Definitions and terminology. Principles of management

Transcription

1 Definitions and terminology Department of Anaesthesia University of Cape Town Regional Anaesthesia Regional anaesthesia affects one part of the body only, such as a limb, versus general anaesthesia, where there is complete loss of consciousness. In terms of the triad of anaesthesia, regional anaesthesia satisfies 2 of the 3 criteria analgesia and muscle relaxation. Hypnosis can be achieved with sedation techniques if necessary. Regional anaesthesia can be divided into central and peripheral techniques. The central techniques include the so-called neuraxial blocks (epidurals, spinals and caudals). The peripheral techniques can be further divided into plexus blocks, such as brachial plexus blocks, and single nerve blocks. Regional anaesthesia may be performed as a single shot or with a continuous catheter through which medication is given over a prolonged period of time. Last but not least, regional anaesthesia can be provided by injecting local anaesthetics directly into the veins of an arm (provided the venous flow is impeded by a tourniquet). This is called intravenous regional anaesthesia (Bier s block). The terminology may be confusing. The terms local- and regional- anaesthesia are used interchangeably: Local anaesthesia, in a strict sense, is anaesthesia of a small part of the body, e.g. tooth or skin area Regional anaesthesia is aimed at anaesthetising a larger part of the body such as a leg or arm Principles of management Patient preparation Patients should be assessed as for any general anaesthetic. Pre-operative preparation of the patient should fulfil the same standards of care as for general anaesthesia. The patient must be starved. This removes the risk of aspiration in the event of conversion to a general anaesthetic (GA) or a complication of systemic toxicity. Informed consent must be taken. A premedicant may be given. Regional anaesthesia can be performed in the operating room; pre-operative holding area (induction room); or in a procedure room. Certain equipment is mandatory prior to administering a local anaesthetic agent (LA). Obviously all drugs, needles, sterile packs and nerve stimulator or ultrasound required for the block should be checked and prepared. It is crucial that adequate monitoring facilities, oxygen, resuscitation equipment and drugs should always be available and checked. A fully trained anaesthetic assistant should also be present. Checklist prior to administration of local anaesthesia: Secure venous access and fluid for infusion Tilting table or trolley if patient vomits Facilities for IPPV and / or self-inflating resuscitator (Ambu bag) Cylinder or pipeline wall O 2 supply and face masks (ideally an anaesthetic machine) Laryngoscopes, Magill forceps, introducer, endotracheal tubes, oral airways Suction Syringes, needles, and drugs for resuscitation Defibrillator Minimum monitoring includes BP, ECG and O 2 saturation Indications for regional anaesthesia Surgical anaesthesia alone Supplement to and in conjunction with a GA Postoperative pain control Acute and chronic pain management

2 Contra-indications 2 Regional anaesthesia Unco-operative patient (blind, deaf, psychiatric disorders, mental impairment, obtunded) Coagulopathy or other bleeding disorders (congenital or acquired; or anticoagulation, e.g. warfarin or heparin). Safe values: Platelets > 75 x 10 9 l -1 and INR < 1,5 Infection, trauma or burns at the site of injection Allergy to LA Inadequate monitoring or resuscitation facilities Patient refusal, despite adequate explanation (this applies to any medical procedure, incl. a GA) Advantages Pre-emptive analgesia: There is evidence that local anaesthetics may prevent the wind up response of pain in the spinal cord. If noxious stimuli are prevented from reaching the CNS, less pain may be experienced postoperatively, and less will analgesia required Postoperative analgesia Less physiologic derangements, especially respiratory and cardiac Rapid postoperative recovery Avoidance of airway instrumentation, and the complications thereof Reduced incidence of potential complications associated with a GA (nausea and vomiting; aspiration; inability to intubate and / or ventilate; malignant hyperthermia) Decreased incidence of deep vein thrombosis (DVT) in orthopaedic joint replacement and fracture surgery of lower limbs Reduction in the surgical stress response: The elimination of painful afferent stimuli from the operative site, plus the blockade of efferent sympathetic nerves to endocrine glands, eliminates or greatly reduces the metabolic and endocrine changes seen after surgical operations. This applies to lower abdominal, perineal and limb surgery. Modification of surgical stress is greatest when local anaesthesia is continued for hours after surgery, e.g. with epidural infusion or indwelling catheter for plexus blocks Disadvantages Patient may prefer to have a GA. The block requires a degree of patient co-operation. Skill is required All blocks have a small but finite failure rate, therefore consent for a GA should also be taken Time factor: Some blocks may require up to 30 minutes before becoming fully effective Risk of systemic toxicity Types of regional anaesthesia Local anaesthetics may provide anaesthesia in various parts of the body by: Topical application Local infiltration Intravenous regional anaesthesia (Bier's block) Peripheral nerve blockade: Plexus or peripheral nerves Neuraxial or central nerve blockade: Spinal, epidural or caudal Topical application and infiltration of local anaesthetics are not true forms of regional anaesthesia (where a whole part of the body is anaesthetised). They are included here for completeness sake. 1) Topical application Types Aerosolised (2-4 % lignocaine in a MacIntosh sprayer to anaesthetise the larynx / vocal cords) Cream: EMLA or Ametop Direct application (drops) Examples Minor eye surgery Laryngoscopy and bronchoscopy Incision and drainage of quinsy (tonsillar abscess) Cystoscopy EMLA or Ametop cream for venepuncture (especially in paediatrics) and skin graft donor sites

3 2) Infiltration anaesthesia This is the injection of local anaesthetic solutions intradermally or subcutaneously to produce anaesthesia at the site of surgery. Regional anaesthesia 3) Intravenous regional anaesthesia of the arm: (Bier s Block) This block can provide intense anaesthesia for short surgical procedures (< min). Commonly used for surgery on the hand and lower forearm, e.g. carpal tunnel release, reduction of Colle s fractures and hand surgery. This is a useful technique to learn. It is simple and safe, and the ideal skill in your armamentarium as a rural community service officer! Ensure that you know how to perform this block, and also its limitations and dangers. Equipment and monitoring must be available and checked Mix 40 ml 0,5 % lignocaine in two 20 ml syringes: Draw up a 5 ml amp of 2 % lignocaine (preservative-free) into each 20 ml syringe and mix with 15 ml of normal saline. Always check the drug name of the ampoules, concentration of drug and the expiry dates. Normal saline amps can be confused with calcium or potassium chloride and the IV instillation of either is catastrophic. NB: IV bupivacaine is contraindicated due to cardiac toxicity! Special double cuff tourniquet is ideal (although one tourniquet may be used). Check cuffs inflate and do not leak. Wrap a layer of wool padding under the cuff. Site a small IV cannula (22 G) on the dorsum of the hand that needs surgery. It is important to put the cannula as low as possible on the operative side (it will not work as well if the cannula is on the forearm or in the ante-cubital fossa). Site a second IV cannula on the other arm, in case sedation or resuscitation is required. Elevate the operative arm and exsanguinate with an elastic compression (Eschmarch) bandage. Start wrapping the band around the hand first and proceed with exsanguination in a distal to proximal direction. Warn the patient that this is often uncomfortable. Inflate the tourniquet to 100 mm Hg above systolic BP. First the distal (lower) one, then the proximal (upper) one (to further aid with exsanguination) and then leave only the proximal cuff inflated. Now remove the Eschmarch bandage Now slowly inject ml of 0,5 % lignocaine into the vein. It will burn initially, warn the patient. Prior to injection of LA, it is useful to ask an assistant to squeeze over the distal forearm or apply a blood-taking tourniquet in an attempt to concentrate the LA over the site of surgery. The cannula is then removed. Anaesthesia is well established after 5-10 minutes. Anaesthesia persists for as long as the tourniquet is inflated, 2 hours is the maximum recommended time. When the tourniquet pain starts after min, inflate the lower (distal) tourniquet first, then deflate the upper (proximal) tourniquet so that the pain can be relieved as the LA block will be working underneath the lower tourniquet. Patients usually tolerate the lower tourniquet for another min. This pain can be quite severe. (N.B. One of the tourniquets must be inflated at all times to maintain the bloodless surgical field). At the end of the procedure the tourniquet should be slowly or sequentially deflated. If the procedure is < minutes, leave the tourniquet inflated until 20 min have elapsed since injection. This is to allow the lignocaine to become fixed. An early rapid IV systemic bolus of lignocaine must be avoided. 4) Peripheral nerve block Most peripheral nerves in the body can be blocked with sufficient expertise and practise. Knowledge of the surface anatomy and nerve pathways is essential for successful blocks and the prevention of complications. Peripheral nerve stimulators and ultrasound will aid in the location of the nerves, and reduce complications of a blind approach. Detailed knowledge of each peripheral nerve and plexus block is beyond the scope of the undergraduate syllabus. Do not attempt to perform these blocks alone without proper training and supervision. Nerve blocks This is the injection of a local anaesthetic solution in proximity of a specific peripheral nerve. Some examples of commonly used peripheral nerve blocks: Digital nerve or ring block for surgery on the finger Wrist block for surgery on the hand Intercostal nerve block for relief of pain from fractured ribs Intra-orbital eye blocks for cataract surgery Femoral and / or sciatic nerve blocks for lower limb surgery Ilio-inguinal nerve block for surgery in inguinal region (hernias, orchidopexy) 3

4 Regional anaesthesia Plexus block The local anaesthetic solution is injected in proximity to a nerve plexus. Multiple approaches to each plexus have been described. The onset of action is usually slow (up to 30 minutes) but a duration of many hours may be achieved (up to 16 hours). Examples Brachial plexus Lumbosacral plexus 5) Neuraxial block There are 3 neuraxial techniques that are commonly used. The terminology is 1) Spinal (intrathecal or subarachnoid) 2) Epidural (peridural or extradural) and 3) Caudal (sacral epidural) anaesthesia Applied anatomy & physiology The principal site of action is the nerve root. LA is injected into the CSF (spinal) or epidural space (epidural) and bathes the nerve root. Neuraxial blocks provide excellent operating conditions: The sensory block will interrupt both somatic and visceral painful stimuli, plus the motor block will produce skeletal muscle relaxation. A differential block will occur due to the different classes of nerve fibres. The concentration of LA decreases with increasing distance from the site of injection and this causes a differential block with a sympathetic block (judged by temperature sensitivity) 2 dermatomes higher than a sensory block (pain, pressure and light touch), which is in turn 2 dermatomes higher than the motor block. Layers that the needle penetrates for the midline approach in neuraxial anaesthesia are as follows: Skin and subcutaneous tissue Supraspinous and interspinous ligaments Ligamentum flavum Epidural space Dura mater CSF Diagram 1. Anatomy of epidural and subarachnoid spaces (Source: Morgan and Mikhail. Anaesthesiology) Indications Neuraxial blocks may be used alone or in conjunction with a GA, for nearly any procedure below the neck! As a primary anaesthetic technique (i.e. without a GA), neuraxial techniques have proved most useful for lower abdominal, inguinal, urogenital, rectal and lower extremity surgery. If such a technique is being considered, informed consent must be obtained after a detailed discussion of risks and benefits with the patient. Always consider potential contra-indications and the appropriateness of this technique for the surgery concerned. Contra-indications Similar to contra-indications for regional anaesthesia as a whole, specific contra-indications for neuraxial blockade are highlighted. 4

5 Regional anaesthesia ABSOLUTE contra-indications Local infection at injection site Coagulopathy or anticoagulation Severe hypovolaemia / shock from any cause (Intolerant of sympathetic blockade and BP) Increased intracranial pressure or active intracranial disease Fixed cardiac output states: Severe aortic and / or mitral stenosis; hypertrophic obstructive cardiomyopathy (HOCM) Allergy to the local anaesthetic drug Patient refusal (Applies to all medical procedures!) RELATIVE contra-indications Sepsis Unco-operative patient or an inability to communicate with the patient (e.g. deaf or blind) Pre-existing neurological deficits, e.g. demyelinating lesions, peripheral neuropathies Severe spinal deformity Prior back surgery at the site of injection Complicated surgery, e.g. prolonged operation, major blood loss, respiratory restriction Complications Complications of neuraxial technique range from bothersome to crippling, and can be life-threatening: Hypotension related to level of spinal block, due to block of sympathetic outflow (T 1 - L 2 ) which results in widespread vasodilatation High block: Hypotension, bradycardia, CVS collapse or arrest, difficulty breathing and apnoea Post dural puncture headache: Possibly related to a leak of CSF from the puncture site in the dura. Smaller gauge needles and pencil point types reduce the incidence Meningitis and epidural abscess Epidural haematoma. Must be surgically relieved in 6 hours or permanent paralysis may result Neurological sequelae: Transient neuritis to paralysis if undiagnosed epidural haematoma Urinary retention. Routine catheterisation is advised Backache (about ⅓ of patients who have GA alone will complain of postoperative backache); the neuraxial injection will not make pre-existing backache worse Pruritis related to opiate use Shivering: If patient feels cold, provide warmth. If warm, then treat with mg pethidine IV Care of the patient Pre-operative: The same preparation is required as for a GA. Premedicate if necessary. Intra-operative: Re-assure the patient and make them comfortable. Monitor the cardiovascular parameters and adequacy of respiration. Oxygen via a facemask if required. Forced air warmer as the patient under neuraxial blockade is also at risk of hypothermia. If indicated, administer additional sedation. Postoperative: Avoid injury, especially thermal, to limbs still insensitive to pain. Check that the block is receding and that patient doesn t experience urinary retention. If the block is not receding and patient does not start to regain motor function of the limbs within 4 hours, be alerted to possible severe complications. An epidural haematoma needs to be evacuated within 6-8 hours. The epidural catheter should be removed by an anaesthetist and the tip should be intact. If the patient is on anti-coagulation, timing of removal is important to prevent bleeding and an epidural haematoma. If in doubt, contact the anaesthetist. Spinal anaesthesia Spinal anaesthesia involves injecting a small volume of local anaesthetic into the CSF. This blocks nerve roots as they pass though the subarachnoid space. The spinal part of the subarachnoid space extends from the foramen magnum superiorly to S 2 in adults and S 3 in children. The spinal cord itself ends at L 1 / L 2 in adults and L 2 / L 3 in children. Injection at below L 1 avoids direct needle damage to the cord. The subarachnoid space is found deep to both the dura and arachnoid mater. Spinals may be used for a wide variety of surgical procedures below the umbilicus: Amputations of lower limbs Hip surgery and fracture repair of lower limbs Trans urethral resection of the prostate (TURP) or bladder (TURBT) Vaginal surgery including vaginal hysterectomy Caesarean sections and tubal ligations Minor rectal surgery 5

6 6 Regional anaesthesia Strict asepsis: The anaesthetist must wear a mask, scrub and put on sterile gloves. An 18 or 16 G intravenous cannula must be placed first and 1 litre of crystalloid or 500 ml colloid (e.g. Ringer s lactate / Plasmalyte L or Voluven / Gelofusine ) should be running well. Monitors: BP, ECG and O 2 saturation. Supplemental O 2 via a facemask if needed. Perform with patient in sitting or lateral position. Position is crucial; the patient must bend to approximate the chin and knees (this opens up the intervertebral spaces). Sterile spinal pack is opened by the assistant. Local anaesthetic solution for both skin infiltration and intrathecal injection drawn up. Check amps for drug concentration and expiry dates. A wide area of the patient s back is carefully cleaned. The site is draped. The site of puncture: L 3 - L 4 (level of iliac crests - intercrestal line) or L 4 - L 5. LA infiltration of skin with 2 % lignocaine and 25 G small brown needle. Warn patient that it burns. Spinal needle (preferably a 25 G pencil point needle, but a 22 G Quincke may be needed). Steps: o Introduce needle through the skin, in the midline, and direct slightly cephalad o Pierce dura with slight loss of resistance, remove stylet and confirm CSF o Once dura is pierced, attach syringe, draw back to ascertain free flow of CSF and inject the LA slowly over 10 seconds, aspirating occasionally to confirm that you are still in the correct space o If you meet complete resistance, it is bone needle is withdrawn and re-inserted o Blood in stylet withdraw to skin and try again FACTORS INFLUENCING THE HEIGHT OF THE BLOCK MAJOR influence Baricity of solution Posture of patient Volume of solution Mass of drug injected Volume of CSF MINOR influence Level of injection Height Age Weight Speed of injection Induced turbulence (barbotage) Posture Choice and dose of local anaesthetic Agent and dose depends on the type of operation and anatomic height of the block required. As mentioned, solutions with a higher specific gravity, relative to CSF, will fall in the dural sac of a patient in the upright position ( heavy" solutions ). Solutions may be: HYPERBARIC With dextrose: Heavy bupivacaine ISOBARIC Plain bupivacaine or lignocaine (Plain bupivacaine is mildly hypobaric at body temperature) Adding an opiate, e.g. fentanyl or morphine, extends the duration of action and enhances analgesia. Epidural anaesthesia The epidural space surrounds the dura mater, i.e. lies on the outside of the dura. The nerve roots travel through this space as they leave the spinal cord. The space also contains fatty connective tissue, lymphatics and a venous plexus. Local anaesthetic solution is injected into the epidural space at a lumbar or thoracic level. Sacral epidural anaesthesia is referred to as a caudal block. Advantages over spinal anaesthesia: Top up doses or a constant infusion may be administered by means of an epidural catheter. Graduated blocks can be performed, where the level of anaesthesia is slowly increased by additional increments into the catheter. This avoids sudden changes in haemodynamics. Basic preparation and positioning is as for a spinal. The needle is a 16 or 18 G Tuohy needle with a blunt bevel, reducing the risk of dural puncture. Identification of the epidural space is achieved with the Loss of resistance technique : Sudden ease of injection of a little saline or air from a syringe (with a freely movable plunger) attached to the Tuohy needle occurs once the epidural space is entered.

7 Regional anaesthesia Uses Thoracic epidural for thoracic surgery, plus GA Thoracic epidural for analgesia in patients with multiple rib fractures, to aid effective breathing Abdominal surgery, plus GA Labour epidural for analgesia Caesarean section Operations on hips and lower extremities Postoperative analgesia Chronic pain management Caudal anaesthesia The caudal route for injection of LA is actually a sacral epidural. The block is mostly performed on paediatric patients, as an adjunct to general anaesthesia. This is done with the child asleep. Occasionally a caudal is performed in adults, particularly for chronic pain management. The anatomy makes the caudal space difficult to reach in adults. Contra-indications are those for neuraxial blocks. Indications in paediatrics Major abdominal surgery Major orthopaedic surgery of lower limb Urogenital surgery Place the patient in a lateral position Identify the sacral hiatus and the 2 posterior superior iliac spines. They form an equilateral triangle Palpate the sacral cornuae (horns) on either side of the hiatus Insert caudal needle here, angled caudally with the needle bevel facing the patient One pop or loss of resistance is felt when passing the sacro-coccygeal ligament Local anaesthetic is injected at this point Aspirate regularly to exclude blood or CSF Doses Adults ml 0,5 % bupivacaine lasts 6-8 hours Paediatrics Block height for children Volume in ml kg -1 of 0,25 % bupivacaine Lumbo-sacral 0,5 Thoraco-lumbar 1,0 Mid thoracic 1,25 Diagram 2. Types of spinal and epidural needles (Source: Morgan and Mikhail. Anaesthesiology) 7