Clinical Features and Treatment

The clinical features and treatment of LA toxicity are described in Chapter 4.

Prevention

The following precautions are useful to minimize the risk of LA toxicity:

Of these, the main safety measure is slow injection. This prevents rapid production of very high plasma concentrations even if the injection is intravascular. By this means, toxicity may be diagnosed early, the injection discontinued and a major reaction avoided. Rapid injection of local anaesthetic is not necessary for the performance of any block. The use of ultrasound-guidance to visualize local anaesthetic spread may be a useful addition to reduce intravascular injection with peripheral nerve block techniques.

Test Dose

This may be used before administration of the main dose of local anaesthetic drug. It is indicated particularly for epidural block, where it should be capable of demonstrating inadvertent intravenous (i.v.) or subarachnoid injection. A test dose of 4 mL plain lidocaine 2% is sufficient to cause mild symptoms in most patients after accidental i.v. injection, and any features of local anaesthetic blockade 2 min after injection are good evidence of accidental subarachnoid block. No test dose is infallible; the most important factor in avoiding local anaesthetic toxicity is slow administration of the main dose.

Sympathetic Blockade

A limited sympathetic block may be produced by peripheral nerve anaesthesia, but only central blocks are likely to produce hypotension by this mechanism.

Total Spinal Blockade

This occurs occasionally during subarachnoid block if excessive spread of local anaesthetic solution occurs, and is a recognized complication of epidural block if the dura has been penetrated (see below). Apnoea may occur if local anaesthetic solution reaches the cerebrospinal fluid (CSF) from perforation of a dural cuff during interscalene brachial plexus block, or the ventricular system during retrobulbar nerve block.

Vasovagal Attack

This is more likely to occur in an anxious patient with a rapidly ascending spinal block. Symptoms are pallor, nausea, and bradycardia associated with hypotension. It can occur with the patient in the supine position and usually resolves rapidy if i.v. atropine 0.3–0.6 mg or ephedrine 5–6 mg is administered. Cautious i.v. sedation (e.g. midazolam 1–2 mg) may be helpful.

Anaphylactoid Reaction

This is very rare with amide local anaesthetics.

Local Anaesthetic Toxicity

This is considered above and in Chapter 4.

 single dose

 intermittent bolus:

 continuous infusion (with optional bolus doses) via a catheter.

 an anaesthetic breathing system through which oxygen may be administered under pressure via a face mask or tracheal tube

 a laryngoscope with two sizes of blade, a range of tracheal tubes and an introducer

 a table which may be rapidly tilted head-down

 suction apparatus

 intravenous cannulae and fluids

 thiopental or propofol to control convulsions

 drugs to treat bradycardia or hypotension, especially atropine, ephedrine and metaraminol or phenylephrine

 lipid emulsion 20% for treating serious systemic toxicity (see Ch 4).

Needles

The use of very fine spinal needles (26G) has significantly reduced the incidence of post-spinal headache as has the use of pencil-point 25G Whitacre and 24G Sprotte needles (Fig. 24.1A). The 27G Whitacre needles appear to be associated with the lowest incidence of post-spinal headache but confident and successful use of these needles requires greater expertise than is needed for the use of larger needles. For peripheral blocks, short-bevelled needles allow greater tactile appreciation of fascial planes and appear to reduce the likelihood of nerve damage. A variety of insulated needles are available for plexus and peripheral nerve blockade using a nerve stimulator (Fig. 24.1B). Ultrasound needle visibility may be improved by using echogenic needles which have ‘corner stone’ reflectors positioned at the distal end of the cannula shaft (Fig. 24.11C).

A recent patient safety initiative aimed at reducing drug administration errors, has recommended the development and evaluation of spinal needles and catheter infusion systems with non-Luer connectors that cannot therefore attach to intravenous equipment or standard syringes. This should help prevent wrong route intrathecal injection and stop the accidental intravenous administration of drugs intended for epidural or regional block.

Immobile Needle Technique

For plexus and major nerve blocks, local anaesthetic drug is drawn into labelled syringes and connected to the block needle by a short length of tubing (Fig. 24.2). This allows the anaesthetist to hold the needle steady while aspiration tests are performed and syringes changed. The system must be primed to prevent air embolism and also to avoid image artefact when using ultrasound-guidance.

Catheters

Continuous administration of local anaesthetic drugs has been made possible by the development of high-quality catheters, which are introduced through a needle (or occasionally over a needle; Fig 24.1A) and may be left in position for hours or even days. Careful fixation is essential to maintain the position of the catheter in the postoperative period. Catheters, in particular spinal (subarachnoid) catheters, should be labelled clearly to prevent accidental overdosage.

Nerve Stimulators

Few anaesthetists now aim to deliberately elicit paraesthesiae when performing a major nerve block; many still use the nerve stimulator (Fig. 24.2) but an increasing number now use ultrasound-guidance. It is important to explain to the patient the sensation elicited by nerve stimulation. It causes little discomfort unless the contracting muscle crosses a fracture site, when duration of stimulation should be kept to the absolute minimum necessary to confirm needle position. The incidence of paraesthesia with short-bevelled insulated needles is very low because of their ability to stimulate without direct neural contact. They are also more likely to displace nerves rather than penetrate them.

Stimulators that deliver a constant current and give a digital display of the current used are readily available. One lead is attached to an electrocardiogram (ECG) electrode on the patient’s skin, and the other to the needle. After skin puncture, the stimulator is set to a frequency of 1 Hz and an initial current of 1–2 mA. Most stimulators have a visual display to confirm a complete circuit when needle touches patient. If this fails, connections should be checked or the ECG electrode replaced. Failure to confirm a complete circuit could result in unwanted paraesthesiae or potential nerve injury from repeated needling.

As the nerve is approached, motor fibre stimulation causes muscle contraction in the appropriate distribution. The current is reduced until maximal contraction is still present at a current of, optimally, around 0.5 mA. At this point, a gentle aspiration test is performed and 2 mL of local anaesthetic solution slowly injected. Muscle contraction should cease immediately due to nerve displacement. If it does not, and an insulated needle is being used, the tip may have moved, be beyond the nerve or placed intravascularly; gentle aspiration should be repeated, the needle withdrawn slightly and the procedure repeated. Severe pain on injection suggests intraneural injection, in which case the needle should be repositioned. When the correct position has been found, the remainder of the anaesthetic solution should be injected slowly with repeated aspiration tests. Performance of the block in the awake patient allows better assessment of early intravascular toxicity and intraneural injection in addition to encouraging gentle and careful technique.

Tourniquet Pain

This may be troublesome if the cuff remains inflated for longer than 30–40 min. It is sometimes alleviated by inflating a separate tourniquet below the first on an area already rendered analgesic by the block; the first cuff is then deflated. Failing this, general anaesthesia is preferable to administration of large and often ineffective doses of opioids and sedatives.

Differential Nerve Blockade

Local anaesthetic solution injected into the CSF spreads away from the site of injection and the concentration of the solution decreases as mixing occurs. A differential blockade of fibres occurs because small fibres are blocked by weaker concentrations of local anaesthetic solution. Sympathetic B fibres are blocked to a level approximately two segments higher than the upper segmental level of sensory blockade. Motor blockade may be several segments caudal to the upper level of sensory block. A sensory level to T3 with SAB may be associated with total blockade of the T1–L2 sympathetic outflow.

Respiratory System

Low SAB has no effect on the respiratory system and the technique is an important part of the anaesthetist’s armamentarium for patients with severe respiratory disease. However, motor blockade extending to the roots of the phrenic nerves (C3–5) causes apnoea and blocks which reach the thoracic level cause loss of intercostal muscle activity. This has little effect on tidal volume (because of diaphragmatic compensation), but there is a marked decrease in vital capacity resulting from a significant decrease in expiratory reserve volume. The patient may experience dyspnoea, and difficulty in taking a maximal inspiration or in coughing effectively. A thoracic block may lead to a reduction in cardiac output and increased ventilation/perfusion imbalance, resulting in a decrease in arterial oxygen tension (PaO₂). Awake patients with a high spinal block should always be given oxygen-enriched air to breathe.

Cardiovascular System

The cardiovascular effects are proportional to the height of the block and result from denervation of the sympathetic outflow tracts (T1–L2). This produces dilatation of resistance and capacitance vessels and results in hypotension. In awake patients, vasoconstriction above the height of the block may compensate almost completely for these changes, thereby maintaining arterial pressure, but general anaesthetic agents may reduce this compensatory response, with consequent profound hypotension. Hypotension is exacerbated by:

Prevention of Hypotension

Both the incidence and the degree of hypotension are reduced by limiting the height of the block and, in particular, by keeping it below the sympathetic supply to the heart (T1–4).

It is common practice to attempt to minimize hypotension during SAB or epidural anaesthesia by preloading the patient with 500–1000 mL of crystalloid solution i.v. before or during the performance of the block. These volumes are usually ineffective even in the short term, may risk causing pulmonary oedema in susceptible individuals either during the procedure or when the block wears off, and may lead to postoperative urinary retention. Appropriate fluid should be given to replace blood and fluid losses and prevent dehydration.

Bradycardia may occur because of:

Careful patient positioning, maintenance of a normal circulating volume and the use of pharmacological agents (see later), if required, should minimize the incidence of hypotension.

SAB has no direct effect on the liver or kidneys, but reductions in hepatic and renal blood flow occur in the presence of hypotension and reduced cardiac output associated with high spinal blocks.

Gastrointestinal System

The vagus nerve supplies parasympathetic fibres to the whole of the gut as far as the transverse colon. Spinal blockade causes sympathetic denervation (proportional to height of block), and unopposed parasympathetic action leads to a constricted gut with increased peristaltic activity. This is regarded by some as advantageous for surgery.

Nausea, retching or vomiting may occur in the awake patient and are often the first symptoms of impending or established hypotension. If nausea or retching occurs, the anaesthetist must assess arterial pressure and heart rate immediately and take appropriate measures.

Types of Surgery

 bleeding diathesis

 hypovolaemia

 sepsis – local or systemic

 severe stenotic valvular heart disease and in particular aortic stenosis – the patient may be unable to compensate for vasodilatation because of a fixed cardiac output

 pre-eclamptic toxaemia – epidural block is used with great benefit in this condition but a platelet count < 100 × 10⁹ L^–1 usually precludes epidural or subarachnoid anaesthesia

 acute neurological diseases/raised intracranial pressure

 lack of patient consent.

Intravenous Access

Intravenous access must be secured before lumbar puncture is performed.

Positioning the Patient

Lumbar puncture for SAB may be performed with the patient sitting or in the lateral decubitus position (Table 24.1, Fig. 24.3). If it is anticipated that lumbar puncture may be difficult, the midline is usually more discernible with the patient in the sitting position, but the risk of hypotension in the sedated patient or following development of the block is increased. The technique of lumbar puncture for the patient in the lateral position is described in the next section.

Technique of Lumbar Puncture

For the right-handed anaesthetist, the patient is positioned on the operating table in the left lateral position. The patient’s back should lie along the edge of the table and must be vertical. A curled position opens the spaces between the lumbar spinous processes. An assistant stands in front of the patient to assist with positioning and to reassure the patient. The anaesthetist must inform the patient before performing each part of the procedure.

A line between the iliac crests lies on the fourth lumbar spinous process; lumbar puncture should be performed at the L3/4 or L4/5 space. A full sterile technique (with gown, gloves and surgical drapes) is adopted. All drugs should be drawn into syringes directly from sterile ampoules using a filter needle to prevent the injection of glass particles into the subarachnoid space. A selection of spinal needles (22–27 gauge) should be available.

The skin and subcutaneous tissues are infiltrated with local anaesthetic using a small needle. The spinal needle is inserted in the midline, midway between two spinous processes. In the well-positioned patient, the needle is directed at right angles to the skin. Passage through the interspinous ligament and ligamentum flavum into the spinal canal is appreciated easily with a 22-gauge needle (Fig. 24.4A), but these needles are now rarely used because of the high incidence of post-dural puncture headache. With some practice, these structures are usually discernible with a 25G or 27G pencil-point needle, which all anaesthetists should aspire to use. The use of an introducer (19-gauge needle) is advisable to brace the smaller needles, which are very flexible. When the needle tip has entered the spinal canal, the stilette is withdrawn from the needle and the hub is observed for flow of CSF; a needle with a transparent hub makes this easier. A gentle aspiration test should be performed if a free flow of CSF is not observed, or the needle carefully rotated through 90°.

The three most common reasons for difficulty are poor patient positioning, failure to insert the needle in the midline and directing the needle laterally (Fig. 24.4B). This last fault is seen most easily from one side and is usually apparent to onlookers, but not to the anaesthetist, who looks only along the line of the needle.

When CSF is obtained, the syringe containing the local anaesthetic solution should be carefully attached firmly to the needle, taking care not to displace the needle. Gentle aspiration confirms the needle position and the solution is injected at a rate of 1 mL every 5–10 s. Aspiration after injection confirms that the needle tip has remained in the correct place. Needle and introducer are withdrawn together and the patient placed supine.

Factors Affecting Spread

The most important factor which affects the height of block in SAB (Table 24.2) is the baricity of the solution, which may be made hyperbaric (i.e. denser than CSF) by the addition of glucose. The specific gravity (SG) of CSF is 1.004. The addition of glucose 5% or 6% to a local anaesthetic produces a solution with SG of 1.024 or greater. A patient who assumes the sitting position for 5 min after injection of 1 mL of hyperbaric solution develops a saddle block which affects the perineum only. Conversely, a patient placed supine immediately after injection of 2–3 mL develops a block to the mid-thoracic region. Slightly larger volumes are advisable to ensure spread above the lumbar curvature (see Fig. 24.3).

Within the range normally used for SAB (2–4 mL), the volume of solution has only a minor effect on spread. Obesity, pregnancy and a high site of injection are minor factors which increase the height of the block; lower volumes may be desirable in these situations. Barbotage and rapid injection may produce high blocks, but increase the unpredictability of spread.

Factors Affecting Duration

The duration of anaesthesia depends on the drug used and the dose of drug injected. Vasoconstrictors added to the local anaesthetic solution significantly increase the duration of action of tetracaine, which is widely used in the USA, but this is not so for other agents.

Agents

Four agents are currently available for SAB in the UK: plain bupivacaine, heavy bupivacaine, plain levobupivacaine and the recently introduced formulation of hyperbaric prilocaine. Ropivacaine is currently undergoing evaluation and seems to have a shorter duration of action compared with both racemic bupivacaine and levobupivacaine. Plain bupivacaine 0.5% is slightly hypobaric at body temperature and spread tends to be more unpredictable, although it does tend to produce a lower maximal block height when used in the lateral position, making it a popular choice for lower limb orthopaedic and vascular surgery. It is used in volumes of 3–4 mL and lasts 2–3 h. Hyperbaric bupivacaine 0.5% is more predictable for abdominal procedures and consistently produces a block to the umbilicus (and usually to T5) in supine patients. As with all hyperbaric solutions, hypotension is encountered more frequently because of higher levels of sympathetic blockade. Volumes of 2–3 mL are used and a duration of 2–3 h is usually assured. Hyperbaric prilocaine 2% has a duration of action of 100–130 minutes and is now available for use in ambulatory surgery. A volume of 2–3mL can be used for surgical procedures anticipated to last up to 1 hour, allowing mobilization at around 4 hours after injection.

Complications

Equipment

Epidural anaesthesia is usually performed using a Tuohy needle (Fig. 24.5). The needle is marked at 1 cm intervals and has a Huber point which allows a catheter to be directed along the long axis of the epidural space. Disposable catheters are available with a single end-hole or with a sealed tip and three side-holes distally.

Technique

Epidural block may be performed at any level of the vertebral column to provide segmental analgesia over an area that can be predetermined with reasonable success. Initial experience should be gained in the lumbar region before progressing to sites above the termination of the spinal cord.

The pressure in the epidural space was originally considered to be subatmospheric, particularly in the thoracic region. In fact, it is slightly positive, but negative pressures are induced by tenting of the epidural space from the Tuohy needle and account for the rapid inward entry of saline using the hanging-drop method. Some older methods of identifying the epidural space (e.g. Odom’s indicator, Macintosh’s balloon) relied on detection of this subatmospheric pressure in the epidural space. However, methods which depend on loss of resistance to injection of air or saline as the tip of the needle penetrates the ligamentum flavum and enters the epidural space have become more popular. A midline lumbar approach is described here, using loss of resistance to saline to detect the epidural space.

The patient is positioned as for SAB and the vertebral level is identified from the iliac crests. The skin and subcutaneous tissues of the third lumbar interspace are infiltrated with local anaesthetic solution in the midline. A sharp needle is used to puncture the skin and the round-ended epidural Tuohy needle is introduced through the skin puncture, subcutaneous tissue and supraspinous ligament. The common reasons for difficulty are the same as those for SAB. When inserted into the interspinous ligament, the unsupported needle remains steady. The stilette is withdrawn and a 10 mL plastic syringe filled with saline is attached and advanced using firm but gentle pressure on the plunger. The needle must be gripped tightly at all times (Fig. 24.6) to prevent sudden forward movement. When the needle penetrates the ligamentum flavum, there is a sudden loss of resistance to pressure on the plunger, but the needle must not be allowed to advance further. The needle must not be rotated after its tip has entered the epidural space, as this increases the risk of penetration of the dura.

Single-Dose Technique

The syringe containing local anaesthetic is connected to the epidural needle, and after aspiration a test dose is administered to detect intravascular or subarachnoid placement. After an appropriate pause, the remainder of the solution is injected at a rate not exceeding 10 mL min^–1 while verbal contact is maintained with the patient.

Catheter Insertion

An epidural catheter should pass freely through the needle into the epidural space. If the catheter does not thread easily, the needle should be repositioned, as forcing the catheter into the epidural space makes intravascular placement more likely. When a sufficient length of catheter (3–5 cm) is in the space, the needle is carefully withdrawn over the catheter. After ensuring that there is no flow of blood or CSF down the catheter, the hub is attached and an aspiration test performed; if blood or CSF is obtained, the catheter should be reinserted in an adjacent space. A filter is connected and a test dose given. If this is satisfactory, the catheter is fixed to the patient’s back with adhesive strapping and the main dose is administered.

Factors Affecting Spread

Epidural spread varies widely among individuals and the initial injection site will govern the pattern of distribution relative to this injection site. The most important determinant of spread appears to be the total mass of drug injected with the same mass of drug given in different concentrations and volumes producing similar spread of sensory blockade. Higher concentrations of drug will tend to increase the intensity of block including motor block. Posture has a minimal effect on spread; in the lateral position the dependent side will have block levels approximately 0–3 segments higher, whereas a supine Trendelenburg position of 15° will result in higher sensory block levels in pregnant women. Patients who are pregnant, obese or aged over 60 years may have an increased likelihood of a high block with a given dose of LA.

Factors Affecting Onset

Onset time may be reduced by increasing the concentration of the LA and by the addition of adrenaline 1:200 000.

Factors Affecting Duration

The choice of LA agent has a major effect on the duration of anaesthesia. The concentration of the drug also has an effect; the higher concentrations of bupivacaine produce a more prolonged block. To some extent this is a reflection of increased dose, which is known to increase the duration of anaesthesia. The addition of adrenaline 1:200 000 to lidocaine increases duration.

Agents

Complications

Oral Anticoagulants

Anticoagulation should be stopped at an appropriate time before surgery if SAB or epidural anaesthesia is planned. The degree of anticoagulation most appropriate for the patient depends on a balance between the risk of withholding anticoagulation and the nature of the surgery, in particular the associated risk of bleeding.

Platelets

The platelet count should ideally be > 150 × 10⁹ L^–1.

Antiplatelet Agents

Concern has been expressed about the antiplatelet effect of aspirin, NSAIDs and dipyridamole with respect to increased risk of vertebral canal haematoma. There is little evidence to support this concern but clopidogrel should be stopped at least 7 days before surgery unless there are overwhelming clinical circumstances, as reports of both serious surgical bleeding and vertebral canal haematoma have been associated with its use.

Heparin

The half-life of heparin given i.v. is 50–160 min, depending on dose. When given s.c., blood concentrations vary widely; in some patients plasma concentrations are in the anticoagulant range. At present, it is regarded as imprudent to use SAB or epidural analgesia when subcutaneous heparin has already been given, especially the low-molecular-weight variety. Removal of an epidural catheter should be timed to precede, rather than follow, administration of a further dose of subcutaneous heparin.

Guidelines for the use of low-molecular-weight heparin and epidural anaesthesia are given in Table 24.5.

Intraoperative Heparinization

Epidural analgesia and SAB offer advantages for major vascular surgery, but the routine use of heparin introduces the theoretical risk of haemorrhage if an epidural catheter is in place. The precise risk is unknown, as prospective trials would require in excess of 10 000 cases. Some large series (3000 patients) have been conducted under epidural analgesia without haematoma formation.

Indications

Caudal anaesthesia is suitable for perineal operations, e.g. haemorrhoidectomy, although in practice a subarachnoid saddle block is usually preferred. It is frequently used in paediatric practice for postoperative analgesia following circumcision, orchidopexy and inguinal hernia and hypospadias repairs.

Method

Caudal blockade may be performed with the patient in the prone position, but the left lateral position is usually more acceptable to the patient and easier in the anaesthetized paediatric patient. Palpation down the sacral spine leads to the depression of the sacral hiatus at S5, flanked by the sacral cornua, through which the needle is inserted. A 21-gauge hypodermic needle or 22-gauge cannula is introduced through skin and sacrococcygeal ligament in a cephalad direction at 45° to the skin (Fig. 24.7). When the membrane is penetrated, injection may be performed or the needle hub may be depressed toward the natal cleft, and inserted a further 2–3 mm along the sacral canal; it must be remembered that the dura may extend to S3. Lidocaine 2%, with or without adrenaline, and bupivacaine 0.5% are suitable agents. In an adult, 10 mL of solution blocks anal sensation consistently.

In conjunction with general anaesthesia, caudal anaesthesia provides smooth operating conditions and good postoperative analgesia. With this combined technique, the advantages of performing caudal block before induction of general anaesthesia are as follows:

For patients undergoing haemorrhoidectomy, many surgeons rely on the tone in the anal sphincter to identify it accurately and avoid damage. In these patients, general anaesthesia may be supplemented by a short-acting opioid such as alfentanil for the intraoperative period, and caudal anaesthesia given following the procedure. Extremely effective postoperative analgesia lasting several hours is provided.

Complications

Misplaced needle. Injection into subcutaneous tissue causes a swelling with fluid, or surgical emphysema with 2–3 mL of air. Intraosseous or subperiosteal injection results in marked resistance to injection. Penetration of rectum and fetal head (in obstetric practice) have been reported but should not occur if the technique is performed carefully.

Dural tap. This is rare, but the procedure should be abandoned if CSF is aspirated.

Awake Intubation

This may be the safest option in a patient with known or anticipated difficulty with intubation from a variety of causes, anatomical or otherwise. Pretreatment with an antisialagogue such as glycopyrrolate 0.2 mg may be useful to decrease secretions and improve anaesthesia obtained with topical application. Sedation with midazolam or a combination with fentanyl or a target-controlled remifentanil infusion is desirable, if this is not likely to exacerbate airway obstruction. A blind, fibreoptic or retrograde technique may be used, and experience and training in these techniques are now more widespread.

The nose is prepared with topical lidocaine 2% with or without a vasoconstrictor such as phenylephrine. The patient may then either suck a benzocaine lozenge, or the posterior tongue and pharynx are sprayed with lidocaine 4%. For laryngeal analgesia, either a ‘spray as you go’ technique through the scope under direct vision is used, or a cricothyroid injection is performed through either a 23-gauge needle or 22-gauge cannula inserted through the cricothyroid membrane (Fig. 24.8A, B) with air aspirated to confirm the position. Two millilitres of lidocaine 4% are injected and the needle is withdrawn immediately. A vigorous cough results and spreads the solution. Although absorption of lidocaine from mucous membranes is rapid, in practice, significant amounts tend to be lost or swallowed and rarely cause systemic toxicity.

Anatomy of the Brachial Plexus

A sound anatomical knowledge is essential to the practice of peripheral regional anaesthesia. The nerve supply of the upper limb is derived mainly from the brachial plexus, which is formed from the anterior primary rami of the fifth to eighth cervical and first thoracic nerve roots. The roots of the plexus divide repeatedly and recombine to form trunks, divisions, cords and terminal nerves (Fig. 24.9). The roots emerge from the intervertebral foramina and combine into three trunks above the first rib. Each trunk separates above the clavicle into anterior and posterior divisions; anterior divisions supply the flexor structures of the arm and posterior divisions the extensor structures. The divisions recombine into three cords, which surround the second part of the axillary artery behind pectoralis minor and then form the terminal nerves.

The roots lie between the anterior and middle scalene muscles and are invested in a sheath, derived from the prevertebral fascia, which splits to enclose the scalene muscles. The cutaneous and deep nerve supplies of the upper limb are depicted in Figure 24.10.

Part of the cutaneous nerve supply of the upper limb is not derived from the brachial plexus; the upper medial part of the arm is supplied by the intercostobrachial nerve (T2) whilst the skin over the shoulder tip is supplied by the supraclavicular nerves of the cervical plexus. The reader is referred to standard texts for a more detailed anatomical description.

Ultrasound-Guidance

Ultrasound-guidance has been greatly increasing in popularity over the last 10 years, particularly for the performance of peripheral upper and lower limb blocks. For the first time, the anaesthetist has been able to visualize anatomical structures and variants, allowing accurate needle placement and importantly, visualization of local anaesthetic spread around these target structures. Potential advantages of these techniques remain a source of debate (Table 24.6). Although definitive outcome studies comparing ultrasound-guidance with nerve stimulation are not available, there is increasing evidence that ultrasound offers a number of advantages including greater block success, faster onset time, reduced procedure-related pain, reduced local anaesthetic dosage and reduced adverse effects such as inadvertent intravascular injection and phrenic nerve paresis with interscalene block.

Axillary Block

This technique represents perhaps the safest approach to the brachial plexus for the trainee to learn whether using peripheral nerve stimulation or ultrasound-guidance. It is useful for elbow, forearm and hand surgery and safe for out-patients, but traditional single-injection approaches are limited by high failure rates of both musculocutaneous and radial nerves. This is due to the anatomical positions of the nerves and the presence, in some individuals, of fibrous septae within the brachial plexus sheath which prevent circumferential spread of local anaesthetic. The most common orientation of nerves around the axillary artery is shown in Figure 24.11A, as are the needle positions necessary for successful complete blockade using nerve stimulation. Ultrasound visualization allows both the detection of anatomical variation and the optimization of local anaesthetic spread around these structures. Dense, complete blockade can often be achieved within 10–15 min using multiple injection techniques.

Infraclavicular Block

Historically less popular than the other approaches due to the variety and imprecision of landmark approaches, high vascular puncture rates and variable efficacy, this technique has become increasingly popular since the advent of ultrasound-guidance. Most techniques are described either below the clavicular mid-point (vertical infraclavicular block) or a more lateral approach caudal and medial to the coracoid process. The latter approach is more popular with ultrasound-guidance (lateral sagittal infraclavicular block) and blocks the three cords of the plexus as they surround the second part of the axillary artery deep to pectoralis minor muscle.

Supraclavicular Block

This approach provides perhaps the best overall efficacy of complete arm block from a single injection as the trunks/divisions of the brachial plexus are closely related at this point.

The key to successful and safe nerve stimulation approaches is accurate palpation of the interscalene groove (see Fig. 24.12) above the clavicle, which helps delineate the position of the first rib and lateral border of pleura as well as locating the plexus. Popularity has been increasing since the introduction of ultrasound-guidance as plexus, subclavian artery, pleura and first rib are all usually straightforward to visualize (Fig 24.13). The needle is introduced in-plane, in a lateral to medial direction and should be visualized continuously to prevent inadvertent pleural puncture.

Interscalene Block

Agents

Lidocaine 1.5%, with adrenaline 1:200 000, bupivacaine, ropivacaine or levobupivacaine 0.2–0.5% are all suitable agents. The more dilute solutions are necessary when larger volumes or additional nerve blocks are required, or may be used when the block is combined with general anaesthesia, particularly if a postoperative local anaesthetic infusion is planned.

Intercostal Nerve Block

Ilioinguinal and Iliohypogastric Blocks

The main nerves which supply the groin are the subcostal (T12), iliohypogastric (L1) and ilioinguinal (L1). Ilioinguinal and iliohypogastric blocks are used for postoperative analgesia after inguinal hernia surgery, hydrocoele repair and orchidopexy, but can also be used to reduce opioid requirements after gynaecological and obstetric surgery. They are frequently used in paediatric practice and can provide analgesia comparable with caudal analgesia for paediatric day case surgery. Block efficacy can be improved and dosage reduced by using ultrasound-guidance. Local anaesthesia is used routinely as the sole anaesthetic for adult inguinal hernia surgery in some centres and may be the method of choice in the unfit patient or in the day-case unit, but only when surgeons are experienced with this technique. When used as the sole anaesthetic technique for adult inguinal hernia repair, supplementary infiltration along the line of skin incision and around the internal ring and hernial sac, is usually necessary to provide complete analgesia.

The traditional ‘blind’ approach requires a short-bevelled needle to be inserted 1.5 cm medial and inferior to the anterior superior iliac spine. The fascial click on penetrating external oblique aponeurosis is readily appreciated as the needle is advanced. A total volume of fifteen to twenty millilitres of local anaesthetic are injected under the aponeurosis to block the iliohypogastric nerve followed by a deeper injection within the internal oblique muscle, to ensure blockade of the ilioinguinal nerve as it penetrates this muscle. Another 5 mL of solution can be deposited superficial to the external oblique aponeurosis medially from this point to obtain blockade of cutaneous T12 fibres. A more proximal injection point, cranial and posterior to the anterior superior iliac spine has been recommended with ultrasound-guidance, as the nerves are easier to visualize and they each tend to lie in the same plane between transversus abdominis and internal oblique at this point. Levobupivacaine or ropivacaine 0.2–0.5% are suitable agents for postoperative analgesia.

Transversus Abdominus Plane (TAP) Block

This block provides analgesia of the anterior and lateral abdominal wall by blocking the T6–L1 afferent fibres as they lie within the neurofascial plane between the transversus abdominis and internal oblique muscles. Injection is made in the mid-axillary line above the iliac crest and can be performed blindly or ideally with ultrasound-guidance. It is suitable as part of a postoperative analgesic strategy following unilateral lower abdominal surgery such as hernia repair and appendicectomy or performed bilaterally for procedures such as retropubic prostatectomy or total abdominal hysterectomy. Local anaesthetic volumes of at least 0.3 mL.kg ⁻¹ are required to ensure adequate spread and dilute solutions will therefore be required if blocks are performed bilaterally, to ensure that dosage is kept within recommended safe limits.

Penile Block

The dorsal nerves to the penis are derived from the pudendal nerves and are blocked with 5–10 mL of LA solution injected inferior to the symphysis pubis in the midline at a depth of 3–4 cm. Care must be taken to avoid intravascular injection in this area and vasoconstrictors must not be used. Plain bupivacaine or levo-bupivacaine 0.5% are suitable agents. The base of the penis is innervated by the genital branch of the genitofemoral nerve, which may be blocked if necessary by s.c. infiltration around the penis.

Penile block is quick and simple, produces a limited effect and is the block of choice for circumcision or other minor penile surgery such as meatotomy. It is commonly used in combination with light general anaesthesia and provides good postoperative pain relief. However, a simpler technique is to smear lidocaine jelly over the wound on a regular 4 to 6-hourly basis in the postoperative period.

 It is not possible to block the whole of the lower limb with one injection.

 Subarachnoid or epidural anaesthesia may prove simpler.

 There is an impression among some anaesthetists that lower limb blocks are difficult and unreliable.

Sciatic Nerve Block

Femoral Nerve Block

Lumbar Plexus Block

A paravertebral approach to the lumbar plexus provides, in many ways, a more logical approach to blockade of the three main terminal branches: femoral, obturator and lateral cutaneous nerve of thigh, than the inguinal 3-in-1 approach mentioned above. It may be used in combination with sciatic block to complete analgesia of the lower limb and has been used as the sole technique for femoral neck surgery in addition to providing postoperative analgesia after major hip or revision surgery carried out under general anaesthesia or central neuronal blockade.

Ankle Block

Intra-Articular Techniques

Intra-articular and wound infiltration techniques, particularly following knee replacement surgery, are becoming increasingly popular as part of a multimodal analgesic strategy aimed at minimizing side effects of parenteral opioids, improving analgesia and promoting early ambulation by avoiding significant motor block. Although at an early stage of development, it appears to be cheap, simple and safe and has recently been suggested to improve early outcomes and reduce hospital stay. The technique for knee replacement surgery involves infiltrating the entire surgical site with 100–120 mL of dilute LA solution such as ropivacaine 0.1% and then leaving an intra-articular catheter for subsequent top-ups.