Most patients are eligible for ambulatory surgery unless there is a specific reason for an overnight stay [14]. Recently, patient choice has become an important factor because of the complexity of ambulatory surgical procedures and the increased incidence of comorbidities. Preoperative assessment and optimization according to medical comorbidities are associated with improved perioperative results.

Patient selection for ambulatory surgery depends on several factors, including surgical, social, medical, and anesthetic factors.

In addition to a general medical assessment, there are also specific areas that should be addressed, including anesthesia history and postoperative nausea and vomiting (PONV) risk an airway assessment should also be done.

General anesthesia is the most common choice, because it is safe, economical, easy to recover from, and familiar to most anesthesiologists. The use of new anesthetics, such as propofol, sevoflurane, and desflurane, allows for easier titration, early awakening, and a reduction in the time required to meet postanesthesia care unit (PACU) discharge criteria [31,32,33,34]. However, the absence of analgesia during the postoperative period requires the addition of opioids, which carry risks of mental obtundation and nausea.

Inhalational agents themselves carry a 20–50% risk of PONV [35], which can be minimized by generous use of prophylactic drugs [36]. The value of using of desflurane versus sevoflurane remains open to discussion [37]. Although the clinical difference between desflurane and sevoflurane is small, in some studies, more rapid emergence from anesthesia was reported with desflurane [38]. Another study reported that in a desflurane group, emergence from anesthesia was more rapid compared with a sevoflurane group, but there were no significant differences between the two groups during the late recovery phase [39].

As an intravenous anesthetic, propofol shows a rapid rate of metabolism, resulting in quick recovery from anesthesia with few side effects [40]. Because of the low incidence of nausea and vomiting, propofol is commonly used for anesthesia induction and maintenance in ambulatory surgery.

Remifentanil is also useful during ambulatory surgery, because of its rapid onset and short duration of action, which leads to rapid awakening and recovery from anesthesia [41]. Because of the rapid analgesic offset of remifentanil, it may be necessary to also use long-acting opioids or non-opioid analgesics to provide postoperative pain relief. The possibility that remifentanil can induce acute tolerance and hyperalgesia after several hours of infusion or repeated administration is still controversial [42]. Lenz et al. [43] reported that intraoperative remifentanil at high doses (0.3–0.5 µg/kg/min) increased postoperative pain and morphine consumption. Another study reported that remifentanil did not increase the frequency of PONV or the use of analgesics after ambulatory surgery [44].

The recently introduced agent sugammadex binds directly to steroidal non-depolarizing muscle relaxants, such as lipid-soluble rocuronium and vecuronium, deactivating the drugs and reversing the effects of muscle relaxation [45]. The effect of sugammadex is faster and stronger than that of anticholinesterase, which indirectly reverses muscle relaxation through increasing acetylcholine concentrations. Additionally, as there are no side effects associated with parasympathetic nerve disorders due to increased acetylcholine concentrations, concomitant use of anticholinergic drugs is unnecessary [46]. Sugammadex is suitable for use in ambulatory anesthesia because of its ability to reverse rocuronium-induced neuromuscular blockade at any stage and improve patient safety [47].

The major types of regional anesthesia include peripheral nerve blockade (with or without a continuous peripheral nerve catheter) and neuraxial blockade [48]. Regional anesthesia can avoid the side effects often caused by general anesthesia, such as nausea, vomiting, dizziness, residual muscle relaxation, and aspiration pneumonia. Additionally, analgesic effects can onset from the early postoperative period [48]. However, regional anesthesia requires more time to take effect, and in cases in which the anesthesia is unsuccessful or incomplete, general anesthesia is used. An anesthesia induction room, in which a nerve block can be activated before surgery, can be of great help in operations [49,50]. Furthermore, the postoperative analgesic effect is greater with supplementation by peripheral nerve block in patients undergoing general anesthesia than with the use of local anesthesia. Thus, the use of narcotic analgesics, and their consequent side effects, can be reduced, leading to a more rapid recovery [51]. However, when using central axonal block, appropriate local anesthetics and anesthetic supplements should be selected and administered at appropriate dosages to prevent delays in the discharge of ambulatory surgery patients [52].

MAC is a method in which patients are anesthetized by intravenous injection of analgesic and sedative drugs. Rather than being used alone, MAC is often used in conjunction with local infiltration anesthesia and peripheral nerve block. MAC can increase patient satisfaction and shorten recovery times compared with general anesthesia or neuraxial block [53,54]. Recently, propofol, low-dose ketamine, and dexmedetomidine have been used increasingly because they can reduce the incidence of respiratory depression caused by sedative-analgesic use [55,56,57]. Because respiratory depression is caused by excessive sedation, special attention must be paid to this possibility by the staff performing ambulatory surgery.

Postoperative pain management, which is an integral facet of successful ambulatory anesthesia, includes regional nerve block and analgesic administration. The infiltration of local anesthetics or nerve block at the surgical site at the conclusion of the operation may reduce the dose of anesthetics and analgesics required thereafter [69]. Thus, the recovery time is shortened, and anxiety or excitement in the recovery room due to pain can be alleviated. Pain control following a successful surgical operation increases the patient's speed of recovery and return to activities of daily living [70]. The use of non-steroidal anti-inflammatory drugs (NSAIDs) alone is relatively ineffective in controlling severe pain, while the use of narcotic analgesics alone may cause various postoperative side effects, such as nausea, vomiting, dizziness, and constipation. Multimodal or balanced analgesia therapy, or the use of more than one pain relief method, can increase analgesic effects while simultaneously reducing the side effects associated with certain medications [71]. Thus, this multimodal approach has become standard in pain control therapy for ambulatory surgical operations [72]. Recently, larger-scale procedures associated with severe postoperative pain, such as laparoscopic nephrectomy, prostatectomy, shoulder and knee reconstruction, and hysterectomy, are increasingly being performed on an ambulatory basis or with short hospitalization periods [73]. The perioperative use of multimodal analgesia therapies with both narcotic and non-narcotic analgesics can increase the speed of a patient's quick recovery and improve satisfaction rates.

Narcotic analgesics continue to play a prominent role in relieving postoperative acute pain. However, as the frequency of reports of minimally invasive surgery with relatively low postoperative pain increases steadily, so too does the role of non-narcotic analgesics as prophylactic agents [73]. Furthermore, NSAIDs, acetaminophen, ketamine, alpha-2 agonists, and gabapentin have been used increasingly in multimodal analgesia therapies for postoperative pain control [74]. Ideally, a combination of these non-narcotic analgesics would be used to ensure excellent pain relief and ultimately eliminate the use of narcotic analgesics. Multimodal analgesia therapy minimizes postoperative pain, reduces organ damage resulting from the use of narcotic analgesics, and facilitates recovery from anesthesia; thus, it has become an important element of ambulatory surgery.

While the frequency of nausea and vomiting varies, approximately 30–50% of patients report such symptoms [75,76]. Even if other problems associated with surgery and anesthesia are alleviated, in cases of severe nausea or vomiting, patient discharge may still be delayed and unexpected hospitalization may be necessary. Despite the development of various new anti-emetics, the incidence of nausea and vomiting due to patient, surgery, and anesthesia-related risk factors remains high, at around 30% [77]. Major risk factors for PONV include female gender, nonsmoking status, a history of nausea and vomiting after motion sickness or surgery, and previous use of inhalation anesthesia or narcotic analgesics [78]. For adults with more than two of these risk factors, the administration of multimodal anti-emetics, such as droperidol, dexamethasone, and ondansetron, is recommended [79]. Treatment of PONV requires the administration of antiemetic drugs of a different pharmacological class than the initial prophylactic drugs, and low-dose 5-hydroxytryptamine receptor antagonists are recommended unless prophylaxis is indicated [80]. Furthermore, to reduce the risk of nausea and vomiting, adequate use of propofol, fluid therapy, and minimization of narcotic analgesics during perioperative treatment are also effective [81].

The process of recovery from anesthesia can be divided into three stages: early, middle, and late [3,66]. Early recovery refers to the period between awakening from anesthesia and restoration of protective reflexes and motor capacity. Up to this point, the patient remains in the PACU, where vital signs and oxygen saturation are monitored. If necessary, oxygen, analgesics, and anti-emetics can be administered. Most hospitals that conduct ambulatory surgery have step-down units or ambulatory surgical units that assist patients in the middle stages with preparation for discharge. Patients in the middle recovery phase stay in step-down units and are nursed in resting chairs. They are considered ready for discharge when they are capable of walking, drinking, and urinating. Transfer decisions from the PACU to the step-down unit commonly follow evaluations done using the modified Aldrete scoring system [82] or White's fast-track criteria [83]. Limitations of the modified Aldrete score include that it does not address pain, nausea, or vomiting, which are common side effects of a PACU stay [82]. The modified Aldrete score is also not ideal for determining fast-tracking bypass in ambulatory settings or patients undergoing regional anesthesia [48]. When a simple operation is performed using short-acting anesthetics, such as propofol, sevoflurane, or desflurane, there are many cases in which the patient recovers consciousness, regular breathing, and stable vital signs in the operating room. The use of a cerebral monitoring device, such as the bispectral index, may be advantageous, with the early aim being to help titration toward a lower anesthetic dose [84,85]. In such cases of early recovery, a fast-tracking method that involves directly moving the patient to the step-down unit without passing through the PACU can be applied to reduce medical expenses. White's fast-track criteria are used to evaluate the decision to admit a patient into a step-down unit without going through the PACU [83]. The more recently introduced ‘WAKE’ score includes not only the modified Aldrete score (maximum score = 10), but also “zero tolerance” criteria to assess post-operative pain, PONV, tremors, itching, and orthostatic symptoms (dizziness, hypotension) [86]. The WAKE score appears more suitable for the evaluation and rapid follow-up of outpatients who have undergone regional anesthesia, general anesthesia, or MAC [48]. The late recovery period refers to the period prior to a patient being able to return to work and daily life, after all functions have recovered fully post discharge. For a safe discharge, the patient must have stable vital signs and show restoration of full orientation. Furthermore, the patient must be able to walk without dizziness and have little to no pain, nausea, vomiting, or surgical-site bleeding. When the patient has completed the second recovery phase, the Post Anesthesia Discharge Scoring System may be used to decide whether or not they can be discharged from the hospital [87]. In US and Canadian hospitals, to return home, all outpatients who receive sedative or analgesic medications must have be escorted by a responsible adult [66]. A responsible adult escort must be provided with printed instructions, including detailed information regarding precautions, guidelines, and the medical personnel to contact in case of an emergency [14]. During this process, close communication between patients and medical staff, as well as postoperative follow-up appointments, should be ensured.

Mandatory oral intake may not be warranted because it can cause nausea and vomiting and may unnecessarily delay discharge [14,66]. Patients at low risk, such as those who have no urinary retention and have not undergone hernia or urology surgery, can be discharged home without urination. They should be instructed to return to the hospital if they cannot void within 6–8 h after returning home [66]. However, it should be a requirement for patients at high risk of urinary retention (such as those undergoing anorectal surgeries and lower limb joint arthroplasty, and those with benign prostatic hyperplasia) to void prior to discharge and display a residual volume < 300 ml, as measured by ultrasound of the bladder [66].