Measured quantities of anaesthetic gases and oxygen through accurate flowmeters and with the use of special vaporizers it is possible to add the vapor of volatile anesthetic liquid to the gas stream. The mixture of oxygen and anaesthetic agent is then delivered to a breathing circuit for administration by Inhalation.
• When gas or vapor is inhaled only a small amount is absorbed
• Whereas the rest is exhaled out in next 1-2 seconds • The drug reaches the brain by leaving the blood • Anaesthetic blood levels of theral Anesthetics are the most dangerous drugs
• Therapeutic index ranges between 2-4
• 2-3 times dose causes circulatory failure
Oral dose delivers the total dose
and the brain are almost equal at equilibrium
Minimum Alveolar Concentration
• MAC is the measure of potency of general anesthetics
• It is the minimum alveolar concentration (MAC) at one atmospheric pressure that produces immobility in 50% patients or animals exposed to noxious stimuli
OTHER ROUTES: These agents are also eliminated in smaller quantities from skin, mucous membrane and the kidneys
The state of general anesthesia is drug induced absence of perception of all sensations
PRINCIPLES OF THE ADMINISTRATION OF GENERAL ANAESTHETICS
Uptake and Distribution of inhalational general anesthetics
measures accurately • Concentrations in the lungs can be easily frequently
and accurately be measured • The partials pressures of the anaesthetic in the lung
venous blood.
Loss of the agent from the arterial blood to all the tissue of the body
ANAESTHESIA MACHINES
Are devices by which the anesthesiologist is able to deliver
Transfer of the gas from the alveoli to the blood
Decreased in disease (ex. emphysema) Rate of transfer is determined by:
Solubility(Blood gas partition coefficient.) Rate of blood flow(directly proportional to the C.O. Partial pressures of the agent in arterial and mixed
Depth of Anesthesia - Tension of anaesthetic agent in brain - controls - rates of induction and recovery
Tension and partial pressure are interchangeable terms
Tension in the arterial blood and brain are same and are determined by:
Concentration of the anaesthetic in the inspired air depends on rate of ventilation
ELIMINATION OF GENERAL ANAESTHETICS
Free gases and vapors wash out of the lungs: The arterial blood tension declines first. Followed by that in the tissues where the anaesthetic agent persists for a longer time. Tissue having low blood flow (muscle) relieve the agent much slowly.