- General anaesthesia removes ability of patient to protect himself
- Safety and physiological control becomes the responsibility of the anaesthetist
- Anaesthetist needs to
- Maintain airway and oxygenation
- Preserve circulation
- Prevent hypothermia
- Prevent injury
- Monitor during anaesthesia
Airway management
- General anaesthesia removes muscle tone
- Without assistance airway will be compromised
- Methods of maintaining airway include
- Manual methods (e.g. Jaw thrust)
- Guedel airway
- Laryngeal mask
- Endotracheal tube
- Tracheostomy tube
Complications of endotracheal intubation
- Failure to intubate and loss of airway control
- Unrecognised oesophageal intubation
- Accidental intubation of a main bronchus
- Trauma to the larynx, trachea or teeth
- Pulmonary aspiration
- Disconnection or blockage of the tube
- Tracheal stenosis
Hypothermia
- Hypothermia develops rapidly during general anaesthesia
- Occurs due to:
- Radiation of body heat
- Vasodilatation
- Infusion of cold fluids
- Evaporation from open body cavities
- Hypothermia develops more rapidly in children
- Heat loss can be reduced by use of:
- Warming blanket
- Warm intravenous fluids
- Warm fluid to irrigate body cavities
Monitoring during anaesthesia
- The continuous presence of an adequately trained anaesthetist is essential
- Accurate monitoring of vital signs is obligatory
- Facilities for cardiopulmonary resuscitation should be immediately available
- Monitoring of the following is considered essential for all patients:
- Temperature
- Heart rate
- Blood pressure
- ECG
- Oxygen content of inspiratory gas mix
- End-tidal carbon dioxide
- Pulse oximetry
- Alarms should indicate
- Oxygen supply failure
- Ventilator disconnection
- The following may be considered for major surgery
- Invasive blood pressure monitoring
- Central venous pressure
- Urine output
Recovery from anaesthesia
- Recovery from anaesthesia should be monitored by a suitable trained nurse
- Should occur in a properly equipped recovery area
- Anaesthetist should be immediately available
- Causes of failure to breath after general anaesthesia include:
- Obstruction of airway
- Central sedation due to opiates or anaesthetic agent
- Hypoxia
- Hypercarbia
- Hypocarbia due to overventilation
- Persistent neuromuscular blockade
- Pneumothorax
- Circulatory failure leading to respiratory arrest
Postoperative nausea and vomiting
Mechanisms of postoperative nausea and vomiting
- Chemoreceptor trigger zone
- Found in the area postrema of the 4th ventricle
- Actions mediated via D2 receptors
- Antagonists include domperidone, metoclopramide, prochlorperazine
- Vestibular apparatus
- Actions mediated via muscarinic and H2 receptors
- Antagonists include cyclizine, hyoscine
- Vagal sensory neural endings
- Actions mediate via serotonin
- Antagonists include serotonin (e.g. ondansetron)
Bibliography
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20: 813-832.
Berti M, Fanelli G, Casati A et al. Hypothermia prevention and treatment. Anaesthesia
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Desborough J P. Body temperature control and anaesthesia. Br J Hosp Med 1997;
57: 440-442.
Ku C M, Ong B C. Postoperative nausea and vomiting. a review of current literature. Singapore
Med J 2003; 44: 364-374.
Royston D, Cox F. Anaesthesia: the patients' perspective. Lancet 2003; 362: 1648-1658.
Sessler D I. Perioperative heat balance. Anesthesiology 2000; 92: 578-596 |