Practical conductof

General AnesthesiaPart1

Prepared byDr. Mahmoud Abdel-Khalek

Jan 2015

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

General Anesthetics

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

AnesthetistsRole 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

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Goals of AnesthesiaAll 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 AnesthesiaThe 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 AnesthesiaBalanced 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

1. Preinduction begins with premed administered and ends when anesthesia induction begins in OR

2. Induction from consciousness to unconsciousness

3. Maintenance surgery takes place during this requires maintenance of physiological function by anesthetist

4. Emergence as surgery is completed (start to wake up), restoration of gag reflex, extubation

5. 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 AnestheticsPhysical Properties

IV AnestheticsEffects 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) Definitionis the minimum alveolar concentration of an inhaled anesthetic agent which prevents reflex movement inresponse 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.

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)

Questions?