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TIVA & TCI Sedation Dr James F Peerless November 2012.

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Presentation on theme: "TIVA & TCI Sedation Dr James F Peerless November 2012."— Presentation transcript:

1 TIVA & TCI Sedation Dr James F Peerless November 2012

2 Objectives TIVA & TCI – What, why, when, where and how Models, Monitoring & Limitations Context-Sensitive Half-Time – Suitability of drugs for TCI

3 TCI Target-Controlled Infusion An infusion system whereby the target concentration of a particular agent is selected.

4 TIVA Total IntraVenous Anaesthesia – Anaesthesia provided solely by IV route – Generally as an infusion which is titrated at a specific rate to achieve a specific concentration C p – plasma concentration C e – effect site concentration

5 Indications/Benefits When: – Inhalational agents unavailable – Administering inhalational agents is difficult – Inhalational agents are contraindicated – Patient has severe PONV Also: – Reduces staff exposure to inhalational agents – Reduces pollution NOT: – Unmonitored sedation at home

6 Pharmacokinetics


8 Why do we use models? At present in clinical use there is no method of measuring drug concentrations real time analogous to the end tidal volatile agent concentration Models only – no actual plasma measurements Most models describe healthy volunteers and there is poor correlation in unwell patients The trend of increasing obesity does alter pharmacokinetics and accuracy of the pumps

9 Models Propofol – Marsh model 3-compartment model optimised by weight, gender & age – Schnider model – Diprivan 2% prefilled syringes Remifentanil – Minto model – Made up to 50 mcg mL -1 (2 mg in 40 mL 0.9% N. Saline)

10 Induction of Anaesthesia Good IV access – visible at all times!! – Dedicated line where possible – Ensure a dripping drip – Anti-reflux valves – Minimise dead-space

11 Induction of Anaesthesia Select a target concentration Press go Ensure adequate O2 Change settings/increase the target concentration in slow, small stages

12 Numbers! Propofol TCI – Sedation: 1 – 2 mcg mL -1 – Anaesthesia EC 50 : 6 – 7 mcg mL -1 Remifentanil – 0.05 – 0.5 mcg kg -1 min -1 – TCI: 4 – 8 ng mL -1 Bear in mind individual variations in pharmacokinetics and drug interactions

13 Limitations Inability to monitor actual drug concentration Slow recovery/wake-up after long operations due to distribution across compartments Increased cost compared with volatile agents Interruption to TCI delivery may go unnoticed longer than with volatiles [fighting with other theatres for use of PK pumps]

14 Context-Sensitive Half-Time The CSHT is: The time taken for the drug concentration to reduce by half once an infusion designed to maintain a constant plasma concentration is stopped. CSHT for a specific drug will vary depending on the length of the infusion

15 CSHT During an infusion, drugs will accumulate and equilibrate within all the tissues/compartments. The longer the duration of the infusion, the higher the degree of accumulation, which will maintain plasma levels once the infusion is stopped. As a result, some drugs are better suited to infusions than others

16 Upon Stopping the Infusion

17 Ideal drugs Small V D Rapid metabolism (no active metabolites) High Cl Short CSHT Propofol, alfentanil, remifentanil

18 Remifentanil – wow! Rapidly metabolised – Non-specific plasma and tissue esterases Short t 1/2elim – 1.3 minutes High Cl – 2.5 L kg -1 hr -1 Small V D – 0.35 L kg -1 = context-insensitive half-time

19 Context-Sensitive Half-Time CSHT (min) Duration of Infusion (hr) Fentanyl Thiopental Alfentanil Propofol Remifentanil

20 Summary Target concentrations are calculated, not measured

21 Questions?

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