Critically Ill Geriatric Patients

Chapter 175 Critically Ill Geriatric Patients



Maureen McMichael, DVM, DACVECC



KEY POINTS



• The number of geriatric pet cats and dogs is growing rapidly in the United States and Europe.

• Maintenance energy requirements decrease in older dogs but appear to increase in older (greater than 12 years) cats, affecting nutritional requirements in these age-groups.

• Many parameters are unchanged in the older animal at rest but differ significantly when stressed with illness or chronic disease.

• Older animals do not appear to possess physiologic reserves, and acute illness can significantly tax their organ systems.


INTRODUCTION


The number of geriatric pets has increased considerably during the last 10 years. In 1995 in the United States the percentage of pet cats over 6 years of age was 24% of the population. Today it is estimated to be approximately 47%.1 In Europe the number of geriatric cats increased by over 100% between 1983 and 1995, and the number of geriatric dogs increased by approximately 50% during that time.2 Unfortunately this growing subset of the pet population has received little scientific scrutiny, and research pertaining to geriatric critical care is extremely sparse.


In geriatric people, several studies have shown that older age alone does not predict mortality. The main determinants of mortality are prior health status and severity of current disease process.3-5 Although these same studies have not been done in veterinary medicine, it seems prudent to offer aggressive treatment to the older dog and cat once comorbid diseases, quality of life for the pet, and the owner’s desires are taken into consideration.


The term geriatric is difficult to define in veterinary medicine because it differs between dogs and cats and among breeds (e.g., a Great Dane has a much shorter lifespan than a Chihuahua). In general, animals older than 7 years are considered geriatric.


The objective of this chapter is to review the physiologic changes that occur as a result of aging as they relate to critical care medicine.



LABORATORY VALUES


In people at rest, the laboratory values of red blood cells, white blood cells, platelets, and hemoglobin do not change with age. However, there is a decrease in the ability of the bone marrow to increase neutrophil production in response to infection and to increase red blood cell production in response to anemia in geriatric people.6 Neutrophil function has also been shown to decrease with age in people.6


There are no established reference ranges for geriatric small animal patients, perhaps because the term geriatric is difficult to define, and therefore the laboratory values are difficult to quantify. Harper and others looked at age-related variations in laboratory values in Beagles and Labrador Retrievers. The data were grouped into categories, and the geriatric category included all animals over 10 years of age. There were no differences between the dogs greater than 10 years of age and the rest of the adults.7 Strasser and others8 looked at age-dependent changes in laboratory values before and after exercise in Beagles. There were no significant differences in the laboratory values between 5-year-old and 10-year-old Beagles at rest. After exercise, however, there were significant differences in many of the parameters. The older dogs had lower hematocrits, red blood cell counts, and hemoglobin concentrations. They also had a significantly lower venous oxygen saturation and lower plasma glucose levels.8 In addition, older dogs have a slower hematopoietic response to acute anemia (phlebotomy) than younger dogs.6


Although there are limited data for older animals, the research suggests that at-rest laboratory values may not be very different between adult and geriatric animals. However, when stressed by exercise, or perhaps by disease, older animals may show significant differences in laboratory values and the disease process may place a large burden on their tenuous reserves.


The coagulation system appears to shift toward hypercoagulability as humans age, and the incidence of pulmonary thromboembolism is increased five-fold in humans older than 85 years.6 Although changes in this system with age have not been investigated in small animal patients, prophylactic treatment for hypercoagulability may be warranted in this age-group, especially in animals with predisposing disease processes.


The human thoracic cage becomes more rigid and the lungs lose elasticity with age. Respiratory muscle strength is decreased by 25%, and the alveolar-arterial gradient increases significantly.9 Loss of diaphragmatic and intercostal muscle mass is thought to be responsible for the decline in respiratory muscle strength. These aging changes may result in a decreased arterial partial pressure of oxygen in older veterinary patients, but this is not well documented. Diseases such as pneumonia, pulmonary thromboembolism, and pulmonary edema place great pressure on the limited pulmonary reserves and may be more difficult to treat for these reasons.


Renal blood flow, glomerular filtration rate, urine concentrating and diluting ability, and creatinine clearance have been shown to decrease with age in people.9 Inability to conserve sodium or concentrate urine and decreased renal blood flow have been reported in geriatric small animals.10 This combination leads to the inability of the aged to respond to hypovolemia or hypervolemia and often places severe restrictions on fluid and electrolyte therapy.

Related posts:

  1. Deteriorating Mental Status
  2. Hyperthermia and Fever
  3. Ventilator-Associated Lung Injury
  4. Allergic Airway Disease in Dogs and Cats and Feline Bronchopulmonary Disease

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Sep 10, 2016 | Posted by in SMALL ANIMAL | Comments Off on Critically Ill Geriatric Patients

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