Introduction
Many surgical procedures in the ambulatory setting are performed using general anesthesia. Recovery time after surgery and anesthesia is an important aspect that should be considered when a general anesthetic is chosen for ambulatory surgical procedures. Although mortality rates are extremely low after general anesthesia in the ambulatory setting, minor morbidity in the form of postoperative pain, nausea and vomiting, fatigue, shivering, headache, and drowsiness continues to affect a large number of patients. With the continuing emphasis on expansion of ambulatory surgery and the inclusion of elderly and stable American Society of Anesthesiologists (ASA) 3 and 4 patients onto operating lists, it is likely that both mortality and morbidity rates will increase in the future. Although some systematic reviews have been published in the literature comparing general with regional anesthesia for major surgery with a focus on outcome, the choice of anesthetic agents for general anesthesia in the ambulatory setting remains controversial. Specifically, the choice of anesthetic in terms of outcome after ambulatory surgery remains poorly explored.
Options
The two commonly used methods for general anesthesia for ambulatory surgery are total intravenous anesthesia (TIVA) and inhalational anesthesia. Although propofol used in conjunction with an opiate is practically the only anesthetic used for TIVA, many inhalational anesthetics are available today, and the choice of these agents has been the subject of many published studies and a great deal of controversy. Surprisingly, only two systematic reviews have been published on this interesting subject, and the studies included both inpatients and outpatients. In this chapter, the evidence is derived from well-performed prospective studies combined with the author’s experience.
Endpoints of Interest in Ambulatory Surgery
To analyze the benefits of one type of general anesthetic over another, it is important to define the endpoints that are of interest to the patient and the hospital. One easily defined endpoint that is of great interest to both the patient and hospital is mortality risk after ambulatory surgery. However, the mortality rate is extremely low in this group of patients ; therefore it would be difficult to confirm that the choice of anesthetic has any significant effect on perioperative mortality risk during ambulatory surgery. Another endpoint of importance, which is less well-defined, is major morbidity. The effect of the choice of anesthetic agent on this important outcome also remains unclear.
A differentiation must be made between measuring “true outcomes” and “surrogate outcomes.” Examples of true outcomes include discharge times, return to work, admission, readmission, and patient satisfaction. Examples of surrogate outcomes include incidence of pain, time to first analgesic consumption, early recovery (response to commands) after anesthesia, and nausea and vomiting. Surrogate measures should be accepted only if they yield the same conclusions as their nonsurrogate endpoints. Patient satisfaction is one of the outcomes that is probably one of the most important factors from the patient’s perspective. Because most patients have not undergone the same operation twice with the use of different anesthetics, gathering of evidence is restricted to asking patients whether they were satisfied with the anesthetic. When patient satisfaction with anesthesia has been studied, the level of satisfaction was very high, around 97% in two different studies. Studies in which the authors have interviewed patients about the preference of inhalational induction compared with intravenous induction (sevoflurane or desflurane versus propofol) have usually shown a preference for propofol over sevoflurane. This could be because of the mood elevation after propofol anesthesia that has been suggested by many authors; however, the mood elevation effect has never been conclusively proved. The following endpoints of quality have been evaluated in this chapter to provide the evidence for the selection of the best maintenance agent during ambulatory surgery: “early” recovery (“time to open eyes” and “time to obey commands”); “intermediate” recovery (“time to transfer from phase I to phase II,” “home-readiness,” and “home discharge”); and minor in-hospital complications (“pain,” “nausea or vomiting,” “antiemetics used,” “dizziness/giddiness,” “drowsiness/somnolence,” “headache,” “shivering,” and “coughing”). Patient satisfaction has been excluded because it has not been studied in relation to the choice of anesthetic for ambulatory surgery, as discussed earlier. Pain as a postoperative complication has not been addressed because of the different ways in which it has been measured and the complexity of its interpretation. Not only do the visual analog scales (VAS) for pain vary among authors but the time to pain assessment differs, the analgesics used vary considerably between studies, and not all authors present data as VAS, preferring to present data as “time to first analgesic requirement” or “the number of patients requesting analgesics.” In addition, because of the variable nature of surgery and, consequently, postoperative pain, data can be very difficult to interpret. Therefore data have not been extracted on pain intensity or analgesic requirements in this review.
Evidence
Total Intravenous versus Inhalational Anesthesia
Two systematic reviews published in the literature comparing inhalational versus intravenous anesthesia have included both inpatients and outpatients, which somewhat limits the scope of the findings. Halothane and enflurane were not taken into consideration in this review because these agents are rarely used during ambulatory surgery today.
Propofol versus Isoflurane
When a comprehensive review was performed, a total of 18 studies were found that had data that could be extracted in the postoperative period. No differences were found between propofol and isoflurane in early recovery or transfer from phase I to phase II, but there was significant heterogeneity between groups in all these parameters ( Table 20-1 ). However, home discharge was significantly earlier in the propofol group (15 minutes; confidence interval [CI], 8 to 23 minutes). There was a greater relative risk of postoperative complications, including nausea (number needed to treat [NNT], 8), vomiting (NNT, 10), and headache (NNT, 22) in the isoflurane group (see Table 20-1 ). The use of antiemetics (relative risk [RR], 2.7; CI, 1.7 to 4.2) was also more common in the isoflurane group. The relative risk for postoperative nausea and vomiting after 24 hours was also significantly higher in the isoflurane group versus the propofol group (see Table 20-1 ).
| Endpoint | Propofol vs. Isoflurane | Propofol vs. Desflurane | Propofol vs. Sevoflurane |
|---|---|---|---|
| Time to open eyes (min) | 0.2 (−1.6 to 1.3) * | 1.3 (0.4 to 2.2) * † (D) | 0.9 (−2.2 to 0.5) * |
| Time to obey commands (min) | 0.5 (−1.0 to 1.9) * | 1.3 (0.4 to 2.3) * † (D) | 1.6 (0.3 to 3.0) * ‡ (S) |
| Time to transfer from phase 1 to phase 2 (min) | 4.3 (−5.4 to 14.1) * | NR | 3.6 (−13.5 to 6.4) * |
| Time to home-readiness (min) | 9.3 (−17 to 36) * | 3.1 (−7.7 to 1.5) | 5.6 (−3.4 to 14.5) * |
| Time to home discharge (min) | 15 (8 to 23) † (P) | 3.9 (−9.3 to 1.5) | 10.3 (3.9 to 16.6) † (P) |
| Postoperative nausea (PON) | 2.0 (1.6 to 2.5) † (P), NNH = 8 | 2.0 (1.4 to 2.8) † (P), NNH = 71.6 | 1.6 (1.2 to 2.0) † (P), NNH = 11 |
| Postoperative vomiting (POV) | 3.2 (1.3 to 7.5) † (P), NNH = 10 | 2.6 (1.4 to 4.8) † (P), NNH = 10 | 2.0 (1.3 to 3.0) † (P), NNH = 15 |
| Postoperative drowsiness | NR | NR | 0.9 (0.1 to 5.9) * |
| Postoperative dizziness | NR | NR | 1.4 (0.8 to 2.3) |
| Postoperative shivering | 0.8 (0.6 to 1.3) | 1.5 (0.4 to 5.4) * | 0.8 (0.5 to 1.3) |
| Postoperative headache | 3.3 (1.1 to 9.6) ‡ (P), NNH = 22 | 3.5 (0.6 to 19.8) | 1.0 (0.2 to 7.1) |
| Antiemetics given | 2.7 (1.7 to 4.2) † (P), NNH = 8.5 | 3.3 (1.8 to 6.0) † (P), NNH = 8 | 4.5 (1.5 to 14.0) † (P), NNH = 11 |
| Postdischarge nausea (PDN) | 1.8 (1.3 to 2.5) † (P), NNH = 8 | 1.2 (0.7 to 2.1) | 1.3 (0.7 to 2.3) |
| Postdischarge vomiting (PDV) | 2.5 § (1.6 to 4.1) (P), NNH = 9 | 2.6 (0.1 to 62.7) | NR |
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