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.
(a) Needle in:tened to inrerspinal ligament
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 interspinous ligaments. A sudden loss of resistance will be felt as it pierces the ligamentum flavum and enters the
epidural space with the saline flowing in freely.
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.
dti\cJJ. ym~:;r~\ (b) Constant pressure on syringe plunger lcJ Saline injected into epidural spa<e 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.