Chapter 30

### INTRODUCTION

Emergence from anesthesia is complex period where, as with induction, several competing interests influence an anesthesiologist's course of action. Timely emergence from anesthesia, adequate ventilatory function, and pain control once emerged from anesthesia; prevention of postoperative nausea and vomiting; and proper management of other comorbidities are some of these interests. This chapter will briefly review the selected issues regarding emergence from anesthesia, including:

• Is there any advantage of target-controlled infusion (TCI) over total intravenous anesthesia (TIVA) when using conventional infusion rates in terms of a timely emergence from anesthesia?

• Are end-tidal potent inhaled agent levels under non–steady-state conditions, such as emergence, useful in predicting wake-up times?

• What is a rational approach to opioid administration for safe postoperative analgesia?

• What technique can be used to estimate intraoperative and postoperative opioid requirements in patients who chronically consume opioids?

### TARGET-CONTROLLED INFUSION VERSUS TOTAL INTRAVENOUS ANESTHESIA

No definitive outcomes study has explored whether administering a total intravenous anesthetic via TCI or with conventional continuous infusion rates impacts emergence. One might hypothesize that if administering a lengthy anesthetic, TCI would provide a more economical anesthetic and avoid unnecessary drug delivery that would perhaps delay emergence. Figure 30–1 presents a simulation of 2 intravenous techniques: one using TCI and the other set infusion rates for 2, 4, 6, and 8 hours. Both approaches used a high-dose remifentanil and low dose propofol technique. In fact the TCI target effect-site concentrations were selected to be near the effect-site concentrations that resulted from propofol infusions of 100 mcg/kg/min and remifentanil 0.2 mcg/kg/min. In general, with increasing duration of the anesthetic, the simulation predicted the time to emergence would become longer. Time to emergence was defined as the time required for the model of loss of responsiveness to predict that only 1 out of 20 people would be unresponsive (5%). Either technique (TCI or TIVA) was within 1 or 2 minutes of the other. For shorter infusions (2 and 4 hours), the TIVA technique was 1 minute ahead of the TCI for emergence. For the long infusion (8 hours), that relationship was reversed; time for emergence from TCI occurred a few minutes before that for TIVA. A potential explanation for the negligible differences between TIVA and TCI is that a high-dose opioid technique was used reducing the amount of propofol used.

###### Figure 30–1

Emergence for anesthesia: is there a difference between total intravenous anesthesia (TIVA) and target-controlled infusion (TCI)? Here are simulations of the predicted probability of unresponsiveness once an anesthetic has been terminated for TCI and TIVA using propofol and remifentanil. TIVA consisted of propofol 100 mcg/kg/min and remifentanil 0.2 mcg/kg/min. TCI consisted of propofol and remifentanil target effect-site concentrations of 3 mcg/mL and 6 ng/mL, respectively. Each technique was administered for 2, 4, 6, and 8 hours. The end of emergence (gray horizontal line) was defined as a 5% probability of unresponsiveness (ie, 19 out of 20 people ...

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