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Techniques of epidural block
Technical skills
Techniques of epidural block
Performing the block A thorough preoperative assessment is essential to explain the procedure to the patient, discuss the common and significant complications and obtain informed consent. A clean, well lit, quiet environment is required, and secure intravenous access and appropriate monitoring should be in place before starting the block. A suitable epidural pack is needed. Packs containing sterile disposable equipment, a loss-of-resistance syringe, Tuohy needle, catheter, and bacterial filters are widely available. Reusable equipment of this type is no longer appropriate or cost effective.
Barrie Fischer Maheshwar Chaudhari
Abstract
Position of the patient The patient positions for an epidural block are the same as for spinal anaesthesia, and are described on page 418. The sitting position avoids the problems of the lateral position but increases cerebrospinal fluid (CSF) hydrostatic pressure and may increase the chances of an inadvertent dural puncture. The lateral position is more comfortable for some patients and allows pre-procedure sedation to be used. Figure 1 demonstrates both positions, and indicates Tuffier’s line.
Spinal, epidural and caudal blockade are the three components of central neuraxial blockade and provide surgical anaesthesia and postoperative analgesia for sub-umbilical surgery (thoracic epidurals provide effective analgesia but not anaesthesia for thoracic and upper abdominal surgery). While spinal and caudal blocks are usually performed as single-shot bolus techniques in adults and provide 2–4 hours postoperative analgesia, epidural techniques can provide prolonged postoperative analgesia by inserting an epidural catheter and infusing a dilute local anaesthetic and opioid drug combination. Although useful regional anaesthetic techniques, all three are invasive procedures, can be technically difficult, and have the potential to cause serious adverse events (direct needle trauma to the spinal cord or the spinal nerve roots, vertebral canal haematoma and meningitis or epidural abscess) if not done to a high standard and managed appropriately. Epidural and caudal blockade have a number of synonyms, which can be confusing. The terms ‘epidural’ (extradural, peridural) and ‘caudal’ (sacral, epidural) are used throughout this article.
Approaches to the epidural space A sterile technique with full aseptic precautions should be used. The skin over the chosen vertebral interspace is infiltrated with lidocaine (1%) using a 25G or 26G needle for the skin wheal. The underlying tissue is then infiltrated using a 21G needle. Some anaesthetists make a small cut in the skin to facilitate insertion of the blunt-tipped Tuohy needle.
Keywords anaesthetic technique; caudal; regional anaesthesia; epidural
The mid-line approach is commonly used to perform lumbar or lower thoracic epidural block. A Tuohy needle is introduced in the mid-line and directed slightly cephalad between the two spinous processes of the desired interspinous space. The needle passes through the skin and supraspinous ligaments, into the interspinous ligament. At this point the Tuohy needle stylet is removed and the loss-of-resistance syringe is attached to detect loss of resistance as the needle traverses the ligamentum flavum and enters the epidural space, which is usually 3–5 cm from the skin in the mid-line. A sudden ‘give’ may be felt as the needle tip exits the ligamentum flavum and the loss-of-resistance indicator (air or saline) is expelled into the epidural space.
Epidural block Epidural anaesthesia was described by Sicard and Catheline in 1901, but became popular only after the introduction of amide local anaesthetic agents and epidural catheters in the late 1960s. Because of its versatility, epidural analgesia is probably the most commonly used regional technique in the UK. It can be performed in the sacral (caudal), lumbar, thoracic or cervical regions, although lumbar block is used the most frequently.
The paramedian approach is more commonly used in the upper thoracic region because of the long, sloping spinous processes and narrow interspinous spaces. The Tuohy needle is inserted at about 1.0–1.5 cm laterally from mid-point of the spinous process immediately above the level of the desired intervertebral space. The needle is then moved forward, perpendicular to the skin, through the underlying subcutaneous tissue and muscle, until it strikes the vertebral lamina. The needle is then withdrawn slightly. The loss-of-resistance syringe is then attached and redirected cephalad and medially so that the needle is walked off the lamina until it pierces the ligamentum flavum and enters the epidural space.
Barrie Fischer, MBChB, FRCA, is Consultant Anaesthetist at the Alexandra Hospital, Redditch (Worcestershire Acute Hospitals NHS Trust), UK. He qualified from the University of Bristol and trained in Truro, Cambridge and Cardiff. His main interests are the role of regional anaesthesia in surgery and acute pain management. He is the immediate past chairman of Great Britain and Ireland on the Board of the European Society of Regional Anaesthesia. Maheshwar Chaudhari, MD, FRCA, is Specialist Registrar in anaesthesia on the Midland Deanery Rotational Scheme. He qualified from the University of Poona, India, and trained in anaesthesia in India, Peterborough, and the West Midlands area, UK. His interests are chronic pain management and regional anaesthesia.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 7:11
Identification of loss of resistance: the pressure in the epidural space is usually sub-atmospheric, particularly in the thoracic region whilst the patient is in the sitting position. In the lateral 422
© 2006 Published by Elsevier Ltd.
Technical skills
Figure 1 Sitting (a) and lateral (b) positions for spinal and epidural block. The dotted line represents Tuffier’s line, which joins the two iliac crests and passes through the L3/L4 interspace or across the spinous process of L4. Patient positions for spinal and epidural block.
position and in the lumbar spine the pressure is less reliably sub-atmospheric. Some early methods of identifying the epidural space (e.g. Macintosh balloon) relied on detecting the negative pressure in the epidural space. The two methods currently used rely on the loss of resistance to the injection of saline or air as the needle penetrates the ligamentum flavum and enters the epidural space. A low-resistance syringe containing 0.9% saline or air is attached to the hub of the Tuohy needle after the tip is moved into the interspinous ligament (mid-line approach) or once the lamina has been identified (paramedian approach). There are advocates for the use of both air and saline for detecting entry into the epidural space and each technique has its own benefits and drawbacks. To minimize bubble formation, dilution of local anaesthetic and the difficulty discerning saline and CSF, a maximum of 3 ml of air or saline can be used. Detecting loss of resistance with saline – the Tuohy needle and syringe combination is moved slowly and continually with the dominant hand, whilst constant pressure is maintained on the plunger of the loss-of-resistance syringe. The non-dominant hand is braced against the skin of the patient’s back to stabilize the needle/syringe combination and prevent sudden uncontrolled forward progress. As the tip of the needle enters the epidural space, there is a simultaneous loss of resistance in the syringe, sometimes an audible ‘click’ and a feeling that the needle is moving forward more easily. The needle should not be moved any further within the epidural space, and the syringe carefully removed. No blood or CSF should drain from the needle. CSF will normally emerge from a Tuohy needle with sufficient volume and velocity to leave no doubt as to its identity, even if saline is used to detect loss of resistance. If further confirmation is required, CSF will show positive for glucose on proprietary stick testing. Detecting loss of resistance with air – the needle is moved forward in 1–2 mm increments, with frequent stops to check the loss of resistance syringe with light bounces of the plunger with the thumb of the dominant hand. If a two-handed technique is used, the wings of the Tuohy needle are held with the thumb and
ANAESTHESIA AND INTENSIVE CARE MEDICINE 7:11
forefinger of each hand, bracing the hands against the skin of the back. After each forward movement of 1–2 mm, the needle is stabilized with the non-dominant hand and tested for loss of resistance. If a single-handed technique is used, the non-dominant hand is braced against the skin to stabilize and control forward movement of the syringe/needle combination. The combination is moved forward with the dominant hand, with intermittent stops to test for loss of resistance. Inserting the catheter: once the epidural space is identified, the distance of the epidural space from the skin is calculated by counting the number of visible 1 cm markers (Lee’s markings) on the shaft of the needle and subtracting that number from 8 cm (the length of a standard Tuohy needle shaft, not including the plastic or metal hub). The catheter is inserted about 4–5 cm into the epidural space. An insertion of less than 4 cm may increase the risk of the catheter being dislodged by patient movement. An insertion greater than 6 cm increases the risk of the catheter moving from the epidural space out through an intervertebral foramen or into the CSF or subdural space, or becoming knotted within the epidural space. The catheter is inserted through the Tuohy needle into the epidural space, and the depth of insertion is noted by counting the markers on the catheter. If the catheter will not move forward beyond the needle tip into the epidural space despite firm ‘persuasion’, it is removed gently from the needle, and the needle position re-confirmed within the epidural space using the loss-of-resistance syringe. If the catheter becomes stuck after initial entry it is not withdrawn through the needle, as this may result in the tip of catheter shearing off and remaining in the epidural space. Remove both the needle and the catheter together and begin the process again. It is normal practice for the catheter to be inserted to a depth of between 15 and 20 cm. The needle is then carefully withdrawn from the epidural space, ensuring that the catheter is not withdrawn with the needle. When the needle has been removed, the catheter is gently withdrawn until the desired depth marker is just visible at the skin-puncture site. To check that CSF or blood 423
© 2006 Published by Elsevier Ltd.
Technical skills
does not run back up the catheter, it is moved below and then above the level of spine, whilst the free movement of the saline meniscus in the catheter is observed. The catheter hub and filter (0.2 μm size) are re-attached, and a sterile dressing applied to the epidural catheter site, ensuring that the catheter is securely attached to the skin of the back and over a shoulder so that the filter and hub can be secured to the anterior chest wall.
Drugs for epidural blockade Local anaesthetics: local anaesthetic drugs are the mainstay of epidural and caudal block. They are usually administered through a catheter or needle in small (5 ml) fractionated doses until a total volume of 10–15 ml for thoracic epidurals or 20–30 ml for lumbar and caudal blocks has been injected. Bupivacaine 0.5% (either in its original racemic form or in the new laevo-isomer form) is the most commonly used drug because it produces a reliable surgical quality block of 2–4 hours duration, after an onset time of 20–30 minutes. Ropivacaine 0.5% or 0.75% also produces reliable anaesthesia/analgesia with slightly less motor block than bupivacaine.
Injection of test dose: unless a ‘single-shot’ epidural block is performed by injecting the local anaesthetic directly through the needle, a test dose is usually injected through the catheter into the epidural space. Local anaesthetic (2–3 ml) with or without epinephrine is commonly used to detect an accidental subarachnoid or intravascular placement of the catheter, although the specificity of such test doses is not high. Table 1 summarizes the guidelines for performing all stages of epidural and caudal block.
Adjuvant drugs: opioids, commonly fentanyl 2 /μg/ml, when added to the local anaesthetic solution will augment the sensory blockade and improve pain scores. These effects allow a lower concentration of local anaesthetic to be used in postoperative epidural infusions, which reduces motor blockade and other unwanted effects of local anaesthetics. Other adjuvant drugs are also used to prolong the duration of bolus doses of epidural or caudal injections, or as part of the infused drug solution (see page 407).
Summary of procedures for central neuraxial blockade Before procedure Patient assessment Check for any contraindications Explain the procedure to the patient Discuss the common and significant complications Answer the patient’s questions and address concerns Obtain informed consent Check monitors, resuscitation equipment Make sure a trained assistant is available
Caudal block The sacral hiatus results from a failure of the fourth and fifth sacral vertebral laminae to fuse; instead the hiatus is covered by the sacrococcygeal membrane and can be palpated as a mid-line indentation between two sacral cornuae, which form the apex of an equilateral triangle, with the posterior superior iliac spines as the base (Figure 2). Caudal block is usually performed with the patient in the lateral position. The most proximal part of the sacral hiatus is identified with the index finger of the non-dominant hand. A 20G or 21G needle (22G intravenous cannula is preferred in small children to avoid dural puncture by needle tip) is then inserted at a perpendicular angle to the skin, through the sacral hiatus, immediately distal to the index finger. The needle encounters resistance from the sacrococcygeal membrane, and as the needle passes through the membrane a loss of resistance is detected when it enters the
During the procedure Check patient identity Obtain intravenous access Institute appropriate monitoring Position the patient appropriately Use rigorous aseptic technique Check and prepare equipment, draw drugs Explain each step to the patient Locate appropriate intervertebral space Infiltrate skin and deeper tissues with local anaesthetic Use appropriate needle (with or without catheter) Identify endpoint Inject local anaesthetic solution via needle or test dose via catheter After procedure and before surgery Position the patient Monitor heart rate, blood pressure, respiration, oxygen saturation Check the onset of sympathetic, sensory and motor block Formally record maximum height of sensory dermatomal level bilaterally Formally record intensity of motor block bilaterally (Bromage scale or similar) Observe patient for any early symptoms or signs of complications
Figure 2 Anatomical features for caudal blockade.
Table 1
ANAESTHESIA AND INTENSIVE CARE MEDICINE 7:11
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© 2006 Published by Elsevier Ltd.
Technical skills
e pidural space and makes contact with the bony ventral surface of the sacral canal. The needle is then withdrawn slightly and re-angled so that it is almost parallel to skin. The needle is then moved forward a few millimetres in a cephalad direction. If the needle is moved too far forward the dural sac, which ends at a level of S2/S3, is at risk of being pierced. The injection of 20–30 ml of local anaesthetic in an adult will produce a block of the low lumbar and sacral nerve roots. Caudal block does not cause sympathetic block, and the risk of dural puncture is low in adults. A single bolus of 20–30 ml bupivacaine 0.5% provides 3–4 hours of postoperative analgesia. In babies and young children, the dural sac terminates more caudally than in adults, and it is important not to move the needle or intravenous cannula forward in a cephalad direction more than is necessary to confirm intracaudal placement. An epidural catheter can be introduced via the caudal approach and threaded up to the lumbar/thoracic region. However, specialist experience is required to use caudal catheters for paediatric surgery.
relative effects of motor, sensory and autonomic blockade. Managing the patient successfully during surgery and the postoperative infusion rely on understanding these physiological changes, balancing fluid replacement, and the use of vagolytic and vasoconstrictors to minimize adverse effects of significant hypotension (a fall of 20% or more in systolic pressure and/or resting heart rate). The clinical effects of the block vary according to the site of injection and the volume and concentration of local anaesthetic injected. Careful monitoring of the patient and taking the appropriate action will prevent the predictable, physiological and harmless side effects of neuraxial block from becoming potentially serious complications.
Indications for central neuraxial blockade Epidural block Intraoperative and postoperative pain relief for lower limb, pelvic and lower/upper abdominal and thoracic surgery, and non-surgical pain • General surgery Gastro-oesophageal Hepatic/pancreatic Small bowel Colorectal • Vascular Aortic aneurysm repair Major vascular reconstruction • Thoracic surgery Pulmonary surgery Oesophageal surgery Some cardiac procedures • Gynaecological surgery Pelvic floor repair Vaginal hysterectomy Colposuspension Radical cancer surgery • Orthopaedic surgery Hip arthroplasty Fractured neck of femur Knee arthroplasty • Urological surgery Nephrectomy Radical prostatectomy Cystectomy/bladder reconstruction • Non-surgical pain Ischaemic pain Pancreatits Trauma (fractured ribs/sternum) Chronic and palliative pain states
Monitoring the onset of the block The effects of local anaesthetics act primarily on the segmental spinal nerve roots, although limited diffusion through the dura allows some of these effects to act on the spinal cord directly. Differential blockade of motor and sensory modalities is related to the size and therefore the sensitivity of different neurons to local anaesthetics. The small sympathetic preganglionic fibres and sensory fibres are more easily blocked than the large motor fibres, and vasodilatation is an early sign of the onset of the block, which usually manifests first in the veins of the feet, with flushing and increased warmth. The level of sympathetic block is normally two segments higher than sensory block level, whilst motor block is up to two segments lower than the sensory block. Because of the differing segmental height for the sympathetic, sensory and motor modalities, it is important to formally monitor and record the sensory and motor block as the epidural begins to work, and to ensure the sensory block is high enough for the intended surgery and that the degree of motor block is appropriate. The upper dermatome limit on both sides should be noted on the anaesthetic record along with the Bromage motor block score for both legs (Table 2). As the block develops, physiological changes occur due to the
A modified Bromage motor power score Score
Criteria
Degree of block
1 2
Full flexion of knees and ankles Just able to flex knees, full flexion of ankles Unable to flex knees, partial ankle flexion Unable to move legs or feet
None Partial
3 4
Caudal block Postoperative pain relief in adults, especially perineal surgery (vaginal repairs, haemorrhoidectomy, external genitalia). All sub-umbilical procedures in children
Almost complete Complete
Table 2
ANAESTHESIA AND INTENSIVE CARE MEDICINE 7:11
Table 3
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© 2006 Published by Elsevier Ltd.
Technical skills
• Autonomic block: limited sympathetic blockade below L1. Sacral outflow of parasympathetic system is blocked.
Contraindications to central neuraxial blockade
Mid-to-low thoracic block (T6–T12) • Sensory blockade of abdominal organs and skin of anterior abdominal wall. • Motor block of anterior abdominal wall muscles and lower intercostal muscles. • Block of sympathetic chain, including coeliac ganglion, causing marked hypotension with compensatory tachycardia, loss of sweating and unopposed parasympathetic activity (maintains gut tone and motility).
Absolute Patient refusal Moderate or severe bleeding diathesis/coagulopathy Infection at the site of insertion Proven local anaesthetic allergy Relative Untreated bacteraemia/septicaemia Some thromboprophylaxis regimens Raised intracranial pressure Hypovolaemic shock Pre-existing neurological injury/disease state Severe valvular cardiac disease /fixed cardiac output states Previous back surgery at the proposed site of blockade
High thoracic block (T1–T5) • Sensory block of chest wall, thoracic viscera and medial aspect of upper arm. • Motor block of upper intercostal muscles and some arm weakness. • Block of sympathetic cardiac accelerator fibres, causing unopposed vagal tone (bradycardia, hypotension and possibly cardiovascular collapse). Epidural and caudal blockade are extensively used in both adult and paediatric practice. Table 3 lists some of the common indications for their use. Other less common indications exist for specialist use. There are a number of absolute and relative contraindications to epidural and caudal blockade (Table 4). ◆
Table 4
Lumbo-sacral block (L1–S5) • Sensory blockade of pelvic visceral organs and somatic tissues from inguinal region and perineum to buttocks and whole of lower limbs. • Motor block of pelvic sphincters, hip, knee and ankle flexors and extensors.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 7:11
426
© 2006 Published by Elsevier Ltd.
Techniques of epidural block
Performing the block A thorough preoperative assessment is essential to explain the procedure to the patient, discuss the common and significant complications and obtain informed consent. A clean, well lit, quiet environment is required, and secure intravenous access and appropriate monitoring should be in place before starting the block. A suitable epidural pack is needed. Packs containing sterile disposable equipment, a loss-of-resistance syringe, Tuohy needle, catheter, and bacterial filters are widely available. Reusable equipment of this type is no longer appropriate or cost effective.
Barrie Fischer Maheshwar Chaudhari
Abstract
Position of the patient The patient positions for an epidural block are the same as for spinal anaesthesia, and are described on page 418. The sitting position avoids the problems of the lateral position but increases cerebrospinal fluid (CSF) hydrostatic pressure and may increase the chances of an inadvertent dural puncture. The lateral position is more comfortable for some patients and allows pre-procedure sedation to be used. Figure 1 demonstrates both positions, and indicates Tuffier’s line.
Spinal, epidural and caudal blockade are the three components of central neuraxial blockade and provide surgical anaesthesia and postoperative analgesia for sub-umbilical surgery (thoracic epidurals provide effective analgesia but not anaesthesia for thoracic and upper abdominal surgery). While spinal and caudal blocks are usually performed as single-shot bolus techniques in adults and provide 2–4 hours postoperative analgesia, epidural techniques can provide prolonged postoperative analgesia by inserting an epidural catheter and infusing a dilute local anaesthetic and opioid drug combination. Although useful regional anaesthetic techniques, all three are invasive procedures, can be technically difficult, and have the potential to cause serious adverse events (direct needle trauma to the spinal cord or the spinal nerve roots, vertebral canal haematoma and meningitis or epidural abscess) if not done to a high standard and managed appropriately. Epidural and caudal blockade have a number of synonyms, which can be confusing. The terms ‘epidural’ (extradural, peridural) and ‘caudal’ (sacral, epidural) are used throughout this article.
Approaches to the epidural space A sterile technique with full aseptic precautions should be used. The skin over the chosen vertebral interspace is infiltrated with lidocaine (1%) using a 25G or 26G needle for the skin wheal. The underlying tissue is then infiltrated using a 21G needle. Some anaesthetists make a small cut in the skin to facilitate insertion of the blunt-tipped Tuohy needle.
Keywords anaesthetic technique; caudal; regional anaesthesia; epidural
The mid-line approach is commonly used to perform lumbar or lower thoracic epidural block. A Tuohy needle is introduced in the mid-line and directed slightly cephalad between the two spinous processes of the desired interspinous space. The needle passes through the skin and supraspinous ligaments, into the interspinous ligament. At this point the Tuohy needle stylet is removed and the loss-of-resistance syringe is attached to detect loss of resistance as the needle traverses the ligamentum flavum and enters the epidural space, which is usually 3–5 cm from the skin in the mid-line. A sudden ‘give’ may be felt as the needle tip exits the ligamentum flavum and the loss-of-resistance indicator (air or saline) is expelled into the epidural space.
Epidural block Epidural anaesthesia was described by Sicard and Catheline in 1901, but became popular only after the introduction of amide local anaesthetic agents and epidural catheters in the late 1960s. Because of its versatility, epidural analgesia is probably the most commonly used regional technique in the UK. It can be performed in the sacral (caudal), lumbar, thoracic or cervical regions, although lumbar block is used the most frequently.
The paramedian approach is more commonly used in the upper thoracic region because of the long, sloping spinous processes and narrow interspinous spaces. The Tuohy needle is inserted at about 1.0–1.5 cm laterally from mid-point of the spinous process immediately above the level of the desired intervertebral space. The needle is then moved forward, perpendicular to the skin, through the underlying subcutaneous tissue and muscle, until it strikes the vertebral lamina. The needle is then withdrawn slightly. The loss-of-resistance syringe is then attached and redirected cephalad and medially so that the needle is walked off the lamina until it pierces the ligamentum flavum and enters the epidural space.
Barrie Fischer, MBChB, FRCA, is Consultant Anaesthetist at the Alexandra Hospital, Redditch (Worcestershire Acute Hospitals NHS Trust), UK. He qualified from the University of Bristol and trained in Truro, Cambridge and Cardiff. His main interests are the role of regional anaesthesia in surgery and acute pain management. He is the immediate past chairman of Great Britain and Ireland on the Board of the European Society of Regional Anaesthesia. Maheshwar Chaudhari, MD, FRCA, is Specialist Registrar in anaesthesia on the Midland Deanery Rotational Scheme. He qualified from the University of Poona, India, and trained in anaesthesia in India, Peterborough, and the West Midlands area, UK. His interests are chronic pain management and regional anaesthesia.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 7:11
Identification of loss of resistance: the pressure in the epidural space is usually sub-atmospheric, particularly in the thoracic region whilst the patient is in the sitting position. In the lateral 422
© 2006 Published by Elsevier Ltd.
Technical skills
Figure 1 Sitting (a) and lateral (b) positions for spinal and epidural block. The dotted line represents Tuffier’s line, which joins the two iliac crests and passes through the L3/L4 interspace or across the spinous process of L4. Patient positions for spinal and epidural block.
position and in the lumbar spine the pressure is less reliably sub-atmospheric. Some early methods of identifying the epidural space (e.g. Macintosh balloon) relied on detecting the negative pressure in the epidural space. The two methods currently used rely on the loss of resistance to the injection of saline or air as the needle penetrates the ligamentum flavum and enters the epidural space. A low-resistance syringe containing 0.9% saline or air is attached to the hub of the Tuohy needle after the tip is moved into the interspinous ligament (mid-line approach) or once the lamina has been identified (paramedian approach). There are advocates for the use of both air and saline for detecting entry into the epidural space and each technique has its own benefits and drawbacks. To minimize bubble formation, dilution of local anaesthetic and the difficulty discerning saline and CSF, a maximum of 3 ml of air or saline can be used. Detecting loss of resistance with saline – the Tuohy needle and syringe combination is moved slowly and continually with the dominant hand, whilst constant pressure is maintained on the plunger of the loss-of-resistance syringe. The non-dominant hand is braced against the skin of the patient’s back to stabilize the needle/syringe combination and prevent sudden uncontrolled forward progress. As the tip of the needle enters the epidural space, there is a simultaneous loss of resistance in the syringe, sometimes an audible ‘click’ and a feeling that the needle is moving forward more easily. The needle should not be moved any further within the epidural space, and the syringe carefully removed. No blood or CSF should drain from the needle. CSF will normally emerge from a Tuohy needle with sufficient volume and velocity to leave no doubt as to its identity, even if saline is used to detect loss of resistance. If further confirmation is required, CSF will show positive for glucose on proprietary stick testing. Detecting loss of resistance with air – the needle is moved forward in 1–2 mm increments, with frequent stops to check the loss of resistance syringe with light bounces of the plunger with the thumb of the dominant hand. If a two-handed technique is used, the wings of the Tuohy needle are held with the thumb and
ANAESTHESIA AND INTENSIVE CARE MEDICINE 7:11
forefinger of each hand, bracing the hands against the skin of the back. After each forward movement of 1–2 mm, the needle is stabilized with the non-dominant hand and tested for loss of resistance. If a single-handed technique is used, the non-dominant hand is braced against the skin to stabilize and control forward movement of the syringe/needle combination. The combination is moved forward with the dominant hand, with intermittent stops to test for loss of resistance. Inserting the catheter: once the epidural space is identified, the distance of the epidural space from the skin is calculated by counting the number of visible 1 cm markers (Lee’s markings) on the shaft of the needle and subtracting that number from 8 cm (the length of a standard Tuohy needle shaft, not including the plastic or metal hub). The catheter is inserted about 4–5 cm into the epidural space. An insertion of less than 4 cm may increase the risk of the catheter being dislodged by patient movement. An insertion greater than 6 cm increases the risk of the catheter moving from the epidural space out through an intervertebral foramen or into the CSF or subdural space, or becoming knotted within the epidural space. The catheter is inserted through the Tuohy needle into the epidural space, and the depth of insertion is noted by counting the markers on the catheter. If the catheter will not move forward beyond the needle tip into the epidural space despite firm ‘persuasion’, it is removed gently from the needle, and the needle position re-confirmed within the epidural space using the loss-of-resistance syringe. If the catheter becomes stuck after initial entry it is not withdrawn through the needle, as this may result in the tip of catheter shearing off and remaining in the epidural space. Remove both the needle and the catheter together and begin the process again. It is normal practice for the catheter to be inserted to a depth of between 15 and 20 cm. The needle is then carefully withdrawn from the epidural space, ensuring that the catheter is not withdrawn with the needle. When the needle has been removed, the catheter is gently withdrawn until the desired depth marker is just visible at the skin-puncture site. To check that CSF or blood 423
© 2006 Published by Elsevier Ltd.
Technical skills
does not run back up the catheter, it is moved below and then above the level of spine, whilst the free movement of the saline meniscus in the catheter is observed. The catheter hub and filter (0.2 μm size) are re-attached, and a sterile dressing applied to the epidural catheter site, ensuring that the catheter is securely attached to the skin of the back and over a shoulder so that the filter and hub can be secured to the anterior chest wall.
Drugs for epidural blockade Local anaesthetics: local anaesthetic drugs are the mainstay of epidural and caudal block. They are usually administered through a catheter or needle in small (5 ml) fractionated doses until a total volume of 10–15 ml for thoracic epidurals or 20–30 ml for lumbar and caudal blocks has been injected. Bupivacaine 0.5% (either in its original racemic form or in the new laevo-isomer form) is the most commonly used drug because it produces a reliable surgical quality block of 2–4 hours duration, after an onset time of 20–30 minutes. Ropivacaine 0.5% or 0.75% also produces reliable anaesthesia/analgesia with slightly less motor block than bupivacaine.
Injection of test dose: unless a ‘single-shot’ epidural block is performed by injecting the local anaesthetic directly through the needle, a test dose is usually injected through the catheter into the epidural space. Local anaesthetic (2–3 ml) with or without epinephrine is commonly used to detect an accidental subarachnoid or intravascular placement of the catheter, although the specificity of such test doses is not high. Table 1 summarizes the guidelines for performing all stages of epidural and caudal block.
Adjuvant drugs: opioids, commonly fentanyl 2 /μg/ml, when added to the local anaesthetic solution will augment the sensory blockade and improve pain scores. These effects allow a lower concentration of local anaesthetic to be used in postoperative epidural infusions, which reduces motor blockade and other unwanted effects of local anaesthetics. Other adjuvant drugs are also used to prolong the duration of bolus doses of epidural or caudal injections, or as part of the infused drug solution (see page 407).
Summary of procedures for central neuraxial blockade Before procedure Patient assessment Check for any contraindications Explain the procedure to the patient Discuss the common and significant complications Answer the patient’s questions and address concerns Obtain informed consent Check monitors, resuscitation equipment Make sure a trained assistant is available
Caudal block The sacral hiatus results from a failure of the fourth and fifth sacral vertebral laminae to fuse; instead the hiatus is covered by the sacrococcygeal membrane and can be palpated as a mid-line indentation between two sacral cornuae, which form the apex of an equilateral triangle, with the posterior superior iliac spines as the base (Figure 2). Caudal block is usually performed with the patient in the lateral position. The most proximal part of the sacral hiatus is identified with the index finger of the non-dominant hand. A 20G or 21G needle (22G intravenous cannula is preferred in small children to avoid dural puncture by needle tip) is then inserted at a perpendicular angle to the skin, through the sacral hiatus, immediately distal to the index finger. The needle encounters resistance from the sacrococcygeal membrane, and as the needle passes through the membrane a loss of resistance is detected when it enters the
During the procedure Check patient identity Obtain intravenous access Institute appropriate monitoring Position the patient appropriately Use rigorous aseptic technique Check and prepare equipment, draw drugs Explain each step to the patient Locate appropriate intervertebral space Infiltrate skin and deeper tissues with local anaesthetic Use appropriate needle (with or without catheter) Identify endpoint Inject local anaesthetic solution via needle or test dose via catheter After procedure and before surgery Position the patient Monitor heart rate, blood pressure, respiration, oxygen saturation Check the onset of sympathetic, sensory and motor block Formally record maximum height of sensory dermatomal level bilaterally Formally record intensity of motor block bilaterally (Bromage scale or similar) Observe patient for any early symptoms or signs of complications
Figure 2 Anatomical features for caudal blockade.
Table 1
ANAESTHESIA AND INTENSIVE CARE MEDICINE 7:11
424
© 2006 Published by Elsevier Ltd.
Technical skills
e pidural space and makes contact with the bony ventral surface of the sacral canal. The needle is then withdrawn slightly and re-angled so that it is almost parallel to skin. The needle is then moved forward a few millimetres in a cephalad direction. If the needle is moved too far forward the dural sac, which ends at a level of S2/S3, is at risk of being pierced. The injection of 20–30 ml of local anaesthetic in an adult will produce a block of the low lumbar and sacral nerve roots. Caudal block does not cause sympathetic block, and the risk of dural puncture is low in adults. A single bolus of 20–30 ml bupivacaine 0.5% provides 3–4 hours of postoperative analgesia. In babies and young children, the dural sac terminates more caudally than in adults, and it is important not to move the needle or intravenous cannula forward in a cephalad direction more than is necessary to confirm intracaudal placement. An epidural catheter can be introduced via the caudal approach and threaded up to the lumbar/thoracic region. However, specialist experience is required to use caudal catheters for paediatric surgery.
relative effects of motor, sensory and autonomic blockade. Managing the patient successfully during surgery and the postoperative infusion rely on understanding these physiological changes, balancing fluid replacement, and the use of vagolytic and vasoconstrictors to minimize adverse effects of significant hypotension (a fall of 20% or more in systolic pressure and/or resting heart rate). The clinical effects of the block vary according to the site of injection and the volume and concentration of local anaesthetic injected. Careful monitoring of the patient and taking the appropriate action will prevent the predictable, physiological and harmless side effects of neuraxial block from becoming potentially serious complications.
Indications for central neuraxial blockade Epidural block Intraoperative and postoperative pain relief for lower limb, pelvic and lower/upper abdominal and thoracic surgery, and non-surgical pain • General surgery Gastro-oesophageal Hepatic/pancreatic Small bowel Colorectal • Vascular Aortic aneurysm repair Major vascular reconstruction • Thoracic surgery Pulmonary surgery Oesophageal surgery Some cardiac procedures • Gynaecological surgery Pelvic floor repair Vaginal hysterectomy Colposuspension Radical cancer surgery • Orthopaedic surgery Hip arthroplasty Fractured neck of femur Knee arthroplasty • Urological surgery Nephrectomy Radical prostatectomy Cystectomy/bladder reconstruction • Non-surgical pain Ischaemic pain Pancreatits Trauma (fractured ribs/sternum) Chronic and palliative pain states
Monitoring the onset of the block The effects of local anaesthetics act primarily on the segmental spinal nerve roots, although limited diffusion through the dura allows some of these effects to act on the spinal cord directly. Differential blockade of motor and sensory modalities is related to the size and therefore the sensitivity of different neurons to local anaesthetics. The small sympathetic preganglionic fibres and sensory fibres are more easily blocked than the large motor fibres, and vasodilatation is an early sign of the onset of the block, which usually manifests first in the veins of the feet, with flushing and increased warmth. The level of sympathetic block is normally two segments higher than sensory block level, whilst motor block is up to two segments lower than the sensory block. Because of the differing segmental height for the sympathetic, sensory and motor modalities, it is important to formally monitor and record the sensory and motor block as the epidural begins to work, and to ensure the sensory block is high enough for the intended surgery and that the degree of motor block is appropriate. The upper dermatome limit on both sides should be noted on the anaesthetic record along with the Bromage motor block score for both legs (Table 2). As the block develops, physiological changes occur due to the
A modified Bromage motor power score Score
Criteria
Degree of block
1 2
Full flexion of knees and ankles Just able to flex knees, full flexion of ankles Unable to flex knees, partial ankle flexion Unable to move legs or feet
None Partial
3 4
Caudal block Postoperative pain relief in adults, especially perineal surgery (vaginal repairs, haemorrhoidectomy, external genitalia). All sub-umbilical procedures in children
Almost complete Complete
Table 2
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Table 3
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Technical skills
• Autonomic block: limited sympathetic blockade below L1. Sacral outflow of parasympathetic system is blocked.
Contraindications to central neuraxial blockade
Mid-to-low thoracic block (T6–T12) • Sensory blockade of abdominal organs and skin of anterior abdominal wall. • Motor block of anterior abdominal wall muscles and lower intercostal muscles. • Block of sympathetic chain, including coeliac ganglion, causing marked hypotension with compensatory tachycardia, loss of sweating and unopposed parasympathetic activity (maintains gut tone and motility).
Absolute Patient refusal Moderate or severe bleeding diathesis/coagulopathy Infection at the site of insertion Proven local anaesthetic allergy Relative Untreated bacteraemia/septicaemia Some thromboprophylaxis regimens Raised intracranial pressure Hypovolaemic shock Pre-existing neurological injury/disease state Severe valvular cardiac disease /fixed cardiac output states Previous back surgery at the proposed site of blockade
High thoracic block (T1–T5) • Sensory block of chest wall, thoracic viscera and medial aspect of upper arm. • Motor block of upper intercostal muscles and some arm weakness. • Block of sympathetic cardiac accelerator fibres, causing unopposed vagal tone (bradycardia, hypotension and possibly cardiovascular collapse). Epidural and caudal blockade are extensively used in both adult and paediatric practice. Table 3 lists some of the common indications for their use. Other less common indications exist for specialist use. There are a number of absolute and relative contraindications to epidural and caudal blockade (Table 4). ◆
Table 4
Lumbo-sacral block (L1–S5) • Sensory blockade of pelvic visceral organs and somatic tissues from inguinal region and perineum to buttocks and whole of lower limbs. • Motor block of pelvic sphincters, hip, knee and ankle flexors and extensors.
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