitted dose increased with flow rate and decreased with longer inhalation delays. Dependence on flow rate was similar for the two antistatic VHCs and more pronounced for the conventional VHC. The two antistatic VHCs showed equivalent results for the emitted dose of albuterol, across a range of flow rates and using different inhalation delays; the relation between the two antistatic VHCs fell within the ± 15% acceptance interval criteria for in vitro equivalence.

CONCLUSIONS

The different inhalation delays and flow rates had similar effects on the delivery of drug via the three VHCs. The two antistatic VHCs were shown to be equivalent in vitro in terms of emitted dose of albuterol.

Spacer devices for metered dose inhalers

Spacer devices are attachments to the mouthpieces of pressurised metered dose inhalers (pMDIs), and range from tube spacers with a volume of <50 mL to holding chambers with a volume of 750 mL. Compared with a pMDI alone, spacers minimise coordination difficulties, reduce oropharyngeal deposition and often increase lung deposition. Spacers may not improve the clinical effect in patients able to use a pMDI properly, but may allow maintenance dosages of bronchodilators and corticosteroids to be reduced. Correct use of spacer devices is important, especially achieving control over electrostatic charge accumulation on the walls of plastic devices. In patients with severe acute asthma or severe chronic obstructive pulmonary disease, a pMDI plus large volume spacer may be a viable alternative to a nebuliser for delivering large bronchodilator doses. Although the addition of a spacer to every pMDI would not be justified, the use of large volume spacers has been recommended for any inhaled asthma drug in young children, and as a means of reducing systemic bioavailability of inhaled corticosteroids in adults and children alike.

Salmeterol administration by metered-dose inhaler alone vs metered-dose inhaler plus valved holding chamber

STUDY OBJECTIVE

To determine whether a spacer device designed as a valved holding chamber with a flow signal increases the efficacy of the long-acting beta(2)-agonist, salmeterol, in patients who use incorrect technique with metered-dose inhaler (MDI) alone.

DESIGN

Double-blind, randomized, placebo-controlled study.

SETTING

University hospital outpatient rooms.

PATIENTS

Twenty adult outpatients with stable persistent asthma, receiving a daily anti-inflammatory drug.

INTERVENTIONS

Patients were randomized to either salmeterol MDI (incorrect use: 1 s after actuating MDI, inhale rapidly) and placebo plus spacer (correct use: inhale slowly as MDI is actuated, continue to inhale slowly and deeply) or placebo MDI (incorrect use) and salmeterol plus spacer (correct use). The following week, patients received the opposite treatment. The dose was two puffs from each device on each treatment day; each puff was separated by 1 min.

MEASUREMENTS AND RESULTS

After baseline peak expiratory flow (PEF), salmeterol was administered and serial PEF determined (0.5, 1, 2, 3, 4, 6, 8, 10, and 12 h). Administration of salmeterol MDI plus spacer resulted in significantly greater increases in PEF from baseline vs MDI at 4 h (44 L/min vs 10 L/min; p < 0.01) and 6 h (49 L/min vs 24 L/min; p < 0.05). Both methods of administration were equally well tolerated.

CONCLUSION

We conclude that patients who have poor timing and rapid inhalation with salmeterol MDI alone will have greater increases in PEF at 4 h and 6 h and no additional side effects if the dose is administered with a valved holding chamber that is used correctly. Further study is needed regarding other errors in MDI technique with salmeterol.

Inhalers and nebulizers: which to choose and why

It is obvious that many factors should be considered when an inhaler is prescribed. Based upon the information discussed above, a rational inhaler strategy could be as follows: (1) Children < or = 5 years and elderly patients are prescribed a spacer with a valve system (and a face mask for the children) for the delivery of all drugs. When they are severely obstructed, some may need a nebulizer. If the patient cannot be taught the correct use of a spacer, a nebulizer should be prescribed. (2) Children > or = 5 years and adults are prescribed a spacer or a Turbuhaler for the administration of inhaled corticosteroids and a dry powder inhaler (preferably multiple dose) or a breath-actuated MDI for other drugs. If these alternatives are not available or the patient prefers, a conventional MDI can be used (preferably not for other corticosteroids than fluticasone propionate) provided that careful tuition is given. Fluticasone dipropionate may be given by DPI, Spacer or MDI. (3) Nebulizers are mainly reserved for severe acute attacks of bronchoconstriction. With this approach, most patients can be taught effective inhaler use with a minimum of instructional time. Finally, it must always be remembered to consider the patient's wish, since prescription of an inhaler which the physician likes but the patient does not is likely to reduce compliance.