TECHNIQUES IN REGIONAL ANALGESIA

Intercostal Nerve Blocks - Suprascapular block - Ring block - Bier's Block (IVRA) - Epidural and subarachnoid analgesia

Regional blocks should be carried out with resuscitation equipment and expertise immediately available. A few of the relatively safe and easy blocks, which have a high rate of success, are described. Intravenous regional anaesthesia is discussed with emphasis on its complications.

In addition, the technique of epidural and spinal analgesia (which should only be performed by the specialist) are outlined, as they are often the method of choice for some types of surgery.

Intercostal Nerve Blocks

Indications

Few therapeutic measures receive as much patient gratitude as intercostal nerve blocks following rib fractures. It is also useful following insertion of a chest drain. Post-herpetic neuralgia may be helped by repeated blocks with bupivacaine mixed with prednisolone.

Preparation

Intercostal nerve blocks can be done with the patient sitting or lying on the side. Bupivacaine is the local anaesthetic (LA) of choice because of its prolonged action. A 20 ml syringe is filled with anaesthetic and a 21G (green) or 23G (blue) needle attached. A sterile technique is used.

Technique

Intercostal nerves are best blocked at the angle of the rib as this ensures that the lateral cutaneous branch is included. The rib is palpated 7-9 cm from the mid-line with the 2nd and 3rd fingers of the left hand, The needle is inserted in a cephalad direction (as shown in Fig 1), until it hits the rib. This gives an unmistakable inelastic feeling like hitting hard wood. The needle is withdrawn a few mm. and advanced in a more caudal direction until it meets the rib again and this procedure repeated until no bone is felt. The needle is then advanced a further few mm. until a sudden 'give' or 'pop' is felt as the needle enters the sheath of the neurovascular bundle running along the lower edge of the rib. Following aspiration to ensure that the needle is not in a blood vessel, 3-4 mls of LA are injected. There should be little resistance as the LA is going into the loose tissue surrounding the neurovascular bundle (Fig 1). The needle should not be advanced any further as there is a risk of entering the pleural cavity and causing a pneumothorax.

The block is then repeated at other intercostal spaces as required. Systemic absorption of anaesthetic is very rapid after intercostal block, so great care must be taken not to exceed the maximum dose of 20 ml of 0.5% bupivacaine (100 mg in the 70 kg patient). Pain relief usually lasts up to 12 hours when the block may be repeated.

Figure 1 Showing techniques of suprascapular (a) and intercostal block (b)

Complications

These include:

• Accidental intravascular injection of LA and subsequent toxicity
  
  
• Excessive absorption of LA from perivascular tissues (intercostal nerve blocks produce the highest systemic concentration of LA per amount injected of any regional block)
  
  
• Pneumothorax due to accidental pleural puncture.

Suprascapular Nerve Block

This block is very simple and safe to perform and provides rewarding relief of shoulder pain (e.g. after trauma or after manipulation or reduction of dislocated shoulder under general anaesthesia).

Technique

It is best done with the patient sitting; the spine of the scapula is palpated and it’s mid point marked on the skin with a pen. A long (6 cm or more) 21 or 23G needle is inserted through the skin one finger width above the pen mark, pointing slightly medially and downwards, until the bone of the supraspinatus fossa is met. This should be very close to the supra-scapular notch where the suprascapular nerve passes (see Fig 1). Paraesthesia, experienced as pain at the tip of the shoulder, may sometimes be elicited. At this joint 5-10 ml of 0.5% bupivacaine is injected, after pulling on the plunger of the syringe to ensure that the tip does not lie in a blood vessel. Analgesia of the shoulder should last for up to 10-12 hours.

Ring Block of the Finger or Toe

Two dorsal and two palmar (or plantar) nerves supply fingers and toes. These can be blocked effectively for minor surgical procedures. A fine 25 G (orange) needle should be used; after preparation of the skin the needle is inserted dorsally at one side of the base of the finger (or toe) and advanced close to the surface of the bone until its tip lies close to the palmar (or plantar) surface. Then, while slowly withdrawing the needle, inject 2-3 ml 2% plain lignocaine. Before the needle is totally withdrawn, it should be deflected and advanced to the other side and a further 0.5-1 ml injected under the skin at the point where the needle is to be reinserted to block the digital nerves on the other side of the finger. Figure 2 (below) sketches this procedure. The injection of anaesthetic must be done slowly because the distension of the tissue in this region is very painful. Note that adrenaline or other vasoconstrictors must NOT be used in this block as they can cause digital ischaemia and even gangrene of the extremity. A rubber tourniquet should be applied immediately around the finger once the block is working to prevent dispersal of the LA and rapid regression of analgesia.

Figure 2 Ring block

Intravenous Regional Anaesthesia (IVRA) of the Arm (Bier's Block)

Introduction

This is a unique regional LA technique as it relies on the nerves being blocked via the venous system. Exactly how this occurs is not known but it is presumed that the LA gains access to the nerve roots by back diffusion from the veins. The technique involves total isolation and drainage of the venous network in the arm using an Esmarch bandage and tourniquet. The former empties the veins whilst the latter prevents further influx of blood. The veins are then filled with LA and within minutes the arm below the tourniquet is analgesic and relaxed. It is suitable for most superficial surgery of the arm and for bony manipulations, e.g. following a Colles fracture of the wrist.

Technique

It cannot be emphasised enough that this block must NOT, under any circumstances, be undertaken without having full resuscitation facilities and expertise at hand. It should be noted that, if the dose of local anaesthetic injected i.v. for the procedure should gain rapid access into the systemic circulation, toxic side effects will be produced, ranging from convulsions to a state of general anaesthesia with respiratory and cardiovascular depression .

The patient should lie supine and comfortably, with the affected arm supported by a side board. A suitable tourniquet (type used for orthopaedic surgery of the arm, or a specially devised double cuff tourniquet) is put round the affected arm over cotton wool padding, and carefully secured to prevent accidental deflation or detachment.

A 21 or 23G Y-canR is then inserted into a vein of the dorsum of the hand. If this location interferes with surgery or is inconvenient, it may be inserted into any other superficial vein of the arm as distally as possible. The arm is raised vertically for three minutes to reduce the volume of blood contained within the venous compartment. A similar cannula is inserted into the other arm so that an open vein is available during the procedure for the injection of adjuvant drugs such as opioids and benzodiazepines as well as drugs for the treatment of toxicity (see later).

If the lesion to be treated surgically is not painful, the Esmarch rubber bandage is tightly applied round the whole limb, starting distally, draining the blood away into the general circulation. If the bandage cannot be applied, the brachial artery may be compressed with the fingers (without obstructing venous return) for 30 seconds while keeping the arm upright. The tourniquet is then inflated rapidly to a pressure about 50 mmHg above the patients systolic B.P. and maintained throughout the procedure. The pressure in the tourniquet must be carefully observed throughout the whole procedure and not allowed to fall.

With the tourniquet inflated, 40 ml of 0.5% lignocaine or prilocaine (up to 3 mg.kg-1) is then injected very slowly through the cannula with the arm horizontal, watching for signs of venous distension (see Fig 3). If veins appear distended, the rate of injection must be reduced or stopped, because pressures may be generated within the venous system sufficient to cause leakage of anaesthetic into the general circulation.

Paraesthesiae are soon felt by the patient, and within 5-10 minutes a complete sensory and motor block should ensue, lasting for as long as the tourniquet is applied (up to 1 hour). If a double cuffed tourniquet is used, the proximal cuff is first inflated. When analgesia of the arm is established, the distal cuff (lying on anaesthetised skin) is inflated to the same pressure and the proximal one deflated. This usually relieves the discomfort associated with the pressure of the cuff.

The tourniquet must not be let down for at least 15 minutes after the injection of the local anaesthetic. This time interval ensures that enough anaesthetic has diffused out of the vascular compartment, such that the amount entering the circulation as a 'bolus' is not sufficient to cause toxic effects.

Figure 3 Technique of intravenous regional analgesia (Bier’s Block)

Advantages

• The only expertise required is ability to cannulate the vein and a rigorous technique
  
  
• Extremely high (> 95%) success rate, higher than any other block

Disadvantages

• Not suitable for deep operations as analgesia is not sufficiently intense
  
  
• Tips of fingers are often missed, an additional ring block may then be necessary (vide infra)
  
  
• The tourniquet may become extremely uncomfortable and thus limit the duration of surgery (using
  a second tourniquet together with the judicious use of adjuvant drugs may overcome this problem)
  
  
• Surgical time is limited to about 1 hour due to the tourniquet, which must not be released during the procedure
  
  
• Postoperative analgesia is extremely short lived

Complications

Should the tourniquet be accidentally deflated less than 15 minutes after injection of lignocaine, the patient must be closely monitored for side effects; paraesthesiae of the tongue and lips is usually the first symptom of systemic overdose.

Should an epileptiform fit occur, 10 mg of diazepam should be injected intravenously through the Y-can in the opposite hand, and 100% oxygen given through a facemask until the convulsion is over. The dose of diazepam may be repeated twice if necessary, but it must be remembered that it will potentiate the respiratory depression caused by lignocaine. An intravenous infusion should be set up in the 'free' arm.

The first toxic symptom may be loss of consciousness. If respiratory depression occurs (also following a convulsion) manual ventilation with 100% oxygen must be started immediately and monitoring of pulse, blood pressure and ECG instituted. The P-Q interval of the ECG is likely to be prolonged, the heart rate slow, and the blood pressure low. If systolic pressure is below 60 mmHg, 3-5 mg boluses of ephedrine may be given intravenously (up to 30 mg total). If the blood pressure is unrecordable (no pulses felt in the carotids) external cardiac massage must be started.

Epidural and Subarachnoid analgesia

Introduction

Epidurals may be performed at any level of the cervical, thoracic, lumbar or sacral spine. Lumbar epidurals at L 2-3 or L 3-4 level are the commonest, followed by the sacral or caudal approach. Lumbar epidural or subarachnoid blocks are suitable for most surgery of the lower abdomen and lower limbs.

Both are effective, firstly upon the sympathetic and then upon the sensory and motor fibres. This is more marked with subrachnoid block (differential block) as it works directly on the nerve sheathes in the CSF. Epidurals work principally on the nerve roots as they traverse the epidural space and the paravertebral foramina, only subsequently penetrating the dura. This indirect action combined with the large volume of distribution of the epidural space means that much higher doses of local anaesthetic are required as compared with the subarachnoid route (5 times the amount). Sympathetic blockade always causes vasodilation in the lower half of the body and a variable fall in blood pressure.

The discovery of opioid receptors in the spinal cord has led to the use of opioids either separately or in combination with local anaesthetics, both intraoperatively or for postoperative analgesia. This is discussed in more detail in the section on postoperative pain.

Epidural and subarachnoid anaesthesia with LA has the following -

Advantages (over, or combined with, general anaesthesia):

• reduced stress of surgery due to sensory and autonomic blockade
• decreased effect on respiratory function and interference with ventilation both during surgery and in the postoperative period
• reduced incidence of postoperative deep vein thrombosis in major orthopaedic surgery
• relief of post-operative and labour pains by use of continuous infusion techniques
• increased cardiovascular stability in patients with ischaemic heart disease and good left ventricular function

Disadvantages

• Technical difficulties and time taken to complete the block and get it working (up to 1 hour in some cases)
  
  
• Sympathetic block with local anaesthetics may produce catastrophic falls in blood pressure, especially if the patient is hypovolaemic

Contraindications:

• patient refusal, despite adequate assurance and explanation.
  
  
• abnormal anatomy or infection at the site of the proposed block
  
  
• coagulopathy, this also includes the relative contraindications of thrombosis prophylaxis with mini-dose heparin or aspirin use in prevention of coronary artery thrombosis

Complications:

• epidural haematoma or abscess rarely occurs post epidural block
  
  
• inadvertent dural tap
  
  
• sympathetic block leading to hypotension and depressed response to sudden blood loss and hypovolaemia can cause severe hypotension which is difficult to reverse

Despite some of the advantages alluded to above, there is no evidence of an overall reduction in morbidity or mortality using epidural/subrachnoid block versus general anaesthesia. In fact, the techniques are often combined.

Epidural analgesia

Firstly, decide that there are no contraindications to the technique and ensure patient acceptance for the technique. Set up an i.v. infusion and (subject to acceptable cardiac function) administer 15 ml.kg-1 of a balanced salt solution or colloid. This reduces the incidence of hypotension on production of the sympathetic block.

Technique and anatomical considerations

The patient is turned onto the left side and the site chosen, usually L 2/3 to L 3/4. The skin is cleaned with an antiseptic solution and a small skin wheal is made with LA. A 16G or 18G Tuohy needle is inserted through the skin and advanced through the supraspinous ligament and then between the spines of the vertebrae into the interspinous ligament. At this stage, the stylet is removed and it will be noticed that the needle is firmly gripped by the ligaments. If not, the needle is still in subcutaneous fat and should be advanced further. A well-lubricated glass or plastic syringe is attached to the hub of the needle and air injected. A 'bounce' is detected if the needle is in the ligament. The patient is then asked to flex the back by bringing the chin onto the chest and the knees up to the abdomen. This opens up the space between the spines and adjacent lumbar laminae, the position is maintained by an assistant. As the needle is advanced further it penetrates the ligamentum flavum, a firm, rubbery ligament with a characteristic 'solid' feel. Still checking for resistance to injection of air, the needle is further advanced through the ligamentum flavum and thence into the epidural space. This is not a true 'space' but contains nerve roots, blood vessels and fat. It offers very little resistance to injection of air and thus a 'loss of resistance' is felt as the needle enters this space. The needle is detached and a check made for leakage of fluid (due to inadvertent dural tap).

N.B. An alternative technique to locate the epidural space is to fill the syringe with saline and advance the needle, still pressing on the plunger, till loss of resistance is achieved. At this stage, it will be easy to inject saline into the space. It is extremely important to make sure that the fluid that will inevitably come back in small quantities using this technique is not CSF!

The anaesthetic solution is slowly injected into the epidural space (Fig 4). Volumes ranging from 8 ml of 0.5% bupivacaine (for relief of pain in labour or post-operatively) to 30 ml of 0.5% bupivacaine or 1.5% lignocaine (for lower abdominal or hip surgery) may be injected directly through a needle or through a fine plastic catheter. The plastic catheter has the advantage of allowing top-ups if left in situ (usually 2-3 cm inside the epidural space).

Complications

Note that the doses are close to those causing systemic side effects. Once the anaesthetic is injected, it will take from 20 minutes (1.5% lignocaine) to 40 minutes (0.5% bupivacaine) to fully establish the sensory block, which then lasts up to 90 minutes with bupivacaine. Occasionally the block produced is unsatisfactory for surgery because one side or a particular segment remains resistant to the effect of the drug regardless of repeated top-ups or repositioning of the catheter.

Caudal are a form of epidural analgesia, but the epidural space is reached through the sacrococcygeal membrane. The nature, rate and seriousness of complications is the same as in lumbar epidurals. Single-shot caudals with 0.5% bupivacaine are often given for post-operative pain relief after perineal surgery (e.g. circumcision in children).

Top-ups

Topping up epidurals through the indwelling catheter carries identical risks to the initial administration. The risk of injecting the wrong drug is always present, and it cannot be emphasised enough that only specially trained personnel, fully aware of (and able to deal with) the possible complications, should perform this technique. Specially trained midwives in labour wards often do it; the blood pressure must be monitored at 5-minute intervals for 20 minutes after topping-up. A well-drilled routine should be established to deal with complications such as precipitous fall in blood pressure or total paralysis.

Subarachnoid (intrathecal) analgesia

The patient is similarly positioned and the subarachnoid space is reached with a fine needle (22 or 25G) by advancing a few mm. beyond the epidural space and through the dura and arachnoid mater as for a diagnostic lumbar puncture (Fig 4). The correct position of the tip of the needle is confirmed by obtaining clear CSF dripping off the hub. Only 1.5-3 ml of anaesthetic is injected to produce a block equivalent to that obtained with 20-30 ml in the epidural space, the effect being obtained within 5-10 minutes.

Figure 4: Subarachnoid anaesthesia: (a) Positioning of the sitting patient, landmarks and direction of needle (b) Horizontal section of lumbar intervertebral space to show the tip of the needle for subarachnoid (A) and epidural (B) anaesthesia. Both needles are usually inserted via the midline route as in A.

Subarachnoid analgesia is very reliable in its effects; patchy blocks are very rare, an advantage over epidurals. Although it is traditionally a single-shot procedure, top-ups are possible using a very fine 32G catheter threaded through the spinal needle. A percentage of young patients, varying from 1 to 3%, complain of headaches post-operatively due to leakage of CSF through the hole made by the needle in the dura (c.f. 'dural tap' during epidural block). The incidence is lowest with fine 25G needles, elderly patients seeming relatively resistant to this complication. The anaesthetic solutions used are normally mixed with 6-9% dextrose to make them hyperbaric (heavier, or denser than CSF), such that by positioning the patient appropriately a more localised block (e.g. one-sided) may be obtained.

The most commonly used anaesthetic solution is heavy bupivacaine (Marcaine) 0.5% in 8% dextrose.

Late complications of epidural and subarachnoid blockage may occur, such as persistent paraesthesia or weakness, often of a patchy nature. Their management is beyond the scope of this document.