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A Review of Ambulatory Anesthesia
The science behind pre-op evaluations, PONV prevention and anesthetic administration.
Ajay Malik
Publish Date: October 10, 2007   |  Tags:   Anesthesia

Ambulatory anesthesia has continued to expand due to the growth of minimally invasive surgery and the desire to reduce the overall cost of care. It has a much wider scope with inclusion of ASA physical status III and IV patients whose systemic diseases have been medically stabilized. Efficient pre-operative screening in a clinic or by telephone, minimal laboratory testing and an anesthetic technique geared toward reducing side effects and an early discharge let the provider curtail cost and decrease inconvenience to the patient.

The use of short-acting anesthetic agents such as propofol, desflurane, sevoflurane and nitrous oxide in conjunction with anti-emetic prophylaxis facilitates the fast-track recovery from general anesthesia. Regional anesthesia in the form of nerve blocks reduces the need for opioid analgesics and the associated nausea and vomiting, leading to a faster discharge from the PACU. The concept of fast-tracking after ambulatory surgery is achieved by taking the patient directly from the operating room to the day-surgery step-down unit (Phase 2 PACU) or simply discharging the patient home from the PACU.

Risk factors for unanticipated hospital admission

Surgical
• Pain
• Bleeding
• Extensive surgery
• Surgical complications
• Abdominal surgery
• ENT and urologic surgery
Social
• Discharge without an escort

Anesthesia
• Nausea and vomiting
• Somnolence
• Aspiration
Medical
• Medical complications related to DM, IHD and sleep apnea
• Medication error

A select group
Procedures appropriate for ambulatory surgery are those that are accompanied by minimal post-operative physiologic disturbance and an uncomplicated recovery.[1, 2] The most common causes for an unanticipated admission after day surgery include blood loss, pain and post-operative nausea and vomiting.[3]

Lists of ambulatory procedures in fact quickly become outdated, simply because they exclude certain procedures that in a short time may become routine in ambulatory settings. Patients undergoing extensive surgeries with excessive fluid shifts, the need for blood transfusions, prolonged immobilization or parenteral opioid analgesic therapy are more suited to a 23-hour or longer stay.

Ambulatory surgery is no longer restricted to ASA physical status I or II patients; ASA status III or IV patients may be appropriate candidates, provided they are medically stable. In a large prospective outcome study by Warner and co-workers, 24 percent of ambulatory surgical patients were physical status III and had a low incidence of morbidity that was similar to ASA I and II patients.[4] Therefore, you shouldn't consider the ASA physical status in isolation because the type of surgical procedure, the anesthetic technique and a multitude of social factors can also influence decisions regarding patients' suitability.[5] Still, a check of local regulations is warranted, as some states prohibit ASA IV patients undergoing procedures in ambulatory surgery centers.

In one review, 258 morbidly obese patients who underwent surgery were compared to patients who weren't morbidly obese. There wasn't a greater incidence of unplanned admissions, minor complications or unplanned contact with healthcare professionals in the morbidly obese group.[6] Interestingly, even the presence of obstructive sleep apnea syndrome wasn't associated with an increased risk of unanticipated admission to the hospital.[7] Patients susceptible to malignant hyperthermia can in fact be treated as outpatients. You should manage these patients with non-triggering anesthetics and observe them for at least four hours post-operatively if their anesthetic course has been uneventful.[8]

Many studies have failed to demonstrate an age-related increase in recovery time or incidence of complications after outpatient anesthesia. In a study of more than 6,000 patients undergoing ambulatory surgery, age was not a predictor of unexplained return to surgery; however, patients younger than 40 years of age who did return after ambulatory procedures were more likely to be treated in the emergency room, whereas patients older than 65 years were more likely to be hospitalized.[9]

Pre-term infants (gestation age <37 weeks) who are younger than 50 weeks post-conceptual age shouldn't be discharged from an ambulatory surgery center for at least 23 hours after a procedure because they're at a risk of developing apnea even without a history of apnea.[10] Treatment with high-dose caffeine (10mg/kg) may prevent prolonged apnea and desaturation, but careful post-operative monitoring is still recommended.[11]

A combined analysis has determined the following: (1) apnea was strongly and inversely related to both gestational and post-conceptual age; (2) an associated risk factor was continuing apnea at home; (3) infants who were small for gestational age seemed to be somewhat protected from apnea; (4) anemia was a significant independent risk factor, particularly for infants less than 43 weeks post-conceptual age; and (5) no relationship exists between apnea and a history of necrotizing enterocolitis, respiratory distress syndrome, bronchopulmonary dysplasia or intraoperative use of opioid analgesics and muscle relaxants.[12]

Pre-operative evaluation
As patients with more complex medical conditions find their way into outpatient surgical settings, it becomes important to have an effective method of screening these patients pre-operatively. Such screening may be accomplished by means of a telephone interview with a trained nurse or by a visit to a pre-operative clinic.

The use of computerized questionnaires before pre-operative evaluation by the anesthesiologist can also be a time-saving and efficient practice. Computerized questionnaires are more accurate in listing positive and negative historical information than a physician interview and can be used to predict the need for pre-operative laboratory testing.[13] The use of a pre-operative questionnaire along with a telephone screening interview was highly effective in reducing cancellations and surgical delays.[14, 15]

The three primary components of a pre-operative assessment include history, physical examination and laboratory testing; 86 percent of diagnosis of pre-existing conditions such as asthma, hypertension and diabetes can be obtained by a good medical history alone. A further 6 percent and 8 percent of diagnoses could be added by careful physical examinations and laboratory investigations, respectively.[16] Identifying and optimizing the patient's need for further diagnostic evaluation or active treatment before surgery remains the primary objective of a pre-operative assessment.

Patients with chronic diseases (hypertension and diabetes, for example) require additional laboratory studies (electrolytes, glucose), but for young, healthy outpatients undergoing superficial surgical procedures (biopsy, D and C, herniorrhaphy, arthroscopy, vein stripping), no laboratory tests appear to be indicated in males and only a pregnancy test may be appropriate for females.[17]

Contraindications to Outpatient Surgery

The following conditions are generally regarded as unsuitable for ambulatory surgery:

1 Any acute illness, especially any communicable disease that might be spread to other patients (chicken pox, for example). Children with URI are a special case and are usually acceptable provided that they don't have bronchitis, a productive cough or a fever.

2 Acute intoxication (with drugs or alcohol).

3 Pregnancy. Elective surgery ordinarily shouldn't be done during pregnancy. The surgery center stocks urine pregnancy tests and one should be conducted pre-op if there is any possible question about this.

4 Patients who've suffered the following conditions within the last six months aren't considered sufficiently medically stable for outpatient ambulatory surgery: myocardial infarction; angina at rest; an episode of CHF requiring treatment in an ER or admission to a hospital.

5 Any patient who's suffering a significant illness requiring ongoing treatment (angina, asthma or diabetes, for example) should have the necessary lab work or office visit to document that their condition is stable performed within three months before surgery.

6 Morbid obesity. A body mass index (BMI) over 45 can significantly increase anesthetic risk. (BMI = weight in kilograms divided by [(height in meters) squared]).

7 Age under six months. This relates to the size of available equipment and the need for extended post-operative monitoring for very young children. Outpatient surgery may need to be delayed until a later age in former premature infants because of an increased risk of post-op apnea, which may require extended inpatient monitoring. Note that there is no maximum age limit.

8 Patients with AICD (automatic implantable cardiac defibrillator) who have such criteria:

   '  ejection fraction of 30% or lower,
   '  unstable pattern of AICD firing, and
   '  anticipated need to use electrocautery.

9 Patients with known active tuberculosis.

10 Patients with ASA Classification of V.

11 Patients with no driver or no competent home caregiver.

Pre-operative preparation
In order to make ambulatory surgery both safer and more acceptable for patients and staff, an optimal preoperative preparation is necessary. With the exception of ACE inhibitors, diuretics and MAO inhibitors, patients should be encouraged to continue on their routine medications up to the time they arrive at the surgery center. Oral medications can be taken with a few sips of water up to 30 minutes before surgery.

Pre-operative concerns leading to anxiety have been shown to increase at least one week before surgery and return to normal levels post-operatively only after an uneventful recovery is ensured.[18] If the anesthesiologist has a succinct, informative pre-operative interview before going to the OR and the discussion exhibits qualities of empathy, caring and reassurance, no pre-op sedation may be needed in most patients.

The most common causes leading to pre-operative anxiety include fears of intra-operative awareness, not waking up after surgery, and post-operative pain and nausea. Many centers have shown encouraging results with use of instructional pre-operative videotapes that offer a complete explanation of the events surrounding the surgery.[19] The use of play-oriented pre-operative teaching - books, pamphlets and video programs - may be particularly beneficial for pediatric patients. Separation anxiety and post-operative behavior changes, prominent in children one year to four years of age, may be diminished with such preparation programs. Pre-operative preparation should also include instructions regarding arrival time and place, fasting instructions, post-operative course, limitations in driving skills and the need for a responsible adult to care for the patient during the initial 24-hour post-operative period.

The aim of pre-medications used for patients presenting for outpatient procedures include anxiolysis, amnesia, sedation, analgesia, vagolysis and prophylaxis against post-operative emesis and aspiration pneumonia. Benzodiazepines are commonly used medications for their amnestic and anxiolytic properties.

Midazolam 1mg to 2mg IV before entering the operating room provides for maximum benefits in adults. Oral midazolam requires a higher dose (0.5mg/kg) because of the first pass metabolism in adults and children. Larger doses of midazolam, with a maximum dose of 20mg, can delay early recovery but not discharge time from ambulatory surgery.[20, 21] In geriatric patients, pre-medication with midazolam 0.5mg to 2mg IV didn't adversely affect mental and psychomotor recovery, even after brief ambulatory procedures.[22]

Temazepam and alprazolam have also been effective as premedicants, but oral lorazepam isn't suitable because of its long duration of action. Oral clonidine 0.1mg to 0.3mg can reduce analgesic dose requirements and produce sedation and anxiolysis while also decreasing the heart rate and blood pressure during anesthesia.

Residual post-operative sedation may be a problem, however, for the elderly outpatient. Dexmedetomidine, a highly selective A2 agonist, can have an anesthetic- and analgesic-sparing effect. However, bradycardia and hypotension may limit its use.

Routine use of narcotic analgesics for pre-medication isn't recommended unless the patient is experiencing acute pain. Potent opioid analgesics may be beneficial if given intravenously before induction of anesthesia because they can provide acute control of pre-operative anxiety, decrease anesthetic induction dosage requirements, minimize hemodynamic response to airway stimulation and skin incision and potentially contribute to post-operative pain relief.[23]

Relief from PONV
The incidence of PONV can be as high as 70 percent to 80 percent of the outpatients with predetermined risk factors.24 Unfortunately, as many as 30 percent to 50 percent of outpatients continue to struggle with post-discharge nausea and vomiting after their arrival at home.[25]

American Society of Anesthesiologists Pre-anesthesia Testing Recommendations

EKG. The Task Force did not reach consensus on a minimum age for patients without risk factors but feels age alone may not be an indication. Indications may include patients with known cardiovascular risk factors or risk factors identified during pre-anesthesia evaluation.

Chest X-ray. Consider smoking, recent upper respiratory infection, COPD and cardiac disease. However, extremes of age, smoking, stable COPD, stable cardiac disease or resolved recent upper respiratory infection are not automatic indications.

Hemoglobin or hematocrit. Routine H&H is not indicated. Consider type and invasiveness of procedure, presence of liver disease, extremes of age, history of anemia, bleeding and other hematological disorders.

Select coagulation studies. Consider bleeding disorders, renal dysfunction, liver dysfunction and type and invasiveness of procedure. Anticoagulant medications and complementary medicines (such as ginkgo biloba) may increase perioperative risk. There are not enough data to comment on the advisability of routine coagulation tests before regional anesthesia in the absence of a known or suspected coagulation disorder.

Serum chemistries. Lab values may differ from normals at extremes of age. Before ordering potassium, glucose, sodium, renal and liver function studies, consider perioperative therapies, endocrine disorders, risk of renal/liver dysfunction, medications and alternative therapies.

Urinalysis. Not indicated except for specific procedures (such as prosthesis implantation and urologic procedures) or when urinary tract symptoms are present.

Pregnancy testing. Consider testing for all female patients of childbearing age. Clinical characteristics to consider include an uncertain pregnancy history or a history suggestive of current pregnancy.

From the Practice Advisory for Preanesthesia Evaluation: A Report by the ASA Task Force on Preanesthesia Evaluation. Go to: writeOutLink("www.asahq.org/publicationsAndServices/preeval.pdf",1).

Smaller doses of droperidol (10mcg/kg) may be as effective as higher doses without delaying recovery or producing unwanted side effects.[26] One study showed that smaller doses of droperidol (<10mcg/kg) in combination with metoclopramide was more effective than ondansetron in preventing PONV after laparoscopic cholecystectomy.[27] Larger doses of droperidol may result in unwanted side effects of the dyskinesia, restlessness, dysphoric reaction and prolonged QT interval.[28, 29] The FDA issued a Black Box warning for droperidol in 2001 that states, "Due to its potential for serious proarrhythmic effects and death, INAPSINE (droperidol) should be reserved for use in the treatment of patients who fail to show an acceptable response to other adequate treatments, either because of insufficient effectiveness or the inability to achieve an effective dose due to intolerable adverse effects from those drugs."

Common factors associated with nausea, vomiting and retching during the perioperative period

Patient-related factors

Adult age, female gender, preexisting disease (diabetes, for example), history of motion sickness or post-operative nausea and vomiting, nonsmoking status, intercurrent illness (viral infection, pancreatic disease)

Anesthesia-related factors

Opioid analgesics, induction agents such as etomidate, reversal (antagonist) drugs, gastric distension, inadequate hydration and residual sympathectomy

Surgery-related factors

ENT and plastic surgery procedures, duration of surgery, blood in gastrointestinal tract, forced oral intake, use of opioid analgesic, premature ambulation and pain

Gastrokinetic drugs, such as metoclopramide and domperidone, enhance gastric motility and increase lower esophageal sphincter tone. A scopolamine patch (centrally active anticholinergic drug) placed several hours before an outpatient laparoscopic procedure was effective in preventing PONV, but was associated with a high incidence of adverse effects, including dry mouth, somnolence, mydriasis and dizziness.[30]

The specific 5-hydroxytryptamine Type 3 receptor antagonists (5-HT3) - ondansetron, granisetron, dolasetron and tropisetron - are highly effective in preventing emesis after ambulatory surgery. They lack the sedative, dysphoric or extrapyramidal effects of other commonly used antiemetics; however, headache in the post-operative period can be a problem. Because ondansetron has a short elimination half-life, it is more effective in reducing the need for rescue antiemetics in the recovery room when it's administered at the end of longer surgical procedures. The neurokinin-1 antagonist aprepitant has superior antinausea and longer-lasting antiemetic properties than the 5-HT antagonist.[31]

Dexamethasone, 4mg to 8mg, given intravenously, is highly effective in the prevention of PONV when administered alone or in combination with other antiemetics.[32,33]

In outpatients with predisposing risk factors for a pulmonary aspiration (pregnancy, scleroderma, hiatal hernia, nasogastric tubes, severe diabetes and morbid obesity, for example), the use of H2 receptor blocking drugs or proton pump inhibitors for premedication may be appropriate. Sodium citrate, a non-particulate antacid that rapidly increases gastric fluid pH is commonly used in outpatient, obstetric and emergency settings because it reduces the consequences of aspiration of gastric contents. Metoclopramide reduces gastric volume by stimulating gastric emptying without altering the pH.

To decrease the risk of aspiration of gastric contents, patients are routinely asked not to eat or drink for at least six hours to eight hours before surgery. No trial has shown that a shortened fluid fast increases the risk of aspiration in healthy patients. Because clear liquids may trigger gastric emptying, residual gastric fluid volume after two hours is less in healthy patients ingesting small amounts of clear fluids than in fasted patients.[34] After an overnight fast, half of outpatients complained of moderate to severe hunger or thirst.

Ingestion of 150ml of water two hours before surgery significantly decreased the severity of thirst without increasing gastric volume in fasted outpatients.[35] Ingestion of 150ml of either black coffee or orange juice two hours to three hours before induction of anesthesia had no significant effect on residual gastric volume or pH in healthy adults. Similarly, pre-operative ingestion of apple juice (3ml/kg) decreased gastric volume, thirst and hunger in children and had no adverse effect on gastric contents.[36] Unless outpatients have delayed gastric emptying or receive a narcotic premedication, the requirement for a 10-hour fast isn't justified. Importantly, adequate hydration before induction of anesthesia is associated with a decreased incidence of post-operative side effects, including pain, dizziness, drowsiness, thirst and nausea.[37]

Commonly used medications
General anesthesia remains the most widely used anesthetic technique in ambulatory settings due to its safety record and rapid onset. Tracheal intubation causes a high incidence of post-operative airway-related complaints, including sore throat, croup and hoarseness. Most outpatients undergoing superficial procedures under general anesthesia don't require tracheal intubation unless they are at higher risk for aspiration. Since its introduction in 1983, the laryngeal mask airway (and similar supraglottic airway devices) has gained popularity as an alternative to tracheal intubation or facemask airway management.

The incidence of post-operative sore throat after ambulatory surgery was 18 percent with an LMA versus 45 percent with tracheal tube and 3 percent with a face mask.[38] The LMA is equally well tolerated during maintenance with sevoflurane or desflurane, despite the pungency of the latter. You can maintain the patient at a lighter level of anesthesia with minimal cardiovascular responses when you use the LMA.

However, the LMA doesn't protect the airway from foreign material and shouldn't be used in patients at higher risk for regurgitation, aspiration or upper airway bleeding. Although the LMA device has been used in paralyzed patients undergoing laparoscopic surgery, most practitioners in North America still prefer tracheal intubation in these situations to minimize the risk of gastric distention and ensure adequate ventilation in Trendelenburg's position.

Here is a review of common anesthetics.

  • Propofol remains the most popular IV induction agent. Its extremely high metabolic clearance rate leads to a faster emergence when compared with a barbiturate, benzodiazepine or ketamine. It not only causes less hiccuping, nausea and vomiting, but may decrease the requirements for anti-emetic medication because it possesses inherent anti-emetic activity. When propofol was administered in sub-hypnotic doses (10mg IV to 20mg IV) to treat PONV, 81 percent of patients showed improvement versus only 35 percent in the control group.39 Unfortunately, 28 percent of patients experienced a relapse of the symptoms within 30 minutes. Administration of lidocaine (40mg IV) immediately before propofol or injection into a larger muscular vein reduces the incidence and severity of pain associated with the propofol injection.
  • Thiopental, 3mg/kg to 6mg/kg IV, results in a relatively short duration of action due to the redistribution of the drug; however, impairment of fine motor skills with cognitive impairment may last for several hours after surgery, making it less desirable for ambulatory surgery.
  • Midazolam, 0.2mg/kg to 0.4mg/kg IV, as an induction agent is unpopular in outpatients because of its comparatively slower onset and prolonged recovery time.
  • Etomidate, 0.2mg/kg to 0.3mg/kg, compares favorably with methohexital in that it results in relatively shorter awakening times than thiopental, but recovery of fine motor skills may require 6 hours to 8 hours after the induction dose. The side effects include pain on injection, high incidence of PONV, myoclonus and transient suppression of adrenal steroidogenesis. Hemo-dynamic stability offers a distinct advantage in patients with significant coronary artery or cerebrovascular disease.
  • Ketamine is useful for induction of patients with asthma and hypovolemic shock because of its bronchodilatory and sympathomimetic effects. Though it is a potent analgesic, adverse reactions in the form of emergence phenomena are more commonly seen in adults if used without benzodiazepine pre-medication.

Volatile anesthetics most commonly used for maintenance include isoflurane, sevoflurane and desflurane. Rapid changes in depth of anesthesia can be achieved because of their rapid uptake and elimination.[40] The rapid elimination of anesthetic vapors ensures faster recovery and earlier discharge from the outpatient facility. Sevoflurane is a useful alternative to halothane for inhalational induction in the outpatient setting because of its lack of pungency, hemodynamic stability and more favorable recovery profile. Thus, it is a popular agent in both pediatric and adult populations.

Clinical studies have shown a greater incidence of post-operative agitation and excitement in patients recovering from sevoflurane and desflurane when compared to traditional volatile anesthetics such as halothane and isoflurane. The use of nitrous oxide during general anesthesia significantly reduces both intravenous and volatile anesthetic requirements during maintenance.

Although nitrous oxide can potentially increase post-operative nausea by increasing pressure in the middle ear, this effect isn't clinically significant for most patients. More importantly, nitrous oxide's anesthetic- and analgesic-sparing effect and rapid recovery lead to a favorable cost-benefit ratio for the healthcare system.[41, 42, 43, 44]

Small doses of rapid-acting opioids (fentanyl, alfentanil, sufentanil or remifentanil) at the time of induction can effectively attenuate the stress response to laryngoscopy and skin incision. As part of a balanced anesthetic technique for maintenance of anesthesia, opioids improve intraoperative conditions and enable more rapid emergence.[45] Because alfentanil has a more rapid onset and shorter duration of action than fentanyl, emergence and recovery of psychomotor function are faster after an anesthetic technique based on alfentanil, though its higher cost and increased incidence of PONV limits its use.

Remifentanil is an ultra-short-acting opioid analgesic with potency similar to fentanyl. It is rapidly metabolized by nonspecific tissue esterases, allowing for rapid elimination, and a context-sensitive half-life of 4 minutes regardless of the duration of infusion. Studies involving the use of remifentanil in combination with a less soluble volatile anesthetic suggest that a low dose infusion (0.05'g/kg/min to 0.2'g/kg/min) can produce a significant anesthetic-sparing effect and thereby contribute to a faster emergence from anesthesia.45, 46 Longer-acting opioids (morphine, hydromorphone, oxymorphone and meperidine) and semi-synthetic opioid agonist-antagonist (butorphanol, nalbuphine and tramadol) are less popular in ambulatory settings.

Succinylcholine remains the most commonly used muscle relaxant to facilitate endotracheal intubation in outpatient surgery because of its rapid onset and short duration of action. Though many superficial outpatient surgical procedures don't require the use of muscle relaxants, short- and intermediate-acting non-depolarizing muscle relaxants (cisatracurium and mivacurium, for example) are commonly used as they allow reversal of neuro-muscular blockade even after brief surgical procedures.

Careful titration of pharmacological antagonists like naloxone and flumazenil may be useful in facilitating the recovery from opioids and benzodiazepines in ambulatory anesthesia, keeping in mind that the rebound of the agonist effect may appear in one hour to two hours. Flumazenil restores alertness more than respiratory drive, and shouldn't be used to routinely "wake up" the patient.

Anesthesia techniques
Spinal anesthesia is a reliable and a simple anesthetic technique; however, the residual effects on the motor, sensory and sympathetic nervous systems can contribute to delayed ambulation, dizziness, urinary retention and impaired balance.[47] Post-dural puncture headache and backache are the main problems after spinal anesthesia. Short-acting local anesthetics (lidocaine and procaine, for example) are preferred over bupivacaine and tetracaine in outpatient settings to ensure a more rapid recovery.

Numerous case reports of transient neuropathic symptoms make the use of lidocaine controversial. The addition of 10'g to 25'g fentanyl to spinal lidocaine prolongs sensory, but not motor, blockade. After complete recovery of motor function before discharge from the ambulatory PACU, residual sympathetic blockade and orthostatic hypertension are less likely to be a problem on ambulation.[48]

Epidural anesthesia is technically more difficult to perform and has a slower onset of action. The potential for intravascular or intrathecal injection, and a greater chance of an incomplete sensory block as compared to spinal anesthesia, can be a concern. The use of 3% 2-chloroprocaine for outpatient knee arthroscopy achieved discharge times comparable to those of spinal lidocaine for outpatient knee arthroscopies.[47] For superficial surgical procedures lasting less than 60 minutes and limited to one extremity, a Bier block with 0.5% lidocaine is costeffective and reliable. The addition of adjuvants (clonidine, 1'g/kg, dexmeditomidine, 0.5'g/kg) may improve the quality of post-operative analgesia.[49, 50, 51]

Peripheral nerve blocks, in the form of profound and prolonged anesthesia of upper or lower extremities can be achieved using a major regional block of brachial plexus or femoral-sciatic nerves. The excellent post-operative analgesia you'll obtain can obviate the use of opioids with their associated PONV, and expedite patient discharge. Historically, caudal anesthesia has been the most popular technique to reduce post-operative pain in children undergoing lower abdominal, perineal and lower extremity procedures. However, this central neural axis block is associated with more side effects and a longer recovery time than peripheral nerve blocks (dorsal penile nerve blocks, for example).

Other popular regional techniques for children include ilioinguinal and iliohypogastric nerve blocks to relieve herniorrhaphy pain and subcutaneous ring blocks for circumcision pain. Out-patient knee arthroscopy can also be performed under local anesthesia (20ml to 30ml of 0.5% bupivacaine, for example), as well as femoral block, fem-sciatic block or general anesthesia.[52]

Monitored anesthesia care (MAC) is a specific anesthesia service where the anesthesia provider has been requested to participate in the care of the patient. It may include the administration of medication for the relief of anxiety as well as other services. It has been suggested that up to 50 percent of all outpatient procedures could be performed with a MAC technique in addition to local anesthesia and that the cost of perioperative care can be reduced by up to 80 percent in compari-son to general anesthesia.[53]

The standard of care for patients receiving MAC should be the same as general or regional anesthesia. Vigilant monitoring is required because patients may progress rapidly from a "light" level of sedation to "deep" sedation or unconsciousness and thus may be at risk of airway obstruction, oxygen desaturation and even aspiration. The common sedation technique is a small dose of midazolam 1mg to 2mg or propofol 0.5mg/kg to 1mg/kg body mass, or both, followed by a propofol infusion at 25'g/kg/min to 100'g/kg/min.[54]

Fast-tracking of ambulatory surgery is accomplished by taking the patient directly from the operating room to the step-down unit to bypass the PACU or simply discharging the patient home from the PACU.[55] With careful titration of short-acting drugs, patients can be discharged home within one hour after surgery, thereby resulting in cost savings for the institution.[56] The criteria used for determining eligibility for fast-tracking has been made even more stringent than the PACU discharge criteria to reduce the need for nursing interventions in areas with fewer nursing personnel.[57]

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