Total Intravenous Anesthesia (TIVA) Education

Total Intravenous Anesthesia (TIVA) Overview

Introduction to TIVA

• Total intravenous anesthesia (TIVA) is a technique for general anesthesia using intravenous medications for induction and maintenance.

• TIVA is less commonly practiced in the U.S. compared to inhaled, volatile-based anesthesia, potentially affecting clinician familiarity and comfort with its administration.

Awareness During Anesthesia

• Intraoperative awareness with recall occurs in 0.001% to 0.2% of cases; TIVA-related incidents often stem from technical errors during setup or monitoring.

• There is limited data comparing TIVA and inhaled anesthesia regarding patient experience and outcomes, highlighting knowledge gaps in this area.

Research Gaps

• High-quality randomized control trials are needed to evaluate intraoperative awareness risks and recovery quality between intravenous Propofol and volatile anesthetics, as addressed by the Thrive Trial.

Setting Up TIVA: A Systematic Approach

Step 1: Establishing IV Access

• Reliable intravenous access is crucial; consider placing an additional IV site if necessary for effective drug delivery throughout the procedure.

Step 2: Channel and Medication Setup

• Determine infusion channels for carrier fluid, Propofol, opioids, and adjunctive agents; label all medications according to institutional policies to prevent errors.

• Example channel assignments include:

• Channel A: Carrier fluid

• Channel B: Propofol

• Channel C: Opioid

• Channel D: Adjunctive agents like dexmedetomidine or vasopressors

Step 3: Applying a Checklist

• Use the mnemonic "TIVAA" for safe drug administration:

• Tether connections securely.

• Infuse correct dosages; double-check rates upon initiation.

• Visualize infusion sites regularly.

• Alarm troubleshooting—be familiar with pump alarms such as line occlusion or air in line.

Enhancing Safety Through Monitoring

Importance of EEG Monitoring

• Clinicians should be familiar with electroencephalographic (EEG) monitoring principles when administering general anesthesia, especially when neuromuscular blockers are used alongside TIVA.

Setting Up EEG Monitoring

• Set up EEG monitoring before induction to visualize waveforms while patients are still awake; this helps recognize changes post-induction more effectively.

Understanding EEG Waveforms

• Familiarity with typical EEG patterns is essential; avoid relying solely on processed numbers like bispectral index which may provide false reassurance during procedures involving neuromuscular blockers.

Visualizing Changes During Anesthesia

• Turn off filters on EEG monitors that obscure slow waves under two hertz—important for assessing depth of anesthesia accurately during procedures involving propofol or volatile agents. Persistent alpha spindles over delta oscillations indicate appropriate hypnotic states during general anesthesia.

EEG Monitoring and Anesthesia Management

Understanding EEG Patterns

• The EEG waveform and spectrogram display changes in power of various EEG frequencies over time, highlighting slow delta oscillations and alpha spindle activity.

• Slow delta oscillations exhibit high amplitude (~100 microvolts), occurring approximately every second, while alpha spindles show smaller voltage swings (~40 microvolts) at a frequency of 8-12 times per second.

Clinical Implications of EEG Findings

• During Propofol anesthesia, patients may not be aware of the presence of slow delta oscillations or alpha spindles; older patients often have less prominent alpha spindles compared to younger individuals.

• It is recommended that institutions utilize EEG monitors for better patient management during anesthesia.

Induction and Monitoring Techniques

• Before inducing anesthesia, it is crucial to identify alpha spindles on top of slow delta oscillations by turning off filters on the EEG monitor to assess appropriate depth of anesthesia.

Key Anesthetic Agents: Propofol and Remifentanil

Propofol Overview

• Propofol is a short-acting hypnotic agent that induces loss of consciousness through GABA A receptor agonism, leading to hyperpolarization of cell membranes.

• Its rapid onset and short duration make it suitable for continuous infusion; it is metabolized by the liver and excreted via kidneys.

Remifentanil Overview

• Remifentanil acts as a selective mu-opioid receptor agonist with properties that increase pain threshold and alter pain perception without relying on renal or hepatic function for metabolism.

Context-Sensitive Half-Life Explained

• The context-sensitive half-life refers to the time required for plasma drug concentration to decrease by 50% after stopping an infusion, which varies significantly among different drugs.

Comparison Between Drugs

• For propofol, the context-sensitive half-life is typically under 30 minutes for infusions lasting up to two hours but increases with longer infusion durations.

• In contrast, remifentanil maintains a constant context-sensitive half-life (less than five minutes), independent of infusion duration due to its pharmacokinetic properties.

Pharmacokinetics in Anesthesia Administration

Compartment Model Conceptualization

• The relationship between dose rate, plasma concentration, and effect site concentration can be visualized using a three-compartment model relevant for administering anesthetics like propofol.

Distribution Dynamics

• The central compartment includes blood/plasma and tissues that equilibrate quickly (e.g., lungs), while peripheral compartments represent muscle (V2) and fat (V3).

Importance of Drug Properties

• Understanding how distribution affects plasma concentrations highlights complexities in administering anesthesia; each drug has unique inter-compartmental clearances influenced by patient factors.

Titration Principles in Anesthesia

• Effective titration aims to maintain optimal drug concentrations at the effect site throughout induction, maintenance, and emergence phases.

Understanding Plasma Concentration Changes in Anesthesia

Target-Controlled Infusion (TCI) and Drug Distribution

• Predicting plasma concentration changes over time is complex, but TCI pumps can help by using equations that describe drug distribution between compartments.

• Currently, TCI pumps are not licensed for use in the U.S., highlighting a gap in available technology for anesthesia management.

• Stand Pump is mentioned as an example of computerized modeling that could assist in understanding TIVA dosing and predicting plasma concentrations.

Patient Factors Influencing Dosing

• During procedures, patient factors such as movement or increased heart rate may necessitate adjustments to propofol infusion rates.

• High-frequency EEG activity or elevated bispectral index (BIS) readings can indicate the need for higher plasma-propofol concentrations, prompting additional boluses and increased infusion rates.

Case Study: Propofol Administration

• A case study of a 50-year-old female patient illustrates the importance of appropriate dosing; she received a 1 mg/kg propofol bolus followed by a maintenance infusion.

• The initial infusion rate was likely too low, as indicated by the yellow line falling below the desired plasma concentration threshold.

Understanding Plasma Concentration Dynamics

• It takes time for plasma concentration to rise after adjusting infusion rates; doubling the rate without a bolus results in delayed increases.

• Administering a bolus dose alongside an increased infusion rate leads to quicker attainment of desired plasma concentrations.

Clinical Monitoring and Adjustments

• Continuous monitoring is essential; even with halved infusion rates, plasma concentrations may remain within desired ranges due to propofol's pharmacokinetics.

• Down-titrating propofol is necessary because it has a longer contact-sensitive half-life compared to remifentanil, which requires careful management during surgical stimuli.

Emergence from Anesthesia

• To facilitate predictable emergence from anesthesia, consider pausing the propofol infusion to allow rapid decreases in plasma concentration before resuming at lower rates or using intermittent boluses.