Spinal Anaesthesia

• What is spinal anaesthesia?
• What is spinal anaesthesia used for?
• How does spinal anaesthesia work? 
• Types of local anaesthetics used in spinal anaesthesia
• Important issues regarding the spinal anaesthesia
• Complications of spinal anaesthesia
• Diseases treated with Spinal Anaesthesia
• Spinal Anaesthesia

What is spinal anaesthesia?

Spinal anaesthesia also known as subarachnoid anaesthesia is a form of local or regional anaesthesia, which involves injection of a anaesthetic drug into the subarachnoid cerebrospinal fluid space (CFS). The injection is usually made in the lumbar region at the L2/3 or L3/4 space, shown in figure 1.

 

 

Figure 1. Site of injection of spinal anaesthesia

What is spinal anaesthesia used for?

Spinal anaesthesia has the advantage of simplicity, rapid onset of action, low failure rate, minimum drug dose, and excellent muscle relaxation, which makes it the technique of choice for both elective and emergency caesarean section when a functioning epidural catheter is not in place. Therefore, it is used for:

• Surgeries below the umbilicus such as genitourinary surgery, hernial repair procedures or surgeries performed on the lower extremities (lower limbs).  
• Caesarean surgeries.

How does spinal anaesthesia work?

Spinal anaesthesia provides rapid and comprehensive anaesthesia for surgery or caesarean section by reversibly blocking nerves in the spinal canal serving both superficial and deep tissues. In doing so, the pain transmission is not delivered to the brain, thus decreasing the brain’s awareness of the pain during procedures and provides pain relieve to the patient.

If spinal anaesthesia is used during childbirth, a midwife or trained medical staff must be continuously present for at least 20 minutes after each bolus dose to record the maternal blood pressure, pulse and the foetal heart every 5 minutes and assess the height of the block. Alternatively if spinal anaesthesia is used during surgeries, the same protocols of close monitoring of respiration, blood pressure and pulse should be followed.

Types of local anaesthetics used in spinal anaesthesia

Some examples of local anaesthetics include bupivacaine hydrochloride, ropivacaine hydrochloride and lignocaine hydrochloride.  

Bupivacaine hydrochloride
Bupivacaine is a local anaesthetic that stabilises the neuronal membrane and prevents the initiation and transmission of nerve impulses. This drug is very potent, four times that of lignocaine, and has a rapid onset of anaesthesia with prolonged duration of action. Bupivacaine is suitable for continuous epidural blockade.

Ropivacaine hydrochloride
Ropivacaine also behaves in the same manner as bupivacaine with exception that ropivacaine has both anaesthetic and analgesic effects. At higher doses it produces surgical anaesthesia with motor block, while at lower doses it produces a sensory block, including analgesia, with little motor block.  

Lignocaine hydrochloride 
Lignocaine has the same mechanism of anaesthetic action to that of bupivacaine and ropivacaine.

Important issues regarding the spinal anaesthesia

Prior to administration of local anaesthesia you must provide consent and tell your doctor, anaesthetist or gynaecologist if you have:

• History of hypersensitivity or allergy to any previous medications including anaesthetics
• Local inflammation or infection
• Spinal deformity or previous spinal surgery
• Bleeding or clotting disorders
• Cardiovascular disease/s such as cardiac failure, cardiac ischemia, hypertension or hypotension and/or any other cardiac complications
• Nervous system disease/s
• Neuromuscular disease such as myasthenia gravis
• Any other medical conditions

In addition, if you are taking any medication/s, you must inform your doctor prior to the procedure. This is because some local anaesthetics can interact with other medications, resulting in unwanted or serious complications.

Complications of spinal anaesthesia

Local anaesthetics are generally safe if used in recommended doses. However, most complications are related to the techniques, resulting in systemic toxicity, or to the effects of the block, rather than to the drugs used. Some examples of these complications are described below.

Central Nervous System Complications

Local anaesthetic, possibly after accidental and unintentional injection, is one cause of convulsion or seizures in the labour ward.  Although your doctor will take into consideration other causes of this symptoms, for instance, high blood pressure, water retention due to oxytocin (a mammalian hormone released during childbirth) toxicity, pre-existing epilepsy, low blood sugar in diabetics, infections.

Management Strategies:
In case of CNS toxicity, the doctor and anaesthetist take the following measures:

• Maintain airway and ensure oxygenation.
• Ventilation if necessary.
• Protect the airway from aspiration by placing a tube in the airway tract.
• Implement appropriate anticonvulsant therapy, such as diazepam, clonazepam, thiopentone, if seizure is prolonged.
• Review any other potential causes and enact treatment accordingly.
• Liase with the obstetrician regarding urgent delivery.

Cardiovascular System Complications 

Vascular system complications are characterised by hypotension (low blood pressure), arrhythmias (disturbed rhythm of the heart), and cardiac arrest.

Management of Hypotension:
If a fall in blood pressure has been noticed, the doctor takes the following measures:

• Check the blood pressure manually.
• Elevate legs.
• Ensure adequate oxygenation.
• Position the patient on the side and administer a rapid infusion of fluid under instruction of anaesthetist.
• If pregnant women, the maternal blood pressure and foetal heart rate should be monitored closely. If the hypotension is an ongoing problem, ephedrine sulfate is used.

Total Spinal Anaesthesia

Total spinal anaesthesia (TSA), which occurs when the injection has been given unintentionally at the wrong site, is a rare but serious complication. TSA is characterised by sudden hypotension, rapidly increasing motor block, temporarily loss of breathing, loss of consciousness, dilated pupils, and is preceded by respiratory distress due to the blockade of some nerve cells.

Management Strategies:
The doctor and anaesthetist take the following measures:

• Maintain airway and ensure oxygenation and position the patient on the side to prevent aspiration of secretions.
• Ventilation with a bag or mask.
• Protect the airway from aspiration by placing a tube in the airway tract.
• Treat hypotension with appropriate medications such as ephedrine.
• Treat slowing of the heart with appropriate medications.
• Loss of consciousness and dilated pupils should resolve once the respiratory and cardiovascular systems are supported.
• In the pregnant women, the foetus should be monitored closely and urgent delivery may be required if the foetal distress is severe and/or resuscitation in difficult.

High Block

Symptoms associated with high block are nasal stiffness and difficulty breathing.

Management Strategies:
If this occurs, the doctor takes the following measures:

• Reassure the patient and provide an explanation of what is happening.
• Treat hypotension with appropriate medications such as ephedrine.
• Treat slowing of the heart with appropriate medications.
• Remain with the patient.
• If the maternal blood pressure is low, help the mother to sit upright.
• Monitor the foetal condition closely.

Postdural Puncture Headache

Postdural puncture headache following accidental subarachnoid or spinal puncture during spinal anaesthesia is the commonest neurological complication of neural blockade.

Postdural puncture headache usually develop 12 to 36 hours postpartum. This type of headache is characterised typically by a throbbing frontal pain, although it can occur elsewhere in the head and neck, and is relieved by lying flat which indicates that it has a postural component.

Management Strategies:
Your doctor will counsel you on the potential problems and management as well as monitoring you regularly. This type of headache often resolves soon, however if the headache re-develops, the following action is taken:

• You doctor will encourage the intake of oral fluids and regular oral pain relieves as well as bed rest.
• You doctor will perform a neurological examination in order to eradicate other causes of headache.
• If you experiences nausea and vomiting, IV fluids may be required.
• Oral caffeine to treat the postdural puncture headache might be considered.

Diseases treated with Spinal Anaesthesia

• Surgeries below the umbilicus such as genitourinary surgery, hernial repair procedures or surgeries performed on the lower extremities (lower limbs).
• Pain during childbirth or caesarean surgeries.

References

1. Therapeutic Guidelines: Analgesics. [online]. Obstetric pain. Version 4, 2006.
   Available at URL: http://www.tg.com.au (last accessed 01/10/07).
2. Impey, L. (2004) Obstetrics and Gynaecology [2nd edition] Blackwell Publishing Ltd: Massachusetts
3. www.anaesthesiauk.com/images
4. Australian Medicine Handbook. Adelaide: AMH Pty Ltd; 2007.
5. Wlaker, R., Edwards, C. Clinical pharmacy and therapeutics. England: Elsevier;2004.
6. MIMS Online. Bupivacaine Hydrochloride. [cited 2007 September 26].
   Available from: http://mims.hcn.net.au.ezproxy.library.uwa.edu.au
7. MIMS Online. Ropivacaine Hydrochloride. [cited 2007 September 26].
   Available from: http://mims.hcn.net.au.ezproxy.library.uwa.edu.au