Recovery Characteristics after 
Ambulatory Anaesthesia and Surgery
by 
Mohamed Ezzat Moemen
founder
of anaesthesia and intensive care,
faculty of medicine, Zagazig university
e-mail: ezzatmoemen@hotmail.com
                                  Eg J Anaesth 2004 ,20 :449-57
             

Abstract:
            The rather recent concept of carrying out elective surgical procedures on an outpatient basis is becoming an important part of the anaesthetist’s workload. S/he should understand the process of recovery and be able to identify criteria that can be used to determine when patients can safely go home early.
            Recovery is a continual process including early, intermediate and late phases; each with specific characteristics. The anaesthetist has, also, the responsibility to be aware of problems that may occur at home after patient discharge in order to provide a good impression of the cost-effective ambulatory anaesthesia and surgery concept.
            Characteristics of recovery in all phases are detailed and discussed.

Key words: outpatient anaesthesia; ambulatory surgery.

Introduction
            Spreading from the United States of America to different countries, a rather recent concept of carrying out elective ambulatory surgical procedures without overnight postoperative hospitalization is flourishing.  Nowadays, more complex procedures are increasingly performed on sicker patients on this basis. So, ambulatory or day-case anaesthesia and surgery with cost-savings forms the predominant part of elective surgical practice in many countries as opposed to inpatient services. (1)
            There are three basic types of outpatient surgical facilities: the hospital care ambulatory surgical facility, the free-standing ambulatory surgical facility and the surgical suite in the physician’s office or the office-based ambulatory surgical facility. (2)
            The acceptability of patients to a given ambulatory facility depends often upon the infrastructure in the medical community. The dedication of day surgery units to safety and cost-effectiveness implies community support resources, the absence of which would preclude ambulatory services. There are several types of patients who should not be offered the option of ambulatory care as patients with non-optimal management of medical disease, patients with malignant hyperthermia, morbidly obese patients, expremature infants and patients with acute substance abuse.
            The list of procedures for day case surgery is constrained by the need of an uncomplicated postoperative course. In recent years, technological advances have revolutionized the number of permissible operations, and will continue to do so.
            What is essential in considering the advisability of ambulatory surgery is a patient-oriented, not a procedure-oriented system. So, those individuals providing ambulatory care should be given the responsibility of the decision whether a particular patient is a proper candidate for a given surgical procedure on ambulatory basis.
            It is imperative for the anaesthetists to provide the best anaesthetic care for ambulatory surgical patients to facilitate their return to daily work. With vigilance of the anaesthetists and careful monitoring, either general, local, or regional anaesthesia can be proper techniques tailored to the needs of the ambulatory surgical patients.
            It is needless to emphasize that the success and safety of an ambulatory surgery program depend on patients’ understanding and compliance. 
            With the increased emphasis on early discharge after ambulatory anaesthesia and surgery, it is important to understand the process of patient recovery and to identify criteria that can be used to determine when patients have recovered enough to go home safely under the care of an escort.

Recovery:
            Recovery is a frequently used term in anaesthetic and surgical practice.  This term may be perceived very differently among patients, surgeons and anaesthetists (3). Patients consider that recovery ensues when they are able to resume their previous life-style. Surgeons consider that their patients have recovered when surgical sutures are removed or when their patients are discharged from the hospital. The variable most often used by surgeons to assess recovery is the duration of patient hospital stay.  Anaesthetists think that their patients have recovered when they regain their consciousness and preoperative physiological and psychological states.
Anaesthetists deal with recovery as a continual process, the early stage of which overlaps the end of intraoperative care.   The recovery process may last many days and can be divided into three distinct phases.(4)
Early (phase I) recovery lasts from discontinuation of anaesthesia until patients awaken and regain their vital protective reflexes and motor functions. Intermediate (phase II) recovery denotes immediate clinical recovery as coordination and ambulation allowing home-readiness.  Patients are then discharged home to complete full recovery including its psychological component, a stage termed late (phase III) recovery.

Early (Phase I) recovery:
Early (phase I) recovery takes place in the postanaesthesia care unit (PACU) under the care of trained nurses until patients have recovered enough to allow their safe transfer to an ambulatory surgical unit (ASU) or to another secondary step-down phase II recovery area. This is usually achieved by using the Aldrete and Kroulik (5) or the modified Aldrete scoring system (6).  Recently, the Bispectral Index (BIS) is evolving as a useful indicator of patient wakefulness in the operating room (OR) and the PACU to be transferred to step-down phase II recovery area (7, 8).

The Aldrete scoring system:
The Aldrete and Kroulik scoring system was first described in 1970(5).  This system assigns a score of 0-2 to activity, respiration, circulation, consciousness and colour, giving a maximum score of 10 (table 1).  A score of ≥ 9 indicates sufficient patient recovery for transference from the PACU to the phase II recovery area. Although not originally designed for ambulatory surgical patients, this scoring system is still used in many PACU’s (9).
Table (1): The standard Aldrete scoring system (5)

BP = blood pressure
The modified Aldrete scoring system:
With the advent of pulse oximetry as a more reliable indicator of oxygenation than clinical observation, a modified Aldrete scoring system has been designed (table 2) (6).  In this modified system, the colour parameter of the original system is replaced by an oxygen or room-air saturation parameter.  Again, the maximum score is 10 and a score of ≥9 indicates sufficient patient recovery for transference form the PACU to phase II recovery area.
Table (2): The modified Aldrete scoring system (6)

BP = blood pressure

The Bispectral Index:
The Bispectral Index (BIS) is a multivariate index derived from the spontaneous electroencephalogram (EEG) (10).  It uses a processed EEG to monitor anaesthetic depth (11).  The electrodes or the sensors of this monitor are attached to three circles on the patient.  The first is a forehead contact 4cm above the nose. The second is a contact above the right or left orbit. The third is a contact on the temple between the hair-line and the outer angle of the orbit (12).
The BIS determines a linear and a non-linear component.  It uses a space lab monitor for a numeric zone and moving wave-form updated every two seconds.  It produces a unitless score of zero to 100, where 100 means that the patient is awake and responsive, 70 means that free recall is lost and 60 means that consciousness is lost (12).  Below a BIS value of 60, there is a very low probability of patient recall.  The range between 60 and 50 may denote deep sedation or light anaesthesia, and below 50, the patient is usually unconscious (13).
The use of BIS has been shown to allow more accurate titration and more economic utilization of anaesthetic agents (14), to reduce time to wakefulness and extubation (15,16) and to promote faster theatre turnaround(7,8).  Intraoperative BIS monitoring could produce significant improvements in patient orientation on arrival at PACU and time to discharge eligibility.  A recent large prospective study compared the recovery characteristics of 50-40 range BIS monitored ambulatory surgical patients with controls using the modified Aldrete score (17).  On arrival to the PACU, the study group patients had better ventilatery functions, more stable haemodynamics and they were more awake and active.  So, they had higher modified Aldrete scores, which produced safer and shorter PACU stay with better recovery characteristics contributing to patient transfer to the step-down phase II recovery area.
It can be concluded that a postoperative BIS score more than 70 allows patient transfer to the PACU or even his fast-tracking to the ASU.
The fast-tracking scoring system
Newer anaesthetics and techniques may allow more rapid awakening and phase I early recovery may be completed in the OR. Then, patients are transferred directly to the ASU, bypassing the PACU, a process known as fast-tracking (18, 19).  A clear and coordinated postoperative plan implemented as a distinct clinical pathway is necessary for a fast-tracking program.
Fast-tracking is important because of its cost-saving potential when patients are transferred directly from the OR to the step-down phase II recovery (20, 21).  Given the inherent risks of complications associated with bypassing the PACU, effective and reliable fast-track criteria would allow the anaesthetist to rapidly assess a patient’s postoperative alertness, physiological stability, and comfort level immediately before transference from the OR (19).
In organizing a fast-tracking program, it is important to minimize postoperative side-effects and to avoid increasing the workload for nurses in the phase II recovery area (20).
In a study carried out by White et al (19), 22-29% of surgical outpatients judged fast-track eligible using the modified Aldrete scoring System subsequently required iv analgesics and anti-emetics at the ASU.  Therefore, they proposed a fast-track system incorporating the elements of the Modified Aldrete scoring system together with assessment of pain and emesis (table 3) (19).
It can be concluded that although the modified Aldrete scoring system is highly acceptable for transferring patients from the PACU, it was not actually designed to determine fast-tracking bypassing the PACU(21).  However, it has also been used in the OR by some anaesthetists to determine fast-tracking eligibility of outpatients undergoing ambulatory surgery (20, 21).  The controversy is that this system fails to consider some common problems needing treatment in the PACU, which urged White et al to propose their fast-tracking criteria (19).
Table (3): Criteria for fast-tracking after outpatient anaesthesia (19)

MAP = mean arterial pressure

The proposed fast-tracking scoring system takes in consideration pain and emetic symptoms, added to the modified Aldrete five parameters completing 14 scoring points.  A minimal score of 12 (with no score < 1 in any individual category) would be required for a patient to bypass the PACU after ambulatory general anaesthesia and surgery (19).  Using these fast-track criteria could limit the number of additional nursing interventions required in the phase II area, in comparison to fast-tracking by the modified Aldrete scoring system (19). Again, fast-tracking children after ambulatory surgery by using this criteria is feasible and beneficial leading to high parent satisfaction (23).
Intermediate (phase II) recovery; home-readiness:
For the ambulatory patient population, it is important to provide a fast recovery with minimal postanaesthetic cognitive and psychomotor impairment and to be able to judge accurately when they are home-ready to be safely discharged home. The safe timing of patient discharge in relation to recovery from general or regional anaesthesia or from monitored anaesthesia care is a major concern.
(A): Home-readiness after general anaesthesia:
Although experienced outpatient anaesthetists can clinically decide when a patient has sufficiently recovered from general anaesthesia (GA) for hospital discharge, a well designed scoring system will provide a reliable guide (24).  
Psychomotor tests:
Many attempts aimed to produce simple reproducible tests to assess a patient’s recovery from GA.  The Trieger dot test, an example of psychomotor performance tests, was proposed to measure patient recovery (25). In this test, patients are asked to connect a series of dots to form a pattern.  The number of dots missed in the lines drawn represents the score.  The score improves as the patient recovers from anaesthesia. This test is only one of a battery of psychomotor tests that measure recovery from anaesthesia, but none of them has been specifically validated by follow-up studies providing adequate criteria to guide patient discharge in the ambulatory setting.
Not surprisingly, these tests have not found their way into routine clinical practice. Most ambulatory units do not depend on such psychomotor tests which are still useful research tools (26).

Clinical guidelines:
Wetchler suggested clinical guidelines for safe patient discharge after ambulatory surgery (table 4) (27).
Table (4): Wetchler’s guidelines for safe patient discharge after ambulatory surgery

• Vital signs stable: these include temperature, pulse, respiration and blood pressure when appropriate. Vital signs should remain stable for a period of not less than half an hour and be consistent with patient’s age and preanaesthesia levels.
• Ability to swallow and cough: the patient must demonstrate the ability to swallow fluids and be able to cough.
• Ability to walk: the patient demonstrates ability to perform movement consistent with age and developmental level (sit, stand, walk).
• Minimal nausea, vomiting and dizziness:
• Minimal nausea: absence of nausea, or if nausea is present, the patient can still swallow and retain some fluids.
• Minimal vomiting: vomiting is either absent or, if present, does not require treatment. Following vomiting that requires treatment, the patient should be able to swallow and retain fluids.
• Minimal dizziness: dizziness is either absent or present only upon sitting and the patient is still able to perform movement consistent with age.
• Absence of respiratory distress: the patient exhibits no signs of snoring, obstructed respiration, stridor, retractions, or croupy cough.
• Alert and oriented: the patient is aware of surroundings and what has taken place and is interested in returning home.

Again, Kortilla summarized widely accepted clinical criteria for safe discharge after ambulatory surgery (table 5) (28).

Table (5): Kortilla’s guidelines for safe patient discharge after ambulatory surgery

• Vital signs must have been stable for at least one hour.
• The patient must be:

oriented to person, place and time.
Able to retain orally administered fluids.
Able to void.
Able to dress.
Able to walk without assistance.

• The patient must not have:

more nausea and vomiting.
Excessive pain.
Bleeding.

• The patient must be discharged by both the person who administered anaesthesia and the person who performed surgery, or by their designates. Written instructions for the postoperative period at home, including a contact place and person, must be reinforced.
• The patient must have a responsible, “vested” adult escort them home and stay with them at home.

Clinical criteria:
The postanaesthesia discharge scoring system
Apart from psychomotor tests and clinical guidelines, Chung (1993) designed his early version of postanaesthesia discharge scoring system (PADSS) including 10 points and patients with scores of ≥9 are considered fit for home discharge (table 6) (29).  In this way patient discharge is addressed in a simple, clear and reproducible manner to meet national medical standards.  Nurses are able to evaluate the postoperative course of the patient in a systematic way.
Table (6): Postanaesthesia discharge scoring system (PADSS) (29)

It has been observed that the summarized clinical criteria and the early version of the PADSS for safe patient discharge required that patients should have taken oral fluids or passed urine before deciding home-readiness. However, Chung found that 20% of outpatients could have been discharged earlier by excluding drinking and urine voiding (29). Fast-tracking children after ambulatory surgery was shown to lead to earlier discharge with high parent satisfaction (23). 
The Children Hospital of Philadelphia has discharged more than 6000 ambulatory surgery children without requiring them to drink before their discharge (30).  Only four children required hospital admission for vomiting. It was concluded that drinking should not be a mandatory item for discharging children home (30).
Another large study on adults proved that eliminating the drinking item can slightly shorten ASU stay without evidence of increasing postoperative nausea and vomiting (PONV) incidence (31).  Therefore, medical staff and nurses were instructed that the drinking item is not necessary before adult patient discharge, and discharge criteria were modified accordingly.
Again, insisting that patients should pass urine can delay hospital discharge. Inability to void and urinary retention have been related to reflex urethral spasm, reflex inhibition of normal bladder detruser muscle activity by pain, distension of the anal canal, or blockade of the automatic innervation of the urinary bladder.  There is evidence that outpatients not at risk of urinary retention (a history of postoperative retention, spinal/ epidural anaesthesia, pelvic or urological surgery, and perioperative catheterization) can be safely discharged before they have voided without urinary retention problems at home (32). Those at risk can be discharged given appropriate follow-up including catheterization by home-care nurses or given the advice to contact a responsible physician if they are unable to void within 6-8 hours after discharge (32).

The modified postanaesthesia discharge scoring system (MPADSS):
Removing the requirements to drink and to void (elimination of input and output), and separating the PONV and pain elements, Chung et al has modified the early version of the PADSS into the modified postanaesthesia discharge scoring system (MPADSS) (33), which was extensively used at the Toronto Hospital for determining home-readiness(34).  
The MPADSS is based on five criteria: vital signs, ambulation, PONV, pain and surgical bleeding (table 7) (33).
Each of these items is assessed independently and assigned a numerical score of 0-2, with a maximal score of 10.  Patients are fit for discharge when their score is ≥9. Patients should be able to stand and take few steps or to sit upright if the surgical procedure does not permit standing. Delays in discharge are related to persistent symptoms such as pain, PONV, hypotension, dizziness, unsteady gait, syncope, asthma or unavailable accompanying care-given (35).  The MPADSS is a simple way to establish a routine of repeated re-evaluation which may result in improved patient supervision.

Table (7): the modified postanaesthesia discharge scoring system (MPADSS) (33)

BP = blood pressure, PO = per orum, IM = intramuscular

(B): Home-readiness after regional anaesthesia or monitored anaesthesia care:
The benefits of avoiding GA may be apparent up to three postoperative days when testing can reveal cognitive defects in GA patients compared to those who receive local anaesthesia (36).  A study comparing three-in-one femoral block with GA for knee arthroscopy found that the block patients could be discharged 40 minutes earlier than GA patients (37).  Interscalene block can provide good analgesia after shoulder arthroscopy and can decrease the incidence of nausea and vomiting with unexpected hospital admission, compared with GA (38).  Peribulbar and retrobulbar blocks are useful local anaesthetic techniques for ophthalmic surgery. Patients with peripheral nerve blocks should not retain full sensation if discharge criteria are achieved (39).
When is it safe to permit patients to ambulate following spinal or epidural anaesthesia? Basically, outpatients recovering from regional anaesthesia must meet the same discharge criteria as patients recovering from GA.
Suitable criteria for ambulation after spinal anaesthesia include normal perianal (S4-5) pinprick sensation, plantar flexion of the foot and proprioception of the big toe.
No residual motor block should be present after spinal or epidural anaesthesia when the patient is asked to stand or walk.  To test the motor block, one can ask the patient to touch both the right and left heel to the opposite big toe and to move each heel up and down the anterior tibial surface of the opposite leg to the knee.
A patient’s ability to walk to the bathroom and urinate may be the best recovery test after spinal or epidural anaesthesia because these abilities indicate recovery of motor and sympathetic functions. 
Spinal anaesthesia for ambulatory surgery is currently struggling to compete with the newer general anaesthetic agents, which allow shortened discharge times.  Selective spinal anaesthesia (SSA) has been defined as “the practice of employing minimal doses of intrathecal agents so that only the nerve roots supplying a specific area and only the modalities that require to be anaesthetized are affected” (40).  Examples of SSA are the technique of unilateral spinal anaesthesia for one limb surgery as arthroscopy (41), the technique of walking spinal for perianal and perineal surgery (42) and the technique for gynaecological laparoscopic surgery (43).  This SSA has opened up the possibility of providing “walk in-walk out” spinal anaesthesia with a real possibility of fast-tracking outpatients bypassing the PACU (44).
Recently, SSA is getting the fidelity of the potential ability to compete with GA for ambulatory surgery.  Outpatient laparoscopy for gynaecological surgery, a procedure traditionally performed under GA, can be safely performed with SSA (43). Table (8) compares the recovery characteristics of SSA and iv propofol GA after gynaecological laparoscopy.
Table (8): Recovery characteristics of gynaecological laparoscopy – patients under propofol GA versus SSA: mean ± SD. (43)

 * Highly significant difference at P< 0.002
n = number  GA = general anaesthesia, SSA = selective spinal anaesthesia, PACU= postanaesthesia care unit

Pamella et al compared the recovery characteristics of gynaecologically laparoscoped patients under SSA versus desflurane inhalation GA (table 9) (45).
Table (9): Recovery characteristics of gynaecological laparoscopy patients under desflurane GA versus SSA: means ± SD.(45)

• Highly significant difference at P< 0.0001, GA = general anaesthesia, SSA = selective spinal anaesthesia

Tables (8, 9) show that SSA competes very well with GA using total intravenous anaesthesia (TIVA) with propofol or inhalational anaesthesia with desflurane, both being ideal for rapid recovery.  After SSA with or without conscious sedation, patients are usually awake and oriented.  Time to reach modified Aldrete score ≥ 9, straight leg raising time and PACU stay are shorter after SSA than after GA. Straight leg raising follows the modified Bromage scale (45) (table 10).
Table (10): The modified Bomage Scale for motor block

One factor limiting the popularity of spinal anaesthesia for ambulatory surgery is postdural puncture headache (PDPH). However, it has been recently documented that needles of gauge ≥ 25 produce an incidence of PDPH of < 1% and that the reported headaches are mild and self-limited (46-50).
Another important factor for spinal anaesthesia is the controversy of neurological complications specially after lidocaine. However, two large studies have reported a very low incidence of transient neurological symptoms in patients receiving hyperbaric lidocaine. (51, 52)
It should be emphasized that after monitored anaesthesia care and after regional anaesthesia with or without sedation, phase I recovery in the PACU follows the modified Aldrete score and that patient fast-tracking from the OR to the ASU follows the same criteria used after GA. Again, home-readiness follows the MPADSS, the same as after ambulatory surgery under GA.
After ambulatory surgery, either under general or regional anaesthesia, it is the physician’s responsibility to ensure that the patient has sufficiently recovered to leave the ASU under the appropriate care of a relative or other care-giver.  Legal action may ensue if a patient who is inadequately supervised or prematurely discharged comes to harm, as a result of residual psychomotor impairment (53). However, a written policy establishing specific discharge criteria is a sound basis for a legally sufficient discharge decision after ambulatory surgery. (54)
Table (11) describes postoperative instructions for patients undergoing any ambulatory surgical procedure.  In addition, procedure-specific instructions should be given to appropriate surgical outpatients.
Table (11): Postoperative instructions for outpatients following ambulatory surgery procedures. (54)

Late (Phase III) recovery:
Recovery does not end once discharge criteria are met, because phase III recovery may take few days to be completed at home. Patients and their escorts are provided with written discharge instructions and information about emergency medical assistance if needed.  It is a good practice to plan a follow-up telephone call from the ambulatory unit 24 hours after discharge to review postoperative progress and satisfaction (55) (table 12). Additional contact with the patient is recommended if s/he has received spinal or epidural anaesthesia or if s/he has some additional difficulty postoperatively.
Table (12) Postoperative evaluation phone-call

Physician name                                          physician signature

It is important to mention that home-readiness after an outpatient surgery carried out under any anaesthetic technique does not coincide with street-fitness. Kortilla studied the effects of different analgesics, sedatives and anaesthetics on the psychomotor skills of volunteers and recommended that patients should refrain from driving for 24 and 48 hours if the duration of surgery was less than 30 minutes or equal to two hours respectively (56).

Conclusion:
In conclusion, ambulatory anesthesia and surgery is becoming a major part of the anaesthetist’s workload.  S/he must ensure that the increasing number of ambulatory surgical patients are discharged into the home environment appropriately.  Fast-tracking ambulatory patients and bypassing the PACU may prove more efficient, but with patients being treated and discharged so speedily, the anaesthetist has a responsibility to be aware of problems as pain, PONV, urinary retention and headaches that may occur at home after discharge. Such problems can delay a patient’s return to full function and may leave a poor impression of the ambulatory anaesthesia and surgery concept.

References:

• White PF. Ambulatory anaesthesia and surgery: past, present, and future.  In: Ambulatory anaesthesia and surgery. White PF (Editor). London: WB Saunders 197; 1-34.
• Labajo ADR. Office-based surgery and anaesthesia.  Curr Opinion Anaesthesiol 1998; 11: 615-621.
• Chumbley GM, Hall GM. Editorial.  Recovery after major surgery: does the anaesthetic make any difference? Br J Anaesth 1997; 78: 347-349.
• Steward DJ, Volgyesi G. Stabilometry: a new tool for measuring recovery following general anaesthesia.  Can Anaesth Soc J 1978; 25: 4-6.
• Aldrete JA, Kroulik D.  A postanaesthetic recovery score.  Anesth Analg 1970; 49: 924-934.
• Aldrete JA.  The postanaesthesia recovery score revisited [letter]. J Clin Anesth 1995; 7: 89-91.
• Nakatsuka M, Tyler B. Bispectral Index monitoring to facilitate faster emergence and shorter turnover time for carotid endarterectomy.  Anesth Analg 1998; 86: S221.
• Sebel PS, Pyne F, San T, et al. Bispectral Analysis (BIS) monitoring improves PACU recovery from propofol alfentanil/ N2O anaesthesia. Anesthesiology 1996; 85(3A): A 468.
• Scott IM, Frances C.  Discharge criteria after ambulatory surgery. Anesth Analg 1999; 88: 508-517.
• Johnasen J, Sebel P. Development and clinical application of electroencephalographic bispectral monitoring. Anesthesiology 2000; 93: 1336-1344.
• Flaishon R, Windsor A, Sigi J et al: Recovery of consciousness after thiopental or propofol: Bispectral Index and the isolated forearm technique. Anesthesiology 1997; 86: 613-619.
• Moemen ME. Monitoring anesthetic depth. In: Monitoring and patient safety. Moemen ME (Editor). First Edition 2004; 86-90 (Cairo).
• Gale T, Leslie K, Kluger M Propofol anaesthesia via target controlled or manually controlled infusion: Effects on Bispectral Index as a measure of anaesthetic depth. Anaesth Intensive care 2001; 29: 579-584.
• Glass PSA, Sebel PS, Rosow CE, et al. Improved propofol titration using the Bispectral Index (BIS). Anesthesiology 1996; 85 (3A): A 351.
• Song D, Joshi BP, White PF. Titration of volatile anaesthetics using Bispectral Index facilitates recovery after ambulatory anaesthesia. Anesthesiology 1997; 87: 842-848.
• Gan T, Glass P, Windsor A, et al. Bispectral Index monitoring allows faster emergence and improved recovery from propofol, alfentanil, and nitrous oxide anesthesia. Anesthesiology 1997; 87: 808-815.
• Burrow B, McKenzie B, Case C. Do anaesthetized patients recover better after Bispectral Index monitoring: Anaesth Intensive care 2001; 29: 239-245.
• Lubarsky DA. Fast-track in postanaesthesia care unit: unlimited possibilities. J Clin Anesth 1996; 8: 70-72.
•  White PF, Fanzca A, Song D. New criteria for fast-tracking after outpatient anaesthesia: a comparison with the modified Aldrete scoring system. Anesth Analg 1999; 88: 1069-1072.
• Song, D, Joshi GP, White PF. Fast-track eligibility after ambulatory anaesthesia: a comparison of desflurane, sevoflurane, and propofol.  Anesth Analg 1998; 86: 267-273.
• Chung F. Recovery pattern and home-readiness after ambulatory surgery. Anesth Analg 1995; 80: 896-902.
•  Song D. van Vlymen J, White PF. Is Bispectral Index useful in predicting fast-track eligibility after ambulatory anaesthesia with propofol and desflurane? Anesth Analg 1998; 87: 1245-1248.
• Patel RI, Verghese ST, Hannallah RS, et al. Fast-tracking children after ambulatory surgery. Anesth Analg 2001; 92: 918-922.
•  Quinn CL, Weaver JM, Beck M. Evaluation of a clinical recovery score after general anaesthesia.  Anaesth Prog 1993; 40: 67-71.
• Newman MG, Triger N, Miller JC. Measuring recovery from anaesthesia: a simple test. Anesth Analg 1969; 48: 136-140.
• Sanders LD. Recovery of psychological function after anaesthesia. Int Anesthesiol Clin 1991; 29: 105-115.
• Wetchler BV. Problem solving in postanaesthesia care unit. In: Wetchler BV (editor): Anaesthesia for ambulatory surgery, 2nd ed. Philadelphia, JB Lippincott, 1990: 400-410.
•  Kortilla K. Recovery from outpatient anaesthesia: factors affecting outcome. Anaesthesia 1995; 50 (Suppl): 22-38.
• Chung F. Are discharge criteria changing? J. Clin Anesth 1993; 5: 645-685.
• Schreiner MS, Nicholson SC, Martin T, et al. Should children drink before discharge from day surgery? Anesthesiology 1992; 76: 528-533.
•  Jin FL, Norris A, Chung F. Should adult patients drink fluids before discharge from ambulatory surgery? Can J Anaesth 1998; (Supp)
• Fritz WT, George L, Krull N, et al. Utilization of a home nursing protocol allows ambulatory surgery patients to be discharged prior to voiding [abstract]. Anesth Analg 1997; 84: S6.
• Chung F, Chan V, Ong D.  A postanaesthetic discharge scoring system for home-readiness after ambulatory surgery. J Clin Anesth 1995; 7: 500-506.
• Marshall S, Chung F. Assessment of home-readiness: discharge criteria and post-discharge complications. Curr Opinion Anaesthesiol 1997; 10: 445-450.
• Chung F. Recovery pattern and home-readiness after ambulatory surgery. Anesth Analg 1995; 80: 896-902.
•  Tzabar Y, Asbury AJ, Millar K. Cognitive failures after general anaesthesia for day case surgery. Br J Anaesth 1996; 76: 194-197.
• Patel NJ, Flashburg MH, Paskin S, et al.  A regional anaesthetic technique compared to general anaesthesia for outpatient knee arthroscopy. Anesth Analg 1986; 65: 185-187.
• Brown AR, Weiss R, Greenberg, et al. Interscalene block for shoulder arthroscopy: comparison with general anaesthesia. Arthroscopy 1993; 9: 295-300.
•  Marshall SI, Chung F. Discharge criteria and complications after ambulatory surgery. Anesth Analg 1999; 88: 508-517.
• Vaghadia H, Viskari D, Michell GWE, et al. Small-dose selective spinal anaesthesia for short duration outpatient gynaecological laparscopy: characteristics of three hypobaric solutions,. Can J Anaesth 2001; 48: 256-260.
•  Jukka VV, Anna MK,Rita MJ, et al. Selective spinal anaesthesia: a comparison of hyperbaric bupivacaine 4mg versus 6 mg for outpatient knee arthroscopy. Anesth Analg 2001; 93: 1377-1379.
• Buckenmaier C, Nielsen KC, Pietrobon R, et al. Small-dose intrathecal lidocaine versus ropivacaine for anorectal surgery in an ambulatory setting. Anesth Analg 2002; 95: 1253-1257.
• Steward AVG, Vaghadia H, Collins L, et al. Small-dose selective spinal anaesthesia for short duration outpatient gynaecological laparoscopy: recovery characteristics compared with propofol anaesthesia. Br J. Anaesth 2001; 86: 570-572.
• Vaghadia H. Spinal anaesthesia for outpatients: controversies and new techniques. Can J Anaesth 1998; 45: 64-70.
• Pamella HL, Vaghadia H, Henderson C, et al. Small-dose selective spinal anaesthesia for short duration, outpatient laparoscopy : recovery characteristics compared to desflurane anaesthesia. Anesth Analg 2002; 94: 346-350.
• Belzrena SD. Clinical effects of intrathecally administered fentanyl in patients undergoing Caesarean Section. Anesth Analg 1992; 74: 653-657.
• Pittoni G, Toffoletto F, Calcarella G. Spinal anaesthesia in outpatient knee surgery: 22 gauge versus 25 gauge Sprotte needle. Anesth Analg 1995; 81: 73-79.
• Kang SB, Goodnough DE, Lee YK, et al. Comparison of 26 and 27 gauge needles for spinal anaesthesia for ambulatory surgical patients.  Anesthesiology 1992; 76: 734-738.
• Brattebo G, Wisborg T, Rodt SA, et al. Intrathecal anaesthesia in patients under 45 years: incidence of postdural puncture symptoms after spinal anaesthesia with 27 G needles.  Acta Anaesthesiol Scand 1993; 37: 545-548.
• Corbey MP, Berg P, Quaynor H. Classification and severity of postdural puncture headache: comparison of 26 gauge and 27 gauge Quincke needles for spinal anaesthesia in day care surgery in patients under 45 years. Anaesthesia 1995; 48; 776-781.
• Corbey MP, Bach AB. Transient radicular irritation (TRI) after spinal anaesthesia in day-care surgery. Acta Anaesthesiol Scand 1998; 42: 425-429.
• Morisaki H, Masuda J, Kaneka S, et al. Transient neurological syndrome in one thousand and forty five patients after 3% lidocaine spinal anaesthesia. Anesth Analg 1998; 86: 1023-1026.
• Kortilla KT. Postanaethetic psychomotor and cognitive function. Eur J Anaesthesiol 1995; 12 (Suppl 10): 43-46.
• Quan KP, Wieland JB. Medicolegal considerations for anaesthesia in the ambulatory setting. Int Anesthesiol Clin 1994; 32: 145-169.
• Pasternak R. Outpatient Anaesthesia. In: Principles and Practice of Anesthesiology. Longnecker DE, Tinker JH, Morgan GE (editors). 2nd ed, Mosby 1998, Chapter 85: 2223-2265.
• Kortilla K, Ostman P, Faure E, et al. Randomised comparison of recovery after propofol-nitrous oxide versus thiopentone-isoflurane-nitrous oxide anaesthesia in patients undergoing ambulatory surgery.  Acta Anaesthesiol Scand 1990; 34: 400-403.