Spinal anaesthesia

CORE: TECHNICAL SKILLS

Spinal anaesthesia

Learning objectives

Christina L Beecroft After reading this article, you should be able to: C discuss spinal needle design and the drugs available for spinal anaesthesia C describe the technique of spinal anaesthesia, including patient selection C discuss both the common and major complications associated with spinal anaesthesia

Abstract Spinal anaesthesia is the injection of local anaesthetic into the subarachnoid space. It is a simple technique that can be used to provide surgical anaesthesia for procedures involving the abdomen, pelvis and lower limbs. To perform the technique safely it is important to understand the physiology of the block and the pharmacology of the drugs commonly used. Although serious complications are rare, they must be recognized and managed quickly.

These have a non-cutting edge that separates, rather than pierces, the fibres of the dura thus reducing the frequency of PDPH.2

Keywords Conduction anaesthesia; local anaesthesia; lumbar puncture; Drugs Only preservative-free agents should be used for spinal anaesthesia because some preservatives may be neurotoxic or induce arachnoiditis. The agents currently available in the UK are lidocaine, bupivacaine, levobupivacaine, ropivacaine and prilocaine, with hyperbaric bupivacaine, hyperbaric prilocaine and plain levobupivacaine licensed for intrathecal use. Preservative-free lidocaine is not recommended for intrathecal use because of the high incidence (up to 25%) of transient neurological symptoms (TNS) following its use.3 Prilocaine is a local anaesthetic with a similar duration of action to lidocaine but with a far lower incidence of TNS. In addition to faster block regression compared with hyperbaric bupivacaine 0.5%,4 hyperbaric 2% prilocaine has a shorter onset time than 0.5% hyperbaric bupivacaine.5 A dose of 40e60 mg hyperbaric prilocaine will give 100e130 minutes of surgical anaesthesia. Opioids are added to intrathecal local anaesthetic to prolong postoperative analgesia; fentanyl (25e50 mg), diamorphine (up to 300 mg) and morphine (up to 300 mg) have all been used. Despite the smaller doses given when compared with those for the intravenous route, intrathecal opioids are still associated with side effects including nausea and vomiting, pruritis and less commonly, respiratory depression. See pages 559e562 (in this issue) for the use of other intrathecal adjuvants.

regional anaesthesia; spinal anaesthesia Royal College of Anaesthetists CPD Matrix: 2G02

Spinal anaesthesia is the injection of local anaesthetic into the subarachnoid space to produce surgical anaesthesia. First performed by August Bier in 1898, it was widely practised until the 1950s when its use declined. This was partly due to improvements in general anaesthesia and partly as a result of the now infamous Woolley and Roe case (Cope1) in which two patients suffered permanent paraplegia following spinals, probably because of accidental acidic contamination of the injectate. However, since the 1970s the technique has regained popularity and is now widely practised.

Indications and contraindications Spinal anaesthesia can be used for lower abdominal, pelvic and lower limb surgery expected to last for less than 3 hours. For longer procedures, a combined spinal-epidural (CSE) or spinal catheter should be considered. With the availability of prilocaine 2% hyperbaric solution (PrilotekalÒ) spinal anaesthesia has become an attractive option for ambulatory surgery. The contraindications to spinal anaesthesia are shown in Table 1.

Technique The procedure, risks and benefits should be discussed with the patient and informed verbal consent obtained. Full resuscitation facilities must be available, as must a trained assistant. The patient should be monitored (ECG, blood pressure and oxygen saturation) and intravenous access secured. Spinal anaesthesia can be performed with the patient either sitting or in the lateral position with the lumbar spine maximally flexed to open the space between the spinous processes. Full aseptic technique should be used (surgical scrub, hat, mask, sterile gown and gloves). Lumbar puncture should always be performed below the level of termination of the spinal cord to minimize the risk of direct damage to the cord. In adults, this is usually at between the L1 and L2 vertebral body. When identifying vertebral levels use the intercristal line (Tuffier’s line), a horizontal line joining the highest points of the iliac crests that usually crosses the spinous process of L4. This allows identification of the L3eL4 and L4eL5

Equipment Spinal needles are available in a variety of gauges, with 25G and 27G most commonly used. Smaller gauge needles are associated with a reduced risk of post-dural puncture headache (PDPH),2 but needles smaller than 27G are technically difficult to use. Narrower gauge needles are usually supplied with a short introducer needle to guide the flexible spinal needle through the tough skin and subcutaneous tissues covering the lumbar spine. Needle-tip design also influences the frequency of PDPH, and cutting tip needles (Quincke) have largely been replaced by atraumatic ‘pencil-point’ needles (Whitacre, Sprotte) (Figure 1).

Christina L Beecroft FRCA FDS RCS is a Consultant Anaesthetist at Ninewells Hospital, Dundee, UK. Conflicts of interest: none declared.

ANAESTHESIA AND INTENSIVE CARE MEDICINE 13:11

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Practical procedure e spinal anaesthesia

Contraindications to spinal anaesthesia Absolute

Relative

Patient refusal Coagulopathy Severe local or systemic sepsis Allergy to any of the drugs

Fixed cardiac output state Hypovolaemia Spinal deformity Active neurological disease

C

C C

Table 1

interspaces. However, clinical estimation of vertebral interspace level is often inaccurate,6 so it is recommended that the lowest palpable space is used for dural puncture. Box 1 describes the procedure in detail.

C

Physiological effects of spinal anaesthesia

C C

Under the influence of posture and gravity, nerves caudad to the injection site are completely blocked. Cephalad to the injection site, there is a differential block, with the small sympathetic nerves blocked two to six dermatomes higher than the sensory block which, in turn, is usually higher than motor block. The systemic effects of spinal anaesthesia depend on the maximum dermatomal height reached by the block. Hypotension is a common consequence of spinal anaesthesia as a result of vasodilatation and consequent pooling of blood in the lower limbs. Blocks above T8 are likely to cause significant hypotension (>25% fall in blood pressure) and blocks at and above T4 may cause bradycardia as the cardiac sympathetic fibres are affected; this may worsen hypotension. As hypotension is a direct result of vasodilatation, treatment is to administer vasoconstrictors; intravenous fluid loading is less effective. Ephedrine (3e6 mg bolus, titrated to effect) is most commonly used, with phenylephrine (50e100 mg) preferred in obstetrics due to its more favourable effects on uterine artery pH. Any block above T10 will also affect the function of the intercostal muscles which might cause or worsen respiratory compromise.

Prepare the skin of the back with antiseptic solution, allow to dry and attach a sterile drape Inject lidocaine 1% subcutaneously at the selected space Both the introducer and needle must be inserted in the midline and advanced slowly; it is helpful to aim towards the umbilicus. When the tough ligamentum is entered it feels as if it is ‘gripping’ the needle in a very characteristic manner. With further gentle needle advancement a classic give or ‘pop’ is felt; this is the change in resistance as the tip of the needle pierces the dura mater Withdraw the trochar and watch for free flow of cerebrospinal fluid (CSF). Attach the syringe containing local anaesthetic and aspirate to ensure CSF is still flowing freely before injecting the local anaesthetic Withdraw the needle and apply a dressing Return the patient to the supine position and monitor for complications. After 10 minutes, the block should be checked; check the autonomic component by observing vasodilatation and feeling the increased warmth of the limbs. The motor component is checked by asking the patient to perform active movements of the limbs, and the sensory height of the block, usually to cold touch, must be documented after testing with ethyl chloride spray

Box 1

the baricity of the local anaesthetic and the posture of the patient that ultimately determines block height. Hyperbaric bupivacaine (‘heavy’ bupivacaine) contains bupivacaine 5.0 mg/ml and 80 mg/ml glucose, the glucose rendering it heavier than CSF so it will preferentially block dependent neurological structures when injected. When injected into a patient who is then positioned supine, the block is likely to reach the level of the most dependent part of the thoracic kyphosis. However, if the patient is left in the sitting position after insertion the block will be restricted to the lower lumbar and sacral nerves producing the so-called ‘saddle’ block. Table 3 shows suggested doses for spinal anaesthesia using hyperbaric bupivacaine 0.5% and also hyperbaric prilocaine 2%. Plain local anaesthetic solutions are isobaric or slightly hypobaric when compared with CSF and when using these, the height of the block depends more on the mass of the injectate than the position of the patient.

Factors affecting block height The main factors influencing the height of the block are shown in Table 2. The ‘baricity’ of a liquid is the ratio of its density relative to that of cerebrospinal fluid (CSF). It is the relationship between

Common tip designs for spinal needles Quincke

Factors affecting block height Whitacre

Sprotte Figure 1 Reproduced, with permission, from Anaesthesia and Intensive Care Medicine 2006; 7: 418e21.

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Patient factors

Anaesthetic factors

Position Pregnancy (increases block height) Height Age

Baricity of solution Mass of drug Volume of solution

Table 2

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Rare complications

Drug doses in spinal anaesthesia Block height

Volume (hyperbaric bupivacaine 0.5%)

‘Saddle’ block e sacral nerve roots T10 T6

1.5e2.0 ml (7.5e10 mg); leave patient sitting for 10 minutes after insertion 2.5e3.0 ml (12.5e15 mg) 3.0e3.5 ml (15e17.5 mg)

The three layers of the meninges surround the spinal cord from the foramen magnum to sacrum. Following spinal injection, there is the potential for the block to extend to the cervical region with phrenic anaesthesia and diaphragmatic paralysis; further extension is to the hindbrain and this rapidly progresses to unconsciousness. This is a so-called ‘total spinal’ and requires urgent management. Intrathecal opioids can cause delayed respiratory depression by the cephalad spread of CSF-containing opioids that act on the respiratory centre in the medulla. Infection of the meninges is always a risk and spinal anaesthesia should be performed under strictly aseptic conditions. Vertebral canal haematoma is rare but serious and is related not only to the patient’s coagulation status before insertion of the spinal and at the time of catheter removal but also to the technical difficulty of the procedure. Particular care must be given to observing recommended time intervals from dosing of anticoagulant drugs and performance of spinal anaesthesia to minimize the risk of vertebral canal haematoma.9 A

Table 3

Complications Fortunately, the incidence of major complications (those leading to permanent harm or death) after spinal anaesthesia is rare; the recent National Audit Project of the Royal College of Anaesthetists found a rate of 2.2 per 100,000 cases (95% CI 1.0e4.4).7 Post-dural puncture headache The actual mechanism causing PDPH is unclear, but this is an unpleasant side effect of spinal anaesthesia. The incidence is between 0 and 14.5% with a 25G pencil point needle;2 it occurs more frequently with larger gauge cutting needles, in younger patients, females and following multiple attempts at spinal anaesthesia. The classic complaint is of a severe headache, usually occipital, which is worse when sitting or standing. Other symptoms include nausea and vomiting, visual disturbance including photophobia, and neck stiffness. Management includes analgesia, good hydration, intravenous caffeine and, if the headache remains resistant to these treatments, an epidural blood patch.

REFERENCES 1 Cope RW. The Woolley and Roe Case; Woolley and Roe versus Ministry of Health and Others. Anaesthesia 1954; 9: 249e70. 2 Turnbull DK, Shepherd DB. Post-dural puncture headache: pathogenesis, prevention and treatment. Br J Anaesth 2003; 91: 718e29. 3 Freedman JM, Li DK, Drasner K, Jaskela MC, Larsen B, Wi S. Transient neurological symptoms after spinal anaesthesia: an epidemiological study of 1863 patients. Anesthesiol 1998; 89: 633e41. 4 Ratsch G, Neibergall H, Hauenstein L, Reber A. Spinal anaesthesia in daycase surgery. Optimisation of procedures. Anaesthesist 2007; 56: 322e7. 5 Camponovo C, Fanelli A, Ghisi D, Cristina D, Fanelli G. A prospective, double-blinded, randomized clinical trial comparing the efficacy of 40 mg and 60 mg hyperbaric 2% prilocaine versus 60 mg plain 2% prilocaine for intrathecal anaesthesia in ambulatory surgery. Anesth Analg 2010; 111: 568e72. 6 Broadbent CR, Maxwell WB, Ferrie R, Wilson DJ, Gawne-Caim M, Russell R. Ability of anaesthetists to identify a marked lumbar interspace. Anaesthesia 2000 Nov; 55: 1122e6. 7 Major complications of central neuraxial block in the United Kingdom: Report and Findings, the 3rd National Audit Project of the Royal College of Anaesthetists. January 2009, p 34. 8 Checketts MR. Wash and go e but with what? Skin antiseptic solutions for central neuraxial block. Anaesthesia 2012; 67: 819e22. 9 Checketts MR. Regional anaesthesia in patients taking anticoagulant drugs. Anaes Int Care Med 2009 Nov; 10: 541e4.

Neurological sequelae Permanent neurological damage following spinal anaesthesia is rare (less than 1:10,000), but it is clearly a potentially devastating complication. It is caused by direct damage to either spinal nerves or the cord itself during insertion of the spinal needle or by the injection of neurotoxic substances during the procedure. Recently, two cases of permanent neurological damage after central neuraxial blockade have been reported; in both cases, injury was attributed to contamination with chlorhexidine gluconate solution. It is essential to avoid contamination of spinal instruments with the cleaning solution, to use a coloured solution to avoid confusion with local anaesthetic or saline and to use the lowest appropriate concentration of chlorhexidine gluconate (0.5%), allowing it to dry completely before performing the block.8 The development of neurological sequelae may be associated with pain occurring during insertion of the needle. Rather than a local pain at the site of injection, this pain is ‘radicular’ in nature, often described as pain like an electric shock that shoots into the buttock or down one leg. If injection then continues, the incidence of nerve damage increases, so it is important to warn the patient that they should immediately report pain of this nature should it occur.

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FURTHER READING Burnell S, Byrne AJ. Continuous spinal anaesthesia. Cont Educ Anaesth Crit Care Pain 2001; 1: 134e7. Checketts MR, Wildsmith JAW. Regional block and DVT prophylaxis. Cont Educ Anaesth Crit Care Pain 2004; 4: 48e51. Whiteside JB, Wildsmith JAW. Spinal anaesthesia: an update. Cont Educ Anaesth Crit Care Pain 2005; 5: 37e40.

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