General anaesthesia

In modern medical practice, general anaesthesia is a complex procedure involving:

preanaesthetic assessment
administration of general anaesthetic drugs
cardirespiratory monitoring
analgesia
airway management
fluid management

Preaneasthetic evaluation

Monitoring

Monitoring involves the use of several technologies to allow for a controlled induction of anaesthesia, maintenance and emergence from anaesthesia.

There are different guidelines concerning monitoring during anaesthesia, illustrated by the Australian and New Zealand College of Anaesthetists recommendations:

1. Continuous electrocardiography (ECG) - placement of electrodes which monitor heart rate and rhythm, as well as showing evidence of other cardiac pathologies (e.g. ischaemic heart disease).

2. Continuous pulse oximetry (SpO2) - Allows early detection of cyanosis and a fall in patients' blood oxygen tension.

3. Blood pressure Monitoring (NIBP or IBP) - Generally non-invasive methods of measuring blood pressure such as a dinamap(TM) or machine which continuously checks blood pressure non-invasively. Alternatively, for major surgery such as cardiac surgery, anaethetists may use invasive monitoring with an arterial cannula.

4. Agent concentration measurement - Common anaesthetic machines have meters to measure the percent of inhalational anaesthetic agent used (e.g. sevoflurane, isoflurane, desflurane, halothane etc).

5. Low oxygen alarm - Almost all circuits have a backup alarm in case the oxygen delivery to the patient becomes compromised. This warns if the fraction of inspired oxygen drops lower than room air (21%) and allows the anaethetist to take immediate remedial action.

6. Circuit disconnect alarm - indicates failure of circuit to achieve a given pressure during mechanical ventilation.

7. Carbon dioxide measurement (capnography)

induction and maintenance of anaesthesia

Muscle relaxation with skeletal muscle relaxants is an integral part of modern anesthesia. The first drug used for this purpose was curare, introduced in the 1940's and now superceded with drugs with fewer side effects. Muscle relaxation allows surgery within major body cavities, eg. abdomen and thorax without the need for very deep planes of anesthesia, and is also usd to facilitate endo-tracheal intubation.

Airway management

External Links:

Australian & New Zealand College of Anaesthetists Monitoring Standard