Anaesthetic Agents PDF

# Anaesthetic agents: REST - Rural Emergency Skills Training ## Anaesthetic Agents (including paralytics) Induction of general anaesthesia in the trauma patient is generally achieved with reduced doses of commonly available agents titrated to effect. Cardiovascular collapse can occur when anaesthe...

# Anaesthetic agents: REST - Rural Emergency Skills Training ## Anaesthetic Agents (including paralytics) Induction of general anaesthesia in the trauma patient is generally achieved with reduced doses of commonly available agents titrated to effect. Cardiovascular collapse can occur when anaesthetic agents are given in standard, elective anaesthesia doses by removing/reducing the compensatory sympathetic response to haemorrhagic shock. Propofol, thiopentone and ketamine are most commonly available in rural Australia. * Thiopentone (barbiturate) is the quickest acting onset but is a vasodilator and can precipitate hypotension. Thiopentone is not that commonly available (or used). * Propofol (GABA agent) has a quick onset and a quick recovery time. It is quite a potent vasodilator and also has antiemetic properties. * Ketamine (NMDA antagonist) produces dissociative anaesthesia, with relative maintenance of brain stem functions (respiration, for example) despite cortical suppression. It provides analgesia, unlike thiopentone and propofol, and tends to preserve sympathetic response to haemorrhagic shock due to catecholamine release. However, there can be a direct myocardial depressant effect with standard dosing, so in the setting of haemorrhagic shock, reduced titrated dosing is still recommended. In addition, traditional teaching was that ketamine is contraindicated in traumatic head injuries due to concern of raised intracranial pressure. Subsequent research and trauma use has shown no convincing evidence of this and no proof of worsening outcomes. ## Fentanyl Fentanyl is the recommended opioid in trauma anaesthesia due to its potency, shorter onset and more minor histamine release than morphine. Rocuronium or suxamethonium are the main paralytics in trauma care. Rocuronium has an advantage in being useful in both rapid sequence intubation and the maintenance of neuromuscular blockade. Suxamethonium remains the fastest onset paralytic with the shortest return of neuromuscular function. ## Maintenance of balanced anaesthesia Maintenance of balanced anaesthesia is typically achieved by an infusion of the induction agent along with an analgesic. Morphine or Fentanyl combined with Midazolam is popular either as cocktail in one syringe or two separate infusions. Propofol with fentanyl is another common option. For pure simplicity, solo ketamine infusion will provide balanced anaesthesia but often needs supplementation with fentanyl or morphine to mitigate tachycardia and hypertension. Another agent to be considered is Ketofol which is a Ketamine/Propofol mix and which is said to give the benefits of Ketamine and Propofol whilst reducing some of the side effects, mainly the hypotensive effects of the Propofol. | Trauma Anaesthetic drug | Induction dosing | Maintenance dosing | Benefits | Precautions | |---------------------------|------------------|---------------------|------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------| | Ketamine | 1mg/kg | 1-4mg/kg/hr infusion | Less risk of cardiovascular collapse, seizure control, analgesic, bronchodilator | Hypertension, tachycardia, hypersalivation. | | Propofol | 0.5-1mg/kg | 2-4mg/kg/hr | Rapid onset/recovery allows better neurological assessment, antiemetic, seizure control. | Not analgesic, vasodilator=hypotension. | | Thiopentone | 3mg/kg | N/A | Fastest onset, seizure control, reduces intracranial pressure | Not analgesic, vasodilator=hypotension | | Fentanyl | 1mcg/kg | 1-2mcg/kg/hr | analgesia | Muscle rigidity with high-dose bolus | | Rocuronium | 0.6-1.2 mg/kg | Repeat every 20-30 min as needed (usually a lower than induction dose and generally quoted as 0.15mg/kg) | | Masking of seizures | | Suxamethonium | 1-2mg/kg | N/A | | Hyperkalaemia | | Morphine/midazolam infusion | Initial 5mls/hr and titrate as needed | | Commonly available, seizure control | Longer recovery time, opioid tolerant may require very high doses (ketamine useful alternative) | | Fentanyl/midazolam infusion | Initial 5mls/hr and titrate as needed | | Commonly available, seizure control | Opioid tolerant may require higher dosing |