Paralytic and muscle relaxant use The biggest risk factor is<unk>  performed by unsupervised trainees and the use of a medication that induces muscle paralysis, such as suxamethonium (succinylcholine) or non-depolarising neuromuscular blocking drugs (muscle relaxants). During general<unk> , the patient's muscles may be paralyzed in order to facilitate tracheal intubation or surgical exposure (abdominal and thoracic surgery can only be performed with adequate muscle relaxation). Because the patient cannot breathe for themselves mechanical ventilation must be used. The paralysing agent does not cause unconsciousness or take away the patient's ability to feel pain, but does prevent the patient from breathing so their airway (trachea) must be protected and their lungs ventilated to ensure adequate oxygenation of the blood and removal of carbon dioxide. A fully paralyzed patient is unable to move, speak, blink the eyes, or otherwise respond to the pain. If neuromuscular blocking drugs are used this causes skeletal muscle paralysis but does not interfere with cardiac or smooth muscle or the functioning of the autonomic nervous system so heart rate, blood pressure, intestinal peristalsis, sweating and lacrimation are unaffected. The patient cannot signal their distress and they may not exhibit the signs of<unk>  that would be expected to be detectable by clinical vigilance because other drugs used during<unk>  may block or obtund these. Many types of surgery do not require the patient to be paralyzed. A patient who is anesthetized but not paralyzed can move in response to a painful stimulus if the analgesia is inadequate. This may serve as a warning sign that the anesthetic depth is inadequate. Movement under general<unk>  does not imply full<unk>  but is a sign that the<unk>  is light. Even without the use of neuromuscular blocking drugs the absence of movement does not necessarily imply amnesia. Light<unk>  For certain operations, such as Caesarean section, or in hypovolemic patients or patients with minimal cardiac reserve, the<unk>  provider may aim to provide "light<unk> " and should discuss this with the patient to warn them. During such circumstances, consciousness and recall may occur because judgments of depth of<unk>  are not precise. The<unk>  provider must weigh the need to keep the patient safe and stable with the goal of preventing<unk> . Sometimes, it is necessary to provide lighter<unk>  in order to preserve the life of the patient. "Light"<unk>  means less drugs by the intravenous route or via inhalational means, leading to less cardiovascular depression (hypotension), but causing<unk> " in the anesthetized subject.<unk> logist error Human errors include repeated attempts at intubation during which the short-acting anesthetic may wear off but the paralysing drug has not, oesophageal intubation, inadequate drug dose, drug given by the wrong route or wrong drug given, drugs given in the wrong sequence, inadequate monitoring, patient abandonment, disconnections and kinks in tubes from the ventilator, and failure to refill the anesthetic machine's vaporizers with volatile anesthetic. Other causes of<unk>  include unfamiliarity with techniques used, e.g. ⁠intravenous anesthetic regimes, or inexperience. Most cases of<unk>  are caused by inexperience and poor anesthetic technique, which can be any of the above, but also includes techniques that could be described as outside the boundaries of "normal" practice. The American Society of<unk> logists in 2007 released a Practice Advisory outlining the steps that<unk>  professionals and hospitals should take to minimize these risks. Other societies have released their own versions of these guidelines, including the Australian and New Zealand College of Anaesthetists. To reduce the likelihood of<unk> , anesthetists must be adequately trained and supervised while still in training. Equipment that monitors depth of<unk> , such as bispectral index monitoring, should not be used in isolation. Current research attributes the incidence of AAGA to a combination of the risks mentioned above, together with ineffective practice from ODPs, anesthetic nurses, HCAs and anesthetists. The main failures include: * Inattention or judgement errors related to drugs and volatile agents * Termination of<unk>  too soon before surgery has finished due to poor communication * Lack of understanding of offset times of volatile agents * Backflow of induction agent up a giving set * Failure to fill vaporizers (which is the cause of 19% of the cases of AAGA) * Under-dosing of induction agent during difficult intubation * Failure to monitor MAC (minimum alveolar concentration of inhaled anaesthetic required to prevent movement in 50% of patients in response to surgical incision) * Syringe swaps * Rushing caused by organizational or individual circumstances (bringing attention to staff shortage and stressful work environment) * Distractions caused by another member of staff Equipment failure Machine malfunction or misuse may result in an inadequate delivery of anesthetic. Many Boyle's machines used in many hospitals have the oxygen regulator serving as a slave to the pressure in the nitrous oxide regulator, to enable the nitrous oxide cut-off safety feature. If nitrous oxide delivery suffers due to a leak in its regulator or tubing, an 'inadequate' mixture can be delivered to the patient, causing<unk> . Many World War II vintage Boyle 'F' models are still functional and used in UK hospitals. Their emergency oxygen flush valves have a tendency to release oxygen into the breathing system, which when added to the mixture set by the<unk> logist, can lead to<unk> . This may also be caused by an empty vaporizer (or nitrous oxide cylinder) or a malfunctioning intravenous pump or disconnection of its delivery tubing. Patient abandonment (when the<unk> logist is no longer present) causes some cases of<unk>  and death. Patient physiology Very rare causes of<unk>  include drug tolerance, or a tolerance induced by the interaction of other drugs. Some patients may be more resistant to the effects of anesthetics than others; factors such as younger age, obesity, tobacco smoking, or long-term use of certain drugs (alcohol, opiates, or amphetamines) may increase the anesthetic dose needed to produce unconsciousness. There may be genetic variations that cause differences in how quickly patients clear anesthetics, and there may be differences in how the sexes react to anesthetics as well. In addition, anesthetic requirement is increased in persons with naturally red hair. Marked anxiety prior to the surgery can increase the amount of<unk>  required to prevent recall.
Anesthesia awareness
Pain tolerance
Neuroscience in space
Neural correlates of consciousness
Theories of general anaesthetic action
Affective sensation
Sense of balance
Sensory phenomena