Advances in senior dog medicine

In dog terms, senior depends on breed and size. Generally, for small and medium-sized breeds, senior refers to dogs of 11 to 12 years or older, while the range for large and giant breeds is seven to 10. Age-related disease occurs at a younger age in larger dogs.

The number of senior dogs is gradually increasing in most practices and these patients account for a significant percentage of practice income. Many of the conditions encountered in this group are chronic and require a coordinated and integrated management plan that is understood by the owner and delivered as a consistent message by the practice. Gerontology remains a poorly developed area of veterinary science, with few studies having looked at the interplay and best management practices in patients whose care is complicated by multiple disease issues.

This article will cover the most common diseases we encounter in senior dogs and review the risk/benefit relationships as we strive to manage them. Particular focus will be on assessing the risks and benefits of undertaking a procedure or prescribing a new medication in situations where more than one disease is present. Central to this is the balance between quality of life for the patient and longevity.

With most chronic disease in senior patients, the degree to which a problem is reducing quality of life can be very difficult to quantify against the background of general ageing as the patient will adapt over time to its disability – masking its severity. Often the extent of compromise is only evident once the disease issues have been addressed.

Dental disease

Virtually all senior dogs will have some level of dental disease unless they have had recent dental intervention. The risk/benefit in such cases is the balance between the consequences of dental disease versus the risk of anaesthesia. Common issues that will increase anaesthetic risks include heart disease, chronic kidney disease (CKD), low body fat levels and, to some extent, liver disease.

However, in the majority of patients liver disease has relatively little impact unless there is severely compromised liver function.

Consequences of dental disease

The consequences of dental disease are:

• pain
• hyporexia and weight loss
• chronic inflammation and bacteraemia associated with periodontal disease
• halitosis and hypersalivation
• extension of infection into surrounding bone/retrobulbar space

History and physical examination will allow some judgement on the degree of pain, hyporexia, weight loss, hypersalivation and halitosis. Any extension of infection will only be evident on imaging at the time of a dental procedure. Perhaps the hardest question to answer is what are the risks associated with chronic inflammation and bacteraemia if a dental procedure is not performed? Periodontal disease has been associated with histopathological changes in the kidneys, myocardium and liver. Increasing severity of disease is also associated with a greater likelihood of endocarditis and cardiomyopathy (Glickman et al, 2009). In humans, associations between periodontal disease and other issues, including respiratory disease, are highlighted by the number of combined medical “searched for” headings (Table 1).

With the advent of our ability to undertake very large database searches we may become aware, over time, of other conditions associated with periodontal disease. The presence of active inflammation in periodontal disease is suggested by a fall in C-reactive protein (CRP) following dental cleaning; unfortunately, in an individual, measuring CRP does not necessarily benchmark the severity of periodontal-associated inflammation in terms of assessing the risk/benefit relationship of undertaking dental investigations.

Osteoarthritis

Many senior dogs receive chronic NSAID medication as part of the management of osteoarthritis (OA). Prevalence of clinically significant OA is breed-dependent, approaching 100% in senior dogs of some breeds. NSAID use can have an impact on two other common problems of older dogs – CKD and cardiac disease – although the magnitude of this risk is poorly quantified (Innes et al, 2010).

Evidence in humans suggests failure to manage osteoarthritic pain is associated with more rapid progression of disease. It is undoubtedly true NSAIDs will affect renal auto-regulatory mechanisms in response to a fall in blood pressure by reducing the extent to which afferent glomerular arteriolar dilation will occur, which serves to maintain glomerular blood flow. Falls in systemic blood pressure are particularly common during anaesthesia, but should also be considered if senior patients are unwell, leading to increased fluid loss (for example, vomiting, diarrhoea, polyuria) or reduced intake.

In patients with pre-existing heart disease, NSAID therapy increases the risk of heart failure in humans as prostaglandins are considered to contribute significantly to the maintenance of compensated heart failure in patients with impaired left ventricular function. Further NSAIDs may interfere with the actions of furosemide and angiotensin-converting enzyme inhibitors (ACEi). For those patients that require management of OA and have concurrent CKD or heart disease, the aim would be to use the lowest effective dose of NSAIDs while maximising other strategies for managing their OA, such as nutraceuticals (omega fatty acids, turmeric, chondroitin, glucosamine, New Zealand green-lipped mussel), weight control, physiotherapy, acupuncture and other forms of pain relief.

Heart disease

Heart disease is common in elderly dogs, with 30% of small breed dogs aged above 10 having significant mitral valve disease. By contrast, larger breed dogs with heart disease tend to have primary myocardial disease rather than valvular disease. In the early stages, myocardial disease can be hard to assess on history and physical examination as there may be only very subtle historical signs that could also be within the normal expectation for ageing, with an absence of physical findings. Both dental disease and the use of NSAIDs (Feenstra et al, 1999) may increase the rate of progression in some cardiac disease patients, but for many patients the clinical dilemma occurs when anaesthesia is required – for example, for dental cleaning.

When considering anaesthesia in senior dogs with heart disease, the key considerations are:

1. Stabilise heart disease as far as is possible prior to anaesthesia; measure blood pressure prior to premedication.
2. Consider measuring N-terminal pro-brain natriuretic peptide (NT-proBNP) as a pre-anaesthetic screen to assess the level of volume loading. In humans, proBNP has been shown to be a better predictor of anaesthetic complications than other commonly used pre-anaesthetic blood tests (Rodseth et al, 2014). Unfortunately, patient-side tests are not available for use in dogs, so the patient must be sampled several days prior to the procedure.
3. Minimise the use of hypotensive drugs or drugs that reduce myocardial function.
   • Many sedative agents – particularly α2-agonists. Acepromazine will cause bradycardia and sedation, but this effect is minimised at low dose (0.01mg/kg to 0.02mg/kg).
   • Rapid injection of propofol can cause severe bradycardia and hypotension.
     Note: alfaxalone has relatively minimal effects on blood pressure and myocardial function.
   • Halothane causes myocardial depression, reduces rate and sensitises the myocardium, increasing the risk of arrhythmia.
   • Isoflurane and sevoflurane cause dose-dependent hypotension through vasodilation.
4. Position the patient (especially large or giant breed dogs) to minimise pressure on the caudal vena cava.
5. Maximise monitoring – particularly blood pressure.
6. Care with fluid rates for longer procedures – surgical fluid rates can cause volume overload if given over a period of hours; however, insufficient fluids may lead to hypotension and a lack of venous return causing low output failure. This is a particular issue if the dog is in dorsal recumbency for its procedure. Fluid loading for short procedures (less than an hour) is rarely a problem.
7. Maintain blood pressure – initially by using crystalloids, but if volumes required are high and sustained, early use of pressor agents – for example, dobutamine (5µg/kg/minute to 10µg/kg/minute as a constant rate infusion) may be required.
8. Ensure the patient’s body temperature is kept as close to normal as possible.
9. Delay NSAID use until the patient is in recovery and blood pressure is stable.

Chronic kidney disease

CKD will impact on cardiac function and cardiac function will impact on CKD. Generally, management of CKD does not impact on other common conditions; however, anaesthesia can be challenging, making it important blood pressure is maintained. This can be facilitated by starting fluid therapy prior to anaesthesia and continuing until the patient has recovered and preferably is eating.

NSAIDs are generally best given following the anaesthetic once the blood pressure is within the reference range and stable – this is particularly important if the proteinuric patients are receiving ACEi or angiotensin receptor blockers. Angiotensin release results in efferent glomerular arteriolar constriction, which is one of the mechanisms of renal autoregulation to maintain glomerular blood pressure.

The most challenging aspects of managing dogs with CKD are in those that also have significant compromise of cardiac function, as the need to maintain circulating volume to maximise glomerular blood flow and to preserve the remaining hyperfiltration nephrons is at variance with the need to prevent volume overload.

These patients are particularly vulnerable should another disease process affect circulating volume and blood pressure – for example, an episode of vomiting and diarrhoea with hyporexia.

Neoplasia

Many older dogs will develop neoplastic disease – presenting the clinician with a number of key decisions that will, in part, depend on the patient’s other co-morbidities, such as:

• Should I be screening my senior dogs for early (subclinical) neoplasia? Should I aspirate every cutaneous/subcutaneous mass discovered?
• What level of investigation is required, both in terms of cost and invasiveness, to stage a discovered neoplasm? How much screening should be done to find/evaluate other co-morbidities?
• Is my patient’s neoplastic disease likely to be fatal within the dog’s predicted life expectancy? How accurately can I predict the rate of progression of the cancer? How accurately can I predict the rate of progression of co-morbid diseases? How might the interaction between the cancer and other known diseases affect life expectancy?
• If this neoplasm is surgically amenable, will my patient tolerate the anaesthetic and surgical procedure?
• Is chemotherapy or other anti-neoplastic drug therapy appropriate in terms of likely success, side effects and requirements placed on the patient and owner to deliver the medication?

Ultimately, this means any decision to treat a senior dog requires appropriate informed owner consent and an accurate assessment of likely costs and time commitment – making it a very individualised patient plan.

Screening for neoplasia

There is clear evidence early detection and treatment of neoplasia leads to improved outcomes. What is unclear is the true risk/benefit analysis of screening in dogs; even in humans this balance is unclear (Lin et al, 2008). Unlike people, few blood tests for neoplastic disease are available (Mian et al, 2006) and those that are lack sensitivity and specificity either as a test or because of the prevalence of that neoplasm in the canine population.

The available tests are listed in Table 2. CT or MRI are sensitive ways of looking for mass lesions associated with any type of tumour; however, in humans, 90% of lumps identified on CT screening are non-neoplastic and the sampling process for such masses is associated with an appreciable complication rate.

The availability and cost of CT/MRI, and the need for general anaesthesia, make this method of screening inappropriate for the majority of veterinary patients. Unfortunately, radiography is significantly less sensitive, abdominal ultrasound time-consuming and very operator-dependent, and routine haematology and biochemistry highly insensitive. Therefore, little screening for neoplastic disease is undertaken in senior dogs.

Conclusions

The optimal management of senior dogs is supported by a sparse evidence base as many have more than one coexisting disease process that either directly affect the progression of disease or provide therapeutic challenge.

Quality of life is most important for the majority of patients and owners and this should be used to guide treatment decisions based on the best available risk/benefit analysis.

It is, however, important to remember age per se is not a disease and that anaesthetic risk is associated with a patient’s disease(s) and not its age, meaning appropriately managed interventions can lead to improved quality of life and longevity in this group.