(such as venipuncture and endotracheal intubation) are needed on the day of the prolonged nonsurvival recording session, and they can be performed with only light anesthesia augmented by analgesics. Following these minor procedures, general anesthesia is provided for the nonsurvival recording session. The difficulty involved in assessing whether paralyzed animals are free of pain and/or distress is acknowledged by the Guide, which states (p. 65): Some classes of drugs—such as sedatives, anxiolytics, and neuromuscular blocking agents—are not analgesic or anesthetic and thus do not relieve pain; however, they might be used in combination with appropriate analgesics and anesthetics. Neuromuscular blocking agents (e.g., pancuronium) are sometimes used to paralyze skeletal muscles during surgery in which general anesthetics have been administered (Klein, 1987). When these agents are used during surgery or in any other painful procedure, many signs of anesthetic depth are eliminated because of the paralysis. However, autonomic nervous system changes (e.g., sudden changes in heart rate and blood pressure) can be indicators of pain related to an inadequate depth of anesthesia. It follows that adequate anesthesia must be established and verified before the administration of NMBDs and initiation of the data-collection session. The animal should be maintained without NMBDs at a fixed anesthetic level until it is physiologically stable. It will take at least 30 minutes, depending on the duration of action of the anesthetics used during the initial surgical preparation period (if there was one), at a fixed anesthetic level and without change in physiological state to ensure that the animal is stable. That period should be used to establish and validate the physiological signs that will be monitored under paralysis to document that the animal is being maintained in a suitable condition. Experience has shown that care should be taken to ensure that the level of anesthesia established during this initial period is adequate but does not compromise neural responsiveness in the areas under study (NIH, 1991). That is critical because reducing the level of anesthesia after NMBDs have been administered is problematic. Obtaining a performance based assessment of the adequacy of the new anesthesia level may require that NMBDs be withdrawn to assess skeletal muscle response; however, this can entail difficulties because a long period may be needed to restore muscle responses (Hildebrand, 1997). Noninvasive assessment of neuromuscular function with examination of evoked responses of skeletal muscle to peripheral motor nerve stimulation can facilitate monitoring both the induction of paralysis and the recovery from NMBDs (Hildebrand, 1997). Anesthesia and general physiologic state should be monitored for each animal during each procedure (Mason and Brown, 1997; NRC, 1996). Notations
OCR for page 91
should include the time, date (if appropriate), drugs or solutions administered, and the name or initials of the person making the entry. A number of physiologic measures are helpful in monitoring animals on NMBDs, including heart rate, electroencephalogram, arterial blood pressure, blood oxygen saturation, urine production and pH, end-tidal CO2 and/or blood gas concentration, rectal temperature, and general autonomic signs of arousal, such as salivation, pupil size, and lacrimation (Hildebrand, 1997; NIH, 1991). Physiologic measures should be documented periodically throughout an experiment. The periodicity of monitoring and documentation should be more frequent during the initial stages of experimentation (such as every 15 minutes) and gradually extended once the animal has been stabilized on NMBDs. The details of the specific physiologic measures to be monitored and the frequency and means of documentation should be described in the research protocol and approved by the IACUC. The use of automated multifunction measuring devices—which maintain a running record of such metabolic measures as blood pressure, blood oxygenation, expiratory CO2, and pulse 