General Anesthesia Part1 Practical conduct of General Anesthesia Part1 Prepared by Dr. Mahmoud Abdel-Khalek Jan 2015

General Anesthesia General Anesthesia is a pharmacologically induced reversible state of unconsciousness which is maintained despite the presence of noxious stimuli

General Anesthetics OR General anesthetics are drugs which produce reversible loss of all sensations and consciousness. OR General anesthetics are a class of drugs used to depress the CNS to a sufficient degree to permit the performance of surgery and other noxious or unpleasant procedures

Anesthetists Role of anesthetists Preoperative evaluation and patient preparation Intraoperative management General anesthesia Inhalation anesthesia Total IV anesthesia Regional Anesthesia& pain management Spinal, epidural & caudal blocks Peripheral never blocks Pain management (acute and chronic pain) Postanesthesia care (PACU management) Management of Anesthesia Complications “

Goals of Anesthesia All techniques strive to achieve the following goals, known as the “Four A’s of Anesthesia”: Lack of Awareness: unconsciousness. Amnesia: lack of memory of the event Analgesia: the abolition of the subconscious reactions to pain, including somatic reflexes (movement or withdrawal) and autonomic reflexes (hypertension, tachycardia, sweating and tearing). Akinesia: lack of overt movement. In some cases, the provision of muscle relaxation may be required.

Anesthesia with single or multi agents In the past, general anesthesia was achieved using a single agent such as ether or chloroform. Because the above-described goals were achieved by a progressive depression of the central nervous system rather than by any direct or specific effect, relatively high concentrations of the gases were required. Consequently the associated side effects were frequent and severe. In current practice, we have many different agents (both intravenous and inhaled) at our disposal. The intravenous agents in particular have specific effects such as analgesia or muscle relaxation and therefore can be used to achieve the desired effect in a dose-related fashion.

Balanced Anesthesia The practice of using combinations of agents, each for a specific purpose, is what is termed “balanced anesthesia”. An example of a balanced technique would be the use of Propofol for “induction” Isoflurane and N2O for “Maintenance” Fentanyl for “Analgesia” Rocuronium for “muscle relaxation”

Benefits of Balanced Anesthesia Balanced technique is still the most common technique used for the provision of general Anesthesia Benefits of balanced technique as compared to “ether anesthesia” of the past include improved hemodynamic stability more effective muscle relaxation More rapid return of respiratory functions, consciousness and airway control following the completion of the procedure Recently the development of short acting IV agents such as propofol makes total intravenous anesthesia possible (TIVA)

Preparation for Anesthesia The anesthetic machine must be tested before use for leaks, misconnections and proper function The breathing system to be used should be new for each patient, or a new filter installed The availability and function of all anesthetic equipment should be checked before starting The anesthetist should be satisfied that the correct operation is being performed upon the correct patient and that consent has been given The patient must be on a tilting bed or trolley the anesthetist should have a competent, trained assistant.

Equipment checking before anesthesia

Equipment checking before anesthesia

Before Starting What you should do? Supervise a safe transfer of the patient from his bed to the operating room table Place anesthetic record on the anesthesia clipboard Check to make sure that all requested labs at the preoperative visit are there (e.g. Hb, ECG, etc.) Attach monitors including an ECG, blood pressure cuff, and pulse oximeter to start with Establish an intravenous line . Prepare your intravenous drugs before the patient arrives Record the patients initial vital signs on the anesthesia record (Baseline vital signs)

Phases of Anesthesia Preinduction begins with premed administered and ends when anesthesia induction begins in OR Induction from consciousness to unconsciousness Maintenance surgery takes place during this requires maintenance of physiological function by anesthetist Emergence as surgery is completed (start to wake up), restoration of gag reflex, extubation Recovery time during when patient returns to full consciousness begins in OR and carries into stay in PACU and beginning healing stages

Drugs commonly used in anesthesia Intravenous anesthetic drugs e.g. Thiopental, Propofol, Ketamine Inhalational anesthetic drugs e.g. Nitrous oxide, Isoflurane, Sevoflurane Neuromuscular blocking drugs e.g. Succinylcholine, atracurium, rocuronium, pancuronium NMB reversal drug e.g. Neostigmine, Atropine, Glycopyrrolate Opioid drugs e.g. Morphine, Fentanyl

IV Anesthetic Agents

IV Anesthetic Agents

IV Anesthetics Physical Properties

IV Anesthetics Effects on Body

Inhalational Anesthetic Agents

Inhalational Anesthetic Agents

Inhalational Anesthetic Agents

Systemic effects of volatile agents

How the inhalational agent pass to the brain?

Potency of Inhalational Anesthetic Agents Just as potency of oral or intravenous drugs is measured in milligrams (or micrograms), potency of volatile anesthetics is associated with the term ‘MAC’ (minimum alveolar concentration)

Minimum alveolar concentration (MAC) Definition is the minimum alveolar concentration of an inhaled anesthetic agent which prevents reflex movement in response to surgical incision in 50% of subjects The effects of inhalational anesthetics are additive: thus 1 MAC-equivalent could be achieved by producing an alveolar concentration of 70% nitrous oxide (0.67 MAC) and 0.4% isoflurane (0.33 MAC)

Signs of Anesthesia

Factors Which Lead to a Reduction in MAC Sedative drugs such as premedication agents, analgesics Nitrous oxide Increasing age Drugs which affect neurotransmitter release such as methyldopa, pancuronium and clonidine Higher atmospheric pressureHypotension Hypothermia Myxedema Pregnancy. Higher atmospheric pressure, as anesthetic potency is related to partial pressure – e.g. MAC for sevoflurane is 2.0% (2.03 kPa) at a pressure of 1 ata, but 1.0% (still 2.03 kPa) at 2 ata

Factors Which Increase MAC Decreasing age Pyrexia Induced sympathoadrenal stimulation, e.g. hypercapnia Drugs: ephedrine, or amphetamine Thyrotoxicosis Chronic alcohol ingestion

Other Factors affecting MAC of inhalational anesthetics The rate at which MAC is attained may be increased by raising the inspired concentration avoidance of airway obstruction increasing ventilation The time taken for equilibration Low blood/gas solubility coefficient of the agent (It follows, therefore, that the inspired concentration must be considerably higher than MAC to produce an adequate alveolar concentration) Those with a high blood/gas solubility coefficient (e.g. halothane) do not reach equilibrium for several hours

Questions?