In veterinary practice, animals require heavy sedation or general anaesthesia for any number of procedures where sedation or anaesthesia would not necessarily be required for a human patient. Note that in the following description and claims when “anaesthesia” is referred to it will be understood that “sedation” will also be covered, and vice versa. Generally, animals require sedation or anaesthesia to facilitate manipulative procedures (e.g. radiographs), for minor surgical procedures (e.g. dental procedures) and for major surgery (e.g. ovariohysterectomy, fracture repair, etc.). In fact, anaesthesia is required for about one third of “income generation” procedures. In busy practices this results in many animals recovering from anaesthesia each day, frequently with several animals recovering from anaesthesia at the same time. Because of economic and manpower needs, animals recovering from anaesthesia are not usually under continuous observation by a trained person. Frequently these animals recover in large recovery or treatment rooms where other procedures are occurring. Therefore, the veterinary staff “keep an eye” on the animals recovering from anaesthesia while their attention is otherwise diverted.
The objective of monitoring a patient recovering from anaesthesia is to detect changes such as:
shivering
increasing chest excursions (rate or volume)
random body limb and neck movements
chewing, especially if the patient is intubated.
All the above changes reflect increased muscle tone associated with increasing activity and awareness of the nervous system as patients recover from the “relaxed” state of general anaesthesia. Problems can occur if it is not realized that a patient is becoming aroused after anaesthesia or during critical care.
For example, animals recovering from anaesthesia frequently remain intubated (a tube passing through the mouth into the larynx and trachea, used to maintain an open airway) until their laryngeal function returns, such as when they swallow or cough. If intubated patients become conscious with the tube in place they usually become startled and start to chew the tube and to struggle. If they are not attended to and the tube removed, it can be “bitten off” with part of the tube remaining in the trachea.
Further, veterinarians need to know if the patient develops an airway obstruction. Whether intubated or not, semi-conscious animals (recovering from anaesthesia or during critical care) are at risk of developing airway obstructions which can result in hypoxia and death. This occurs because either an intubated patient may close its mouth/jaws on the endo-tracheal tube or a non intubated patient moves about and can collapse with it's head twisted in a position where the airway becomes obstructed.
In addition to monitoring state of consciousness in animals recovering from anaesthesia, veterinarians need to know that the patients temperature is returning to normal. Small animals, such as cats and dogs, have a relatively high surface area to body weight ratio and anaesthesia reduces muscle movement and shivering. Consequently hypothermia is the most common and potentially critical complication occurring during anaesthesia in small animals and during critical care of small semi-conscious patients. It is difficult to increase body temperature in patients that are already covered by sterile drapes for surgery particularly where a surgical procedure results in exposure of internal organs and cavities. Therefore once patients are placed in the recovery area their temperature is usually taken intermittently using a mercury or electronic thermometer and then efforts are made to increase their body temperature such as use of heating blankets, hot water bottles and heating lamps. While the goal is to prevent further decrease in body temperature and to warm the patient, it is also possible to induce hyperthermia and occasionally severe skin burns if patients treated with heating devices are not adequately monitored. Accidents often happen where there are a lot of patients to observe. This may, for example, result in severe burns to a patient being warmed excessively or further, hypothermia can develop in the case of patients who have lost too much body heat and rewarming temperature monitoring has not been adequate. With the current methods, intermittent monitoring using mercury or electronic thermometers, this is more likely to happen.
All the above problems are compounded where there are a lot of patients being monitored simultaneously in a recovery or treatment room. It is very difficult to “keep an eye” on all the patients at the same time, and it may be the case that an animal becomes aroused without the veterinary staff being aware. These problems may occur, therefore, and often do in practising veterinary hospitals.