Introduction		Factors affecting epidural anaesthesia
Indications		Physiological effects of epidural blockade
Contradictions		Epidural management and choice of drugs
Epidurals and Anticoagulants		Complications and side effects
Anatomy of the Epidural Space		Further Reading
Technique of Epidural Anaesthesia

Introduction

Epidural anaesthesia is a central neuraxial block technique with many applications. The epidural space was first described by Corning in 1901, and Fidel Pages first used epidural anaesthesia in humans in 1921. In 1945 Tuohy introduced the needle which is still most commonly used for epidural anaesthesia. Improvements in equipment, drugs and technique have made it a popular and versatile anaesthetic technique, with applications in surgery, obstetrics and pain control. Both single injection and catheter techniques can be used. Its versatility means it can be used as an anaesthetic, as an analgesic adjuvant to general anaesthesia, and for postoperative analgesia in procedures involving the lower limbs, perineum, pelvis, abdomen and thorax. 0

Indications

General

Epidural anaesthesia can be used as sole anaesthetic for procedures involving the lower limbs, pelvis, perineum and lower abdomen. It is possible to perform upper abdominal and thoracic procedures under epidural anaesthesia alone, but the height of block required, with its attendant side effects, make it difficult to avoid significant patient discomfort and risk. The advantage of epidural over spinal anaesthesia is the ability to maintain continuous anaesthesia after placement of an epidural catheter, thus making it suitable for procedures of long duration. This feature also enables the use of this technique into the postoperative period for analgesia, using lower concentrations of local anaesthetic drugs or in combination with different agents.

Specific uses

• Hip and knee surgery. Internal fixation of a fractured hip is associated with less blood loss when central neuraxial block is used. The rate of deep venous thrombosis is reduced in patients undergoing total hip and knee replacement, when epidural anaesthesia is used.
• Vascular reconstruction of the lower limbs. Epidural anaesthesia improves distal blood flow in patients undergoing arterial reconstruction surgery.
• Amputation. Patients given epidural anaesthesia 48-72 hours prior to lower limb amputation may have a lower incidence of phantom limb pain following surgery, although this has not been substantiated.
• Obstetrics. Epidural analgesia is indicated in obstetric patients in difficult or high-risk labour, e.g. breech, twin pregnancy, pre-eclampsia and prolonged labour. Furthermore, Caesarean section performed under central neuraxial block is associated with a lower maternal mortality owing to anaesthetic factors than under general anaesthetic.
• Low concentration local anaesthetics, opioids, or combinations of both are effective in the control of postoperative pain in patients undergoing abdominal and thoracic procedures. Epidural analgesia has been shown to minimise the effects of surgery on cardiopulmonary reserve, i.e. diaphragmatic splinting and the inability to cough adequately, in patients with compromised respiratory function, such as those with chronic obstructive airway disease, morbid obesity and in the elderly. Epidural analgesia allows earlier mobilization, reduces the risk of deep venous thrombosis, and allows better cooperation with chest physiotherapy, preventing chest infections.
• Thoracic trauma with rib or sternum fractures. Adequate analgesia in patients with thoracic trauma improves respiratory function by allowing the patient to breathe adequately, cough and cooperate with chest physiotherapy. 

Contraindications

Absolute

• Patient refusal
• Coagulopathy. Insertion of an epidural needle or catheter into the epidural space may cause traumatic bleeding into the epidural space. Clotting abnormalities may lead to the development of a large haematoma leading to spinal cord compression.
• Therapeutic anticoagulation. As above
• Skin infection at injection site. Insertion of the epidural needle through an area of skin infection may introduce pathogenic bacteria into the epidural space, leading to serious complications such as meningitis or epidural abscess.
• Raised intracranial pressure. Accidental dural puncture in a patient with raised ICP may lead to brainstem herniation (coning).
• Hypovolaemia. The sympathetic blockade produced by epidurals, in combination with uncorrected hypovolaemia, may cause profound circulatory collapse.

Relative

• Uncooperative patients may be impossible to position correctly, and be unable to remain still enough to safely insert an epidural.
• Pre-existing neurological disorders, such as multiple sclerosis, may be a contraindication, because any new neurological symptoms may be ascribed to the epidural.
• Fixed cardiac output states. Probably relative rather than absolute. This includes aortic stenosis, hypertrophic obstructive cardiomyopathy (HOCM), mitral stenosis and complete heart block. Patients with these cardiovascular abnormalities are unable to increase their cardiac output in response to the peripheral vasodilatation caused by epidural blockade, and may develop profound circulatory collapse which is very difficult to treat.
• Anatomical abnormalities of vertebral column may make the placement of an epidural technically impossible.
• Prophylactic low dose heparin (see discussion below) 

Epidurals and anticoagulants

(see also page 7 )

• Full oral anticoagulation with warfarin or standard heparin (SH) are absolute contraindications to epidural blockade.
• Partial anticoagulation with low molecular weight heparin (LMWH) or low dose warfarin (INR <1.5) are relative contraindications.
• Minihep (low dose standard heparin (SH), 5,000units bd s/c is not associated with an increased risk of epidural haematoma. Wait for 4 hours after a dose before performing epidural. Minihep/SH should not be given until 1 hour following epidural injection. These guidelines also apply for removal of epidural catheters.
• LMWH (<40mg enoxaparin and dalteparin): allow 12hr interval between LMWH administration and epidural; this also applies to removal of epidural catheters.
• NSAID's (including aspirin) do not increase the risk of epidural haematoma.
• Intraoperative anticoagulation using 5000units i/v heparin following epidural/spinal injection appears safe, but careful postoperative observations are recommended. Bloody tap or blood in epidural catheter is controversial. Some teams delay surgery for 12hr, others (if pre-op coagulation normal) delay i/v bolus of heparin for 1hour.
• Fibrinolytic and thrombolytic drugs: avoid epidural block for 24 hrs, check clotting prior to insertion.
• Thrombocytopaenia: epidurals are relatively contraindicated below platelet count of 100,000/mm³.
• An epidural haematoma should be suspected in patients who complain of severe back pain a few hours/days following any central neuraxial block or with any prolonged or abnormal neurological deficit (including. sensory loss, paraesthesiae, muscle weakness and disturbance of bladder control and anal sphincter tone). A high index of suspicion is required, with early orthopaedic or neurosurgical referral for decompression of the haematoma. Even with early recognition, the morbidity of this condition is still very high. 

Anatomy of the epidural space (figure 1)

The epidural space is that part of the vertebral canal not occupied by the dura mater and its contents. It is a potential space that lies between the dura and the periosteum lining the inside of the vertebral canal. It extends from the foramen magnum to the sacral hiatus. The anterior and posterior nerve roots in their dural covering pass across this potential space to unite in the intervertebral foramen to form segmental nerves. The anterior border consists of the posterior longitudinal ligament covering the vertebral bodies, and the intervertebral discs. Laterally, the epidural space is bordered by the periosteum of the vertebral pedicles, and the intervertebral foraminae. Posteriorly, the bordering stuctures are the periosteum of the anterior surface of the laminae and articular processes and their connecting ligaments, the periosteum of the root of the spines, and the interlaminar spaces filled by the ligamentum flavum. The space contains venous plexuses and fatty tissue which is continuous with the fat in the paravertebral space.

(Continued ...)

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