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Recognition and Alleviation of Pain and Distress in Laboratory Animals
Salivation should be controlled with a suitable drug, or some other innocuous means should be used to prevent the accumulation of secretion in the throat.
The duration of paralysis must be dictated by the time over which the physiologic condition of the animal, and hence its comfort and well-being, can readily be maintained. For most species that will not exceed about 4–6 hours. Some form of intravenous supplementation might be needed, as will cannulation of the bladder in some species (such as tree shrews) if emptying does not occur spontaneously.
If an animal is to recover from the paralysis and re-establish its respiration, it should happen while the animal is under general anesthesia. The skilled use of chemical antidotes can ease the process of recovery so that anesthesia can be brief and light.
No procedure should be undertaken in an unanesthetized paralyzed animal until it has been shown—when the animal is fully alert, unparalyzed, and capable of expressing its reactions—that an identical procedure elicits no sign of discomfort or distress. That specifically includes, but is not limited to, insertion or manipulation of recording or other devices; electric, chemical, or other stimulation; and the measurement of optical reflexes.
In an otherwise comfortable situation, the principal source of stress that occurs in paralyzed humans (and therefore, presumably, animals) is the sense of respiratory distress that accompanies an increase in arterial PaCO2. Therefore, end-tidal CO2 should be continuously monitored with a reliable, calibrated instrument and its concentration should be kept substantially below the 4.7% at which respiratory distress can begin. It should be understood that CO2 monitors designed for use in humans typically do not accurately measure end-tidal CO2 in smaller animals, because excessive gas mixing occurs in the sampling apparatus. Also, relatively short periods of artificial ventilation are often accompanied by blood-chemical and pulmonary-function changes that alter the normal relationship between end-tidal CO2 and arterial PaCO2. Regular direct measurement of arterial blood gases is an indispensable component of monitoring, and monitoring with a respiratory-gas analyzer alone is inadequate.
The heart rate should be monitored. Preferably, a rate-meter sounds an alarm if heart rate is above or below its natural resting range. Indeed, once an immobilized animal has recovered from general anesthesia, the heart rate might provide the experimenter with a ready index of the animal's state; an increase due to a relatively innocuous stimulus provides some assurance that the animal is alert and is not experiencing a severe stress.
Body temperature should be monitored and strictly maintained within the limits normal for resting animals of the species in question. Body temperature will fall gradually because of immobilization, and there should be provision for keeping the animal warm. But devices used for that purpose should be incapable of overheating to a point that causes dangerously high temperatures or uncomfortable heating of the skin.