Chapter 29

### INTRODUCTION

Anesthetic technique has expanded and improved with the advent of newer drugs, methods to deliver them, and drug displays that present real-time anesthetic drug interactions. This chapter will briefly explore the following:

• Use of pharmacodynamic interaction models to compare common anesthetic techniques

• How substantially different dosing regimens yield near-equivalent effects

• The pronounced opioid effect from common remifentanil dosing regimens

• How target-controlled infusion (TCI) and total intravenous anesthesia (TIVA) compare in terms of anesthetic effects

### TOTAL INTRAVENOUS ANESTHESIA VERSUS COMBINED TECHNIQUE

Anesthesiologists have long used both TIVA and potent inhaled agents combined with opioids. Both techniques are effective. TIVA is better suited for patients with a known or suspected history of postoperative nausea and vomiting; procedures such as microlaryngoscopy and rigid bronchoscopy, where delivery of potent inhaled agents is not possible; and females of childbearing age. Potent inhaled agents are better suited for patients with known or suspected ischemic cardiovascular disease. Major advantages are that there is less postoperative nausea and vomiting; improved cognitive function, at least during the first few hours after surgery1; and smooth emergence; patients simply appear happier as well. Potential disadvantages of TIVA are that it is more expensive; more complicated; and associated with a perception of more risk of awareness, although studies suggest a low risk of awareness.2 Use of inhalation agents is popular because they are easier to use and less expensive, allow for the monitoring of end-tidal concentrations, and are associated with a perceived lower risk of awareness.

With regard to the ability of either technique to provide an adequate level of anesthesia, consider the simulations presented in Figure 29–1. They present predictions of unresponsiveness for a TIVA technique using infusion rates (ie, mcg/kg/min), an intravenous technique using TCIs, and a potent inhaled agent in combination with an opioid technique. The 3 techniques used common dosing regimens that led to a predicted high probability of unresponsiveness.

###### Figure 29–1

Total intravenous anesthesia (TIVA) versus target-controlled infusion (TCI) versus combined techniques: simulation of the probability of unresponsiveness for 3 anesthetic dosing regimens: TIVA, TCI, and a combined potent inhaled agent (sevoflurane) and opioid technique. Unresponsiveness was defined as an Observer's Assessment of Alertness and Sedation greater than 2. All simulations assumed a 50-year-old, 165-cm, 70-kg female undergoing a 90-minute procedure associated with minimal postoperative pain. All 3 techniques provide a high probability of unresponsiveness. The TIVA technique consisted of induction with fentanyl 1.5 mcg/kg and propofol 2 mg/kg followed by maintenance with propofol 100 mcg/kg/min and remifentanil 0.2 mcg/kg/min. A fentanyl bolus (1.5 mcg/kg) was administered as a transition opioid 15 minutes before the end of the procedure. The TCI technique consisted of a target propofol effect-site concentration of 3 mcg/mL and a target remifentanil effect-site concentration of 6 ng/mL. The combined potent inhaled agent–opioid technique consisted of induction as described for the TIVA followed by 2% sevoflurane in ...

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