Equine Respiratory Medicine and the Aerohippus Equine Aerosol Chamber

Posted by Ranvet NZ , 10 Apr, 2009

Veterinary, Horse Health

Respiratory conditions are common in many domestic species however, are particularly detrimental to performance animals such as the horse.
Lower airway disorders are among the most common conditions encountered by equine veterinarians and are reported to be second only to musculoskeletal disease as a cause of wastage among performance horses (Rossdale, Hopes et al. 1985). However, the recent advances of tailored systems for aerosol drug administration in horses facilitate the use of aerosolized medications to be administered target specifically (directly to the lungs), minimising undesirable side effects commonly encountered when drugs, particularly corticosteroids are administered systemically via injectable or oral routes.
The most recent development into the efficient delivery of drugs to the lungs is the AeroHippus® Equine Aerosol Chamber (Image 1). Studies investigating lung deposition efficacy have been conducted at The Cummings School of Veterinary Medicine, Massachusetts USA whereby scintigraphy studies (Image 2) determined an aerosol deposition of 18.2% which is far more efficient than any similar administration devices such as the Aeromask® (6% deposition) and Equinehaler® (8.2% deposition), making the AeroHippus® the most efficient device available. Additionally, as can be seen (Image 3), the Flow-Vu® indicator enables easy counting of the number of breaths the horse has taken through the chamber and also ensures a satisfactory seal, both of which aid the correct and optimal delivery of drug to the lungs.
When we consider that the primary function of the respiratory system is to deliver oxygen to, and remove carbon dioxide from the body, we also need to consider that the equine respiratory tract provides the largest interface between internal and external environments and for this reason, is consistently exposed to high levels of potentially detrimental and pro-inflammatory air contaminants.

Risk Factors Associated with Airway Inflammation;
Intensive stabling due to continuous and cumulative exposure to respiratory burdens in the confined stable area.

Frequent participation in strenuous activity.

Regular transportation and co-mingling with other horses.

Poor stable hygiene.

Poor stable ventilation.
Treatment of Lower Airway Inflammation
Important treatment strategies now extend to beyond traditional forms of medication, with
specific pharmaceutical goals for treatment being reduction in the severity of airway
inflammation, short term attenuation of cough, and maintenance treatments to prevent
further exacerbations. Furthermore, environmental management strategies should also
be employed to minimize exposure to airborne irritants.
Image 1.
Image 2.
Pharmaceutical Intervention
Although the efficacy of systemic treatments is proven, there has been increased interest in the aerosol mode of delivery,
which has the advantage of specifically targeting direct lung drug delivery and decreasing systemic effects such as immune
suppression and laminitis, particularly encountered with systemic corticosteroids.
Therapy
Devices which deliver drugs from metered dose inhalers (MDI's) (Image 4) emerged in human medicine approximately 40 years ago, though interest in their use for delivery of medications in horses has surged only in the last decade. Interestingly, the characteristics of the equine airways and patterns of breathing are well suited to inhalation therapy, particularly the obligate nasal breathing of the horse encourages aerosol deposition deep within the lung.

The most common aerosol therapy is the utilization of Metred Dose Inhalers, which are hand-held devices containing active drugs for aerosolisation (classically referred to as ‘puffers' in human medicine). The MDI is actuated into the spacer of the AeroHippus® from
which the drug is inhaled, essentially providing breath actuated delivery of aerosolized drugs.
Significantly aiding an increase in the use of aerosol therapy in the horse has been the introduction of appliances specifically designed for MDI administration such as the AeroHippus®. As a direct result of these technical advances, effective delivery of drugs to the equine respiratory system by aerosol inhalation is now a viable alternative.
Aerosol therapy confers a number of advantages over systemic therapy including;
Higher concentrations of the drug deposited specifically in the airways.
Lower drug dosages due to target specific drug delivery.
Improvement in drug safety and efficacy by reducing the total therapeutic dose.
Minimising drug exposure to other body systems.
Potent delivery of drug to the lungs.
It should also be considered that studies indicate clinical improvements in respiratory health can be seen as a direct result of implementing environmental control measures to ensure a minimum dust management regimen to lower the respiratory burden;

Replacement of bedding when soiled or wet.

Adequate cross-flow stable ventilation.

Using sawdust as opposed to straw or shavings for bedding material.

The dampening or addition of oil to the ration.

Storing feed and bedding material away from the stable.

Removing horses from the stable while mucking out.

Soaking hay for 30 minutes prior to feeding reduces respirable concentrations of airborne particles

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