Many people think that having an anaesthetic consists of just a needle, which the anaesthetist injects to make you ‘go to sleep’; after this the anaesthetist leaves you and you ‘wake up’ when the operation is over. In fact, as well as constantly looking after you during your anaesthetic, your anaesthetist gives you quite a few medications – usually somewhere between three and fifteen – all for different reasons.
There are four main types of medications used in general anaesthesia:
- induction medications to produce unconsciousness
- analgesics to provide pain relief
- muscle relaxants to induce muscle relaxation
- inhalational anaesthetics to keep you unconscious.
Other medications which are given include:
- medications that produce short-term memory loss or amnesia
- medications that minimise nausea and vomiting (anti-emetics)
- medications that counter-act the effect of other medications (antagonists)
- and medications that suppress certain nervous reflexes, such as slowing of the heart.
Also, some patients may not have a general anaesthetic but may remain conscious, with part of their body made numb by the use of local anaesthetics.
These medications include thiopentone or pentothal (which was introduced in the 1930s), and propofol. When given by intravenous injection, these medications quickly make you unconscious. This rapid loss of consciousness makes the induction of anaesthesia much more pleasant than previously, when patients had to breathe ether or chloroform.
These medications, also known as painkillers, are mostly opiates or narcotics. They are either derived from the opium poppy (such as morphine) or are synthesised in a laboratory (such as pethidine or meperidine, anileridine, fentanyl, alfentanil, sufentanil, and remifentanil).
These medications work specifically to weaken or relax most of the (voluntary) muscles of the body. However, they do not affect the muscles of the heart, nor those of the intestines. Before muscle relaxants were introduced in the 1940s, patients had to be given large amounts of anaesthetic medications to ensure that they were deeply anaesthetised. This was necessary to cause their muscles to relax so that the surgeon could operate within the abdomen, or perform other delicate surgery. Now, with the use of muscle relaxants, patients do not have to receive very large amounts of anaesthetic medications nor be so deeply anaesthetised. This helps to reduce the side-effects of anaesthesia. Muscle relaxants include suxamethonium (or succinyl choline), pancuronium, atracurium, vecuronium, and rocuronium.
These medications keep you unconsciousness during the operation. They can also be used to induce anaesthesia, especially in small children. These medications are called inhalational agents because you inhale them or breathe them in. In the 1950s, a new inhalational agent, halothane, was introduced and rapidly replaced the older agents such as ether. Halothane has now been largely superseded by even better inhalation medications, and the commonly used agents include enflurane, isoflurane, sevoflurane, and desflurane.
These medications help reduce nausea and vomiting and so are termed anti-nauseants or anti-emetics. They include droperidol, Stemetil, Gravol, and ondansetron.
Your anaesthetist may use other medications to decrease the chance of you remembering anything that happens in the Operating Room. These medications include diazepam and midazolam, which belong to the class of medications known as benzodiazepines. Some medications are given to counteract the effects of other medications. These include naloxone, to counter the effects of an opiate or narcotic; flumazenil, to counter the effects of a benzodiazepine; and neostigmine, to reverse the actions of most of the muscle relaxants. Medications which are used to change your heart rate include atropine (to increase it) and esmolol (to decrease it). Other medications can raise your blood pressure (epinephrine or adrenaline) or lower it (nitroprusside).
Injection of a local anaesthetic around a nerve or a group of nerves temporarily blocks the transmission of the electrical impulses in the nerve. The lack of transmission causes the area of the body supplied by the nerve to become numb. This is also known as a ‘sensory block’, which may progress to muscle weakness, depending on the concentration and dose of the local anaesthetic used.