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Best use of the medicinal armoury in otitis

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01 February 2013, at 12:00am

FILIPPO DE BELLIS begins a two-part article reviewing the medical interventions available for the management of ear diseases, covering cleaning, flushing and myringotomy

OTITIS externa is the inflammation of the external ear canal and is very common in dogs. Involvement of the middle ear compartment is also possible, being also quite common in dogs and cats.

Ear problems are seen in first opinion and referral practice and, due to their frequently recurrent nature, constitute a frustrating problem for owners and veterinarians alike.

The ear inflammation and infection can result from a plethora of different factors and recognition and correction of these is the key to successful management.

Management of ear diseases includes medical and surgical options and the aim of these notes, divided in two articles, is to describe the medical interventions available for otitis externa and media. Part one covers ear cleaning, ear flushing and myringotomy; part two will cover topical medications, systemic mediations and ototoxicity.

Medical treatment of otitis externa and media: ear cleaning, ear flushing, myringotomy

Therapy of otitis consists of identifying and controlling all the factors involved and medical options include topical and systemic therapy, potentiated by ear cleaning and, when needed, by ear flushing.

Length of treatment and prognosis varies based on causes and factors. It is paramount to highlight that the owner’s involvement is important as most of the topical procedures will be performed at home by clients and this will likely influence the success of treatment.

Additionally, the relevance of attending follow-up visits for examination and repeated cytology should be stressed as often getting the clients to continue with regular treatment can be challenging.

Ear cleaning – when?

Whilst is commonly accepted that cleaning is not necessary in healthy ears, it is beneficial in the following conditions:

  • Seborrhoeic ears (Figure 1)
  • Hairy ears (Figure 2)
  • Stenotic ears (Figure 3)
  • Pendulous ears
  • Purulent discharge (Figure 4

Ear cleaning is valuable in any treatment regimen as it can remove debris and pus, potentiate the action of topical antimicrobials such as gentamicin and polimixin B and permit complete diagnostic evaluation of the ear canal and tympanic membrane.

Manual cleansing can be done at home by the owners; however, it is important to instruct them on how to perform the cleaning and how often to use the different preparations.

How to instruct owners

For good compliance, it is helpful to explain the cleaning step by step: 

1. Squirt a good amount directly intothe dog’s ear canal – avoid touching the insides of the ear with the tip of the bottle (Figure 5). 

2. Use the dog’s ear to close the ear opening and massage all of the liquid around inside his ear (Figure 6).

3. Then, let go of his ear and let your dog shake all of the excess ear wash out. 

4. Finally, wipe a small piece of cotton wool around the entrance and superficial portion of the ear canal (Figure 7).

The cleaning fluids most commonly contain: 

  • Ceruminolytics, surfactants and foaming agents. These help soften, emulsify and dissolve cerumen and debris. Sodium dioctyl sulphosuccinate and triethanolamine polypeptide oleate condensate are potent ceruminolytic agents; carbamine peroxide is slightly less potent and acts more as a humectant and foaming agent. Other molecules include sodium lauryl sulphate and squalene. Less effective ingredients include propylene glycol, glycerine, and landline.
  • Astringents or drying agents. These are used to prevent maceration of the ear canal and include isopropyl alcohol, acetic acid, boric acid, benzoic acid and milder cleansing agents such as salicylic acid and lactic acid. 
  • Antimicrobial agents. These are active ingredients of many ear cleansing solutions and include parachlorometaxylenol (PCMX), some astringent and drying agents such as isopropyl alcohol, acetic acid and boric acid and chlorhexidine (at a concentration lower than 2%).

In a study (Swinney et al., 2008), the antimicrobial efficacy of different ear cleaners against Staphylococcus intermedius, Pseudomonas aeruginosa and Malassezia pachydermatis was evaluated in vitro. Antimicrobial activity appeared to be associated with the presence of isopropyl alcohol, PCMX and a low pH. A more recent in vitro study (S. I. Steen, 2012) partially contradicted these results.

More in vivo studies are needed to correctly assess the efficacy of cleansing products within the ear as the otic environment may influence the action of the molecules. Additionally, a single in vitro methodology may fail to assess the multimodal action of cleaners containing different molecules with different properties and activities.

Ethylene diamine tetra acetic acid (EDTA)-tris has no cleansing properties. It is commonly used as either a pre-soak or a carrier vehicle in the treatment of Gram-negative infections. EDTA promotes increased permeability to extracellular solutes, increased sensitisation to antibiotics and enhances the antibacterial action of PCMX.

Recently (Guardabassi et al., 2010) the in vitro antimicrobial activity of a commercial ear antiseptic containing chlorhexidine (0.15%) and Tris-EDTA was evaluated; according to the results, this product was active against all the pathogens most commonly involved in canine otitis.

A combination of acetic acid and boric acid has been shown to be useful in the treatment of Malassezia otitis.

Although ear cleaners are normally not recommended to be used more than every 48 hours, in one study (Cole et al., 2003) one cleaner (EpiOtic, Virbac) used up to twice daily caused no adverse effects. Manual cleansing doesn’t remove tightly adherent debris or material present in the deep portion of the ear canal and therefore is best used as routine cleansing at home once ear flushing has been performed. Additional manual cleaning can be ineffective or challenging when ears are painful and ulcerated.

Ear flushing

Ear flushing is indicated when the entire external ear canal and/or the middle ear need thorough cleaning. It should always be performed under general anaesthesia with an endotracheal tube placed and cuffed, to avoid the fluids running from the ear to the respiratory tract though the Eustachian tube.

In the presence of hyperplastic, stenotic or particularly inflamed ear canals, systemic glucocorticoid treatment is recommended (0.5- 1mg/kg once daily 2-3 weeks prior to the flushing).

Ear flushing is best performed using a video-otoscope or, if not available, with a urinary catheter or a feeding tube connected to a syringe and fluids (sterile saline), preferably through a three-way tap. Before ear flushing is performed, some cases may require use of an ear cleansing solution to emulsify and remove debris.

If the ear drum cannot be visualised, care should be used as ear cleaners (with the exception of those containing only squalene) are not licensed for applications in the middle ear and are all potentially ototoxic.

Myringotomy

Iatrogenic rupture of the tympanic membrane is indicated when otitis media is suspected and/or confirmed by diagnostic imaging techniques, to take samples for cytology and culture from the tympanic bulla and to allow flushing of the middle ear cavities.

It should be performed under general anaesthesia and under direct visualization after lavage of the external ear, when the canal is dry. The preferred method used by the author is using a 6 French urinary catheter cut obliquely to a 60o and attached to a 2ml syringe containing sterile saline solution.

The catheter is advanced through the ventral and posterior quadrant of the membrane with subsequent aspiration of the fluids. An aliquot can be used for direct cytological examination and the remaining for culture.