Pre-anaesthetic assessment and preparation
General considerations: All equipment, drugs, and ancillary supplies and materials must be ready and easily accessible before anaesthesia of any tiger is attempted. It is important to ensure that equipment is functional and clean, and supplies are restocked, before and after each anaesthetic event. After use ensure appropriate and secure storage.
Weight and condition estimation: Although it is difficult to assess the condition of a free-ranging, snared or box-trapped tiger accurately without causing it unnecessary pre-anaesthetic stress, an estimate of weight is crucial to calculate the required amount of anaesthetic drugs. This should be carried out by two people as quietly and quickly as possible, causing the minimum of disturbance. (One of the reasons to weigh all animals that are anaesthetised is to increase field staff’s ability to accurately estimate weights in the future). In some cases it will also be possible to estimate general body condition and gender, presence and severity of wounds and injuries etc. These factors should all be taken into account when selecting anaesthetic drugs and doses.
Pre-anaesthetic excitement: It is very important to minimize pre-anaesthetic excitement, although any wild tiger being approached by humans will inevitably be excited to some degree. Excited animals require higher anaesthetic doses, take longer to become recumbent, and are prone to more anaesthetic complications. Avoid actions that may increase pre-anaesthetic excitement. During weight estimation, the preparation of darts, any on-site discussion of problems and procedures, etc, keep the number of people involved and noise levels to a minimum. Make preparations out of sight, sound, and downwind of the tiger if possible. People that are not involved at this stage should stay well back and out of sight until safe anaesthesia is achieved. A critical period for a snared or trapped tiger is the time between when it first detects a person nearby and when it is darted. Stress apparently increases dramatically when an animal detects a person nearby and it may injure itself trying to escape. Thus, such tigers should be anesthetized as quickly as possible following initial detection.
Environmental assessment: Consider the physical hazards of the area in which anaesthesia will be conducted. Note obstacles that could injure the animal or staff, the slope of the ground, shade, cover in case of heavy rain, holes and ditches that could trip people working in the area etc. In most cases, conditions will be far from ideal, and there is ample scope and need for improvisation. It may be necessary to move a tiger once anaesthetised to a more suitable area if, for example, there is nearby water in which it could drown or cliffs from which it could fall during recovery. To prevent wind chill that may contribute to hypothermia it may be necessary to move an anaesthetised animal to a more protected location during cold seasons. During hot seasons it may be necessary to move an anaesthetised animal to a more shaded place to help prevent hyperthermia if additional shade cannot be provided at the induction site. In all cases these moves should be made early in anaesthesia and not later when there is a greater chance of the tiger waking up.
NB: Oxygen must be provided to tigers being anaesthetised at altitudes above 2000 metres above sea level. It is also important to choose injectable anaesthetic drugs (or drug combinations) that do not depress breathing. The most suitable induction agent would be tiletamine-zolazepam (“Zoletil”).
Roles and responsibilities: One person should have overall responsibility and be in charge of the procedure – usually an experienced field biologist or veterinarian. Each team member should be assigned clearly defined responsibilities. For example, one person should be responsible for anaesthesia, another for assessing injuries or fitting a radio-collar, and yet another for collecting biological samples, etc. Everyone involved must understand their specific roles and responsibilities and the plan of action before the process of anaesthesia is started. Bystanders that are not involved in the anaesthetic and handling process should be kept well out of the way at all times.