Introduction

Recent advances in veterinary oncology have increased owner awareness and the readiness of many veterinary practitioners to treat cancer patients. This means that greater numbers of pets with cancer are being managed long term. In general, the goal of treatment in the majority of cases is to maintain optimum quality of life for their pet, as opposed to quantity. Cancer can be a painful disease, and to provide acceptable quality of life, pain must be recognised and treated appropriately, through constant reevaluation, tailoring of analgesic protocols to address patients' changing needs and being prepared to re-think/change the plan whenever appropriate.

Sources of Pain in Cancer Patients

There have been few clinical studies into cancer pain in animals but, based on clinical experience, information extrapolated from human medicine and knowledge of other chronic pain states (e.g., osteoarthritis), it is assumed that veterinary cancer patients experience pain. It is thought that the initial and most common cause of pain is tumour invasion. Any tumour may cause pain, but not all tumours are painful, and individual patients may react to/perceive pain differently. Therapeutic or diagnostic procedures may be painful, depending on their nature, e.g., surgical procedures or cancer-related pathological fractures may cause severe acute pain; or, if complications occur, chemotherapy (e.g., extravasation) and radiotherapy (e.g., desquamation) may cause pain.

Reasons to Treat Pain

Pain is the awareness of suffering, distress, an unpleasant physical or emotional experience associated with potential or actual tissue damage. It is sensed and transmitted by nociceptive free nerve endings, which are abundant in superficial and deep body tissues. Compassionate care requires that patients are kept as free as possible from the adverse effects associated with cancer and its treatment.

Types of Pain

Pain may be classified as:

 Somatic (originating in the layers of skin and muscle tissue)

 Visceral (arising from stimulation of nociceptors in internal organs)

 Neuropathic (resulting from central or peripheral nervous system damage or altered nervous system processing)

Tumour invasion may cause tissue-stretching, compression or ischaemia, resulting in visceral pain. Neuropathic pain may occur through invasion or compression of nerves by tumour growth, central sensitisation or secondary to nerve damage, caused by chemotherapy or radiation therapy.

Acute Pain

Acute pain is abrupt in onset, often severe, but may be relatively short in duration. It is generally associated with inflammation induced by surgery, trauma or infection. Acute pain may be linked with many diagnostic and therapeutic procedures in cancer patients, in addition to that caused by the disease process.

Chronic Pain

Chronic pain persists beyond an acute trauma or expected injury healing time. It may be more difficult to diagnose and may be masked by adaptive behavioural changes. It is characterised by non-specific signs, e.g., reduced level of activity, depression, anorexia, character change and/or anxiety. It is debilitating, and may cause cachexia. In addition, oncology patients may suffer from pre-existing conditions, e.g., osteoarthritis, which should not be overlooked.

Monitoring Pain

In order to ensure effective analgesia, recognition and monitoring pain is paramount--the following could be considered to be pain related:

 Vocalisation

 Tachypnoea

 Tachycardia

 Pyrexia

 Lameness/loss of function

 Aggression/resentment of handling--especially the injured area

 Anorexia

 Restlessness, inability to settle, sitting hunched or in unnatural positions

 Unresponsiveness to handling

Any of these signs should be recorded and brought to the attention of the veterinary surgeon promptly. If there is any doubt, analgesia should be provided.

Nursing Management

Nursing staff have an essential role to play in the pain management of oncology patients. In conjunction with drug therapy, patient comfort may be optimised by provision of excellent nursing, for example:

 Ensuring a warm, comfortable environment

 Minimising stress--boxes for cats to hide in; separate cat/dog wards, etc.

 Provision of appropriate nutrition

 Allowing regular opportunities for urination/defecation, or expression of bladder when indicated

 Keeping the patient clean and dry

 Regular interaction with the patient

 Continuous observation for signs of discomfort

 Fitting Elizabethan collars when necessary, to prevent self trauma which will exacerbate pain

 The use of support bandages, where appropriate

Simple things, such as quiet companionship, gentle grooming, massage and/or the application of heat packs, the provision of soft, warm bedding or cool comfortable surfaces, may help to settle and reassure pets, and can have a real impact on their comfort.

Pain clinics may be established to regularly reassess a patient's quality of life. In general, owners of cancer-bearing pets are very committed and it is important that there is a close communication between them and the nursing team. The patient's appetite, willingness to exercise/play, its interaction with family/other pets and general demeanour, as well as the owner's perception of the pet's pain/ overall quality of life may be used to measure the success of treatment.

Pain Management Strategies

Strategies for managing pain are based on the concept of interfering with nociception, the conscious perception of pain. Providing analgesia (Figure 1) before painful stimuli initiate nociception is termed pre-emptive analgesia, and should be employed whenever possible. Untreated pain causes central sensitisation ('wind up'). This often occurs in ongoing chronic pain syndromes, such as cancer. Many cancer patients undergo multiple procedures during the course of their therapy, and anxiety and fear can become a significant part of the pain experience; therefore sedation, combined with pre-emptive analgesic drugs, may relieve stress in veterinary cancer patients.

Figure 1. Pharmacological analgesic options.

For moderate to severe cancer pain, full agonist opioids are the drugs of choice. Care is needed at high doses as unwanted side effects (e.g., dysphoria, sedation, respiratory depression, bradycardia and reduced gut motility) may occur.

Regional nerve blocks may be incorporated into anaesthetic protocols for surgical oncology patients, e.g., extradural blocks may be administered to provide analgesia for up to 24 hours, or analgesic catheters, placed at surgery, may be infused with local anaesthetic.

Painful surgeries require intraoperative analgesic supplementation--constant rate infusions (CRI) and nitrous oxide help control emergent pain. CRIs can be continued postoperatively. Patients with mild to moderate postoperative pain may be managed with boluses, but it is imperative to anticipate the need for further analgesic before the effect of the previous dose has worn off, with regular patient assessment to avoid overdose.

For longer-term pain management, the use of non-steroidal anti-inflammatory drugs (NSAIDs), often in combination with a partial or full opioid is a good option: this targets multiple points along the pain pathways, allowing reduction of the doses of each drug and creating balanced analgesia. Various doses and/or drugs may have to be tried to meet an individual's needs. However, if pain is sufficiently severe as to cause drug doses to be repeatedly elevated or pain is uncontrolled, quality of life and the ethics of pursuing treatment must be questioned.

Conclusion

Veterinary nurses can help implement a more proactive and humane method of treating veterinary cancer patients. By understanding and recognising cancer pain, we can help identify the level of analgesia required for individual patients. Providing compassionate care and managing the long-term comfort of veterinary cancer patients can be a rewarding nursing experience that we should readily embrace.

References

1.  Lascelles BDX. Relief of chronic cancer pain. In: Dobson, JM; Lascelles, BDX. eds. BSAVA manual of canine and feline oncology (second edition). Gloucester: BSAVA, 2003; 137-151.

2.  Flecknell P, Waterman-Pearson, A. eds. Pain management in animals. London: Saunders, 2000.

3.  Seymour C, Gleed R. eds. Manual of small animal anaesthesia and analgesia. Cheltenham: BSAVA, 1999.