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The safe spinal anaesthetic: spinal anaesthesia is not without its complications and should only be performed for the correct indications.

Spinal anaesthesia is relatively easy to perform and can potentially be excellent for below the umbilicus. However, it can also give rise to serious side-effects and complications. To perform a safe procedure, the anaesthetist must have adequate knowledge of the indications and contra-indications, and of the relevant anatomy, physiology and pharmacology of spinal anaesthesia. The patient must be assessed before administration of the spinal anaesthetic and the theatre must be correctly prepared. The anaesthetist must be familiar with the correct technique. After administration of the anaesthetic, the patient must be monitored so that side-effects and complications are recognised immediately and treated early. Sedatives must be titrated with care. During the postoperative period the patient should be admitted to the recovery room and monitored.

Indications and contra-indications

A spinal anaesthetic should only be administered for the correct indications. If relative contra-indications exist, extreme caution should be taken, and if there are absolute contra-indications, it should be avoided. Indications and contra-indications are listed in Table 1.

Table 1. Indications and contra-indications for spinal anaesthesia

Indications

Surgical procedures to the lower body below the umbilicus

Caesarean section

Respiratory disease (avoid high blocks)

Pain relief

Relative contra-indications

Aortic stenosis/mitral stenosis (fixed cardiac output states)

Systemic sepsis

Neurological disease (medicolegal implications)

Anatomical deformities of the patient's back

Difficult airway

Long operating time

Children

Absolute contra-indications

Inadequate drugs and equipment

Clotting disorders/anticoagulation

Refusal

Severe hypovolaemia or shock

Localised sepsis

Increased intracranial pressure

Physiology

Local anaesthetic solution injected into the subarachnoid space blocks conduction of impulses along all nerves with which it comes in contact. It acts mainly at spinal nerve roots, although some effect is possible at the cord itself. Smaller autonomic and sensory fibres are blocked more easily than motor fibres. Consequently, it produces a rapid sympathetic block, which causes peripheral vasodilatation and hypotension, and the patient may be aware of pressure or movement but feel no pain when surgery starts.

Intravenous access and preloading

Obtain IV access before starting the block. A large bore is recommended, preferably an 18G IV catheter. It seems that no amount of fluid preloading can prevent hypotension in all cases, but 500--1 000 ml is advantageous. Crystalloids are more effective than no fluids and colloids are more effective than crystalloids in preventing hypotension. (1) No differences were detected for different doses, rates or methods of administering colloids or crystalloids.1

Positioning the patient, anatomy, and factors affecting spread of local anaesthetic

Patients should be sitting or lying on their side. Back flexion opens the intervertebral spaces. The spinal cord terminates at L1/2 and the subarachnoid space at S2 in adults. It is advisable to enter the lumbar subarachnoid space below the termination of the cord, usually between vertebrae L4 and L5. The line joining the iliac crests is at L3/4 and is called Tuffier's line. Aim to identify the L3/4, L4/5 or L5/S1 interspace. Considering the inaccuracy of clinical means of identifying lumbar interspaces, the tendency of anaesthetists to err upwards, (2) and the uncertainty of the length of the spinal cord, even in normal individuals, (3) it is recommended that spinals should not be inserted above L3/4. Several cases of trauma to the conus are documented in the literature, (4) mostly involving spinal insertion believed to be above L3/4. Evidence suggests that injection of fluid into the cord may not always be involved, and that simple needle trauma is sufficient to produce a syrinx resulting in foot drop, numbness and sometimes urinary problems. It is recommended not to inject once pain is experienced, but the damage may already have been done.

A number of factors affecting the spread of the injected local anaesthetic solution within the CSF and the ultimate extent of the block are given in Table 2.
Table 2. Factors affecting the spread of the local anaesthetic solution

Factor Mechanism

Baricity of the local Blocks can be better controlled with
anaesthetic solution hyperbaric solutions

Position of the Level of the block may change if the
patient patient's position is altered

Concentration of and A higher concentration produces a denser
volume injected block; a larger volume produces a block
 over a larger area

Speed of injection Rapid injection produces eddy currents
 within the CSF and a less predictable
 spread

Increased abdominal Leads to engorgement of the epidural
pressure veins and reduction in CSF volume


Local anaesthetics

Any anaesthetic technique must produce adequate surgical anaesthesia of sufficient duration and with minimal side-effects. The main side-effect of spinal anaesthesia is a reduction in blood pressure. Reducing the dose of intrathecal local anaesthetic will improve cardiovascular stability but may not provide adequate surgical anaesthesia. The anaesthetist needs to decide which local anaesthetic to use and the dose.

Some preparations of local anaesthetics contain additives such as preservatives and are not suitable for intrathecal administration. Bupivacaine has a faster onset and longer duration (2--3 hours) of analgesia and motor block than both ropivacaine and levobupivacaine. The duration of action of lignocaine may be too short to guarantee adequate surgical time and it has a higher incidence of transient radicular irritation. (5) A guideline for the volume of local anaesthetic to be used is given in Table 3. The lower volumes should generally be given to small individuals.
Table 3. Guideline for local anaesthetic volume (not applicable to
pregnant patients)


Type of block 0.5% hyperbaric bupivacaine

Saddle block 1 ml
Lumbar block 2--3 ml
Mid-thoracic block 2--4 ml


Fixation time, assessing the block and the level

About 15--20 minutes after injection of a local anaesthetic into the subarachnoid space, the level of the block is fixed to a certain degree. However, it can take more than 60 minutes to fix finally. (6) If the patient is unable to lift his/her legs from the bed, the block is at least up to the mid-lumbar region. Test for a loss of temperature sensation.

Problems with the block

* No block. If after 10 minutes the patient still has full power in the legs and normal sensation, then the block has failed, probably because the injection was not intrathecal.

* The block is one-sided. Position the patient on the side that is inadequately blocked for a few minutes.

* The block is not high enough. Tilt the patient slightly head-down or flatten the lumbar curvature by raising the patient's knees.

* The block is too high. Do not tilt the patient head-up. See treatment of a high or total spinal anaesthetic below.

Monitoring

Establish full monitoring before administering a spinal anaesthetic, including blood pressure monitoring (preferably with an automatic oscillometric monitor), an electrocardiogram and pulse oximetry. Confirm the alarm levels for every patient before starting the anaesthetic.

Side-effects and complications

The side-effects and complications of spinal anaesthesia are shown in Table 4.
Table 4. Side-effects and complications of spinal anaesthesia

Side-effect/complication Mechanism Treatment

Hypotension Sympathetic block Vasoconstrictor drugs
 causes and IV fluids
 vasodilatation

High or total spinal High level of block See treatment of a
 high or a total
 spinal anaesthetic
 below

Respiratory depression Severe hypotension, Treat hypotension and
 high level of block support ventilation
 or sedatives

Toxicity Cardiotoxicity Intralipid
 Neurotoxicity Anticonvulsants

Nausea and vomiting Hypotension or Treat hypotension and
 related to opioids administer
 anti-emetic
 medication

Pruritus Related to opioids Naloxone 50--100 ug
 IV or an
 antihistamine

Headache Continuing loss of Hydration,
 CSF through the hole analgesics, caffeine
 made in the dura by and an epidural blood
 the spinal needle patch

Epidural haematoma Bleeding with Urgent CT/MRI scan
 haematoma formation and neurosurgical
 management

Epidural abscess Introduction of Urgent CT/MRI scan
 bacteria with and neurosurgical
 infection and abscess management plus
 formation antibiotics

Nerve injury Damage to the nerve, Assessment by a
 or injection of neurologist
 inappropriate drugs

Urinary retention Block of sacral Catheterisation
 autonomic fibres or
 related to opioids


Treatment of hypotension

Hypotension is due to vasodilatation and a functional decrease in the effective circulating volume. This should be treated by reversing the vasodilatation with vasoconstrictor drugs and increasing the circulating volume by giving IV fluids.

Phenylephrine is probably the vasoconstrictor of choice. It is a pure peripheral vasoconstrictor ([[alpha].sub.1]-agonist) available in 10 mg ampoules and must be diluted before use. It can be administered as 50--100 [mu]g boluses or as a continuous infusion of 0.5--3.0 [mu]g/kg/min. A reflex bradycardia may occur.

Other vasoconstrictors that can be used include etilefrine, ephedrine and low doses of a diluted adrenaline solution.

Treatment of respiratory depression

If the patient complains of feeling suffocated, of experiencing difficulty breathing or of not being able to raise their voice easily, immediately measure the blood pressure, the [SpO.sub.2] and the level of the spinal anaesthetic. If the patient is hypotensive, take measures to raise the blood pressure. Serious respiratory depression or apnoea often happens because the medullary respiratory centre does not function well, secondary to hypoxia in the brain stem caused by profound hypotension. When the level of anaesthesia is above T2 and the tidal volume decreases, supplementary oxygen must be provided per facial mask. If the patient suffers severe respiratory depression or respiratory arrest, artificial ventilation must be commenced immediately. Endotracheal intubation is not always necessary if artificial ventilation with a mask or an LMA device is possible and if there is no risk of regurgitation and aspiration.

Treatment of a high or total spinal anaesthetic

Although rare, total spinal anaesthesia can occur rapidly and result in death if not quickly recognised and treated.

The warning signs that high or total spinal anaesthesia is developing are:

* Hypotension--nausea may be the first sign. Large volumes of fluid and repeated doses of vasopressors may be necessary.

* Bradycardia--administer atropine.

* Increasing anxiety--reassure.

* Numbness or weakness of the arms--the block has reached the high thoracic or cervical region.

* Difficulty breathing--if the intercostal nerves are blocked patients may feel that they cannot take a deep breath. If the phrenic nerves (C3--5), which supply the diaphragm, are blocked, the patient will initially only be able to whisper and will then stop breathing.

* Loss of consciousness.

Call for help:

* ABC resuscitation.

* Intubate and ventilate the patient with 100% oxygen.

* Treat hypotension with IV fluids, vasopressors and atropine. If treatment is not started quickly the combination of hypoxia, hypotension and bradycardia may result in cardiac arrest.

* Once the airway has been controlled and the circulation restored, consider sedating the patient as consciousness may return before muscle power.

* Continue ventilation until the spinal block recedes and the patient is able to breathe unaided.

Sedation

Surgery is often stressful for patients and even when pain free after successful spinal anaesthesia, they often request some sedation. Too much sedation may lead to hypoventilation, hypoxia or silent regurgitation of gastric contents. The optimal level of sedation can be difficult to judge. As a general rule, it should be possible to easily arouse the drowsy patient and to maintain verbal contact. In the event of an inadequate spinal anaesthetic it is preferable to electively administer a light general anaesthetic and safeguard the airway than to over-sedate.

Postoperative care

The patient should be admitted to the recovery room as is the case with any other anaesthetised patient. The level of anaesthesia can take more than 90 minutes after insertion of the spinal anaesthetic to fix finally (6) and it is recommended that the patient be carefully observed during this period. Patients should be given an indication of the duration of the spinal block and told to remain in bed until full sensation and muscle power have returned.

References available at www.cmej.org.za

RELATED ARTICLE: IN A NUTSHELL

* A spinal anaesthetic should only be performed for the correct indications.

* Facilities for resuscitation and progression to general anaesthesia must be available.

* Obtain IV access before starting the block.

* Establish full monitoring before administering the spinal anaesthetic.

* Spinal anaesthesia should not be administered above L3/4.

* The principal side-effect of spinal anaesthesia is hypotension.

* The treatment of hypotension is with vasoconstrictor drugs and IV fluids.

* Total spinal anaesthesia can occur rapidly and result in death if not quickly recognised and treated.

* If the spinal anaesthesia is inadequate, rather administer a light general anaesthetic than to over-sedate a patient.

* The block can take more than 60 minutes to fix finally.

Mariane Gertruida Senekal, BMedSc, MB ChB, DA, MMed (Anaesthesiology) Principal Specialist, Department of Anaesthesiology, 3 Military Hospital, and Senior Lecturer, Department of Anaesthesiology, University of the Free State, Bloemfontein Mariane Senekal did her undergraduate training at Stellenbosch University and her postgraduate anaesthesia training at the University of the Free State where she obtained the MMed (Anaesthesiology) in 2005. She has an interest in obstetric anaesthesia, orthopaedic anaesthesia, anaesthesia-related physiology and teaching and training of anaesthesia.

Correspondence to: M Senekal (mariane.senekal@vodamail.co.za)
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Author:Senekal, Mariane Gertruida
Publication:CME: Your SA Journal of CPD
Date:Jun 1, 2012
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