1. The main aim of anaesthesia is the prevention of pain during surgery and at other times.
2. Anaesthesia involves a balanced approach, in which the individual patient’s psyche and pathophysiology are taken into account and drugs are used to modify and control any aspect as required.
3. The decision to use a particular drug or technique must be made after careful consideration of the pathophysiological features of the individual case and how these may affect the phar­macokinetic handling and tissue response to the drugs available.
4. Any associated disease or pathophysiological abnormality should wherever possible be treated or corrected before operation, and potentially dangerous physiological disturbances avoided during and after anaesthesia.
5. Anaesthetic drugs are relatively non-toxic but there are some important effects. Halothane is occasionally associated with hepatitis and methoxyflurane with kidney damage. Malignant hyperpyrexia, the aetiology of which is uncertain, is a rare but often fatal condition which can be triggered off by several anaesthetic drugs in genetically susceptible individuals.
6. Drugs used in anaesthesia can be involved in significant unwanted interactions with other drugs.
7. The treatment of respiratory failure is usually the responsibility of the anaesthetist. Although ventilatory assistance, physiotherapy, etc. are often the mainstay of treatment, drugs of different pharmacological classes are used.
8. Pain perception is an individual sensation. Symptomatic treatment of acute pain should not therefore be based on a concept of the painfulness of certain conditions, although some anal­gesics may be more appropriate for pain of certain conditions.
9. Strong analgesics for severe chronic pain should preferably be given orally, in adequate dosage, and on a regular individualised dosage schedule.

General Considerations

Although achieving insensibility to pain and to unpleasant surroundings has been the goal of much human activity since prehistoric times, it is only since 1846 with the introduction of ether by Morton that this could be done with any re­liable chance of success. Anaesthesia has devel­oped and been refined considerably since that time, and several important milestones are re­cognized and worthy of recall. These include the discovery of the local anaesthetic action of co­caine by Koller in 1884 and its use to produce spinal anaesthesia by Bier in 1898, the perfec­tion of endotracheal anaesthesia by Magill and Rowbotham about 1920, the introduction of the first barbiturate for induction of anaesthesia in 1932, and the introduction of curare in 1942.
In recent years, the specialty of anaesthesia has been broadened, and its scope is well de­scribed in a definition for the US Department of Labor (Dripps 1966):

Anesthesiology is a practice of medicine dealing with:

• The management of procedures for ren­dering a patient insensible to pain during surgical procedures.
• The support of life functions under the stress of anesthetic and surgical manipu­lations.
• The clinical management of the patient unconscious from whatever cause.
• The management of problems in pain re­lief.
• The management of problems in cardiac and respiratory resuscitation.
• The application of specific methods of inhalational therapy.
• The clinical management of various fluid electrolyte and metabolic disturbances.

The modern concept is one of ‘balanced an­aesthesia’, in which the whole of the patient’s psyche and pathophysiology are taken into ac­count and drugs are used to modify and control any aspect as required. Thus, as well as general anaesthetic agents, drugs of many classes – tran­quillisers, analgesics, muscle relaxants, drugs af­fecting the autonomic system etc. – all fall within the sphere of interest of the anaesthetist. ( Some of the more important of these will be discussed further at later part – Drugs Used in Anaesthesia .)

Although the use of cathartics and enemas is traditional, these measures are most unlikely to reduce absorption since this usually occurs rap­idly in the upper small intestine. They can only add to the misery and discomfort of the patient Efficacy in removal of drug has never been es­tablished. In one recent study, saline catharsis had no beneficial effect whatsoever on the ab­sorption of aspirin taken with charcoal (Sketris et al. 1982).

Whole Gut Lavage

One situation where attempts to empty the bowel may be helpful is in poisoning with ‘slow’ or ‘timed release’ formulations. The number of such preparations on the market is increasing and since they usually contain a much larger dose of drug than ordinary tablets, intoxication may be severe and prolonged.

In such circumstances, rapid emptying of the bowel might limit in absorption. The preferred technique is ‘whole gut lavage’ in which normal saline is given by nasogastric tube at a rate of 2 litres an hour (Woo et al. 1976). Although this technique is readily controlled and rapidly effective in emptying the bowel in conscious patients being prepared for abdominal surgery, its efficacy in removing un-absorbed drug has yet to be established. It may not be effective and could possibly be dangerous in poisoned patients with grossly depressed gas­trointestinal motility.

Activated Charcoal

Activated charcoal has great adsorptive ca­pacity and can reduce the absorption of many compounds if taken orally at the same time (Neuvonen 1982; Pond 1986). The charcoal must be given in great excess (at least 10 times the weight of the drug) and efficacy falls off rap­idly as the time interval between ingestion of the poison and administration of the charcoal increases. After 1 hour, there is little inhibitory effect on the absorption of most drugs, although a significant reduction has been reported with phenytoin.

The time interval during which ac­tivated charcoal can significantly reduce ab­sorption following overdosage may be increased by the presence of food in the stomach (Olkkola & Neuvonen 1984). Oral activated charcoal ap­pears to be as effective as emesis induced by syrup of ipecac in limiting absorption (Neuvo­nen et al. 1983), but its administration after gas­tric lavage is of little or no benefit (Comstock et al. 1982).

Although the delay between inges­tion of the drug and arrival in hospital is usually such that significant reduction in absorption by oral activated charcoal is unlikely, there is no contraindication to its use and repeated admin­istration greatly increases the elimination of some drugs.