Principles of General Anaesthesia

Principles of general Anaesthesia Induction, maintenance and recovery • • • Induction: - Refers to the transition from awake state to an anaesthetised state. - This process is the first stage of a sequential process that begins with the patient preparation and assessment and continues in the safe and monitored environment of the anaesthetic or the operating theatre where the administration of the drug takes place. - During this phase there is a rapid and smooth loss of consciousness. Maintenance: - In this phase the patient is remains anaesthetised. - The patient is kept at a state of sedation, less of consciousness and loss of sensation. - In this phase the anaesthetises closely monitors the patient’s vital signs and adjusts the anaesthetic delivery as need to maintain an appropriate depth. - Sevoflurane is the most commonly used inhaled anaesthetic. ✓ Like most halogens it works by binding to ligand gated ion channels to block CNS transmission. It is suggested that the binds to enhance the GABA receptors, glycine receptors, and inhibits excitatory synaptic channels by binding to serotonin, nicotinic Ach and glutamate receptors. ✓ Causes respiratory and myocardial depression. ✓ The most significant adverse effect is malignant hyperthermia; however, it is rare. Recovery: - This begins when then maintenance phase by the anaesthetists stops giving the drug to wear off or gives another drug to reverse their effects so that the patient regains their consciousness or sensation. - This has two phases: ✓ Phase I: ensures the patient’s full recovery from anaesthesia and return the vitals to baseline. In this phase the patient is moved to a recovery room where the patient continues to monitor their breathing and heart function. ✓ Phase II: this phase focuses on preparing patients for hospital discharge, including education regrading the surgeon’s post-operative instructions and any prescribed discharge medication. Intraoperative monitoring • Oxygen: - Oxygen analyser -> should be in continuous operation for every patient when an anaesthesia breathing system is in use. - Pulse oximeter -> should be in use for every patient undergoing general anaesthesia or sedation. • Ventilation: - Breathing system disconnection or ventilator failure alarm -> this is done via a monitor that is capable of doing so. It should be automatically activated for continuous use during the operation. - Carbon dioxide monitor -> should be used for every patient undergoing general anaesthesia and should be immediately available for any patient undergoing sedation. • Cardiovascular: - ECG -> should be used for every patient undergoing general and major regional anaesthesia. - Intermittent non-invasive blood pressure monitor -> should be available for every anaesthetised patient. - Continuous invasive blood pressure monitor -> equipment to provide continuous invasive blood pressure monitoring should be available. This refers to a monitor connected via a transducer to an intra-arterial line. Monitoring effects on the brain: - When clinically indicated, equipment to monitor the anaesthetic effect on the brain should be available for use on patients, especially those at high risk of awareness during general anaesthesia. • • • Inhalation anaesthetic agent monitor: - To identify and monitor the inspired and end-tidal concentration of inhalational anaesthetics should be in use for every patient undergoing general anaesthesia from an anaesthesia delivery system where the inhalation anaesthesia agents are delivered. Temperature monitor: To monitor “core temperature” continuously should be available for every patient undergoing general anaesthesia. - Temperature monitoring should be used whenever warming devices are being used. Neuromuscular function monitor: - Quantitative neuromuscular function monitoring should be available for every patient when neuromuscular blockade has been induced and should be used whenever the anaesthetist is considering extubating following the use of nondepolarising neuromuscular blockade. - •