Intravenous general anaesthesia

Advantages of intravenous general anaesthesia include a quick set-in of anaesthesia without the excitement stage and favourable nature of the patient's sleep. However, the drugs used for intravenous anaesthesia act for a short period and are therefore not suitable for major operations, if used alone.

Derivatives of barbiturate acid (sodium thiopental and hexenal) produce a fast anaesthetic sleep without the excitement stage. Anaesthesia is maintained for 20 minutes, and awakening is fast. The clinical profiles of sodium thiopental and hexenal are identical, hexenal inhibiting the respiratory system at a lesser degree.

Barbiturates are used prepared ex tempore: the content of the vial (1 g of the drug) before the anaesthesia is dissolved in 100 ml of normal saline to prepare 1% the drug. The drug is given slowly at a rate of 1 ml per 10-15 seconds. After giving 3-5 ml for a period of 30 seconds the patient is examined for sensitivity to barbiturates, after which the process is continued to induce the surgical stage of anaesthesia. The total dose should not exceed 1, 000 mg. During giving the drug the nurse controls the patient's condition (pulse, breathing rate and blood pressure). The anaesthetist checks the state of the pupils, eyeballs and corneal reflexes to assess the depth of anaesthesia.

Suppression of respiration is characteristic of barbiturate anaesthesia, especially that induce by thiopental, which necessitates having a ventilator. With the onset of apnoea artificial respiration is started with the mask of the ventilator. If the drug is given too fast, it can cause hypotension and bradycardia, which requires that the giving of the drug be stopped.

In surgical practice, barbiturate anaesthesia is used for minor operations (10-20 minutes in duration) such as incision and drainage, manipulation of fractures and dislocations and dilatations. Barbiturates are also used to initiate anaesthesia.

Viadryl is used in a dose of 15 mg/kg (average: of 1, 000 mg). It induces anaesthesia which is difficult to control and is therefore given only in small doses in combination with nitrous oxide. In high doses the drug can cause hypotension, phlebitis and thrombophlebitis. To prevent these, it is recommended that the drug be given slowly and into the central vein as 2, 5% solution. Viadryl is used to initiate anaesthesia or to perform the short-term procedures.

Propanidide (epontol, sombrevin) is available in 10 ml ampoules of 5% solution. The dosage is 7-10 mg/kg given as an intravenous bolus (500 mg within 30 seconds). Sleep is induced instantly, «at the tip of the needle». Anaesthetic sleep lasts for 5-6 minutes. awakening is fast and quiet. Propanidide causes hyperventilation, which sets in immediately after the loss of consciousness. Occasional apnoea may call for the use of the artificial ventilation machine. The disadvantage of this drug is the risk of hypotension that occurs during its injecting. It is mandatory to control the blood pressure and pulse. The drug is used to initiate anaesthesia, for outpatient surgical manipulations and for momentary surgeries.

Sodium oxybutyrate is given intravenously and slowly, the average dose being 100-150 mg/kg. The drug produces superficial anaesthesia and is therefore often given in combination with other anaesthetics, for example with barbiturates, propanidide. It is often used to initiate anaesthesia.

Ketamine (ketalar) can be injected either intravenously or intramuscularly. The dose is as high as 2-5 mg/kg. It can be used as a monoanaesthetic or as an initiator. Ketamine gives superficial anaesthesia, stimulates cardiovascular function, elevates blood pressure, accelerates pulse rate. Thus hypertension is a contraindication for the use of ketamine. It is widely used in hypotension and shock. Ketamine may produce hallucinations at the end of anaesthesia when the patient is waking up.

Endotracheal anaesthesia

Endotracheal anaesthesia is the type of anaesthesia in which the anaesthetic enters the body through a tube placed in the trachea. Advantages of this method are as follows:

• provides a free passage of the respiratory tract;

• can be used for operations on the neck, face and head;

• lowers the risk of aspirating vomitus or blood;

• reduces the amount of anaesthetic to be used;

• improves gas metabolism by means of a decrease in the «dead» space.

Indicated for major surgeries, endotracheal anaesthesia is used in the form of polyvalent anaesthesia with muscle relaxation (combined anaesthesia). The sum effect of using several anaesthetics in small quantities reduces the toxic effect imposed by each of them separately.

Currently, combined anaesthesia seeks to provide analgesia, unconscious state and relaxation. Analgesia and unconscious state are achieved with one or several anaesthetics (inhalation and non-inhalation). Anaesthesia is maintained at the 1^st level of the surgical stage of anaesthesia. Muscle relaxation or relaxation is achieved by fractional injection of muscle relaxants.

There are three stages of anaesthesia:

Stage 1 - Induction. To initiate anaesthesia, whichever anaesthetic that can produce adequate narcotic sleep without the excitement stage can be used. Barbiturates, fentanyl combined with sombrevin, or promedol combined with sombrevin, are generally used. Also, sodium thiopental is often used. The drugs are used in the form of 1% solution, given intravenously at a dose of 400-500 mg, maximal one being 1, 000 mg. Intubation of the trachea is performed after the muscle relaxant has been given.

Stage 2 - Maintenance. For maintenance of general anaesthesia, whichever anaesthetic that can protect the body from the trauma of operation can be used (halothane, cyclopropane, nitrous oxide with oxygen), as well as the neuroleptanalgesics. Anaesthesia is maintained at the 1^st and 2^nd levels of the surgical stage of anaesthesia, and to prevent muscle resistance, muscle relaxants that cause myoplegia of all the skeletal muscles (including the respiratory ones) are given. This accounts for why an artificial ventilation machine is currently used, which provides rhythmic compressing the bag, or bellows.

Nowadays, neuroleptanalgesia is being most widely used: nitrous oxide with oxygen, fentanyl, droperidol and muscle relaxants. Anaesthesia is maintained with nitrous oxide + oxygen in the ratio of 2: 1, fractional injection of fentanyl and droperidol 1-2 ml each 15-20 minutes is provided. Tachycardia requires injection of fentanyl, whereas hypertension necessitates administration of droperidol. This type of anaesthesia is the safest for the patient.

Stage 3 - Conclusion. At the end of anaesthesia the anaesthetist gradually stops giving the anaesthetic and muscle relaxants. The patient regains consciousness, starts to breathe on his/her own and muscle tonus is reestablished. The indices of P_O2, P_CO2, and pH are the indicators of the respiratory adequacy. After the main homeostatic indicators have been restored, the patient can be extubated and transported for further observation in the recovery ward.

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