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