Phases of general anaesthesia:

1. Induction

This commences with the patient's arrival into the anaesthetic room (or if not available into the operating theatre). It is here that compulsory, together with any additionally required, monitoring equipment is placed on to the patient.

a. Observation (monitoring)

It is a requirement that the patients' vital functions be observed, continuously monitored, by means of electrocardiogram (ECG), pulse oximeter, and traditional blood pressure measurement (cuff on upper arm). Based on the patient's general condition, and the type of operation/intervention, these parameters have to be recorded at appropriate time intervals (2-5 minutes).

The ECG is important because it gives indications about possible disturbances of the heart muscles' blood- and/or oxygen supply. An increase in the heart rate may, among other things, also suggest either that the patient is sensing pain or side effects of applied drugs. In order to be able to observe the ECG, three (in some cases five) self-adhesive electrodes are placed on the chest.

This is complimented by pulse oximetry, which is done by placing a ''painless clip'' onto one of the fingers of your hand. Besides measuring your heart rate, it also measures the oxygen saturation of your blood, that is, how saturated with oxygen, the haemoglobin molecules circulating in your blood are.

The traditional (non-invasive) measurement of blood pressure on the forearm also enables the continuous monitoring of changes in the patient's body, reflecting the patient's reaction to certain phases of the intervention/operation, as well as the effects of medications administered in order to maintain the pain-free unconscious sleep.

Generally, before the anaesthetic procedure is begun, the first readings of the above mentioned parameters (ECG, pulse oximetry, blood pressure) are recorded, giving baseline values, to which later readings can be compared to.

b. Initiation of anaesthesia

Simultaneously to the placement of the monitoring, a venous cannula is sited on either the back of the hand, or forearm. This looks like a small Teflon plastic tube, with a needle inside it. After correct placement of the cannula, the needle is removed, leaving the plastic tube in place, with an opening at the end, through which medication, infusions, etc. may be injected. The insertion of the cannula feels like a small mosquito bite.

In children, usually the first step is inhalation of a mixture of oxygen and anaesthetic gas through a mask placed in front of the child's mouth. Consequently, the cannula is only inserted when the child is asleep deep enough, not to feel the pain. In older co-operative children (after the skin on the back of the hand has been numbed by cream), the venous cannula is sited straight away as in adults.

Following this, in all cases oxygen is given through a mask, for a few minutes, after which medication based on the child's/adult's weight is administered in order to ensure a deep pain-free sleep. This is when the patient actually falls asleep. After this the child/adult does not perceive anything.

The airways are secured as indicated by the diagnostic/surgical intervention, since in deep unconsciousness, and/or if as necessary the muscles are relaxed, the patient is unable to breath on their own. Generally there are three possibilities for the patient to get air: through a face-, laryngeal mask, or through a tube introduced in to the trachea. This is one of the most critical phases of general anaesthesia.

2. Maintenance

a. Maintaining sleep, and the absence of consciousness

The anaesthetic gas is given continually during the intervention/operation, and as necessary the painkiller, and/or muscle-relaxant, together with any other medication, is repeatedly administered.

b. Ventilation

At the end of the day, the anaesthetist visits the patients he anaesthetised. The sole purpose of this visit is to ensure that the patient is doing well after the intervention, and is pain-free. Additionally, in instances where the nature of the operation/intervention allowed it, he may enquire whether the patient was able to drink fluids, maybe eat, did he feel sick, etc. If during this visit any outstanding problems are recognised, then solutions are suggested in consultation with the ward nursing team, which may include administration of medication.

Patients, who had major interventions/operations or are in a worse general condition originally, are re-visited by the anaesthetist the following day, in order to resolve problems that may have occurred during the night with the ward, before going into the operating theatre.

Regional

- Neuraxial anaesthesia

This is one of the more frequently used methods of regional (local) anaesthesia, consisting of two modalities: epidural and spinal anaesthesia. These can also be combined with each other, while epidural anaesthesia may also be combined with general anaesthesia.

Our spine consists of vertebrae. Individually varying, 33-35 vertebrae make up the spinal column. Between 24 of these vertebrae, small ''joints'' (discs) exist, which enable the flexible movement of our back. The sagittal and transverse figures illustrate the layers underneath the skin on our back.

It is through these layers in the disk spaces that we reach the epidural space, in epidural anaesthesia. The local anaesthetic injected into here spreads around the epidural space, reaching the different types of nerve roots that exit the spinal chord at that level. Since the epidural space is like a tube, the fluid flows in the direction of gravity first, and once it has reached the bottom, then in spreads further in the direction contrary to gravitation.

During spinal anaesthesia, the needle penetrates the layers further through the so-called dura mater (latin meaning ''tough mother''), which is the outermost layer of the three membranes directly surrounding the spinal chord. Behind it is the liquid surrounding the spinal chord, so-called liquor or cerebro-spinal fluid. It is into this liquid that the local anaesthetic is injected. The liquid is directly in contact with the nerve roots exiting the spinal chord. Simultaneously liquor circulates in a vertical direction, consequently spreading the local anaesthetic both to vertebrae and nerve roots above and below the original point of injection.

Like all local anaesthetic drugs, during neuraxial anaesthesia local anaesthetics work in the following manner. One has to imagine nerve cells like dominos standing behind one-another. When you nudge one domino, the others fall in order, one after the other. This continues until all the dominos have fallen, i.e., the information has reached the brain. This ''propagation'' of information may be interrupted in any way, e.g. by removing a domino from the line-up, or otherwise preventing it from falling. Similarly to this process, the local anaesthetic inhibits certain channels at the cellular level, whose functioning are necessary in the relay of information. Thus the information cannot pass beyond these obstacles, and the information about pain doesn't reach the brain, wherefore it doesn't exist according to our senses.

Like everything, neuraxial anaesthesia has its associated risks too. The majority of these rarely occur, e.g. nerve injury (approx. 0.015%), headache (1%), very rarely back pain. In the presence of diseases or medication affecting the coagulation, haematomas may occur. During the anaesthetic blood pressure may drop, besides the usual potential complications associated with any type of anaesthetic: heart-cardiovascular, lung-respiratory, and/or allergic reactions. Aside from other reasons, the recognition of heart-cardiovascular, lung-respiratory, and/or allergic reactions require the same routine monitoring (ECG, pulse oximetry, blood pressure) as described above for general anaesthesia.

- Peripheral regional anaesthesia

This is a form of peripheral regional anaesthesia, whose principles are similar to those of neuraxial anaesthesia. It involves the injection of local anaesthetics around the peripheral nerve roots of the body, mainly upper and lower extremities, before they branch of into the individual nerves.

In order to understand the advantage of conduction regional anaesthesia over pure local anaesthesia, we have to talk a few words about nerves. The way nerves transmit information to the brain have already been discussed above, where it was also mentioned that there exist different types of nerves. It is adequate for us to discuss the type of information these structurally and functionally different nerve fibres conduct, without having to go deeper into their different conduction properties. The simplified table below shows the six types of nerve fibres, and their basic functions.

Nerve fibres	Function	Fibre diameter	Conduction velocity
Aalpha	skeletal muscle (motor)	15 mm	100 m/s
Abeta	skin (sensory, tension)	8 mm	50 m/s
Agamma	muscle spindles (motor)	5 mm	20 m/s
Adelta	skin (temperature, pain)	<3 mm	15 m/s
B	praeganglionic autonomic	3 mm	7 m/s
C	skin (pain sensation)	1 mm	1 m/s

Let's look at an example, in order to understand the difference between ''pure'' local anaesthesia, and peripheral regional anaesthesia. If we wish to numb the hand for a surgical intervention we have two options:

	1. Block the peripheral nerve root before the different nerves branch off from it. This branching off happens somewhere between the armpit and the first couple of centimetres of the upper arm. This way all nerves responsible for moving and feeling all the different types of sensations (hot/cold, pain, tension, etc.) of our forearm, hand and fingers, are numbed with one single injection of local anaesthetic around the nerve sheath.
	2. Local block of the individual nerves necessary for the intervention, e.g. motion and/or sensation of different fingers, forearm, etc. after they have branched off. The disadvantage of this method is that single nerves innervate several areas of the hand, forearm, therefore several nerves might have to be blocked (which might entail several injections,) in order to ensure lack of motor and pain information being transmitted to the brain.

Obviously the kind of regional anaesthetic technique required depends on the type of intervention. While surgery on one single finger is feasible with a ''pure'' local block, inserting screws to fix a broken forearm would require a peripheral conduction block.

Besides the usual potential complications associated with any type of anaesthetic, specific risks associated with peripheral/local regional anaesthesia include: infection, nerve injury, and haematomas.