As demonstrated by the above illustration, the dog's ear canal has a vertical and a horizontal component. This predisposes the dog to ear infections as debris must work its way upward rather than straight out.
 
Disease of the ear usually stems from over-production of wax as occurs in response to irritation. Allergic skin disease affecting the ears is one possible cause (especially in recurring cases); other causes of ear infections include ear mites, foreign bodies (such as grass awns or foxtails), or hair growth deep in the canal (common in poodles and schnauzers especially). The moisture of the wax promotes bacterial growth and infection. Soon wax in ears is joined by pus.
 
Dogs show discomfort around their ears by scratching, rubbing their ears on the floor or furniture, or by shaking the head. If the infection reaches the middle ear, affected animals may have a head tilt, a lack of balance, and unusual eye movements.

Aural Hematoma
When a dog with uncomfortable ears shakes and scratches vigorously, a blood vessel in the ear flap may rupture. This leads to bleeding into the tissues of the pinna (see above illustration). The usual recommendation is to have the blood clots removed and the ear bandaged and cleaned under anesthesia. If the aural hematoma is not so big as to occlude the ear canal (thus preventing medication), the option to forgo surgery exists; but without surgery, the ear may scar down into an abnormal appearance.

Treatment 
Step One
Most ear infections are cleared up simply with professional cleaning followed by medication at home. If only mild debris is present in the ear canals, simple disinfection and washing of the ear is adequate; however, in most cases, a full ear flush is needed to even examine the ear drum. For patient comfort, we recommend sedation for this procedure as the ears are sore and the instruments can be damaging if the pet jumps at the wrong time.

Step Two
Some dogs have chronic ear problems (the infection is not controlled by general medication or returns when general medication is discontinued). In these cases, the ear discharge should be cultured so that the precise organism can be pinpointed and treated specifically. Regular treatment at home with disinfecting ear washes should become part of the pet's grooming routine.

Further testing may be in order to determine why the infection continues to recur. Allergy is the most common reason for recurrent ear problems.

Step Three
Depending on the severity of the problem, the vertical canal may need to be opened surgically. This enables debris to be removed more effectively. This is done to prevent severe scarring after prolonged specific medical therapy has been ineffective. This procedure is called a lateral ear resection, Zepp procedure, or LaCroix procedure. 

If the canal becomes so scarred that it is practically closed, ablation may be the final option. In this surgical procedure, the entire ear canal is removed and healthy tissue is allowed to grow in. This procedure is a last resort after severe infection has made effective medical treatment impossible. A specialist is called in for these cases and although surgery is expensive, dogs with chronic severe otitis usually require no further ear treatment for the rest of their lives.

Some Special Information on Pseudomonas Infection
Pseudomonas aeruginosa is a very special species of bacteria; it is resistant to almost every possible antibiotic. It is common for ear infections to be recurrent and in time, many antibiotics have been used. The unfortunate tendency is for most bacteria to be killed off, leaving infection with the very resistant and practically immortal (not to mention especially smelly) Pseudomonas.

If one is lucky, a culture of the ear discharge will reveal that the Pseudomonas is still sensitive to oral quinolone antibiotics such as enrofloxacinor orbifloxacin. It should be noted that especially high doses of this type of antibiotic are needed to treat Pseudomonas in the ear and that inadequate dosing will just make Pseudomonas even more resistant. In other words, a Pseudomonas must be treated definitively from the moment it is diagnosed; once it becomes resistant to oral therapy, treatment becomes vastly more difficult.

Oral therapy is generally combined with some kind of topical treatment of the ear. Fortunately there are several concoctions that should be useful though some your veterinarian must mix him/herself.

Silvadene/silver sulfadiazine
This product is manufactured as a wound creme and is especially helpful in hastening the healing of damaged external tissues. It also has activity against several bacteria including Pseudomonas. The creme can be prepared in water for an easier ear administration.

Tris-EDTA
EDTA is a binder of metals which are important to the bacterial cell wall. Tris is used to buffer the EDTA to a pH that is not irritating to the ear and to maximize the anti-bacterial effect.

Injectable Medications
It would be unusual for a Pseudomonas species to be resistant to absolutely everything. While there may not be an oral treatment available, sometimes an owner may be taught to give injectable treatments. These are often expensive, however. These same medications can also be mixed up for topical use; many are already available as commercially prepared solutions.

Chronic ear infections, as mentioned, typically have an underlying cause (usually allergy). It is important to address this problem in addition to the infection itself so as to minimize on-going ear inflammation.