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Total Intravenous Anaesthesia (TIVA)
Total intravenous anaesthesia can be defined as a technique of general anaesthesia using a combination of agents given solely by the intravenous route and in the absence of all inhalational agents including nitrous oxide1.
For 20 years, TIVA has gained popularity over its counterpart gas anaesthesia, especially since the arrival of new syringe pumps allowing a Target Controlled Infusion (TCI). TCI is very easy to use and gives the anaesthetist the possibility of controlling precisely the desired plasma or effect site concentration of drug, based on the patient’s gender, age, weight and height.
The most popular drugs used in TIVA are propofol, remifentanil, alfentanil and sufentanil.
Target Controlled Infusion (TCI)
Target Controlled Infusion is a technique of controlled drug administration where a concentration of drug is set and infusion rates are automatically calculated to reach that concentration2.
In practice, the anaesthetist uses a TCI system made of one or two infusion pumps controlled by a microprocessor, necessary to calculate the infusion rates. Based on a given patient’s physiology and a desired drug concentration, the TCI pump will determine the drug delivery rate.
TCI pumps have rapidly evolved since their introduction in 1996 and it is now possible to use TCI for generic propofol (“Open TCI”) and remifentanil.
Non-return valve (or One way valve)
The importance of non-return valves is greatly underestimated. When multiple infusions are delivered through one cannula, there is a real risk of backflow of drugs (usually with the faster infusion rates) up the other lines with lower infusion rates. This means that the patient does not receive the amount of drug the TCI pump says it does. And this could eventually lead to a case of awareness. Any subsequent changes in the drug delivery rates could also lead to an inadvertent bolus and possible overdose.
It is therefore highly recommended to use an anti-reflux valve on the IV fluid line to prevent backflow. Also recommended are anti-siphon valves on each syringe pump line to prevent backflow as well as free flow. Free flow can indeed happen, for example, if the syringe barrel or plunger is not engaged firmly in the pump mechanism and the pump is located higher than the patient.
Anti-reflux valves have a low opening pressure to allow gravity to let the IV fluid through.
Anti-siphon valves have a high opening pressure to prevent free flow or siphoning.
1 Total intravenous anaesthesia, Lynne Campbell, Frank H Engbers & Gavin N C Kenny, CDP Anaesthesia, 2001
2 Absalom AR, Struys MMRF (2002). An overview of TCI & TIVA. Gent: Academia Press, 2005
3 Safe Anaesthesia Liaison Group “Guaranteeing Drug Delivery in Total Intravenous Anaesthesia” (http://www.rcoa.ac.uk/docs/tiva_info.pdf)
Use a dedicated TIVA set
A safe drug delivery in TIVA/TCI
Using TCI pumps gives many advantages such as a smooth induction and an easier control of anaesthesia. A good quality TIVA does not only rely on advanced syringe pumps but also on a safe administration set (or infusion set).
It is not uncommon for clinicians to assemble different components together to connect their syringe pumps to the patient’s cannula. These often involve extension lines, 3-way stopcocks, one way valves, Y connectors, etc. Common problems involve kinking and blocking of lines as well as leaks, disconnections and cannula dislodgement. Following numerous incidents involving TIVA, the Safe Anaesthesia Liaison Group (SALG) issued recommendations in October 2009 to increase safety in Total Intravenous Anaesthesia.
- When administering TIVA a non-return valve is always used on any intravenous fluid line
- Sites of intravenous infusions should be visible so they may be monitored for disconnection, leaks or infusions into subcutaneous tissues
- When using equipment, it is essential that clinical staff know its uses and limitations
- Organisations give preference to clearly labelled intravenous connectors and valves
Visibility of cannula site
Problems occurring at or near the cannula, such as kinking of tubing, cannula being tissued or dislodged, are unfortunately common. To minimise these incidences, the clinician is strongly advised to keep the site visible for regular monitoring. If this should not be possible then medical tape can be used to secure the infusion set away from the cannula.
Knowing the equipment being used
Anaesthetists - TIVA enthusiasts - always advise beginners to be fully confident with the technique before using it for a complicated case. Training in TCI / TIVA is available through study days and workshops promoted by the industry (Mediplus TIVA study day) and by clinicians (SIVA, Totally TIVA).
Use of clearly labelled products
The clinician should make sure that the products used are fit for purpose. It is not just a non-return valve or one way valve; it is an anti-reflux or anti-siphon valve. It is also important to check that products are compatible with the drugs used (some plastics can crack when in contact with propofol). When using Y connectors, the priming volumes and dead space should also be looked at.
Other things to consider
Low priming volume lines should be used for drug delivery when using syringe pumps. This will reduce drug wastage after surgery and limit the impact of free flow, should this happen.
Ideally, microbore lines (1mm internal diameter) should be used for syringe pumps.
The dead space (or common space), which is the volume where all drugs and IV fluids are mixing, should also be kept to a minimum. When the IV drip is stopped, there could be a significant delay in drug delivery (depending on the volume of the dead space). When the drip starts again, the dead space full of drug would be flushed into the patient, possibly leading to an overdose.
Finally, the number of connections between pump and patient should be kept to a minimum. This will save time, reduce risks of disconnections and limit the possibility of using wrong components.