全身麻酔: 概要

General anesthesia induces temporary unconsciousness by altering neuronal transmission in the central nervous system. It creates a reversible state where patients lose sensation and awareness, enabling painless surgery. The mechanism involves either inhibiting excitatory systems or activating inhibitory ones within the CNS, allowing surgeons to operate safely while maintaining patient comfort.

General anesthesia requires four essential components: amnesia, analgesia, unconsciousness, and immobility in response to noxious stimulation. Additionally, it must attenuate autonomic responses to surgical stress. These combined effects ensure patients remain unaware, pain-free, and unable to move during procedures, while their physiological responses to surgical trauma are minimized.

The choice of anesthetic depends on the patient's physical condition, anatomical site of surgery, and procedure duration. Anesthesiologists also consider pharmacokinetic properties and side effect profiles of available agents. Examples include inhalational agents like volatile halogenated ethers and intravenous agents such as propofol and barbiturates, each suited to different clinical scenarios.

General anesthesia decreases systemic arterial blood pressure through direct vasodilation, myocardial depression, and reduced central sympathetic tone. Respiratory effects include reduced ventilatory drive and diminished reflexes maintaining airway patency, necessitating assisted or controlled ventilation. Endotracheal intubation is often required to prevent aspiration during anesthesia.

Hypothermia occurs from multiple factors: low ambient operating room temperatures, exposed body cavities, cold intravenous fluids, and altered thermoregulatory control caused by anesthetics. Additionally, general anesthesia reduces metabolic rate, further contributing to heat loss. Preventing hypothermia is a critical monitoring priority during surgery to maintain physiological homeostasis.

Adjunct agents such as benzodiazepines, analgesics, α2-agonists, and neuromuscular blockers enhance general anesthetic effectiveness and manage side effects. These agents work synergistically with primary anesthetics to optimize unconsciousness, pain relief, and muscle relaxation. They also help mitigate postoperative complications like nausea and vomiting.

Common postoperative complications include nausea and vomiting, induced by anesthetics acting on the chemoreceptor trigger zone and brainstem vomiting center. Hypothermia, altered consciousness recovery, and hemodynamic instability may also occur. Proper monitoring during surgery and careful anesthetic selection help minimize these adverse effects and improve postoperative outcomes.