sedation

Question 1

Midazolam

Answer 1

Midazolam acts by potentiating GABA inhibitory action in the CNS by binding to benzodiazepine specific receptors on GABA/Benzodiazepinereceptor complex. This results in sedation, amnesia and anxiolysis. It has no analgesic properties.

Onset of action IV 2-5 minutes
Half-life 1-4 hours (compared to Diazepam 20-48 hours)
2 hours required for full recovery
Dose 1-2mg slow IV push with 1mg aliquots every 2 minutes
Caution with obese, elderly and alcohol/opiates as sedative effects increased
Side effects are predominantly cardiorespiratory depression:
hypotension
respiratory depression/apnoea.

Question 2

Propofol

Answer 2

The exact mechanism of action is unknown but its main CNS depressant action is thought to be via the GABA receptor at a site different to that of barbiturates and benzodiazepines. May also shorten channel opening times at nicotinic acetylcholine receptors and sodium channels in the cerebral cortex. Propofol has no analgesic properties.

Rapid onset of action 30-90 seconds. Ranges from deep to general anaesthetic.
Duration of action is dose dependant, 5-10 minutes after bolus administration
Dose 0.5-1mg/kg IV
Side effects:
pain on injection
apnoea
hypotension.

Question 3

Ketamine

Answer 3

It is an NMDA receptor antagonist producing a dissociative and amnesic state. It is also exhibits partial agonism at mu-receptors so giving analgesia. The considered benefit of Ketamine is that it does not affect pharyngeal-laryngeal reflexes and can be considered when fasting status cannot be assured.

Onset of action IV is 1 minute
Duration of action 5-10 minutes
Dose 0.5-1 mg/kg
It is contraindicated when an increase in blood pressure is considered hazardous
General contraindication is when patient is required to remain still e.g. CT/MRI
Side effects:
hypertension
tachycardia
hypersalivation
laryngospasm.

Question 4

conscious sedation

Answer 4

Is a drug-induced depression of consciousness during which patients are able to respond purposefully to verbal commands or light tactile stimulation. * Interventions to maintain a patent airway, spontaneous ventilation or cardiovascular function may, in exceptional situations, be required. * Conscious sedation may be achieved by a wide variety of drugs including midazolam, and may accompany local anaesthesia. * All conscious sedation techniques should provide a margin of safety that is wide enough to render loss of consciousness unlikely.

Question 5

Deeper sedation

Answer 5

Is characterised by depression of consciousness that can readily progress to the point where consciousness is lost and patients respond only to painful stimulation. * It is associated with loss of the ability to maintain a patent airway, inadequate spontaneous ventilation and/or impaired cardiovascular function, and has similar risks to general anaesthesia, requiring an equivalent level of care.

Question 6

Causes of concern for procedural sedation

Answer 6

all children less than 2 years of age * the elderly * those with severely limiting heart, cerebrovascular, lung, liver or renal disease * morbid obesity * significant obstructive sleep apnoea * known or suspected difficult endotracheal intubation * acute gastrointestinal bleeding particularly with cardiovascular compromise or shock, severe anaemia * the potential for aspiration of stomach contents (which may necessitate endotracheal intubation) * previous adverse events due to sedation, analgesia or anaesthesia * patients in ASA Grades P 4-5 (ANZCA PS09 - Appendix 1): o P4 - A patient with severe systemic disease that is a constant threat to life o P 5 - A moribund patient who is not expected to survive without the operation