Steps in Conducting General Anesthesia
Steps in Conducting General Anesthesia
First Step of General Anesthesia: Preoperative Evaluation, Anesthesia Plan and Premedication
Safe conduction of anesthesia depends on preoperative evaluation, anesthesia plan, monitoring & responding to a homeostatic change throughout anesthesia and operation. The fundamental purpose of preoperative evaluation is to obtain pertinent information regarding the patient's current and past medical history and to formulate an assessment of the patient's intraoperative risk and requisite clinical optimization. At a minimum, the preanesthesia visit should include an interview with the patient to review the medical history (including medications, allergies, coexisting diseases, and previous operations), an appropriate physical examination, review of laboratory data, consultation with the operating surgical team and/or involvement of other specialties according the patient's condition and need, and a formulation and discussion of the planned anesthetic with the patient. To be valuable, performing a preoperative test implies that an increased perioperative risk exists when the results are abnormal and a reduced risk exists when the abnormality is corrected.
Following preoperative evaluation and obtaining informed consent an anesthetic plan should be formulated that will optimally accommodate the patient's baseline physiological state, including any medical conditions, previous operations, the planned procedure, drug sensitivities, previous anesthetic experiences, and psychological makeup. Inadequate preoperative planning and errors in patient preparation are the most common causes of anesthetic complications. Anesthesia and elective operations should not proceed until the patient is in optimal medical condition. Anesthesia plan may include administration of premedication for anxiolysis (diazepam 5-10 mg orally/IV), prophylaxis of aspiration (metoclopramide 10mg IV/orally, Cimetidine 200-300mg orally or Ranitidine 150mg orally), drying air way (Atropine 0.5 - 1mg), etc and with holding some drugs like oral hypoglycemic agent should be considered
Second Step of General Anesthesia: Induction and Securing the Air Way
Induction, the process of initiating general anesthesia (unconsciousness) by administration of drug or combination of drugs, is the most critical phase in the whole process. Selection of drugs for induction and maintenance of anesthesia depends on the patient preexisting condition which is identified during preoperative evaluation and according to anesthetic plan. Before induction, minimum basic standard monitor should be applied & base line values are recorded. Intravenous access should be opened always before anesthesia.
Before administering anesthesia we have to administer 100% oxygen for 3 to 5 minutes to replace the air which contains 78 % of nitrogen in the functional residual capacity of the lungs with oxygen. This practice should increase the margin of safety during periods of upper airway obstruction or apnea that may accompany induction of anesthesia.
Induction of general anesthesia can be achieved by IV injection of induction agents (e.g., Ketamine 1-2 mg IV or 5- 10 mg IM, Thiopentone 3-5mg IV & propofol 1-2.5 mg/kg) or by the slower inhalation of anesthetic vapors (e.g., halothane) with a face mask, or a combination of both. In addition to the induction drug, most patients receive an injection of narcotic analgesic (e.g., pethedine .5 to 1 mg/kg, Fentanyl 1-2 μg/kg). The next step of the induction process is the securing of the airway. This may be done manually holding the patient's jaw such that his or her natural breathing is unimpeded by the tongue or may demand the insertion of airway device such as a laryngeal mask airway or endotracheal tube. Not all surgery requires muscle relaxation. If you need endotracheal tube insertion suxamethonium 1-2 mg IV is used
Third Step: Maintenance
Maintenance phase: It is the time from the end of induction to emergence phase in which procedures are performed safely. At this point, the drugs used to initiate the anesthetic are beginning to wear off, and the patient must be kept anesthetized using a maintenance agent.
- For the most part, this refers to the delivery of anesthetic gases into the patient's lungs. These may be inhaled as the patient breathes himself or delivered under pressure by bagging manually, or each mechanical breath of a ventilator
- The maintenance phase is usually the most stable part of the anesthesia. However, it is important to understand that anesthesia is a continuum of different depths. A level of anesthesia and relaxation that is satisfactory for surgery to the skin of an extremity may be inadequate for manipulation of the bowel.
- Appropriate levels of anesthesia must be chosen both for the planned procedure and for its various stages.
- If muscle relaxants have not been used, inadequate anesthesia is easy to spot. The patient will move, cough, or obstruct his airway if the anesthetic is too light for the stimulus being given.
- If muscle relaxants have been used, then clearly the patient is unable to demonstrate any of these phenomena. In these patients, the anesthetist must rely on careful observation of autonomic phenomena such as hypertension, tachycardia, sweating, and capillary dilation to decide that the patient requires a deeper anesthetic.
- Excessive anesthetic depth, on the other hand, is associated with decreased heart rate and blood pressure, and, if carried to extremes, can jeopardize perfusion of vital organs or be fatal. Short of these serious misadventures, excessive depth results in slower awakening and more side effects.
Fourth Step: Emergence
Emergence: It is the phase awakening. Emergence from general anesthesia should ideally be smooth and gradual awakening in a controlled environment. Experience and close communication with the surgeon enable the anesthetist to predict the time at which the application of dressings and casts will be complete. In advance of that time, anesthetic vapors have been decreased or even switched off entirely to allow time for them to be excreted by the lungs. Residual muscle relaxant is reversed using neostigmine 0.2 - 0.5mg/kg with atropine 0.1- 0.2mg/kg IV. Removal of endotracheal tubes or other air way device shall be performed when the patient has regained sufficient control of his or her airway reflexes and after proper suctioning.
The patient recovering from anesthesia should be monitored for common problems in the postoperative period to ensure their safety, providing for a smooth and uneventful recovery. Common complications may include, Hypoxemia related to airway obstruction or inadequate respiration, hypoventilation which results in hypoxemia and hypercarbia, hypotension due to ongoing loss or bleeding, hypothermia, pain, nausea and vomiting and changes in heart rate and rhythm these should be addressed accordingly in Post Anesthesia Care Unit (PACU) until full recovery of consciousness and complications are managed.
It is the art of rendering a part of the body insensible for surgical operation or manipulation based on the concept that the pain is conveyed by nerve fibers which are amenable to interruption anywhere along their path way (Table2:2).
|Spinal anesthesia||It is a massive & temporary interruption of nerve transmission within the subarachnoid space produced by injection of a local anesthetic solution into cerebrospinal fluid to produce a reversible loss of sensation & motor function.|
|Epidural anesthesia||It involves the use of local anesthetics injected into the epidural space to produce a reversible loss of sensation and motor function.|
|Intravenous regional anesthesia||It is an Injection of local anesthetic in to an exsanguinated limb to produce anesthesia by direct diffusion of the anesthetic from the vessels in to the nearby nerves.|
|Topical anesthesia||It is an application of local anesthetic in the form of spray or jelly to the skin, mucous membrane of the eye, ear, nose and mouth as well as other mucous membranes to provide effective short term analgesia.|
|Infiltration||Intradermal & or subcutaneous infiltration or injection of local anesthetics to provide anesthesia for minor surgical procedures.|
|Field block anesthesia||Produced by subcutaneous injection of a solution of local anesthetic in order to anesthetize the region distal to the injection. For example, subcutaneous infiltration of the proximal portion of the palmar surface of the forearm results in an extensive area of cutaneous anesthesia that starts 2 to 3 cm distal to the site of injection.|
|Nerve block Anesthesia||Injection of a solution of a local anesthetic into or about individual peripheral nerves or nerve plexuses produces greater areas of anesthesia. Blockade of mixed peripheral nerves and nerve plexuses also usually anesthetizes somatic motor nerves, producing skeletal muscle relaxation, which is essential for some surgical procedures.|
Documentation is written relevant information about the patient which contains an evidence of client findings, detail of procedure and events happened during the procedure. It is an indicator of quality care and is the responsibility of an anesthetist to record throughout the procedure on time. While anesthesia care is a continuum, it is usually viewed as consisting of preanesthesia, intraoperative/procedural anesthesia and post anesthesia components. Anesthesia care should be documented to reflect these components and to facilitate review.