Regional Anaesthesia Neuraxial Blockade Neuraxial (central) block with subarachnoid (SAB) or epidural (EDB) injection of local anaesthetic (LA) can provide excellent peri-operative anaesthesia and analgesia with many advantages over general anaesthesia. ADVANTAGES Comparative advantages over general anaesthesia • Stress response and the hypercoagulable state due to surgery are minimized. • Pre-emptive, intra, and post operative analgesia • Reduced bleeding • Muscle relaxation with spontaneous respiration • Thrombo embolism is reduced in the high risk patient. • Safer recovery, early mobilization and feeding, and better respiratory outcome • Minimal equipment and drugs which reduces cost A voids disadvantages of general anaesthesia • Unconsciousness, loss of protective reflexes, difficult airway • Awareness, PONY, sore throat, hangover • Gaseous pollution • Equipment hazards • High cost CONTRAINDICATIONS TO CENTRAL BLOCKADE Absolute • Patient refusal of technique • Sepsis at the site of injection • Coagulation disorders and anticoagulant therapy • Hypovolaemia and severe fixed output states Relative • Cardiac compromised patients and severe hypertension • Neurological disorders e.g. multiple sclerosis (medico-legal) • Previous surgery to the spine (technically difficult) • Systemic sepsis (risk of epidural abscess or meningitis) • LMWH or aspirin (see page 5.11)
EFFECTS OF NEURAXIAL BLOCKADE 1. Sensory block Touch and deep pressure nerves (Af) ) are not as densely blocked as those relaying pain (Ao and C). This should be explained to the patient. 2. Motor block Level of motor block is lower than sensory block by 2-3 segments in SAB and 5-6 segments in EDB as deeply situated larger motor (Aa) and proprioceptor nerves require higher concentrations. 3. Sympathetic block Sympathetic block is the highest level, as these small diameter nerves are blocked by very low concentrations of local anaesthetics. If the block is above TIO, hypotension occurs due to reduced cardiac output. This is due to reduced venous return (venodilatation) and systemic vascular resistance (vasodilatation). Hypotension is minimized by compensatory tachycardia and vasoconstriction above the level of block. Bradycardia occurs if cardiac accelerator nerves are blocked (Tl-T4). 4. Parasympathetic overaction The gut is contracted and bladder sensation is lost. RELEVANT ANATOMY AND LANDMARKS Spinal cord ends at Ll-2 in adults and L3 in children (rarely lower). Dura mater extends to S2/3. Tuffier' s line at the level of the iliac crests crosses the L4 vertebral spine with the L3/ L4 space above and the L4/5 space below it. Vertebral spinal processes define the midline. If difficult to identify, ask the patient to indicate the midline. Epidural space is widest at L3/4 (Smm) and narrows cranially to a minimum of 2mm at C7.
LOCAL ANAESTHETIC AGENTS (see page 19.23 for toxicity) Lignocaine : Low lipid solubility and potency (use 0.5-2% ); low pKa 7.9 (onset 5-10 min.); low protein binding 70% (duration short 30-60 min); maximum safe dose (MSD) 3 mg/kg. Vasodilates, so use with adrenaline to increase duration to 2-3h, and MSD to 7 mg/kg. Bupivacaine: High lipid solubility (use 0.1-0.5%); high pKa 8.1(onset10-15min); high protein binding 95% (duration 2-4h). No vasodilatation. MSD 2mg/kg. Ropivacaine : Pure 'S' enantiomer of bupivacaine, with less lipophylicity, toxicity, and motor block, and therefore most useful for nerve blocks, labour and post-operative pain relief. Use 0.2%. Onset 10 min. Duration 2-6h. MSD 3-4mg/kg. PRE-OPERATIVE ASSESSMENT Similar to that ofgeneral anaesthesia but should specifically include : 1. An examination of the spine (kyphoscoliosis, skin lesions, local sepsis and fat deposition which renders landmark identification difficult) 2. Evaluation of coagulopathy and anti coagulant therapy (see page 5.11) 3. Informed consent with explanation of technique, advantages and risks TECHNIQUE 1. Check anaesthetic machine, resuscitation equipment and drugs ( vasopressors ). 2. Set up a rapid intravenous infusion of saline (0.9%NaCl). 3. Monitor pulse, NIBP, heart rate and Sp02• Precautions I. Do not place antiseptic solutions on the equipment tray as antiseptics and talc in the sub-arachnoid space may cause chemical meningitis. 2. Ensure asepsis with cap, mask, scrub up, sterile gown and gloves. Clean skin with iodine and 70% alcohol. 3. Antiseptics must dry on the skin before the needle is inserted. 4. If there is shooting pain or paraesthesia after insertion of the needle, withdraw the needle slightly and ensure that there is no pain before proceeding. Never inject the LA if the patU!nt complains of pain (to avoid neurological sequelae). Positions • The seated position is the easiest. Sit patient on the operating table side-ways with the legs on a stool, and arms crossed on a pillow placed on the lap. Ask the patient to flex the neck and arch the back to open up the spinal interspaces. • Lateral decubitus (foetal) position with the hips and knees maxhnally flexed and the chest and neck flexed towards the knees (Fig. 6.1 ). Identify landmarks Select the lowest lumbar space L3/4 or L4/5 (safest) to avoid the conus medullaris. Midline approach : just below the mid point between two spines Paramedian approach: 1-2 finger breadths lateral (to bypass calcified ligaments) 5
ASSESSMENT OF BLOCK Autonomic block by appreciation of cold (spirit swab or cold water) Sensory block by pin prick only if necessary (avoid hurting the patient) Motor block by Bromage scale I. No block : Able to lift the legs against gravity : Able to flex the knees II. Partial block III. Almost complete block: Unable to flex the knees but able to flex feet N. Complete block : Unable to flex knees and feet. MANAGEMENT OF PATIENT AFTER NEURAXIAL BLOCK 1. Position carefully to avoid strain on ligaments in the paralyzed areas. A pillow under the shoulders or table tilt can control the spread of block. 2. Oxygen should be given especially in the elderly and sedated patients. 3. Monitoring • NIBP, ECG, and Sp02 • Level of consciousness and verbal contact indicates adequacy of cerebral perfusion • Ventilation, speech, cough and handgrip if reduced, indicates a block above Tl 4. Anaesthetist's presence is crucial. Never leave the patient unattended. Sedation • Do not use sedation as a substitute for an inadequate block. • Elderly may become disorientated, restless, un-cooperative with benzodiazepines and phenothiazines. • Aim for drowsiness, but maintain verbal contact, and patient co-operation. • If disorientation occurs, give GA in preference to further sedation. • If sedation or light GA is used, watch for airway obstruction, hypoxaemia, and hypotension particularly in the elderly. • Drugs : midllZolam 2mg, fentanyl 50µg, promethazine 25mg Ramsay Sedation Score (Aim for 2 or 3) 1. Awake : Anxious I agitated I restless 2. Awake : Co-operative, orientated, tranquil 3. Awake : Drowsy, responds to commands only 4. Asleep : Brisk response to glabella tap or loud noise 5. Asleep : Sluggish response to glabella tap 6. No response
Sub Arachnoid Anaesthesia (SAB) SAB is a simple, easy, cheap technique, with a clearer end-point and therefore is more popular than EDB. TECHNIQUE Needle Use 25/27G pencil point needles (Whitacre I Spratte) to avoid post dural puncture headaches. (Incidence 5% with 25G and 1 % with 27G). Use 22G in the elderly if the ligaments are calcified. Drugs Hyperbaric bupivacaine (S.G. 1.02 with 8% dextrose), 0.5% (5mg/ml), 10-15mg Fentanyl 10-15 µg improves quality of block specially if the viscera are handled. Morphine I diamorphine 0.2mg increases duration of analgesia Injection 1. With a 27G needle, raise a wheal of 2% lignocaine at the point of injection. 2. Insert the introducer needle with a 15° cephalad tilt to <3 cm to avoid the dura mater. 3. Insert the spinal needle through it and feel two clicks as it passes the ligamentum flavum and dura mater. A flash back of CSF will be seen. 4. Withdraw the needle immediately if the patient complains of shooting pain. 5. Fix the needle with the non dominant hand, attach the syringe containing drug, (1.5ml for perinea! and 3ml for a high block), and inject over 15 seconds. TECHNICAL PROBLEMS
If the needle strikes bone, withdraw to subcutaneous level before changing the direction of the needle (Fig. 6.2). If bone is then encountered at a deeper level, the change of direction is correct. If the bone encountred is more superficially, change of direction is incorrect. In the lateral position the skin crease sags and gives a false idea of the midline. In the paramedian approach, insert the needle 1 finger breadth lateral to the point of mid line approach and direct it 15° medially. If the lamina is contacted, withdraw slightly, re-inserting the needle 30° cephalad to pass over the lamina and enter the sub-arachnoid space. In scoliosis, the approach should be lateral rather than midline, with the point of injection on the convex part of the scoliotic spinal curve where the transverse processes are splayed out. FACTORS AFFECTING SPREAD OF DRUG IN THE SUBARACHNOID SPACE LUM&Alt Figure 6.3 The spinal curves in the supine position. 1. Gravity Hyperbaric solutions : spread is markedly influenced by gravity and therefore the position of the patient in the first 15 minutes is important. In the supine horizontal position, hyperbaric solutions will spread towards the trough of the thoracic spine at TS (Fig. 6.3 ). Upward spread can be limited by placing a pillow under the shoulders. If seated for 3-5minutes after the injection, a saddle block will be obtained. 2. Barbotage and rapid injection increases spread, but levels are unpredictable. 3. Drug volume : 1-3 ml depending on the level of the block required. Heavy bupivacaine: l.5ml for saddle block, 2.5ml for TlO, 3ml for T4. Volume should be reduced due to a tendency to higher than normal levels in: o Pregnancy and obesity (reduced subarachnoid space due to increase of blood vessels and fat in the epidural space) o Height below 5 ft. Age has no significant correlation with levels of block for spinal anaesthesia.
Epidural Anaesthesia (EDB) The epidural space is a potential space between the ligamentum flavum and the dura mater, occupied by areolar tissue, loose fat and the internal vertebral venous plexus. The ligamentum flavum and the epidural space are both widest (5mm) at L3/4. TECHNIQUE Needle Use 18G Tuohy needles (8, 9 or 11 cm length) as the curved Huber tip decreases the possibility of dural puncture and facilitates passage of the catheter. Note the 1 cm markings on the needle. Injection 1. Raise a wheal with 2% lignocaine ( 27G needle) at the selected point. 2. Infiltrate the expected path of the epidural needle via a moving needle to avoid intravenous injection. Wait 30 seconds for lignocaine to act. 3. Insert the epidural needle through the supra-spinous ligament. 4. Attach a syringe with 7ml of saline. Steady the back of the non-dominant hand against the back of the patient. Hold the hub of the needle firmly, and push the needle inwards steadily and continuously. Simultaneously, hold the syringe between the fingers of the dominant hand, and lightly, but firmly apply the thumb to the plunger with gentle, continuous pressure to appreciate changes in resistance. Feel the resistance to the needle while it traverses the supra-spinous and inter-spinous ligaments. A sudden loss of resistance will be felt as it pierces the (a) Needle in:tened to inrerspinal ligament dti\cJJ. ym~:;r~\ (b) Constant pressure on syringe plunger ligamentum flavum and enters the lcJ Saline injected into epidural spa<e epidural space with the saline flowing in freely. Figure 6.4 Technique of Epidural injection Note the markings on the needle from the skin to the epidural space (usually about 4cm, but may range from 3-5cm). Avoid going beyond 5cm (except in the very obese) as the sub-arachnoid space is likely to be entered. 5
Catheter placement The catheter is marked at lcm intervals starting at 5cm from the tip. There are double lines at IOcm, triple lines at 15cm and 4 lines at 20cm. 1. Check the catheter by flushing it and the filter with saline. 2. Gently insert the catheter up to 15 -20cm. 3. Push the catheter in while removing the needle to prevent it being pulled out. 4. Withdraw the catheter to 8-lOcm (distance from skin to ED space plus 4-5cm). 5. Connect the filter. Administer the test dose. Test dose Aim: to identify catheter or needle in i.v. or sub-arachnoid space • Lignocaine 2% 3 to 5ml 5 ml i.v. : causes circumoral tingling, tinnitus, dizziness 3 ml SAB : causes sensory and motor block in the foot within 5 min. • Lignocaine 1.5 -2% with 1:200,000 adrenaline 3 ml. i.v. causes tachycardia >30bpm in 30 sec, which lasts 30 sec (detected by ECG or Sp02 monitoring). • Bupivacaine 0.125% IO ml or 0.5% 3ml as "every dose is a test dose" Drug Bupivacaine 0.5% for anaesthesia and 0.1-0.25% for analgesia Fentanyl 2 µg /ml added quickens onset and improves the quality of analgesia. Morphine and diamorphine (2-3 mg) prolongs the duration of analgesia (12-24 h) Volume Volume depends on the distance between the point of injection and the site of surgery, and is calculated at 1-2 ml I segment. Injectate moves in both directions, but more easily cephalad. Volume should be reduced in: • elderly (less leak through the ossified intervertebral foramina) • obesity, pregnancy (epidural space is reduced due to fat and distended veins) Onset of block To quicken onset time from 15 to 5 minutes, add fentanyl. Wait 5 minutes to assess block (check both upper and lower limits, unlike in SAB). Management of inadequate block No detectable block after adequate dose and time : re-site the epidural. Partial block: withdraw catheter 1-2cm and repeat the dose with fentanyl. Check for unblocked areas and maintain the inadequate side in a dependent position.
Caudal Anaesthesia Positions 1. Lateral position with hips and knees flexed (foetal position) 2. Prone position with the pelvis raised on a pillow and feet turned medially Drugs 15-20 ml (0.5% bupivacaine or 1.5% lignocaine or mixture) will fill the sacral canal of an adult, and provide a perinea! block. Increasing the volume further will push the fluid into the lumbar canal. Add fentanyl 50µg for quick onset, and better quality of block. Add morphine (preservative free) 2mg to provide post operative analgesia for 12-24h. Anatomy • The dural sac ends at S2 in adults and lower in children. • The sacral hiatus is identified with the non dominant hand by moving the finger down along the midline of the sacrum till a give is felt which is usually just above the natal cleft and bordered by the two sacral comua. It forms an equilateral triangle with the posterior superior ilac spines. The sacral hiatus is covered by the sacro-coccygeal membrane. Injection 1. Clean the area with antiseptic. Avoid spirits as it is irritant to the anus. 2. Infiltrate lignocaine and insert a short beveled (2") 20-21G needle at 90 °. 3. When the ligament is reached, lower the needle to 45° and pierce it. 4. When the loss of resistance is felt, check for absence of CSF. 5. Connect to syringe, and aspirate gently to check for blood. 6. Inject a test dose of 3-4 ml, followed by the rest if there are no signs of i.v. injection or CSF aspiration. 7. Check block by touching anus with a probe to assess relaxation of the sphincter. COMPLICATIONS • LA toxicity with i.v. injection (see page 19.23) • SAB with total spinal • Subdural block resulting in high sensory block • Urinary retention
Combined Subarachnoid Epidural Anaesthesia (CSE) CSE combines the advantages of SAB (rapid onset, reliable, profound motor block) and EDB (controlled level, and extension of analgesia for a prolonged period). TECHNIQUE Without a special CSE set, separate injections have to be given for SAB and EDB, either in the same space or preferably in adjacent spaces. If the SAB is given first, the EDB cannot be tested for separately. If the ED catheter is passed before the SAB, there is a theoretical risk of damage to the catheter by the SAB needle. With a special CSE set 1. Enter the ED space with a Tuohy needle with loss of resistance to saline. This acts as an introducer for the subarachnoid needle. 2. Introduce a long (12cm), 25-29G pencil point needle through the ED needle. 3. Hold the hubs of both needles with a steady non-dominant hand while pulling out the stylet to prevent displacement (if there is no locking device). 4. Inject 0.5-lml heavy bupivacaine as required with fentanyl 10-15mg. 5. Remove the sub-arachnoid needle. 6. Introduce the epidural catheter. Fix it in place and position the patient. ED top ups should be smaller (2-5ml) as the SAB rises with epidural pressure.' Injection of saline will also increase the level of SAB. (EVE : epidural volume expansion) Position Pillow under shoulders if heavy bupivacaine is used, unless a high block is required. MANAGEMENT OF A FAILED BLOCK SUB-ARACHNOID BLOCK If emergency, or surgery has already commenced: Give GA If not: Repeat SAB after 15min, in the seated position (easier), with a normal dose. (Advancing the needle 1 mm more after CSF is seen may help) EPIDURAL BLOCK Check catheter for dislodgement. Withdraw catheter l-2cm and repeat the dose. If still inadequate, re-site the epidural injection preferably at another space.
Neuraxial Blockade and Anticoagulation The combination of neuraxial block and DVT prophylaxis is essential in some forms of surgery (e.g. orthopaedic and gynaecological) as the complications of avoiding regionals and thromboprophylaxis far outweigh the very rare complication of an epidural haematoma. The key to safety is balancing the risks, avoiding regional techniques in those at very high risk, adjustment of the total daily dose and timing of the first and subsequent doses of anti-coagulant with the timing and management of the neuraxial block. The use of indwelling catheters need to be coordinated with the entire patient care team, including the surgeons who are likely to be writing the anticoagulant orders, and the nurses who will be administering the drugs. PRECAUTIONS 1. Avoid EDB or SAB in patients with blood dyscrasia, thrombocytopaenia (platelet count of< 50xl09) or prior full anticoagulation. 2. Check for coagulopathy if on anti-thrombotic and anti-platelet drugs Heparin : APTT, Warfarin : INR (should be <1.5). Aspirin (action I week) and NSAIDs (action 3 days) : Bleeding time Aspirin and NSAID therapy are not contraindications, but special care is needed if thrombo-prophylaxis is also prescribed. Give NSAID 2-3 hours after the block rather than immediately post-op. Stop ticlopidine 14 days and clopidogrel 7 days before the block and re-start after 12-24h (if uncomplicated block). 3. Thrombo-prophylaxis (LMWH) Give enoxaparin 20-40mg, tinzaparin 3500units, dalteparin 2500 units, or fondaparinux 2.5mg s.c. 6-Sh after surgery. 4. Timing epidural techniques with anti-coaguletion Siting and removal of ED catheter : Wait for 12 h after LMWH, 24h after fondaparinux, and 4 hours after unfractionated heparin. Next dose : Wait for 2-4h after siting I removal for both LMWH and heparin TECHNIQUE 1. Use an atraumatic technique a) Use the smallest possible needle (27G for SAB and 18G for epidural). b) Use midline approach to avoid the laterally placed epidural veins. 2. If a bloody tap occurs in patients on anticoagulants, abandon the regional technique, or if already in the space give narcotics only, to avoid motor block. 3. Minimize prolonged motor block a) Use short acting local anaesthetics (lignocaine or prilocaine ). b) Use narcotics in the first few hours post-operatively or test before every top up for ascending motor block. Monitoring for epidural haematoma (see page 5.17)
Complications of Neuraxial Blockade COMPLICATIONS OF NEURAXIAL BLOCKADE Technical • Dural tap during epidural needle insertion (0.2-4%) • High spinal block (total spinal 1: 10,000) • Subdural block (0.1-0.8%) • Inadvertant i.v. injection (1: 10,000) Early • Hypotension and bradycardia • Restlessness • Nausea/vomiting • Hypoventilation (intercostal block with splinting of diaphragm) • Opioid induced pruritus • Shivering Late • Post dural puncture headache (1 :200 for SAB) • Urinary retention (detrusor power reduced up to 8h) • Backache (due to sacro-iliac strain in lithotomy or prolonged surgery) • Opiate respiratory depression (8-24h) if i.v./ i.m. opiates added (1 %) • Epidural haematoma (1: 150,000 for EDB, 1:220,000 for SAB) • Neurological sequelae ( 1: 10,000) • Meningitis I spinal abscess (I: 100.000) • Anterior spinal artery syndrome COMPLICATIONS OF THE TECHNIQUE DURAL TAP DURING EPIDURAL NEEDLE INSERTION Identified by a gush of CSF through the epidural needle. Do not panic! Keep the needle in place and inject the CSF filling the syringe back into the subarachnoid space. Then, choose one of two options : • Pass the ED catheter through the needle into the CSF and inject Sm! of saline. Continue as a SAB titrating the local anaesthetic to the level of block required. Leave the catheter in place for 24 hours to allow fibroblastic action to seal the hole. Inject 10 ml of saline before removing the catheter to minimize PDPH. • A second attempt may be made preferably by a more experienced anaesthetist and continuous epidural analgesia given.
HIGH SPINAL BLOCK SIGNS OF ACCIDENTAL HIGH SPINAL I TOTAL SPINAL BLOCK • Rapidly rising block with numbness. tingling, and weakness of arms • Agitation, anxiety, and slurred speech • Inadequate cough and hand grip • Inadequate air movement to generate voice (whispering) • Hypotension and bradycardia • Nausea and vomiting • Difficulty in breathing and swallowing • Engorgement of nasal mucosa (unopposed parasympathetic) • Absent intercostal muscle function and respiration Cardiac arrest I unconsciousness I fixed dilated pupils Treatment 1. Reassure patient that breathing is adequate, though not felt because sensory nerves are blocked, and the effect wears off in 15-30min. Inform obstetrician. 2. Head up tilt. Give 100% oxygen by mask. Check movement of the reservoir bag. 3. Support BP (hypotension is imminent and more dangerous than hypoventilation) • Elevate the legs to increase venous return. • Ephedrine 30-60mg i.v., or phenylephrine infusion lOOµg/min, or metaraminol 10 mg in 500 ml saline titrated to effect. • Intravenous crystalloids I colloids 4. Intubation is not urgent, and indicated only if: • • Respiration is absent with no movement of the reservoir bag Sp02 <90% on 100% oxygen • "Full stomach" with absent cough (for airway protection) Intubate gently reassuring and requesting cooperation of the patient. Awake intubation is possible as cough reflex and hand movements are absent. Midazolam I mg may be given. A void thiopentone as there is a danger of hypotension and cardiac arrest. A void suxamethonium as there is a danger of failed intubation. Ventilate with the soda lime absorber circuit to avoid hypercapnia. Extubate when the cough reflex returns (usually in 30min-lh). SUB-DURAL BLOCK Occurs with inadvertent injection of drug between the dura mater and arachnoid mater. Slow onset (20-30min) of inappropriately extensive block. Patchy, asymmetrical block, with no motor block of lower limbs. May extend to cervical dermatomes with Homer's syndrome. A total spinal may occur with a small top up dose. 5
EARLY COMPLICATIONS HYPOTENSION 30% reduction from pre-operative levels in hypertensive, or < 80mmHg systolic in normotensive patients Usually occurs in the first 20 minutes but may be delayed. Nausea is an early sign. Causes Reduced preload • Venodilatation in extensive blocks • Head high positions • Aorto-caval compression by the uterus, tumours, retractors, etc. • Blood loss and concealed hypovolaemia which becomes evident when bringing down the legs after surgery in the lithotomy position (TURP) Reduced afterload • Arterial vasodilatation in extensive block • Reduced compensatory vasoconstriction due to sedation and GA • Reduced compensation in the elderly, cardiac compromised Reduced contractility • Cardiac failure due to fluid overload (elderly and cardiac compromised) Reduced heart rate • Bradycardia due to block of cardiac sympathetic nerves (Tl-4) Prevention • Preload with infusion of 500 ml normal saline (avoid in the elderly). • Elevate legs to ensure adequate venous return. • Do not delay to replace fluid losses as compensatory mechanisms are depressed. Treatment 1. Oxygen inhalation 2. Cardiac failure must be excluded prior to treating hypovolaemia. • Fluid load given may have been excessive in relation to losses. • Confirm by auscultation of lungs for fine crepitations. 3. Hypovolaemia (relative or absolute) • Elevate the legs and infuse saline I colloid I blood according to losses. • Vasopressors should be titrated against blood pressure. 5.14 Ephedrine 5-10 mg i. v. boluses (tachyphylaxis after 60 mg) Phenylephrine 100/µgmin infusion titrated to effect Metaraminol lOmg in 500 ml of saline titrated to effect
RESTLESSNESS Causes and Treatment • Cerebral ischaemia : correct hypotension and give oxygen • Discomfort of prolonged surgery : change position, sedate or give GA • Anxiety : reassure, sedate if necessary • Disorientation due to benzodiazepine : reverse with flumezanil or give GA BRADYCARDIA Due to block of cardiac sympathetic nerves T 1-4 with vagal tone unopposed. Due to reduced venous return "the empty heart beats slowly" concept. Treat with atropine, ephedrine and fluids. NAUSEA I VOMITING Commonly due to hypotension, parasympathetic surgical stimulation, or opiates. Treat appropriately with ephedrine, promethazine, metoclopramide or naloxone. OPIOID SIDE EFFECTS Pruritus is common (specially with higher doses) but responds to naloxone O.lmg i.v. Delayed (12-24h) respiratory depression due to morphine (not diamorphine) should be treated with naloxone infusion. SHIVERING Due to differential inhibition of spinal cord afferent thermoreceptors Treat with pethidine 25mg i.v. or midazolam lmg i.v. LATE COMPLICATIONS POST DURAL PUNCTURE HEADACHE (PDPH) It is minimized by pencil point needles 25 I 27G (incidence <l % ) CHARACTERISTICS OF PDPH • Onset l 2-24h after injection. Duration <I week, subsiding gradually • Postural (worse sitting up, relieved when supine or with abdominal binder) • Occipital, neck or frontal headache with radiation to neck and neck stiffness • Associated tinnitus, hearing Joss, diplopia, photophobia, nausea, vertigo • Common in young females (parturients) and with bevelled 22G needles 5.15
naesthesia Headache usually occurs on the second post operative day after ambulation. It is due to leak of CSF which reduces intra-cranial pressure (causing the brain to sink, stretching the meninges and compensatory vasodilatation. DD : PIH, migraine, sinusitis, tension headache, meningitis, pneumoencephalus, cortical vein I sinus thrombosis, subdural haematoma, hypertensive encephalopathy Treatment 1. Bed rest relieves, but does not prevent headaches. It only postpones the headache and predisposes to DVT. 2. Abdominal binder increases epidural blood flow and compresses the dura. 3. Simple analgesics (paracetamol, diclofenac) are useful. 4. Caffeine 500mg i.v. in IL saline or IO cups coffee/day (reduces vasodilatation but may cause arrhythmias) 5. If severe for 24 hours, offer an epidural blood patch. Epidural blood patch I. Exclude sepsis (pyrexia or high WBC). 2. Obtain informed consent and advise bed rest before injection (reduces CSF leak). 3. Two anaesthetists should scrub up, one to draw 20ml blood, the other to inject it into the epidural space at or below the previous site of injection. 4. Inject 15-20ml slowly with the patient in the seated position till the headache disappears. Stop injection if the patient complains of backache or radicular pain. Reinject only if radicular pain is relieved. 5. Flush needle with 2 ml saline. 7. Advise bed rest for 2-4h to allow clot formation. Avoid straining, lifting etc. EPIDURAL HAEMATOMA Haematoma formation is extremely rare but may occur in patients on anticoagulant and antiplatelet therapy. 50% of haematomata are seen in those over 50 years. It is a potentially devastating complication and high risk patients should have a careful assessment to balance the risks and benefits. Be aware of the danger in the following : • Patients on DVT prophylaxis, heparinization, antiplatelet therapy • Traumatic technique and bloody tap Precautions (see page 5.11)
Signs of epidural haematoma • Sudden onset of sharp transient backache and leg pains • Prolonged or ascending motor block with flaccidity and obtunded reflexes • MRI preferable to CT to show cord compression (should be done without delay) • CSF is normal Management Arrange for emergency surgical laminectomy as neurological recovery is best if decompressed within 8h. Differential diagnosis 1. Epidural abscess Onset 1-3 days, associated infection, fever, malaise, backache Reflexes exaggerated early Flaccid paralysis early and later spastic MRI I CT shows epidural compression ESR and CSF cell counts increased 2. Anterior Spinal Artery Syndrome Sudden onset in the elderly (arteriosclerosis), with no symptoms, following a hypotensive episode Flaccid paralysis with obtunded reflexes MRI, CSF and blood normal
Intra Venous Regional Anaesthesia (IVRA) (Bier's block) IVRA with lignocaine or prilocaine provides· dense analgesia for short surgical procedures (1 hour) of the upper limb. It is less reliable in the lower limb. CONTRAINDICATIONS • Wherever a tourniquet is contraindicated e.g. sickle cell disease • Bupivacaine or adrenaline is lethal and is absolutely contraindicated. TECHNIQUE Monitoring : Pulse, BP, ECG, Sp02 Upper limb Technique 1. Insert 2 i. v. cannulae in each arm with one distal to the surgical site. 2. Give fentanyl I midazolam i.v. to minimize discomfort of Eschmarch bandage. 3. Set up 2 reliable pneumatic cuffs in the upper arm. 4. Exsanguinate the arm by applying an Eschmarch elastic bandage, up to the upper cuff or if the surgical site is painful, by elevating the arm for five minutes. 5. Inflate the upper cuff to lOOmmHg above systolic pressure. 6. Inject 30 ml of 0.5% lignocaine or prilocaine (safest) slowly over 90 seconds. For hand surgery, grip forearm during injection to maximise LA spread distally. 7. Wait five minutes and inflate the distal cuff as before (area is now analgesic). 8. Deflate the upper cuff and allow surgery to commence and continue for <2h. 9. Continuously monitor cuff pressure as accidental leaks are dangerous. 10. Release only after 20-30 min when the local anaesthetic is fixed to the tissue. If released in less than 20 minutes local anaesthetic toxicity may occur. If only 20-45 minutes has elapsed, deflate and re-inflate for 1 minute. Look for signs of toxicity : circumoral numbness and tingling, twitching, convulsions, bradycardia and hypotension. Lower limb Technique IVRA is less reliable for the lower limbs. The tourniquet is applied at mid calf level and 50 ml of lignocaine is used. Toxicity is commoner since blood may flow between tibia and fibula and the tourniquet is not as effective as when used in the arm over the humerus. If tourniquet is applied at the thigh, 100 ml is required (exceeds the safe dose). 5.18