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General anaesthesia: Difference between revisions
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(Created page with "'''General anaesthesia''' is a state characterised by: * Reversible loss of consciousness * Absence of pain (analgesia) * Blocking of noxious autonomous reflexes * Loss of memory (amnesia) * Relaxation of skeletal muscles Multiple drugs are needed to achieve general anaesthesia. Many different drugs are used as general anaesthetics. They’re either inhalation anaesthetics or intravenous anaesthetics, according to the method of delivery. These two types can be...") |
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* Relaxation of skeletal muscles | * Relaxation of skeletal muscles | ||
Multiple drugs are needed to achieve general anaesthesia. Many different drugs are used as general anaesthetics. They’re either [ | Multiple drugs are needed to achieve general anaesthesia. Many different drugs are used as general anaesthetics. They’re either [https://new.greek.doctor//wiki/Inhalation_anaesthetics inhalation anaesthetics] or [https://new.greek.doctor//wiki/Intravenous_anaesthetics intravenous anaesthetics], according to the method of delivery. These two types can be combined to exploit the favourable properties of each type while minimizing the unfavourable properties. | ||
There are six stages of achieving general anaesthesia: | There are six stages of achieving general anaesthesia: | ||
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== Preparation == | == Preparation == | ||
During induction, the patient will not be breathing (apnoea) momentarily, from the administration of anaesthetic to when an airway device is inserted and the patient can be ventilated. To prevent hypoxaemia (desaturation) during this period, the patient is preoxygenated before induction. This involves giving the patient 100% FiO2 oxygen for a few minutes. This replaces the room air (which is 21% oxygen) in the patient's lungs with pure oxygen. When the patient later becomes apnoeic, the oxygen in the lungs acts as a "reserve". Oxygen should be administered with > 10 L/min. | During induction, the patient will not be breathing (apnoea) momentarily, from the administration of anaesthetic to when an airway device is inserted and the patient can be ventilated. To prevent hypoxaemia (desaturation) during this period, the patient is preoxygenated before induction. This involves giving the patient 100% FiO2 oxygen for a few minutes. This replaces the room air (which is 21% oxygen) in the patient's lungs with pure oxygen. When the patient later becomes apnoeic, the oxygen in the lungs acts as a "reserve". Oxygen should be administered with > 10 L/min. | ||
Preoxygenation is usually achieved with a face mask. [ | Preoxygenation is usually achieved with a face mask. [https://new.greek.doctor//wiki/Non-invasive_ventilation Non-invasive ventilation] should be used for [https://new.greek.doctor//wiki/Obesity obese] or [https://new.greek.doctor//wiki/Pregnancy?action=edit&redlink=1 pregnant] patients, or those who are critically ill. Preoxygenation should last for approximately 3 minutes or for 8 vital capacity breaths. | ||
== Induction == | == Induction == | ||
Induction refers to the transition from wakefulness to loss of consciousness. An analgesic (usually an [ | Induction refers to the transition from wakefulness to loss of consciousness. An analgesic (usually an [https://new.greek.doctor//wiki/Opioid?action=edit&redlink=1 opioid]) is usually administered first, followed by the anaesthetic. When the patient is sufficiently anaesthetised and no longer spontaneously breathing, the patient is ventilated with a bag-mask and a muscle relaxant is administered to facilitate intubation. When the relaxant is effective, the patient is intubated. From this time until the endotracheal tube is successfully placed, the patient is not breathing; this is the apnoeic period. | ||
During the apnoeic period one can administer oxygen nasally while placing the airway device. This is low-risk and should be used in those with difficult airways (where intubation may take longer than the oxygen reservoir lasts). | During the apnoeic period one can administer oxygen nasally while placing the airway device. This is low-risk and should be used in those with difficult airways (where intubation may take longer than the oxygen reservoir lasts). | ||
Confirm successful tube placement by visualisation of the chest elevating, auscultation of bilateral breathing sounds, and confirming elevated end-tidal CO2 (CO2 in the exhaled air) on the [ | Confirm successful tube placement by visualisation of the chest elevating, auscultation of bilateral breathing sounds, and confirming elevated end-tidal CO2 (CO2 in the exhaled air) on the [https://new.greek.doctor//wiki/Capnography?action=edit&redlink=1 capnograph]. | ||
=== Rapid sequence induction === | === Rapid sequence induction === | ||
For patients who are not fasting or vomiting and are therefore at risk of aspiration during ventilation with a face mask. | For patients who are not fasting or vomiting and are therefore at risk of aspiration during ventilation with a face mask one can do a rapid sequence induction (RSI), where fast-acting muscle relaxant ([https://new.greek.doctor//wiki/Suxamethonium suxamethonium] or [https://new.greek.doctor//wiki/Rocuronium rocuronium]) are used and given simultaneously as the induction anaesthetic and the patient isn't bag-mask ventilated prior to intubation. One can also apply pressure to the cricoid cartilage with the intention to "block" the oesophagus, reducing the risk of aspiration, although the effectiveness of this manoueuvre is disputed. | ||
== Maintenance == | == Maintenance == | ||
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=== Circulation === | === Circulation === | ||
The fluid intake (infusions) is monitored and compared to the fluid loss, usually as blood which is suctioned and as urine in the [ | The fluid intake (infusions) is monitored and compared to the fluid loss, usually as blood which is suctioned and as urine in the [https://new.greek.doctor//wiki/Bladder_catheter bladder catheter], if present. During long-lasting open surgeries, insensible fluid loss must be taken into account as well. | ||
== Reversal and recovery == | |||
The muscle relaxant must be reversed, either by [https://new.greek.doctor//wiki/Neostigmine neostigmine] (cheap) or [https://new.greek.doctor//wiki/Sugammadex sugammadex] (expensive, only works for a few muscle relaxants), to allow the patient to start breathing again and the patient to be extubated. The general anaesthetic is slowly weaned off, and the patient is stimulated to be woken up. | |||