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ANAESTHESIOLOGY depth will begin to lighten and minute ventilation will increase again, completing the cycle. to gradually become light due to anaesthetic vapor dilution. It’s recommended to use the rebreathing bag to periodically apply a positive pressure breath (intermittent sighing) to the patient at least once every five minutes. This will help decrease positional pulmonary atelectasis and improve the cyclical levels of anaesthesia in spontaneously ventilating patients. Controlled ventilation, employing a mechanical ventilator with intermittent positive pressure ventilation (controlled IPPV), provides the most consistent control level of anaesthesia because the patient is not relying on its own minute ventilation to determine anesthetic vapor uptake. 6. Can you describe your active scavenging unit? Tachypnoeic anesthetised patients can develop ventilatory dead space, resulting in little to no anaesthetic gas exchange in the alveoli. Positive pressure ventilation (intermittent or controlled) will help mitigate tachypnoea and dead space ventilation. Some people use the oxygen flush valve to provide positive pressure ventilation to their anaesthetised patients. Because the oxygen flush valve bypasses the flow meter and vaporizer, when pressed, 50 to 80 psi will be delivered to the patient’s alveoli, causing barotrauma. In addition, using the oxygen flush valve as a mode of ventilation will cause the patient Is the active scavenging system made by a credible manufacturer? Active scavenging systems are manufactured to provide the correct draw against the patient breathing system and should include ample safety mechanisms. The interface between the scavenging system and breathing system contains its own reservoir bag, a pressure control needle valve, and a positive and negative pressure safety valve. If the negative pressure safety valve malfunctions, there will be an excessive draw against the patient breathing system, resulting in anesthetic gases being pulled away from the patient. This problem is typically manifested by a continually deflated breathing system reservoir bag and variable levels of patient ana esthetic depths. Ways to mitigate excess scavenging system draw against the patient breathing system are to turn up the flow rate to match the draw, adjust (close) the interface needle valve, or partially close the adjustable pressure limiting device (pop-off valve). Scavenging systems problems are rare, but they can occur. I would recommend you continue to use the passive system until the problem is solved. Onset and Peak Clinical Effects of Premedication Agents Drug Onset of action Peak effect Comments Acetylpromazine 15 minutes 45 minutes Tranquilisation, not sedation – wait until peak effect before induction. No analgesic properties. Morphine 10 minutes 45 minutes Clinical effects relevant within 10 minutes. Butorphanol 15 minutes 45 minutes Provides good sedation although minimal analgesia. Buprenorphine 20 minutes 45 minutes Analgesia to the same level as NSAID’s although bind receptors with higher affinity than morphine. Diazepam 30 seconds 3 minutes Functions better as a co-induction agent, although not consistently induction agent sparing. No analgesic properties. Strictly IV – propylene glycol formulation poorly absorbed via other routes. Medetomidine 5 minutes 20 minu tes Excellent sedative and analgesic, although effects last approximately an hour. These parameters can be applied to intramuscular administration in healthy, adult animals. Effects may be prolonged in cardiovascularly unstable animals or those with hepatic or renal dysfunction. References 1. 2. 3. KuKanich, B., Wiese, A.J. 2015. Opioids. In: Grimm et al. eds. Lumb and Jones Veterinary Anesthesia and Analgesia. Iowa: Wiley, pp. 207-226 Murrel, J.C. 2016. Pre-anaesthetic medication and sedation. In: Duke-Novakovski, T, de Vries, M & Seymour, C eds. BSAVA Manual of Canine and Feline Anaesthesia and Analgesia. Gloucester: Brit- ish Small Animal Veterinary Association, pp. 170-189 Rankin, D.C. 2015. Sedatives and Tranquilizers. In: Grimm et al. eds. Lumb and Jones Veterinary Anesthesia and Analgesia. Iowa: Wiley, pp. 196-206 Dr Abdur R Kadwa BVSc Anaesthesiology Resident Department of Companion Animal Clinical Studies Faculty of Veterinary Science, UP Issue 03 | JULY 2018 | 13