Vet360 Vet360 Vol 05 Issue 03 - Page 12

ANAESTHESIOLOGY popular belief, butorphanol is NOT an effective primary analgesic (especially in dogs) and does not last very long. Morphine, hydromorphone, methadone, fentanyl, oxymorphone and other full mu agonist opioids are much more effective analgesics. 2. What is the time-frame between premedication, induction and maintenance anaesthesia for surgery? Is there enough time allotted for the premedications to work before induction and surgery? For example, buprenorphine, although an effective partial mu agonist, takes 20 to 30 minutes for full analgesic effects. Starting surgery before analgesic onset will result in elevated levels of nociception, contributing to patient arousal. called β€œMAC no movement”). Administering analgesic drugs before and during surgery (intermittent or continuous rate infusions) decreases the necessity for high vaporizer outputs. 4. What breathing systems are being used? Are the breathing systems being checked for leaks? Are the patients intubated? There are two major types of breathing systems used on conventional anaesthetic machines for small animal patients: rebreathing and non-rebreathing. The rebreathing systems can be further divided into adult and pediatric circle systems. The choice of breathing system is based on patient size: patients weighing < 5 kg require a non-rebreathing system, those between 5 and 10 kg need a pediatric rebreathing system, and those > 10 kg require an adult rebreathing system. 3. How are patients being monitored? In response to an increase in sympathetic tone, heart rate will increase during light periods of anaesthesia; however, judging anaesthetic depth solely based on heart rate is inaccurate. Because heart rate can be affected by so many other variables, it is a poor indication of anaesthetic depth. For example, a patient entering a deeper plane of anaesthesia (level 3 to 4) will commonly become tachycardic because of increased sympathetic tone from decreased ventilation and elevated partial pressure of carbon dioxide (pCO2). The person monitoring the patient notices the tachycardia and mistakenly turns up the inhalant anesthetic, thinking the patient is arousing. Gradually the patient will reach deeper levels of anaesthesia, which can become serious. Besides heart rate, other monitoring parameters include arterial blood pressures, end-tidal pCO2, jaw tone, eye position, response to a toe pinch, respiratory rate and character, mucous membrane color and capillary refill time. Other than tachypnea, no other parameters included in the question help judge the patient’s level of anaesthesia. 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