Total intravenous anesthesia (TIVA)

Learning objectives

Describe the indications for total intravenous anesthesia
Describe the techniques and models used for total intravenous anesthesia
Describe the advantages, disadvantages, and safety measures for total intravenous anesthesia

Total intravenous anesthesia (TIVA) is a technique where intravenous agents are used to induce and maintain general anesthesia, avoiding the use of inhalational anesthetics
Continuous intravenous infusion is commonly done by a target-controlled infusion (TCI) pump, but can also be achieved using intermittent boluses or manual infusion techniques
TCI allows precise and individualized administration of intravenous anesthetics
Both hypnosis and analgesia can be achieved using an intravenous technique
Goals for TIVA: Smooth induction, reliable and titratable maintenance, and rapid emergence

Sophisticated TCI syringe drivers incorporate real-time pharmacokinetic models that deliver the appropriate dose to achieve and maintain the requested target concentration
The microprocessor within the syringe driver continuously calculates the appropriate infusion rates
A bolus/elimination/transfer principle is used to maintain an appropriate plasma level of anesthetic agents
Induction is achieved by a rapid propofol infusion, giving a bolus calculated to achieve the required plasma concentration
This is followed by a progressively decreasing infusion rate calculated to match the transfer between compartments and elimination of the drug, maintaining the required plasma level
Once the compartments reach a steady-state concentration, the infusion rate slows to match elimination only
To increase the target plasma level, the syringe driver delivers an additional bolus to achieve the desired concentration and then maintains a higher infusion rate
To decrease the target plasma level, the syringe driver stops infusing until the microprocessor calculates that the new target has been achieved, and the new level is maintained
Modern TCI pumps also have software that allows titrating to effect-site concentration (the concentration in the brain)
Depth of anesthesia monitoring (e.g., bispectral index) is required, as there is considerable variation in the uptake and effect of anesthetic agents in individual patients

Propofol TCI allows easy control and rapid change of the target propofol concentration
Unpremedicated adult patients >55 years: Target propofol concentration 4-8 µg/mL for induction (usually takes 60-120 seconds)
When co-administering an analgesic, maintenance at 3-6 µg/mL
Lower target concentrations are used in the elderly population due to the risk of side-effects
Propofol TCI is not routinely used in children
Propofol TCI models:
- Marsh
  - Calculations based on the assumption that the central compartment volume is proportional to the patient’s weight, ignoring age
  - Assumes that the central compartment volume is 19.4 L for an 85 kg patient
  - Designed primarily to target plasma concentrations
  - Only used for patients >16 years of age
- Schnider
  - Requires age, height, and body weight
  - Calculates a sex-specific lean body mass and determines the dosages accordingly
  - Assumes that the fixed central compartment volume is 4.27 L for an 85 kg patient (4-fold difference with the Marsh model)
  - Allows for effect site concentration to be targeted
  - More commonly used in the elderly population
- Paedfusor
  - Variant of the Marsh model for patients 1-16 years of age
  - Uses weight to calculate target plasma concentration and features a nonlinear scaling of central compartment volume as age exceeds 12 years
- Kataria
  - Can be used for patients 3-16 years of age with a minimum weight of 15 kg
  - Uses weight to calculate target plasma concentration

Since propofol has no analgesic properties, TIVA is commonly achieved by combining propofol infusion with a regional block or supplemental opioids
Supplemental short-acting opioids:
- Remifentanil
  - Elimination half-time: 3-10 min
  - Does not accumulate in hepatic or renal failure
  - Context insensitive: the time required for the drug concentration to fall by 50% is always the same (~3 min), regardless of age, weight, sex, or hepatic or renal function
  - Opioid of choice for TIVA for many anesthesiologists
  - Can be given using the Minto model (allows easy titration based on patient age, gender weight and height
  - Target plasma concentration: 3-8 ng/mL for induction, up to 15 ng/ml in stimulating procedures
  - Ensure adequate analgesia after remifentanil has worn off
- Alfentanil
  - Short onset time (90 s)
  - Given using Maitre model (calculations based on age, gender and weight)
- Sufentanil
  - Much more potent than remifentanil
  - Longer duration of action
  - Tends to accumulate during prolonged infusion
  - Two TCI models: Gepts (fixed compartment volume) and Bovill (assumes that the central compartment volume is proportional to body weight)

Advantages	Disadvantages
More predictable onset and stability of maintenance	Pharmacokinetic and pharmacodynamic variability of response to the injected agent
Elimination of volatile anesthetics along with their possible liver and kidney toxicity, potential rise in intracranial pressure, their effect on the uterus, and possible environmental effects	Lack of ability to accurately assess actual blood levels
No need for accurately calibrated vaporizers	Variations in the hemodynamic state of the patient
Fast recovery with fewer complications, decreased time to discharge	Requirement for dedicated IV access, and risk of disconnection
Propofol is a powerful antiemetic	Risk of accidental awareness
Avoidance of nitrous oxide with its effect on air emboli and pneumothoraces, bone marrow suppression

Ensure the cannula is visible and accessible at all times and checked regularly to prevent disconnection or tissuing
Check the pump setup regularly to prevent tubing disconnection, ensure clamps are open/closed accordingly, pump alarms are rectified and no backtracking of drug occurs
Ensure the drug concentration matches the programmed concentration
Ensure the correct syringe is placed in the correct syringe driver
Use anti-reflux and anti-syphon valves with clamps in multilumen tubing for safe delivery
Use a processed EEG monitor when a neuromuscular blocker is used