The ideal general anesthetic state is characterized by a loss of all sensations and includes analgesia and muscle relaxation. Neuronal depression in specific areas of the CNS is believed to be largely responsible for such an anesthetic state. The areas involved include many cortical regions that are represented by excitatory pyramidal cells and inhibitory/excitatory stellate cells. Excitation of the pyramidal cells helps to maintain consciousness, whereas the degree of inhibition or excitation of stellate cells determines the overall activity level of the pyramidal cells with which they synapse. As the concentration of the anesthetic agent increases in the brain, the degree of overall neuronal depression also increases, resulting in progressively deeper stages of anesthesia. Based on observations using diethyl ether, Guedel in 1920 originally described this progression as four distinct stages, and Gillespie subsequently further subdivided these stages, as described in the following sections.

Stage 1: Analgesia

Characterized by a mild depression of higher cortical neurons, this stage is suitable for minor surgical procedures that do not require significant neuromuscular relaxation. Depression of thalamic centres probably accounts for the observed analgesia, because many of the neuronal systems that mediate pain sensation traverse through this anatomic area. Some general anesthetic agents do not possess significant analgesic activity, but they all produce a loss of consciousness that, in turn, can produce some degree of insensitivity to painful stimuli.

Stage 2: Delirium

As depression of inhibitory neurons in the CNS progresses, especially in the reticular formation (a network of neurons in the brainstem), a resultant excitation of cortical motor neurons leads to significant involuntary muscle activity, such as urination, delirium, uncontrolled skeletal muscular movements, and increased heart rate, blood pressure, and respiration. These paradoxical responses are caused by suppression of inhibitory neurons that normally function to closely regulate such neuronal activity. Ideally, an anesthetic agent should produce little or no excitatory phase. Together, stages 1 and 2 comprise the induction period, which ideally should be of short duration.

Stage 3: Surgical Anesthesia

This stage is divided into four planes characterized by increasing CNS depression: first, loss of spinal reflexes; second, decreased skeletal muscle reflexes; third, paralysis of intercostal muscles; and fourth, loss of most muscle tone. Stage 3 is also characterized by regular breathing, a loss of many reflexes, and roving eyeball movements

Journal of Surgery and Anaesthesia is a peer reviewed, open access journal dedicated to publishing research on all aspects of surgery and anaesthesia. This journal aims to keep anaesthesiologists, anaesthetic practitioners, surgeons and surgical researchers up to date by publishing clinical & evidence based research. This scientific Journal leads the specialty in promotion of original research by providing immediate open access to all articles after publication. Journal of Surgery and Anesthesia addresses all aspects of surgery & anesthesia practice, including anesthetic administration, pharmacokinetics, preoperative and postoperative considerations, coexisting disease and other complicating factors, General Surgery, Robotic Surgery, Orthopedic Surgery, GI Surgery, Neurosurgery, Plastic Surgery, Cardiothoracic Surgery, Vascular Surgery, Urology, Surgical Oncology, Radiology, Ophthalmology, Pediatric Surgery, Trauma Services, Minimal Access Surgery, Endocrine Surgery, Colorectal Surgery, Laparoscopic and Endoscopic Techniques and Procedures, Preoperative and Postoperative Patient Management, Complications in Surgery and New Developments in Instrumentation and technology related to surgery, Intra-Operative Regional Anesthesia Administration Techniques, Peri-Operative Pain, Obstetric Anesthesia, Pediatric Anesthesia, General Anesthesia, Sedation, Regional Anesthesia, Outcome Studies and Associated Complications, etc.

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