The bone marrow makes large macrophages– big eating machines - and B
cells, while the thymus gland in the neck produces T-cells (there are three
types, one turns on B-cells, another turns on the third type of T-cells the
ones that destroy virus and tumor infected cells). Like any army, the immune
system needs to coordinate and communicate, and it does so through
hormone like substances called cytokines– including interleukins (ILs),
interferon (INF) and tumor necrosis factor (TNF). Psychological stress
causes sleep disturbances, decreased appetite and delays wound healing.
Restraint, isolation and physical manipulation are very stressful to animals.
Unfortunately, going to the vets tends to involve many of these stressful procedures
and in an already sick dog may contribute to a worsening of his condition.
Vets can help minimize the stress by making sure pets that require hospitalization
are kept in adequately sized cages, that floors are dry, the environment
is comfortable and clean and at an optimal temperature, noise should be
minimized; species kept separately,water and food of good quality and
appropriate for the animal’s condition provided, and periods of light and dark
maintained so that the dog’s normal patterns of rest and sleep aren’t disturbed.
Many vets will provide Dog appeasing pheromone diffusers, pheromones
mimicking those produced by bitches when they nurse their puppies,
and which calm and comfort many agitated dogs. Owners who have trained
their dogs to accept all manner of handling and have them crate trained while
they are healthy can help minimize the stress their dog experiences when being
examined or hospitalized. Physical stress – surgery and trauma – as well as
psychological stress result in suppression of the immune system.
As we might expect surgical trauma causes a reduction in the immune response,
however - beyond the physical stress, the psychological stress and the
pain often present before but also involved in the surgery - anesthesia itself
causes immunosuppression. These multiple stresses to the system can lead
to postoperative problems – hypothermia,low blood pressure, increased pain, sleep difficulties, impaired respiration,increased cardiac demand, gastrointestinal problems – ulcers and/or
loss of normal motility - as well as loss of appetite, weight loss, delayed healing,
infection and growth of malignant tumors.Controlling pain before, during and
after surgery is of paramount importance. It has been shown that the more
pain an animal experiences, the more likely that any tumor present will metastasize.
Most effective in blocking endocrine metabolic responses is the
use of analgesics applied to nerves serving the surgical site – nerve blocks,
spinal and epidural anesthesia. Local/ regional anesthesia can abolish surgical
stress. Maintaining the block post surgically can further reduce immunosuppression
and speed healing. Opioids and non steroidal anti-inflammatory
drugs (NSAIDs) have little effect in reducing stress at recommended doses,
although they do reduce inflammation,which infiltrative anesthetics do not
affect. Some immune cells however,have opioid receptors; and T and perhaps
B cells can produce opioid immunopeptides – beta-endorphin, enkephalin
and dynorphin. Local application of opioids is far less likely to
produce immunosuppression, and can be very helpful in treating such conditions
as arthritis.Other preoperative strategies that may help reduce surgical stress are a single
dose of glucocorticoids; in patients with heart disease beta blockers are
helpful; adequate nutrition, especially feeding carbohydrates, may stop the
body breaking down muscle and other tissues.Hypothermia is a threat to surgical patients
on several fronts. Immunosuppression makes the body more susceptible
to bacterial infections. Blood vessels constrict near the skin, and reduce
blood flow that is needed for repair of damaged tissues and further decreases
the activity of local immune defense factors. Neutrophil – white blood cell
– function is compromised so they are less effective at eliminating bacteria,
the production of cytokines and reproduction of T cells is also reduced.
Even a central hypothermia of 1.9oC tripled the incidence of surgical wound
infections in one study. Lowered blood pressure, as a result of blood loss and
various anesthetic agents, further exacerbates these problems.
The longer the animal is anesthetized and surgery lasts, the greater the risk of infection of the

wound and respiratory infection. One study showed that insurgeries lasting less than an hour, the
concentration of B and T cells took about 7 days to return to normal, but
for longer surgeries the return to normal took significantly longer.
Because of the immunosuppression produced by anesthesia and surgery,
vaccinations should not be given at the time of surgery, and elective surgery
should be delayed at least 3 weeks after vaccination. This must obviously be weighed against further stress when dealing with wild or feral animals, but in the domestic dog there is no medical
excuse to vaccinate an animal at the time of surgery. This practice can not
only diminish the immune response to and efficacy of the vaccine, but is more
likely to result in anaphylactic (allergic) reaction, thrombocytopenia
(lowering of platelets and risk of bleeding).

A big thank you to Linda Aronson,DVM, for her contribution to PON Digest