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The Virtual Anaesthesia Textbook

Intravenous agents, TCI and TIVA

Last modified 9/11/2014. Comments to: Chris Thompson

Contents:


General

Propofol has largely replaced thiopentone as the intravenous induction agent of choice.

Detailed PDF reviews of the intravenous induction agenst are available from AnesthesiologyNews, ICU Adelaide and the Royal College of Anaesthetists. Alan Palmer has a set of slides.

The UK Society for Intravenous Anaesthesia includes a substantial abstracts database as well as useful abstracts from previous meetings. Also check out the European Society for Intravenous Anaesthesia (EuroSIVA).

The Journal of Consciousness Studies discusses the metaphysics of consciousness.

WFSA Update on Induction Agents.


Propofol

Widely used anaesthetic induction agent with slightly slower onset than thiopentone, a greater tendency to drop blood pressure. The rapid, pleasant offset makes it suitable for monitored sedation, maintenance of anaesthesia, and patient sedation in ICU. Pain on injection is probably pH related and can be ameliorated by addition of plain lignocaine (2-5ml of 1% to 20ml propofol works fine. New target controlled infusion (TCI) technique makes continuous administration easier.


Thiopentone

The old favourite has almost totally been replaced by propofol in most markets. The main advantage of thiopentone is rapid onset, but it has a narrower safety margin. Has well documented cerebral protective effects at burst suppression doses, though propofol is probably just as good. Can cause acute episode of porphyria in susceptible patients.


Etomidate

An induction agent presented in propylene glycol with less cardiovascular depression than thiopentone. Causes pain on injection, occasional involuntary movements, suppresses cortisol production. Depresses cerebral metabolism but conflicting evidence for cerebral protection.


Ketamine

An intravenous NMDA-receptor antagonist anaesthetic agent with analgesic, intoxicating and dissociative hallucinatory properties. Associated catecholamine output which masks cardiac depression. Potent analgesic properties, mild respiratory depression and some maintenance of muscle tone.

Can be used as a total intravenous anaesthetic, particularly useful for trauma or field situations.

Also useful in low doses (eg 0.05mg/kg/hr) by infusion with general anaesthesia to inhibit NMDA-receptor associated nocioceptive 'wind-up' and reduce intra-operative opioid requirements. Management of post-operative pain, especially in patients already using opioids, maybe be markedly improved by maintaining a ketamine infusion for a few days (adjust rate to results vs side-effects, often starting at 0.02 mg/kg.hr). Limited cerebral protection.

Recreationally abused ("Special-K") for intoxicating and hallucinatory effects. Confusion and disorientation are undesirable after anaesthesia.


TCI and TIVA

TCI means 'Target Controlled Infusion' in which a microprocessor-controlled syringe pump automatically and variably controls the rate of infusion of a drug to attain a user defined target level in an effect site in the patient (usually blood). This greatly simplifies maintenance of a steady blood level. Thousands of papers can be found with google. At present commercial TCI systems are only available for propofol.

  • SIVA UK includes a comprehensive set of abstracts about TCI
  • Armin Holas wrote this paper on sedation for blocks. but his other TCI papers are unavailable at present
  • Chris Thompson's context sensitive decrement times paper includes drug offset diagrams which allow comparison of intravenous agents to inhaled agents.
  • The first commercial TCI system for propofol was the Diprifusor, funded by ICI/AstraZeneca and advocated by Gavin Kenny. A magnetically tagged syringe meant that TCI could only be activated using the AZ prefilled syringes. Their Marsh dataset results in slightly generous bolus/loading doses - but personally I think this is ideal in the clinical environment. OpenTCI discuss this in some detail.
  • I strongly recommend reading Absolom et al Br. J. Anaesth. (2009) 103 (1): 26-37. doi: 10.1093/bja/aep143
  • Now there are a range of pumps some with significant TCI algorithm variations. Always run a pump with familiar settings, and check how big the loading dose will be, its steady-state infusion rate, and the rapidity with which it predicts a rise in effect site. Effect-site prediction accuracy can be confirmed by observing effect (sedation or % burst suppression) after 'locking in' a given setting. A good algorithm will neither over nor under-shoot. Schnider models imply much faster effect site equilibration than the orginal Diprifusor models.
  • With TCI pumps, care must be taken when entering weight of patients with unusual body habitus. Bodybuilders at 120kg are very different from morbidly obese inactive adults of the same weight and height - but the pump cannot tell the difference. Unless you adjust the weight entered in an appropriate way for both the pump and the patient, you may get inappropriate dosing. Users should test each kind of pump before use with different imaginary patients to check the bolus dose that it will administer.
  • This paper in Anesthesiology expresses surprise that TCI pumps remain unavailable in the USA.
  • Pump manufacturers include Carefusion/Alaris (pumps), Smiths Medical, Fresenius.
  • Davey has performed evaluations of some TCI pumps.

TIVA means 'Total intravenous Anaesthesia'. In its pure form this means no inhalational agents of any kind. It can be done without TCI pumps, however they certainly make it a lot easier.


Flumazenil

Information about benzodiazepines from MetroHealth.

Flumazenil product info from Roche USA.


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visitors to this chapter since April 29th 2000.

Original concept for the Virtual Anaesthesia Textbook by:
Dr. Chris Thompson
Senior Staff Specialist Anaesthetist
Royal Prince Alfred Hospital
Sydney Australia