Practical conduction anaesthesia cannot be learned from a book, but only by working with an experienced practitioner. For a detailed description of some common techniques, see Anaesthesia at the District Hospital (WHO, 2001).

Techniques of conduction (regional) anaesthesia use locally acting drugs to block nerve impulses before they reach the central nervous system.

Local anaesthetic drugs depress the electrical excitability of tissues. When injected close to nerves, they block the passage of the depolarization wave necessary for the transmission of nerve impulses.

TOXICITY AND SAFETY OF LOCAL ANAESTHETIC DRUGS

All local anaesthetic drugs:

These reactions are most likely to occur if the drug is accidentally injected into a vein or if an overdose is given by using either too high a concentration or too large a volume of drug.

Toxic effects – usually cardiac dysrhythmias – may also occur after intravascular injection or rapid absorption of a vasoconstrictor drug, such as epinephrine, which is frequently mixed with local anaesthetic to prolong the latter’s action. Occasionally, patients have a true allergic reaction to the local anaesthetic drug, but this is unusual.

If a severe toxic reaction occurs, prompt resuscitation is needed:

It follows from the above that full facilities for resuscitation should be available whenever you use conduction anaesthesia, just as they should when you use general anaesthesia.

As with all drugs, the maximum safe dose is related to the size and condition of the patient. Avoid toxicity by using the most dilute solution that will do the job, for example:

The rate of absorption of the drug can also be reduced by injecting it together with a vasoconstrictor drug, such as epinephrine, which is most often used in a dilution of 5 mg/ml (1:200 000); for infiltration, 2.5 mg/ml (1:400 000) is
enough. Pre-mixed ampoules of local anaesthetic and epinephrine are often available but, if they are not, you can easily mix your own.

To make a 1:200000 dilution of epinephrine (adrenaline), add 0.1 ml of 1:1000 epinephrine to 20 ml of local anaesthetic solution.

The addition of epinephrine has two useful effects:

When injecting local anaesthetic, use a small gauge needle:

This reduces the risk of toxicity; it is easy to inject an excessive dose through a large-bore needle.

The maximum safe doses of various local anaesthetic drugs are shown in the following table.

Drug Maximum dose Maximum dose
mg/kg mg/60 kg adult
Lidocaine 1% 4 240
Lidocaine 1% + epinephrine 1:200 000 7 420
Bupivacaine 0.25%/0.5% 2 120

Contraindications and precautions

It is a common misconception that general anaesthesia is more dangerous than conduction anaesthesia. In fact, for major surgery, there is no evidence of any difference in morbidity and mortality between patients undergoing good-quality general anaesthesia and those undergoing conduction anaesthesia.

Certain specific contraindications to conduction anaesthesia exist, including:

General precautions and basic equipment:

Sedation during conduction anaesthesia

Patients undergoing surgery under conduction anaesthesia often need some sedation to reduce anxiety or to help them to lie still. This is best achieved by oral premedication – drugs taken orally are safer and less expensive. A small additional dose of intravenous sedative is sometimes necessary, but do not use this to “cover up” an inadequate conduction technique.

Do not let “sedation” drift into unconsciousness with an uncontrolled airway. A sedated patient should still be able to talk to you.

SPINAL ANAESTHESIA

Spinal anaesthesia is a technique commonly used for caesarean section (CS). When given by an experienced anaesthetist for an elective caesarean section, it can be safe and very effective. Nevertheless, it represents a major physiological
disturbance and may be dangerous or even fatal when used in emergency for a patient who is dehydrated, hypovolaemic or shocked.

For sick patients undergoing emergency caesarean section, the recommended techniques are:

Management of a high or total spinal

Do not ignore signs that your spinal anaesthetic is progressing higher than the maximum permissible level of T4 (the nipple line). As soon you have given the spinal and positioned the patient, observe the effects. These commence faster with lidocaine than with bupivacaine. The onset of the spinal block at the correct height should make the mother comfortable because the pains of labour are abolished. Signs of respiratory distress and hypotension include:

These are very serious warning signs. Additionally, you may find the blood pressure and heart rate have fallen unacceptably (below 80 mmHg systolic and less than 50–60 beats/minute). Ask the patient to squeeze your hand: if she cannot, she may be unconscious or paralysed. It is usually not possible to know precisely if the patient is unresponsive because of hypotension (reduced cerebral blood flow) or because the spinal solution has spread too high.
Act immediately to treat the unresponsive patient, whether the cause is hypotension or a high spinal.

Managing unexpected effects of a spinal anaesthetic

To treat hypotension:

To treat the respiratory difficulty, give oxygen and IPPV, using an anaesthetic face mask and self-inflating bag or bellows, or the anaesthetic machine patient circuit.

At this point, it is possible that the situation will resolve itself: the heart rate and blood pressure may rise again, the patient breathes unassisted and you continue with spinal anaesthesia.

Equally, however, the high spinal may progress further, or even become a “total spinal”. In this condition, there is no detectable cardiopulmonary activity. Start the following emergency measures without delay, as for any cardiopulmonary resuscitation:

The question often arises: how should you intubate a mother who is clearly unable to breathe (and when inflation by mask is insufficient) but who is still conscious? Do you need to give thiopental and suxamethonium?

In the presence of hypotension:

A high or total spinal is a “pharmacological” cardiopulmonary arrest occurring in a healthy person. Every case should make a complete recovery. Death or cerebral damage from delayed recognition of the signs or poor management
is inexcusable.

A death or complication after spinal anaesthesia is usually due to neglect of vital signs.