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Proceedings for Pain Management and Humane Endpoints

Implementing Assessment Techniques for Pain Management and Humane Endpoints

David B. Morton
Department of Biomedical Science and Biomedical Ethics
The Medical School, University of Birmingham
Edgbaston, Birmingham, B15 2TT, UK

Several systems of assessing pain in animals have been used but inevitably, as with human babies, they all rely on observer assessment rather than 'patient reporting'. Such schemes include visual analogue scales (the observer indicates by a mark on a line which indicates normal to severe pain), numerical rating scales (same as VAS but using a scale from 0-10), and simple descriptive scales (e.g. no pain, mild - moderate - substantial - severe -- pain and distress) but all have their drawbacks notably observer variability (see Holton et al, 1998). Clinical signs, by definition (those observable and not reported by the patient), aim to provide an objective, rather than a subjective judgment, but it needs an observer with an empathetic attitude, good powers of observation, knowledge of the normal, and good clinical skills. This means that it has to be a multidisciplinary approach and a combined effort is needed for all those involved. A system of clinical signs has been described for humans to help mothers know when to call in a doctor (Morley et al, 1991) and also for animals (Morton & Griffiths, 1985; Baumans et al, 1994) and the animal scheme has been strengthened by being made more rigorous with less room for observer interpretation (Morton, 1990; 1995a,b; 1997a,b; 1998a,b). Finally, in animal research, unlike clinical practice, healthy animals have standardized scientific procedures carried out on them and so any assessment system should be routinely applicable to those animals undergoing that procedures, and should also be applicable in different laboratories.

Adverse effects experienced by animals during experimentation include more than pain, and include conscious emotions such as fear (probably the commonest), discomfort, dystress (stress with which an animal fails to thrive or cope - see Morton, 1998b) and mental distress (frustration, boredom etc). However, before any of these states can be alleviated or assessed, or experiments refined in any way so as to cause less pain and suffering, we have first to be able to recognize when animal wellbeing is being affected, both positively as well as negatively. (Recognition can be considered as a fourth R, following on after the Three As - Avoidance, Assessment and Alleviation of animal suffering in research.) Moreover, it is important to eliminate any animal suffering in order to achieve science of high quality and specificity in relation to the scientific question being asked, as well as to practise humane science at the least economic cost (Claassen, 1994; Balls et al, 1995). We have approached this problem by using clinical signs as a way of determining the degree to which an animal's physiology and mental state has deviated from normal, and then used these perturbations for an assessment of severity. This approach is applicable not only to mammals, but to vertebrates and even non-vertebrates, providing there is a good knowledge of their normal ethology and physiology.

The Score Sheet System

Score sheets are drawn up specifically for each scientific procedure, and for each species, and sometimes even strain, undergoing that procedure; they can rarely be generalized. The sheets list the cardinal clinical signs that are observable and measurable and are developed through the experience of a team of observers. The animal caretakers will be crucial in this regard as they are most likely to know when an animal is 'not right' which will often indicate a change in behavior, posture, appearance or even the feel or smell of an animal. The veterinarian should be skilled in identifying objective clinical signs and should have a knowledge of the biology of the species, including the range of its relevant behavioral and physiological responses (see van den Heuvil, 1990; Kuipers et al, 1991; Morton & Townsend, 1995; Schlede et al, 1992). Scientists should be conversant with the perturbations that might be expected during an experiment due to the scientific paradigm. All these factors will be important guides in the assessment of the effects of a scientific procedure on an animal. By detailing the cardinal signs of any particular protocol and regularly observing animals at critical periods during the experiment, an objective assessment of animal wellbeing can be made throughout the experimental period.

Lists of signs are developed by observing the first few animals undergoing a novel scientific procedure very closely and then the list is modified with experience until a set of cardinal signs that most animals will show during that experiment, and that are relevant to the assessment of suffering, is made. These key clinical signs are set out against time in the score sheet (an example is given in Table 1). Crucially, any clinical sign has to be reduced to a level which reduces the scope for observer interpretation and can only be recorded as being present or absent - indicated by a plus or a minus sign (sometimes a +/- if the observer is unsure). The convention is that negative signs indicate normality, i.e. within the normal range, and positive signs indicate that the animal is outside the normal range. In this way it is possible to scan a score sheet to gain an overall impression of animal wellbeing: the more plusses, the more an animal has deviated from normality with the inference that it is suffering more than before. Animals should be scored during critical periods when they could predictably give rise to concern (e.g. in the immediate post-operative period; or in a study on infection after the incubation period).

Practically, it is important to develop a disciplined strategy to the recognition of adverse effects in animals. At the beginning of an assessment the animal should be viewed from a distance, and its natural undisturbed behavior and its appearance noted. Next, as the observer approaches the pen or removes the cage lid, the animal will inevitably start to interact with the observer and its response can be used to determine whether it is normal or abnormal. Finally, a detailed clinical examination can be carried out by handling and restraining the animal in some way and observing its appearance carefully as well as making any relevant clinical measurements e.g. bodyweight, temperature, in addition to its behavior (it may have become more aggressive or fearful, or even vocalize).

At the bottom of the sheet there are guidance notes for animal caretakers and veterinary technicians about what they should provide in terms of husbandry and care for animals undergoing that scientific procedure. There are also guidelines on how to record qualitative clinical signs (such as diarrhea and respiration), as well as criteria by which to implement humane end points. Finally, if an animal has to be killed there are instructions about what other actions should be taken, such as tissues to be retrieved or placed in formal saline; this helps ensure that the maximum information is always obtained from any animal in a study. While these sheets take time to fill in it is not difficult for an experienced person to see if an animal is unwell, so the NAD box (Nothing Abnormal Detected) is simply checked. However, if an animal is not normal, it does take time to check it and to make judgements over what actions to be taken, but is that not the price for practising humane science?

In order to promote good care and good continuity of care we allocate an animal technician/caretaker or veterinary technician to be responsible for liaising with scientists and other technical staff, and to maintain and update the score sheets. The roles of the technician in charge are:

  • to check that the appropriate licenses and approved protocols are in order and to cross check them what the scientist actually intends to do that day to the animal(s);
  • to check the score sheet is appropriate before an experiment begins;
  • to know the purpose of the experiment and the scientific objectives, and to become familiar with the scientific procedures to be carried out on the animals and the clinical signs that may occur;
  • to ensure all personnel (caretakers, technicians, scientists, veterinarians) know how to use score sheets and can recognize the clinical signs and can interpret the signs clearly into humane end points;
  • to check that caretakers and technicians not familiar with that experiment, say doing a weekend or holiday rota, are informed about animals;
  • to liaise with scientists over the experiment e.g. timing, numbers of animals, equipment, end points;
  • to update the score sheets based on new signs or combinations of signs observed; and
  • to report to the responsible persons (e.g. the veterinarian, senior scientist) any concerns over the animals or personnel involved.

Interpreting the Score Sheet

It can be seen from Table 1 that there are more plusses to the right than to the left. Several other points can also be noted: first, along the top, that as the animal became unwell, so it was scored more frequently. During Day 0 (the day of the operation) it scored abnormal in one or two predictable signs as it was recovering from the anaesthetic and the surgery (low body temperature and hunched) and so the NAD box was ticked. The next day (21st June) basic observations were made of amount of food eaten, temperature and bodyweight, and again the NAD box checked. However, towards the end of that day, the coat became starey (ruffled), the body temperature rose, and the breathing became more rapid. By the next morning, there was a significant bodyweight loss (12%) which increased during the day to 18% - a strong indication that the animal had not eaten or drunk much, if anything, and that it probably had diarrhea. In fact there were so many abnormal clinical signs that it was decided to kill the animal on humane grounds before the end of the experiment. The sudden appearance of diarrhea and the concomitant rapid weight loss and dehydration, labored breathing, abnormal posture, lack of a red light response (animals are placed under a red light to see if they will show their normal nocternal active behavior), etc all confirmed that the animal was becoming severely physiologically compromised and was not going to yield valid results in relation to the scientific objective. Even more significantly, its temperature was now at 35.1°C - a very poor sign, and the extremities were blue (i.e. the color of the feet and ears). In our experience, this animal would have died that night if not sooner.

Some Advantages of the Score Sheet System

This scheme of scoring clinical signs for the recognition and assessment of adverse effects on animals during scientific procedures has been shown to have the following advantages:

  • Closer observation of animals is now carried out by all staff at critical times in the experiment as the sheets have indicated the times when animals find their circumstances most aversive.
  • Subjective assessments of suffering by staff and scientists are avoided, thereby promoting more fruitful dialogue, as evidence-based opinion becomes possible based on the clinical signs. In a sense they empower the technicians by helping them illustrate to less experienced persons why an animal is 'not right'.
  • Consistency of scoring is increased as the guidance is clear and the scoring options are limited.
  • Single signs or combination of signs can be used to indicate overall severity of the procedure, as well as alleviative therapies or scientific procedures at set points in an experiment (e.g. blood sampling).
  • The sheets help determine the effectiveness of any therapy intended to relieve adverse effects.
  • The sheets can be used to determine which experimental models cause least pain, distress e.g. by comparing alternative animal models thus helping to refine scientific procedures.
  • The sheets help in training those inexperienced in the assessment of adverse effects or in that particular scientific procedure.
  • The sheets can be used to analyze retrospectively the adverse effects of any scientific procedure and its level.
  • The sheets have been found to add to the science as a more careful observation of animals is carried out.

The score sheet system provides a visual aid, opens up discussion between interested parties, and helps focus attention on to an animals' condition throughout the procedures. An analysis of the score sheets can reveal patterns of recovery or deterioration and so gives a better picture of the effect of a procedure on the animals from start to finish. The sheet encourages all involved to observe the behavior of animals, to recognize normal and abnormal behaviors. This will help in determining animals' responses to various procedures which will help us to devise ways of refining experimental technique by highlighting the type and timing of any adverse effects. The sheets are constantly being developed and updated with further experience and it is surprising how the process never seems to stop as new staff pick up new signs, or new signs develop as the experimental model is slightly modified. Staff also start to perceive patterns of adverse effects that, when taken as a whole, which indicate early death or early deterioration sufficient to warrant the animal being killed on scientific grounds alone. Such information has led to better animal care as well as providing useful scientific information such as the recognition of neurological deficits, times of epilepsy or weight loss, as well as unexpected findings such as urinary retention in a model of renal failure. Furthermore, by picking up signs of poor animal wellbeing early, we can implement humane endpoints sooner rather than later and so avoid animals being inadvertently lost from an experiment through unexpected death (see Redgate et al, 1991; Olfert, 1995; Soothill et al, 1993; Townsend & Morton, 1994; Mellor & Morton, 1997; Cussler et al, 1998; UKCCCR, 1998). In the UK, where severity limits are imposed on every scientific procedure, the sheet can be used to indicate when such limits have been breached, or are about to be breached, or may have to be reviewed, by the precise observation of the clinical signs.

The scoring system has proved to be especially useful with new procedures, or when users are not always sure of what effects a procedure will have. In my experience the literature rarely records adverse effects on the animals, or how to avoid or measure them and I believe scientists have a moral obligation to do so (Morton, 1992). We now look more closely at ways of improving our peri-operative care and in some experiments we have found that recovery is slower than it could be if we used different anesthetics or analgesics, or intra-operative procedures such as maintaining body temperature or giving a bolus of warm saline before recovery. We try to operate early in the day so animals have maximum time under close observation and can be given more support such as fluid therapy or special diets (e.g. jelly, fruit, vegetables). This has proven to save animalsÕ lives as well as improve the speed recovery.


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Table 1 - Animal Score Sheet (completed) for Heterotopic Kidney Transplant

RAT No. HN1ISSUE No: 234
Inactive? Try red light response ^-++
Hunched posture++/--/+++
Starey coat-++++
Rate of breathing5460647040
*Type of breathingRRL
Not inquisitive & alert----+
** Eating/Jelly Mash? amount eaten-50%-???
Not drinking--???
Bodyweight (g)254260250221215205
% change from start-6%0%-12%-14%-18%
Body Temperature (degrees C)3536.537383836.535.5
Crusty red eyes/nose---++
Excessive Wetness on lower body----+
Sunken Eyes ^-----
Dehydration ^---++
Coat/wet soiled----+
Pale eyes & ears-----
Blue extremities ^----+
Stitches OK?/Date Removed:-----
*** Swelling of graft ^-----/+

Special Husbandry Requirements:
Animals should be put on a cage liner with tissue paper and a small piece of VetBed.

Scoring details:
* Type of breathing: R = rapid, S = shallow, L = laboured, N = normal.
** Eaten/Jelly mash - amount? - Record as 0/25/50/75/100%
*** Swelling score 0=Normal 4+ = rejection and large swelling

Humane End-Points and actions:

  1. Weight loss of 15% or more inform the investigator, veterinarian and technician I/C
  2. Pre-moribund state (indicating a failing graft)
  3. Any major clinical sign recurs after 24hr. (marked ^, less than 35°C)

Scientific measures
Take 1ml of blood and urine, if possible, - place at 4°C
Place transplanted kidney into 10 ml formal saline

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