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Introduction
Regional anesthesia techniques (peripheral nerve blocks and neuraxial blocks) offer significant advantages in the ambulatory setting.[1] These not only can provide good surgical conditions for intraoperative anesthesia, but also excellent postoperative analgesia. They may be used as (a) the only anesthetic provided, (b) together with sedation, or (c) as a supplement to general anesthesia. Studies show that regional anesthesia lowers the incidence of nausea and vomiting, improves pain scores, and decreases narcotic use.[2,3] The growth and popularity in regional anesthesia has coincided with dramatically improved intravenous (IV) sedative medications such as propofol,[4] low-dose ketamine,[5,6] and dexmedetomidine. Monitoring “depth” of anesthesia and better titration techniques for IV sedatives have evolved, whereas regional anesthesia-specific technologies have evolved from peripheral nerve stimulation[7] to ultrasound.[8]
Perhaps more than any other specialty, orthopedic surgery lends itself to the practice of regional anesthesia.[9] Nonetheless, general surgery, ophthalmology, and otolaryngology are also leaning towards use of regional anesthesia techniques.
Preoperative preparation
Patient assessment
Patients due for regional anesthesia should basically have the same preoperative assessment and precautions as patients due for general anesthesia. This is both because regional anesthesia has cardiorespiratory risks and complications as well, and also there may be a change of plan intraoperatively, because regional anesthesia may be changed into general anesthesia.
Patients receiving regional anesthesia to extremities should be reminded to avoid using the blocked extremity for at least 24 hours. In addition, patients should be warned that protective reflexes and proprioception for the blocked extremity may be diminished or absent for 24 hours.
Accepted by the surgeon
If the surgeon is unwilling or not cooperative during loco-regional anesthesia, the chance of problems and failure will increase significantly. Sometimes it may simply be a matter of providing the surgeon with better information about the benefits of loco-regional anesthesia or discussing the option of providing adequate sedation in order to let the surgeon work undisturbed. In other cases the surgeon may have valid concerns about muscle relaxation and surgical access, or the surgeon and patient may have made alternative plans in their prior consultations.
Accepted by the patient
Patients who do not consent to loco-regional anesthesia, even after full discussion of the technique, should not be forced into it, unless strong contraindications to general anesthesia are present (see later). Nevertheless, it is wise to spend time with reluctant patients, first stating that their opinions will be heard, then presenting the pros and cons of their treatment options, and ending by stating what method is normally used in cases such as theirs. For both surgeons and patients it is reassuring and positive to know whether the loco-regional technique is used routinely by the team for the specific procedure and type of patient in question; it is also good to remember that “routine” never means “always,” and that exceptions will be made from time to time.
Avoid preoperative delay
With some blocks, such as spinal anesthesia, administration and onset take no longer than general anesthesia induction. However, with other blocks, such as epidural anesthesia and brachial plexus blocks, the administration of the block may take time, testing takes time, and failure may occur, especially in inexperienced hands or with obese patients. The use of a separate induction/block room to prepare the blocks may be an advantage, especially in units with anesthetists in training or where operating room (OR) availability creates a bottleneck in the treatment chain. If an induction room is not an option, the block has to be done in the OR. An effective measure, then, is to automatically assume that the block will be effective. The implication of this is that the patient can be immediately placed in position, washed, and draped as soon as the block is done. Usually these procedures are carried out while the plexus block takes effect, and a rapid test of block efficacy may be done using the surgeon’s forceps immediately before the start of surgery. In rare cases (a benchmark goal should be less than 1 case out of 10–20) of insufficient block, a very low threshold should be set for immediately starting propofol and opioid, and/or sevoflurane, perhaps with an LMA to induce general anesthesia within 2–3 min, before starting the operation.
Monitoring
As per the ASA standards and recommendations, qualified anesthesia personnel shall be present in the room throughout the conduct of all general anesthetics, regional anesthetics and monitored anesthesia care. During all anesthetics, the patient’s oxygenation, ventilation, circulation, and temperature shall be continually evaluated. Standard ASA monitors include continuous EKG; blood pressure every 5 min, pulse oximetry, and end-tidal CO2 analysis. Respiratory rate and mental status should also be monitored.
Regional anesthesia equipment
1. Regional block carts: a regional anesthesia cart should have all drawers clearly labeled and be portable to enable transport to the patient’s bedside. It should have relevant drugs, and equipment available.
a. Ruler and marking pen for measuring and marking landmarks and injection points.
b. Alcohol and chlorhexidine swabs.
c. 25-gauge needle and syringe.
d. 1% lidocaine to anesthetize the skin for needle puncture.
e. Chlorhexidine gluconate, antimicrobial skin cleaner.
f. Syringes for sedation.
g. Local anesthetic drugs.
h. Sterile gloves, clear occlusive dressing, lubricating gel, transducer covers.
i. Suction and airway resuscitation devices.
j. Standard advanced cardiac life support (ACLS) resuscitation equipment and drugs.
k. Intralipid lipid emulsion.
2. Stimulating needles of various sizes. Stimulating needles are typically beveled at 45° rather than at 17°, as are more traditional needles, to enhance the tactile sensation of the needle passing through tissue planes and to reduce the possibility of neural trauma. To facilitate the ease of needle visualization, specialized needle designs are being developed that allow greater visibility of the needle when performing ultrasound-guided peripheral nerve blocks (PNBs). Echogenic needle design incorporates echogenic “dimples” at the tip to improve visibility.
3. Continuous epidural and peripheral nerve catheter sets.
4. Ultrasound machines with linear and curved ultrasound probes and a printer.
5. Peripheral nerve stimulators. Peripheral nerve stimulation has greatly aided the practice of regional anesthesia by providing objective evidence of needle proximity to targeted nerves. In the majority of PNBs, stimulation of nerves at a current of 0.5 mA or less suggests accurate needle placement for injection of local anesthetic. Sometimes a combination of peripheral nerve stimulation and ultrasound guidance is used to place PNBs.
6. Injection pressure monitor device. From animal studies, injection pressure has been suggested to be an important and potentially reliable predictor of nerve injury from intraneural injection. Although it has not been proven in humans that there is a relationship between high-pressure intraneural injection and nerve injury, if such relationship does exist then it will be vital for anesthesiologists to have the ability to maintain low injection pressures at all time points during injection for PNBs. Alternatively, the compressed air injection technique (CAIT) has been studied which involves drawing 10 ml of air into the syringe above the 20 ml saline and compressing this air to 5 ml prior to and during the injection, which could limit the injection pressures generated below 1034 mmHg (25 psig) in an in vitro system.[10,11]
Role of ultrasonography (USG) in regional anesthesia
Ultrasound refers to the use of sound waves (typically from 2 to 15 MHz, but in modern probes up to 22 MHz), which are above the frequency of those sound waves that can be heard by the human ear (20–20,000 Hz range). Technological advances in piezoelectric materials, electronics, and software have enabled improved probe design and software capability; this has led to the development of small, portable 2D machines with good resolution and penetration available for bedside “point-of-care” use.
The advantages of the ultrasound technique include the following.
i. Ability to visualize and identify the target nerve(s) and their relationship to surrounding structures (e.g., arteries, veins, lungs, other nerves).
ii. Allow for patient variability (e.g., size, shape, anatomical variations).
iii. Determine depth, angle, and path of the needle to the target nerve.
iv. Real-time visualization of the technique and guidance of the needle to the target.
v. Visualization of the spread of local anesthetic (encircling nerve) and placement of a catheter.
vi. Allow the procedure to be carried out on anesthetized patients safely (e.g., children) and even to be repeated if ineffective.
vii. Portability and safety (no ionizing radiation).
The ultrasound appearance of a nerve is primarily dependent on its size and the amount and make-up of the support tissue (epineurium, perineurium). Axons, or in reality fascicles (collection of axons), appear black (hypoechoic) and the supporting tissue appears bright (hyperechoic).
The most commonly used probe is a high-frequency, linear array probe (5–10 MHz), as this gives good spatial resolution for the nerves and plexuses, which are usually superficial (1–5 cm deep). A low-frequency curvilinear probe (2–5 MHz) can be useful for deeper nerves and plexuses, but it is limited by its poor spatial resolution at increasing depth.[12]
The use of USG in performing blocks has not only increased the success rate of the blocks, but also has proved to be safer and has decreased the rate of complications, especially in high-risk patients. Studies have reported the use of reduced volumes of local anesthetics with USG,[13–15] sufficiently low vascular complications,[16–20] pneumothorax,[21–24] and hemidiaphragmatic paresis.[25] These make it useful in reducing the incidence of local anesthetic induced systemic toxicity (LAST). However, a recent advisory of the American Society of Regional Anesthesia and Pain Medicine concluded that the overall effectiveness of the USG in reducing the frequency of LAST remains to be determined.[26] Speed of performance, learning curve, and availability of the appropriate equipment and logistics still remain as obstacles.
Local anesthetics and adjuvants
Local anesthetics by blocking sodium channels cause reversible neural conduction block. Several local anesthetic agents are available with varying concentrations, onset times, durations, safety profiles, and potencies. Local anesthetic agents are chosen based on desired effects. Profiles of various local anesthetics for infiltration and PNBs are summarized in Table 6.1. Local anesthetic toxicity is always a concern because regional anesthetic techniques involve injection of large volumes of local anesthetics solutions.
| Drug | Concentration (mg/ml) | Onset (min) | Duration (hours) | Maximal dose (mg/kg)b Infiltration | Maximal dose mg/kg)b with epinephrine PNBs |
|---|---|---|---|---|---|
| Lidocaine | 5–20 | Fast 10–20 | Medium (2–3) | 10 | 7 |
| Mepivacaine | 5–20 | Fast 10–20 | Medium (3–6) | 10 | 7 |
| Bupivacaine | 2.5–5 | Medium 15–30 | Long (6–12) | 2.5 | 3 |
| Levobupivacaine | 2.5–5 | Medium 15–30 | Long (6–12) | 4 | 3 |
| Ropivacaine | 2–7.5 | Medium 15–30 | Long (6–12) | 3.5 | 3.5 |
a Will always depend on the potential for rapid diffusion of a large amount into the circulation, weighed against the potential for side effects with each drug.
b The maximum dose may be increased when adrenaline adjunct is used and also when there is infiltration into a large area with a minor risk of the full dose coming into circulation (major vessels) at the same time
Ropivacaine and levobupivacaine have been introduced as less-toxic alternatives to bupivacaine. Levobupivacaine is very similar and equipotent to racemic bupivacaine. Ropivacaine seems to be slightly different and less potent in most applications. Further, ropivacaine seems to have a better separation between motor and sensory block, and has been approved for spinal use and continuous postoperative nerve block infusion. Mepivacaine and preservative-free 2-chloroprocaine have been introduced as short-acting alternatives to lidocaine for spinal anesthesia, with less risk of transient neurologic symptoms (TNS), which are often seen with lidocaine use.
Local anesthetic systemic toxicity (LAST)
Signs and symptoms of LAST include lightheadedness, sight disturbances, tinnitus, perioral paresthesia, drowsiness, confusion, slurred speech, and muscle twitches. With further increasing plasma and CNS concentrations seizures may occur. With even higher concentrations, cardiac arrhythmias and cardiorespiratory arrest are possible. The first signs of minor symptoms of toxicity should always warrant alarm, alert, and preparations for the more serious symptoms of convulsions and cardiac symptoms, which may occur within minutes.
ASRA guidelines
Use incremental injection of local anesthetics. Basically, slow injection of up to 15–20 ml in a healthy, normal adult is considered safe with all commonly used preparations and drugs. When exceeding this amount administer 3–5 ml aliquots, pausing 15–30 s between each injection. When using a fixed needle approach – e.g., landmark, paresthesia-seeking, or electrical stimulation – the time between injections should encompass one circulation time.
When injecting potentially toxic doses of local anesthetic, the use of an intravascular marker is recommended. Although epinephrine is an imperfect marker and its use is open to physician judgment, its benefits likely outweigh its risks in the majority of patients. Ultrasound guidance may reduce the frequency of intravascular injection, but actual reduction of LAST remains unproven in humans.
Treatment of LAST
Stop injecting local anesthetic; get help.
Prompt and effective airway management (intubate if needed; i.e., non-fasting patient or failure to control ventilation otherwise), 100% oxygen.
If seizures occur, halt with benzodiazepines. If benzodiazepines are not readily available, small doses of propofol or thiopental are acceptable. Future data may support the early use of lipid emulsion for treating seizures.
If cardiac arrest occurs, we recommend standard ACLS with the following modifications:
If epinephrine is used, small initial doses. Vasopressin is not recommended.
Avoid calcium channel blockers and alpha-adrenergic receptor blockers.
If ventricular arrhythmias develop, amiodarone is preferred.
Lipid emulsion therapy dosing:
▪ 1.5 ml/kg 20% lipid emulsion bolus,
▪ 0.25 ml/kg per minute of infusion, continued for at least 10 min after circulatory stability is attained.
▪ If circulatory stability is not attained, consider rebolus and increasing infusion to 0.5 ml/kg per minute.
▪ 10 ml/kg lipid emulsion for 30 min is recommended as the upper limit for initial dosing.
Failure to respond to lipid emulsion and vasopressor therapy should prompt institution of cardiopulmonary bypass (CPB). Because there can be considerable lag in beginning CPB, it is reasonable to notify the closest facility capable of providing it when cardiovascular compromise is first identified during an episode of LAST.[26]
It should be kept in mind that cardiac arrest from local anesthetic overdose implies sodium channel block in the heart nerves and muscles. Thus, resuscitation may take time for the heart to start again as the sodium channel block needs to be “washed away” first. Thus it is important to prepare for adequate compression and ventilation for some time, and not accept diagnosis of death until at least 45–60 min of non-responsive resuscitation has passed.
Adjuncts
Various agents have been tried as adjuncts to local anesthetics to prolong local anesthetic duration of action and to improve the quality of regional blocks. Except for epinephrine there is a valid controversy if these adjuncts have a true loco-regional effect, or whether the effect sometimes seen is a result of systemic absorption, which could have been achieved with an I. V. dose as well.
Epinephrine: is added to decrease the systemic absorption of local anesthetic and to limit systemic toxicity. There are limited data regarding the efficacy of epinephrine for prolonging the analgesic duration of long-acting local anesthetics. Furthermore, the use of USG and concerns of neurotoxicity may reduce the enthusiasm of its use for some physicians. Brummett and Williams recommend the use of epinephrine for nerve blocks done without ultrasound guidance or blocks in which the needle tip and local anesthetic spread is not adequately visualized, as a safety measure to detect intravascular injection.[27]
Buprenorphine, opioids: Buprenorphine is an opioid receptor, mu agonist, and kappa antagonist. While earlier studies have shown efficacy from the addition of buprenorphine to combinations of mepivacaine, tetracaine, and epinephrine,[28] the results from more recent studies[29] were not very impressive. The rationale for adding opioids to local anesthetic infiltration has been the demonstration of opioid receptors in peripheral tissue. While these are evident in tissues after some period of inflammation, their presence is disputed in native tissue.[30] It remains unclear whether the co-administration of adjuvants such as an opioid, a α2-agonist, or ketamine is beneficial. Further studies are needed to elucidate this controversial topic. The question of dosage and volume is another interesting area of investigations.
Clonidine: Meta analyses and systematic reviews clearly show an analgesic benefit from the addition of clonidine to the local anesthetics.[31,32] Most studies used between 100 and 150 µg with higher doses causing sedation, bradycardia, and hypotension.[31]
Bicarbonate: This does not seem to have any effect on block duration, although some studies report a shortening time to block onset[33] and less aching during induction, especially with acid local anesthetic solutions such as lidocaine- and epinephrine-containing drugs.
Dexamethasone: Further research is needed to better delineate the impact of dexamethasone with long-acting local anesthetics both with and without other adjuvants.
Neuraxial anesthesia
Anatomy
The spinal cord in adults extends from the base of the skull up to L1/L2 in adults and L3 vertebral level in infants. The dural sac extends from the base of the skull up to sacral (S2) vertebral in adults. In adults, it is generally safe to place a spinal needle below L2, unless there is a known anatomical variation.
A few landmarks that are worth a look and are relevant in day-to-day clinical practice would be:
The C7 spinous process – most prominent in the cervical region when the neck is flexed.
A line drawn at the level of the prominent spinous process passes through the T4 vertebra.
A line drawn at the level of the tip of the scapulae passes through the T7 vertebra.
A line drawn between the iliac crests passes though the L4 vertebra.
The sacral cornu is at the level of the S5 vertebra.
Spinal anesthesia (subarachnoid block)
Spinal anesthesia remains one of the oldest regional techniques and involves injection of local anesthetic in the subarachnoid space. Its rapid onset, minimal expense, and easy administration are key advantages in outpatient procedures. Spinal anesthesia can be used for lower extremity, lower abdominal, and urogenital surgeries. However, limitations include pain with regression, urinary retention, and the inability to ambulate resulting from weak lower extremities.[34]
Limitations and arguments against the use of spinal anesthesia for day-case surgery are problems in ambulation due to motor weakness and disturbed proprioception, immediate onset of pain at home when it wears off, urinary retention, and insufficient monitoring of side effects such as PDPH (post-dural puncture headache) and TNS and severe neurologic disturbances such as spinal hematoma.[35] Salinas and Liu reviewed some of the major controversies.[36]
As ambulatory patients are mobilized and are prone to feel symptoms of a spinal headache, a thin needle (i.e., 27G) of pencil point design should be used and the incidence of mild headache is expected to be less than 1–2% and even lower in the elderly or obese patients. Theoretically 29 G needles should be even better in this respect, but in clinical use they are more difficult to direct even with an introducer, and spinal flow is so low that there is a risk of multiple dural punctures and also failure.
The occurrence of TNS has been associated particularly with ambulatory surgery (rapid mobilization), the lithotomy position, or manipulation of the hip joint during knee arthroscopy, and almost exclusively with lidocaine.[36] TNS is a benign and self-limiting condition, but in a study by Tong et al. the patients with TNS had more pain during the first 72 h after surgery and reduced activities of daily living for 24 h compared with the patients without TNS.[37] Variation of the lidocaine concentration or hyperbaricity seems to have little influence on the incidence,[37] but there seems to be a lower incidence when the lidocaine dose is reduced.[36] In a study of 36 patients with 25 mg lidocaine spinally, no TNS was observed.[38] However, in order for lidocaine doses of less than 40 mg to be effective, an opioid adjunct is usually needed.[36] In the study of Buckenmaier et al., 20 μg fentanyl was added to 25 mg lidocaine for anorectal procedures,[39] whereas Lennox et al. added sufentanil 10 μg to only 10 mg lidocaine for gynecologic laparoscopy.[40] In the latter study it seems as though anesthesia was on the lower threshold for acceptance, as 30% of the patients reported perioperative discomfort. However, motor recovery and discharge readiness were even faster than in a comparator group receiving desflurane anesthesia.[40] A mixture of lidocaine (20 mg) with fentanyl (20 μg) was sufficient for knee arthroscopy in the study of Ben-David et al.[41] Another approach to avoid TNS is to use ropivacaine or bupivacaine. In studies of identical doses of these two drugs, either 12 mg[42] or 15 mg,[43] there was no TNS. A conclusion in favor of ropivacaine was made, as motor block was less prominent and recovery faster compared with bupivacaine. This may be due to non-equipotency in dosing, as bupivacaine should probably be dosed lower than ropivacaine for equal effect.[44] Future studies are needed to clarify whether a clinical issue of less motor block and shorter recovery with ropivacaine at the minimal effective dose remains.
Bupivacaine for ambulatory spinal anesthesia is usually combined with an opioid to reduce the dose needed and the duration of motor block. With a combination of bupivacaine 15 mg + fentanyl 10 μg, 50–75% of patients had impairment of walking and standing for more than 90 min. This was in spite of a low incidence of motor block: fewer than 25% of the patients had measurable perioperative weakness in the leg musculature.[45] Urinary retention delayed average discharge by 30 min when spinal levobupivacaine (10 mg) or ropivacaine (15 mg) was compared with lidocaine.[5,44] In a study of hernia repair, Gupta et al. used fentanyl (25 μg) together with bupivacaine (either 6 mg or 7.5 mg).[46] The 6 mg dose necessitated supplemental I. V. analgesia in some cases, and average discharge time was in the range of 5–6 h in both groups. In this study, 17% of the patients needed catheterization, resulting in 5% being admitted overnight.[46] In a study of bupivacaine (10 mg) spinally for hysteroscopy, recovery and discharge were significantly longer than with remifentanil + propofol anesthesia.[47]
It is debatable whether patients undergoing ambulatory surgery with spinal anesthesia can be discharged before voiding. Mulroy et al. claim that otherwise healthy patients less than 70 years old, with no history of voiding problems, and who are not undergoing surgery in the perianal or perineal region or having hernia repair may be discharged safely 2 h after bupivacaine (6 mg) spinally, even if they not have voided.[38]
An approach for further bupivacaine dose reduction is to administer hyperbaric bupivacaine and then place the patient in the lateral decubitus position for 10–15 min to achieve unilateral spinal block. This was used successfully by Korhonen et al., who compared 4 mg bupivacaine with a mixture of 3 mg bupivacaine + 10 μg fentanyl for knee arthroscopy.[48] Of the two, the latter group had a higher rate of fast-tracking and their recovery unit stay was shorter, but discharge-readiness was similar in both groups, with a mean value of 3 h.[47] A major problem with opioid adjunct to spinal anesthesia is the high frequency of pruritus, at an incidence of 25–75%.[41,47] With a combination of I. V. droperidol[41] and nalbuphine, Ben-David et al. were able to reduce significantly the incidence of both pruritus and nausea, without provoking any more pain.[41] Another interesting adjunct is clonidine, which was optimally dosed at 15 μg with better block quality and no delay in recovery (i.e., about 2 h) when added to 8 mg ropivacaine.[49] Merivirta and co-workers added clonidine 15 μg to 5 mg unilateral bupivacaine, and found an increased need for initial vasopressors with clonidine, but a better block quality, and no delay in discharge-readiness.[50]
A simpler and promising development in ambulatory spinal anesthesia is the launch of new, safe, short-acting local anesthetic agents. Articaine 50 mg was shown to provide discharge-readiness within 3 h, significantly faster than prilocaine,[51] and 40–50 mg of 2-chloroprocaine seems even faster with ambulation and discharge-readiness within 2 h.[52]
The 2-chloroprocaine (introduced in 1952) fell into disgrace in the 1980s after reports of neurotoxicity following an unintentional intrathecal injection of large doses of 2-chloroprocaine with sodium bisulphite during intended epidural anesthesia. There is growing evidence that this problem originated from the antioxidant sodium bisulphite rather than from the local anesthetic itself. Several encouraging volunteer studies and clinical studies were carried out during the last few years. Therefore, it is worthwhile considering new data gained with a preservative-free solution of 2-chloroprocaine.[53]
Choice of adjuncts
For outpatients, lipophilic opioids and low-dose clonidine can be used as intrathecal adjuncts, whereas several other agents studied (adrenaline, neostigmine, morphine) are not suitable because they cause delayed home discharge and/or side effects.
Low doses of lipophilic intrathecal opioids improve the quality of anesthesia[54] without delaying home discharge significantly.[40,55–57] Compared with morphine, small doses of lipophilic opioids have a shorter duration of action and a low risk of respiratory depression.[58] Fentanyl (10–25 µg) or sufentanil (10 µg) have been used together successfully with different local anesthetics.
Clonidine 15 µg combined with ropivacaine or 2-chloroprocaine (2 CP) improves the quality of spinal anesthesia with a recovery time suitable for day surgery. Hypotension, bradycardia, or sedation developed after higher doses of clonidine (45–75 µg), whereas with a 15-µg dose these systemic side effects were avoided.[49,59]
Epidurals
There are few recent reports in the literature on epidural anesthesia for ambulatory care. Epidural anesthesia is usually regarded as more time-consuming compared with other techniques. Our data on epidural anesthesia with mepivacaine showed discharge readiness after 2 h, whereas that after a lidocaine spinal was about 30 min less.[60] A study by Mulroy and co-workers actually showed a faster discharge, namely about 2 h after surgery, with epidural block with either lidocaine or 2-chloroprocaine when compared with spinal lidocaine or low-dose bupivacaine.[38] In another study of 256 hemorrhoidectomy patients, either 20 ml lidocaine 1% or bupivacaine 0.5% epidurally was used, but the observation time in hospital was a minimum of 5 h and 2% of the patients were admitted due to urinary retention.[61] In a study of lower body surgery, epidural administration of 16 ml lidocaine 1.6% was used, but all the patients were observed for 6 h in the hospital.[62] Although epidural needles are thick and some outpatients used NSAIDs or had a history of bruising, epidural steroid injections caused no hematoma in a mixed population of 1035 patients.[63] However, a recent case report describes a 35-year-old woman with no risk factors, apart from perioperative ketorolac administration, who developed an epidural hematoma after discharge from an ambulatory arthroscopy under epidural anesthesia.[64] More recently, studies have concluded that epidural washout (epidural bolus of 30 ml saline at the end of surgery) facilitates the regression of both motor and sensory block following epidural anesthesia without reducing the postoperative analgesic benefit.[65]
Caudal anesthesia
Caudal epidural block involves injection of a drug into the epidural space through the sacral hiatus.
Caudal block is applicable widely in pediatric day surgery, providing excellent analgesia for most day-case procedures below the umbilicus. Using weaker local anesthetic solutions can minimize the potential for lower limb weakness delaying discharge with caudal block (e.g. 0.125% bupivacaine).[66] Several studies have failed to demonstrate that urinary retention is a significant problem after day-case caudal block.[67,68]
One of the main drawbacks with single-shot local anesthetic caudal block is that effective analgesia lasts for only a few hours. Recently, addition of NMDA antagonists and alpha-2 antagonists has been shown to significantly prolong caudal analgesia initiated by local anesthetics. Thus, clonidine 1–2 μg/kg doubles and ketamine 0.5 mg kg quadruples the duration of analgesia.[69] These drugs are suitable for day-case practice as their use is not associated with significant cardiorespiratory, sedative, or untoward psychological effects.
Combined spinal epidural anesthesia
Combined spinal epidural (CSE) anesthesia is well established for inpatient surgery and obstetrics but is still in its infancy in day-case surgery.[70] It combines the rapidity, density, and reliability of subarachnoid block with the flexibility of continuous epidural block. Although, at first sight, CSE techniques appear to be more complicated than epidural or spinal block alone, intrathecal drug administration and siting of the epidural catheter are both enhanced by the combined, single space, needle-through-needle method. CSE is an effective way to reduce the total drug dosage required for anesthesia and analgesia, thus making a truly selective blockade possible.[71] The security of an epidural catheter allows minimal dosing of local anesthetic and therefore more precise predictability of day-surgery spinal anesthesia.[70] In contrast with epidural anesthesia, the other leading central neuraxial technique, CSE has a lower failure rate and a faster onset time.[72] For ambulatory knee surgery, CSE allowed Urmey and colleagues to reduce the dose of spinal lidocaine from 80 mg to 40 mg.[73] Similarly, Pawlowski and others used CSE to identify appropriate doses of spinal mepivacaine in order to eliminate the risk of TNS.[74]
Truncal peripheral nerve blocks
Paravertebral blocks
Paravertebral anesthesia is a unilateral alternative to epidural anesthesia with prolonged postoperative pain relief. It has been used successfully for ambulatory breast surgery[75] and inguinal hernia repair.[76] In a study using paravertebral ropivacaine for hernia repair, the average time for block administration was 12 min and analgesia was provided for 15 h, which was significantly better than with local infiltration block with ropivacaine.[77] However, in a series of 30 patients, there were two cases of block failure and two cases of prolonged recovery due to epidural effects.[76]
Unilateral paravertebral anesthesia may be a good choice alone or as an adjunct to sedation for breast cancer surgery. In one study the data actually indicated a lower incidence of cancer relapse after this block, although some confounders could be present from the nonrandomized retrospective design.[78] In any case, there seems to be better initial pain relief after this block and minor side effects, at least after moderate or more extensive procedures.[79]
Transversus abdominis plane (TAP) block
A recent review of seven randomized controlled studies of TAP blocks for postoperative pain showed that there is a substantial reduction in postoperative opioid consumption and improved pain scores after surgeries involving the anterior abdominal wall.[80] When used regularly, the landmark approach is effective, reliable, and relatively easy to perform. The key to a successful block is proper identification of the triangle of Petit and directing the needle in a slightly anterior direction. There is also a general agreement that reliable spread of the drug occurs between the T10 and L1 dermatomes with an ultrasound-guided approach. In particular, adequate volume is more important than a high concentration of local anesthetic. With either technique 20–40 ml of the local anesthetic is injected. The block is gaining popularity because of the easy technique and favorable risk profile. Its use is limited by the need for bilateral blocks when incisions cross the midline and the limitation to analgesia for somatic pain, sparing visceral coverage.[81] Recently, ultrasound-guided TAP catheters with ambulatory perineural infusions have been used successfully in patients undergoing inguinal hernia repair.[82]
Ilioinguinal field block for inguinal hernia repair
Aasbo et al. compared preoperative inguinal field block plus perioperative sedation with general anesthesia and wound infiltration for inguinal hernia repair.[83] They found that patients anesthetized with an inguinal field block had a shorter recovery time, less pain, better mobilization, and greater satisfaction than patients who received general anesthesia and wound infiltration. These differences lasted for the whole 1-week observation period. Even though there are reports of transient femoral nerve palsy following this technique,[84] the use of inguinal field block seems to be highly recommended for inguinal hernia repair in day-case surgery as an alternative to skilled surgeons doing the local anesthesia infiltration themselves.
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