Tips for Anaesthesia Attachments- observe different local and regional anaesthetic techniques, in particular:
epidural;
spinal;
upper and lower limb nerve blocks;- discuss the advantages and disadvantages of local and regional anaesthesia;
- learn how to calculate the safe dose of local anaesthetic drugs;
- discuss the intraoperative complications of regional anaesthetic techniques;
- discuss the signs, symptoms and treatment of toxicity due to local anaesthetic drugs.
When referring to local and regional techniques and the drugs used, the terms ‘analgesia’ and ‘anaesthesia’ are used loosely and interchangeably. For clarity and consistency the following terms will be used:
- Analgesia: the state when only relief of pain is provided. This may allow some minor surgical procedures to be performed. An example is infiltration analgesia for suturing.
- Anaesthesia: the state when analgesia is accompanied by muscle relaxation, usually to allow major surgery to be undertaken. Regional anaesthesia may be used alone or in combination with general anaesthesia.
The Role of Local and Regional Anaesthesia
Regional anaesthesia is not just an answer to the problem of anaesthesia in patients regarded as not well enough for general anaesthesia. The decision to use any of these techniques should be based on the advantages offered to both the patient and surgeon. The following are some of the considerations taken into account:
- analgesia or anaesthesia is provided predominantly in the area required, thereby avoiding the systemic effects of drugs;
- spontaneous ventilation can be preserved and respiratory depressant drugs avoided in patients with chronic respiratory disease;
- there is generally less disturbance of the control of coexisting systemic disease requiring medical therapy, such as diabetes mellitus;
- the airway reflexes are preserved and, in a patient with a full stomach, particularly due to delayed gastric emptying (for example, in pregnancy), the risk of aspiration is reduced;
- central neural blockade may improve access and facilitate surgery, for example by causing contraction of the bowel or by providing profound muscle relaxation;
- blood loss can be reduced with controlled hypotension;
- there is a considerable reduction in the equipment required and the cost of anaesthesia – this may be important in underdeveloped areas;
- when used in conjunction with general anaesthesia, only sufficient anaesthetic (inhalational or IV) is required to maintain unconsciousness, with analgesia and muscle relaxation provided by the regional technique;
- some techniques can be continued postoperatively to provide pain relief, for example an epidural;
- complications after major surgery, particularly orthopaedic surgery, are significantly reduced.
Whenever a local or regional anaesthetic technique is used, facilities for resuscitation must always be immediately available in order that allergic reactions and toxicity can be dealt with effectively. As a minimum this will include the following:
- equipment to maintain and secure the airway, give oxygen and provide ventilation;
- intravenous cannulas and a range of fluids;
- drugs, including adrenaline, atropine, vasopressors and anticonvulsants;
- suction;
- a surface for the patient that is capable of being tipped head-down.
Local and Regional Anaesthetic Techniques
Local anaesthetics can be used:
- topically to a mucous membrane, such as the eye or urethra;
- for subcutaneous infiltration;
- intravenously after the application of a tourniquet (IVRA);
- directly around nerves, for example the brachial plexus;
- in the extradural space (‘epidural anaesthesia’);
- in the subarachnoid space (‘spinal anaesthesia’).
The latter two techniques are more correctly called ‘central neural blockade’; however, the term ‘spinal anaesthesia’ is commonly used when local anaesthetic is injected into the subarachnoid space and it is in this context that it will be used. The following is a brief introduction to some of the more popular regional anaesthetic techniques; those who require more detail should consult the texts in ‘further useful information’.
Infiltration Analgesia (Fig. 5.1)
Lidocaine 0.5% is used for short procedures, for example suturing a wound, and 0.5% bupivacaine or chirocaine for pain relief from a surgical incision. A solution containing adrenaline can be used if a large dose or a prolonged effect is required, providing that tissues around end arteries are avoided. Infiltration analgesia is not instantaneous and lack of patience is the commonest reason for failure. The technique used is as follows:
In a clean wound, local anaesthetic can be injected directly into the exposed wound edge. This technique can also be used at the end of surgery to help reduce wound pain postoperatively.
Brachial Plexus Block
The nerves of the brachial plexus can be anaesthetised by injecting the local anaesthetic drug either above the level of the clavicle (supraclavicular approach or interscalene approach) or where they enter the arm through the axilla along with the axillary artery and vein (axillary approach). A nerve stimulator is used to locate the nerves and increasingly ultrasound is also being used allow more precise insertion of the needle and avoid nerve injury and intravascular injection of the local anaesthetic drug. All of the drugs in Table can be used. These techniques can be used for a wide range of surgical procedures; interscalene blocks are used for shoulder surgery whereas an axillary block is useful for operations below the elbow. Both will provide good analgesia in the immediate postoperative period. The block may last several hours, and so it is important to warn both the surgeon and patient of this.
Transversus Abdominis Plane (TAP) Block
As the name suggests, this block aims to deposit local anaesthetic in the plane between the transversus abdominis and internal oblique muscles (Fig. 5.2a) to anaesthetise the nerves supplying the skin and muscles of the anterior abdominal wall (and parietal peritoneum). Although the block can be performed blind using anatomical landmarks, ultrasound guidance is increasingly used to locate the correct plane between the muscles. The needle is inserted in the midaxillary line midway between the costal margin and iliac crest. When the needle reaches the correct plane, 2–3 ml saline is injected to confirm the location, followed by the local anaesthetic (Fig. 5.2b). Alternatively, a catheter can be inserted and an infusion of local anaesthetic given for prolonged analgesia. For midline incisions, bilateral blocks will be required and care must be taken not to exceed the maximum safe dose of local anaesthetic. The block is most useful in lower abdominal surgery, for example appendicectomy, hernia repair, abdominal hysterectomy, operations on the kidney and laparoscopic surgery.
Figure 5.2 (a) Ultrasound image of anatomy for TAP block. 1; internal oblique, 2; transverses abdominis, 3; peritoneal cavity, 4; bowel. (b) Ultrasound image of TAP block. 1; internal oblique, 2; displaced transverses abdominis, 3; pool of local anaesthetic solution. Dotted line indicates position of needle. (Courtesy Dr J Corcoran).
Epidural Anaesthesia
Epidural (extradural) anaesthesia involves the deposition of a local anaesthetic drug into the potential space outside the dura (Fig. 5.3a). This space extends from the craniocervical junction at C1 to the sacrococcygeal membrane, and anaesthesia can theoretically be safely instituted at any level in between. In practice, an epidural is sited adjacent to the nerve roots that supply the surgical site; that is, the lumbar region is used for pelvic and lower limb surgery and the thoracic region for abdominal surgery. A single injection of local anaesthetic can be given, but more commonly a catheter is inserted into the epidural space and either repeated injections or a constant infusion of a local anaesthetic drug is used.
