Health

H

Dr Rod Pearce

HEALTH The complexities of anaesthesia

General anaesthetic gives us our ability to “put people to sleep” and make operations possible, or just stop a procedure, like sewing up a laceration, from hurting.

It puts you into a “coma” so you’re not aware of what’s happening, you don’t remember, and you don’t feel the pain.

These are three separate processes and drugs are used to affect different parts of the brain to make sure they all happen.

During operations, it is also sometimes important to control heart rates, sweating and other reflexes, and to relax the muscles for ease of surgery.

When a small area or specific site needs to be numbed, a different “ local” anaesthetic is used. One example is lignocaine (lidocaine) to anaesthetize a laceration for sewing up.

When we use the local anaesthetic, we are just putting the local nerve to sleep by stopping it working at a chemical level.

Doing the same thing in the spinal cord is what produces the pain-relieving effect in an epidural (spinal anaesthetic), commonly used for pregnancy delivery but suitable for other more complex procedures.

Under certain conditions it can be used for prostate and bladder surgeries and some general surgical procedures.

The general anaesthetic is far more complex and has five components which all require subtle differences.

The original anaesthetics, like ether, basically shut down the brain. Barbiturates, in their original form, switched the brain off, risking overdose and death.

Now we can use injections, or inhaled anaesthetics, to do different things. The various depths of anaesthetic have been described as “stages”. The anaesthetist is the person who will have a favourite and proven-safe programme for anaesthetic. He or she is the appropriate person to talk to about what is being used, what is being done and why different medication will be used.

Stage 1, also known as induction, is the period between the administration of induction agents and loss of consciousness. During this stage, you are progressing from analgesia without amnesia to analgesia with amnesia. You can possibly still carry out a conversation at this time.

Stage 2, also known as the excitement stage, is the period following loss of consciousness and marked by excited and delirious activity. During this stage, the breathing and heart rate might become irregular. In addition, there might be uncontrolled movements, vomiting and pupil dilation.

Because of the combination of spastic movements, vomiting, and irregular respiration, this might compromise the patient’s airway, so rapidly acting drugs are used to minimize time in this stage and reach the next stage as quickly as possible.

In stage 3, also known as surgical anaesthesia, the skeletal muscles relax, vomiting stops, respiratory depression occurs, and eye movements slow and then stop. You are unconscious and ready for surgery.

Stage 4, also known as overdose, occurs when too much anaesthetic medication is given relative to the amount of surgical stimulation. There is severe basic brain depression resulting in a cessation of respiration and potential cardiovascular collapse. This stage is lethal without cardiovascular and respiratory support.

To avoid the serious side effects, drugs have been developed that reduce the “depression” of the brain and other functions but stop you being aware of what is happening.

For the most part, contemporary practice dictates that adult patients, and most children aged at least 10, be induced with intravenous drugs.

Agents like sevoflurane, a welltolerated anaesthetic vapour, allows for elective inhalation induction of anaesthesia in adults. In addition to the induction drug, many people will receive an injection of an opioid analgesic. Induction agents and opioids work synergistically to induce anaesthesia.

Anticipation of events that are about to occur, such as endotracheal intubation and incision of the skin, generally raises the blood pressure and heart rate of the patient. Opioid analgesia helps reduce this undesirable response, which can prove catastrophic in patients with severe cardiac disease.

Traditional opioid analgesics (morphine, meperidine, and hydromorphone) are widely used in anaesthesia as well as in emergency departments, surgical wards, and obstetric suites.

There is also a range of synthetic opioids, including fentanyl, sufentanil, and remifentanil which, in general, cause less fluctuation in blood pressure and are shorter acting.

The anaesthetist is the person who will have a favourite and proven-safe programme for anaesthetic. He or she is the appropriate person to talk to about what is being used, what is being done and why different medication will be used.

There is some choice, and there are safe changes that can be offered if previous anaesthetics and/or surgical procedures have had problems.

There are lots of options for being “put to sleep” and twilight anaesthetics as well as simple local or regional anaesthetics. Ask the anaesthetist what the best option is; and any anaesthetic should be best for the operation needed.